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Wood fiber reinforced thermoplastic composites are regarded as a kind of environmentally friendly material obtained by combining recycled thermoplastic and wood fibers together. However, they are difficult to be decorated for using due to their non‐polar, dense, and smooth surface characteristics. In this study, methods for improving the bonding strength between wood veneer and wood fiber/high‐density polyethylene (WF/HDPE) board were explored. A macromolecular coupling agent, allyl polyoxyethylene polyoxypropylene epoxy‐terminated polyether (AEPH) grafted γ‐aminopropyl triethoxysilane (KH‐550) was synthesized to treat wood veneer prior to lamination with WF/HDPE board. For further improving the bonding strength between wood veneer and WF/HDPE board, a low‐density polyethylene (LLDPE) film was inserted between as adhesive. As control, KH‐550, a commonly used coupling agent and water were also used to treat the veneer. Infrared spectroscopy measurement showed that the LLDPE film combines well with both the veneer and WF/HDPE composite board. Surface bonding strength test proved that all treated veneers significantly improved the combination with WF/HDPE substrated and the LLDPE intermediate film played a key role in it. The veneering endowed the WF/HDPE composite board much better flexural properties, up to 77.39 MPa, which is 50% higher than that of WF/HDPE substrate. The AEPH‐KH‐550‐treated veneer presented the highest bonding strength and best water resistant for glue line.

To reduce the pollution resulting from discarding waste plastic film and burning straw, a new method of preparing straw-reinforced LLDPE composites was developed to utilize these wastes. The straws were first laid parallel on an LLDPE film and then rolled up. The rolls containing long straws were laid into a mat and then hot-pressed into a long straw composite board (the mass of straw accounted for 60%). Slope-cutting the straw, grinding the straw, and twisting the roll were designed to improve the physical and mechanical properties of long straw composites. Among them, slope-cutting the straw combined with twisting the roll provided the best properties. Compared to the extruded straw particle composite, the composite prepared with the new method improved the tensile strength, bending strength, impact strength, and water resistance by 358%, 151%, 416%, and 81%, respectively. Slope-cutting exposed more inner surface at the end of the straw. Scanning electron microscope observations showed that the straw inner surface was more tightly bonded with the LLDPE matrix than the outer surface. Meanwhile, the integrity of the straw was retained as much as possible, and thus greatly improved the performance of the resulting composites. Dynamic mechanical analysis, differential scanning calorimetry, and thermogravimetric analysis show that the viscous deformation of the composites prepared by the new method was reduced and the rigidity was increased, and the combination of straw and LLDPE forms a dense composite material with good interfacial bonding. It greatly slowed down the degree of its pyrolysis.

Straw utilization is a key issue related to agricultural production and air pollution control. In this study, a novel extrusion process was proposed to improve the physical and mechanical properties of the straw-reinforced linear low-density polyethylene (LLDPE) composite. Instead of crushing the straw and mixing it with plastic matrix, the new method mixes straw with plastic matrix in its original form. The intact long rice straws were parallelly spread on the LLDPE film and then rolled up together into a prefabricated roll. The rolls experienced three extrusion processes as follows: (1) twin-screw melting, cooling and crushing, single-screw extruding; (2) twin-screw melting and single-screw extruding; (3) directly single-screw extruding. The testing results showed that the straw/LLDPE composite (with a ratio of 6:4) prepared by Method (2) exhibited optimized properties. Characterization by scanning electron microscopy indicated that the damage to rice straw fibers was relatively minor, the orientation of long fibers was good, and the binding of fibers with the LLDPE matrix was excellent in this case. The results of dynamic mechanical testing (DMA), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis demonstrated that composites prepared by the new process exhibited significantly improved thermal stability and energy storage modulus, compared with those prepared by conventional processes (e.g., extruded straw particles/LLDPE composite). The new proposed method yielded significantly enhanced mechanical properties while reducing dust pollution.

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