Search Results (413)

4,4’-Methylenebis(N,N-diglycidylaniline) (AG80), as a high-performance thermosetting material, holds significant application value due to the enhancement of its strength, toughness, and thermal stability. However, conventional toughening methods often lead to a decrease in material strength, limiting their application. Modification of AG80 epoxy resin was performed using hydroxy-terminated polyphenylpropylsiloxane (Z-6018) and a self-synthesized epoxy compatibilizer (P/E30) to regulate the phase structure of the modified resin, achieving a synergistic enhancement in both strength and toughness. The modified resin was characterized by Fourier transform infrared analysis (FTIR), proton nuclear magnetic resonance (¹H NMR) spectroscopy, silicon-29 nuclear magnetic resonance (²⁹Si NMR) spectroscopy, and epoxy value titration. It was found that the phase structure of the modified resin significantly affects mechanical properties. Thus, P/E30 was introduced to regulate the phase structure, achieving enhanced toughness and strength. At 20 wt.% P/E30 addition, the tensile strength, impact strength, and fracture toughness increased by 50.89%, 454.79%, and 152.43%, respectively, compared to AG80. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses indicate that P/E30 regulates the silicon-rich spherical phase and interfacial compatibility, establishing a bicontinuous structure within the spherical phase, which is crucial for excellent mechanical properties. Additionally, the introduction of Z-6018 enhances the thermal stability of the resin. Full article

Thermosets are plastic composite materials widely used in many industrial sectors of modern society with an increasing presence in the environment. The adverse effects of this material on environmental compartments and biota of thermosets are still unknown. In this work, we studied the potential effects of two thermoset polyester resin-derived microplastics (R930A-SP and R930A-DVE1) on the survival, behavior, morphological changes and subcellular damage of earthworms Eisenia fetida. The proposed experimental conditions simulated environmentally relevant concentrations, taking as a reference other related microplastics present in the environment. Thus, E. fetida specimens were exposed to five concentrations (100, 500, 1000, 1500 and 2000 mg resin per kg soil) of these two resins for 14 days. At concentrations and exposure times studied, no significant effects on growth, measured as weight loss, or on the enzyme biomarkers (cholinesterase, carboxylesterase and glutathione S-transferase) were observed. Similarly, no behavioral changes were detected in earthworms, and the survival rate was 100%. Likewise, no differences were observed between the different formulations of the polyester resins studied. However, this study could serve as a starting point for further studies with higher concentrations and/or exposure times, as well as in combination with other pollutants. Full article

This research paper employed the recently developed Elium thermoplastic resin and basalt fabrics as an alternative to thermoset/synthetic fibre composites to reduce their environmental impact. Elium^® 191 XO/SA and Epoxy Prime^TM 37 resin were reinforced with mineral-based semi-unidirectional basalt fibre (BF). Physical, chemical, tensile, and flexural performance was investigated under the effect of hydrothermal seawater ageing at 45 °C for 45 and 90 days. The results show that the BF/Elium composite exhibited superior tensile and flexural strength, as well as good stiffness, compared with the BF/Epoxy composite. Digital images and scanning electron microscope images were used to describe the fracture and failure mechanisms. The tensile and flexural strength values of the BF/Elium composite were 1165 MPa and 1128 MPa, greater than those of the BF/Epoxy composite by 33% and 71%, respectively. The tensile and flexural modulus values of the BF/Elium composite were 44.1 GPa and 38.2 GPa, which are 30% and 12% greater than those of the BF/Epoxy composite. The result values for both composites were normalised with respect to the density of each composite laminate. Both composites exhibited signs of resin decomposition and fibre surface degradation under the influence of seawater ageing, resulting in a more recognisable reduction in flexural properties than in tensile properties. Full article

This work presents the development of two vanillin-based vitrimer epoxy flax fibre-reinforced composites, with both the VER1-1-FFRC (a vitrimer-to-epoxy ratio of 1:1) and VER1-2-FFRC (a vitrimer-to-epoxy ratio of 1:2), via a vacuum-assisted resin infusion. The thermal and mechanical properties of the resulting vitrimer epoxy flax composites were characterised using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical four-point bending tests, alongside studies of solvent resistance and chemical recyclability. Both the VER1-1-FFRC (degradation temperature T_deg of 377.0 °C) and VER1-2-FFRC (T_deg of 395.9 °C) exhibited relatively high thermal stability, which is comparable to the reference ER-FFRC (T_deg of 396.7 °C). The VER1-1-FFRC, VER1-2-FFRC, and ER-FFRC demonstrated glass transition temperatures T_g of 54.1 °C, 68.8 °C, and 83.4 °C, respectively. The low T_g of the vitrimer composite is due to the low crosslink density in the vitrimer epoxy resin. Particularly, the crosslinked density of the VER1-1-FFRC was measured to be 319.5 mol·m⁻³, which is lower than that obtained from the VER1-2-FFRC (434.7 mol·m⁻³) and ER-FFRC (442.9 mol·m⁻³). Furthermore, the mechanical properties of these composites are also affected by the low crosslink density. Indeed, the flexural strength of the VER1-1-FFRC was found to be 76.7 MPa, which was significantly lower than the VER1-2-FFRC (116.2 MPa) and the ER-FFRC (138.3 MPa). Despite their lower thermal and mechanical performance, these vitrimer composites offer promising recyclability and contribute to advancing sustainable composite materials. Full article

In this work, the mechanical properties of composites with a polymer matrix and reinforced with carbon particles have been studied. It has been established that the obtained engineering materials have increased elastic and plastic characteristics. The thermosetting polymers used are epoxy, polyester, and vinylester resins. The carbon particles are carbon nanotubes and waste carbon from the plasma decomposition of methane in the production of green hydrogen. The carbon particles used are in an amount of 1 wt% and 2 wt% of the weight of the composite, and they are not subjected to pre-treatment (modification). The studied composites are used in shipping, automotive, and aviation technology, and the presence of carbon particles in them is a prerequisite for improving their anti-radar properties. 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

Glass fiber reinforced polypropylene composite plates have gradually attracted more attention because of their repeated molding, higher toughness, higher durability, and fatigue resistance compared to glass fiber reinforced thermosetting composites. In practical engineering applications, composite plates have to undergo bending effect at different angles in corrosive environment of concrete, including bending bars from 0~90°, and stirrups of 90°, which may lead to long-term performance degradation. Therefore, it is important to evaluate the long-term performance of glass fiber reinforced polypropylene composite bending plates in an alkali environment. In the current paper, a new bending device is developed to prepare glass fiber reinforced polypropylene bending plates with the bending angles of 60° and 90°. It should be pointed out that the above two bending angles are simulated typical bending bars and stirrups, respectively. The plate is immersed in the alkali solution environment for up to 90 days for long-term exposure. Mechanical properties (tensile properties and shear properties), thermal properties (dynamic mechanical properties and thermogravimetric analysis) and micro-morphology analysis (surface morphology analysis) were systematically designed to evaluate the influence mechanism of bending angle and alkali solution immersion on the long-term mechanical properties. The results show the bending effect leads to the continuous failure of fibers, and the outer fibers break under tension, and the inner fibers buckle under compression, resulting in debonding of the fiber–matrix interface. Alkali solution (OH⁻ ions) corrode the surface of glass fiber to form soluble silicate, which is proved by the mass fraction of glass fiber decreased obviously from 79.9% to 73.65% from thermogravimetric analysis. This contributes to the highest degradation ratio of tensile strength was 71.6% (60° bending) and 65.6% (90° bending), respectively, compared to the plate with bending angles of 0°. A high curvature bending angle (such as 90°) leads to local buckling of fibers and plastic deformation of the matrix, forming microcracks and fiber–resin interface bonding at the bending area, which accelerates the chemical erosion and debonding process in the interface area, bringing about an additional maximum 10.56% degradation rate of the shear strength. In addition, the alkali immersion leads to the obvious degradation of storage modulus and thermal decomposition temperature of composite plate. Compared with the other works on the long-term mechanical properties of glass fiber reinforced polypropylene, it can be found that the long-term performance of glass fiber reinforced polypropylene composites is controlled by the corrosive media type, bending angle and immersion time. The research results will provide durability data for glass fiber reinforced polypropylene composites used in concrete as stirrups. Full article

The cure kinetics in frontal polymerization (FP) of short carbon-fiber-reinforced composites are investigated numerically, focusing on the influence of fiber aspect ratio, volume fraction, and orientation. A classical heat conduction equation is used in FP, where the enthalpic reaction generates heat. The heat generation term is expressed in terms of the rate of degree of cure ($\mathrm{d}\mathsf{\alpha }/\mathrm{d}\mathrm{t}$) in thermoset resin. A rate equation of the degree of cure for epoxy is established in terms of a pre-exponential factor, activation energy, Avogadro’s gas constant, and temperature. The cure kinetics parameters for epoxy resin used in this study are determined using the Ozawa method. The numerical model was validated with experimental data. The results reveal that the aspect ratio of fibers has a minimal effect on the polymerization time. The volume percentage of fibers significantly influences the curing time and temperature distribution, with higher fiber volume fractions leading to faster curing due to enhanced heat transfer. Additionally, fiber orientation plays a critical role in cure kinetics, with specific angles facilitating more effective heat transfer, thereby influencing the curing rate and frontal velocity. The results offer valuable insights into optimizing the design and manufacturing processes for high-performance epoxy-based composites through FP, where precise control over curing is critical. Full article

Epoxy resins are limited by their flammability and brittleness. In this study, a phosphorus- and silicon-based additive was synthesized to improve fire resistance and mechanical performance. The incorporation of just 1 wt% phosphorus from this additive into epoxy resin achieved a limiting oxygen index of 33% and a V-0 fire rating. The modified epoxy exhibited a 52.43% reduction in the peak heat release rate and a 35.70% decrease in total smoke production compared to the unmodified resin, demonstrating enhanced heat resistance and smoke suppression. Notably, the modified epoxy thermoset displayed superior mechanical properties, with tensile and impact strengths increasing by 48.41% and 130%, respectively. This research presents a promising approach for developing high-performance epoxy resins with improved flame retardancy, smoke suppression, and mechanical strength. Full article

Currently, the main drivers for the production of phosphate glass fiber-reinforced composites are the growing demand for lightweight materials, reduced energy consumption, improved durability, and minimized environmental impact. This study aims to develop thermoset-based composites using chopped and continuous phosphate glass fibers (PGFs) combined with polyester and epoxy matrices, processed via contact molding. Physical, mechanical, thermal, and morphological characterizations were conducted. The addition of PGFs led to a steady increase in density and fiber volume fraction. For polyester composites with short PGFs, density rose from 1.60 g/cm³ (0 wt%) to 1.77 g/cm³ (22.8 wt%), with a corresponding volume fraction increase from 0% to 14.4%. Similarly, epoxy composites showed density values from 1.70 g/cm³ to 1.87 g/cm³ and volume fractions up to 15.2%. Thermogravimetric analysis (TGA) showed that as the fiber content increased, the thermal degradation of the resin was delayed, as evidenced by a rise in onset degradation temperature and greater residual mass—indicating improved thermal stability of the composites. Tensile strength increased from 20.8 MPa to 71.3 MPa (polyester) and from 26.8 MPa to 75.9 MPa (epoxy) with chopped fibers, reaching 145.7 MPa and 187.9 MPa, respectively, with continuous fibers. Flexural strength reached 167.9 MPa (polyester) and 218.0 MPa (epoxy) in continuous-fiber configurations. Young’s modulus values closely matched Hirsch model predictions. These findings confirm the potential of PGF-reinforced thermoset composites for high-performance and sustainable material applications. Full article

An enhanced process for shaping thermoset fiber-reinforced composites using Modified Double-Diaphragm Forming (mDDF) in Prepreg Compression Molding (PCM) is proposed to address limitations in conventional forming quality. To minimize surface defects, prepregs were pre-cut to reduce wrinkle formation and trimmed after preforming. Complex geometries were managed through draping analysis, which enabled identification and mitigation of wrinkle-prone regions. A challenging layup configuration (±45/0/90/0/90/0/±45) was selected, and temperature-dependent behavior of the prepreg—such as resin fluidity and wrinkle characteristics—was evaluated from room temperature to 80 °C. Material characterization included tensile, bias extension, bending, friction, and density tests. Forming simulations using AniForm Suite 3.0 incorporated fitted material parameters for predictive analysis. Experimental validation confirmed that the mDDF process significantly improved fiber alignment and eliminated wrinkle defects, especially in 16 previously identified critical zones. The final parts exhibited superior surface quality and dimensional accuracy compared to conventional PCM, highlighting the potential of mDDF for precision manufacturing of complex thermoset composite structures. Full article

Benzoxazines are a kind of high-performance thermosetting resin that can undergo ring-opening polymerization to generate cross-linking structures. Here, two benzoxazine monomers, bisphenol A/aniline type (BA-a) and bisphenol A/tert-butylamine type (BA-tb), were synthesized and mixed with three tertiary amine catalysts like 2-methylimidazole (2MI), 1,2-dimethylimidazole (12MI), 4-dimethylaminopyridine (DMAP). Differential scanning calorimetry (DSC) was performed to study the curing behaviors and the curing kinetics of two benzoxazine/catalyst systems. The results indicated that all amines had a catalytic effect on the polymerization of both benzoxazines, and the BA-a/catalyst systems showed relatively higher activity. In addition, Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra were procured to analyze structural changes in the benzoxazine/catalyst systems during the curing process. The presence of the catalysts promoted the progress of the ring-opening reactions and the formation of the phenolic units in the cross-linking structures, and these evolutions were more obvious for the BA-a/catalyst system than the BA-tb/catalyst system. Furthermore, a thermogravimetric analysis (TGA) was conducted to analyze the thermal stability of the cured systems. Finally, possible curing reaction mechanisms were proposed for these benzoxazine/amine systems. Full article

This research work focuses on the chemical recycling of a Carbon Fiber-Reinforced Composite (CFRC) manufactured through a vacuum-assisted resin infusion (VARI) process, characterized by a high Young’s modulus of approximately 7640 MPa. The recycling reaction was performed using a mixture of eco-sustainable solvents, composed of acetic acid and hydrogen peroxide, and was conducted at three different temperatures (70, 80, and 90 °C). The reaction yield values, evaluated with an innovative approach that involved the use of thermogravimetric analysis (TGA), confirmed the importance to recycle at a temperature corresponding to the glass transition temperature (Tg = 90.3 °C) of the resin. Spectroscopic investigations highlighted that the chemical bond cleavage occurred through the selective breaking of the C-N bonds of the cross-linked matrix structure, allowing the recovery of both the reinforcing phase of the epoxy matrix and the initial oligomers/monomers of the epoxy matrix. The morphological and electrical investigations carried out on the recovered fibers further confirmed the efficiency of the recycling process conducted at the highest explored temperature, allowing the recovery of cleaner fibers with an electrical conductivity value (8.04 × 10² S/m) closer to that of virgin fibers (2.20 × 10³ S/m). The proposed strategy is a true challenge in terms of saving energy, solving waste disposal problems, preserving the earth, and preventing the depletion of planet resources. Full article

Lost circulation has become one of the important problems restricting the speed and efficiency of oil and gas drilling and production. To address severe drilling fluid losses in high-temperature fractured formations during deep/ultra-deep well drilling, this study developed a high-temperature and high-strength gelled resin gel plugging system through optimized resin matrix selection, latent curing agent, flow regulator, filling material, etc. Comparative analysis of five thermosetting resins revealed urea-formaldehyde resin as the optimal matrix, demonstrating complete curing at 100–140 °C with a compressive strength of 9.3 MPa. An organosilicon crosslsinker-enabled water-soluble urea-formaldehyde resin achieved controlled solubility and flow–cure balance under elevated temperatures. Orthogonal experiments identified that a 10% latent curing agent increased compressive strength to 6.26 MPa while precisely regulating curing time to 2–2.5 h. Incorporating 0.5% rheological modifier imparted shear-thinning and static-thickening behaviors, synergizing pumpability with formation retention. The optimal formula (25% urea-formaldehyde resin, 10% latent curing agent, 10% high-fluid-loss filler, 0.5% rheological modifier) exhibited superior thermal stability (initial decomposition temperature 241 °C) and mechanical integrity (bearing pressure 13.95 MPa in 7 mm wedge-shaped fractures at 140 °C). Microstructural characterization confirmed interlocking crystalline layers through ether-bond crosslinking, providing critical insights for high-temperature wellbore stabilization. Full article

Fused deposition modelling (FDM) technology provides a flexible and cost-effective solution for the manufacture of polymer components, enabling the precise design of structures and the incorporation of a variety of composite materials. Its development is confirmed by numerous studies on fibre reinforcements (e.g., GFRP and CF) and thermosetting resin modifications, resulting in improved impact strength and fracture toughness and increased thermal stability of products. The final mechanical properties are significantly influenced by processing parameters (e.g., fill density, layer height, and printing speed) and internal geometry (e.g., lattice structures), which can be further optimised by numerical analyses using constitutive models such as the Johnson–Cook model. The focus of the study presented here is on the fabrication of composites from FDM dies filled with F8 polyurethane resin. Filaments, including PETG carbon and PETG, were tested for potential applications with the resin. A static compression test, supported by numerical analysis using the Johnson–Cook model, was carried out to identify key mechanical characteristics and to predict the material’s behaviour under different loading conditions. The results indicate that these structures exhibit numerous potential delamination planes and voids between filament paths, leading to relatively low maximum stress values (σ_m ≈ 2.5–3 MPa). However, the impregnation with polyurethane resin significantly enhances these properties by bonding the layers and filling the pores, resulting in a more homogeneous and stronger composite. Additionally, numerical simulations effectively captured key aspects of structural behaviour, identifying critical stress concentration areas, particularly along the side walls and in regions forming triangular stress zones. These findings provide valuable insights into the potential of resin-filled FDM structures in engineering applications, demonstrating their improved performance over purely printed samples. Full article