Effect of biochar content and particle size on mechanical properties of biochar-bioplastic composites

The recent increase in plastic use and the resulting pollution have put bioplastics in a strong position to expand. However, better understanding of bio-fillers and their effect on popular bioplastics, such as poly (lactic acid) (PLA), is required for this to occur. Biochar (BC), a stable form of carbon derived from high temperature conversion of organic material, has potential as a plastic filler. Although BC's effect on petroleum-based plastics has been widely studied, there are still major gaps in the literature surrounding BC use as a filler in PLA/starch composites. In this work, the effects of BC particle size and mass loading were examined when paired with a PLA/starch matrix. Mechanical and thermal testing was performed on composites that varied in filler loading (0–20 wt%), as well as particle size following a factorial design. At 20 wt% BC, the finer BC particles produced a drop in the viscosity, which could be attributed to degradation of polymer chains. Mechanical characterization showed that increasing the BC filler loading increased the stiffness of the composite. A similar effect was seen when decreasing the particle size of the BC at a constant loading. The most significant finding was that a combination of decreased particle size and filler loading of 5 wt%, increased the tensile strength by about 54% relative to the control (no BC) and slightly increased the elongation, thereby increasing the composites toughness. These results indicate that particle size and loading are important design considerations when using BC as a filler.