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Green Composites

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Composites".

Deadline for manuscript submissions: closed (30 September 2015) | Viewed by 94086

Special Issue Editor

Prof. Dr. Marco Morreale

E-Mail Website
Guest Editor
Department of Engineering and Architecture, Kore University of Enna, 94100 Enna, Italy
Interests: green composites and biocomposites; biodegradable polymers; nanocomposites; polymer blends; polymer processing; mechanical behaviour of polymer-based systems; rheological behaviour of polymer-based systems; aging of polymer-based systems
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The recent concerns in terms of environmental protection and the search for more and more versatile and polymer-based materials has led to an increasing interest in the use of polymer composites filled with natural-organic fillers (biodegradable and/or coming from renewable resources) as a replacement for traditional mineral-inorganic fillers, with the aim to reduce the use of petroleum-derived, non-renewable resources and to achieve a more intelligent utilization of environmental and financial resources. These “green composites” are very promising, can find applications in several fields (automotive, construction, furnishing, etc.) and a further degree of environmental friendliness is achieved when also the polymer matrix is biodegradable and/or coming from renewable sources. On the other hand, some issues may occur regarding ductility, dimensional stability, and processability. This requires an effort from the research community in order finding the best solutions (which can rely on a suitable choice of the components and their amounts, chemical modifications, use of adhesion promoters, and additives) and it is of fundamental importance to investigate new formulations and to refine the processing techniques. The market for these composites is currently increasing its volumes, and this trend will certainly go on, leading to further reduction of costs and improvements of the quality of the composites, as well as a broadening of the application range.

In this Special Issue, we aim at providing a comprehensive overview of recent developments in this field. Reviews, full papers, short communications, covering the many aspects of the current research on green composites are all welcome.

Dr. Marco Morreale
Guest Editor

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Keywords

  • processing of green composites
  • rheology of green composites
  • characterization and structure-property relationships of green composites
  • chemical modification of natural-organic fillers
  • synthesis and characterization of biodegradable polymer matrices for application in green composites
  • polymer-natural organic filler adhesion promoters
  • environmental impact and LCA of green composites
  • industrial and commercial applications of green composites
  • testing of green composites

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Published Papers (12 papers)

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Research

4347 KiB  
Article
Effects of Wet/Dry-Cycling and Plasma Treatments on the Properties of Flax Nonwovens Intended for Composite Reinforcing
by Heura Ventura, Josep Claramunt, Antonio Navarro, Miguel A. Rodriguez-Perez and Mònica Ardanuy
Materials 2016, 9(2), 93; https://doi.org/10.3390/ma9020093 - 3 Feb 2016
Cited by 18 | Viewed by 5633
Abstract
This research analyzes the effects of different treatments on flax nonwoven (NW) fabrics which are intended for composite reinforcement. The treatments applied were of two different kinds: a wet/dry cycling which helps to stabilize the cellulosic fibers against humidity changes and plasma treatments [...] Read more.
This research analyzes the effects of different treatments on flax nonwoven (NW) fabrics which are intended for composite reinforcement. The treatments applied were of two different kinds: a wet/dry cycling which helps to stabilize the cellulosic fibers against humidity changes and plasma treatments with air, argon and ethylene gases considering different conditions and combinations, which produce variation on the chemical surface composition of the NWs. The resulting changes in the chemical surface composition, wetting properties, thermal stability and mechanical properties were determined. Variations in surface morphology could be observed by scanning electron microscopy (SEM). The results of the X-ray photoelectron spectroscopy (XPS) showed significant changes to the surface chemistry for the samples treated with argon or air (with more content on polar groups on the surface) and ethylene plasma (with less content of polar groups). Although only slight differences were found in moisture regain and water retention values (WRV), significant changes were found on the contact angle values, thus revealing hydrophilicity for the air-treated and argon-treated samples and hydrophobicity for the ethylene-treated ones. Moreover, for some of the treatments the mechanical testing revealed an increase of the NW breaking force. Full article
(This article belongs to the Special Issue Green Composites)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>SEM images of (<b>a</b>) untreated; and (<b>b</b>) wet/dry cycled flax bundles taken at 10 kV and ×1500 magnification.</p> Full article ">Figure 2
<p>Effect on the surface roughness of the fiber due to increasing time in Ar-plasma treatment of samples: (<b>a</b>) NW C-Ar5; (<b>b</b>) NW C-Ar10; (<b>c</b>) NW C-Ar20; and (<b>d</b>) NW C-Ar30. SEM images were taken at 10 kV and ×10,000 magnification.</p> Full article ">Figure 3
<p>SEM image of the sample NW C-Ar30 taken at 10 kV and ×500 magnification. Arrows mark the craters formed.</p> Full article ">Figure 4
<p>SEM image of surfaces of samples (<b>a</b>) NW C-Cr1010; and (<b>b</b>) NW C-Cr20 taken at 10 kV and ×1500 magnification.</p> Full article ">Figure 5
<p>SEM image of surfaces of samples (<b>a</b>) NW C-Ar5-Et5; (<b>b</b>) NW C-Ar5-Et10; (<b>c</b>) NW C-Cr1010-Et10; and (<b>d</b>) NW C-Et10 taken at 10 kV and ×1500 magnification.</p> Full article ">Figure 6
<p>Comparative SEM images taken at 10 kV and ×10,000 magnification, of the surfaces of samples (<b>a</b>) NW C-Ar5; (<b>b</b>) NW C-Ar5-Et5; and (<b>c</b>) NW C-Ar5-Et10; and (<b>d</b>) NW C-Cr1010; and (<b>e</b>) NW C-Cr1010-Et10.</p> Full article ">Figure 7
<p>Deconvoluted curves of XPS C1s peaks of (<b>a</b>) NW C-Cr1010; and (<b>b</b>) NW C-Cr1010-Et10 samples. CPS stands for counts per second as a measure of the intensity.</p> Full article ">Figure 8
<p>Comparative of the C1s peaks found in the deconvolution curves: (<b>a</b>) for the C1-peaks of all samples; (<b>b</b>) for the C2-peaks; (<b>c</b>) for the C3-peaks; (<b>d</b>) for the C4-peaks.</p> Full article ">Figure 9
<p>Deconvoluted curves of XPS O1s peaks of (<b>a</b>) NW C-Ar5; and (<b>b</b>) NW C-Ar5-Et10 samples.</p> Full article ">Figure 10
<p>TGA curves of selected samples. Curve NW C-Ar20 can be considered the representative curve for all Ar-plasma-treated samples (NW C-Ar5, NW C-Ar10, NW C-Ar30, NW C-Ar5-Et5, and NW C-Ar5-Et10) due to their similarity.</p> Full article ">Figure 11
<p>X-ray diffraction patterns of some selected treated and the untreated samples.</p> Full article ">Figure 12
<p>Breaking force of the NW normalized by the sample weight for comparative purposes only.</p> Full article ">
2062 KiB  
Article
Evaluation of Castor Oil Cake Starch and Recovered Glycerol and Development of “Green” Composites Based on Those with Plant Fibers
by José Luis Guimarães, Ana Cristina Trindade Cursino, Cyro Ketzer Saul, Maria Rita Sierrakowski, Luiz Pereira Ramos and Kestur Gundappa Satyanarayana
Materials 2016, 9(2), 76; https://doi.org/10.3390/ma9020076 - 27 Jan 2016
Cited by 17 | Viewed by 6017
Abstract
Continuous efforts are being made in some countries for the recovery of crude glycerin (RG/CG) and castor oil cake (COC), the two byproducts of biodiesel production. These are expected to help, not only in addressing environmental safety, but also in adding value to [...] Read more.
Continuous efforts are being made in some countries for the recovery of crude glycerin (RG/CG) and castor oil cake (COC), the two byproducts of biodiesel production. These are expected to help, not only in addressing environmental safety, but also in adding value to those byproducts, which otherwise may go to waste. Finding ways to utilize those byproducts underlines the main objective of this study. This paper presents the evaluation of (i) COC, glycerin and banana and sugarcane fibers for moisture content; (ii) COC for structural and thermal properties; and (iii) CG for its chemical characteristics. The possibility of using COC and CG with the selected fibers as reinforcement in the development of bio-composites is attempted through thermo-molding. Results revealed enhanced mechanical properties for these composites. The obtained results are discussed in terms of the observed morphology. Full article
(This article belongs to the Special Issue Green Composites)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Castor plant; (<b>b</b>) Castor beans; (<b>c</b>) Castor bean cake after extraction of oil; (<b>d</b>) Dry castor bean cake after grinding in a vibratory mill.</p> Full article ">Figure 2
<p>TGA/DTA curves of castor oil cake samples: (<b>a</b>) without treatment (MST); and (<b>b</b>) with solvent extraction treatment (MT).</p> Full article ">Figure 3
<p>FTIR spectra of pure glycerol and recovered glycerol (RG).</p> Full article ">Figure 4
<p>X-ray diffraction patterns of untreated (MST) and treated (MT) castor oil cake.</p> Full article ">Figure 5
<p>Plots of tensile properties of COC + RG with banana fibers and sugarcane bagasse fibers.</p> Full article ">Figure 6
<p>SEM photographs of castor oil cake—recovered glycerol (RG)—sugarcane bagasse fiber after the tensile test: (<b>a</b>) panoramic view of the fractured surface showing rough surface, fibers, cracks and voids; (<b>b</b>) region showing one fiber lying parallel and other embedded fractured fiber in the matrix; (<b>c</b>,<b>d</b>) pulled-out fiber covered with plasticizer (at two magnifications); (<b>e</b>) non-structured starch showing small polymorph granules.</p> Full article ">Figure 7
<p>SEM photographs of COC—pure glycerol-banana fiber composite after the tensile test: (<b>a</b>) panoramic view of surface showing matrix, fibers and some cracks; (<b>b</b>) zoomed image of the encircled region near the crack edge seen (<b>a</b>); (<b>c</b>) fractured fiber embedded in the matrix.</p> Full article ">Figure 8
<p>SEM photographs of 70 castor oil cake—30 recovered glycerol (RG) and its composite with banana fiber after the tensile test. (<b>a</b>) rough surface with cracks; (<b>b</b>) zoomed image of the region indicating the cracks shown in (<b>a</b>); (<b>c</b>) higher magnification of zoomed region of encircled region in figure (<b>b</b>); (<b>d</b>) panoramic view of the fractured surface of the composite showing rough surface, fibers and voids; (<b>e</b>) higher magnification of a region of (<b>a</b>) showing more cracks in the matrix, embedded failed fiber; (<b>f</b>) high magnification image showing pulled-out fiber with plasticizer coating and non-structured starch showing small polymorph granules.</p> Full article ">
3600 KiB  
Article
Biodegradable Nanocomposite Films Based on Sodium Alginate and Cellulose Nanofibrils
by B. Deepa, Eldho Abraham, Laly A. Pothan, Nereida Cordeiro, Marisa Faria and Sabu Thomas
Materials 2016, 9(1), 50; https://doi.org/10.3390/ma9010050 - 14 Jan 2016
Cited by 160 | Viewed by 12275
Abstract
Biodegradable nanocomposite films were prepared by incorporation of cellulose nanofibrils (CNF) into alginate biopolymer using the solution casting method. The effects of CNF content (2.5, 5, 7.5, 10 and 15 wt %) on mechanical, biodegradability and swelling behavior of the nanocomposite films were [...] Read more.
Biodegradable nanocomposite films were prepared by incorporation of cellulose nanofibrils (CNF) into alginate biopolymer using the solution casting method. The effects of CNF content (2.5, 5, 7.5, 10 and 15 wt %) on mechanical, biodegradability and swelling behavior of the nanocomposite films were determined. The results showed that the tensile modulus value of the nanocomposite films increased from 308 to 1403 MPa with increasing CNF content from 0% to 10%; however, it decreased with further increase of the filler content. Incorporation of CNF also significantly reduced the swelling percentage and water solubility of alginate-based films, with the lower values found for 10 wt % in CNF. Biodegradation studies of the films in soil confirmed that the biodegradation time of alginate/CNF films greatly depends on the CNF content. The results evidence that the stronger intermolecular interaction and molecular compatibility between alginate and CNF components was at 10 wt % in CNF alginate films. Full article
(This article belongs to the Special Issue Green Composites)
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Figure 1

Figure 1
<p>(<b>A</b>) Tensile strength and (<b>B</b>) Tensile modulus of cellulose nanofibril (CNF)-reinforced alginate films as the function of the CNF content (lower case letters (a, b, c) show Duncan grouping; distinct letters represent means significantly different (<span class="html-italic">p</span> &lt; 0.05)).</p> Full article ">Figure 2
<p>Scanning electron microscopy images of cross-section of the (<b>a</b>) alginate; (<b>b</b>) alginate with 5 wt % CNF; (<b>c</b>) alginate with 10 wt % CNF; and (<b>d</b>) alginate with 15 wt % CNF films (arrow indicates the CNF agglomeration in alginate matrix).</p> Full article ">Figure 3
<p>Fourier Transform Infrared (FTIR) spectra of cellulose nanofibrils (CNF), alginate film, alginate with 10 wt % of CNF film.</p> Full article ">Figure 4
<p>Specific surface free energy (<math display="inline"> <semantics> <mrow> <mo>∆</mo> <msubsup> <mi>G</mi> <mi>S</mi> <mrow> <mi>s</mi> <mi>p</mi> </mrow> </msubsup> </mrow> </semantics> </math>) obtained for cellulose nanofibrils (CNF) and alginate films at 25 °C.</p> Full article ">Figure 5
<p>Schematic representation of the interaction between cellulose nanofibrils (CNF) and alginate matrix.</p> Full article ">Figure 6
<p>Effect of CNF content on the moisture absorption and water solubility of alginate/CNF films (lower case letters (a, b, c, d, e) show Duncan grouping; distinct letters represent means significantly different (<span class="html-italic">p</span> &lt; 0.05)).</p> Full article ">Figure 7
<p>Effect of CNF content on the swelling ratio of alginate/CNFfilms (lower case letters (a, b, c, d, e) show Duncan grouping; distinct letters represent means significantly different (<span class="html-italic">p</span> &lt; 0.05)).</p> Full article ">Figure 8
<p>Effect of CNF content on the rate of degradation of alginate/CNF films (lower case letters (a, b, c) show Duncan grouping; distinct letters represent means significantly different (<span class="html-italic">p</span> &lt; 0.05)).</p> Full article ">
2836 KiB  
Article
Processing and Characterization of Cellulose Nanocrystals/Polylactic Acid Nanocomposite Films
by Erin M. Sullivan, Robert J. Moon and Kyriaki Kalaitzidou
Materials 2015, 8(12), 8106-8116; https://doi.org/10.3390/ma8125447 - 1 Dec 2015
Cited by 102 | Viewed by 8958
Abstract
The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization [...] Read more.
The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization behavior, thermo-mechanical behavior, and mechanical behavior were determined as a function of CNC content using scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, dynamic mechanical analysis, and tensile testing. Film crystallinity increases with increasing CNC content indicating CNC act as nucleating agents, promoting crystallization. Furthermore, the addition of CNC increased the film storage modulus and slightly broadened the glass transition region. Full article
(This article belongs to the Special Issue Green Composites)
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Figure 1

Figure 1
<p>Representative scanning electron micrographs images of cryo-fracture surfaces for (<b>a</b>) 0 wt % cellulose nanocrystals/poly lactic acid composites (CNC/PLA) and (<b>b</b>) 3 wt % CNC/PLA composites.</p> Full article ">Figure 2
<p>Non-isothermal initial heating thermograms of CNC/PLA (<b>a</b>) fibers; (<b>b</b>) films; (<b>c</b>) fiber cold crystallization peaks; and (<b>d</b>) film cold crystallization peaks.</p> Full article ">Figure 3
<p>Diffraction patterns obtained for the CNC/PLA (<b>a</b>) fibers and (<b>b</b>) films as a function of CNC content.</p> Full article ">Figure 4
<p>Diffraction pattern of a CNC mat with cellulose I and cellulose II primary diffraction peaks indicated.</p> Full article ">Figure 5
<p>Average crystal lamella thickness of the two dominant diffraction peaks, 16.7° and 19.1°, for the CNC/PLA films as a function of CNC content.</p> Full article ">Figure 6
<p>(<b>a</b>) Storage modulus and (<b>b</b>) loss modulus of the CNC/PLA films as a function of CNC content.</p> Full article ">Figure 7
<p>Elastic modulus of CNC/PLA films as a function of CNC content.</p> Full article ">Figure 8
<p>Representative results of the thermogravimetric analysis (TGA) of the (<b>a</b>) as-received PLA pellets and (<b>b</b>) 3 wt % CNC/PLA film.</p> Full article ">
5346 KiB  
Article
New Polylactic Acid Composites Reinforced with Artichoke Fibers
by Luigi Botta, Vincenzo Fiore, Tommaso Scalici, Antonino Valenza and Roberto Scaffaro
Materials 2015, 8(11), 7770-7779; https://doi.org/10.3390/ma8115422 - 16 Nov 2015
Cited by 49 | Viewed by 6840
Abstract
In this work, artichoke fibers were used for the first time to prepare poly(lactic acid) (PLA)-based biocomposites. In particular, two PLA/artichoke composites with the same fiber loading (10% w/w) were prepared by the film-stacking method: the first one (UNID) reinforced [...] Read more.
In this work, artichoke fibers were used for the first time to prepare poly(lactic acid) (PLA)-based biocomposites. In particular, two PLA/artichoke composites with the same fiber loading (10% w/w) were prepared by the film-stacking method: the first one (UNID) reinforced with unidirectional long artichoke fibers, the second one (RANDOM) reinforced by randomly-oriented long artichoke fibers. Both composites were mechanically characterized in tensile mode by quasi-static and dynamic mechanical tests. The morphology of the fracture surfaces was analyzed through scanning electron microscopy (SEM). Moreover, a theoretical model, i.e., Hill’s method, was used to fit the experimental Young’s modulus of the biocomposites. The quasi-static tensile tests revealed that the modulus of UNID composites is significantly higher than that of the neat PLA (i.e., ~40%). Moreover, the tensile strength is slightly higher than that of the neat matrix. The other way around, the stiffness of RANDOM composites is not significantly improved, and the tensile strength decreases in comparison to the neat PLA. Full article
(This article belongs to the Special Issue Green Composites)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Scheme of the manufacturing process to obtain PLA sheets and PLA/artichoke fiber laminates.</p> Full article ">Figure 2
<p>Stress-strain curves obtained from quasi-static tensile tests. UNID, unidirectionally; RANDOM, randomly.</p> Full article ">Figure 3
<p>(<b>a</b>) Tensile modulus and (<b>b</b>) tensile strength of neat PLA and artichoke composites.</p> Full article ">Figure 4
<p>SEM micrographs of the fracture surface of UNID composites at two different magnifications: (<b>a</b>) scale bar 100 µm; (<b>b</b>) scale bar 20 µm.</p> Full article ">Figure 5
<p>Photograph of a representative fractured RANDOM composite.</p> Full article ">Figure 6
<p>SEM micrographs of the fracture surface of the RANDOM composite. Red arrows indicate matrix-poor areas.</p> Full article ">Figure 7
<p>Temperature dependence of (<b>a</b>) storage modulus <span class="html-italic">E</span>’ and (<b>b</b>) tan delta.</p> Full article ">Figure 8
<p>Comparison between Hill (H) and experimental data (EXP) for tensile moduli.</p> Full article ">Figure 9
<p>Simplified representation of the cross-section of artichoke fiber.</p> Full article ">
5971 KiB  
Article
Mechanical, Thermomechanical and Reprocessing Behavior of Green Composites from Biodegradable Polymer and Wood Flour
by Marco Morreale, Antonio Liga, Maria Chiara Mistretta, Laura Ascione and Francesco Paolo La Mantia
Materials 2015, 8(11), 7536-7548; https://doi.org/10.3390/ma8115406 - 11 Nov 2015
Cited by 67 | Viewed by 6767
Abstract
The rising concerns in terms of environmental protection and the search for more versatile polymer-based materials have led to an increasing interest in the use of polymer composites filled with natural organic fillers (biodegradable and/or coming from renewable resources) as a replacement for [...] Read more.
The rising concerns in terms of environmental protection and the search for more versatile polymer-based materials have led to an increasing interest in the use of polymer composites filled with natural organic fillers (biodegradable and/or coming from renewable resources) as a replacement for traditional mineral inorganic fillers. At the same time, the recycling of polymers is still of fundamental importance in order to optimize the utilization of available resources, reducing the environmental impact related to the life cycle of polymer-based items. Green composites from biopolymer matrix and wood flour were prepared and the investigation focused on several issues, such as the effect of reprocessing on the matrix properties, wood flour loading effects on virgin and reprocessed biopolymer, and wood flour effects on material reprocessability. Tensile, Dynamic-mechanical thermal (DMTA), differential scanning calorimetry (DSC) and creep tests were performed, pointing out that wood flour leads to an improvement of rigidity and creep resistance in comparison to the pristine polymer, without compromising other properties such as the tensile strength. The biopolymer also showed a good resistance to multiple reprocessing; the latter even allowed for improving some properties of the obtained green composites. Full article
(This article belongs to the Special Issue Green Composites)
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Figure 1

Figure 1
<p>Comparison on stress-strain curves for virgin BioFlex at different wood flour content.</p> Full article ">Figure 2
<p>Storage modulus (<b>a</b>) and damping factor (<b>b</b>) for the investigated samples (V = pristine polymer, R4 = four-times reprocessed polymer, V15 and V30 = 15% and 30% filled composites, R4-15 and R4-30 = 15% and 30% filled composites prepared with polymer that has been reprocessed four times).</p> Full article ">Figure 3
<p>Elastic modulus of pristine BioFlex and related composites (abbreviations as in <a href="#materials-08-05406-t005" class="html-table">Table 5</a>).</p> Full article ">Figure 4
<p>Creep curves of the composites at 60 °C and 1.5 MPa load (15% and 30% filled composites: V15 and V30; 15% and 30% filled composites prepared after repeated recycling of the polymer matrix: R15 and R30).</p> Full article ">Figure 5
<p>Morphology of fractured surfaces of samples (<b>a</b>,<b>b</b>) V-15; (<b>c</b>,<b>d</b>) V-30; (<b>e</b>,<b>f</b>) R4-15; (<b>g</b>,<b>h</b>) R4-30 at different magnifications.</p> Full article ">Figure 5 Cont.
<p>Morphology of fractured surfaces of samples (<b>a</b>,<b>b</b>) V-15; (<b>c</b>,<b>d</b>) V-30; (<b>e</b>,<b>f</b>) R4-15; (<b>g</b>,<b>h</b>) R4-30 at different magnifications.</p> Full article ">
6832 KiB  
Article
Thermo-Mechanical Behaviour of Flax-Fibre Reinforced Epoxy Laminates for Industrial Applications
by Giuseppe Pitarresi, Davide Tumino and Antonio Mancuso
Materials 2015, 8(11), 7371-7388; https://doi.org/10.3390/ma8115384 - 3 Nov 2015
Cited by 27 | Viewed by 6985
Abstract
The present work describes the experimental mechanical characterisation of a natural flax fibre reinforced epoxy polymer composite. A commercial plain woven quasi-unidirectional flax fabric with spun-twisted yarns is employed in particular, as well as unidirectional composite panels manufactured with three techniques: hand-lay-up, vacuum [...] Read more.
The present work describes the experimental mechanical characterisation of a natural flax fibre reinforced epoxy polymer composite. A commercial plain woven quasi-unidirectional flax fabric with spun-twisted yarns is employed in particular, as well as unidirectional composite panels manufactured with three techniques: hand-lay-up, vacuum bagging and resin infusion. The stiffness and strength behaviours are investigated under both monotonic and low-cycle fatigue loadings. The analysed material has, in particular, shown a typical bilinear behaviour under pure traction, with a knee yield point occurring at a rather low stress value, after which the material tensile stiffness is significantly reduced. In the present work, such a mechanism is investigated by a phenomenological approach, performing periodical loading/unloading cycles, and repeating tensile tests on previously “yielded” samples to assess the evolution of stiffness behaviour. Infrared thermography is also employed to measure the temperature of specimens during monotonic and cyclic loading. In the first case, the thermal signal is monitored to correlate departures from the thermoelastic behaviour with the onset of energy loss mechanisms. In the case of cyclic loading, the thermoelastic signal and the second harmonic component are both determined in order to investigate the extent of elastic behaviour of the material. Full article
(This article belongs to the Special Issue Green Composites)
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Figure 1

Figure 1
<p>Typical tensile curve of a unidirectional (UD) Flax Fibre Reinforced Composite (FFRC) along the reinforcement orientation.</p> Full article ">Figure 2
<p>(<b>a</b>) Macro photo of the fabric; (<b>b</b>) Close-up photo revealing the twisted fibres in yarn filaments.</p> Full article ">Figure 3
<p>(<b>a</b>) Tensile stress <span class="html-italic">vs.</span> strain curves for the three manufactured batch types and (<b>b</b>) tangent modulus <span class="html-italic">vs.</span> strain.</p> Full article ">Figure 4
<p>Evolution of the tensile curve for the same VB specimen retested after 24 h for three times.</p> Full article ">Figure 5
<p>Transverse tensile stress <span class="html-italic">vs.</span> strain curves.</p> Full article ">Figure 6
<p>Evolution of Poisson’s coefficient with strain for the: (<b>a</b>) hand lay-up; (<b>b</b>) vacuum bag and (<b>c</b>) resin infusion laminated composites.</p> Full article ">Figure 7
<p>Tensile test with embedded load-unload R = 0 cycles for a VB sample. (<b>a</b>) Definition of load-controlled cycling history; (<b>b</b>) Stress-strain plot.</p> Full article ">Figure 8
<p>Tensile stress <span class="html-italic">vs.</span> strain curve with application of six step cycling loads.</p> Full article ">Figure 9
<p>Evolution of Young’s modules with mean (<b>a</b>) and amplitude (<b>b</b>) stress during cycling loading.</p> Full article ">Figure 10
<p>Evolution of temperature during monotonic tensile tests overlapped to the stress strain curves for for the: (<b>a</b>) hand lay-up, (<b>b</b>) vacuum bag and (<b>c</b>) resin infusion laminated composites.</p> Full article ">Figure 11
<p>Thermoelastic signal amplitude and phasefrom an HL sample under loading step 1 (see <a href="#materials-08-05384-t004" class="html-table">Table 4</a>). (<b>a</b>) Amplitude; (<b>b</b>) Phase.</p> Full article ">Figure 12
<p>Thermoelastic signal amplitude <span class="html-italic">ΔT</span> in (°C) from an HL sample at the various loading steps. (<b>a</b>) load step 1; (<b>b</b>) load step 2; (<b>c</b>) load step 3; (<b>d</b>) load step 4; (<b>e</b>) load step 5; (<b>f</b>) load step 6.</p> Full article ">Figure 13
<p>Thermoelastic signal amplitude <span class="html-italic">ΔT</span> in (°C) from a VB sample at the various loading steps. (<b>a</b>) load step 1; (<b>b</b>) load step 2; (<b>c</b>) load step 3; (<b>d</b>) load step 4; (<b>e</b>) load step 5; (<b>f</b>) load step 6.</p> Full article ">Figure 14
<p>Thermoelastic signal amplitude <span class="html-italic">ΔT</span> in (°C) from a RI sample at the various loading steps. (<b>a</b>) load step 1; (<b>b</b>) load step 2; (<b>c</b>) load step 3; (<b>d</b>) load step 4; (<b>e</b>) load step 5; (<b>f</b>) load step 6.</p> Full article ">Figure 15
<p>Full field second harmonic signal amplitude in (°C) from an HL sample at the various loading steps. (<b>a</b>) load step 1; (<b>b</b>) load step 2; (<b>c</b>) load step 3; (<b>d</b>) load step 4; (<b>e</b>) load step 5; (<b>f</b>) load step 6.</p> Full article ">Figure 16
<p>Comparison of second harmonic maps (<b>a</b>) RI sample under load step 3; (<b>b</b>) RI sample under load step 6; (<b>c</b>) VB sample under load step 3; (<b>d</b>) VB sample under load step 3.</p> Full article ">
4099 KiB  
Article
Damage Characterization of Bio and Green Polyethylene–Birch Composites under Creep and Cyclic Testing with Multivariable Acoustic Emissions
by Alencar Bravo, Lotfi Toubal, Demagna Koffi and Fouad Erchiqui
Materials 2015, 8(11), 7322-7341; https://doi.org/10.3390/ma8115382 - 2 Nov 2015
Cited by 24 | Viewed by 8421
Abstract
Despite the knowledge gained in recent years regarding the use of acoustic emissions (AEs) in ecologically friendly, natural fiber-reinforced composites (including certain composites with bio-sourced matrices), there is still a knowledge gap in the understanding of the difference in damage behavior between green [...] Read more.
Despite the knowledge gained in recent years regarding the use of acoustic emissions (AEs) in ecologically friendly, natural fiber-reinforced composites (including certain composites with bio-sourced matrices), there is still a knowledge gap in the understanding of the difference in damage behavior between green and biocomposites. Thus, this article investigates the behavior of two comparable green and biocomposites with tests that better reflect real-life applications, i.e., load-unloading and creep testing, to determine the evolution of the damage process. Comparing the mechanical results with the AE, it can be concluded that the addition of a coupling agent (CA) markedly reduced the ratio of AE damage to mechanical damage. CA had an extremely beneficial effect on green composites because the Kaiser effect was dominant during cyclic testing. During the creep tests, the use of a CA also avoided the transition to new damaging phases in both composites. The long-term applications of PE green material must be chosen carefully because bio and green composites with similar properties exhibited different damage processes in tests such as cycling and creep that could not be previously understood using only monotonic testing. Full article
(This article belongs to the Special Issue Green Composites)
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Figure 1

Figure 1
<p>Specimens dimensions (in millimeters) according to the standards of ISO 527-4(1A).</p> Full article ">Figure 2
<p>Tensile machine testing apparatus with acoustic sensors and extensometer on the testing sample.</p> Full article ">Figure 3
<p>Tensile test results for specimens with different fiber weights for (<b>a</b>) HDPE; (<b>b</b>) NHDPE; (<b>c</b>) superimposition of the monotonic and load-unload test results for 20 wt% fiber HDPE and (<b>d</b>) NHDPE.</p> Full article ">Figure 4
<p>Comparison of the family of bio and green PE/birch composites developed with commonly used engineering plastics and composites [<a href="#B20-materials-08-05382" class="html-bibr">20</a>,<a href="#B21-materials-08-05382" class="html-bibr">21</a>,<a href="#B22-materials-08-05382" class="html-bibr">22</a>]: (<b>a</b>) Young’s modulus (<b>b</b>) Tensile strength.</p> Full article ">Figure 5
<p>Mechanical damage index <span class="html-italic">versus</span> strain for 10 wt% (<b>a</b>) and 30 wt% (<b>b</b>) fiber composites. Residual strain <span class="html-italic">versus</span> strain for 10 wt% (<b>c</b>) and 30 wt% (<b>d</b>) fiber composites.</p> Full article ">Figure 6
<p>Typical amplitude histogram successfully discriminated by fuzzy logic for bio (<b>a</b>) and green (<b>b</b>) composites at 10 wt% fiber with no coupling agent.</p> Full article ">Figure 7
<p>Typical load-unload stress curves (left vertical axis) and burst amplitudes with damage mode classification (right vertical axis) for 10 wt% specimens: (<b>a</b>) bio, no CA; (<b>b</b>) green, no CA; (<b>c</b>) bio with CA; and (<b>d</b>) green with CA.</p> Full article ">Figure 8
<p>Comparison of the specimen typical damage using the mechanical damage index and cumulative AE damage measured using energy by mode for 10 wt% fiber specimens: (<b>a</b>) bio, no CA; (<b>b</b>) green, no CA; (<b>c</b>) bio with CA; and (<b>d</b>) green with CA.</p> Full article ">Figure 9
<p>Typical Kaiser and Felicity diagrams for 10 wt% fiber specimens: (<b>a</b>) bio, no CA; (<b>b</b>) green, no CA; (<b>c</b>) bio with CA; and (<b>d</b>) green with CA.</p> Full article ">Figure 10
<p>Typical creep strain curves (left vertical axis) and hit mode share participation (right vertical axis) for 10 wt% fiber specimens: (<b>a</b>) bio, no CA; (<b>b</b>) green, no CA; (<b>c</b>) bio with CA; and (<b>d</b>) green with CA.</p> Full article ">Figure 11
<p>Typical creep strain curves (left vertical axis) and burst amplitudes with damage mode classification (right vertical axis) for 40 wt% specimens: (<b>a</b>) bio, no CA; (<b>b</b>) green, no CA; (<b>c</b>) bio with CA; and (<b>d</b>) green with CA.</p> Full article ">Figure 12
<p>SEM images of the fractured face for 40 wt% specimens (at 500× magnification): (<b>a</b>) bio, no CA; (<b>b</b>) bio with CA; (<b>c</b>) green, no CA; and (<b>d</b>) green with CA.</p> Full article ">
4114 KiB  
Article
Effect of Extrusion on the Mechanical and Rheological Properties of a Reinforced Poly(Lactic Acid): Reprocessing and Recycling of Biobased Materials
by Víctor Peinado, Pere Castell, Lidia García and Ángel Fernández
Materials 2015, 8(10), 7106-7117; https://doi.org/10.3390/ma8105360 - 19 Oct 2015
Cited by 45 | Viewed by 6440
Abstract
The aim of this research paper is to study the behaviour of a common used biopolymer (Poly(Lactic Acid) (PLA)) after several reprocesses and how two different types of additives (a melt strength enhancer and a nanoadditive) affect its mechanical and rheological properties. Systematic [...] Read more.
The aim of this research paper is to study the behaviour of a common used biopolymer (Poly(Lactic Acid) (PLA)) after several reprocesses and how two different types of additives (a melt strength enhancer and a nanoadditive) affect its mechanical and rheological properties. Systematic extraction of extrudate samples from a twin-screw compounder was done in order to study the effect in the properties of the reprocessed material. Detailed rheological tests on a capillary rheometer as well as mechanical studies on a universal tensile machine after preparation of injected specimens were carried out. Results evidenced that PLA and reinforced PLA materials can be reprocessed and recycled without a remarkable loss in their mechanical properties. Several processing restrictions and specific phenomena were identified and are explained in the present manuscript. Full article
(This article belongs to the Special Issue Green Composites)
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Graphical abstract
Full article ">Figure 1
<p>Flexural Modulus of the three formulations by each extrusion.</p> Full article ">Figure 2
<p>Graphical Representation of the (<b>a</b>) Tensile Modulus (E<sub>t</sub>); (<b>b</b>) Tensile Strength (σ<sub>t</sub>) and (<b>c</b>) Stress at break (σ<sub>b</sub>) of the three formulations by each extrusion.</p> Full article ">Figure 3
<p>Apparent viscosity curves at different apparent Shear rates of each extrusion sample for: (<b>a</b>) Natural PLA at 170 °C; (<b>b</b>) Natural PLA at 180 °C; (<b>c</b>) Natural PLA at 190 °C.</p> Full article ">Figure 4
<p>Apparent viscosity curves at different apparent Shear rates of each extrusion sample of: (<b>a</b>) PLA BS at 170 °C; (<b>b</b>) PLA BS at 180 °C; (<b>c</b>) PLA BS at 190 °C.</p> Full article ">Figure 5
<p>Apparent viscosity curves at different apparent Shear rates of each extrusion sample of: (<b>a</b>) PLA nano at 170 °C; (<b>b</b>) PLA nano at 180 °C; (<b>c</b>) PLA nano at 190 °C.</p> Full article ">Figure 6
<p>(<b>a</b>) Average Variation of Viscosity value at 170 °C by number of extrusions (compared <span class="html-italic">versus</span> 0 extrusions batch); (<b>b</b>) Viscosity value variation at 170 °C by shear rate (compared 0 extrusions <span class="html-italic">versus</span> 20 extrusions batch).</p> Full article ">Figure 7
<p>(<b>a</b>) Average Variation of Viscosity value @ 180 °C by extrusion batch (compared <span class="html-italic">versus</span> 0 extrusions batch); (<b>b</b>) Viscosity value variation by shear rate [compared 0 extrusions <span class="html-italic">versus</span> 20 extrusions batch] @ 180 °C.</p> Full article ">Figure 8
<p>(<b>a</b>) Average Variation of Viscosity value @ 190 °C by extrusion batch (compared <span class="html-italic">versus</span> 0 extrusions batch); (<b>b</b>) Viscosity value variation by shear rate [compared 0 extrusions <span class="html-italic">versus</span> 20 extrusions batch] @ 190 °C.</p> Full article ">
2669 KiB  
Article
Rice Husk Ash to Stabilize Heavy Metals Contained in Municipal Solid Waste Incineration Fly Ash: First Results by Applying New Pre-treatment Technology
by Laura Benassi, Federica Franchi, Daniele Catina, Flavio Cioffi, Nicola Rodella, Laura Borgese, Michela Pasquali, Laura E. Depero and Elza Bontempi
Materials 2015, 8(10), 6868-6879; https://doi.org/10.3390/ma8105346 - 9 Oct 2015
Cited by 23 | Viewed by 8432
Abstract
A new technology was recently developed for municipal solid waste incineration (MSWI) fly ash stabilization, based on the employment of all waste and byproduct materials. In particular, the proposed method is based on the use of amorphous silica contained in rice husk ash [...] Read more.
A new technology was recently developed for municipal solid waste incineration (MSWI) fly ash stabilization, based on the employment of all waste and byproduct materials. In particular, the proposed method is based on the use of amorphous silica contained in rice husk ash (RHA), an agricultural byproduct material (COSMOS-RICE project). The obtained final inert can be applied in several applications to produce “green composites”. In this work, for the first time, a process for pre-treatment of rice husk, before its use in the stabilization of heavy metals, based on the employment of Instant Pressure Drop technology (DIC) was tested. The aim of this work is to verify the influence of the pre-treatment on the efficiency on heavy metals stabilization in the COSMOS-RICE technology. DIC technique is based on a thermomechanical effect induced by an abrupt transition from high steam pressure to a vacuum, to produce changes in the material. Two different DIC pre-treatments were selected and thermal annealing at different temperatures were performed on rice husk. The resulting RHAs were employed to obtain COSMOS-RICE samples, and the stabilization procedure was tested on the MSWI fly ash. In the frame of this work, some thermal treatments were also realized in O2-limiting conditions, to test the effect of charcoal obtained from RHA on the stabilization procedure. The results of this work show that the application of DIC technology into existing treatment cycles of some waste materials should be investigated in more details to offer the possibility to stabilize and reuse waste. Full article
(This article belongs to the Special Issue Green Composites)
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Graphical abstract
Full article ">Figure 1
<p>Picture of the employed experimental DIC instrument.</p> Full article ">Figure 2
<p>X-ray diffraction analysis of TQ rice husk ashes treated at different temperatures (see <a href="#materials-08-05346-t001" class="html-table">Table 1</a>).</p> Full article ">Figure 3
<p>Concentration of Zn (<b>a</b>) and Pb (<b>b</b>) in the leaching solutions of the COSMOS-RICE samples obtained by using the whole RHA samples (see <a href="#materials-08-05346-t001" class="html-table">Table 1</a>).</p> Full article ">Figure 4
<p>(<b>a</b>) SEM images of internal and external surfaces of untreated rice husk (TQ) and pre-treated by T1 and T2 DIC treatments. (<b>b</b>) SEM images of internal surfaces of corresponding RHA shown in <a href="#materials-08-05346-f004" class="html-fig">Figure 4</a>a.</p> Full article ">Figure 5
<p>XRD patterns collected on COSMOS-RICE samples, obtained by using TQ RHA (see <a href="#materials-08-05346-t001" class="html-table">Table 1</a>). ✻: Calcite (CaCO<sub>3</sub>); Σ: Halite (NaCl); Δ: Gypsum [CaSO<sub>4</sub>·2(H<sub>2</sub>O)]; θ: Thaumasite [Ca<sub>3</sub>(SO<sub>4</sub>)[Si(OH)<sub>6</sub>](CO<sub>3</sub>)·12(H<sub>2</sub>O)]; ▪: Quartz (SiO<sub>2</sub>); ᴥ Potassium chloride (KCl).</p> Full article ">Figure 6
<p>Pictures of several “green composites” realized by using the material produced with the COSMOS-RICE technology as a filler. It was inserted in polyethylene (30% in weight) and polyethylene foils (5% in weight). In addition, it was also employed to obtain tiles, with different colors (from 30% to 50% in weight).</p> Full article ">
2042 KiB  
Article
Effects of Fiber Reinforcement on Clay Aerogel Composites
by Katherine A. Finlay, Matthew D. Gawryla and David A. Schiraldi
Materials 2015, 8(8), 5440-5451; https://doi.org/10.3390/ma8085258 - 21 Aug 2015
Cited by 25 | Viewed by 6631
Abstract
Novel, low density structures which combine biologically-based fibers with clay aerogels are produced in an environmentally benign manner using water as solvent, and no additional processing chemicals. Three different reinforcing fibers, silk, soy silk, and hemp, are evaluated in combination with poly(vinyl alcohol) [...] Read more.
Novel, low density structures which combine biologically-based fibers with clay aerogels are produced in an environmentally benign manner using water as solvent, and no additional processing chemicals. Three different reinforcing fibers, silk, soy silk, and hemp, are evaluated in combination with poly(vinyl alcohol) matrix polymer combined with montmorillonite clay. The mechanical properties of the aerogels are demonstrated to increase with reinforcing fiber length, in each case limited by a critical fiber length, beyond which mechanical properties decline due to maldistribution of filler, and disruption of the aerogel structure. Rather than the classical model for reinforced composite properties, the chemical compatibility of reinforcing fibers with the polymer/clay matrix dominated mechanical performance, along with the tendencies of the fibers to kink under compression. Full article
(This article belongs to the Special Issue Green Composites)
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Graphical abstract
Full article ">Figure 1
<p>Hemp (<b>a</b>), silk (<b>b</b>) and soy silk fibers (<b>c</b>) used in this study.</p> Full article ">Figure 2
<p>Stress-strain curve for a hemp sample, circled portion shows delamination plateau.</p> Full article ">Figure 3
<p>Cross sections of soy silk samples, 2–20 mm fiber lengths, uncut samples in bottom row.</p> Full article ">Figure 4
<p>In-plane tensile stiffness <span class="html-italic">vs.</span> the fiber length for the soy silk, silk, and hemp compression series (purple—soy silk, blue—silk, green—hemp).</p> Full article ">
1637 KiB  
Article
Correlation between Mechanical Properties with Specific Wear Rate and the Coefficient of Friction of Graphite/Epoxy Composites
by Mahdi Alajmi and Abdullah Shalwan
Materials 2015, 8(7), 4162-4175; https://doi.org/10.3390/ma8074162 - 8 Jul 2015
Cited by 58 | Viewed by 8825
Abstract
The correlation between the mechanical properties of Fillers/Epoxy composites and their tribological behavior was investigated. Tensile, hardness, wear, and friction tests were conducted for Neat Epoxy (NE), Graphite/Epoxy composites (GE), and Data Palm Fiber/Epoxy with or without Graphite composites (GFE and FE). The [...] Read more.
The correlation between the mechanical properties of Fillers/Epoxy composites and their tribological behavior was investigated. Tensile, hardness, wear, and friction tests were conducted for Neat Epoxy (NE), Graphite/Epoxy composites (GE), and Data Palm Fiber/Epoxy with or without Graphite composites (GFE and FE). The correlation was made between the tensile strength, the modulus of elasticity, elongation at the break, and the hardness, as an individual or a combined factor, with the specific wear rate (SWR) and coefficient of friction (COF) of composites. In general, graphite as an additive to polymeric composite has had an eclectic effect on mechanical properties, whereas it has led to a positive effect on tribological properties, whilst date palm fibers (DPFs), as reinforcement for polymeric composite, promoted a mechanical performance with a slight improvement to the tribological performance. Statistically, this study reveals that there is no strong confirmation of any marked correlation between the mechanical and the specific wear rate of filler/Epoxy composites. There is, however, a remarkable correlation between the mechanical properties and the friction coefficient of filler/Epoxy composites. Full article
(This article belongs to the Special Issue Green Composites)
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Figure 1
<p>(<b>a</b>) Tensile specimen dimensions; (<b>b</b>) Used tensile test mold; (<b>c</b>) Tribological specimen geometry; (<b>d</b>) Tribological mold and fiber position.</p> Full article ">Figure 2
<p>Specific wear rate of the filler/epoxy composites after a 7.5-km sliding distance.</p> Full article ">Figure 3
<p>Coefficient of friction of the fillers/epoxy composites after a 7.5-km sliding distance.</p> Full article ">Figure 4
<p>Correlation between the individual mechanical properties and specific wear rate (SWR) of the materials. (<b>a</b>) Tensile strength; (<b>b</b>) Modulus of elasticity; (<b>c</b>) Elongation at the break; (<b>d</b>) Hardness.</p> Full article ">Figure 5
<p>Correlation between the combined mechanical properties and SWR of materials. (<b>a</b>) (<span class="html-italic">Me</span>)<sup>−1</sup>; (<b>b</b>) (<span class="html-italic">MeH</span>)<sup>−1</sup>; (<b>c</b>) (<span class="html-italic">SH</span>)<sup>−1</sup>; (<b>d</b>) (<span class="html-italic">SMH</span>)<sup>−1</sup>.</p> Full article ">Figure 6
<p>Correlation between the individual mechical properties and COF of the materials. (<b>a</b>) Tensile strength; (<b>b</b>) Elongation at the break; (<b>c</b>) Modulus of elasticity; (<b>d</b>) Hardness.</p> Full article ">Figure 7
<p>Correlation between the combined mechanical properties and COF of the materials. (<b>a</b>) (<span class="html-italic">Se</span>)<sup>−1</sup>; (<b>b</b>) (<span class="html-italic">SH</span>)<sup>−1</sup>; (<b>c</b>) (<span class="html-italic">eH</span>)<sup>−1</sup>; (<b>d</b>) (<span class="html-italic">SM</span>)<sup>−1</sup>; (<b>e</b>) (<span class="html-italic">Me</span>)<sup>−1</sup>.</p> Full article ">Figure 8
<p>Micrographs of neat epoxy after adhesive testing. (fg: fragmentation; so: softening; Cr: cracks)</p> Full article ">Figure 9
<p>Micrographs of 5% graphite/epoxy composites after adhesive testing. (fl: film transfer; gr: graphite; mc: micro-crack)</p> Full article ">Figure 10
<p>Micrographs of 3% graphite/date palm fiber/epoxy after tensile test. (Pg: plowing; Cr: Crack; Db: debonding)</p> Full article ">
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