Search Results (465)

Pultrusion is an efficient continuous manufacturing process for fiber-reinforced polymer (FRP) composites, but conventional open-bath impregnation has limitations such as resin exposure, quality variation, and resin loss. To overcome these limitations, closed-injection pultrusion (CIP) and short-pot-life resin systems have recently been introduced. However, the effects of processing variables on the quality and properties of composites manufactured using such resin systems have not been fully clarified. In this study, the effects of resin viscosity and pulling speed on the quality and mechanical properties of carbon FRP (CFRP) and glass FRP (GFRP) composites manufactured by CIP were investigated. CFRP and GFRP composites were fabricated at resin temperatures of 30 and 40 °C and pulling speeds of 300, 400, and 500 mm/min. The manufactured composites were evaluated in terms of void content, microstructure, hardness, and tensile properties. The results showed that increasing pulling speed increased void content and promoted macrovoids and locally poor impregnation, whereas the influence of resin temperature was relatively limited. Hardness, tensile strength, and elastic modulus decreased as pulling speed increased. These results demonstrate that CFRP and GFRP composites can be successfully manufactured by CIP using short-pot-life resin systems, and that precise control of resin viscosity and pulling speed is essential for achieving high quality and mechanical performance. Full article

The impending wave of retired wind turbines has brought the issue of blade recycling to the forefront, presenting a major test for global sustainable resource management. Among the recycling methods, pyrolysis can be regarded as the most effective treatment approach, which can recycle the glass fibers that account for about 80% of the total weight of the blade. However, the pyrolytic char remaining on the fiber surface and the damage to the fiber structure caused by the excessively high pyrolysis temperature can both have a negative impact on fiber recycling. In this paper, a pyrolysis and in situ oxidation process with low treatment temperature is proposed for the recycling of glass fibers from the thermosetting epoxy resin–glass fiber composite material in the blades. Pyrolysis is performed at 450 °C, yielding a residual char content of 3.56%. Subsequently, in situ oxidation is conducted at the same temperature by switching the atmosphere to air, while the char content is reduced to below 0.01%, meeting the industrial recycling standard and achieving a glass fiber yield of 74%. Characterization reveals that the fiber structure and properties are well maintained. Additionally, through a series of characterization and density functional theory (DFT) calculations, the pyrolysis pathway from the resin repeating unit to various liquid phase products is supposed, and the corresponding pyrolysis mechanism is concluded. This paper provided a practical and feasible process scheme and theoretical basis for the efficient and clean resource recovery of retired wind turbine blades. Full article

Lost circulation in oil-based drilling fluids (OBDFs) under high-temperature conditions remains a significant challenge in deep and ultra-deep drilling. In this study, a high-temperature-resistant composite lost circulation material (LCM) was developed based on a synergistic strategy combining rigid bridging–consolidation and flexible embedding–filling. Rigid self-consolidating particles were prepared by coating skeleton materials with modified thermosetting resin, while flexible oil-absorbing resin was synthesized via suspension polymerization. The materials exhibited excellent lipophilicity, thermal stability, and structural integrity at 150 °C, with oil absorption capacity up to 3.43 g/g. The optimized composite LCM showed superior plugging performance, achieving compressive strengths above 11 MPa in white oil and 5 MPa in base mud at 150 °C. Effective sealing of 1–3 mm pore structures was obtained with leakage volumes below 10 mL, and fractured formations could be successfully consolidated. Mechanistically, rigid particles provide structural bridging, flexible resin enables pore filling via swelling, and modified resin(thermosetting resin chemically modified to achieve self-consolidation) enhances consolidation and micro-pore sealing, resulting in a dense and high-strength plugging layer. This work provides a promising approach for designing high-performance LCMs for OBDFs in high-temperature drilling environments. Full article

This paper focuses on developing reinforced self-healing supramolecular resins that meet both functional and structural needs for industrial use. The formulated advanced nanocomposites are made from compounds that allow for reversible self-healing interactions. The self-healing molecules bond with the toughened epoxy matrix using hydrogen bonding. To enhance the epoxy’s typical insulating properties, electrically conductive carbon nanotubes (CNTs) were added to achieve an electrical percolation threshold (EPT) with a low amount of nanofiller. This study found that self-healing efficiency can reach nearly 99%. The addition of healing compounds significantly raises the glass transition temperature to over 200 °C. Tunneling Atomic Force Microscopy (TUNA), which is an innovative tool for correlating local topography with electrical properties, reveals the structural properties and compatibility of these materials, mapping conductive pathways at the micro- and nanoscale. Full article

Pavement repair has become an increasingly time-critical operation as traffic volumes grow and lane-closure windows shrink. This has driven demand for materials that gain full structural strength quickly, reopen to traffic within hours, and hold up longer than conventional patches. This study evaluates polymer concrete (PC), a thermosetting resin-bound aggregate system, through combined laboratory characterization and three-dimensional finite element analysis. Compressive strength, splitting tensile strength, unit weight, and apparent porosity were measured at 1, 3, 7, and 28 days of curing. PC reached 85.97 MPa in compression and 7.63 MPa in tension by day three, with near-zero porosity (0.15%) maintained throughout. These three-day values were used directly as material inputs in the three-dimensional finite element analysis (FEA), reflecting the early traffic reopening scenario that defines rapid repair practice. Structural performance was assessed through 36 static analyses in ANSYS 2024 R2, covering flexible (Hot Mix Asphalt, HMA) and rigid (Jointed Plain Concrete Pavement, JPCP) pavement types, three patch sizes (250 × 250 mm, 500 × 500 mm, and 1000 × 1000 mm), and nine load scenarios per configuration. Safety factors (SF) against internal cracking, interfacial debonding, and compressive failure were computed for both PC and traditional patches. PC consistently outperformed HMA and Portland cement concrete patches across all metrics. On rigid pavements, interfacial safety factors exceeded 22.0, confirming that standard surface preparation is sufficient. On flexible pavements, adopting 0.78 MPa as a conservative lower-bound estimate of PC-HMA interfacial bond strength, five scenarios exhibit debonding risk (250-C, 500-C, 500-D, 1000-C, and 1000-D; SF = 0.47–0.99), while the remaining four show high interfacial risk (SF = 1.11–1.30); primer application and mechanical scarification are required for all PC repairs on flexible pavements regardless of patch geometry. Taken together, the experimental and numerical evidence positions PC as a credible, high-performance option for highway repair. Full article

Epoxy resins have been extensively applied in aerospace and automotive fields. Nevertheless, their inherent flammability significantly restricts broader applications. In this study, carboxylated multi-walled carbon nanotubes (COOH-MWCNTs) were first aminated to obtain aminated Multi-Walled Carbon Nanotubes (NH₂-MWCNTs). Subsequently, NH₂-MWCNTs and ammonium polyphosphate (APP) were incorporated into the epoxy resin via mechanical stirring, thereby constructing a phosphorus–carbon synergistic flame-retardant system. Compared with the neat epoxy thermoset, the EP/17.5APP/0.1NH₂-MWCNTs composite showed a limiting oxygen index (LOI) value of 29.6% and attained a UL-94 V-0 rating. In addition, for the modified composite material, the maximum thermal decomposition rate (R_Tmax) is 12.4 wt%/min, the char residue at 600 °C (C₆₀₀) reaches 44.2%, and the smoke density is 425.8. The impact strength and tensile modulus are increased to 10.1 Mpa and 3.0 Gpa, respectively, while the compressive strength remains essentially unchanged. Furthermore, the synergistic flame-retardant mechanism between phosphorus and carbon was investigated by analyzing the char residues of the epoxy resin and its composites. This study offers a promising approach for designing epoxy composites with improved flame retardancy and enhanced thermal stability for high fire-safety applications, such as electronic encapsulation and structural materials. Full article

Epoxy resins are widely used thermosetting polymers, but their limited toughness and flexural resilience restrict broader applications. In this study, diglycidyl ether of bisphenol A (DGEBA) epoxy was reinforced with 5 wt.% ceramic fillers of different origins: sol–gel alumina calcined at 550 °C (γ-Al₂O₃) and 1000 °C (α-Al₂O₃), silica derived from rice husk, silica from diatomaceous earth, and a hybrid alumina–silica mixture prepared by sol–gel and calcined at 1000 °C. Fillers were structurally characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field-emission scanning electron microscopy (FESEM). Mechanical properties were evaluated through tensile (ASTM D638) and flexural (ASTM D790) testing. All reinforcements enhanced the performance of neat epoxy. γ-Al₂O₃ provided superior tensile reinforcement compared to α-Al₂O₃, underscoring the importance of particle morphology and surface reactivity. The hybrid alumina–silica filler achieved the highest flexural strength of 50.6 MPa, compared to 9.91 MPa for the neat epoxy. Bio-derived silica showed improved flexural properties, although its tensile reinforcement was less pronounced compared to the sol–gel derived fillers. These results establish clear structure–property relationships and confirm that filler phase, morphology, and calcination temperature critically govern the mechanical performance of epoxy composites. Full article

Air pollution has drawn increasing attention. The channel-type structure, as an ideal energy-saving and resistance-reducing strategy for air filters, can effectively lower filtration resistance. However, current commercial channel-type filters generally exhibit only medium or low filtration efficiency, and the use of plant fibers as raw material limits their application in high-efficiency filters. In this study, high-efficiency glass fiber filter paper was combined with a channel-type structure, and the formulation and processing techniques suitable for the channel-type design were systematically investigated, leading to the fabrication of channel-type high-efficiency filters. The optimal formulation was determined to be a blend of glass wool fibers and 6 mm Tencel fibers in a 6:4 ratio, coated with a thermosetting resin, which yielded filter paper suitable for wave-pleating. The resulting filter paper demonstrated a filtration efficiency of 99.9624%, a pressure drop of 265.6 Pa, and a pleat aspect ratio of 0.209. Using this formulation, pilot-scale filter paper was produced and wave-pleated under processing conditions including a roller speed of 5 m/min, a roller gap of 0.4 mm, and a roller temperature of 160 °C, which was then used to fabricate channel-type high-efficiency filters. The finished channel-type filters achieved a filtration efficiency of 99.9940% with a pressure drop of 164.0 Pa. Compared to traditional pleated filters of the same volume and efficiency rating, the channel-type filter exhibited a 49.53% larger filtration area, a 33.13% lower face velocity, and a 31.67% reduction in pressure drop. This work offers a novel approach to reducing resistance and enhancing efficiency in air filtration systems. Full article

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

The brittleness of bismaleimide (BMI) resin is a major issue that restricts its use as a matrix for advanced composites. Blending with thermoplastics constitutes an effective toughening approach that preserves the thermal resistance and mechanical properties of the resin. Reaction-induced phase separation is the primary toughening mechanism in thermoplastic-toughened BMI resin. However, the complex phase-separated structure causes the relationship between the glass transition temperature (T_g) and the curing degree to deviate from that described by the classical DiBenedetto equation. In this paper, two improved models, incorporating power-law correction and threshold inhibition, were constructed to address the phase-separation effect. An aerospace-grade BMI resin was toughened by a thermoplastic polyimide. The relationship between T_g and the curing degree was fitted by the DiBenedetto equation and the improved models. It was found that the adjusted coefficient of determination for the power-law correction and threshold inhibition models for the toughened resin increased to 0.978 and 0.995, respectively, whereas that of the DiBenedetto equation was only 0.612. This work provides a new, readily applicable empirical model for the prediction of T_g in thermoplastics-toughened thermosetting resins and offers theoretical support for optimizing the curing process and controlling the performance of multiphase resins. Full article

The development of filled photopolymer composites for Digital Light Processing (DLP) additive manufacturing requires optimizing processing parameters to achieve the desired mechanical properties. Traditional experimental approaches are time-intensive, while physics-based models often struggle to capture the complex interactions among parameters. This study presents a physics-informed machine learning framework that combines Random Forest with Bayesian optimization (RF-BO) to predict the ultimate tensile strength in recycled thermoset resin composites manufactured via DLP. A validation dataset of 19 systematically varied formulations (each with n = 5 measurement replicates for reliability) was generated and augmented with 1500 physics-informed synthetic samples to enable robust model training. The limited experimental dataset, while insufficient for traditional statistical inference, provided critical validation of physical trends, including non-monotonic particle-size effects and optimal processing windows. Six machine learning algorithms were evaluated, with RF-BO achieving superior performance (R² = 0.9125, MSE = 1.07 MPa). The framework identified optimal processing conditions of 59–64 μm particle size, 5.0 ± 0.5 wt.% concentration, and 60 min cure time, predicting a maximum UTS of 43.84 MPa with a prediction error of less than 1.0 MPa. Feature importance analysis revealed that cure time was the dominant parameter (40%), followed by particle size (30%), validating the physical interpretability. This approach demonstrates significant potential for accelerating materials design in composite additive manufacturing while maintaining physically meaningful predictions. Full article

Polyester resin biocomposites containing biochar have attracted attention for improving mechanical strength and thermal stability while promoting sustainability. The pyrolysis temperature of biochar and its proportion in the polymer matrix are key factors affecting biocomposite performance. This study examined how biochar pyrolysis temperatures (400, 600, 800 °C) and incorporation levels (10, 20, 30 wt.%) influence the physical, chemical, mechanical, flammability, and morphological properties of polyester-based biocomposites. The samples were analyzed for density, water absorption, FTIR, XRD, flexural and tensile strength, ignition time, structural degradation, volumetric loss, and SEM microstructure. Biocomposites with 30 wt.% biochar produced at 800 °C showed the best mechanical properties, with a flexural strength of 95.3 MPa and an elastic modulus of 4417.4 MPa, representing increases of 14.5% and 45.7%, respectively, over the control. FTIR and XRD results revealed decreased aliphatic groups and increased aromaticity at higher pyrolysis temperatures, improving interactions between the matrix and biochar. These biocomposites also demonstrated enhanced thermal stability, with an ignition time of approximately 963 s, delayed structural degradation, and reduced volumetric loss (~19.3%). Overall, pyrolysis temperature and biochar content significantly influence the structural, mechanical, and thermal properties of polyester biocomposites, showing that biochar serves as a sustainable, performance-enhancing component in thermoset polymer matrices. Full article

In ultra-high-voltage GIS and GIL systems, epoxy resin insulators are still the mainstream choice. However, as a thermosetting material, epoxy resin is difficult to recycle after disposal, which limits its environmental benefits. Thermoplastic insulators, due to their recyclability, are potential alternatives. This study focuses on 30% glass fiber-reinforced PET and PA6 materials. Their injection molding behavior, hydraulic pressure performance, and insulation performance were systematically analyzed using Moldflow, ANSYS, and COMSOL, respectively. For injection molding, Moldflow simulations were conducted for filling, packing, and cooling stages. Melt temperature was varied from 260 to –310 °C (PET) and 250–300 °C (PA6), while mold temperature was varied from 80 to –130 °C (PET) and 70–120 °C (PA6). An optimization objective function, Y = Δp/20 + Δx/0.5 + Δs/1.8, was developed to determine optimal processing parameters. Based on this function, the optimal parameters identified are: PET at 290 °C melt temperature and 120 °C mold temperature; PA6 at 250 °C melt temperature and 70 °C mold temperature. For hydraulic testing, Moldflow–ANSYS coupled simulations were performed under 2.4 MPa pressure with the compliance criteria of bulk stress < 90 MPa and insert-contact stress < 20 MPa. PA6 passed within a processing window of melt temperature < 270 °C and mold temperature < 120 °C. PET failed under all tested conditions, with insert-contact stress ranging from 24.25 to 27.55 MPa, consistently exceeding the 20 MPa threshold. In terms of insulation performance, this paper utilizes COMSOL to study the electric field distribution of thermoplastic insulators in SF₆ GIS/GIL and provides optimization suggestions for insulator geometry design. This study systematically compares the injection molding processes and hydraulic pressure performance of PET and PA6 thermoplastic insulators. These results provide important process insights and design guidance for evaluating thermoplastic materials as potential alternatives to epoxy resin in GIS/GIL applications. Full article

In liquid composite moulding processes, the curing behaviour of thermoset matrices plays a decisive role in determining manufacturing quality and cycle time. Premature demoulding may lead to insufficiently cured components, whereas excessively long curing times reduce production efficiency. Reliable monitoring and modelling of the curing process are therefore essential for process optimisation. In this study, the cure kinetics of a fast-curing epoxy resin system are modelled using the Grindling kinetic model, which accounts for diffusion-controlled reaction behaviour and vitrification effects. Model parameters are identified using both dynamic and isothermal differential scanning calorimetry (DSC) measurements. In addition, the glass transition temperature is described as a function of the degree of cure using the DiBenedetto relationship. To demonstrate the applicability of the model for process monitoring, an experimental mould equipped with temperature sensors was developed to simulate real-time estimation of the degree of cure during isothermal processing. The predicted degree of cure is validated by post-process DSC analysis of the manufactured samples. Initial comparisons reveal systematic deviations caused by temperature measurement uncertainties. After implementing a temperature correction based on experimentally determined sensor deviations, the predicted degree of cure shows significantly improved agreement with DSC measurements. The results demonstrate that combining kinetic modelling with temperature monitoring enables reliable real-time estimation of the curing state for fast-curing epoxy systems. The study also highlights the critical importance of accurate temperature measurement for curing monitoring and provides insights into the practical implementation of sensor-based monitoring strategies in liquid composite moulding processes. Full article

Photopolymer-based additive manufacturing processes such as stereolithography (SLA) offer high precision and surface quality but generate cured thermoset waste that is typically non-recyclable. In microgravity environments, conventional recycling approaches—based on gravitational settling, open solvent handling, and buoyancy-driven degassing—are ineffective, motivating the development of fully contained, gravity-independent material recovery systems for on-orbit manufacturing. This work presents a conceptual, design-stage closed-loop system architecture for recycling photopolymer resins in microgravity. The system integrates eight subassemblies enabling mechanical fragmentation, solvent-assisted dissolution, filtration, low-pressure degassing, pressurized storage, injection molding, and ultraviolet curing. A hermetically sealed dual-screw shredder produces resin fragments of 1–3 mm, suitable for dissolution. Gas removal is achieved through low-vacuum degassing at approximately 0.1–0.3 bar, with characteristic residence times of 5–10 min, ensuring stable processing prior to injection. Material transport is governed by mechanical conveyance and controlled pressure, eliminating reliance on gravity. The architecture maintains full containment of solids, liquids, and vapors throughout the process. Supported by engineering design considerations, the system establishes a microgravity-compatible pathway for closed-loop recycling of SLA materials. Experimental validation is planned in future work. Full article