Versatile biochar for wood‐plastic composites: Improving mechanical properties, dimensional and thermal stability

Abstract In this study, three types of biochar including wood biochar (WB), rice husk biochar (RHB), and bamboo biochar (BB) were used as fillers to mix with wood flour (WF), polypropylene (PP), and maleic anhydride polypropylene (MAPP) to prepare wood polymer biochar composites (WPBC). The influences of biochar types and addition amounts (10 wt%, 20 wt%, 30 wt%, and 40 wt%) on the mechanical properties, dimension stability, and thermal stability of WPBC were investigated. The results showed that the water absorption rate and thickness swelling rate of WPBC were lower than control group due to the hydrophobic nature of the biochar. Additionally, the presence of biochar was beneficial to the interfacial bonding and stress transmission in composites, resulting in better mechanical properties. Composites containing 20 wt% RHB showed the highest flexural modulus among all, which increased by 11.27% compared to control group. Adding WB also enhanced the tensile and impact strength of composites at a loading level of 10 wt%, with the value of 39.10 MPa and 15.55 KJ/m 2 , respectively. The thermal stability and flame retardancy of WPBC was improved due to the presence of SiO 2 in biochar, which could hinder heat transmission and thermal degradation during combustion process. Concurrently, the rate of heat release and smoke generation in WPBC also decreased significantly. The oxygen limiting index (LOI) of composites with 20 wt% RHB was as high as 26.64%, increasing by 30.14% compared to control group. The results suggested that biochar was a promising alternative to commercial additives for the cost‐effective production of composites. Highlights Effects of biochar loading level and type were compared. Enhanced the mechanical properties by optimizing interfacial bonding. Biochar improved the dimensional and thermal stability. Biochar is a versatile and cost‐effective additive.