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Volume 16
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Polymers, Volume 16, Issue 7 (April-1 2024) – 156 articles

Cover Story (view full-size image): The production of personal protective equipment has increased dramatically in recent years, not only because of the pandemic but also because of stricter legislation in the field of employee protection. This increase puts additional pressure on waste collectors. For this reason, it is significant to find high-quality solutions for this type of waste. A detailed analysis of recovered recyclates is necessary to improve the properties and find the right end use, which also increase the value of the materials. View this paper
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21 pages, 11647 KiB  
Article
Novel Polymer Composites for Lead-Free Shielding Applications
by Mazen A. Baamer, Saad Alshahri, Ahmed A. Basfar, Mohammed Alsuhybani and Alhanouf Alrwais
Polymers 2024, 16(7), 1020; https://doi.org/10.3390/polym16071020 - 8 Apr 2024
Viewed by 1582
Abstract
Polymer nanocomposites have recently been introduced as lead-free shielding materials for use in medical and industrial applications. In this work, novel shielding materials were developed using low-density polyethylene (LDPE) mixed with four different filler materials. These four materials are cement, cement with iron [...] Read more.
Polymer nanocomposites have recently been introduced as lead-free shielding materials for use in medical and industrial applications. In this work, novel shielding materials were developed using low-density polyethylene (LDPE) mixed with four different filler materials. These four materials are cement, cement with iron oxide, cement with aluminum oxide, and cement with bismuth oxide. Different weight percentages were used including 5%, 15%, and 50% of the cement filler with LDPE. Furthermore, different weight percentages of different combinations of the filler materials were used including 2.5%, 7.5%, and 25% (i.e., cement and iron oxide, cement and aluminum oxide, cement and bismuth oxide) with LDPE. Bismuth oxide was a nanocomposite, and the remaining oxides were micro-composites. Characterization included structural properties, physical features, mechanical and thermal properties, and radiation shielding efficiency for the prepared composites. The results show that a clear improvement in the shielding efficiency was observed when the filler materials were added to the LDPE. The best result out of all these composites was obtained for the composites of bismuth oxide (25 wt.%) cement (25 wt.%) and LDPE (50 wt.%) which have the lowest measured mean free path (MFP) compared with pure LDPE. The comparison shows that the average MFP obtained from the experiments for all the eight energies used in this work was six times lower than the one for pure LDPE, reaching up to twelve times lower for 60 keV energy. The best result among all developed composites was observed for the ones with bismuth oxide at the highest weight percent 25%, which can block up to 78% of an X-ray. Full article
(This article belongs to the Section Polymer Applications)
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Graphical abstract
Full article ">Figure 1
<p>Experimental set-up for radiation attenuation experiments.</p> Full article ">Figure 2
<p>Distribution of the number of X-rays for 120 kVp extracted from SpekCalc with no filters and with ISO filter.</p> Full article ">Figure 3
<p>Tensile strength and elongation at break for the most promising results for X-ray shielding.</p> Full article ">Figure 4
<p>TGA thermograms of the most promising samples relative to pure LDPE.</p> Full article ">Figure 5
<p>DTG thermograms of the most promising samples relative to pure LDPE.</p> Full article ">Figure 6
<p>SEM micrographs for pure LDPE and LDPE 50 wt.% + Bi<sub>2</sub>O<sub>3</sub> 25 wt.% + cement 25 wt.% composite.</p> Full article ">Figure 7
<p>EDS spectrum for pure LDPE.</p> Full article ">Figure 8
<p>EDS spectrum for L50C25Bio25 composite.</p> Full article ">Figure 8 Cont.
<p>EDS spectrum for L50C25Bio25 composite.</p> Full article ">Figure 9
<p>FTIR spectra for the most promising samples compared to pure LDPE.</p> Full article ">Figure 9 Cont.
<p>FTIR spectra for the most promising samples compared to pure LDPE.</p> Full article ">Figure 10
<p>X-ray shielding properties of all developed composites compared to pure LDPE.</p> Full article ">Figure 10 Cont.
<p>X-ray shielding properties of all developed composites compared to pure LDPE.</p> Full article ">Figure 11
<p>X-ray shielding properties of pure LDPE and composite of cement and Fe<sub>2</sub>O<sub>3.</sub></p> Full article ">Figure 11 Cont.
<p>X-ray shielding properties of pure LDPE and composite of cement and Fe<sub>2</sub>O<sub>3.</sub></p> Full article ">Figure 12
<p>X-ray shielding properties of pure LDPE and composites of cement and AL<sub>2</sub>O<sub>3.</sub></p> Full article ">Figure 12 Cont.
<p>X-ray shielding properties of pure LDPE and composites of cement and AL<sub>2</sub>O<sub>3.</sub></p> Full article ">Figure 13
<p>X-ray shielding properties of LDPE 50% with Bi<sub>2</sub>O<sub>3</sub> 25% and cement 25% composites compared to pure LDPE.</p> Full article ">Figure 14
<p>Comparison of MAC of the X-ray properties for the various prepared composites compared to pure LDPE.</p> Full article ">Figure 15
<p>Comparison of LAC of the X-ray properties for all developed composites compared to pure LDPE.</p> Full article ">Figure 16
<p>Comparison of MFP of the X-ray properties for the developed composites compared to LDPE.</p> Full article ">Figure 17
<p>Comparison of HVL of the X-ray properties for all developed composites compared to pure LDPE.</p> Full article ">Figure 18
<p>Comparison of RPE of the X-ray properties for all developed composites compared to pure LDPE.</p> Full article ">
15 pages, 9064 KiB  
Article
A Comparative Study of Removal of Acid Red 27 by Adsorption on Four Different Chitosan Morphologies
by Hongli Wu, Jiaying Zhou, Sai Zhang, Ping Niu, Haoming Li, Zhongmin Liu, Ning Zhang, Chunhui Li, Liping Wang and Yudong Wang
Polymers 2024, 16(7), 1019; https://doi.org/10.3390/polym16071019 - 8 Apr 2024
Cited by 2 | Viewed by 961
Abstract
To investigate the relationship between structures and adsorption properties, four different morphologies of chitosan, with hydrogel (CSH), aerogel (CSA), powder (CSP), and electrospinning nanofiber (CSEN) characteristics, were employed as adsorbents for the removal of Acid Red 27. The structures and morphologies of the [...] Read more.
To investigate the relationship between structures and adsorption properties, four different morphologies of chitosan, with hydrogel (CSH), aerogel (CSA), powder (CSP), and electrospinning nanofiber (CSEN) characteristics, were employed as adsorbents for the removal of Acid Red 27. The structures and morphologies of the four chitosan adsorbents were characterized with SEM, XRD, ATR-FTIR, and BET methods. The adsorption behaviors and mechanisms of the four chitosan adsorbents were comparatively studied. All adsorption behaviors exhibited a good fit with the pseudo-second-order kinetic model (R2 > 0.99) and Langmuir isotherm model (R2 > 0.99). Comparing the adsorption rates and the maximum adsorption capacities, the order was CSH > CSA > CSP > CSEN. The maximum adsorption capacities of CSH, CSA, CSP, and CSEN were 2732.2 (4.523), 676.7 (1.119), 534.8 (0.885), and 215.5 (0.357) mg/g (mmol/g) at 20 °C, respectively. The crystallinities of CSH, CSA, CSP, and CSEN were calculated as 0.41%, 6.97%, 8.76%, and 39.77%, respectively. The crystallinity of the four chitosan adsorbents was the main factor impacting the adsorption rates and adsorption capacities, compared with the specific surface area. With the decrease in crystallinity, the adsorption rates and capacities of the four chitosan adsorbents increased gradually under the same experimental conditions. CSH with a low crystallinity and large specific surface area resulted in the highest adsorption rate and capacity. Full article
(This article belongs to the Special Issue Smart Textile and Polymer Materials II)
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Graphical abstract
Full article ">Figure 1
<p>Chemical structures of (<b>a</b>) chitosan and (<b>b</b>) Acid Red 27 (AR 27).</p> Full article ">Figure 2
<p>(<b>a</b>) Digital image and (<b>b</b>) microscope photograph of chitosan hydrogel (CSH) dispersed in AR 27 solution. SEM images of (<b>c</b>) CSH, (<b>d</b>) chitosan aerogel (CSA), (<b>e</b>) chitosan powder (CSP), and (<b>f</b>) chitosan electrospinning nanofiber (CSEN).</p> Full article ">Figure 2 Cont.
<p>(<b>a</b>) Digital image and (<b>b</b>) microscope photograph of chitosan hydrogel (CSH) dispersed in AR 27 solution. SEM images of (<b>c</b>) CSH, (<b>d</b>) chitosan aerogel (CSA), (<b>e</b>) chitosan powder (CSP), and (<b>f</b>) chitosan electrospinning nanofiber (CSEN).</p> Full article ">Figure 3
<p>XRD patterns of CSH, CSA, CSP, and CSEN.</p> Full article ">Figure 4
<p>ATR − FTIR spectra of the purchased chitosan powder, CSH, CSA, CSP, and CSEN.</p> Full article ">Figure 5
<p>(<b>a</b>) N<sub>2</sub> adsorption–desorption curves and (<b>b</b>) pore size distribution of CSH, CSA, CSP, and CSEN. (<b>a</b>) the circular symbol denotes the desorption curve, while the square-shaped symbol indicates the adsorption curve.</p> Full article ">Figure 6
<p>(<b>a</b>) Plots of <span class="html-italic">Q<sub>t</sub></span> vs. time for AR 27 on CSH, CSA, CSP, and CSEN. (<b>b</b>) Fitting curves of PSO model.</p> Full article ">Figure 7
<p>Equilibrium adsorption of AR 27 on the four chitosan adsorbents at different temperatures.</p> Full article ">Figure 8
<p>Langmuir plot at different temperatures on (<b>a</b>) CSH, (<b>b</b>) CSA, (<b>c</b>) CSP, and (<b>d</b>) CSEN.</p> Full article ">
20 pages, 25840 KiB  
Article
Experimental and Numerical Investigation of Prepreg-RTM Co-Curing Molding Composite Bolted T-Joint under Bending Load
by Tao Zhang, Zhitao Luo, Kenan Li and Xiaoquan Cheng
Polymers 2024, 16(7), 1018; https://doi.org/10.3390/polym16071018 - 8 Apr 2024
Cited by 2 | Viewed by 950
Abstract
A set of polymer composite bolted T-joints with a novel configuration consisting of an internal skeleton and external skin was fabricated using a prepreg-RTM co-curing molding process. Experiments were conducted to study their mechanical properties under a bending load. A finite element model [...] Read more.
A set of polymer composite bolted T-joints with a novel configuration consisting of an internal skeleton and external skin was fabricated using a prepreg-RTM co-curing molding process. Experiments were conducted to study their mechanical properties under a bending load. A finite element model with a polymer resin area between the skin and skeleton was established and verified by the experimental results. Then, the damage propagation process and failure mechanism of the joint and the influence of three factors related to the layer characteristics of the skin and skeleton were investigated by the validated models. The results show that the bending stiffness and the yield limit load of the novel composite T-joint are 0.81 times and 1.65 times that of the 2A12 aluminum T-joint, respectively, while at only 55.4% of its weight. The damage of the joint is initiated within the resin area and leads to the degradation of the joint’s bending performance. The preferred stacking sequence of the skeleton is [0/+45/90/−45]ns when primarily subjected to bending loads. The decrease in the bending performance is within 5% of the inclining angle of the skeleton, less than 12 degrees. The more 90° layers in the skin, the better the bending performance of the joints, while the more 0° layers, the poorer the bending performance. Full article
(This article belongs to the Special Issue Multiscale Modeling and Simulation of Polymer-Based Composites)
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Figure 1
<p>Configuration of bolted π-joint: novel configuration (<b>a</b>) and conventional configuration (<b>b</b>).</p> Full article ">Figure 2
<p>Novel configuration of polymer composite bolted T-joint.</p> Full article ">Figure 3
<p>The dimensions of specimen.</p> Full article ">Figure 4
<p>Manufacturing process of polymer composite bolted T-joint with novel configuration.</p> Full article ">Figure 5
<p>The diagram of loading scheme.</p> Full article ">Figure 6
<p>The experimental setup.</p> Full article ">Figure 7
<p>Damage morphologies of the specimen.</p> Full article ">Figure 8
<p>Profile of base panel near the R-corner area after the test.</p> Full article ">Figure 9
<p>Profile of lug near the R-corner region after the test.</p> Full article ">Figure 10
<p>Load–displacement curves obtained from the tests.</p> Full article ">Figure 11
<p>Boundary conditions, loading condition, and nodes for result output in FE model.</p> Full article ">Figure 12
<p>Flow chart of finite element model.</p> Full article ">Figure 13
<p>Comparison of numerical and experimental damage morphologies: polymer resin damage between skin and skeleton (<b>a</b>), skin damage area around the hole (<b>b</b>), and skeleton damage area along the thickness (<b>c</b>).</p> Full article ">Figure 14
<p>Load–displacement curves for specimen 90# by experimental and numerical analysis. (For Points O–C: O is the starting point, A is the damage initiation point, B is the ultimate load point and C is a point in the final destruction process).</p> Full article ">Figure 15
<p>Mises stress distribution at point A: the whole T-joint (<b>a</b>) and polymer resin area (<b>b</b>).</p> Full article ">Figure 16
<p>Shear stress distribution of the polymer resin area at point A: shear stress S13 (<b>a</b>) and shear stress S23 (<b>b</b>).</p> Full article ">Figure 17
<p>Damage distribution at point B (<b>a</b>). Deformation of T-joint at point B (<b>b</b>).</p> Full article ">Figure 18
<p>Variation in mechanical properties with the stacking sequence of the skeleton: bending stiffness (<b>a</b>) and ultimate load (<b>b</b>).</p> Full article ">Figure 19
<p>Diagram of inclining angle (<b>a</b>). Variation in mechanical properties with the change in the inclining angle of the layer in the skeleton: bending stiffness (<b>b</b>) and ultimate load (<b>c</b>).</p> Full article ">Figure 20
<p>Variation in mechanical properties with changes in the stacking sequence of the skin: bending stiffness (<b>a</b>) and ultimate load (<b>b</b>).</p> Full article ">
15 pages, 11367 KiB  
Article
Microbially Mediated Rubber Recycling to Facilitate the Valorization of Scrap Tires
by Sk Faisal Kabir, Skanda Vishnu Sundar, Aide Robles, Evelyn M. Miranda, Anca G. Delgado and Elham H. Fini
Polymers 2024, 16(7), 1017; https://doi.org/10.3390/polym16071017 - 8 Apr 2024
Cited by 1 | Viewed by 1150
Abstract
The recycling of scrap tire rubber requires high levels of energy, which poses challenges to its proper valorization. The application of rubber in construction requires significant mechanical and/or chemical treatment of scrap rubber to compatiblize it with the surrounding matrix. These methods are [...] Read more.
The recycling of scrap tire rubber requires high levels of energy, which poses challenges to its proper valorization. The application of rubber in construction requires significant mechanical and/or chemical treatment of scrap rubber to compatiblize it with the surrounding matrix. These methods are energy-consuming and costly and may lead to environmental concerns associated with chemical leachates. Furthermore, recent methods usually call for single-size rubber particles or a narrow rubber particle size distribution; this, in turn, adds to the pre-processing cost. Here, we used microbial etching (e.g., microbial metabolism) to modify the surface of rubber particles of varying sizes. Specifically, we subjected rubber particles with diameters of 1.18 mm and 0.6 mm to incubation in flask bioreactors containing a mineral medium with thiosulfate and acetate and inoculated them with a microbial culture from waste-activated sludge. The near-stoichiometric oxidation of thiosulfate to sulfate was observed in the bioreactors. Most notably, two of the most potent rubber-degrading bacteria (Gordonia and Nocardia) were found to be significantly enriched in the medium. In the absence of added thiosulfate in the medium, sulfate production, likely from the desulfurization of the rubber, was also observed. Microbial etching increased the surface polarity of rubber particles, enhancing their interactions with bitumen. This was evidenced by an 82% reduction in rubber–bitumen separation when 1.18 mm microbially etched rubber was used. The study outcomes provide supporting evidence for a rubber recycling method that is environmentally friendly and has a low cost, promoting pavement sustainability and resource conservation. Full article
(This article belongs to the Special Issue Application of Polymeric Materials in the Building Industry II)
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Figure 1
<p>Thiosulfate and sulfate concentrations in flask bioreactors with (<b>A</b>) crumb rubber 30 (CR-30) and (<b>B</b>) CR-16 during incubation. SC = sludge control (no crumb rubber). The data are averages with SD of duplicate or triplicate bioreactors.</p> Full article ">Figure 2
<p>Microbial community composition of the inoculate at day 0 and in the bioreactors at the end of incubation (day 41).</p> Full article ">Figure 3
<p>FT-IR spectra of both crumb rubber sizes after acetone washing. FT-IR spectra in both cases draw a comparison between (<b>a</b>) CR16-1 and CR30-1 and (<b>b</b>) CR16-2 and CR30-2.</p> Full article ">Figure 4
<p>Cigar tube test results to study the phase separation phenomenon of the rubberized asphalt binder.</p> Full article ">Figure 5
<p>(<b>a</b>) G*/sinδ and (<b>b</b>) G*sinδ values for microbially desulfurized rubberized asphalt binders.</p> Full article ">Figure 6
<p>Percentage recovery of the accumulated strain from MSCR test results for rubberized binders.</p> Full article ">Figure 7
<p>Bending beam rheometer (BBR) results for the rubberized asphalt binders.</p> Full article ">
15 pages, 4456 KiB  
Article
TEMPO-Oxidized Nanocellulose Films Modified by Tea Saponin Derived from Camellia oleifera: Physicochemical, Mechanical, and Antibacterial Properties
by Nan Jiang, Yudi Hu and Yuhang Cheng
Polymers 2024, 16(7), 1016; https://doi.org/10.3390/polym16071016 - 8 Apr 2024
Cited by 1 | Viewed by 1467
Abstract
Nanocellulose materials have been widely used in biomedicine, food packaging, aerospace, composite material, and other fields. In this work, cellulose obtained from Camellia shells through alkali boiling and subbleaching was micro-dissolved and regenerated using the DMAc (N,N-Dimethylacetamide)/LiCl system, and [...] Read more.
Nanocellulose materials have been widely used in biomedicine, food packaging, aerospace, composite material, and other fields. In this work, cellulose obtained from Camellia shells through alkali boiling and subbleaching was micro-dissolved and regenerated using the DMAc (N,N-Dimethylacetamide)/LiCl system, and TOCNs (TEMPO-oxidized cellulose nanofibers) with different degrees of oxidation. The membrane was prepared by filtration of polytetrafluoroethylene (pore size 0.1 μm), and the oxidized nanocellulose film was obtained after drying, Then, the crystallinity, mechanical properties and oxygen barrier properties of the TOCN film were investigated. Furthermore, based on TS (tea saponin) from Camellia oleifera seed cake and TOCNs, TS-TOCN film was prepared by the heterogeneous reaction. The TS-TOCN film not only shows excellent oxygen barrier properties (the oxygen permeability is 2.88 cc·m−2·d−1) but also has good antibacterial effects on both Gram-negative and Gram-positive bacteria. The antibacterial property is comparable to ZnO-TOCN with the same antibacterial content prepared by the in-situ deposition method. Antioxidant activity tests in vitro showed that TS-TOCN had a significant scavenging effect on DPPH (2,2-Diphenyl-1-picrylhydrazyl) radicals. This design strategy makes it possible for inexpensive and abundant Camellia oleifera remainders to be widely used in the field of biobased materials. Full article
(This article belongs to the Special Issue Bio-Based Polymeric Films II)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic presentation of TS-TOCN synthesis and property.</p> Full article ">Figure 2
<p>SEM scan of surface topography (<b>a</b>–<b>e</b>): (<b>a</b>) untreated cellulose C-0; (<b>b</b>) DMAc/LiCl (LiCl 3 wt%) treated cellulose C-3; (<b>c</b>) DMAc/LiCl (LiCl 5 wt%) treated cellulose C-5; (<b>d</b>) DMAc/LiCl (LiCl 7 wt%) treated cellulose C-7; (<b>e</b>) DMAc/LiCl (LiCl 9 wt%) treated cellulose C-9; and (<b>f</b>) average diameter of TOCN and SEM scan of cross section of TOCN film (<b>g</b>–<b>l</b>). (<b>g</b>) TOCN-0; (<b>h</b>) TOCNs-3; (<b>i</b>) TOCNs-5; (<b>j</b>) TOCNs-7; (<b>k</b>) TOCNs-9; and (<b>l</b>) TS-TOCN film.</p> Full article ">Figure 3
<p>(<b>a</b>) XRD spectra of C-<span class="html-italic">x</span>; (<b>b</b>) XRD spectra of TOCN-<span class="html-italic">x</span>.</p> Full article ">Figure 4
<p>(<b>a</b>) FT−IR spectra of TOCN-<span class="html-italic">x</span> film and (<b>b</b>) FT-IR spectra of TS-TOCN film and the controls.</p> Full article ">Figure 5
<p>(<b>a</b>) Stress–strain curves of TOCN-<span class="html-italic">x</span> film; (<b>b</b>) stress–strain curves of TS–TOCN film.</p> Full article ">Figure 6
<p>Consecutive antibacterial test results for TS-TOCN films. The bacterial solution was diluted 100 times after co-incubation with the films.</p> Full article ">Figure 7
<p>Comparison of antibacterial test results between TS−TOCN film, ZnO−TOCN film, and Ag−TOCN film. The bacterial solution was diluted 100 times after co-incubation with the films.</p> Full article ">Figure 8
<p>The oxygen permeability of TOCN−<span class="html-italic">x</span> films and TS-TOCN film.</p> Full article ">Figure 9
<p>(<b>a</b>) UV–vis spectra and (<b>b</b>) DPPH scavenging percentage of DPPH solution after being scavenged by TOCN-5 film and TS−TOCN film for 60 min.</p> Full article ">
21 pages, 8837 KiB  
Article
Computational Requirements for Modeling Thermal Conduction in Polymeric Phase-Change Materials: Periodic Hard Spheres Case
by Kevin A. Redosado Leon, Alexey Lyulin and Bernard J. Geurts
Polymers 2024, 16(7), 1015; https://doi.org/10.3390/polym16071015 - 8 Apr 2024
Viewed by 1231
Abstract
This research focuses on modeling heat transfer in heterogeneous media composed of stacked spheres of paraffin as a perspective polymeric phase-change material. The main goal is to study the requirements of the numerical scheme to correctly predict the thermal conductivity in a periodic [...] Read more.
This research focuses on modeling heat transfer in heterogeneous media composed of stacked spheres of paraffin as a perspective polymeric phase-change material. The main goal is to study the requirements of the numerical scheme to correctly predict the thermal conductivity in a periodic system composed of an indefinitely repeated configuration of spherical particles subjected to a temperature gradient. Based on OpenFOAM, a simulation platform is created with which the resolution requirements for accurate heat transfer predictions were inferred systematically. The approach is illustrated for unit cells containing either a single sphere or a configuration of two spheres. Asymptotic convergence rates confirming the second-order accuracy of the method are established in case the grid is fine enough to have eight or more grid cells covering the distance of the diameter of a sphere. Configurations with two spheres can be created in which small gaps remain between these spheres. It was found that even the under-resolution of these small gaps does not yield inaccurate numerical solutions for the temperature field in the domain, as long as one adheres to using eight or more grid cells per sphere diameter. Overlapping and (barely) touching spheres in a configuration can be simulated with high fidelity and realistic computing costs. This study further extends to examine the effective thermal conductivity of the unit cell, particularly focusing on the volume fraction of paraffin in cases with unit cells containing a single sphere. Finally, we explore the dependence of the effective thermal conductivity for unit cells containing two spheres at different distances between them. Full article
(This article belongs to the Special Issue Modeling and Simulation of Polymer Composites)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>A two-dimensional representation of a TES microstructure composed of different size paraffin particles (orange) stacked in the pores of a foam (blue). The pores are bounded by a metal border, indicated symbolically by the thin black lines. In the actual porous metal foam, direct pathways connecting one pore with another are also contained—this is not included in the sketch.</p> Full article ">Figure 2
<p>Conservation of a general scalar variable in a discrete element <span class="html-italic">C</span> of volume <math display="inline"><semantics> <msub> <mi>V</mi> <mi>c</mi> </msub> </semantics></math>.</p> Full article ">Figure 3
<p>Cell in a structured uniform grid (<b>a</b>) and in a structured irregular grid (<b>b</b>).</p> Full article ">Figure 4
<p>(<b>a</b>) Computation domain of structured cells constituting one region for the background mesh. (<b>b</b>) Structured background mesh with spherical inclusion surface. (<b>c</b>) New computational domain after <span class="html-small-caps">snappyHexMesh</span> consisting of two regions.</p> Full article ">Figure 5
<p>A two-dimensional representation of a periodic domain showing the following: (<b>a</b>) <math display="inline"><semantics> <msup> <mi>n</mi> <mn>2</mn> </msup> </semantics></math> cells of <span class="html-italic">h</span> size composing a <math display="inline"><semantics> <msup> <mi>L</mi> <mn>2</mn> </msup> </semantics></math> simulation box. (<b>b</b>) A single sphere with a diameter of <span class="html-italic">D</span> embedded within the simulation box. (<b>c</b>) Two spheres, each with a diameter <span class="html-italic">D</span>, whose centers are separated by a distance of <span class="html-italic">H</span>.</p> Full article ">Figure 6
<p>An embedded sphere in a periodic domain at different resolutions denoted by <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mi>D</mi> <mo>/</mo> <mi>h</mi> </mrow> </semantics></math>. The predicted temperature fields <span class="html-italic">T</span> are shown below in terms of <math display="inline"><semantics> <mrow> <msup> <mi>T</mi> <mo>*</mo> </msup> <mo>=</mo> <mrow> <mo>(</mo> <mi>T</mi> <mo>−</mo> <msub> <mi>T</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mo>/</mo> <mrow> <mo>(</mo> <msub> <mi>T</mi> <mn>1</mn> </msub> <mo>−</mo> <msub> <mi>T</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> </mrow> </semantics></math> in which <math display="inline"><semantics> <msub> <mi>T</mi> <mn>0</mn> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi>T</mi> <mn>1</mn> </msub> </semantics></math> are the imposed temperatures on the bottom and top, respectively.</p> Full article ">Figure 7
<p>Temperature profile of sphere embedded in a cubic domain at different resolutions <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mi>D</mi> <mo>/</mo> <mi>h</mi> </mrow> </semantics></math>.</p> Full article ">Figure 8
<p>(<b>a</b>) The <math display="inline"><semantics> <msub> <mi>L</mi> <mn>1</mn> </msub> </semantics></math>—error for different spatial resolutions <span class="html-italic">M</span>. (<b>b</b>) The computational cost of the solver and <span class="html-small-caps">SnappyHexMesh</span> time against the total number of cells.</p> Full article ">Figure 9
<p>(<b>a</b>) Temperature field with an embedded sphere at <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mn>16</mn> </mrow> </semantics></math> with different sample planes (<math display="inline"><semantics> <mrow> <mi>z</mi> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>z</mi> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>z</mi> <mo>=</mo> <mn>3</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>z</mi> <mo>=</mo> <mn>3.9</mn> </mrow> </semantics></math>) to determine <math display="inline"><semantics> <msub> <mi>κ</mi> <mrow> <mi>e</mi> <mi>f</mi> <mi>f</mi> </mrow> </msub> </semantics></math> and (<b>b</b>) <math display="inline"><semantics> <msub> <mi>κ</mi> <mrow> <mi>e</mi> <mi>f</mi> <mi>f</mi> </mrow> </msub> </semantics></math> at different spatial resolutions <span class="html-italic">M</span> evaluated on different sample planes.</p> Full article ">Figure 10
<p>Effective thermal conductivity of binary mixture of still air and paraffin inclusions. The numerical approximation is compared with the Maxwell-Garnett model at a resolution of <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mn>32</mn> </mrow> </semantics></math> per sphere diameter.</p> Full article ">Figure 11
<p>Two-sphere cases, illustrated as a red and green sphere of the same material, for different separations measured in terms of <math display="inline"><semantics> <mrow> <mi>S</mi> <mo>=</mo> <mi>H</mi> <mo>/</mo> <mi>D</mi> </mrow> </semantics></math>, expressing the distance between the centers of the two spheres in units <span class="html-italic">D</span>.</p> Full article ">Figure 12
<p>SnappyHexMesh refinement for spheres, illustrated as a red and green sphere of the same material, separated by a small gap (<math display="inline"><semantics> <mrow> <mi>S</mi> <mo>=</mo> <mn>1.05</mn> </mrow> </semantics></math>) for different resolutions (<math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mn>4</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mn>8</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mn>32</mn> </mrow> </semantics></math>).</p> Full article ">Figure 13
<p>Vertical temperature profiles for various separations <span class="html-italic">S</span> and spatial resolutions <span class="html-italic">M</span>.</p> Full article ">Figure 14
<p>ETC of a vertically aligned two-sphere system at a spatial resolution of <math display="inline"><semantics> <mrow> <mi>M</mi> <mo>=</mo> <mn>16</mn> </mrow> </semantics></math> as a function of the distance <span class="html-italic">S</span> between the sphere centers.</p> Full article ">
17 pages, 8889 KiB  
Article
Effect of Biodegradable Nonwoven Mulches from Natural and Renewable Sources on Lettuce Cultivation
by Paula Marasovic, Dragana Kopitar, Tomislava Peremin-Volf and Marcela Andreata-Koren
Polymers 2024, 16(7), 1014; https://doi.org/10.3390/polym16071014 - 8 Apr 2024
Cited by 1 | Viewed by 1153
Abstract
Numerous research showed that mulching with conventional agro foils elevates soil temperature and promotes plant growth, but negatively influences soil health and brings environmental concerns. Most of the published research on nonwoven mulches for plant cultivation includes nonwoven fabrics produced by extrusion processes [...] Read more.
Numerous research showed that mulching with conventional agro foils elevates soil temperature and promotes plant growth, but negatively influences soil health and brings environmental concerns. Most of the published research on nonwoven mulches for plant cultivation includes nonwoven fabrics produced by extrusion processes providing nonwoven fabric structures similar to films. A limited number of studies investigate the impact of nonwoven mulches produced by a mechanical process on the cards and bonded by needling on plant cultivation. For this study, nonwoven mulches of mass per unit area of 400 g m−2 made from jute, hemp, viscose (CV), and polylactide (PLA) fibers were produced on the card bonded by needle punching. The field experiment was conducted two consecutive years in a row, in spring 2022 and 2023, by planting lettuce seedlings. The nonwoven mulches maintain lower temperatures and higher soil moisture levels compared to agro foil and the control field. The fibrous structure and their water absorption properties allow natural ventilation, regulating temperatures and retaining moisture of soil, consequently improving soil quality, lettuce yield, and quality. The fiber type from which the mulches were produced, influenced soil temperature and humidity, soil quality, and lettuce cultivation. The nonwoven mulches were successful in weed control concerning the weediness of the control field. Based on the obtained results, the newly produced mulches are likely to yield better results when used for the cultivation of vegetables with longer growing periods. Newly produced biodegradable nonwoven mulches could be an eco-friendly alternative to traditional agro foil, minimizing environmental harm during decomposition. The obtained results suggest that the newly produced mulches would be even more suitable for growing vegetables with longer growing seasons. Full article
(This article belongs to the Section Biobased and Biodegradable Polymers)
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<p>Nonwoven mulches made of (<b>a</b>) jute, (<b>b</b>) hemp, (<b>c</b>) viscose, (<b>d</b>) polylactide (PLA) fibers, (<b>e</b>) traditional agro foil, and (<b>f</b>) control field.</p> Full article ">Figure 2
<p>The nonwoven mulches, agro foil, and control field placed on the soil in the four replication plots.</p> Full article ">Figure 3
<p>Gentilina lettuce (<span class="html-italic">Lactuca sativa</span> L.).</p> Full article ">Figure 4
<p>Nonwoven mulches and agro foil before lettuce planting and after lettuce harvesting.</p> Full article ">Figure 5
<p>Phases of lettuce growth: (<b>a</b>) after planting, (<b>b</b>) after one month, (<b>c</b>) on the day of harvest (50 days).</p> Full article ">Figure 6
<p>Lettuce yields for years 2022 and 2023.</p> Full article ">
11 pages, 2654 KiB  
Article
Fluorine-Containing Ionogels with Stretchable, Solvent-Resistant, Wide Temperature Tolerance, and Transparent Properties for Ionic Conductors
by Xiaoxi Fan, Wenlong Feng, Shuang Wang, Yinpeng Chen, Wen Jiang Zheng and Jie Yan
Polymers 2024, 16(7), 1013; https://doi.org/10.3390/polym16071013 - 8 Apr 2024
Cited by 1 | Viewed by 1307
Abstract
Stretchable ionogels, as soft ion-conducting materials, have generated significant interest. However, the integration of multiple functions into a single ionogel, including temperature tolerance, self-adhesiveness, and stability in diverse environments, remains a challenge. In this study, a new class of fluorine-containing ionogels was synthesized [...] Read more.
Stretchable ionogels, as soft ion-conducting materials, have generated significant interest. However, the integration of multiple functions into a single ionogel, including temperature tolerance, self-adhesiveness, and stability in diverse environments, remains a challenge. In this study, a new class of fluorine-containing ionogels was synthesized through photo-initiated copolymerization of fluorinated hexafluorobutyl methacrylate and butyl acrylate in a fluorinated ionic liquid 1-butyl-3-methyl imidazolium bis (trifluoromethylsulfonyl) imide. The resulting ionogels demonstrate good stretchability with a fracture strain of ~1300%. Owing to the advantages of the fluorinated network and the ionic liquid, the ionogels show excellent stability in air and vacuum, as well as in various solvent media such as water, sodium chloride solution, and hexane. Additionally, the ionogels display impressive wide temperature tolerance, functioning effectively within a wide temperature range from −60 to 350 °C. Moreover, due to their adhesive properties, the ionogels can be easily attached to various substrates, including plastic, rubber, steel, and glass. Sensors made of these ionogels reliably respond to repetitive tensile-release motion and finger bending in both air and underwater. These findings suggest that the developed ionogels hold great promise for application in wearable devices. Full article
(This article belongs to the Special Issue Soft Polymeric Materials: Synthesis, Characterizations and Applications)
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<p>Mechanical properties of the ionogels. (<b>a</b>) Tensile stress-strain curves of PEA, PBA, and PPA ionogels (gel fraction is 50%); (<b>b</b>) tensile strength of five kinds of ionogels (gel fraction is 50%) including pure PHFBA, PBA, PEA ionogels, and copolymerized P(HFBA-<span class="html-italic">co</span>-BA), P(HFBA-<span class="html-italic">co</span>-EA) ionogels; (<b>c</b>) tensile stress-strain curves of P(HFBA-<span class="html-italic">co</span>-BA) ionogels (gel fraction is 50%) with different molar ratio between HFBA and BA of 1:0, 7:3, 5:5, 3:7, 0:1, where 1:0 and 0:1 represent pure PHFBA and PBA ionogels respectively; (<b>d</b>) strength and fracture strain of P(HFBA-<span class="html-italic">co</span>-BA) (7:3) ionogels with gel fraction of 30%, 40% and 50%. All samples are cut into dumbbell shapes with a 12 mm length of test section, and the tensile speed is 100 mm/min.</p> Full article ">Figure 2
<p>Stability of ionogels under different environments. (<b>a</b>) Contact angle of deionized water and hexane on P(HFBA-<span class="html-italic">co</span>-BA) ionogels; (<b>b</b>) swelling ratio of P(HFBA-<span class="html-italic">co</span>-BA) ionogels in NaCl solution, de-ionized water and hexane; (<b>c</b>) mass stability of P(HFBA-<span class="html-italic">co</span>-BA) ionogels in air with relative humidity of 85% and 33%; (<b>d</b>) mass stability of P(HFBA-<span class="html-italic">co</span>-BA) ionogels in vacuum for 24 h.</p> Full article ">Figure 3
<p>Adhesion properties of P(HFBA-<span class="html-italic">co</span>-BA) ionogels. (<b>a</b>) Molar ratio of HFBA to BA on adhesion strength of P(HFBA-<span class="html-italic">co</span>-BA) ionogels to steel plates; (<b>b</b>) adhesion demonstrations in air and underwater of ionogels on various substrates, such as silicone rubber, copper foil, glass bottle, and plastic cap; (<b>c</b>) adhesion strength of P(HFBA-<span class="html-italic">co</span>-BA) (7:3) ionogels on different substrates.</p> Full article ">Figure 4
<p>Thermal stability and conductivity of ionogels. (<b>a</b>) The TG results of the ionogels made of different molar ratios between HFBA and BA; (<b>b</b>) the DSC curves of the ionogels; (<b>c</b>) Conductivity of ionogels with gel fraction ranging from 30% to 50%; (<b>d</b>) the temperature-dependent ionic conductivity of the P(HFBA-<span class="html-italic">co</span>-BA) (7:3) ionogel with gel fraction of 30%.</p> Full article ">Figure 5
<p>Electrical and sensing properties of the P(HFBA-<span class="html-italic">co</span>-BA) (7:3) ionogel. (<b>a</b>) Schematics of the ionic conductor; (<b>b</b>) relative resistance of the ionic conductor under different strains ranging from 10% to 400%; (<b>c</b>) real-time recording of relative resistance variation of the ionic conductor under different tensile-release frequencies ranging from 0.5 Hz to 1 Hz; (<b>d</b>) relative resistance response under tensile-release processes with a strain of 10% for over 1000 cycles; (<b>e</b>) real-time recording of the stress of the ionogel gel under recycle tensile-release processes with a strain of 10%; (<b>f</b>) the maximum stress value measured during each tensile-release cycle, the two red lines in the graph are parallel to the x-axis, and the data points are gradually shifted downwards as the number of loops increases; (<b>g</b>) average of the maximum stress values in different cycling phases, including cycle 1 to 20, 500 to 520, as well as 1000 to 1020; (<b>h</b>) signals of relative resistance during finger bending in air; (<b>i</b>) relative resistance change during finger bending underwater.</p> Full article ">Scheme 1
<p>Preparation and display of the ionogels. (<b>a</b>) Schematic illustration of the one-step preparation process of the ionogels, HFBA and acrylic ester monomers are copolymerized in IL under irradiation of 365 nm UV, and simultaneously crosslinked by PEGDA to obtain ionogels; (<b>b</b>) transmittance spectrum of ionogels P(HFBA-<span class="html-italic">co</span>-BA) and pure PBA with a film thickness of 2 mm. Inset: photograph of the ionogel with a thickness of 2 mm over an image with a polka dot pattern; (<b>c</b>) demonstration of the elasticity of the ionogel.</p> Full article ">
20 pages, 11339 KiB  
Article
Polymer Waste Recycling of Injection Molding Purges with Softening for Cutting with Fresnel Solar Collector—A Real Problem Linked to Sustainability and the Circular Economy
by Ma. Guadalupe Plaza, Maria Luisa Mendoza López, José de Jesús Pérez Bueno, Joaquín Pérez Meneses and Alejandra Xochitl Maldonado Pérez
Polymers 2024, 16(7), 1012; https://doi.org/10.3390/polym16071012 - 8 Apr 2024
Viewed by 1872
Abstract
A plastic injection waste known as “purge” cannot be reintegrated into the recycling chain due to its shape, size, and composition. Grinding these cannot be carried out with traditional mills due to significant variations in size and shape. This work proposes a process [...] Read more.
A plastic injection waste known as “purge” cannot be reintegrated into the recycling chain due to its shape, size, and composition. Grinding these cannot be carried out with traditional mills due to significant variations in size and shape. This work proposes a process and the design of a device that operates with solar energy to cut the purges without exceeding the degradation temperature. The size reduction allows reprocessing, revalorization, and handling. The purges are mixtures of processed polymers, so their characterization information is unavailable. Some characterizations were conducted before the design of the process and after the cut of the purges. Some of the most representative purges in a recycling company were evaluated. The flame test determines that all material mixtures retain thermoplasticity. The hardness (Shore D) presented changes in four of the purges being assessed, with results in a range of 59–71 before softening and 60–68 after softening. Young’s modulus was analyzed by the impulse excitation technique (IET), which was 2.38–3.95 GPa before softening and 1.7–4.28 after softening. The feasibility of cutting purges at their softening temperature was evaluated. This was achieved in all the purges evaluated at 250–280 °C. FTIR allowed for corroboration of no significant change in the purges after softening. The five types of purges evaluated were polypropylene-ABS, polycarbonate-ABS-polypropylene, yellow nylon 66, acetal, and black nylon 66 with fillers, and all were easily cut at their softening temperature, allowing their manipulation in subsequent process steps. Full article
(This article belongs to the Special Issue Polymer Waste Recycling and Management II)
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<p>Purges of injection processes collected from industrial sources.</p> Full article ">Figure 2
<p>(<b>a</b>) Flame test, (<b>b</b>) hardness Shore D test, and (<b>c</b>) RFDA setup.</p> Full article ">Figure 3
<p>Three stages in softening plastic purges: (<b>a</b>) Concentrated solar power collector, (<b>b</b>) Heating and softening chamber, (<b>c</b>) Segmenting the pieces.</p> Full article ">Figure 4
<p>Design of the complete device. (<b>a</b>) Solar collector indicating the corresponding parts, (<b>b</b>) the collector subsystem, and (<b>c</b>) the softening zone.</p> Full article ">Figure 5
<p>Correlation between (<b>a</b>) height and diameter and (<b>b</b>) height and temperature.</p> Full article ">Figure 6
<p>(<b>a</b>) Location of the thermocouples (indicated with yellow arrows). (<b>b</b>) Location of fan.</p> Full article ">Figure 7
<p>Distribution and averages of hardness values before and after softening.</p> Full article ">Figure 8
<p>RFDA test set results screen.</p> Full article ">Figure 9
<p>Comparison of Young’s modulus average before and after softening.</p> Full article ">Figure 10
<p>DSC and TGA analyses for the five polymers studied, showing their graphs before and after the heat treatments by indirect sunlight heating (<b>a</b>) PP ABS, (<b>b</b>) Acetal, (<b>c</b>) Nylon 66 black, (<b>d</b>) Nylon 66 yellow, and (<b>e</b>) PC ABS PP.</p> Full article ">Figure 11
<p>FT-IR spectra for the five polymers studied, showing their vibrational bands before and after the heat treatments by indirect sunlight heating (<b>a</b>) PP ABS, (<b>b</b>) Acetal, (<b>c</b>) Nylon 66 black, (<b>d</b>) Nylon 66 yellow, and (<b>e</b>) PC ABS PP.</p> Full article ">
13 pages, 6193 KiB  
Article
Maximizing Interlaminar Fracture Toughness in Bidirectional GFRP through Controlled CNT Heterogeneous Toughening
by Hongchen Zhao, Yunxiao Zhang, Yunfu Ou, Longqiang Wu, Juan Li, Xudan Yao, Xiongwu Yang and Dongsheng Mao
Polymers 2024, 16(7), 1011; https://doi.org/10.3390/polym16071011 - 8 Apr 2024
Viewed by 1322
Abstract
“Interleaving” is widely used for interlaminar toughening of fiber-reinforced composites, and the structure of interleaving is one of the important factors affecting the toughening efficiency of laminates. Several experiments have demonstrated that compared to continuous and dense structures, toughening layers with structural heterogeneity [...] Read more.
“Interleaving” is widely used for interlaminar toughening of fiber-reinforced composites, and the structure of interleaving is one of the important factors affecting the toughening efficiency of laminates. Several experiments have demonstrated that compared to continuous and dense structures, toughening layers with structural heterogeneity can trigger multiple toughening mechanisms and have better toughening effects. On this basis, this work further investigates the application of heterogeneous toughening phases in interlaminar toughening of bidirectional GFRP. CNT was selected to construct toughening phases, which was introduced into the interlaminar of composites through efficient spraying methods. By controlling the amount of CNT, various structures of CNT toughening layers were obtained. The fracture toughness of modified laminates was tested, and their toughening mechanism was analyzed based on fracture surface observation. The results indicate that the optimal CNT usage (0.5 gsm) can increase the initial and extended values of interlayer fracture toughness by 136.0% and 82.0%, respectively. The solvent acetone sprayed with CNT can dissolve and re-precipitate a portion of the sizing agent on the surface of the fibers, which improves the bonding of the fibers to the resin. More importantly, larger discrete particles are formed between the layers, guiding the cracks to deflect in the orientation of the toughened layer. This generates additional energy dissipation and ultimately presents an optimal toughening effect. Full article
(This article belongs to the Special Issue Advances in Polymers Science and Technology: From Nano-Engineering to Multifunctional Applications)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Flow chart of glass fiber modification via CNT and the process of laminate preparation.</p> Full article ">Figure 2
<p>DCB sample in mode Ⅰ interlaminar fracture toughness test.</p> Full article ">Figure 3
<p>(<b>a</b>) SEM and (<b>b</b>) TEM images of short CNT; (<b>c</b>) a typical Raman spectrum of short CNT powders.</p> Full article ">Figure 4
<p>GF surface treated with different amounts of acetone spray and CNT/acetone dispersion spray.</p> Full article ">Figure 5
<p>Statistical results of GF surface roughness.</p> Full article ">Figure 6
<p>SEM images of glass fabrics and CNT spray coating: (<b>a</b>) is commercial glass fabrics without any modification; (<b>b</b>–<b>f</b>) are fabrics coated with short CNT with areal densities of 0, 0.3, 0.5, 0.7, and 1.0 gsm.</p> Full article ">Figure 7
<p>Representative load-opening displacement curves (<b>a</b>) and R-curves (<b>b</b>) of specimens with and without CNT spray coating; (<b>c</b>) is the comparison of crack growth speed, initiation, and propagation value of G<sub>IC</sub>.</p> Full article ">Figure 8
<p>Comparison of fracture surfaces: (<b>a</b>) baseline sample without CNT modification; (<b>b</b>–<b>f</b>) samples modified with 0, 0.3, 0.5, 0.7, and 1.0 gsm CNT spray coating.</p> Full article ">Figure 9
<p>Possible modes of crack propagation in laminates with control sample (<b>a</b>,<b>d</b>) and CNT-toughened samples whose areal densities are (<b>b</b>,<b>e</b>) 0.5 and (<b>c</b>,<b>f</b>) 1.0 gsm, respectively.</p> Full article ">
13 pages, 2268 KiB  
Review
Recent Progress on Conversion of Lignocellulosic Biomass by MOF-Immobilized Enzyme
by Juan Tao, Shengjie Song and Chen Qu
Polymers 2024, 16(7), 1010; https://doi.org/10.3390/polym16071010 - 8 Apr 2024
Cited by 1 | Viewed by 1731
Abstract
The enzyme catalysis conversion of lignocellulosic biomass into valuable chemicals and fuels showed a bright outlook for replacing fossil resources. However, the high cost and easy deactivation of free enzymes restrict the conversion process. Immobilization of enzymes in metal–organic frameworks (MOFs) is one [...] Read more.
The enzyme catalysis conversion of lignocellulosic biomass into valuable chemicals and fuels showed a bright outlook for replacing fossil resources. However, the high cost and easy deactivation of free enzymes restrict the conversion process. Immobilization of enzymes in metal–organic frameworks (MOFs) is one of the most promising strategies due to MOF materials’ tunable building units, multiple pore structures, and excellent biocompatibility. Also, MOFs are ideal support materials and could enhance the stability and reusability of enzymes. In this paper, recent progress on the conversion of cellulose, hemicellulose, and lignin by MOF-immobilized enzymes is extensively reviewed. This paper focuses on the immobilized enzyme performances and enzymatic mechanism. Finally, the challenges of the conversion of lignocellulosic biomass by MOF-immobilized enzyme are discussed. Full article
(This article belongs to the Collection Lignin)
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<p>The chemical structures of lignocellulosic biomass main components. (<b>a</b>) Cellulose; (<b>b</b>) hemicellulose; (<b>c</b>) lignin basic units.</p> Full article ">Figure 2
<p>Comparison of the advantages and disadvantages between chemical and biological conversion methods.</p> Full article ">Figure 3
<p>Schematic diagram of polysaccharide degradation by cellulase (endo-β-1,4-glucanase (EG), exo-β-1,4-glucanase (CBH), and β-glucosidase (BG)), lytic polysaccharide monooxygenase (LPMO), and hemicellulases.</p> Full article ">Figure 4
<p>Three methods of cellulase immobilization by MOF.</p> Full article ">Figure 5
<p>A fragment of the lignin chemical structure and its schematic diagram of degradation by laccase (Lac), lignin peroxidases (LiP), and manganese peroxidase (MnP).</p> Full article ">
18 pages, 4435 KiB  
Article
Development and Characteristics of Protein Edible Film Derived from Pork Gelatin and Beef Broth
by Agnieszka Ciurzyńska, Monika Janowicz, Magdalena Karwacka, Małgorzata Nowacka and Sabina Galus
Polymers 2024, 16(7), 1009; https://doi.org/10.3390/polym16071009 - 7 Apr 2024
Cited by 3 | Viewed by 3758
Abstract
The aim of this work was to develop edible films derived from gelatin and beef broth and to analyze the physical properties of the output products. The presented research is important from the point of view of searching for food packaging solutions that [...] Read more.
The aim of this work was to develop edible films derived from gelatin and beef broth and to analyze the physical properties of the output products. The presented research is important from the point of view of searching for food packaging solutions that may replace traditionally used plastic packaging. This study’s conceptual framework is in line with the trend of sustainable development and zero waste. This study was conducted to develop a recipe for edible films derived from beef gelatin with gelatin concentrations at 4%, 8%, and 12% enriched with additions of beef broth in amounts of 25, 50, 75, and 100%. Selected physical properties of the output edible films were examined in terms of thickness, swelling in water, opacity, water content, water solubility, structure, and mechanical properties. The conducted research made it plausible to conclude that the addition of broth has a positive effect on the extensibility of the edible films and the other physical properties under consideration, especially on decreasing the film thickness, which was found to vary between 50.2 and 191.6 µm. When gelatin and broth were added at low concentrations, the tensile strength of the films increased, and subsequently decreased; however, an opposite effect was observed for elongation at break. The increased broth concentration caused the film opacity to increase from 0.39 to 4.54 A/mm and from 0.18 to 1.04 A/mm with gelatin concentrations of 4% and 12%, respectively. The water solubility of the gelatin films decreased as a result of the broth addition. However, it was noticed that increasing the content of broth caused the water solubility to increase in the tested films. The mere presence of broth in the gelatin films changed the microstructure of the films and also made them thinner. Full article
(This article belongs to the Special Issue Edible, Active and Intelligent Food Packaging Polymeric Materials)
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<p>Technological diagram for preparing the edible films for the research test purpose.</p> Full article ">Figure 2
<p>The influence of the gelatin concentration (<b>a</b>) and beef broth concentration (<b>b</b>) on the thickness of the edible protein films.</p> Full article ">Figure 3
<p>The edible films with 12% gelatin concentration and broth concentration at 0%, 25%, 50%, 75%, and 100%.</p> Full article ">Figure 4
<p>The influence of the gelatin concentration (<b>a</b>) and broth concentration (<b>b</b>) on the opacity of the edible protein films.</p> Full article ">Figure 5
<p>The influence of the gelatin concentration (<b>a</b>) and broth concentration (<b>b</b>) on the water content of the edible protein films.</p> Full article ">Figure 6
<p>The influence of the gelatin concentration (<b>a</b>) and broth concentration (<b>b</b>) on the water solubility of the protein edible films.</p> Full article ">Figure 7
<p>Average values of the tensile strength (TS) and relative elongation (E) for the respective gelatin and broth concentrations.</p> Full article ">Figure 8
<p>The influence of the gelatin concentration (<b>a</b>) and broth concentration (<b>b</b>) on the average values of the elongation (E) of the protein edible films.</p> Full article ">Figure 9
<p>The influence of the gelatin concentration (<b>a</b>) and broth concentration (<b>b</b>) on the average values of the tensile strength (TS) of the protein edible films.</p> Full article ">Figure 10
<p>Cross-sectional structures of the tested gelatin and gelatin–broth edible films.</p> Full article ">
13 pages, 4091 KiB  
Article
A Novel Nanofiber Hydrogel Adhesive Based on Carboxymethyl Cellulose Modified by Adenine and Thymine
by Chong Xie, Runde Yang, Xing Wan, Haorong Li, Liangyao Ge, Xiaofeng Li and Guanglei Zhao
Polymers 2024, 16(7), 1008; https://doi.org/10.3390/polym16071008 - 7 Apr 2024
Viewed by 1466
Abstract
Natural polymer-based adhesive hydrogels have garnered significant interest for their outstanding strength and versatile applications, in addition to being eco-friendly. However, the adhesive capabilities of purely natural products are suboptimal, which hampers their practical use. To address this, we engineered carboxymethyl cellulose (CMC) [...] Read more.
Natural polymer-based adhesive hydrogels have garnered significant interest for their outstanding strength and versatile applications, in addition to being eco-friendly. However, the adhesive capabilities of purely natural products are suboptimal, which hampers their practical use. To address this, we engineered carboxymethyl cellulose (CMC) surfaces with complementary bases, adenine (A) and thymine (T), to facilitate the self-assembly of adhesive hydrogels (CMC-AT) with a nanofiber configuration. Impressively, the shear adhesive strength reached up to 6.49 MPa with a mere 2% adhesive concentration. Building upon this innovation, we conducted a comparative analysis of the shear adhesion properties between CMC and CMC-AT hydrogel adhesives when applied to delignified and non-delignified wood chips. We examined the interplay between the adhesives and the substrate, as well as the role of mechanical interlocking in overall adhesion performance. Our findings offer a fresh perspective on the development of new biodegradable polymer hydrogel adhesives. Full article
(This article belongs to the Special Issue Carbohydrate Biopolymers)
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<p>Schematic diagram of preparation process and adhesion mechanism of CMC-AT nanofiber hydrogel adhesive.</p> Full article ">Figure 2
<p>SEM image of membrane: (<b>a</b>) CMC AND (<b>b</b>) CMC-AT; the white scale bar in the figure is 1 μm. Images of aqueous solutions: (<b>c</b>) Tyndall effect of 2 wt.% CMC on the right and CMC-AT on the left; (<b>d</b>) inverted 2 wt.% CMC-AT.</p> Full article ">Figure 3
<p>FTIR spectra of CMC, CMC-AT, thymidine, and adenine.</p> Full article ">Figure 4
<p>Solid-state nuclear magnetic resonance carbon spectra of CMC and CMC-AT.</p> Full article ">Figure 5
<p>X-ray diffraction (XRD) spectra of (<b>a</b>) CMC, CMC-AT, (<b>b</b>)thymidine, and adenine.</p> Full article ">Figure 6
<p>Stress–strain curves of CMC and CMC-AT.</p> Full article ">Figure 7
<p>SEM image of the surface of the basswood chips with different coating amounts of CMC-AT: (<b>a</b>) 0, (<b>b</b>) 120 g/m<sup>2</sup>, (<b>c</b>) 360 g/m<sup>2</sup>; the white scale bar in the figure is 50 μm.</p> Full article ">Figure 8
<p>Shear adhesion strength curve.</p> Full article ">
17 pages, 5405 KiB  
Article
Coarse-Grained Simulations on Polyethylene Crystal Network Formation and Microstructure Analysis
by Mohammed Althaf Hussain, Takashi Yamamoto, Syed Farooq Adil and Shigeru Yao
Polymers 2024, 16(7), 1007; https://doi.org/10.3390/polym16071007 - 7 Apr 2024
Viewed by 1589
Abstract
Understanding and characterizing semi-crystalline models with crystalline and amorphous segments is crucial for industrial applications. A coarse-grained molecular dynamics (CGMD) simulations study probed the crystal network formation in high-density polyethylene (HDPE) from melt, and shed light on tensile properties for microstructure analysis. Modified [...] Read more.
Understanding and characterizing semi-crystalline models with crystalline and amorphous segments is crucial for industrial applications. A coarse-grained molecular dynamics (CGMD) simulations study probed the crystal network formation in high-density polyethylene (HDPE) from melt, and shed light on tensile properties for microstructure analysis. Modified Paul–Yoon–Smith (PYS/R) forcefield parameters are used to compute the interatomic forces among the PE chains. The isothermal crystallization at 300 K and 1 atm predicts the multi-nucleus crystal growth; moreover, the lamellar crystal stems and amorphous region are alternatively oriented. A one-dimensional density distribution along the alternative lamellar stems further confirms the ordering of the lamellar-stack orientation. Using this plastic model preparation approach, the semi-crystalline model density (ρcr) of ca. 0.913 g·cm−3 and amorphous model density (ρam) of ca. 0.856 g·cm−3 are obtained. Furthermore, the ratio of ρcr/ρam ≈ 1.06 is in good agreement with computational (≈1.096) and experimental (≈1.14) data, ensuring the reliability of the simulations. The degree of crystallinity (χc) of the model is ca. 52% at 300 K. Nevertheless, there is a gradual increase in crystallinity over the specified time, indicating the alignment of the lamellar stems during crystallization. The characteristic stress–strain curve mimicking tensile tests along the z-axis orientation exhibits a reversible sharp elastic regime, tensile strength at yield ca. 100 MPa, and a non-reversible tensile strength at break of 350%. The cavitation mechanism embraces the alignment of lamellar stems along the deformation axis. The study highlights an explanatory model of crystal network formation for the PE model using a PYS/R forcefield, and it produces a microstructure with ordered lamellar and amorphous segments with robust mechanical properties, which aids in predicting the microstructure–mechanical property relationships in plastics under applied forces. Full article
(This article belongs to the Special Issue Polymer Dynamics: From Single Chains to Networks and Gels)
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Full article ">Figure 1
<p>Pictorial representation of the initial models: (<b>A</b>) Polyethylene chain with 1000 UA; (<b>B</b>) Independent chains folding in Material Studio 2022 (version 22.1.0.3462, Accelrys, San Diego, CA, USA) Forcite module; (<b>C</b>) Folded chains with the penetrating interphases; (<b>D</b>) Folded chains packed to obtain the two-lamellae layers.</p> Full article ">Figure 2
<p>The isotropic mixture formation in the melting and equilibration step is accounted for 10C<sub>1000</sub> model using potential energy (<b>A</b>), pressure (<b>B</b>), density (<b>C</b>), and temperature (<b>D</b>) for the NVT 1 ns melting and equilibration for 10 ns time length and NPT conditions of 450 K and 1 atm.</p> Full article ">Figure 3
<p>The density (<b>A</b>) and number of entanglements per chain (<b>B</b>) changes during the temperature-quenching simulation of 10C<sub>1000</sub> model accounted for 450 K to 300 K at 1 atm and NPT conditions.</p> Full article ">Figure 4
<p>Structural changes during the MD simulations, starting from the LAMMPS data file to the isothermally crystallized model at 1µs for 10-chain models. Each chain represents a color in the studied model.</p> Full article ">Figure 5
<p>The computed total density (<b>A</b>) and degree of crystallinity (<b>B</b>,<b>C</b>) in isothermal crystallization at 300 K and 1 atm conditions are given for the 10C<sub>1000</sub> model in blue. The <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>χ</mi> </mrow> <mrow> <mi>c</mi> </mrow> </msub> </mrow> </semantics></math> is shown with the nanosecond simulation time (ns).</p> Full article ">Figure 6
<p>Z-axis dimensional density in the 10C<sub>1000</sub> model evidences the formation of random-order polymer chains sandwiched between two highly oriented lamellar stems. The rectangular boxes represent the HDPE chain structures; each chain represents a unique color in both models. The graph with a density of ca. 1.0 g·cm<sup>−3</sup> represents the crystalline phase (blue dotted region), and the amorphous state represents the density of ca. 0.85 g·cm<sup>−3</sup> (red dotted lines).</p> Full article ">Figure 7
<p>The S-S curve of the 10C<sub>1000</sub> model is computed at 300 K and zero-pressure conditions using the NPT ensemble. The model is deformed to 1000% of the initial box length in all axis directions, aligning the lamellar stack orientation. The colors in the models represent each chain.</p> Full article ">Figure 8
<p>Strain-rate-dependent S-S curves for the 10C<sub>1000</sub> model at 300 K and zero-pressure conditions using the NPT ensemble. Each model deformed to 1000% of the initial box length in the Z-axis direction, aligning the lamellar stack orientation.</p> Full article ">
22 pages, 5039 KiB  
Article
Synthesis of Water-Dispersible Poly(dimethylsiloxane) and Its Potential Application in the Paper Coating Industry as an Alternative for PFAS-Coated Paper and Single-Use Plastics
by Syeda Shamila Hamdani, Hazem M. Elkholy, Alexandra Alford, Kang Jackson, Muhammad Naveed, Ian Wyman, Yun Wang, Kecheng Li, Syed W. Haider and Muhammad Rabnawaz
Polymers 2024, 16(7), 1006; https://doi.org/10.3390/polym16071006 - 7 Apr 2024
Cited by 1 | Viewed by 2512
Abstract
Polyethylene-, polyvinylidene chloride-, and per- and polyfluoroalkyl substance-coated paper generate microplastics or fluorochemicals in the environment. Here, we report an approach for the development of oil-resistant papers using an environmentally friendly, fluorine-free, water-dispersible poly(dimethylsiloxane) (PDMS) coating on kraft paper. Carboxylic-functionalized PDMS (PDMS-COOH) was [...] Read more.
Polyethylene-, polyvinylidene chloride-, and per- and polyfluoroalkyl substance-coated paper generate microplastics or fluorochemicals in the environment. Here, we report an approach for the development of oil-resistant papers using an environmentally friendly, fluorine-free, water-dispersible poly(dimethylsiloxane) (PDMS) coating on kraft paper. Carboxylic-functionalized PDMS (PDMS-COOH) was synthesized and subsequently neutralized with ammonium bicarbonate to obtain a waterborne emulsion, which was then coated onto kraft paper. The water resistance of the coated paper was determined via Cobb60 measurements. The Cobb60 value was reduced to 2.70 ± 0.14 g/m2 as compared to 87.6 ± 5.1 g/m2 for uncoated paper, suggesting a remarkable improvement in water resistance. Similarly, oil resistance was found to be 12/12 on the kit test scale versus 0/12 for uncoated paper. In addition, the coated paper retained 70–90% of its inherent mechanical properties, and more importantly, the coated paper was recycled via pulp recovery using a standard protocol with a 91.1% yield. Full article
(This article belongs to the Special Issue Advances in Biodegradable Polymeric Materials with Applications in the Food Industry II)
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Full article ">Figure 1
<p><sup>1</sup>H-NMR spectrum of PDMS-COOH.</p> Full article ">Figure 2
<p>Ionization of PDMS-COOH using ammonium carbonate to obtain a water-based white emulsion that we used for paper coating.</p> Full article ">Figure 3
<p>(<b>A</b>) FTIR spectra of blank kraft paper (B-KP), modified coated paper samples, and solid materials used for coating, including PDMS-CCOOH and solid starch (SS). (<b>B</b>) FTIR spectra of starting materials, <span class="html-italic">meso</span>-butane-1,2,3,4-tetracarboxylic dianhydride (MBTCA), carbinol (hydroxyl)-terminated polydimethylsiloxane 50–65 cSt (DMS-C16), and PDMS-functionalized carboxylates (PDMS-COOH).</p> Full article ">Figure 4
<p>SEM images (200×) of (<b>A-1</b>) blank kraft paper (B-KP), (<b>A-2</b>) 5% starch-coated paper 5-S, (<b>A-3</b>) P1S0, (<b>A-4</b>) P2S1, and (<b>A-5</b>) P4S1. The bar scale shows 100 µm, The area in white boxes shows the pores and cracks present on paper surface. EDX spectra of blank kraft paper (<b>B-1</b>) and P4S1 (<b>B-2</b>).</p> Full article ">Figure 4 Cont.
<p>SEM images (200×) of (<b>A-1</b>) blank kraft paper (B-KP), (<b>A-2</b>) 5% starch-coated paper 5-S, (<b>A-3</b>) P1S0, (<b>A-4</b>) P2S1, and (<b>A-5</b>) P4S1. The bar scale shows 100 µm, The area in white boxes shows the pores and cracks present on paper surface. EDX spectra of blank kraft paper (<b>B-1</b>) and P4S1 (<b>B-2</b>).</p> Full article ">Figure 5
<p>(<b>A</b>) Cobb60 values (g/m<sup>2</sup>) of blank kraft paper and coated paper samples using various concentrations of PDMS-COOH and starch. (<b>B</b>) Water contact angles (WCAs) measured after the intervals of 30 and 5 min of putting water droplets on the surface of blank kraft paper and various coated paper samples. (<b>C</b>) A comparison of the Cobb60 values (g/m<sup>2</sup>) of blank kraft paper, coated paper P4S1, and two commercial control paper plates.</p> Full article ">Figure 6
<p>(<b>A</b>) Kit ratings of blank kraft paper and paper samples coated using various concentrations of PDMS-COOH and starch. (<b>B</b>) Oil contact angles (OCAs) were measured after the interval of 30 and 5 min of putting castor oil droplets on the surface of blank kraft paper and various coated paper samples. (<b>C</b>) A comparison of the kit ratings of blank kraft paper, coated paper P4S1, and two commercial control paper plates (Dixie and Glad).</p> Full article ">Figure 7
<p>Tensile strength (<b>A</b>), bending stiffness (<b>B</b>), ring crush test (<b>C</b>), and internal tearing resistance (<b>D</b>) of blank kraft paper and coated paper samples.</p> Full article ">Figure 8
<p>(<b>A</b>) FTIR spectra of recycled paper samples, which included blank kraft paper (B-KP), recycled B-KP that had been washed with NH<sub>4</sub>HCO<sub>3</sub> (B-KP-NH<sub>4</sub>), recycled paper P4S1 that had been washed with NH<sub>4</sub>HCO<sub>3</sub>, and PDMS-COOH solid material. (<b>B</b>) The sample P1S0 after repulping (<b>B-1</b>), screen-rejected material of P1S0-coated paper (<b>B-2</b>), and screen-accepted material of P1S0 (<b>B-3</b>).</p> Full article ">Scheme 1
<p>Illustration of the synthetic route leading to PDMS-COOH.</p> Full article ">
15 pages, 3341 KiB  
Article
Investigating How the Properties of Electrospun Poly(lactic acid) Fibres Loaded with the Essential Oil Limonene Evolve over Time under Different Storage Conditions
by Leah Williams, Fiona L. Hatton, Maria Cristina Righetti and Elisa Mele
Polymers 2024, 16(7), 1005; https://doi.org/10.3390/polym16071005 - 7 Apr 2024
Viewed by 1470
Abstract
Essential oils have been identified as effective natural compounds to prevent bacterial infections and thus are widely proposed as bioactive agents for biomedical applications. Across the literature, various essential oils have been incorporated into electrospun fibres to produce materials with, among others, antibacterial, [...] Read more.
Essential oils have been identified as effective natural compounds to prevent bacterial infections and thus are widely proposed as bioactive agents for biomedical applications. Across the literature, various essential oils have been incorporated into electrospun fibres to produce materials with, among others, antibacterial, anti-inflammatory and antioxidant activity. However, limited research has been conducted so far on the effect of these chemical products on the physical characteristics of the resulting composite fibres for extended periods of time. Within this work, electrospun fibres of poly(lactic acid) (PLA) were loaded with the essential oil limonene, and the impact of storage conditions and duration (up to 12 weeks) on the thermal degradation, glass transition temperature and mechanical response of the fibrous mats were investigated. It was found that the concentration of the encapsulated limonene changed over time and thus the properties of the PLA–limonene fibres evolved, particularly in the first two weeks of storage (independently from storage conditions). The amount of limonene retained within the fibres, even 4 weeks after fibre generation, was effective to successfully inhibit the growth of model microorganisms Escherichia coli, Staphylococcus aureus and Bacillus subtilis. The results of this work demonstrate the importance of evaluating physical properties during the ageing of electrospun fibres encapsulating essential oils, in order to predict performance modification when the composite fibres are used as constituents of medical devices. Full article
(This article belongs to the Special Issue Medical Applications of Polymer Fibers)
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<p>Selection of SEM images of electrospun mats of (<b>a</b>) PLA and (<b>b</b>) PLA–limonene fibres.</p> Full article ">Figure 2
<p>(<b>a</b>) TGA curves for electrospun mats of PLA (solid black line), PLA–limonene at time equal to 0 weeks (just after electrospinning; solid green line), PLA–limonene after 12 weeks of storage in normal conditions (dashed green line). Inset: first derivatives of the TGA curves, showing the stages of thermal degradation for the PLA–limonene fibres. (<b>b</b>) Limonene contained in the PLA–limonene fibres, at different time points, after storage in normal conditions. The remaining limonene percentage is obtained from the TGA thermograms considering the weight loss of the samples at 183 °C.</p> Full article ">Figure 3
<p>Glass transition temperature values at different time points for: (<b>a</b>) PLA fibres (grey histograms) and PLA–limonene fibres (green histograms) after storage under normal conditions (unsealed containers); (<b>b</b>) PLA–limonene fibres stored in normal conditions and PLA–limonene fibres stored in sealed DSC pans (light green histograms); (<b>c</b>) PLA–limonene fibres stored in normal conditions, PLA–limonene fibres stored in sealed DSC pans and PLA–limonene fibres stored in a sealed Petri dish (light-green, patterned histograms).</p> Full article ">Figure 4
<p>Box plots of (<b>a</b>) strain at break and (<b>b</b>) stress at break for PLA–limonene fibres stored under normal conditions for 12 weeks. Comparison between (<b>c</b>) strain at break and (<b>d</b>) stress at break for PLA–limonene fibres stored under normal conditions (unsealed, box plot on the left-hand side) and inside sealed Petri dishes (sealed, box plot on the right-hand side) for weeks 8, 10 and 12. The green symbols represent the individual measurements (repeats). Maximum and minimum values within 1.5 interquartile range (IQR) are indicated by the whiskers; lower and upper ends of the boxes represent the 25th and 75th percentile, while the middle line represents the median.</p> Full article ">Figure 5
<p>(<b>a</b>) Selected digital photographs of agar plates showing the growth of <span class="html-italic">E. coli</span>, <span class="html-italic">S. aureus</span> and <span class="html-italic">B. subtilis</span> after 0 h (white spots) and 24 h of incubation with PLA–limonene electrospun fibres. Similar results were obtained for all time points examined (weeks 0, 1, 2, 3 and 4). (<b>b</b>) Viability loss of <span class="html-italic">E. coli</span>, <span class="html-italic">S. aureus</span> and <span class="html-italic">B. subtilis</span> cultures incubated with PLA–limonene fibres that were kept in unsealed containers for up to 4 weeks.</p> Full article ">
16 pages, 6797 KiB  
Article
Structure and Properties of Exopolysaccharide Produced by Gluconobacter frateurii and Its Potential Applications
by Yingying Ning, Huiying Cao, Shouqi Zhao, Dongni Gao and Dan Zhao
Polymers 2024, 16(7), 1004; https://doi.org/10.3390/polym16071004 - 7 Apr 2024
Cited by 3 | Viewed by 1346
Abstract
An exopolysaccharide (EPS)-producing bacterium was isolated from apricot fermentation broth and identified as Gluconobacter frateurii HDC-08 (accession number: OK036475.1). HDC-08 EPS is a linear homopolysaccharide mainly composed of glucose linked by α-(1,6) glucoside bonds. It contains C, H, N and S elements, with [...] Read more.
An exopolysaccharide (EPS)-producing bacterium was isolated from apricot fermentation broth and identified as Gluconobacter frateurii HDC-08 (accession number: OK036475.1). HDC-08 EPS is a linear homopolysaccharide mainly composed of glucose linked by α-(1,6) glucoside bonds. It contains C, H, N and S elements, with a molecular weight of 4.774 × 106 Da. Microscopically, it has a smooth, glossy and compact sheet structure. It is an amorphous noncrystalline substance with irregular coils. Moreover, the EPS showed surface hydrophobicity and high thermal stability with a degradation temperature of 250.76 °C. In addition, it had strong antioxidant properties against DPPH radicals, ABPS radicals, hydroxyl radicals and H2O2. The EPS exhibited high metal-chelating activity and strong emulsifying ability for soybean oil, petroleum ether and diesel oil. The milk solidification test indicated that the EPS had good potential in fermented dairy products. In general, all the results demonstrate that HDC-08 EPS has promise for commercial applications as a food additive and antioxidant. Full article
(This article belongs to the Special Issue Advances in Natural Polysaccharides: Function and Application)
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<p>The colony morphology of strain HDC-08 on MRS (<b>A</b>) and MRS-S (<b>B</b>) agar plate at 10×; phylogenetic tree of strain HDC-08 by Neighbor-Joining method (<b>C</b>).</p> Full article ">Figure 2
<p>Ultraviolet spectrum (<b>A</b>), GPC (<b>B</b>), HPLC (<b>C</b>), FT-IR spectrum (<b>D</b>) of <span class="html-italic">G. frateurii</span> HDC-08 EPS.</p> Full article ">Figure 3
<p><sup>1</sup>H (<b>A</b>),<sup>13</sup>C (<b>B</b>), COSY (<b>C</b>), HSQC, (<b>D</b>) NMR spectra of <span class="html-italic">G. frateurii</span> HDC-08 EPS.</p> Full article ">Figure 4
<p>Surface morphology of <span class="html-italic">G. frateurii</span> HDC-08 EPS at various magnifications: 400× (<b>A</b>), 1000× (<b>B</b>).</p> Full article ">Figure 5
<p>The XRD spectra of <span class="html-italic">G. frateurii</span> HDC-08 EPS (<b>A</b>); plots of the λmax of Congo red and Congo red + <span class="html-italic">G. frateurii</span> HDC-08 EPS in solutions with various concentrations of NaOH (<b>B</b>); water contact angle analysis of <span class="html-italic">G. frateurii</span> HDC-08 in MRS (<b>C</b>) and MRS-S (<b>D</b>). <span class="html-italic">p</span> &lt; 0.05 (*) indicates significant differences.</p> Full article ">Figure 6
<p>The DPPH (<b>A</b>), ABTS (<b>B</b>), hydroxyl radical (<b>C</b>) and H<sub>2</sub>O<sub>2</sub> (<b>D</b>) scavenging activity of <span class="html-italic">G. frateurii</span> HDC-08 EPS. <span class="html-italic">p</span> &lt; 0.05 (*) and <span class="html-italic">p</span> &lt; 0.01 (**) indicate significant differences.</p> Full article ">Figure 7
<p>Coagulation effect of <span class="html-italic">G. frateurii</span> HDC-08 on 10% skim milk at 24 h (<b>A</b>), 36 h (<b>B</b>) and 48 h (<b>C</b>).</p> Full article ">Figure 8
<p>Metal adsorption activity (<b>A</b>), thermogravimetry (<b>B</b>) and viscosity characteristic (<b>C</b>) of <span class="html-italic">G. frateurii</span> HDC-08 EPS. <span class="html-italic">p</span> &lt; 0.05 (*) and <span class="html-italic">p</span> &lt; 0.01 (**) indicate significant differences.</p> Full article ">
19 pages, 2079 KiB  
Review
Radio-Absorbing Magnetic Polymer Composites Based on Spinel Ferrites: A Review
by Vladimir G. Kostishin, Igor M. Isaev and Dmitrij V. Salogub
Polymers 2024, 16(7), 1003; https://doi.org/10.3390/polym16071003 - 6 Apr 2024
Cited by 4 | Viewed by 2028
Abstract
Ferrite-containing polymer composites are of great interest for the development of radar-absorbing and -shielding materials (RAMs and RSMs). The main objective of RAM and RSM development is to achieve a combination of efficient electromagnetic wave (EMW) absorption methods with advantageous technological and mechanical [...] Read more.
Ferrite-containing polymer composites are of great interest for the development of radar-absorbing and -shielding materials (RAMs and RSMs). The main objective of RAM and RSM development is to achieve a combination of efficient electromagnetic wave (EMW) absorption methods with advantageous technological and mechanical properties as well as acceptable weight and dimensions in the final product. This work deals with composite RAMs and RSMs containing spinel-structured ferrites. These materials are chosen since they can act as efficient RAMs in the form of ceramic plates and as fillers for radar-absorbing polymer composites (RAC) for electromagnetic radiation (EMR). Combining ferrites with conducting fillers can broaden the working frequency range of composite RAMs due to the activation of various absorption mechanisms. Ferrite-containing composites are the most efficient materials that can be used as the working media of RAMs and RSMs due to a combination of excellent dielectric and magnetic properties of ferrites. This work contains a brief review of the main theoretical standpoints on EMR interaction with materials, a comparison between the radar absorption properties of ferrites and ferrite–polymer composites and analysis of some phenomenological aspects of the radar absorption mechanisms in those composites. Full article
(This article belongs to the Special Issue Magnetic Polymer Composites: Obtaining, Properties and Application)
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<p>(<b>a</b>) Basic diagram of electromagnetic parameter measurement using a vector network analyzer and (<b>b</b>) typical RAM and (<b>c</b>) RSM measurement setups.</p> Full article ">Figure 2
<p>Crystal structure of zinc spinel ferrite.</p> Full article ">Figure 3
<p>Illustration of the effect of filler electrical properties on the radar absorption properties of ferrite–polymer composites with Mn-Zn and Ni-Zn ferrite fillers. The results were obtained at NUST MISiS by the Department of Electronics Materials Technology. (<b>a</b>) <span class="html-italic">R<sub>l</sub></span>(<span class="html-italic">f</span>) spectrum of PVDF/Ni-Zn ferrite composite, (<b>b</b>) <span class="html-italic">SE<sub>T</sub></span>(<span class="html-italic">f</span>) spectrum of PVDF/Ni-Zn ferrite composite, (<b>c</b>) <span class="html-italic">R<sub>l</sub></span>(<span class="html-italic">f</span>) spectrum of PVDF/Mn-Zn ferrite composite, (<b>d</b>) <span class="html-italic">SE<sub>T</sub></span>(<span class="html-italic">f</span>) spectrum of PVDF/Mn-Zn ferrite composite.</p> Full article ">Figure 3 Cont.
<p>Illustration of the effect of filler electrical properties on the radar absorption properties of ferrite–polymer composites with Mn-Zn and Ni-Zn ferrite fillers. The results were obtained at NUST MISiS by the Department of Electronics Materials Technology. (<b>a</b>) <span class="html-italic">R<sub>l</sub></span>(<span class="html-italic">f</span>) spectrum of PVDF/Ni-Zn ferrite composite, (<b>b</b>) <span class="html-italic">SE<sub>T</sub></span>(<span class="html-italic">f</span>) spectrum of PVDF/Ni-Zn ferrite composite, (<b>c</b>) <span class="html-italic">R<sub>l</sub></span>(<span class="html-italic">f</span>) spectrum of PVDF/Mn-Zn ferrite composite, (<b>d</b>) <span class="html-italic">SE<sub>T</sub></span>(<span class="html-italic">f</span>) spectrum of PVDF/Mn-Zn ferrite composite.</p> Full article ">Figure 4
<p>(<b>a</b>) Schematic of polyaniline/Ni-Zn ferrite synthesis setup, (<b>b</b>) <span class="html-italic">R<sub>l</sub></span>(<span class="html-italic">f</span>) spectra of paraffin/Ni-Zn ferrite/polyaniline composites with different polyaniline/Ni-Zn ferrite ratios (legend: (a) Ni-Zn ferrite, (b) polyaniline/Ni-Zn ferrite = 2:1, (c) polyaniline/Ni-Zn ferrite = 1:2, (d) polyaniline, (e) polyaniline/Ni-Zn ferrite = 1:1) and (<b>c</b>) <span class="html-italic">R<sub>l</sub></span>(<span class="html-italic">f</span>) spectra of paraffin/Ni-Zn ferrite/polyaniline composites for 1:1 polyaniline/Ni-Zn ferrite ratio and different RAC thicknesses.</p> Full article ">Figure 4 Cont.
<p>(<b>a</b>) Schematic of polyaniline/Ni-Zn ferrite synthesis setup, (<b>b</b>) <span class="html-italic">R<sub>l</sub></span>(<span class="html-italic">f</span>) spectra of paraffin/Ni-Zn ferrite/polyaniline composites with different polyaniline/Ni-Zn ferrite ratios (legend: (a) Ni-Zn ferrite, (b) polyaniline/Ni-Zn ferrite = 2:1, (c) polyaniline/Ni-Zn ferrite = 1:2, (d) polyaniline, (e) polyaniline/Ni-Zn ferrite = 1:1) and (<b>c</b>) <span class="html-italic">R<sub>l</sub></span>(<span class="html-italic">f</span>) spectra of paraffin/Ni-Zn ferrite/polyaniline composites for 1:1 polyaniline/Ni-Zn ferrite ratio and different RAC thicknesses.</p> Full article ">Figure 5
<p>Scheme of the main mechanisms of absorption of electromagnetic waves in magnetic polymer composites with ferrite filler.</p> Full article ">
21 pages, 9016 KiB  
Article
New Composites Derived from the Natural Fiber Polymers of Discarded Date Palm Surface and Pineapple Leaf Fibers for Thermal Insulation and Sound Absorption
by Mohamed Ali, Zeyad Al-Suhaibani, Redhwan Almuzaiqer, Ali Albahbooh, Khaled Al-Salem and Abdullah Nuhait
Polymers 2024, 16(7), 1002; https://doi.org/10.3390/polym16071002 - 6 Apr 2024
Cited by 4 | Viewed by 2194
Abstract
New composites made of natural fiber polymers such as wasted date palm surface fiber (DPSF) and pineapple leaf fibers (PALFs) are developed in an attempt to lower the environmental impact worldwide and, at the same time, produce eco-friendly insulation materials. Composite samples of [...] Read more.
New composites made of natural fiber polymers such as wasted date palm surface fiber (DPSF) and pineapple leaf fibers (PALFs) are developed in an attempt to lower the environmental impact worldwide and, at the same time, produce eco-friendly insulation materials. Composite samples of different compositions are obtained using wood adhesive as a binder. Seven samples are prepared: two for the loose natural polymers of PALF and DPSF, two for the composites bound by single materials of PALF and DPSF using wood adhesive as a binder, and three composites of both materials and the binder with different compositions. Sound absorption coefficients (SACs) are obtained for bound and hybrid composite samples for a wide range of frequencies. Flexural moment tests are determined for these composites. A thermogravimetric analysis test (TGA) and the moisture content are obtained for the natural polymers and composites. The results show that the average range of thermal conductivity coefficient is 0.042–0.06 W/(m K), 0.052–0.075 W/(m K), and 0.054–0.07 W/(m K) for the loose fiber polymers, bound composites, and hybrid composites, respectively. The bound composites of DPSF have a very good sound absorption coefficient (>0.5) for almost all frequencies greater than 300 Hz, followed by the hybrid composite ones for frequencies greater than 1000 Hz (SAC > 0.5). The loose fiber polymers of PALF are thermally stable up to 218 °C. Most bound and hybrid composites have a good flexure modulus (6.47–64.16 MPa) and flexure stress (0.43–1.67 Mpa). The loose fiber polymers and bound and hybrid composites have a low moisture content below 4%. These characteristics of the newly developed sustainable and biodegradable fiber polymers and their composites are considered promising thermal insulation and sound absorption materials in replacing synthetic and petrochemical insulation materials in buildings and other engineering applications. Full article
(This article belongs to the Special Issue Fiber and Polymer Composites: Processing, Simulation, Properties and Applications II)
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Full article ">Figure 1
<p>Loose fibers: (<b>a</b>) date palm surface fibers (DPSFs) and (<b>b</b>) pineapple leaf fibers.</p> Full article ">Figure 2
<p>Solar cooker oven ((<b>a</b>) closed and (<b>b</b>) open) and (<b>c</b>) electric convection oven.</p> Full article ">Figure 3
<p>Loose fibers in the wooden mold: (<b>a</b>) PALF and (<b>b</b>) DPSF.</p> Full article ">Figure 4
<p>Process of preparing the bound or hybrid polymer samples: (<b>a</b>) stainless steel mold holding the sample, (<b>b</b>) presser, (<b>c</b>) drying solar oven, (<b>d</b>) drying electric oven, (<b>e</b>) the removed dried sample, (<b>f</b>) the heat flow meter for thermal conductivity measurement.</p> Full article ">Figure 5
<p>Bound and hybrid composite boards of PALF and DPSF: (<b>a</b>) bound composite PALF (# 2), (<b>b</b>) bound composite DPSF (# 4), (<b>c</b>) hybrid composite of PALF + DPSF (# 5), (<b>d</b>) hybrid composite of PALF + DPSF (6), and (<b>e</b>) hybrid composite of PALF + DPSF (# 7).</p> Full article ">Figure 6
<p>The specimen dimensions used in the three-point flexural test.</p> Full article ">Figure 7
<p>Three-point flexural test results for the bound and hybrid samples: (<b>a</b>) force-deflection profiles and (<b>b</b>) flexure stress–strain curves.</p> Full article ">Figure 8
<p>Comparison of the mechanical properties of the bound and hybrid composite samples.</p> Full article ">Figure 9
<p>PALF: (<b>a</b>) texture of the loose fiber polymers (Lo # 1) at 2000 magnification, (<b>b</b>) thickness of the ground leaves, and (<b>c</b>) composite (Bo # 2); red spots show the polymerized binder.</p> Full article ">Figure 10
<p>DPSF surface morphology at 250 magnification: (<b>a</b>) loose fiber polymers (Lo # 3) at 25 magnification and (<b>b</b>) bound composite (Bo # 4) at 250 magnification.</p> Full article ">Figure 11
<p>Hybrid composite surface morphology of DPSF and PALF and the binder. (<b>a</b>) Hy # 5 composite at 50 magnification, (<b>b</b>) Hy # 6 composite at 100 magnification, and (<b>c</b>) Hy # 7 at 100 magnification, see text for details.</p> Full article ">Figure 12
<p>Thermal conductivity coefficient profiles for (<b>a</b>) loose and bound samples of DPSF and PALF and (<b>b</b>) loose and hybrid samples of DPSF and PALF.</p> Full article ">Figure 13
<p>Variation of thermal conductivity coefficients with the density of each sample at different temperatures: (<b>a</b>) loose and bound samples and (<b>b</b>) loose and hybrid samples.</p> Full article ">Figure 14
<p>Sound absorption coefficients at a wide range of frequencies for the bound and hybrid samples.</p> Full article ">Figure 15
<p>Noise reduction coefficients for bound and hybrid composites.</p> Full article ">Figure 16
<p>Thermal degradation and decomposition of PALF, see text for details.</p> Full article ">Figure 17
<p>Thermal degradation and decomposition of DPSF, see text for details.</p> Full article ">Figure 18
<p>Thermal degradation and decomposition of some composites: (<b>a</b>) bound of PALF sample (2), (<b>b</b>) bound of DPSF sample (4), (<b>c</b>) hybrid of PALF and DPSF sample (5), and (<b>d</b>) TGA profiles for the three composites, see text for details.</p> Full article ">Figure 19
<p>Moisture content profiles. (<b>a</b>) Samples 1, 2, 4, 5, 6, and 7 and (<b>b</b>) loose DPSF sample 3.</p> Full article ">Figure 20
<p>Moisture content profile for all samples at steady state conditions.</p> Full article ">
26 pages, 1276 KiB  
Review
Recent Progress of Carrageenan-Based Composite Films in Active and Intelligent Food Packaging Applications
by Bharath Kokkuvayil Ramadas, Jong-Whan Rhim and Swarup Roy
Polymers 2024, 16(7), 1001; https://doi.org/10.3390/polym16071001 - 6 Apr 2024
Cited by 9 | Viewed by 3729
Abstract
Recently, as concerns about petrochemical-derived polymers increase, interest in biopolymer-based materials is increasing. Undoubtedly, biopolymers are a better alternative to solve the problem of synthetic polymer-based plastics for packaging purposes. There are various types of biopolymers in nature, and mostly polysaccharides are used [...] Read more.
Recently, as concerns about petrochemical-derived polymers increase, interest in biopolymer-based materials is increasing. Undoubtedly, biopolymers are a better alternative to solve the problem of synthetic polymer-based plastics for packaging purposes. There are various types of biopolymers in nature, and mostly polysaccharides are used in this regard. Carrageenan is a hydrophilic polysaccharide extracted from red algae and has recently attracted great interest in the development of food packaging films. Carrageenan is known for its excellent film-forming properties, high compatibility and good carrier properties. Carrageenan is readily available and low cost, making it a good candidate as a polymer matrix base material for active and intelligent food packaging films. The carrageenan-based packaging film lacks mechanical, barrier, and functional properties. Thus, the physical and functional properties of carrageenan-based films can be enhanced by blending this biopolymer with functional compounds and nanofillers. Various types of bioactive ingredients, such as nanoparticles, natural extracts, colorants, and essential oils, have been incorporated into the carrageenan-based film. Carrageenan-based functional packaging film was found to be useful for extending the shelf life of packaged foods and tracking spoilage. Recently, there has been plenty of research work published on the potential of carrageenan-based packaging film. Therefore, this review discusses recent advances in carrageenan-based films for applications in food packaging. The preparation and properties of carrageenan-based packaging films were discussed, as well as their application in real-time food packaging. The latest discussion on the potential of carrageenan as an alternative to traditionally used synthetic plastics may be helpful for further research in this field. Full article
(This article belongs to the Special Issue Bio-Based Polymeric Films II)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Development of carrageenan-based composite packaging film.</p> Full article ">Figure 2
<p>Application of carrageenan films in the active packaging of food.</p> Full article ">Figure 3
<p>Fabrication and application of carrageenan films in the intelligent packaging of foods.</p> Full article ">
16 pages, 6175 KiB  
Article
Mechanically Tough and Conductive Hydrogels Based on Gelatin and Z–Gln–Gly Generated by Microbial Transglutaminase
by Zhiwei Chen, Ruxin Zhang, Shouwei Zhao, Bing Li, Shuo Wang, Wenhui Lu and Deyi Zhu
Polymers 2024, 16(7), 999; https://doi.org/10.3390/polym16070999 - 5 Apr 2024
Viewed by 1480
Abstract
Gelatin-based hydrogels with excellent mechanical properties and conductivities are desirable, but their fabrication is challenging. In this work, an innovative approach for the preparation of gelatin-based conductive hydrogels is presented that improves the mechanical and conductive properties of hydrogels by integrating Z–Gln–Gly into [...] Read more.
Gelatin-based hydrogels with excellent mechanical properties and conductivities are desirable, but their fabrication is challenging. In this work, an innovative approach for the preparation of gelatin-based conductive hydrogels is presented that improves the mechanical and conductive properties of hydrogels by integrating Z–Gln–Gly into gelatin polymers via enzymatic crosslinking. In these hydrogels (Gel–TG–ZQG), dynamic π–π stacking interactions are created by the introduction of carbobenzoxy groups, which can increase the elasticity and toughness of the hydrogel and improve the conductivity sensitivity by forming effective electronic pathways. Moreover, the mechanical properties and conductivity of the obtained hydrogel can be controlled by tuning the molar ratio of Z–Gln–Gly to the primary amino groups in gelatin. The hydrogel with the optimal mechanical properties (Gel–TG–ZQG (0.25)) exhibits a high storage modulus, compressive strength, tensile strength, and elongation at break of 7.8 MPa at 10 °C, 0.15 MPa at 80% strain, 0.343 MPa, and 218.30%, respectively. The obtained Gel–TG–ZQG (0.25) strain sensor exhibits a short response/recovery time (260.37 ms/130.02 ms) and high sensitivity (0.138 kPa−1) in small pressure ranges (0–2.3 kPa). The Gel–TG–ZQG (0.25) hydrogel-based sensors can detect full-range human activities, such as swallowing, fist clenching, knee bending and finger pressing, with high sensitivity and stability, yielding highly reproducible and repeatable sensor responses. Additionally, the Gel–TG–ZQG hydrogels are noncytotoxic. All the results demonstrate that the Gel–TG–ZQG hydrogel has potential as a biosensor for wearable devices and health-monitoring systems. Full article
(This article belongs to the Special Issue Sustainable Biopolymer-Based Composites: Processing, Characterization, and Application II)
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<p>Schematic of the formation of the Gel–TG–ZQG hydrogel and the interactions between the side groups in the hydrogel.</p> Full article ">Figure 2
<p>MSD curves collected at 50 °C during Gel–TG–ZQG hydrogel formation. (<b>a</b>) Gel−TG, (<b>b</b>) Gel–TG–ZQG (0.05), (<b>c</b>) Gel–TG–ZQG (0.125), (<b>d</b>) Gel–TG–ZQG (0.25), (<b>e</b>) Gel–TG–ZQG (0.5), (<b>f</b>) Gel–TG–ZQG (0.75) and (<b>g</b>) Gel–TG–ZQG (1). (<b>h</b>) Schematic diagram of the covalent crosslinks between gelatin chains (for Gel−TG). (<b>i</b>) Schematic diagram of the interactions between gelatin chains including covalent crosslinking and π–π stacking (for Gel–TG–ZQG (0.05), Gel–TG–ZQG (0.125), and Gel–TG–ZQG (0.25)). (<b>j</b>) Schematic diagram of the π–π stacking interactions between gelatin chains (for Gel–TG–ZQG (0.5), Gel–TG–ZQG (0.75), and Gel–TG–ZQG (1)).</p> Full article ">Figure 3
<p>TGA (<b>a</b>) and DTG (<b>b</b>) curves of the Gel−TG and Gel–TG–ZQG hydrogels.</p> Full article ">Figure 4
<p>Microstructures and pore size distributions of the freeze-dried hydrogels. (<b>a</b>) Gel−TG, (<b>b</b>) Gel–TG–ZQG (0.05), (<b>c</b>) Gel–TG–ZQG (0.125), (<b>d</b>) Gel–TG–ZQG (0.25), (<b>e</b>) Gel–TG–ZQG (0.5), (<b>f</b>) Gel–TG–ZQG (0.75), and (<b>g</b>) Gel–TG–ZQG (1).</p> Full article ">Figure 5
<p>Storage moduli of the gelatin-based hydrogels tested under a frequency sweep at 15 °C (<b>a</b>) and under a temperature sweep (<b>b</b>).</p> Full article ">Figure 6
<p>Mechanical properties of the gelatin-based hydrogels. (<b>a</b>) Compressive stress-strain curves of hydrogels with different contents of Z–Gln–Gly. (<b>b</b>) Typical images of Gel–TG–ZQG (0.25) before and after compression. (<b>c</b>) Comparison of the tensile strength and elongation at break values of hydrogels with different Z–Gln–Gly contents.</p> Full article ">Figure 7
<p>Equilibrium swelling ratios of the Gel−TG and Gel–TG–ZQG hydrogels in PBS solution at pH 7.4.</p> Full article ">Figure 8
<p>Viability of HeLa cells cultured on media supplemented with different hydrogel extracts for 24 h and 48 h.</p> Full article ">Figure 9
<p>Electrical conductivities of the Gel–TG–ZQG hydrogels.</p> Full article ">Figure 10
<p>(<b>a</b>) Response/recovery time of the Gel–TG–ZQG (0.25) pressure sensor. (<b>b</b>) Sensitivity of the Gel–TG–ZQG (0.25) pressure sensor. (<b>c</b>) Curves of relative resistance versus time under different strains. Relative resistance versus time based on Gel–TG–ZQG (0.25) pressure sensors for cyclic motion at the throat (<b>d</b>), fist €, knee joints (<b>f</b>), and fingers (<b>g</b>,<b>h</b>).</p> Full article ">
16 pages, 14563 KiB  
Article
Tribological Behavior of Sulfonated Polyether Ether Ketone with Three Different Chemical Structures under Water Lubrication
by Xiaozhi Chen, Tao Hu, Wei Wu, Xiaohong Yi, Fenghua Li and Chenhui Zhang
Polymers 2024, 16(7), 998; https://doi.org/10.3390/polym16070998 - 5 Apr 2024
Viewed by 1129
Abstract
With the development of the shipbuilding industry, it is necessary to improve tribological properties of polyether ether ketone (PEEK) as a water-lubricated bearing material. In this study, the sulfonated PEEK (SPEEK) with three distinct chemical structures was synthesized through direct sulfonated polymerization, and [...] Read more.
With the development of the shipbuilding industry, it is necessary to improve tribological properties of polyether ether ketone (PEEK) as a water-lubricated bearing material. In this study, the sulfonated PEEK (SPEEK) with three distinct chemical structures was synthesized through direct sulfonated polymerization, and high fault tolerance and a controllable sulfonation degree ensured the batch stability. The tribological and mechanical properties of SPEEK with varying side groups (methyl and tert-butyl) and rigid segments (biphenyl) were compared after sintering in a vacuum furnace. Compared to the as-made PEEK, as the highly electronegative sulfonic acid group enhanced the hydration lubrication, the friction coefficient and wear rate of SPEEK were significantly reduced by 30% and 50% at least without affecting the mechanical properties. And lower steric hindrance and entanglement between molecular chains were proposed to be partially responsible for the lowest friction behavior of SPEEK with methyl side groups, making it a promising and competitive option for water-lubricated bearings. Full article
(This article belongs to the Special Issue Advances in the Processing and Application of Polymers and Their Composites III)
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<p>Preparation of the SPEEK and as-made pure PEEK specimens with three chemical structures: (<b>a</b>) reaction equations and processes; (<b>b</b>) sinter procedure; and (<b>c</b>) schematic of the working principle of the tribometer.</p> Full article ">Figure 2
<p>The <sup>1</sup>H NMR spectra of SMPEEK, STPEEK, and STDPEEK.</p> Full article ">Figure 3
<p>The FTIR spectra of SPEEK and the corresponding pure PEEK.</p> Full article ">Figure 4
<p>Full XPS, O1s, and S2p spectra of (<b>a</b>–<b>c</b>) SMPEEK, (<b>d</b>–<b>f</b>) STPEEK, and (<b>g</b>–<b>i</b>) STDPEEK.</p> Full article ">Figure 5
<p>DSC and TGA profiles of (<b>a</b>,<b>b</b>) SMPEEK, (<b>c</b>,<b>d</b>) STPEEK, and (<b>e</b>,<b>f</b>) STDPEEK and their corresponding as-made pure PEEK.</p> Full article ">Figure 6
<p>Friction coefficient of SPEEK and corresponding as-made pure PEEK with three chemical structures in aqueous lubrication through the rotating tribometer: (<b>a</b>) as-made pure PEEK, (<b>b</b>) SPEEK, and SPEEK at different (<b>c</b>) loads and (<b>d</b>) sliding speeds.</p> Full article ">Figure 7
<p>(<b>a</b>) Wear surface topography of SPEEK and as-made pure PEEK after rotating friction tests, and (<b>b</b>) their profile curves along the direction perpendicular to the velocity and (<b>c</b>) wear rate of the SPEEK and as-made pure PEEK with three chemical structures.</p> Full article ">Figure 8
<p>(<b>a</b>) Static contact angles of SPEEK and the corresponding pure PEEK. (<b>b</b>) Model of the hydration lubrication.</p> Full article ">Figure 9
<p>SEM and EDS images of the wear surface of (<b>a</b>) SMPEEK, (<b>b</b>) STPEEK, and (<b>c</b>) STDPEEK after a rotating test for 60 min.</p> Full article ">
21 pages, 2986 KiB  
Article
Determining the Relationship between Delivery Parameters and Ablation Distribution for Novel Gel Ethanol Percutaneous Therapy in Ex Vivo Swine Liver
by Erika Chelales, Katriana von Windheim, Arshbir Singh Banipal, Elizabeth Siebeneck, Claire Benham, Corrine A. Nief, Brian Crouch, Jeffrey I. Everitt, Alan Alper Sag, David F. Katz and Nirmala Ramanujam
Polymers 2024, 16(7), 997; https://doi.org/10.3390/polym16070997 - 5 Apr 2024
Viewed by 1641
Abstract
Ethyl cellulose–ethanol (ECE) is emerging as a promising formulation for ablative injections, with more controllable injection distributions than those from traditional liquid ethanol. This study evaluates the influence of salient injection parameters on forces needed for infusion, depot volume, retention, and shape in [...] Read more.
Ethyl cellulose–ethanol (ECE) is emerging as a promising formulation for ablative injections, with more controllable injection distributions than those from traditional liquid ethanol. This study evaluates the influence of salient injection parameters on forces needed for infusion, depot volume, retention, and shape in a large animal model relevant to human applications. Experiments were conducted to investigate how infusion volume (0.5 mL to 2.5 mL), ECE concentration (6% or 12%), needle gauge (22 G or 27 G), and infusion rate (10 mL/h) impacted the force of infusion into air using a load cell. These parameters, with the addition of manual infusion, were investigated to elucidate their influence on depot volume, retention, and shape (aspect ratio), measured using CT imaging, in an ex vivo swine liver model. Force during injection increased significantly for 12% compared to 6% ECE and for 27 G needles compared to 22 G. Force variability increased with higher ECE concentration and smaller needle diameter. As infusion volume increased, 12% ECE achieved superior depot volume compared to 6% ECE. For all infusion volumes, 12% ECE achieved superior retention compared to 6% ECE. Needle gauge and infusion rate had little influence on the observed depot volume or retention; however, the smaller needles resulted in higher variability in depot shape for 12% ECE. These results help us understand the multivariate nature of injection performance, informing injection protocol designs for ablations using gel ethanol and infusion, with volumes relevant to human applications. Full article
(This article belongs to the Special Issue Advanced Preparation and Application of Cellulose)
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<p>Comparison of force during injection for 6% and 12% ECE through 22 G needles. (<b>A</b>) Force measurements for 6% ECE and 12% ECE through a 22 G needle at 10 mL/h. The force required for 12% ECE was significantly larger than the force for 6% (* <span class="html-italic">p</span> &lt; 0.05). (<b>B</b>–<b>F</b>) Plots of the force measured over time during an infusion for 0.5–2.5 mL infusions through a 22 G needle at 10 mL/h.</p> Full article ">Figure 2
<p>Comparison of force during injection for 6% and 12% ECE through 27 G needles. (<b>A</b>) Force measurements for 6% ECE and 12% ECE through a 27 G needle at 10 mL/h. The force required for 12% ECE was significantly higher than 6% ECE (* <span class="html-italic">p</span> &lt; 0.05). (<b>B</b>–<b>F</b>) Plots of the force measured over time during an infusion for 0.5–2.5 mL infusions through a 27 G needle at 10 mL/h.</p> Full article ">Figure 3
<p>Comparison of infusions of 6% and 12% ECE through a 27 G needle. (<b>A</b>,<b>B</b>) Representative 3D segmentations of the depot volume for 0.5 mL, 1 mL, 1.5 mL, 2 mL, and 2.5 mL infusion volumes for 6% ECE (<b>A</b>) and 12% ECE (<b>B</b>) using 27 G needles and a 10 mL/h infusion rate. (<b>C</b>,<b>D</b>) Box plots showing the resultant depot volume achieved at various (0.5–2.5 mL) infusion volumes of 6% ECE (<b>C</b>) and 12% ECE (<b>D</b>) using 27 G needles and a 10 mL/h infusion rate (* <span class="html-italic">p</span> &lt; 0.05). No significant differences were observed between any of the infusion volumes (0.5–2.5 mL) for 6% ECE. However, both 2 mL and 2.5 mL infusion volumes achieved significantly larger distribution volumes than the 0.5 mL infusion volume for 12% ECE. (<b>E</b>,<b>F</b>) Box plots showing the percent infusion volume retained in the depot for various infusion volumes (0.5–2.5 mL) of 6% ECE (<b>E</b>) and 12% ECE (<b>F</b>) using 27 G needles and a 10 mL/h infusion rate. Significant differences were not observed for either 12% ECE or 6% ECE. (<b>G</b>,<b>H</b>) Box plots of the aspect ratio achieved at various infusion volumes (0.5–2.5 mL) for 6% ECE (<b>G</b>) and 12% ECE (<b>H</b>) using 27 G needles and a 10 mL/h infusion rate. While no significant differences in the aspect ratio were found, there was a larger range of aspect ratios for 12% ECE compared to 6% ECE.</p> Full article ">Figure 4
<p>Comparison of infusions of 6% and 12%ECE through a 22 G needle. (<b>A</b>,<b>B</b>) Representative 3D segmentations of the depot volume for 0.5 mL, 1 mL, 1.5 mL, 2 mL, and 2.5 mL infusion volumes for 6% ECE (<b>A</b>) and 12% ECE (<b>B</b>) using 22 G needles and a 10 mL/h infusion rate. (<b>C</b>,<b>D</b>) Box plots showing the resultant depot volume achieved at various (0.5–2.5 mL) infusion volumes of 6% ECE (<b>C</b>) and 12% ECE (<b>D</b>) using 22 G needles and a 10 mL/h infusion rate (* <span class="html-italic">p</span> &lt; 0.05). No significant differences were observed between any of the infusion volumes (0.5–2.5 mL) for 6% ECE. However, 1.5 mL, 2 mL, and 2.5 mL infusion volumes achieved significantly larger distribution volumes than the 0.5 mL infusion volume for 12% ECE. (<b>E</b>,<b>F</b>) Box plots showing the percent infusion volume retained in the depot for various infusion volumes (0.5–2.5 mL) of 6% ECE (<b>E</b>) and 12% ECE (<b>F</b>) using 22 G needles and a 10 mL/h infusion rate (* <span class="html-italic">p</span> &lt; 0.05). A significantly lower percent of the infusion volume was retained in the depot for 2.5 mL compared to 0.5 mL infusions for 6% ECE. Significant differences were not observed for 12% ECE. (<b>G</b>,<b>H</b>) Box plots of the aspect ratio achieved at various infusion volumes (0.5–2.5 mL) for 6% ECE (<b>G</b>) and 12% ECE (<b>H</b>) using 22 G needles and a 10 mL/h infusion rate. No significant differences in aspect ratio were found for 12% ECE or 6% ECE.</p> Full article ">Figure 5
<p>Trends in the relationship between depot volume and percent infusion volume retained in the depot to the infusion volume. (<b>A</b>,<b>B</b>) Line plots of the relationship between the depot volume and infusion volume for infusions performed with 22 G (<b>A</b>) and 27 G (<b>B</b>) needles. For the 22 G needle (<b>A</b>), the 6% ECE (<span class="html-italic">p</span> &lt; 0.05, r<sup>2</sup> = 0.24) and 12% ECE (<span class="html-italic">p</span> &lt; 0.05, r<sup>2</sup> = 0.40) both show positive relationships between depot volume and infusion volume, with the 12% ECE achieving a stronger correlation between depot volume and infusion volume. Similar to the 22 G, for the 27 G needle (<b>B</b>), the 6% ECE (<span class="html-italic">p</span> &lt; 0.05, r<sup>2</sup> = 0.14) and 12% ECE (<span class="html-italic">p</span> &lt; 0.05, r<sup>2</sup> = 0.40) both show positive relationships between depot volume and infusion volume, with the 12% ECE achieving a stronger correlation between depot volume and infusion volume. (<b>C</b>,<b>D</b>) Line plots of the relationship between the percent of the infusion volume retained in the depot and infusion volume for infusions performed with 22 G (<b>A</b>) and 27 G (<b>B</b>) needles. For the 22 G needle (<b>C</b>), the 6% ECE (<span class="html-italic">p</span> &lt; 0.05, r<sup>2</sup> = 0.20) shows a negative relationship between the percent retained and the infusion volume. The 12% ECE (<span class="html-italic">p</span> &lt; 0.05, r<sup>2</sup> = 0.00) shows a more stable percent retained as infusion volume increases. Similar to the 22 G, for the 27 G needle (<b>D</b>), the 6% ECE (<span class="html-italic">p</span> &lt; 0.05, r<sup>2</sup> = 0.11) shows a slightly negative relationship between the percent retained and the infusion volume. The 12% ECE (<span class="html-italic">p</span> &lt; 0.05, r<sup>2</sup> = 0.02) shows a similar slight negative relationship between the percent retained and the infusion volume, but with greater retention at all volumes compared to the 6% ECE.</p> Full article ">Figure 6
<p>Comparison of manual infusion and 10 mL/h infusion rates for 0.5 mL and 1 mL infusions of 12% ECE. (<b>A</b>) Representative 3D segmentations of the depot volume for 0.5 mL and 1 mL infusion volumes for 12% ECE using both 22 G and 27 G needles and 10 mL/h and manual infusion rates. (<b>B</b>) Box plots showing the resultant depot volumes achieved at small infusion volumes (0.5–1 mL) of 12% ECE for both 22 G and 27 G needles at both 10 mL/h (blue) and manual (red) infusion rates. No significant differences were observed. (<b>C</b>) Box plots showing the percent infusion volume retained in the depot for at small infusion volumes (0.5–1 mL) of 12% ECE for both 22 G and 27 G needles at both 10 mL/h (blue) and manual (red) infusion rates. No significant differences were observed. (<b>D</b>) Box plots showing the aspect ratio at small infusion volumes (0.5–1 mL) of 12% ECE for both 22 G and 27 G needles at both 10 mL/h (blue) and manual (red) infusion rates. No significant differences were observed.</p> Full article ">
22 pages, 5929 KiB  
Article
Development of Polylactic Acid Films with Alkali- and Acetylation-Treated Flax and Hemp Fillers via Solution Casting Technique
by Anamol Pokharel, Kehinde James Falua, Amin Babaei-Ghazvini, Mostafa Nikkhah Dafchahi, Lope G. Tabil, Venkatesh Meda and Bishnu Acharya
Polymers 2024, 16(7), 996; https://doi.org/10.3390/polym16070996 - 5 Apr 2024
Cited by 1 | Viewed by 1682
Abstract
This study aims to enhance value addition to agricultural byproducts to produce composites by the solution casting technique. It is well known that PLA is moisture-sensitive and deforms at high temperatures, which limits its use in some applications. When blending with plant-based fibers, [...] Read more.
This study aims to enhance value addition to agricultural byproducts to produce composites by the solution casting technique. It is well known that PLA is moisture-sensitive and deforms at high temperatures, which limits its use in some applications. When blending with plant-based fibers, the weak point is the poor filler–matrix interface. For this reason, surface modification was carried out on hemp and flax fibers via acetylation and alkaline treatments. The fibers were milled to obtain two particle sizes of <75 μm and 149–210 μm and were blended with poly (lactic) acid at different loadings (0, 2.5%, 5%, 10%, 20%, and 30%) to form a composite film The films were characterized for their spectroscopy, physical, and mechanical properties. All the film specimens showed C–O/O–H groups and the π–π interaction in untreated flax fillers showed lignin phenolic rings in the films. It was noticed that the maximum degradation temperature occurred at 362.5 °C. The highest WVPs for untreated, alkali-treated, and acetylation-treated composites were 20 × 10−7 g·m/m2 Pa·s (PLA/hemp30), 7.0 × 10−7 g·m/m2 Pa·s (PLA/hemp30), and 22 × 10−7 g·m/m2 Pa·s (PLA/hemp30), respectively. Increasing the filler content caused an increase in the color difference of the composite film compared with that of the neat PLA. Alkali-treated PLA/flax composites showed significant improvement in their tensile strength, elongation at break, and Young’s modulus at a 2.5 or 5% filler loading. An increase in the filler loadings caused a significant increase in the moisture absorbed, whereas the water contact angle decreased with an increasing filler concentration. Flax- and hemp-induced PLA-based composite films with 5 wt.% loadings showed a more stable compromise in all the examined properties and are expected to provide unique industrial applications with satisfactory performance. Full article
(This article belongs to the Special Issue Synthesis, Characterization and Applications of Natural Polymers)
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<p>(<b>a</b>) Flax and (<b>b</b>) hemp (adapted from [<a href="#B5-polymers-16-00996" class="html-bibr">5</a>]). Scalebar: 1 cm.</p> Full article ">Figure 2
<p>FTIR spectra of fillers and films. Flax fiber and hemp fiber (<b>a</b>–<b>d</b>). Control and composites containing treated and untreated fibers (<b>e</b>–<b>j</b>).</p> Full article ">Figure 3
<p>High-resolution XPS spectra. Signal assessments of different binding energies of (<b>a</b>) untreated flax, (<b>b</b>) untreated hemp, (<b>c</b>) alkali-treated flax, (<b>d</b>) alkali-treated hemp, (<b>e</b>) acetylated flax, and (<b>f</b>) acetylated hemp.</p> Full article ">Figure 4
<p>TGA and DTG of PLA/flax and PLA/hemp films with (<b>a1</b>,<b>a2</b>) alkali treatment and (<b>b1</b>,<b>b2</b>) acetylation treatment.</p> Full article ">Figure 5
<p>Color of PLA/flax and PLA/hemp films. Red dashed line was the neat PLA as the control sample.</p> Full article ">Figure 6
<p>Water contact angle: (<b>a</b>) untreated flax/PLA, (<b>b</b>) alkali-treated flax/PLA, (<b>c</b>) acetylation-treated flax/PLA (green dashed line), (<b>d</b>) untreated hemp/PLA, (<b>e</b>) alkali-treated hemp/PLA, and (<b>f</b>) acetylation-treated hemp/PLA (green dashed line).</p> Full article ">Figure 7
<p>Moisture absorption of PLA/flax (<b>a</b>,<b>b</b>) and of PLA/hemp (<b>c</b>,<b>d</b>) films. The bar chart represents the difference between untreated, alkali-treated, and acetylation-treated fibers loaded into the PLA films.</p> Full article ">Figure 8
<p>WVP of PLA/flax and PLA/hemp films. (<b>a</b>) PLA/Flax Particle size &lt; 75 μm, (<b>b</b>) Particle size 149–210 μm, (<b>c</b>) PLA/Hemp Particle size &lt; 75 μm, (<b>d</b>) Particle size 149-210 μm.</p> Full article ">Figure 9
<p>Mechanical characteristics of PLA/flax films. Particle size &lt; 75 μm: (<b>a</b>) tensile strength, (<b>c</b>) elongation at break, and (<b>e</b>) Young’s modulus. Particle size 149–210 μm: (<b>b</b>) tensile strength, (<b>d</b>) elongation at break, and (<b>f</b>) Young’s modulus. Particle size &lt; 75 μm: (<b>g</b>) stress–strain curves of PLA/flax films.</p> Full article ">Figure 9 Cont.
<p>Mechanical characteristics of PLA/flax films. Particle size &lt; 75 μm: (<b>a</b>) tensile strength, (<b>c</b>) elongation at break, and (<b>e</b>) Young’s modulus. Particle size 149–210 μm: (<b>b</b>) tensile strength, (<b>d</b>) elongation at break, and (<b>f</b>) Young’s modulus. Particle size &lt; 75 μm: (<b>g</b>) stress–strain curves of PLA/flax films.</p> Full article ">Figure 10
<p>Mechanical characteristics of PLA/hemp films. Particle size &lt; 75 μm: (<b>a</b>) tensile strength, (<b>c</b>) elongation at break, (<b>e</b>) Young’s modulus. Particle size &lt; 149–210 μm: (<b>b</b>) tensile strength, (<b>d</b>) elongation at break, (<b>f</b>) Young’s modulus. Particle size &lt; 75 μm: (<b>g</b>) stress–strain curves of PLA/hemp films.</p> Full article ">Figure 11
<p>A chart displaying the properties of natural and synthetic materials is presented, with Young’s modulus plotted (adapted and modified from [<a href="#B4-polymers-16-00996" class="html-bibr">4</a>]). Values obtained in this study are denoted by stars.</p> Full article ">
10 pages, 1758 KiB  
Article
Effect of Environmental pH on the Mechanics of Chitin and Chitosan: A Single-Molecule Study
by Song Zhang, Yunxu Ji, Yiwei He, Juan Dong, Haohang Li and Shirui Yu
Polymers 2024, 16(7), 995; https://doi.org/10.3390/polym16070995 - 5 Apr 2024
Viewed by 2268
Abstract
Chitin and chitosan are important structural macromolecules for most fungi and marine crustaceans. The functions and application areas of the two molecules are also adjacent beyond their similar molecular structure, such as tissue engineering and food safety where solution systems are involved. However, [...] Read more.
Chitin and chitosan are important structural macromolecules for most fungi and marine crustaceans. The functions and application areas of the two molecules are also adjacent beyond their similar molecular structure, such as tissue engineering and food safety where solution systems are involved. However, the elasticities of chitin and chitosan in solution lack comparison at the molecular level. In this study, the single-molecule elasticities of chitin and chitosan in different solutions are investigated via atomic force microscope (AFM) based single-molecule spectroscopy (SMFS). The results manifest that the two macromolecules share the similar inherent elasticity in DOSM due to their same chain backbone. However, obvious elastic deviations can be observed in aqueous conditions. Especially, a lower pH value (acid environment) is helpful to increase the elasticity of both chitin and chitosan. On the contrary, the tendency of elastic variation of chitin and chitosan in a larger pH value (alkaline environment) shows obvious diversity, which is mainly determined by the side groups. This basic study may produce enlightenment for the design of intelligent chitin and chitosan food packaging and biomedical materials. Full article
(This article belongs to the Special Issue Mechanics of Polymeric Structures across Scales)
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<p>Chemical structures of chitin and chitosan.</p> Full article ">Figure 2
<p>Typical F-E curves of chitosan obtained in DMSO. (<b>A</b>) The original F-E curves. (<b>B</b>) The normalized effects of those shown in (<b>A</b>).</p> Full article ">Figure 3
<p>Experimental F-E of chitin and chitosan compared with the theoretical curve from QM-FJC model.</p> Full article ">Figure 4
<p>F-E curves of chitin and chitosan obtained in DI water (<b>A</b>), pH = 5 (<b>B</b>) and pH = 3 (<b>C</b>) compared with the inherent F-E curve.</p> Full article ">Figure 5
<p>Comparison of chitin (<b>A</b>) and chitosan (<b>B</b>) obtained in aqueous conditions with different pH. (<b>C</b>) The nonbonding energy along the chain of chitin and chitosan.</p> Full article ">
13 pages, 5119 KiB  
Article
A Study on the Effect and Suppression of Hydrogen Permeation Behavior on the Friction Characteristics of PEEK/PTFE Composites via Molecular Dynamics Simulation
by Henan Tang, Minghui Wang, Yunlong Li and Yan Wang
Polymers 2024, 16(7), 1000; https://doi.org/10.3390/polym16071000 - 5 Apr 2024
Cited by 1 | Viewed by 1519
Abstract
To research the effect of hydrogen permeation on the friction characteristics of the seal materials on the hydrogen equipment, the molecular models of 10% PEEK/PTFE composites and its frictional models were established, respectively, and molecular dynamics (MDs) and giant canonical Monte Carlo (GCMC) [...] Read more.
To research the effect of hydrogen permeation on the friction characteristics of the seal materials on the hydrogen equipment, the molecular models of 10% PEEK/PTFE composites and its frictional models were established, respectively, and molecular dynamics (MDs) and giant canonical Monte Carlo (GCMC) methods were used to simulate the diffusion coefficient, dissolution coefficient and permeability coefficient of the hydrogen in PEEK/PTFE composites. The effect of a different amount of hydrogen on the friction and wear of PEEK/PTFE composites was also studied. The results showed that few permeations of the hydrogen gas mainly demonstrated having a positive effect on the surface of the PEEK/PTFE composites, and the wear rate of the PEEK/PTFE composites showed a slight decreasing trend. The wear rate of the PEEK/PTFE composites gradually decreased when more hydrogen molecules penetrated the matrix. With the further penetration of the hydrogen molecules, the wear rate and friction coefficient of the PEEK/PTFE composites rapidly increased, showing a negative effect. With the further penetration of the hydrogen molecule, the friction coefficient of the composite displayed a small fluctuation and then a rapid decreasing trend. Meanwhile, effective improvement measures were proposed, and the introduction of the graphene was verified to be effective to reduce the negative effect of the hydrogen permeation, thereby improving the friction performance of the PEEK/PTFE composites. Full article
(This article belongs to the Section Polymer Physics and Theory)
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<p>Surface morphology of the specimen with compressed hydrogen medium in long-term wear. (<b>a</b>) 100× and (<b>b</b>) 500×.</p> Full article ">Figure 2
<p>Surface morphology of specimen without compression medium (50×). (<b>a</b>) Unworn and (<b>b</b>) worn.</p> Full article ">Figure 3
<p>PEEK/PTFE composites.</p> Full article ">Figure 4
<p>Free volume (FFV) distribution of PTFE/PEEK composite (blue is the Connolly surface, and gray is the van der Waals surface).</p> Full article ">Figure 5
<p>Adsorption isotherm curve.</p> Full article ">Figure 6
<p>Relationship curve between mean azimuth shift and time.</p> Full article ">Figure 7
<p>Fe and PEEK/PTFE composites frictional model.</p> Full article ">Figure 8
<p>Friction process of PEEK/PTFE composites.</p> Full article ">Figure 9
<p>Variation in the friction coefficient and wear rate.</p> Full article ">Figure 10
<p>Basic principled diagram of improving polymer gas barrier performance with flake nanomaterials.</p> Full article ">Figure 11
<p>Fe and 3% GRAPHENE/PEEK/PTFE composites model.</p> Full article ">Figure 12
<p>Comparison diagram of 3% GRAPHENE/PEEK/PTFE friction process.</p> Full article ">Figure 13
<p>Broken line diagram of friction coefficient and wear rate.</p> Full article ">
20 pages, 4813 KiB  
Article
Conventional Dental Impressions vs. Impressions Reinforced with Rigid Mouthguards
by Andreea Codruta Novac, Anca Tudor, Daniela Maria Pop, Carina Sonia Neagu, Emanuela Lidia Crăciunescu, Mihai Romînu, Meda Lavinia Negruțiu, Virgil-Florin Duma and Cosmin Sinescu
Polymers 2024, 16(7), 994; https://doi.org/10.3390/polym16070994 - 4 Apr 2024
Viewed by 1632
Abstract
The impression materials utilized today in dental medicine offer a good reproducibility and are easily accepted by patients. However, because they are polymer-based, they have issues regarding their dimensional stability. In this respect, the present work proposes a new type of dental impression, [...] Read more.
The impression materials utilized today in dental medicine offer a good reproducibility and are easily accepted by patients. However, because they are polymer-based, they have issues regarding their dimensional stability. In this respect, the present work proposes a new type of dental impression, which is reinforced with rigid mouthguards. The aim of the study is to test the performances of such new impressions by comparing them to conventional ones—from this critical point of view, of the dimensional stability. Three types of polymeric materials were considered for both types of impressions: alginate, condensation silicone, and addition silicone. In order to obtain the new type of impressions, a manufacturing technique was developed, comprising the following phases: (i) conventional impressions were made; (ii) a plaster model was duplicated, and 15 rigid mouthguards were obtained; (iii) they were inserted in the impression technique, with each mouthguard positioned on the cast before the high-consistency material was inserted in the tray and the practitioner took the impression; (iv) the mouthguard remained in the tray and the low-viscosity material was inserted over the mouthguard; (v) the impression was positioned on the model, and after the material hardened, the mouthguard-reinforced impression was analyzed. In the evaluation of the dimensional stability, rigorous statistical analysis was essential to discern the performance differences between conventional and mouthguard-reinforced dental impressions. Statistical analyses employed non-parametric Mann–Whitney U tests because of the non-normal distribution of the data. They indicated a statistically significant improvement in the dimensional stability of addition silicone impressions when reinforced with mouthguards (p < 0.05), showcasing superior performance over conventional methods. Conversely, alginate and condensation silicone reinforced impressions did not exhibit the same level of stability improvement, suggesting the need for further optimization of these materials. In conclusion, from the three considered elastomers, addition silicone was found to be the prime candidate for high-precision dental impressions, with the potential to improve their quality from conventional impressions by utilizing the proposed reinforcing technique. Full article
(This article belongs to the Special Issue Advanced Polymeric Materials for Dental Applications III)
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<p>The measurement of a condensation silicone impression (1) in the standard impression tray (2): (<b>a</b>) dental impression positioned on (3) the sliding platform to allow for repeatability, with the position of the impression marked on the green paper; (<b>b</b>) the image captured by the camera (4) mounted on the system (5) for vertical adjustment of its position, as visualized on the screen. The image in (<b>b</b>) shows abutment 13 with markings for measuring both mesial-distal (MD) and buccal-oral (BO) distances. The button (6) for saving the images and the button (7) for measuring the distance between two points, while (8) shows the library with all saved images. Two distances are marked on the figure: the mesial-distal distance for the considered abutment (13 MD) and the buccal-oral distance for this abutment (13 BO).</p> Full article ">Figure 2
<p>The impression procedure for the impressions obtained from condensation silicone using rigid mouthguards: (<b>a</b>) placing the mouthguard on the model; (<b>b</b>) the first step of the impression; (<b>c</b>) the putty material with the mouthguard in the impression; (<b>d</b>) the insertion of the fluid in the impression; (<b>e</b>) the second step of the impression; (<b>f</b>) the final impression.</p> Full article ">Figure 3
<p>(<b>a</b>) Alginate impression with the mouthguard between the layers of the material, prepared for measuring the two distances on perpendicular directions for each abutment. Notations: (1) impression tray; (2) impression material; (3) impression of abutment 23; (4) impression of abutment 26; (5) impression of abutment 13; (6) impression of abutment 16. (<b>b</b>) Detailed image of the impression for abutment 26, with the MD and BO marked for measuring.</p> Full article ">Figure 4
<p>Results of the analysis performed at specific time moments for alginate regarding the comparison between conventional impressions (Group 1: CA) and mouthguard-reinforced impressions (Group 4: RA) for (<b>1</b>) BO and (<b>2</b>) MD, for the four considered abutments: (<b>a</b>) 13, (<b>b</b>) 16, (<b>c</b>) 23, and (<b>d</b>) 26.</p> Full article ">Figure 5
<p>Results of the analysis performed at specific time moments for condensation silicone regarding the comparison between conventional impressions (Group 2: CCS) and mouthguard-reinforced impressions (Group 4: RCS) for (<b>1</b>) BO and (<b>2</b>) MD, for the abutments (<b>a</b>) 13, (<b>b</b>) 16, (<b>c</b>) 23, and (<b>d</b>) 26.</p> Full article ">Figure 6
<p>Results of the analysis performed at specific time moments for addition silicone regarding the comparison between conventional impressions (Group 3: CAS) and mouthguard-reinforced impressions (Group 5: RAS) for (<b>1</b>) BO and (<b>2</b>) MD, for the abutments (<b>a</b>) 13, (<b>b</b>) 16, (<b>c</b>) 23, and (<b>d</b>) 26.</p> Full article ">Figure 7
<p>Boxplots for the mouthguard-reinforced impressions compared to conventional impressions for each of the three considered materials, for: (<b>a</b>) 16 BO, (<b>b</b>) 13 BO, (<b>c</b>) 23 BO, and (<b>d</b>) 26 BO. Explanations of the notations are made in the text.</p> Full article ">Figure 8
<p>Boxplots for the mouthguard-reinforced impressions compared to conventional impressions for each of the three considered materials, for: (<b>a</b>) 16 MD, (<b>b</b>) 13 MD, (<b>c</b>) 23 MD, and (<b>d</b>) 26 MD. Explanations of the notations are made in the text.</p> Full article ">Figure 9
<p>Defects in impressions using the mouthguard, for the three considered polymeric materials: (<b>a</b>) alginate; (<b>b</b>) condensation silicone; (<b>c</b>) addition silicone.</p> Full article ">
14 pages, 4131 KiB  
Article
Synthesis, Structure and Properties of Polyester Polyureas via a Non-Isocyanate Route with Good Combined Properties
by Liuchun Zheng, Qiqi Xie, Guangjun Hu, Bing Wang, Danqing Song, Yunchuan Zhang and Yi Liu
Polymers 2024, 16(7), 993; https://doi.org/10.3390/polym16070993 - 4 Apr 2024
Viewed by 1800
Abstract
Polyureas have been widely applied in many fields, such as coatings, fibers, foams and dielectric materials. Traditionally, polyureas are prepared from isocyanates, which are highly toxic and harmful to humans and the environment. Synthesis of polyureas via non-isocyanate routes is green, environmentally friendly [...] Read more.
Polyureas have been widely applied in many fields, such as coatings, fibers, foams and dielectric materials. Traditionally, polyureas are prepared from isocyanates, which are highly toxic and harmful to humans and the environment. Synthesis of polyureas via non-isocyanate routes is green, environmentally friendly and sustainable. However, the application of non-isocyanate polyureas is quite restrained due to their brittleness as the result of the lack of a soft segment in their molecular blocks. To address this issue, we have prepared polyester polyureas via an isocyanate-free route and introduced polyester-based soft segments to improve their toughness and endow high impact resistance to the polyureas. In this paper, the soft segments of polyureas were synthesized by the esterification and polycondensation of dodecanedioic acid and 1,4-butanediol. Hard segments of polyureas were synthesized by melt polycondensation of urea and 1,10-diaminodecane without a catalyst or high pressure. A series of polyester polyureas were synthesized by the polycondensation of the soft and hard segments. These synthesized polyester-type polyureas exhibit excellent mechanical and thermal properties. Therefore, they have high potential to substitute traditional polyureas. Full article
(This article belongs to the Special Issue Emerging Smart Applications of Functional Polymeric Materials)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Synthesis route of PBD<sub>x</sub>PU<sub>y</sub>.</p> Full article ">Figure 2
<p><sup>1</sup>H NMR spectra of PBD<sub>x</sub>PU<sub>y</sub> (Pre-PBD and Pre-PU): (<b>a</b>) the full spectra. (<b>b</b>) partially enlarged spectra.</p> Full article ">Figure 3
<p>FTIR spectra of Pre-PBD, Pre-PU and PBD<sub>x</sub>PU<sub>y</sub>. The arrows in the diagram are used to indicate the wavenumbers and corresponding function groups.</p> Full article ">Figure 4
<p>Fitting curves of FTIR spectra of PBD<sub>x</sub>PU<sub>y</sub>.</p> Full article ">Figure 5
<p>DSC of PBD<sub>x</sub>PU<sub>y</sub>: second heating (<b>a</b>) and cooling scans (<b>b</b>).</p> Full article ">Figure 6
<p>tan δ versus temperature for PBD<sub>x</sub>PU<sub>y</sub>.</p> Full article ">Figure 7
<p>TGA curves (<b>a</b>) and DTG curves (<b>b</b>) for PBD<sub>x</sub>PU<sub>y</sub>.</p> Full article ">Figure 8
<p>WAXD diffraction pattern of PBD<sub>x</sub>PU<sub>y</sub> films.</p> Full article ">Figure 9
<p>Fitting curves of WAXD diffraction pattern of PBD<sub>x</sub>PU<sub>y</sub>.</p> Full article ">Figure 10
<p>Stress-strain curves of PBD<sub>x</sub>PU<sub>y</sub>.</p> Full article ">Figure 11
<p>SEM images of quenched section of (<b>a</b>) PBD<sub>80%</sub>PU<sub>20%</sub>, (<b>b</b>) PBD<sub>70%</sub>PU<sub>30%</sub>, (<b>c</b>) PBD<sub>60%</sub>PU<sub>40%</sub>, (<b>d</b>) PBD<sub>50%</sub>PU<sub>50%</sub>.</p> Full article ">
19 pages, 4157 KiB  
Article
A Novel Method to Enhance the Mechanical Properties of Polyacrylonitrile Nanofiber Mats: An Experimental and Numerical Investigation
by Jaymin Vrajlal Sanchaniya, Inga Lasenko, Vishnu Vijayan, Hilary Smogor, Valters Gobins, Alaa Kobeissi and Dmitri Goljandin
Polymers 2024, 16(7), 992; https://doi.org/10.3390/polym16070992 - 4 Apr 2024
Cited by 5 | Viewed by 1857
Abstract
This study addresses the challenge of enhancing the transverse mechanical properties of oriented polyacrylonitrile (PAN) nanofibers, which are known for their excellent longitudinal tensile strength, without significantly compromising their inherent porosity, which is essential for effective filtration. This study explores the effects of [...] Read more.
This study addresses the challenge of enhancing the transverse mechanical properties of oriented polyacrylonitrile (PAN) nanofibers, which are known for their excellent longitudinal tensile strength, without significantly compromising their inherent porosity, which is essential for effective filtration. This study explores the effects of doping PAN nanofiber composites with varying concentrations of polyvinyl alcohol (PVA) (0.5%, 1%, and 2%), introduced into the PAN matrix via a dip-coating method. This approach ensured a random distribution of PVA within the nanofiber mat, aiming to leverage the synergistic interactions between PAN fibers and PVA to improve the composite’s overall performance. This synergy is primarily manifested in the structural and functional augmentation of the PAN nanofiber mats through localized PVA agglomerations, thin films between fibers, and coatings on the fibers themselves. Comprehensive evaluation techniques were employed, including scanning electron microscopy (SEM) for morphological insights; transverse and longitudinal mechanical testing; a thermogravimetric analysis (TGA) for thermal stability; and differential scanning calorimetry (DSC) for thermal behavior analyses. Additionally, a finite element method (FEM) analysis was conducted on a numerical simulation of the composite. Using our novel method, the results demonstrated that a minimal concentration of the PVA solution effectively preserved the porosity of the PAN matrix while significantly enhancing its mechanical strength. Moreover, the numerical simulations showed strong agreement with the experimental results, validating the effectiveness of PVA doping in enhancing the mechanical properties of PAN nanofiber mats without sacrificing their functional porosity. Full article
(This article belongs to the Special Issue Advances in Thermal, Electrical and Mechanical Properties of Polymer Composites)
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<p>Fabrication process of PVA-doped PAN nanofiber mats.</p> Full article ">Figure 2
<p>Schematic representation of the geometric parameters of nanofibers doped with PVA within an established domain.</p> Full article ">Figure 3
<p>Boundary conditions applied to observe the normal stress response of the samples to displacement.</p> Full article ">Figure 4
<p>SEM images of a PAN nanofiber mat doped with a 2.0% PVA solution: (<b>a</b>) localized agglomerations of PVA within the nanofiber mat (red) and coating on fibers (green); (<b>b</b>) cross-sectional image of the localized agglomerations of PVA.</p> Full article ">Figure 5
<p>Representative stress–strain graphs: (<b>a</b>) longitudinal direction, (<b>b</b>) transverse direction.</p> Full article ">Figure 5 Cont.
<p>Representative stress–strain graphs: (<b>a</b>) longitudinal direction, (<b>b</b>) transverse direction.</p> Full article ">Figure 6
<p>TGA and DTG of the pure PAN nanofiber mat and PVA film, highlighting their thermal degradation points and initial mass loss due to solvent evaporation.</p> Full article ">Figure 7
<p>TGA and DTG of the PAN nanofiber mats doped with different concentrations of PVA, illustrating the effect of the PVA concentration on their thermal degradation and early mass loss.</p> Full article ">Figure 8
<p>First DSC heating cycle of the pure PAN nanofiber mat and PVA film, showcasing their heat flow and glass transition temperatures.</p> Full article ">Figure 9
<p>First DSC heating cycle of PAN nanofiber mats doped with PVA, showing their increased heat absorption with higher PVA concentrations.</p> Full article ">Figure 10
<p>Second DSC heating cycle of the PAN nanofiber mat, the PVA film, and the PAN nanofiber mats doped with PVA, indicating their glass transition temperatures.</p> Full article ">Figure 11
<p>Normal stress on X axis for nanofiber mat doped with 2% PVA.</p> Full article ">Figure 12
<p>Comparison of the elastic moduli obtained from the experiments and the FE model.</p> Full article ">
23 pages, 7344 KiB  
Article
Enhancing the Weld Quality of Polylactic Acid Biomedical Materials Using Rotary Friction Welding
by Chil-Chyuan Kuo, Hua-Xhin Liang, Song-Hua Huang and Shih-Feng Tseng
Polymers 2024, 16(7), 991; https://doi.org/10.3390/polym16070991 - 4 Apr 2024
Viewed by 1376
Abstract
Polylactic acid (PLA) stands out as a biomaterial with immense potential, primarily owing to its innate biodegradability. Conventional methods for manufacturing PLA encompass injection molding or additive manufacturing (AM). Yet, the fabrication of sizable medical devices often necessitates fragmenting them into multiple components [...] Read more.
Polylactic acid (PLA) stands out as a biomaterial with immense potential, primarily owing to its innate biodegradability. Conventional methods for manufacturing PLA encompass injection molding or additive manufacturing (AM). Yet, the fabrication of sizable medical devices often necessitates fragmenting them into multiple components for printing, subsequently requiring reassembly to accommodate the constraints posed by the dimensions of the AM platform. Typically, laboratories resort to employing nuts and bolts for the assembly of printed components into expansive medical devices. Nonetheless, this conventional approach of jointing is susceptible to the inherent risk of bolts and nuts loosening or dislodging amid the reciprocating movements inherent to sizable medical apparatus. Hence, investigation into the joining techniques for integrating printed components into expansive medical devices has emerged as a critical focal point within the realm of research. The main objective is to enhance the joint strength of PLA polymer rods using rotary friction welding (RFW). The mean bending strength of welded components, fabricated under seven distinct rotational speeds, surpasses that of the underlying PLA substrate material. The average bending strength improvement rate of welding parts fabricated by RFW with three-stage transformation to 4000 rpm is about 41.94% compared with the average bending strength of PLA base material. The average surface hardness of the weld interface is about 1.25 to 3.80% higher than the average surface hardness of the PLA base material. The average surface hardness of the weld interface performed by RFW with variable rotational speed is higher than the average surface hardness of the weld interface performed at a fixed rotating friction speed. The temperature rise rate and maximum temperature recorded during RFW in the X-axis of the CNC turning machine at the outer edge of the welding part surpassed those observed in the internal temperature of the welding part. Remarkably, the proposed method in this study complies with the Sustainable Development Goals due to its high energy efficiency and low environmental pollution. Full article
(This article belongs to the Special Issue New Strategies for the Application of Biopolymer-Based Materials)
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<p>Research process in this study.</p> Full article ">Figure 2
<p>Slicing results of the PLA biomedical polymer rod in the slicing software.</p> Full article ">Figure 3
<p>Experimental configuration devised for gauging the welding temperature of PLA biomedical polymer rods during RFW.</p> Full article ">Figure 4
<p>Seven rotational speeds used in the RFW.</p> Full article ">Figure 5
<p>Schematic diagram of three temperature measurement locations in the (<b>a</b>) <span class="html-italic">Z</span>-axis and (<b>b</b>) <span class="html-italic">X</span>-axis directions of the CNC turning machine.</p> Full article ">Figure 6
<p>Bending strength of the base material and welding parts fabricated by RFW with seven rotational speeds.</p> Full article ">Figure 7
<p>Fracture surfaces of the specimens fabricated by (<b>a</b>) 3D printing and (<b>b</b>) welding parts fabricated by RFW with three-stage transformation after the bending test.</p> Full article ">Figure 8
<p>Maximum interface temperature of welding parts fabricated by RFW with seven rotational speeds.</p> Full article ">Figure 9
<p>Average Shore A surface hardness in the weld interface of welding parts fabricated by RFW with seven rotational speeds.</p> Full article ">Figure 10
<p>Shore A surface hardness distributions of the welding parts fabricated by RFW with seven rotational speeds.</p> Full article ">Figure 11
<p>Temperature histories of the three temperature measurement locations in the <span class="html-italic">Z</span>-axis of the CNC turning machine: (<b>a</b>) 1000 rpm, (<b>b</b>)2000 rpm, (<b>c</b>) 2500 rpm, (<b>d</b>) 3000 rpm, (<b>e</b>) 4000, (<b>f</b>) two-stage transformation to 4000 rpm, and (<b>g</b>) three-stage transformation of the rotational speed to 4000 rpm.</p> Full article ">Figure 11 Cont.
<p>Temperature histories of the three temperature measurement locations in the <span class="html-italic">Z</span>-axis of the CNC turning machine: (<b>a</b>) 1000 rpm, (<b>b</b>)2000 rpm, (<b>c</b>) 2500 rpm, (<b>d</b>) 3000 rpm, (<b>e</b>) 4000, (<b>f</b>) two-stage transformation to 4000 rpm, and (<b>g</b>) three-stage transformation of the rotational speed to 4000 rpm.</p> Full article ">Figure 11 Cont.
<p>Temperature histories of the three temperature measurement locations in the <span class="html-italic">Z</span>-axis of the CNC turning machine: (<b>a</b>) 1000 rpm, (<b>b</b>)2000 rpm, (<b>c</b>) 2500 rpm, (<b>d</b>) 3000 rpm, (<b>e</b>) 4000, (<b>f</b>) two-stage transformation to 4000 rpm, and (<b>g</b>) three-stage transformation of the rotational speed to 4000 rpm.</p> Full article ">Figure 11 Cont.
<p>Temperature histories of the three temperature measurement locations in the <span class="html-italic">Z</span>-axis of the CNC turning machine: (<b>a</b>) 1000 rpm, (<b>b</b>)2000 rpm, (<b>c</b>) 2500 rpm, (<b>d</b>) 3000 rpm, (<b>e</b>) 4000, (<b>f</b>) two-stage transformation to 4000 rpm, and (<b>g</b>) three-stage transformation of the rotational speed to 4000 rpm.</p> Full article ">Figure 12
<p>Temperature rise rate during RFW in the <span class="html-italic">Z</span>-axis of the CNC turning machine using seven rotational speeds.</p> Full article ">Figure 13
<p>Maximum temperatures measured during RFW in the <span class="html-italic">Z</span>-axis of the CNC turning machine using seven rotational speeds.</p> Full article ">Figure 14
<p>Temperature histories of the three temperature measurement locations in the <span class="html-italic">X</span>-axis of the CNC turning machine: (<b>a</b>) 1000 rpm, (<b>b</b>) 2000 rpm, (<b>c</b>) 2500 rpm, (<b>d</b>) 3000 rpm, (<b>e</b>) 4000, (<b>f</b>) two-stage transformation to 4000 rpm, and (<b>g</b>) three-stage transformation of the rotational speed to 4000 rpm.</p> Full article ">Figure 14 Cont.
<p>Temperature histories of the three temperature measurement locations in the <span class="html-italic">X</span>-axis of the CNC turning machine: (<b>a</b>) 1000 rpm, (<b>b</b>) 2000 rpm, (<b>c</b>) 2500 rpm, (<b>d</b>) 3000 rpm, (<b>e</b>) 4000, (<b>f</b>) two-stage transformation to 4000 rpm, and (<b>g</b>) three-stage transformation of the rotational speed to 4000 rpm.</p> Full article ">Figure 14 Cont.
<p>Temperature histories of the three temperature measurement locations in the <span class="html-italic">X</span>-axis of the CNC turning machine: (<b>a</b>) 1000 rpm, (<b>b</b>) 2000 rpm, (<b>c</b>) 2500 rpm, (<b>d</b>) 3000 rpm, (<b>e</b>) 4000, (<b>f</b>) two-stage transformation to 4000 rpm, and (<b>g</b>) three-stage transformation of the rotational speed to 4000 rpm.</p> Full article ">Figure 14 Cont.
<p>Temperature histories of the three temperature measurement locations in the <span class="html-italic">X</span>-axis of the CNC turning machine: (<b>a</b>) 1000 rpm, (<b>b</b>) 2000 rpm, (<b>c</b>) 2500 rpm, (<b>d</b>) 3000 rpm, (<b>e</b>) 4000, (<b>f</b>) two-stage transformation to 4000 rpm, and (<b>g</b>) three-stage transformation of the rotational speed to 4000 rpm.</p> Full article ">Figure 15
<p>Temperature rise rate during RFW in the <span class="html-italic">X</span>-axis of the CNC turning machine using seven rotational speeds.</p> Full article ">Figure 16
<p>Maximum temperatures measured during RFW in the <span class="html-italic">X</span>-axis of the CNC turning machine using seven rotational speeds.</p> Full article ">
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