Effect of biochar content and particle size on mechanical and water absorption properties of landscaping waste/polylactic acid composites

The high-value utilization of landscaping waste to produce wood-plastic composites provides a promising approach to waste management, yet remains a challenge. In this study, wood-plastic composites were prepared using landscaping waste and polylactic acid (PLA) through an extrusion-molding process, with biochar (BC) as the reinforcing material. First, the effects of biochar content (0.5 %, 1 %, 2 %, 3 %, 4 %) and particle size (100mesh, 300mesh, 800mesh, 1200 mesh) on the physico-mechanical and dynamic thermo mechanical properties of the composites were analyzed. A multivariate nonlinear model was employed to fit the flexural properties of the composites. Additionally, the water absorption properties were investigated under immersion conditions at three different temperatures (20°C, 35°C, 50°C). The results demonstrated that biochar significantly improved the interfacial compatibility between landscaping waste and PLA, enhancing the mechanical properties of this composite. When the biochar content was 1 % and particle size was 100 mesh, flexural strength reached 25.16 MPa, respectively, representing increases of 19.20 % over composites without biochar, while the change in impact strength was small. In addition, the water absorption process of composites with 1 % BC were well fitted by Fick's law. SEM morphology observation indicated that interfacial bonding was reduced after water absorption, which was consistent with the test results. Combined with Arrhenius equation and Fick's law, the water absorption model of the composites at each water immersion temperature was obtained, which can predict the water absorption behavior at 60°C.