Search Results (170)

Materials derived from renewable and recycled resources offer a promising route toward more sustainable thermoset composites. In this study, waste poly(ethylene terephthalate) (PET) was depolymerized by glycolysis with propylene glycol to obtain a glycolysate, and subsequently polycondensed with biobased propylene glycol, maleic anhydride, and trimethylolpropane diallyl ether to synthesize biobased UV-curable unsaturated polyester resin (UV-bUPR). The composites were prepared with acryloyl-modified Kraft lignin (K_rL-A) as a reactive bio-filler using a dual-curing approach, in which rapid UV curing was followed by thermal/redox post-curing to improve conversion and network homogeneity. The structure of the synthesized resin and composites was confirmed by FTIR and NMR spectroscopy. Mechanical properties were evaluated by tensile testing and hardness measurements, while morphology and fracture behavior were analyzed by scanning electron microscopy. The unmodified lignin decreased tensile performance due to limited compatibility with the polyester matrix and the formation of interfacial defects and agglomerates. In contrast, K_rL-A exhibited improved dispersion and stronger filler–matrix interactions, resulting in superior mechanical performance. The most pronounced effect of lignin modification was observed at 15 wt.% filler loading, where the tensile strength reached 27.83 MPa, compared with 13.91 MPa for the corresponding unmodified system. The developed composites also showed improved sustainability, assessed through the E-factor, due to the combined use of recycled PET and renewable lignin. Full article

Artificial composite stones have recently attracted attention as multifunctional materials for construction and defense-related applications. In this study, a novel composite stone was developed using waste limestone as the primary mineral filler, combined with an unsaturated polyester resin matrix and reinforced with glass powder and chopped glass fibers. The influence of binder content and reinforcement type on physico-mechanical and microstructural behavior was investigated. Experimental characterization included water absorption, compressive strength, abrasion resistance, acid resistance, and optical microscopy. The results demonstrated that fine fillers improved matrix densification and reduced porosity, while short glass fiber reinforcement enhanced load-bearing capacity. Abrasion resistance and durability were found to depend on binder content and particle packing characteristics. Overall, the developed composite material exhibits promising mechanical performance, low water absorption, and improved durability, suggesting its potential as a candidate material for applications requiring environmental resistance, including potential use in defense-related camouflage applications. Full article

The growing volume of fiber-reinforced polymer composite waste creates an urgent need for efficient recycling technologies. While solvolysis effectively breaks down thermoset matrices for fiber reinforcement recovery, the process generates hydrocarbon-rich liquid by-products that require further management. This study validates the use of these liquid recycling streams—derived from the solvolysis of unsaturated polyester and epoxy resins—as sustainable carbon precursors for the growth of carbon nanomaterials. Synthesis was performed via catalytic chemical vapor deposition (CVD) at 850 °C using iron nanoparticles impregnated on a zeolite substrate. Morphological analysis confirmed the production of one-dimensional nanostructures (carbon nanotubes/nanofibers), with average diameters below 100 nm. Raman spectroscopy revealed a high degree of graphitization, with I_D/I_G ratios ranging from 0.25 to 0.58, which is comparable to structures synthesized from conventional precursors. Thermogravimetric analysis (TGA) demonstrated high thermal stability and carbon purity reaching up to 90.3%. These findings demonstrate a viable upcycling pathway that enhances the economic attractiveness of composite recycling by transforming waste into advanced nanomaterials. Full article

Unsaturated polyester resin (UPR)–quartz composites have become increasingly important in structural, sanitary, and architectural applications. However, their manufacturing processes still rely heavily on empirical knowledge. This review compiles recent developments in materials science, curing kinetics, and digital manufacturing, outlining a pathway toward data-driven, adaptive production of quartz-filled thermosets. The chemical and physical fundamentals of UPR polymerization are summarized, including the influence of initiator systems, filler characteristics, and thermal management on network formation. Challenges associated with highly filled formulations—such as viscosity control, dispersion, shrinkage, and exothermic peak prediction—are discussed in detail. Recent advances in digital twins (DTs) and artificial intelligence (AI) are reviewed, demonstrating how physics-based simulations, machine learning models, and hybrid mechanistic–data-driven approaches improve the prediction of rheology, curing behavior, and quality outcomes in thermoset polymer processes. A practical application example demonstrates the prediction of peak time in quartz–UPR composites using Random Forest and Gradient Boosting ensemble models. Two prediction scenarios are evaluated: Scenario A with gel time by Leave-One-Out cross-validation, and Scenario B without gel time, representing post-mixing and pre-process prediction contexts, respectively. Stratified bootstrap augmentation improves Gradient Boosting in both scenarios. Principal component analysis confirms that the curing process is governed by three independent physical dimensions: curing reactivity, thermal environment and resin thermal state. Full article

Polyester resin composites containing expanded graphite often exhibit reduced mechanical strength due to the porous structure of the filler. The aim of this study was to enhance mechanical performance without compromising electrical behaviour. Although carbon fibre and expanded graphite are chemically identical carbon allotropes, their distinct morphologies motivated the use of carbon fibre to reinforce expanded graphite-filled polyester composites. To examine the role of expanded graphite porosity, ultrasonicated EG was used to produce exfoliated, lower-porosity particles, while vacuum processing was applied to remove entrapped air prior to curing. Adding 0.5–5 wt% milled carbon fibre increased electrical conductivity by up to three orders of magnitude relative to neat polyester while maintaining 70–80% of the original specific strength at moderate fibre contents. Ultrasonicated EG reduced tensile strength by more than 50% at 5 wt% loading and decreased conductivity due to additional grain boundary formation. Vacuum-processed EG not only provided slight mechanical enhancements but also significantly improved electrical properties by lowering surface resistance by 6–10 orders of magnitude, reaching the tens-of-Ω range at 3–5 wt% EG. This performance is comparable to previously reported conductive EG/polymer systems, which exhibit surface resistances of 10–10² Ω at 5 wt% EG. This systematic comparison offers practical guidelines for balancing conductive percolation and mechanical reinforcement in expanded graphite polyester composites. Full article

Natural fiber-reinforced polymer composites have been increasingly investigated for sustainable structural applications, including small wind turbine blades operating under low wind-speed conditions. However, despite their environmental advantages, there is a lack of experimental validation of structural models applied to real aerodynamic blade geometries manufactured with carded natural fibers, whose intrinsic fiber dispersion and microstructural heterogeneity challenge classical laminate-based approaches. The objective of this study is to evaluate the structural performance, modeling validity, and manufacturing feasibility of a small wind turbine blade produced from polyester resin reinforced with carded jute fibers, combining Classical Laminate Theory (CLT), additive-manufactured tooling, vacuum infusion processing, and quasi-static bending experiments. A 3D-printed ABS mold was used to manufacture an S1210 aerodynamic profile, enabling a low-cost and rapid tooling approach aligned with current trends in digital composite prototyping. The blade was structurally modeled using CLT with elastic properties obtained from previous experimental characterization and was experimentally evaluated through quasi-static bending tests instrumented with strain gauges at three spanwise stations. Numerical predictions showed strong agreement with experimental strain measurements, validating the applicability of CLT to carded natural-fiber laminates despite their inherent angular dispersion and microstructural variability. All monitored regions exhibited fully linear elastic behavior, with maximum stresses of approximately 5 MPa—well below the composite tensile strength (~60 MPa)—resulting in a safety factor close to 12. These results confirm the structural reliability, manufacturing feasibility, and sustainability potential of jute-reinforced polyester composites for small wind turbine blades operating in low-wind-speed environments (<2 m/s). Full article

In the context of global trends in sustainability and the circular economy (CE), this article aims to investigate the potential of microparticles derived from citrus peel waste (grapefruit, key lime, lemon, and orange), constituting approximately 50% of the fruit weight, as eco-friendly bio-fillers in polymer composites, thereby reducing the consumption of petrochemical resins. The composites were fabricated by gravity casting using polyester resin (PR) as the matrix at filler concentrations of 2.5%, 5%, and 10% by weight. Functional properties were assessed using static tensile testing (measuring Peak Load, Peak Stress, and Young’s modulus) and Shore D hardness testing. The incorporation of unprocessed fillers generally decreased tensile strength (Peak Stress REF: 31.48 MPa), attributed to poor interfacial adhesion. The lowest Peak Stress value was recorded for the 2.5O composite (16.04 MPa). The exception was the 10K composite (10 wt.%key limee), which achieved a Peak Load (1.28 kN) nearly identical to the neat resin (1.29 kN), although the Peak Stress remained lower due to the reduced effective cross-sectional area. Stiffness (Young’s modulus REF: 3.26 GPa) increased by more than 10 wt.% for 5G (3.63 GPa), indicating effective reinforcement at this concentration. A key positive finding was a universal increase in Shore D hardness across all biocomposites (REF: 78.4 ShD), with a maximum of 83.8 ShD for 10L (lemon), a typical response to rigid fillers that suggests enhanced surface resistance. The results suggest that citrus peel waste could be considered for non-structural applications where surface durability and efficient waste management are priorities. Full article

The pursuit of alternatives to nonrenewable materials has stimulated the development of sustainable materials with improved performance, particularly polymer composites reinforced with plant-based fibers. In this study, eucalyptus fibers were thermally treated and evaluated as eco-friendly reinforcements for polyester composites, aiming to enhance their physical and mechanical properties. The fibers were subjected to heat treatments between 140 and 230 °C in a Macro-ATG oven, followed by analyses of anatomical characteristics and chemical composition. Composites containing 25% fiber reinforcement were produced using an orthophthalic unsaturated polyester matrix catalyzed with methyl ethyl ketone peroxide, with untreated fibers used as references. Thermal treatment induced significant modifications in fiber morphology and composition, including increases in cell wall fraction at 170 and 200 °C and higher cellulose contents at 140 and 170 °C. Mechanical performance was assessed through tensile, flexural (modulus of rupture—MOR), modulus of elasticity (E_B), and impact tests. Composites reinforced with heat-treated fibers exhibited lower apparent density and, notably, those treated at 230 °C showed markedly reduced water absorption and enhanced tensile strength compared with the control. Overall, treatment at 230 °C proved most effective, highlighting the potential of thermally modified eucalyptus fibers as viable reinforcements for high-performance, bio-based polymer composites. Full article

Fiber-reinforced polymer composites (FRPCs) are increasingly used in construction due to their high performance and low environmental footprint. However, their widespread adoption has raised concerns over end-of-life management, particularly under European regulations mandating high recycling rates for construction and demolition waste (CDW). This study evaluates different systems for the chemical recycling of FRPCs through microwave (MW)-assisted solvolysis using green solvents, including deep eutectic solvents (DESs) and biobased acetic acid. The process targets thermoset resin depolymerization while preserving fiber integrity, operating at reduced temperatures (≤230 °C) and lower energy demand than conventional techniques, such as pyrolysis. A systematic experimental design was applied to CDW-derived polyester composites and extended to industrial epoxy and vinyl ester composites. Among the tested solvents, glacial acetic acid + ZnCl₂ (5 wt.%), achieved the highest degradation efficiency, exceeding 94% in small-scale trials and maintaining over 78% upon upscaling. Recovered fibers showed moderate property retention, with tensile strength and elongation losses of ~30% and ~45% for infusion-based epoxy composites, while those from pultrusion-based epoxy composites exhibited 16–19% and retained similar properties to the virgin material, respectively. The method facilitates fiber recovery with limited degradation and aligns with circular economy principles through solvent reuse and minimizing environmental impact. Full article

Epoxy resins often require toughening to broaden their engineering applications, such as in durable concrete repair. This study addresses this need by developing high-performance polyurethane/epoxy (PU/EP) interpenetrating polymer networks (IPNs). The composites were synthesized via prepolymer and stepwise methods using polyether polyol (PPG-1000), isocyanate (MDI-50), and E51 epoxy. At an optimal PU prepolymer content of 15 wt%, the polyether-based IPNs achieved a balanced mechanical profile (tensile strength: 59.90 MPa; elongation at break: 6.46%; compressive strength: 69.99 MPa). Further tuning of the soft segment by introducing polyester polyol (PS-2412) yielded superior performance at a PS-2412/PPG-1000 ratio of 30/70. This formulation increased tensile and compressive strengths by 11.4% and 6.07% (to 66.74 MPa and 74.24 MPa), and dry and wet bond strengths by 12.1% and 36.3% (to 5.68 MPa and 4.62 MPa), respectively. The enhancement is attributed to the increased crosslinking density and more uniform network structure imparted by PS-2412, which improves stress distribution and interfacial adhesion. This work provides an effective soft-segment design strategy for fabricating toughened epoxy composites with robust mechanical and adhesive properties. Full article

The reuse of industrial residues has gained importance due to environmental and public health concerns associated with improper waste disposal. Steel scale (CDA), a by-product of machining and rolling operations, represents a residue with technological potential for incorporation into polymer composites. This study developed a low-cost and sustainable material by reinforcing an orthophthalic polyester matrix with CDA and systematically evaluated its mechanical, thermal, and structural properties. Four formulations were prepared based on the maximum feasible filler loading: R (pure resin), C1 (50% CDA), C2 (100% CDA), and C3 (150% CDA). Composites were manufactured by cold-press molding under a two-ton compressive load. Characterization included tensile, flexural, and impact testing, thermogravimetric analysis (TGA), thermal conductivity, apparent density, liquid absorption, and morphological assessment by scanning electron microscopy (SEM). CDA incorporation reduced tensile and flexural strength but increased elastic modulus, impact toughness, and thermal conductivity. The C3 composite exhibited the highest thermal stability, retaining more than 50% of its initial mass at 500 °C. Density and liquid absorption increased proportionally with filler loading, and SEM revealed heterogeneous microstructures with particle agglomeration, sedimentation, and interfacial gaps, explaining the mechanical and thermal trends. The findings demonstrate the feasibility of producing dense and low-cost polyester composites reinforced with steel scale. The structure–property relationships identified in this study establish a foundation for subsequent investigations focusing on additional functional behaviors of this waste-derived material system. Full article

Unsaturated polyester resins (UPRs) were synthesized from camphoric acid and diluted with styrene, partially replaced (up to 30%) by trimethylolpropane triacrylate (TMPTA). Rheological tests showed increased but sustainable viscosity due to TMPTA’s higher polarity. These UPRs served as matrices for composites reinforced with non-woven bamboo and flax mats from recycled waste. Mechanical testing revealed that C_f-UPR/TMPTA30 exhibited the highest tensile strength (25.2 MPa) and modulus (0.96 GPa), compared to 18.7 MPa and 0.74 GPa for the styrene-based resin, respectively, attributed to greater cross-link density. Bamboo composites showed lower tensile properties (13.6 MPa) due to random fiber orientation and porosity, while flax-reinforced systems, especially C_f-UPR/TMPTA30–FLAX, reached 42.7 MPa tensile and 95.5 MPa flexural strength, indicating synergy between TMPTA-modified resin and flax fibers. Dynamic-mechanical analysis confirmed stable thermo-mechanical behavior, and water uptake tests showed reduced absorption (by ~10%), suggesting improved fiber/matrix adhesion. SEM images revealed brittle fracture and fiber pull-out in styrene systems, but fiber breakage and ductile textures in TMPTA-based ones, proving better stress transfer. Thermal analysis indicated slightly earlier degradation onset for TMPTA-modified resins but higher char yield in fiber composites. Overall, TMPTA substitution and flax reinforcement enhance the mechanical, interfacial, and thermal properties of bio-based UPRs, supporting sustainable high-performance composites. Full article

This study examines the potential of jute–sisal (JS) fibre, both coated and uncoated, as a sustainable alternative to solar panels with polyethylene terephthalate (PET) back sheets. The coated version was developed using a zeolite–polyester resin composite to enhance thermal performance. The investigation was carried out in two phases: controlled laboratory testing using a solar-cell tester and a 90-day real-world evaluation under natural environmental conditions. In controlled conditions, solar panels with coated JS (CJS) fibre back sheets exhibited improved electrical performances compared to PET panels, including higher current (1.23 A), voltage (12.79 V), maximum power output (14.79 W), efficiency (13.47%), and fill factor (94.03%). Lower series resistance and higher shunt resistance further indicated superior electrical characteristics. Under real-world conditions, CJS panels consistently outperformed PET-based panels, showing a 6% increase in current and an 8% increase in voltage. The model showed strong agreement with the experimental results. These findings suggest that coated JS fibre is a viable, eco-friendly alternative to PET for back sheets in solar panels. Further research should examine its long-term durability, environmental resistance, and commercial scalability. Full article

Glass fiber (GF) reinforced unsaturated polyester resin (UP) composites are used in cured-in-place pipe (CIPP) rehabilitation technology of drainage systems due to their low cost and excellent force chemical properties. However, the weak interfacial compatibility between GF and the polymer matrix limits the stress transfer efficiency. Herein, a strategy of a polyhydric boehmite (AlOOH) layer coated on GF (GF-AlOOH) was developed for improving the mechanical properties of UP composites, and the enhancement effects of the coating process were analyzed. The AlOOH-modified GFs significantly improved the flexural and tensile strengths of the modified composites by 41.21% and 21.05%, respectively. Moreover, the enhancement mechanism was explored by analyzing the surface chemical structure of GF-AlOOHs. The nano-AlOOH was grafted on the GF surface by O=Al–OH. Meanwhile, the increase in the mechanical properties of UP/GF-AlOOH was mainly attributed to the combined effect of mechanical interlocking interaction, covalent bonding and hydrogen bonding, which improved the interfacial adhesion between GF and UP. In summary, this work provides effective guidance for achieving high-quality interfaces in GF composites and offers important insights into designing durable and cost-effective materials for CIPP rehabilitation and broader infrastructure applications. Full article

This study investigates the behavior of glass fiber/polyester layered composites under low-velocity impact conditions, focusing on optimizing layer configurations and fiber types to enhance impact resistance. Composites were fabricated using a combination of E-glass mat and woven glass fibers with orthophthalic polyester resin, employing the hand lay-up method. Impact tests were conducted using a drop hammer device. Key variables included the number of layers and fiber types, with impacts performed using flathead and hemispherical impactors. The results showed that increasing the number of layers significantly enhanced energy absorption and peak contact force. Specifically, five-layer samples exhibited a 351% increase in energy absorption and a 212% increase in peak contact force compared to two-layer samples. Mat fibers outperformed woven fibers, with mat-only samples absorbing 21.8% more energy and showing 5.8% higher peak forces. Additionally, flathead impactors generated 101% higher peak forces and caused more severe damage than hemispherical impactors. Observed failure modes included fiber breakage, matrix cracking, and delamination, all influenced by impact parameters and material characteristics. These findings provide valuable guidance for designing composite materials with improved resistance to impact, with potential applications in the aerospace, marine, and automotive industries. Full article