Search Results (3,146)

The mechanical properties of concrete degrade rapidly when exposed to elevated temperatures. Adding fibres to concrete can enhance its thermal stability and residual mechanical characteristics under high-temperature conditions. Various types of fibres, including steel, synthetic and natural fibres, are available for this purpose. This paper provides a comprehensive review of the impact of synthetic fibres on the performance of fibre-reinforced concrete at high temperatures. It evaluates conventional synthetic fibres, including polypropylene (PP), polyethylene (PE), and polyvinyl alcohol (PVA) fibres, as well as newly emerging macro fibres that improve concrete’s fire resistance properties. The novelty of this review lies in its focus on macro fibres as a promising alternative to conventional synthetic fibres. The findings reveal that PE fibres significantly influence the residual mechanical properties of fibre-reinforced concrete at high temperatures. Although PVA fibres may reduce compressive strength at elevated temperatures, they help reduce micro-cracking and increase flexibility and flexural strength. Finally, this review demonstrates that while conventional synthetic fibres are effective in limiting fire-induced damage, macro fibres offer enhanced benefits, including improved toughness, energy absorption, durability, corrosion resistance, and post-cracking capacity. This study provides valuable insights for developing fibre-reinforced concrete with superior high-temperature performance. Steel fibres offer superior strength but are prone to corrosion and spalling, while PP fibres effectively reduce explosive spalling but provide limited strength improvement. PE fibres enhance flexural performance, and PVA fibres improve tensile strength and shrinkage control, although their performance decreases at high temperatures. Macro fibres stand out for their post-cracking capacity and toughness, offering a lightweight alternative with better overall durability. Full article

The automotive industry is under growing pressure from regulatory agencies to improve the recyclability of its plastic components. Simultaneously, manufacturers are adopting natural fiber composites in vehicles to reduce their carbon footprint and decrease reliance on petroleum-based materials. This presents a challenge at vehicle end-of-life, however, as natural fiber-reinforced polymers are substantially more difficult to recycle than their unreinforced counterparts. This study investigated the development of a mechanical recycling process for paper fiber-reinforced polypropylene composites, focusing on the impact of injection molding parameters—specifically, injection temperature and rate—on the thermal, mechanical, and water uptake properties of the composites. The results showed that processing temperature had a greater influence on composite performance than injection rate, with some limited interaction effects between the two. Higher processing intensity damaged the paper fibers, increasing the number of nucleation sites and resulting in greater polypropylene crystallinity. These structural changes reduced tensile properties at higher intensities, while flexural properties improved. Objective function analysis was applied to identify optimal processing conditions, balancing these competing trends. Overall, the findings demonstrate that paper fiber-reinforced polypropylene composites can be recycled into automotive-relevant injection molding compounds using conventional plastic manufacturing techniques, though careful tuning of processing parameters is essential to achieve optimal performance. Full article

Electromagnetic wave-absorbing materials (EMAMs) and structures are crucial in aerospace and electronic communications due to their ability to absorb electromagnetic waves. The development of materials that are lightweight, sustainable, and cost-effective, exhibiting high-performance absorption across a broad frequency spectrum, is therefore important. However, homogeneous electromagnetic absorbing materials require assistance to meet all these criteria. Therefore, developing multi-layer absorbing coatings is essential for enhancing performance. The present study uses 21 different composites of varying weight fractions of polypropylene, graphene nanoplatelets, and multiwall carbon nanotubes nanocomposites to develop multi-layer absorbing materials and optimize their performance. These multi-layer carbon polymer nanocomposites were meticulously constructed using evolutionary algorithms like Non-sorted Genetic Algorithm-II and Particle Swarm Optimization to achieve ultra-broadband electromagnetic wave absorption capabilities. Among the designed electromagnetic absorbing materials, a two-layer model, i.e., 1.5 wt% MWCNT/PP/epoxy with a thickness of 1.052 mm and 2.7% GNP/PP/epoxy with a thickness of 4.456 mm totaling 5.506 mm, was identified as optimal using NSGA-II. The structure has exhibited exceptional absorption performance with a minimum reflection loss of −21 dB and a qualified bandwidth extending to 4.2 GHz. PSO validated and optimized this structure, confirming NSGA-II’s efficiency and effectiveness in quickly obtaining optimal solutions. This broadband absorber design combines the structure design and material functioning through additive manufacturing, allowing it to absorb well over a wide frequency range. Full article

High volumetric shrinkage and rheological behavior of polypropylene (PP) are the main problems that make material extrusion (MEX) uncommon for this material. The complexity is raised when recycled materials are used. This research covered different aspects of the MEX process of virgin and recycled PP, from the analysis of rough materials to the mechanical evaluation of the final products. Two types of virgin PP (one in pellet and the other in filament form) and one recycled PP were analyzed. Thermal characterization and rheological analysis of these materials were initially employed to understand the peculiar properties of all investigated PP and set filament extrusion. The 3D parts were then printed using processed filaments to check fabrication quality through visual analysis and mechanical tests. A well-structured approach was proposed to encompass the limitations of PP 3D printing by accurately evaluating the influence of the material properties on the final part performance. The results revealed that the dimensional and mechanical performances of the recycled PP were comparable with the virgin filament commonly employed in MEX, making it particularly suitable for this application. Full article

To investigate the reinforcement–soil interfacial effects in fiber-reinforced soil, this study developed a novel horizontal pullout tester and conducted pullout tests on coarse polypropylene fibers in plain soil, cemented soil, and fine fiber-reinforced cemented soil. Three soil types were analyzed: low liquid limit clay, high liquid limit clay, and clay sand. The pullout tester proved to be both scientifically robust and efficient. Depending on the soil properties, coarse polypropylene fibers were pulled out intact or fractured. The pullout curves displayed distinct multi-peak patterns, with wavelengths closely linked to the fiber’s intrinsic characteristics. The pullout curve wavelength for plain soil matched the fiber’s intrinsic wavelength, while it was slightly greater in cemented soils. The peak pullout force increased with extended curing periods, higher cement content, more excellent compaction, and the addition of fine polypropylene fibers. Among these factors, compaction had the most significant impact on enhancing the soil–fiber interfacial effect. Friction, cohesion, and fiber interweaving created interlocking effects, inhibiting fiber sliding. Cement hydration processes further deformed the fiber, increasing its friction coefficient and sliding resistance. Hydration products also fill soil voids, improving soil compactness, enlarging the fiber–soil contact area, and enhancing frictional and occlusal forces at the interface. Full article

Polypropylene is one of the most widely used polymers in various applications, ranging from packaging materials to automotive components. This paper proposes the Computational Fluid Dynamics (CFD) and AI/ML simulation of a polypropylene fluidized bed reactor to reduce reactor loss and facilitate process understanding. COMSOL Multiphysics 6.2^® solves a 2D multiphase CFD model for the reactor’s complex gas–solid interactions and fluid flows. The model is compared to experimental results and shows excellent predictions of gas distribution, fluid velocity, and temperature gradients. Critical operating parameters like feed temperature, catalyst feed rate, and propylene inlet concentration are all tested to determine their impact on the single-pass conversion of the reactor. The simulation simulates their effects on polypropylene yield and reactor efficiency. It also combines CFD with artificial intelligence and machine learning (AI/ML) algorithms, like artificial neural networks (ANN), resulting in a powerful predictive tool for accurately predicting reactor metrics based on operating conditions. The multifaceted CFD-AI/ML tool provides deep insight into improving reactor design, and it also helps save computing time and resources, giving industrial polypropylene plant growth a considerable lift. Full article

Contamination by heavy metals (HMs) such as Pb, Cd, Cr, and Hg poses significant risks to the environment and human health owing to their toxicity and persistence. Geopolymers (GPs) have emerged as promising materials for immobilizing HMs and reducing their mobility through physical encapsulation and chemical stabilization. This study explored the novel use of isotactic polypropylene functionalized in the molten state with maleinized hyperbranched polyol polyester (PP-g-MHBP) as an additive in coal fly ash (CFA)-based GPs to enhance HM immobilization. Various characterization techniques were employed, including compressive strength tests, XRD, ATR-FTIR, SEM-EDX, XPS analyses, and TCLP leaching tests, to assess immobilization effectiveness. These results indicate that although the addition of PP-g-MHBP does not actively contribute to the chemical interactions with HM ions, it acts as an inert filler within the GP matrix. CFA/PP-g-MHBP-based GPs demonstrated significant potential for Cd²⁺ immobilization up to 3 wt% under acidic conditions, although the retention of Pb²⁺, CrO₄²⁻, and Hg²⁺ varied according to the specific chemistry of each metal, weight percentage of the added metal, matrix structure, and regulatory standards. Notably, high immobilization percentages were achieved for CrO₄²⁻ and Hg²⁺, although the leaching concentrations exceeded US EPA limits. These findings highlight the potential of CFA/PP-g-MHBP-based GPs for environmental applications, emphasizing the importance of optimizing formulations to enhance HM immobilization under varying conditions. Full article

Modern construction is largely dependent on steel and concrete, with natural materials such as earth being significantly underutilised. Despite its sustainability and accessibility, earth is not being used to its full potential in developed countries. This study explores innovative building materials using Alhambra Formation soil (Granada, Spain) reinforced with difficult-to-recycle agricultural waste: polypropylene fibres contaminated with organic matter and leachates. Fibres were added at a ratio between 0.20 and 0.80% of the soil mass, leachates at a ratio between 4.25 and 8.50%, and lime was incorporated at 2.00% and 4.00% for specimens with higher residue content. Physico-mechanical properties, including uniaxial compressive strength and longitudinal strain, were analysed together with the microstructure. The results showed that polypropylene fibres, in comparison to the use of leachates, improved compressive strength and ductility, reaching a compressive strength of 1.76 MPa with a fibre content of 0.40%. On the other hand, this value is 7.4% lower than the reference sample without additives. The fibre-reinforced samples showed a higher porosity compared to the samples with leachates or without additives. This approach highlights the potential of agricultural waste for the development of sustainable construction materials, offering enhancements in the strength and ductility of reinforced soils. Full article

Filament winding is a widely used out-of-autoclave manufacturing technique for producing continuous fiber-reinforced thermoplastic composites. This study focuses on optimizing key filament winding process parameters, including heater temperature, roller pressure, and winding speed, to produce thermoplastic composites. Using Box–Behnken response surface methodology (RSM), the study investigates the effects of these parameters on the compressive load of glass fiber-reinforced polypropylene (GF/PP) and polyphenylene sulfide (GF/PPS) composite cylinders. Mathematical models were developed to quantify the impact of each parameter and optimal processing conditions were identified across a wide temperature range, enhancing both manufacturing efficiency and the overall quality of the composites. This study demonstrates the potential of thermoplastic filament winding as a cost-effective and time-efficient alternative to conventional methods, addressing the growing demand for lightweight, high-performance, out-of-autoclave composites in industries such as aerospace, automotive, and energy. The optimized process significantly improved the performance and reliability of filament winding for various thermoplastic applications, offering potential benefits for industrial, aerospace, and other advanced sectors. The results indicate that GF/PPS composites achieved a compressive load of 3356.99 N, whereas GF/PP composites reached 2946.04 N under optimized conditions. It was also revealed that operating at elevated temperatures and reduced pressure levels enhances the quality of GF/PPS composites, while for GF/PP composites, maintaining lower temperature and pressure values is crucial for maximizing strength. Full article

Tire wear particles (TWPs) are among the most relevant sources of microplastic pollution of the environment. Nevertheless, common analytical methods like IR and Raman spectroscopy are highly impaired by additives and filler materials, leaving only thermogravimetric methods for chemical analysis of TWPs in most cases. We herein present quantitative NMR spectroscopy (qNMR) as an alternative tool for the quantification of the polymeric material used for the production of tires, including natural rubber (NR), styrene–butadiene–copolymer (SBR), polyethylene–co-propylene (EPR) and polybutadiene (BR). Limits of quantification (LOQ) between 3 µg and 43 µg per sample and recovery rates of 72–92% were achieved for all tested polymer types. The first results of combining these measurements with Soxhlet extraction as a sample preparation tool are presented alongside the qNMR experiments. Full article

In order to reveal the effects of microplastics (MPs) on the growth and rhizosphere soil environmental effects of wheat (Triticum aestivum L.), three microplastic types (polypropylene MPs (PP-MPs), high-density polyethylene MPs (HDPE-MPs), and polylactic acid MPs (PLA-MPs)), particle sizes (150, 1000, and 4000 μm), and concentrations (0.1, 0.5, and 1 g·kg⁻¹) were selected for a pot experiment under natural environment conditions. The differences in germination rate (GR), germination inhibition rate (GIR), growth characteristics, physicochemical properties, and enzymatic activities of wheat in rhizosphere soil were analyzed using statistical analysis and variance analysis. The results show that the germination rate of wheat seeds decreased under different MPs, and the HDPE-MPs, medium particle size (1000 μm), and medium concentration (0.5 g·kg⁻¹) had the greatest inhibitory effect on wheat seed germination. The effects of MPs on wheat seed growth characteristics were inconsistent; the germination potential (GP), germination index (GI), and vitality index (VI) showed a significant decreasing trend under the PLA-MPs and medium-concentration (0.5 g·kg⁻¹) treatment, while the mean germination time (MGT) showed a significant increasing trend; the GP and MGT showed a significant decreasing and increasing trend under the high-particle-size (4000 μm) treatment, respectively, while the GI and VI showed a significant decreasing trend under the medium-particle-size (1000 μm) treatment. The growth characteristics of wheat plants showed a significant decreasing trend under different MPs, with the SPAD, nitrogen concentration of the leaves, and plant height decreasing the most under PLA-MP treatment, the SPAD and nitrogen concentration of leaves decreasing the most under low-particle-size (150 μm) and low-concentration (0.1 g·kg⁻¹) treatments, and the decreases in plant height under the high-particle-size (4000 μm) and high-concentration (1 g·kg⁻¹) treatments being the largest. There were significant increasing trends for ammonium nitrogen (NH₄⁺), total phosphorus (TP), soil urease (S-UE), soil acid phosphatase (S-ACP), and soil sucrase (S-SC) under different microplastics, while the PLA-MPs had a significant increasing trend for nitrate nitrogen (NO₃⁻) and a significant decreasing trend for pH; there was a significant decreasing trend for total nitrogen (TN) under the HDPE-MPs and PLA-MPs, and for each particle size and concentration, the PLA-MPs and low-concentration (0.1 g·kg⁻¹) treatments showed a significant decreasing trend for soil catalase (S-CAT). The research results could provide certain data and theoretical bases for evaluating the effects of MPs on crop growth and soil ecological environments. Full article

Glass short fiber-reinforced thermoplastics (GSFRTPs) are a cost-effective alternative to other short fiber-reinforced thermoplastics (SFRTPs). Their excellent mechanical properties make them a suitable material for components that require rigidity and light weight in widely diverse fields, including transportation and office automation equipment. The melt-mixing process is used to shorten glass fibers. The notched impact strength of molded products is strongly affected by the fiber length. An important issue is how to conduct melt-molding processing while keeping the fibers long. In this regard, a survey of cases in which additives were used to increase the fiber length revealed no useful reports. However, a growing trend toward the reuse of plastic material wastes has emerged. When reusing GSFRTP wastes, the objective is to recycle the material as GSFRTPs. This promotion of the reuse of GSFRTPs necessitates the production of molded products with the fiber length maintained to the greatest extent feasible. Moreover, GSFRTPs should be recycled in a manner consistent with the original GSFRTPs. In recent years, there has also been a growing movement to reuse polyvinyl butyral (PVB) in accordance with Sustainable Development Goals (SDGs). It has been established that PVB can be extracted from the laminated glass state with high efficiency using mechanical methods. This study evaluated the mechanical properties of GSFRTPs with a PP matrix when PVB was added. The results show that the incorporation of PVB and maleic anhydride-modified PP in quantities of less than 1 wt% into GSFRTPs leads to sizing effects wherein the fibers are dispersed in bundles. Furthermore, this combination enhances the notched impact strength of the resulting molded product by 0.5 kJ/m² at the maximum. Full article

This study investigates the potential of reusing punched-steel waste, a significant component of solid inorganic waste, in composite materials for construction applications. Driven by the growing global demand for raw materials (which is projected to quadruple by 2050) and the need for sustainable waste management practices, this research explores the creation of a composite material (PPLK) incorporating punched-steel tape (LPM-4 grade) embedded in a polypropylene matrix. Experimental testing of PPLK specimens (310 × 90 × 6.30 mm) and finite element analysis (FEA) were employed to evaluate the mechanical properties and stress concentration coefficient. The results show that the PPLK composite exhibits a load-carrying capacity of 21.64 kN, exceeding the sum of its individual components by 11.37%, demonstrating a synergistic effect between the steel (average tensile strength 220.65 MPa) and polypropylene. FEA further revealed that increasing the matrix’s modulus of elasticity to 42 MPa significantly reduces the stress concentration coefficient in the steel component, resulting in a 24% enhancement of the elastic force. The findings suggest a viable path toward sustainable waste management and improved material utilisation in the construction industry. Full article

The escalating use of plastic materials in agricultural practices has substantially increased the amount of plastic waste directed to landfills, leading to significant environmental and ecological challenges. Conventional disposal methods have been found to release hazardous pollutants, including microplastics and toxic chemicals, exacerbating these concerns. This study aims to address the environmental impact of agricultural plastic waste by exploring advanced reprocessing technologies and characterising the processed waste to assess its physical, mechanical, and thermal properties. Synthetic polymer-based bale twine (BT) waste, commonly used in livestock farming, was processed using an economically viable melting machine developed by Ritchie Technology. The BT and processed bale twine (PrBT) were analysed to understand their properties. Fourier transmission infrared spectroscopy revealed that the waste primarily consisted of polypropylene (PP). Thermal analysis indicated that the melting temperature of the PrBT was 162.49 °C, similar to virgin PP. Additionally, tensile testing revealed that the PrBT had an ultimate strength of 13.06 MPa and a Young’s modulus of 434.07 MPa. The PrBT was further transformed into a bench that can be applicable in outdoor applications. Furthermore, the PrBT was extruded into 3D printable filament. Therefore, it is evident that bale twine waste can be given a second life through an economically viable technology. Full article

Increasing environmental awareness has boosted interest in sustainable alternatives for binding natural reinforcing fibers in composites. Utilizing lignin, a biorenewable polymer byproduct from several industries, as a component in polymer matrices can lead to the development of more eco-friendly and high-performance composite materials. This research work aimed to investigate the effect of two types of lignin (lignosulfonate and soda lignin) on the properties of hemp fiber-reinforced polypropylene composites for furniture applications. The composites were produced by thermoforming six overlapping layers of nonwoven material. A 20% addition of soda lignin or lignosulfonate (relative to the nonwoven mass) was incorporated between the nonwoven layers made of 80% hemp and 20% polypropylene (PP). The addition of both types of lignin resulted in an increase in the tensile and bending strength of lignin-based composites, as well as a decrease in the absorbed water percentage. Compared to oriented strand board (OSB), lignin-based composites exhibited better properties. Regarding the two types of lignin used, the addition of lignosulfonate resulted in better composite properties than those containing soda lignin. Thermal analysis revealed that the thermal degradation of soda lignin begins long before the melting temperature of polypropylene. This early degradation explains the inferior properties of the composites containing soda lignin compared to those with lignosulfonate. Full article