Physical and Mechanical Properties of Bamboo Fiber/Glass Fiber Mesh Reinforced Epoxy Resin Hybrid Composites: Effect of Fiber Stacking Sequence

To further improve the preparation efficiency and properties of bamboo fiber reinforced polymer composites (BFRPs) fabricated by the vacuum-assisted resin transfer molding (VARTM) process. Here, the bamboo fiber/glass fiber mesh reinforced polymer hybrid composites (BGRPs) were fabricated by VARTM to determine the effects of three fiber stacking sequences (namely, GBBGBBG, BGBGBGB, and BBGGGBB; B: bamboo fiber, G: glass fiber mesh) on the physical and mechanical properties, as well as void characteristics of BGRPs (i.e. BGRP-1, BGRP-2, and BGRP-3). The results showed that the incorporation of glass fiber meshes could shorten the injection time of epoxy resin and improve the mechanical properties of BFRPs. BGRP-1 exhibited the lowest water absorption (1.31%) and the highest shear strength (15.55 MPa). Glass fiber meshes on the surface and bottom of BGRP-1, respectively, served as buffer layers to retard mechanical damage, so that BGRP-1 had the best drop hammer impact properties. BGRP-2 represented the highest flexural strength and flexural modulus of 92.22 MPa and 6.69 GPa, respectively. The mechanical properties of BGRP-3 were inferior to those of BGRP-1 and BGRP-2, and more voids were observed in the middle of BGRP-3 in micro-CT slices induced by inadequate epoxy resin impregnation on bamboo fibers

Mechanical, Thermal Properties and Void Characteristics of Bamboo Fiber-Reinforced Epoxy Resin Composites Prepared by Vacuum-Assisted Resin Transfer Molding Process

This study aimed to examine the effect of epoxy resin (EP) systems on the impregnation of bamboo fibers (BFs) by EP and the properties of BF/EP composites prepared by vacuum-assisted resin transfer molding (VARTM) process. BF preforms obtained by solution suspension method were used as reinforcement, and epoxy/anhydride system (EP-1), epoxy/amine system (EP-2) and two-component epoxy system (EP-3) were employed as matrix; on this basis, BF/EP-1, BF/EP-2 and BF/EP-3 composites were prepared by VARTM. The physical, mechanical and thermal properties and void characteristics of BF/EP composites were characterized. The results showed that EP-1 with a viscosity of 265 mPa·s at 23°C and an operating time of room temperature without curing was beneficial for the EP-1 to impregnate BFs adequately and uniformly. The incorporation of BFs into EP-1 significantly improved the flexural, shear and impact properties, thermal properties and interface properties of EP-1. Moreover, the properties of BF/EP-1 composites were better than those of BF/EP-2 and BF/EP-3 composites. Three-dimensional X-ray microscopy scans revealed that the volume and distribution of voids in the BF/EP composites differed significantly depending on the EP systems, and the percentage of void volume in the BF/EP-1 composites was only 0.14% in 3D reconstruction models

Jute yarn-wound composites: optimization of methods for evaluating mechanical properties and improvement of mechanical properties

Filament winding (FW) technology is an important molding technology to obtain high-performance filament-wound composites. However, current methods for evaluating the mechanical properties of plant fibers for FW are directly borrowed from those of synthetic fibers, which may not be appropriate due to the heterogeneity of plant fibers and the unique twisting structure of plant fiber yarns. Herein, jute yarn Naval Ordnance Laboratory (JY-NOL) composites were prepared by FW technology using jute yarns (JYs) and epoxy resin (EP) to propose suitable methods for evaluating mechanical properties. Moreover, the improvement mechanism of mechanical properties of JY-NOL composites was elucidated by exploring the effects of the impregnation method, resin mass fraction and winding tension on the mechanical properties of JY-NOL composites. The results showed that the methods for evaluating the mechanical properties of JY-NOL composites with different JY specifications based on a five-layer winding structure were more scientific and reliable than the methods for evaluating the mechanical properties based on a 3-mm thickness. With the increase in the metric count and the decrease in the number of yarn strands of JYs, the glue loading of JYs gradually increased, and JYs had a unique twisting structure, making it difficult for the interiors of JYs to be impregnated with EP. Therefore, the winding parameters related to the impregnation method, resin mass fraction and winding tension were optimized, aiming at improving the impregnation effect of EP on JYs and reducing the voids in JY-NOL composites, thus strengthening the mechanical properties of JY-NOL composites

Enhancing thermoelectric performance of Sb2Te3 through swapped bilayer defects

Lattice defects are typically used to tailor the thermoelectric properties of materials. It is desirable that such defects improve the electrical conductivity, while, at the same time, reduce the thermal conductivity, for an overall improvement on the thermoelectric properties of materials. Here, we report on an extended defect in Sb2Te3 consisting of swapped bilayers with chemical intermixing of Sb and Te atoms, which can be generated and effectively manipulated in polycrystalline samples through synthetic methods and thermal treatments. The swapped bilayers bridge the spatial gaps between the Sb2Te3 quintuple-layer blocks, enhancing the charge carrier mobility and thus the electrical conductivity. These defects also result in a reduced lattice thermal conductivity through suppressing phonon transport. These synergistic effects contribute together to an improved thermoelectric quality factor and an enhanced figure of merit (zT) value in Sb2Te3

Tunable Physical-Mechanical Properties of Eco-Friendly and Sustainable Processing Bamboo Self-Bonding Composites by Adjusting Parenchyma Cell Content

Parenchyma cells (PCs) and bamboo fibers (BFs) are the main component units of natural bamboo. However, PCs have long been discarded as waste during the industrial processing and utilization of bamboo, i.e., papermaking, textile, and composites, because of their inferior mechanical properties and higher hygroscopicity compared to the BFs. Here, we proposed to mechanically separate PCs from BFs and subsequently recombine them to generate formaldehyde-free bamboo self-bonding composites (BSCs), which physical–mechanical properties were tuned for the first time by adjusting the PC content. The PC effects were examined on the formation and material properties of the BSCs in terms of microstructure and physical–mechanical properties. Microscopic observation revealed that PCs with a high cavity-to-cell wall ratio were more likely to deform and bridge adjacent particles during hot pressing, thus forming a dense interlocking structure with heat-sealed points between the BFs. The inclusion of the PCs into the BSCs led to much lower water absorption and thickness swelling than without the PCs. The BSCs containing 40% BFs and 60% PCs had a thickness swelling of 13.3%, fulfilling the performance requirements of commercial high-density fiberboards used in humid environments. The 40% BFs/60% PCs made BSCs also exhibited the highest flexural strength, flexural modulus, and internal bonding strength, increasing by 99.8, 60.8, and 189.9%, respectively, compared with sole BF-made BSCs. The eco-friendly and formaldehyde-free BSCs with tunable properties are promising for use in furniture, packaging, and interior decorations