Search Results (132)

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

Sustainable structural composites can significantly lower vehicle-related emissions. To evaluate the recycling of different composite materials, laboratory-scale pyrolysis was conducted and assessed both technically and environmentally. Two demonstrators were studied: a truck side skirt made from natural flax and hemp fibres with polypropylene (PP), and a car front header composed of glass fibres and PP. Additional materials examined included thermoplastic composites containing polyamide 6 (PA6), bio-based polyamide 11 (PA11) and thermoset polyester. Results showed that material type strongly influenced the pyrolysis outcome, product composition and recycling potential. Glass fibres could be recovered and reused as reinforced fibres, while natural fibres could be recovered as biooil for potential use in biofuel production. Polymers were recovered as pyrolysis products that, depending on their composition, can be used in different applications, from recovering monomers from PA6 to producing hydrocarbons that may replace naphtha (from PP) or aromatics (from polyester) in the petrochemical industry. Life cycle assessment (LCA) findings revealed that the climate impact of composite recycling is primarily driven by the environmental burdens of the recycling process itself and by the ability of recovered materials and chemicals to substitute conventional fossil-based alternatives. Efficient recycling pathways are therefore essential to maximising environmental benefits. Full article

The transition to sustainable thermosetting resins is frequently hindered by the trade-off between high bio-based content and processability. This study reports a novel strategy in developing a highly bio-based, styrene-free unsaturated polyester resin (UPR) by leveraging maltodextrin-derived mixed esters dissolved in dimethyl itaconate (DMI). Unlike conventional polysaccharide-based systems that suffer from extreme viscosity, our functionalized prepolymer–DMI system achieves a low-viscosity curing solution without requiring petroleum-derived diluents such as styrene. Fourier-transform infrared spectroscopy confirmed the formation of a robust crosslinked network via the complete consumption of C=C bonds. Consequently, the cured resin exhibits exceptional thermal and mechanical performance, outperforming many existing bio-based analogs: a glass transition temperature (T_g) reaching 141 °C, a decomposition onset near 250 °C, and superior dimensional stability with a linear thermal expansion coefficient as low as 77 ppm/°C. Demonstrating a fully renewable, easy-to-process formulation with a flexural strength of 44 MPa, this work provides a design template for the next generation of high-performance, eco-friendly industrial thermosets. Full article

In this study, we develop bio-epoxy composites incorporating bio-oils obtained from the pyrolysis of almond and walnut shells at 400 °C and 600 °C, with the aim of evaluating their potential as renewable precursors for epoxy resin modification. The influence of pyrolysis temperature on bio-oil yield and chemical composition is examined to identify phenolic-rich fractions relevant to epoxy curing. Bio-oil production increased with temperature, reaching 40.46% for walnut shells and 36.84% for almond shells at 600 °C. Chemical analysis revealed that aromatic compounds, particularly phenolics, were the major constituents associated with epoxy curing reactivity. For walnut hulls, the total aromatic fraction increased from 30.4% at 400 °C to 35.2% at 600 °C, while almond hulls showed an increase from 23.8% to 26.1% over the same temperature range. Incorporation of bio-oil into the epoxy matrix promoted three-dimensional network formation through reactions between epoxy groups and the functional moieties present in the bio-oil, resulting in a higher cross-linking degree, Young’s modulus, and tensile strength. However, compared to neat epoxy, the bio-oil-modified systems exhibited reduced storage modulus (E′) and glass transition temperature (Tg), attributed to the plasticizing effect of lighter oxygenated species. Overall, although bio-oil incorporation decreases Tg and cross-linking degree, it still provides a viable pathway toward partially bio-based epoxy resins with enhanced stiffness and competitive mechanical performance. 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

Polyurethanes (PUs) are indispensable polymeric materials widely employed across diverse industrial sectors due to their excellent thermal stability, chemical resistance, adhesion, and mechanical durability. However, the intrinsic three-dimensional crosslinked network that underpins their performance also presents a fundamental barrier to reprocessing and recycling. Consequently, most end-of-life PU waste is currently managed through landfilling or incineration, resulting in significant resource loss and environmental impact. To address these challenges, this review presents an integrated perspective on sustainable PU systems by unifying green synthesis strategies with closed-loop recovery approaches. First, recent advances in bio-based polyols and phosgene-free isocyanate synthesis derived from renewable resources—such as plant oils, carbohydrates, and lignin—are discussed as viable means to reduce dependence on petrochemical feedstocks and mitigate toxicity concerns. Next, emerging chemical recycling methodologies, including acidolysis and aminolysis, are reviewed with a focus on the selective recovery of high-purity monomers. Finally, PU vitrimers and dynamic covalent polymer networks (DCPNs) based on urethane bond exchange reactions are examined as reprocessable architectures that combine thermoplastic-like processability with the mechanical robustness of thermosets. By integrating synthesis, recovery, and reuse within a unified framework, this review aims to outline a coherent pathway toward establishing a sustainable circular economy for PU materials. Full article

Façades account for approximately 15–20% of a building’s embodied carbon, making them a key target for material decarbonization. While bio-composites are increasingly explored for façade insulation, cladding systems remain dominated by carbon-intensive materials such as aluminum and fiber-reinforced polymers (FRPs). This paper presents findings from a study investigating the use of food-waste-derived bulk fillers in bio-composite materials for façade cladding applications. Several food-waste streams, including hazelnut and pistachio shells, date seeds, avocado and mango pits, tea leaves, and brewing waste, were processed into fine powders (<0.125 μm) and combined with a furan-based biobased thermoset resin to produce flat composite sheets. The samples were evaluated through mechanical testing (flexural strength, stiffness, and impact resistance), water absorption, freeze–thaw durability, and optical microscopy to assess microstructural characteristics before and after testing. The results reveal substantial performance differences between waste streams. In particular, hazelnut and pistachio shell fillers produced bio-composites suitable for façade cladding, achieving flexural strengths of 62.6 MPa and 53.6 MPa and impact strengths of 3.42 kJ/m² and 1.39 kJ/m², respectively. These findings demonstrate the potential of food-waste-based bio-composites as low-carbon façade cladding materials and highlight future opportunities for optimization of processing, supply chains, and material design. Full article

This study compares the chemical modification and polymerization behavior of canola, carinata, and crambe oils to evaluate their suitability as renewable building blocks for polymer synthesis. The vegetable oils were characterized in terms of fatty-acid composition and oxidative stability, and the data showed distinct profiles: canola with 0% erucic acid, carinata around 42.08%, and crambe reaching 56.25%, differences that end up influencing how each one responds during the modification steps. Epoxidation and acrylation were confirmed by ¹H NMR, ¹³C NMR, and FTIR-ATR, mainly through the disappearance of the olefinic peaks and the appearance of oxirane- and acrylate-related signals (some of them quite clear, others less pronounced). After acrylation, the oils were subjected to solution polymerization, forming bulk crosslinked materials, whose properties reflected their original fatty-acid profiles: the canola-based polymer reached the highest glass transition temperature (T_g), 47.73 °C, followed by the carinata-based polymer (T_g = 41.86 °C), while the crambe-derived polymer, with lower functionality due to its high erucic acid content, showed a much lower T_g of 20.26 °C. Altogether, these differences highlight how variations in fatty-acid composition subtly shape the efficiency of functionalization and the architecture of the resulting networks. The polymers obtained here point to potential uses in renewable coatings, thermoset resins, and other applications that depend on bio-based crosslinked materials. Full article

This study explores the potential of a bio-based thermosetting adhesive system incorporating recycled fillers to enhance structural bonding applications while promoting sustainability. Diglycidylether of vanillyl alcohol (DGEVA) was selected as the resin matrix due to its favorable thermomechanical properties and low moisture absorption. To improve mechanical performance and support circular economy principles, recycled carbon fibers (RCFs) and mineral wool (MW) were integrated into the adhesive formulation in varying proportions (10, 30, and 50 phr). A cationic thermal initiator, ytterbium (III) trifluoromethanesulfonate (YTT), was used to permit polymerization. Comprehensive characterization was performed to assess the curing behavior, thermal stability, and mechanical performance of the adhesive. FTIR spectroscopy monitored the polymerization process, while DSC and dynamic DSC provided insights into reaction kinetics, including activation energy, and curing rates. The mechanical and thermomechanical properties were evaluated using dynamic mechanical thermal analysis (DMTA) and shear lap testing on bonded joints. Additionally, SEM imaging was employed to examine fillers’ morphology and joint interfaces. The results indicated that increasing filler content slowed polymerization and raised activation energy but still permitted high conversion rates. Both RCF- and MW-containing formulations exhibited improved stiffness and adhesion strength, particularly in CMC joints. These findings suggest that DGEVA-based adhesives reinforced with recycled fillers offer a viable and sustainable alternative for structural bonding, contributing to waste valorization and green material development in engineering applications. Full article

In this study, the blends of bio-based polybenzoxazine (V-fa type) and poly(ethylene glycol) (PEG) with PEG contents from 50 to 95 wt% and different molecular weights were developed to improve the flexibility of thermosetting polymers. Of these blends, PEG 8k at 80 wt%, which exhibited the best processability, was selected for further development via compositing with carbon black (CB) from 0 to 20 phr. Differential Scanning Calorimetry (DSC) analysis revealed that the melting temperature (T_m) increased from 70 to 83 °C and glass transition temperatures (T_g) increased from –53 to –48 °C at 20 phr. Thermogravimetric Analysis (TGA) demonstrated high thermal stability, with T_dmax (for all CB contents) presented at ca. 416 °C. Moreover, char yield was increased from 10% (without CB) to 28% (20 phr), reflecting improved decomposition resistance. Mechanical properties demonstrated that CB significantly reinforced the composites. The flexural modulus and flexural strength were increased from 117.18 MPa (without CB) to 456 MPa (10 phr) and from 2.42 MPa (without CB) to 3.94 MPa (2.5 phr), respectively. The SEM images confirmed uniform morphology and good filler dispersion. Conclusively, the composites of 8k PEG 80 wt% filled with 2.5 phr of CB provided an optimal balance of mechanical and thermal stability and engineering polymer applications. Full article

This review paper explores the transformative potential of polymer composites and adhesives in reducing the weight of aircraft landing gear, thereby improving fuel efficiency and lowering emissions. The replacement of conventional metallic materials and mechanical fastenings with advanced thermoset/thermoplastic composites and adhesives can significantly enhance durability and performance in demanding operational environments. Unlike traditional fastening methods, the structural adhesives eliminate the weight penalties associated with mechanical fasteners, offering a lighter and more reliable solution that meets the rigorous demands of modern aerospace engineering. Furthermore, the review highlights a variety of manufacturing techniques and innovative materials, including bio-based polymers, self-healing materials, noobed composites, helicoid composites, and hybrid composites. The use of thermosets and vitrimers in adhesive bonding are presented, illustrating their ability to create robust and durable joints that enhance the structural integrity of landing gear systems. The paper also addresses current challenges, including recycling limitations and high material costs. Sustainability considerations, including the integration of self-healing materials, structural health monitoring systems, and circular economy principles, are discussed as essential for aligning the aerospace sector with global climate goals. Full article

Driven by the growing demand for sustainable materials, spent coffee grounds have emerged as a promising bio-based reinforcement in polymer composites, particularly for additive manufacturing applications. As a readily available byproduct of the coffee industry, spent coffee grounds contain cellulose, hemicellulose, lignin, proteins, and oils, making them attractive fillers for both thermoplastic and thermoset matrices. Incorporating spent coffee grounds into composites supports waste valorization, cost reduction, and environmental sustainability by transforming organic waste into functional materials. This review first examines the issue of spent coffee ground waste, addressing its environmental footprint and disposal challenges. It then explores the composition and properties of spent coffee grounds. The paper provides a comprehensive overview of composites based on spent coffee grounds for 3D printing, covering processing methods, potential applications, and current challenges in additive manufacturing. Special attention is given to the preparation and processing of these composites, including key steps such as drying, grinding, sieving, and surface modification to enhance compatibility with polymer matrices. Various additive manufacturing techniques influence the printability, processability, and mechanical performance of such composites. While spent coffee grounds offer notable sustainability advantages, challenges such as weak interfacial adhesion, moisture sensitivity, and reduced mechanical properties necessitate optimized processing conditions, surface treatments, and tailored material formulations. This review highlights recent advancements and outlines future research directions, emphasizing the need for stronger interactions between spent coffee grounds and polymer matrices, improved recyclability, and scalable additive manufacturing solutions to establish spent coffee grounds as a viable and eco-friendly alternative for 3D printing applications. Full article

Hybrid thermosetting terpolymers based on epoxidized linseed oil (ELO), eugenol-based benzoxazine monomer (EPB), and thiols (2SH and 3SH) were synthesized and studied by focusing on the effects of the thiol-bearing functionality over the final performances. The curing dynamics were monitored by differential scanning calorimetry (DSC) and Fourier transform infrared spectrometry (FTIR). FTIR results showed that the curing process takes place in multiple steps and depends on the concentration of thiol used as a crosslinker. At the same time, the complexity of the reactions that take place within each system was highlighted by the curing profiles from DSC. Dynamic mechanical analysis (DMA) and nanoindentation data revealed that the mechanical features of the terpolymers can be modulated to achieve high stiffness, as in the case where 2SH and 3SH thiols were used in 0.25 wt.% or increased flexibility where 1% thiol concentrations were employed. Higher crosslinking density for hybrid terpolymers in comparison with the epoxy/benzoxazine sample indicated a good compatibility between the monomers and the crosslinking agents and the formation of additional chemical bonds within the networks. The ternary samples demonstrated good thermal stability (up to 300 °C) and high residual mass (>25%), which make them suitable candidates as flame-resistant coatings. Full article

Fiber-reinforced composites (FRCs) have emerged as transformative alternatives to traditional marine construction materials, owing to their superior corrosion resistance, design flexibility, and strength-to-weight ratio. This review comprehensively examines the current state of FRC technologies in marine deck and underwater applications, with a focus on manufacturing methods, durability challenges, and future innovations. Thermoset polymer composites, particularly those with epoxy and vinyl ester matrices, continue to dominate marine applications due to their mechanical robustness and processing maturity. In contrast, thermoplastic composites such as Polyether Ether Ketone (PEEK) and Polyether Ketone Ketone (PEKK) offer advantages in recyclability and hydrothermal performance but are hindered by higher processing costs. The review evaluates the performance of various fiber types, including glass, carbon, basalt, and aramid, highlighting the trade-offs between cost, mechanical properties, and environmental resistance. Manufacturing processes such as vacuum-assisted resin transfer molding (VARTM) and automated fiber placement (AFP) enable efficient production but face limitations in scalability and in-field repair. Key durability concerns include seawater-induced degradation, moisture absorption, interfacial debonding, galvanic corrosion in FRP–metal hybrids, and biofouling. The paper also explores emerging strategies such as self-healing polymers, nano-enhanced coatings, and hybrid fiber architectures that aim to improve long-term reliability. Finally, it outlines future research directions, including the development of smart composites with embedded structural health monitoring (SHM), bio-based resin systems, and standardized certification protocols to support broader industry adoption. This review aims to guide ongoing research and development efforts toward more sustainable, high-performance marine composite systems. Full article

The dependence of conventional epoxy resins on fossil fuels and the environmental and health hazards associated with bisphenol A (BPA) demand the creation of sustainable alternatives. Because lignin is a natural resource and has an aromatic ring skeleton structure, it could be used as an alternative to fossil fuels. This study effectively resolved this challenge by utilizing a sustainable one-step epoxidation process to transform lignin into a bio-based epoxy resin. The results verified the successful synthesis of epoxidized bamboo lignin through systematic characterization employing Fourier transform infrared spectroscopy, hydrogen spectroscopy/two-dimensional heteronuclear single-quantum coherent nuclear magnetic resonance, quantitative phosphorus spectroscopy, and gel permeation chromatography. Lignin-based epoxy resins had an epoxy equivalent value of 350–400 g/mol and a weight-average molecular weight of 4853 g/mol. Studies on the curing kinetics revealed that polyetheramine (PEA-230) demonstrated the lowest apparent activation energy (46.2 kJ/mol), signifying its enhanced curing efficiency and potential for energy conservation. Mechanical testing indicated that the PEA-230 cured network demonstrated the maximum tensile strength (>25 MPa), whereas high-molecular-weight polyetheramine (PEA-2000) imparted enhanced elongation to the material. Lignin-based epoxy resins demonstrated superior heat stability. This study demonstrates the conversion of bamboo lignin into bio-based epoxy resins using a simple, environmentally friendly synthesis process, demonstrating the potential to reduce fossil resource use, efficiently use waste, develop sustainable thermosetting materials, and promote a circular bioeconomy. Full article