Yan Cao

To develop eco-friendly wood-plastic composites (WPCs) with enhanced performance, this study focused on improving the interfacial compatibility between polar plant fibers and the weakly polar polylactic acid (PLA) matrix by grafting glycidyl methacrylate (GMA) onto PLA via solid-phase modification. Using benzoyl peroxide as an initiator in a high-speed mixer, 10 PLA-g-glycidyl methacrylate (PLA-g-GMA) copolymers with varying grafting ratios were synthesized. The chemical structures of these copolymers were characterized using FTIR and ¹H NMR spectroscopy. The results indicated that the grafting degree of PLA initially increased and then decreased with increasing GMA content, peaking at 15% GMA with a grafting rate of 9.62%. Bamboo plastic composites (BPCs) were prepared by hot-pressing PLA-g-GMA with bamboo flour (BF). Physical and mechanical testing showed that both water resistance and mechanical properties of the composites initially improved and then declined with increasing GMA content. Notably, the composite based on 13% GMA-modified PLA exhibited the best water resistance, with a 24 h water absorption of only 1.05%. Composites prepared with 15% GMA-modified PLA showed the best overall performance, showing increases in static flexural strength, elastic modulus, and impact strength by 168.86%, 94.06%, and 45.67%, respectively, compared to the unmodified composite. Additionally, the 15% GMA modification slowed soil-burial degradation. These findings indicate that moderate grafting of PLA significantly enhances interfacial adhesion and performance in biobased composites, providing a theoretical foundation and data support for the design of high-performance, environmentally friendly WPCs.

The preparation of biodegradable wood plastic composites using polylactic acid (PLA) as the matrix and plant flours as the reinforcing phase aligns with the principles of sustainable development. However, there is a large polarity difference and poor compatibility between PLA and plant flours. To improve the performance of PLA/bamboo flour (BF) composites and simplify the process, this study modified PLA using glycidyl methacrylate (GMA), methacrylic acid (MAA), and maleic anhydride (MAH) as reactive compatibilizers. Composites were prepared from the modified PLA and BF using the hot-pressing method. The results indicated that all three reactive compatibilizers increased the polarity and surface free energy of PLA. GMA, MAA, and MAH were successfully grafted onto the PLA molecular chain, resulting in the formation of PLA-g-GMA, PLA-g-MAA, and PLA-g-MAH graft copolymers. In addition, the interfacial compatibility between PLA-g-GMA and BF was the best, and the PLA-g-GMA/BF composite had the lowest 24 h water absorption (2.17%). Furthermore, the PLA-g-GMA/BF composite showed the highest bending, tensile and impact strengths of 33.3 MPa, 14.7 MPa, and 1.33 kJ/m2, respectively, which were 63.8%, 104.9% and 4.7% higher than those of untreated PLA/BF composites, respectively.

This article aims to investigate the characteristics of wood plastic composites (WPC) prepared from polyethylene (PE) reinforced with lignocellulosic fibers derived from the xylem and bark of Masson pine, fir, cypress, as well as from Moso bamboo. The surface polarity and elemental composition of fibers were determined through contact angle measurements and X-ray photoelectron spectroscopy (XPS). The lignocellulosic fiber/PE composites were manufactured through hot-pressing technique, and their water absorption, mechanical properties, and mildew resistance were evaluated. The results revealed that the surface free energy of xylem fibers was higher than that of bark fibers among the three conifer species. XPS analysis showed that the O/C ratio of bark was consistently lower than that of xylem fiber. Among the three conifers, the Masson pine bark had the lowest O/C ratio (22.25%), while its xylem fibers had the highest ratio of 41.64%. WPC made with bark fibers had better water resistance. Additionally, the composites reinforced with xylem fibers showed superior static bending strength, impact strength, and mildew-resistant properties as compared to the composites reinforced with bark fibers. WPC made from bamboo fibers exhibited the best water resistance, with a water absorption rate and thickness swelling rate of 1.83% and 1.42%, respectively. They also had the highest static bending strength, elastic modulus, and impact strength, at 41.31 MPa, 3.82 GPa, and 10.24 kJ/m2, respectively. The WPC made from fir xylem fibers showed the most effective mildew resistance, with the smallest damage (0.50).

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.

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.

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.