The influence of nano-silica (nSiO₂) and micro-silica (mSiO₂) in the shell and wood fiber filler in the core on the thermal expansion behavior of co-extruded wood/polyethylene composites (Co-WPCs) was investigated to optimize the thermal expansion resistance. The cut Co-WPCs samples showed anisotropic thermal expansion, and the thermal expansion strain and linear coefficient of thermal expansion (LCTE) decreased by filling the shell layer with rigid silica, especially nSiO₂. Finite element analysis indicated that the polymer-filled shell was mainly responsible for the thermal expansion. The entire Co-WPCs samples exhibited a lower thermal expansion strain than the cut Co-WPCs samples due to protection by the shell. Increasing the wood fiber content in the core significantly decreased the thermal expansion strain and LCTE of the Co-WPCs. The Co-WPCs whose core layer was filled with 70% wood fiber exhibited the greatest anisotropic thermal expansion.

Wood–plastic composites (WPCs) have received growing attention due to their good water resistance, environmental friendliness, and recyclability. For the application of WPCs in interior decoration and other high–value fields, it is necessary to preserve these characteristics whilst enhancing their mechanical properties and surface aesthetics. In this study, we used a sandwich structure and four interface modifiers to prepare wood veneer/wood flour–polyvinyl chloride composites (WWPVCs). The results revealed that the WWPVCs treated with a silane coupling agent exhibited superior interfacial bonding and mechanical properties compared to those obtained using other interface modifiers. The interfacial bonding strength of the treated sample reached 1.22 MPa, which was 122% higher than that of the untreated sample. In addition, the wood failure ratio of the optimal sample reached 80%. Furthermore, the dipping–peeling length was found to be shorter than those achieved using other interface modifiers after tests at 63 and 100 °C, indicating that the material treated using the silane coupling agent exhibits an excellent resistance to moisture and heat. Notably, silane coupling agents are easily prepared as solvent–based modifiers, and they do not release harmful gases (e.g., formaldehyde), thereby rendering them highly effective in the preparation of environmentally friendly WPC products.

Core–shell composites with strong weather resistance, mechanical strength and creep resistance can be prepared using co-extrusion technology. Considering the weak bonding strength between core–shell interfaces, this study started from the concept of a mortise and tenon combination; three types of conical, rectangular and trapezoidal mortise and tenon joints were prepared, and their bending properties, long-term creep properties, interfacial bonding properties, and dimensional stability properties were tested. Results showed that the mortise and tenon structure could form a mechanical interlock between the outer-shell-layer polyvinyl chloride (PVC) wood–plastic composite (WPVC) and the inner-core-layer laminated veneer lumber (LVL), which could effectively improve the interface bonding property between the two layers. Among them, the trapezoidal mortise and tenon structure had the largest interface bonding force compared with the tapered and rectangular mortise and tenon structure, where the interface bonding strength reached 1.01 MPa. Excellent interface bonding can effectively transfer and disperse stress, so the trapezoidal mortise and tenon structure had the best bending properties and creep resistance, with a bending strength of 59.54 MPa and a bending modulus of 5.56 GPa. In the long-term creep test, the deformation was also the smallest at about 0.2%, and its bending properties, creep resistance and interface bonding performance were also the best. The bending strength was 59.54 MPa and the bending modulus was 5.56 GPa; in the long-term creep test, the strain curve was the lowest, about 0.2%. In addition, the mortise and tenon structure could disperse the stress of the inner shell LVL after water absorption and expansion, thus significantly improving the dimensional stability of the co-extruded composite after water absorption.

This study explores the lamination performance of wood-plastic composite boards designed for indoor decoration, aiming to enhance adhesion between a wood fiber/high-density polyethylene (HDPE) composite board and poplar wood veneer by incorporating fabrics (canvas or polyester fibers) as an intermediate layer. Traditional adhesives, such as polyvinyl acetate (PVAc) and isocyanate, were utilized to create decorative panels with a multi-interface sandwich structure. The impacts of factors such as the hot-pressing temperature, wood fiber content in the substrate, and fabric type on the performance of the panels were systematically investigated. The results indicated that the hot-pressing temperature of the substrate had minimal effect on the lamination performance. Panels that used canvas fabric as the intermediate layer and bonded with a mixed adhesive of PVAc and isocyanate exhibited superior surface bonding strength (2.76 MPa), bending properties (strength = 49.21 MPa; modulus = 3.92 MPa), and tensile properties (strength = 31.62 MPa; modulus = 1.51 GPa). The enhanced performance was attributed to the covalent bonding formed by isocyanate with canvas fabric, polyester fibers, and wood veneer, whereas PVAc primarily established physical bonds through penetration.

This study employed a low–speed drop–hammer–impact test combined with the digital image correlation technique to investigate the dynamic failure performance of bamboo fiber/high–density polyethylene (BPE) composites and to explore the mechanism of fiber content’s influence on it. Results indicated that with the increasing of BF content, the density, acoustic velocity, and Poisson’s ratio of BPE gradually decreased, while the elastic modulus initially decreased and then increased. Although the introduction of Bamboo Fiber (BF) enhanced the rigidity of BPE, allowing the materials to withstand greater impact forces during initial fracture stages, it reduced the toughness of BPE. BPE with 80% BF content showed a higher crack propagation rate and a shorter fracture process compared to composites with lower BF content. However, according to the stress intensity factor (SIF) history, the introduction of BF could enhance the resistance of crack propagation, which depends on the dispersibility of BF and the interfacial bonding properties between BF and high–density polyethylene (HDPE). Overall, BF could increase the rigidity of BPE and restrict the crack propagation at the initial fracture stages. As an eco-friendly and sustainable material, the dynamic fracture toughness of BPE can contribute to the application and promotion of biomass fiber-filled composites.