Bamboo fibers are considered as a more attractive option for the reinforcement of wood plastic composites as compared to wood fiber due to its fast growth rate and good toughness. Heat treatment is an environment-friendly method of improving the integrated performance of bamboo materials. This paper highlights the heat treatment of bamboo fiber for suitable properties as reinforcements in bamboo plastic composites. The effects of vacuum heat treatment on the surface characteristics of bamboo fibers and the properties of bamboo plastic composites were analyzed by studying the chemical composition, surface elements and polarity of bamboo fiber before and after treatment, and the physical and mechanical properties of bamboo plastic composite. The results showed that after vacuum heat treatment, the bamboo fibers became darker and experienced a transition from green to red. Moreover, FTIR, XPS and contact angle analysis indicated that the hemicellulose content, the oxygen/carbon ratio and the polar component of the bamboo fiber had a decreasing trend as the treatment temperature increased. In addition, the 24 h water absorption and the 24 h thickness expansion rate of the water absorption showed a trend of first decreasing and then increasing as the treatment temperature increased, while the bending performance of bamboo plastic composite showed a trend of increasing first and then decreasing as a result of increased treatment temperature. Therefore, a combined process of vacuum heat treatment and the addition of MAPE could improve the physical and mechanical properties of bamboo plastic composites to a certain extent.

In this study, the influence of fiber particle size on the mechanical properties of a wood-–plastic composite (WPC) was investigated using a combination of experimental measurements and numerical modeling. Four different sizes of wood fibers (10–20 mesh, 20–40 mesh, 40–80 mesh, and 80–120 mesh) were used to reinforce high-density polyethylene (HDPE), either separately or in combination. The different sizes of fibers produced varying properties in the resulting composites. The smallest fiber size (80–120 mesh) resulted in the lowest flexural and tensile properties, but the highest impact strength (15.79 kJ/m²) compared to the other three sizes (12.18–14.29 kJ/m²). Using a blend of fiber sizes resulted in improved mechanical properties. Composites containing a mix of 20–40 mesh and 40–80 mesh fibers exhibited the best flexural (strength 74.16 MPa, modulus 5.35 GPa) and tensile performance (strength 48.27 MPa, modulus 4.30 GPa), while composites containing a mix of all four fiber sizes had the highest impact-resistant strength (16.08 kJ/m²). Several models, including the Rule of Mixtures (ROM), the Inverse Rule of Mixtures (IROM), and the Hirsch models, were used to predict the performance of WPCs. The ROM model was found to be the most accurate in describing the mechanical properties of WPCs reinforced with multi-size wood fibers, based on the sum squared error (SSE) analysis.

The enhancement of the physical and mechanical properties and the anti-mildew performance of wood–plastic composites are of great significance for broadening their application field. In this research, bamboo fibers underwent treatments with safe, environmentally friendly bio-enzymes. Subsequently, a bamboo–plastic composite (BPC) was developed using the modified bamboo fibers and polyethylene. The effects of biological enzymatic treatments on the surface free energy, the chemical composition of the bamboo fibers, water resistance, thermal stability, bending performance, impact performance, and anti-mildew performance of the BPC samples were analyzed. This study revealed that treating bamboo powder with bio-enzymes (xylanase, lipase, laccase, pectinase, hemicellulase, or amylase) decreased the surface free energy and the polar components of the bamboo fibers while improving the surface O/C atomic ratio of the bamboo fibers. These enzyme treatments enhanced the water resistance, bending performance, and anti-mildew performance of the BPC samples. However, on the whole, the thermal stability of the composites decreased. Particularly, after hemicellulase treatment, the composites had the lowest water absorption, reflecting a decrease of 68.25% compared to the control group. With xylanase modification, the 24 h water absorption thickness swelling rate of the composites was the lowest, reflecting a decrease of 71.27% compared to the control group. After pectinase modification, the static bending strength and elastic modulus of the prepared composites were the highest, with an increase of 15.45% and 13.31%, respectively, compared to the unmodified group. After xylanase modification, the composites exhibited the best anti-mildew effect, with an anti-mold effectiveness of 74.67%. In conclusion, bio-enzyme treatments can enhance the physical and mechanical properties and anti-mildew performance of BPCs. This research provides a theoretical foundation for the preparation of high-performance wood–plastic composites.

Improving the physical, mechanical, and creep properties of wood fiber-reinforced polymer composites is crucial for broadening their application prospect. In this research, seven types of high-density polyethylene (HDPE) composites reinforced with different mass ratios of Masson pine (Pinus massoniana Lamb.) and Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] were prepared by a two-step extrusion molding method. The mass ratios of the two fibers were 60:0, 50:10, 40:20, 30:30, 20:40, 10:50, and 0:60, respectively. The surface color, density, dimension stability, bending, tensile, impact properties, dynamic mechanical properties, and 24 h creep properties at a 10% stress level of the seven composites were investigated. Additionally, the Rule of Mixtures (ROM), the Inverse Rule of Mixtures (IROM), the Hirsch models, and the improved model were employed to simulate the mechanical properties, while the Findley index model, the two-parameter index model, and the modified ExpAssoc model were employed to simulate the creep performance of the composites. This study revealed that as the proportion of Chinese fir wood flour increased, the mechanical properties of the composites gradually improved, the storage modulus showed an increasing trend, while the loss modulus decreased, and the overall creep strain of the composites increased. Among the various models, the modified model simulated the mechanical properties of the composites the best, while the modified ExpAssoc model simulated the creep behavior most effectively.

To investigate the influence of reinforced fiber size on the service performance of wood-plastic composites (WPCs), high-density polyethylene (HDPE) composites were prepared using poplar fibers of seven different sizes. Their bending and impact properties, dynamic thermal mechanical properties, and 24 h creep-24 h recovery performance were analyzed. The WPCs reinforced with 80 to 120 mesh fibers had the worst mechanical properties. The WPCs reinforced with 10 to 120 mesh fibers had the highest bending strength, reaching 28.1 MPa, while WPCs reinforced with 20 to 40 mesh fibers had the greatest bending modulus of 2.73 GPa. The WPCs with 20 to 80 mesh fibers had the highest impact strength, reaching 7.75 kJ/m2. Excessively large or small fiber sizes did not benefit the mechanical properties of WPCs. As the temperature increased, the storage modulus of WPCs decreased. Additionally, as the mesh size of wood fibers increased, the loss modulus increased, while the loss tangent gradually decreased, resulting in reduced toughness and more pronounced elastic behavior. Under a 50 N load, WPCs with the mixed mesh fiber outperformed WPCs with single mesh fibers in 24 h creep performance, WPCs reinforced with 20 to 80 mesh fiber showing the best creep resistance.