Search Results (4,617)

Hierarchical porous carbon materials hold great potential for energy storage applications due to their high porosity, large specific surface area, and excellent electrical conductivity. Cellulose and sodium alginate are naturally abundant high-molecular-weight biopolymer materials. Utilizing them as precursors for the fabrication of high-performance electrochemical carbon materials is highly significant for achieving carbon neutrality goals. In this study, porous carbon aerogels were successfully synthesized using a combination of freeze-drying and a simple carbonization process, with nanocellulose and sodium alginate as precursors. Among the prepared samples, SC-0.03 (sodium alginate: nanocellulose = 0.1:0.03) exhibited the best performance, achieving a specific surface area of 713.7 m² g⁻¹. This material features an optimized hierarchical pore structure and a substantial intrinsic oxygen doping content, resulting in excellent capacitance performance. Benefiting from these structural advantages and their synergistic effects, the SC-0.03 electrode demonstrated a high specific capacitance of 251.5 F g⁻¹ at a current density of 0.5 A g⁻¹. This study shows that the construction of three-dimensional porous structures by taking advantage of the self-supporting properties of natural polymer materials does not require the introduction of external binders. Due to the nanoscale dimensions and high aspect ratio, nanocellulose enables the formation of a more refined and interconnected hierarchical pore network, enhancing ion accessibility and conductivity. The hierarchical porous carbon aerogel developed in this study, based on a biomass self-reinforcement strategy, not only shows great promise as an advanced energy storage material but also possesses environmentally friendly properties, offering new insights for the development of sustainable energy materials. Full article

To address the existing challenges of lacking a unified and reliable shear capacity prediction model for fiber-reinforced polymer (FRP)-strengthened reinforced concrete beams (FRP-SRCB) and the excessive experimental workload, this study establishes a shear capacity prediction model for FRP-SRCB based on machine learning (ML). First, the correlation between input and output parameters was analyzed by the Pearson correlation coefficient method. Then, representative single model (ANN) and integrated model (XGBoost) algorithms were selected to predict the dataset, and their performance was evaluated based on three commonly used regression evaluation metrics. Finally, the prediction accuracy of the ML model was further verified by comparing it with the domestic and foreign design codes. The results manifest that the shear capacity exhibits a strong positive correlation with the beam width and effective height. Compared to the ANN model, the XGBoost-based prediction model achieves determination coefficients (R²) of 0.999 and 0.879 for the training and test sets, respectively, indicating superior predictive accuracy. Furthermore, the shear capacity calculations from design codes show significant variability, demonstrating the superior predictive capability of ML algorithms. These findings offer a guideline for the design and implementation of FRP reinforcement in actual bridge engineering. Full article

Silylation treatment improves the hydrophobicity of cellulose by reducing the number of hydroxyl groups in the cellulose chains that are available to react with moisture in the surrounding environment. Additionally, silylation increases stress transfer from cellulose to synthetic nanofillers by forming covalent bonds between the hydroxyl groups of cellulose and the oxidized surface of these nanofillers. This study investigates the impact of silane coupling agents on the tensile properties of cellulose nanocomposites. The cellulose nanocomposites are reinforced with four types of C/SiC-based nanofillers: carbon nanotubes, graphene nanoplatelets, silicon carbide nanotubes, and silicon carbide nanoplatelets. Subsequently, the nanofillers are subjected to surface treatment using the silane coupling agent KH550. The mechanical properties of the cellulose nanocomposites are evaluated by molecular dynamics simulations based on the polymer’s consistent forcefield. The results indicate that the reinforcements of silylated silicon carbide nanotubes and carbon nanotubes increase the tensile modulus of cellulose by 18.03% and 24.58%, respectively, compared to their untreated counterparts. Furthermore, the application of silylation treatment on the surface of C/SiC nanofillers increases the yield strength and ultimate tensile strength of cellulose nanocomposites due to enhanced load transfer between cellulose and these reinforcements. Full article

This study investigates the degradation mechanisms of fiber-reinforced polymer (FRP) matrices in composite insulators under partial discharge (PD) conditions. The degradation products may further cause deterioration of the electrical and chemical resistance (ECR) glass fibers. Using pyrolysis–gas chromatography-mass spectrometry (PY-GC-MS) and high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS-MS), the thermal degradation gas and liquid products of the degraded FRP matrix were analyzed, revealing the presence of organic acids. These acids form when the epoxy resin’s cross-linked bonds break at high temperatures, generating anhydrides that hydrolyze into carboxylic acids in the presence of moisture. The hydrolyzation process is accelerated by hydroxyl radicals produced during PD. The resulting carboxylic acids deteriorate the glass fibers within the FRP matrix by degrading surface coupling agents and reacting with the alkali metal–silica network, leading to the substitution and precipitation of metal ions. Organic acids, particularly carboxylic acids, were found to have a more severe deteriorating effect on glass fibers compared to inorganic acids, with high temperatures exacerbating this process. These findings provide critical insights into the deterioration mechanisms of FRP under operational conditions, offering valuable guidance for optimizing manufacturing processes and enhancing the longevity of composite insulators. Full article

FRCM (Fabric-Reinforced Cementitious Matrix) composites, while providing an effective alternative to FRP (Fiber-Reinforced Polymer) strengthening systems when epoxy resins cannot be used, typically fail to achieve their full strengthening potential. Research indicates that appropriate mesh anchorage systems can minimize some of the undesirable effects that limit FRCM composite performance. This study investigates the effectiveness of different anchorage systems for PBO (p-Phenylene Benzobis Oxazole) fibers in FRCM composites used for strengthening reinforced concrete slabs. A series of unidirectionally bent RC slabs were tested under four-point bending: an unstrengthened control element, slabs strengthened with PBO-FRCM without anchorage, with bar anchorage (GFRP bar in a groove), and with cord anchorage (PBO cord through the slab). The research focused on analyzing the load–deflection behavior and key strain mechanisms that influence structural performance. The findings indicate that a single layer of PBO-FRCM increases bending capacity, raises yield load, and delays initial cracking. Most significantly, the research reveals substantial differences in composite mesh utilization efficiency. This study confirms that mechanical anchorage, particularly bar anchorage, significantly enhances the effectiveness of PBO-FRCM strengthening systems by delaying composite detachment and allowing for greater utilization of the high-strength fiber material. These results contribute valuable insights for RC slabs using FRCM composite systems and the anchorage of their mesh. Full article

The work presents and examines a fiber anchoring system of NSM CFRP strips proposed for strengthening RC beams. The study included 11 beams: 3 unstrengthened beams, 3 beams strengthened with NSM CFRP strip without anchorage, and 5 beams strengthened with NSM CFRP strips with additional anchorage in two variants (the fiber anchor wrapped around the CFRP strip end and fan-folded on the beam surface; the fiber anchor connected with a 20 cm overlap to the strip). All beams were loaded until failure with two concentrated forces (four-point loading test). The measurements were carried out using digital image correlation (DIC). The obtained ultimate load values reached an average of 43.5 kN for unstrengthened beams, while for strengthened beams, they ranged between 56.6 kN and 60.2 kN. The strengthening efficiency was comparable for all beams regardless of the anchorage used and ranged from 29% to 37%. All strengthened beams failed due to strip debonding. The obtained results did not allow confirmation of the effectiveness of the proposed anchoring system. Detailed analysis showed that the lack of anchoring effectiveness was related to the debonding initiating factor, i.e., vertical crack opening displacement, which has not been described in proper detail by the researchers. Full article

Adhesively bonded fibre-reinforced polymer (FRP) anchors have emerged as a progressive alternative to traditional steel anchors in concrete structures, owing to their superior corrosion resistance, high tensile strength, and light weight. Despite their increasing use, a robust mechanics-based bond model capable of accurately predicting the load transfer behaviour has not yet been developed. This study presents a fracture mechanics-based analytical bond model for post-installed adhesive FRP anchors embedded in concrete. The model formulation is derived from fundamental equilibrium and compatibility principles, incorporating a bilinear bond–slip law that captures both elastic and softening behaviours. A new expression for the effective bond length is also proposed. Validation of the model against a comprehensive database of direct pull-out tests reported in the literature shows excellent agreement between predicted and experimental pull-out forces (R² = 0.980; CoV = 0.058). Future research should aim to extend the proposed model to account for confinement effects, long-term durability, the impact of adhesive type, and cyclic loading conditions. Full article

Based on the formula for the sizing agent for basalt fiber, this paper presents a comprehensive study of the effects of lubricants on the properties of sizing agents, basalt fiber, and epoxy resin composite materials. Through testing and analysis of physical and chemical parameters, a new sizing agent with excellent performance was developed. The results demonstrated that the components and proportions of the lubricant significantly affected the physical and chemical parameters of the emulsion, as well as the mechanical properties of the basalt fibers and their epoxy resin composite materials. The lubricant with the combination ratio of 0.70% saturated fatty acid polyoxyethylene ester and 0.30% unsaturated fatty acid polyoxyethylene ester and imidazoline lubricant-I produced basalt fiber with the best mechanical properties. The single fiber tensile strength and yarn breaking strength increased by 18.42% and 12.5%. Furthermore, the lubricant with the combination ratio of 0.70% saturated fatty acid polyoxyethylene ester and 0.30% unsaturated fatty acid polyoxyethylene ester and imidazoline lubricant-III resulted in the best mechanical properties for Epoxy–BFRP composite materials. The tensile strength of the Epoxy–BFRP composite material increased by 13.2%, the tensile modulus increased by 45.2%, and the flexural strength increased by 12.0%. Full article

Moment-resisting frames (MRFs) are characterized by high energy dissipation capacity relying on plastic hinge formation at the two ends of beams. Despite their numerous advantages, Fiber-Reinforced Polymer (FRP) profile sections used in MRF systems suffer from low ductility, which remains a dilemma. FRP profiles have emerged as a novel and valuable material with significant advancement in structural engineering. In this paper, an MRF system composed of novel gusset plate steel connections (to provide ductility) and FRP profile sections for beams and columns is proposed and investigated numerically and parametrically. The results indicate that up to a rotation of 0.04 rad, the proposed gusset plate dissipates energy, whereas the beam and columns remain essentially elastic. Accordingly, with an increase in the ratio of vertical length to thickness of the gusset plate, energy dissipation is reduced. Through an increase in the ratio of horizontal length to thickness of the gusset plate from 63.5 to 127 and 254, the ultimate strength of the connection is reduced by 4% to 10% and 3% to 7%, respectively. It is suggested that gusset plate thickness be selected in such a way that its slenderness is not less than 47. Subsequently, the required equation is proposed to achieve the optimum performance of the system. Full article

This study presents the development and analysis of hybrid polyurea composite materials. Neat polyurea was reinforced with cellulose nanocrystals (CNCs) and isocyanate-modified CNCs (CNC-ISOs) via a two-step prepolymer process. Introducing CNC considerably increased the mechanical strength and stiffness of the polyurea matrix. The tensile strength increased by up to 16.4%, and the Young modulus improved by approximately 29% compared to the pure polyurea. When CNC was functionalized with isocyanate, the interfacial bonding was further improved, and superior dispersion and load transfer were achieved. At 1.5% CNC-ISO loading, the modulus increased by approximately 128% compared to the unmodified matrix. Comprehensive analyses using FT-IR, XPS, DSC, TGA, DMA, tensile testing, and SEM showed that CNC-ISO films not only achieved higher tensile strength and better thermal stability but also formed a denser polymer network as evidenced by the increased crosslinking density. These findings highlight the importance of tailored nanofiller modification to create advanced polyurea composites with enhanced performance suitable for demanding protective and structural applications. Full article

There is a sizeable amount of sawdust produced from wood industries such as timber and furniture. In the past, sawdust has been utilized as a fuel source and in the manufacturing of furniture. Based on the limited use of sawdust, there is plenty of sawdust accessible from the industries. Sawdust is the material of choice due to its cost effectiveness, environmental friendliness, and biodegradability. However, if sawdust is not appropriately disposed or utilized better, it may have negative impact on the aquatic life and organic products. Hence, this review paper discusses the best possible methods or proper routes for the utilization of sawdust to benefit the environment, society, and the economy at large. Sawdust possesses superior capabilities as a reinforcing filler in various polymer matrices for advanced applications. This paper provides an in-depth discussion on sawdust hybrid composites in comparison to other natural fibres hybrid composites. The applications of various sawdust hybrid polymer composites for specific systems are also mentioned. Furthermore, the morphology and preparation of the sawdust/polymer composites and/or sawdust hybrid polymers composites are also discussed since it is well known that the properties of the natural fibre composites are affected by the preparation method and the resultant morphology. Based on the above, the current paper also plays a critical role in providing more information about waste to value added products. Full article

Current hydrogels used for cartilage tissue engineering often lack the mechanical strength and structural integrity required to mimic native human cartilage. This study addresses this limitation by developing reinforced hydrogels based on a ternary polymer blend of poly(vinyl) alcohol (PVA), gelatin (GL), and chitosan (CH), with gentamicin sulfate (GS) as an antimicrobial agent and a crosslinker. The hydrogels were produced using two crosslinking methods, the freeze/thaw and heated cycles, and reinforced with forcespun polycaprolactone (PCL) nanofiber to improve mechanical performance. Chemical characterization revealed that GS forms weak hydrogen bonds with the ternary polymers, leading to esterification with PVA, and covalent bonds are formed as the result of the free amino group (-NH₂) of chitosan that reacts with the carboxylic acid group (-COOH) of gelatin. SEM images help us to see how the hydrogels are reinforced with polycaprolactone (PCL) fibers produced via force spinning technology, while mechanical properties were evaluated via uniaxial tensile and compressive tests. Water retention measurements were performed to examine the crosslinking process’s influence on the hydrogel’s water retention, while the hydrogel surface roughness was obtained via confocal microscopy images. A constitutive model based on non-Gaussian strain energy density was introduced to predict experimental mechanical behavior data of the hydrogel, considering a non-monotonous softening function. Loading and unloading tests demonstrated that GS enhanced crosslinking without compromising water retention or biocompatibility because of the reaction between the free amino group of CH and the carboxylic group of gelatin. The PCL-reinforced PVA/GL/CH hydrogel shows strong potential for cartilage repair and tissue engineering applications. Full article

This study presents a new approach to chemical processing using pyridine-based solvolysis to produce high-quality glass fiber from epoxy composites. Pyridine was chosen due to its solubility parameter, which precisely matches the parameters calculated for the epoxy matrix segment. Experiments with exposure in a pyridine medium demonstrated effective swelling and the potential for destruction. The solvolysis experiments were conducted in a round-bottomed flask with a reflux condenser and stirrer, under ambient conditions (20 °C) until the boiling point was reached (115.2 °C). Additionally, data from experimental studies conducted at subcritical temperatures before reaching 280 °C are presented. The dependences of changes in the mass of composites on time and temperature during the solvolysis process were determined. The tensile strength of the recovered fibers was examined, and thermogravimetric analysis was used to determine their properties. Fiberglass recovered at the boiling point is characterized by 91% tensile strength and 20% residual degradation products on the surface. The residual strength of fiberglass-reinforced plastic (FGRP) is 70.3%. The use of subcritical pyridine helps improve the quality of plastic products made from recycled fibers. This process retains 93% of the residual tensile strength for fibers that have been processed at 250 °C for two hours. Recycled fibers also contain 2.82% organic components on their surfaces. Using this material results in an increase in flexural strength of FGRP by 16.1%, compared to the reference samples. Full article

In the field of enhanced oil recovery (EOR), particularly for water control in high-temperature reservoirs, there is a critical need for effective in-depth water shutoff and conformance control technologies. Polymer-based in situ-cross-linked gels are extensively employed for enhanced oil recovery (EOR), yet their short gelation time under high-temperature reservoir conditions (e.g., >120 °C) limits effective in-depth water shutoff and conformance control. To address this, we developed a hydrogel system via the in situ cross-linking of polyacrylamide (PAM) with phenolic resin (PR), reinforced by silica sol (SS) nanoparticles. We employed a variety of research methods, including bottle tests, viscosity and rheology measurements, scanning electron microscopy (SEM) scanning, density functional theory (DFT) calculations, differential scanning calorimetry (DSC) measurements, quartz crystal microbalance with dissipation (QCM-D) measurement, contact angle (CA) measurement, injectivity and temporary plugging performance evaluations, etc. The composite gel exhibits an exceptional gelation period of 72 h at 130 °C, surpassing conventional systems by more than 4.5 times in terms of duration. The gelation rate remains almost unchanged with the introduction of SS, due to the highly pre-dispersed silica nanoparticles that provide exceptional colloidal stability and the system’s pH changing slightly throughout the gelation process. DFT and SEM results reveal that synergistic interactions between organic (PAM-PR networks) and inorganic (SS) components create a stacked hybrid network, enhancing both mechanical strength and thermal stability. A core flooding experiment demonstrates that the gel system achieves 92.4% plugging efficiency. The tailored nanocomposite allows for the precise management of gelation kinetics and microstructure formation, effectively addressing water control and enhancing the plugging effect in high-temperature reservoirs. These findings advance the mechanistic understanding of organic–inorganic hybrid gel systems and provide a framework for developing next-generation EOR technologies under extreme reservoir conditions. Full article

In order to deeply investigate the effects of various factors on the shear behavior of RC beams strengthened with fiber-reinforced polymer (FRP) grid–polymer cement mortar (PCM) composite, and to construct a more accurate formula for the shear behavior of reinforced concrete beams, the following work is carried out in this investigation: Firstly, the finite element numerical simulation of FRP grid–PCM composite RC beams model is carried out using ABAQUS and compared with the test results to verify the correctness of the model; then, the effects of the amount of FRP grid reinforcement, the elastic modulus of the FRP grid, the shear span ratio of the beam, the concrete strength, and the shear reinforcement ratio on the shear performance of the strengthened beams are analyzed; finally, based on the effective strain of the FRP grid to quantify its actual shear contribution, a calculation formula of the shear behavior Capacity of RC Beams Strengthened with an FRP grid–PCM composite is proposed. The results show that the model established in this paper can effectively simulate the shear behavior of the beams in the test; additionally, the effects of the amount of FRP grid reinforcement, the shear span ratio, and the concrete strength are more significant. Finally, the theoretical results of the calculation formula fit well with the collected experimental ones. Full article