High-Biocontent Polymer Blends and Their Wood Plastic Composites: Blending, Compatibilization, and Their Recyclability

Poly(lactic acid) (PLA) was melt-blended separately with low concentrations of polypropylene (PP) and low-density polyethylene (LDPE) that maintained the total biopolymer content above 89 wt%. Additionally, a multifunctional reactive chain extender was also incorporated to assess the potential compatibility among the constituents. The blends were exposed up to five reprocessing cycles to simulate recycling, with material collection occurring at one and three recycling stages for characterization. Rheology, thermal, and mechanical properties were then evaluated to assess the processing – properties of the resulting materials. In addition, wood flour powder (≤ 250 μm) was compounded into two different system types (PLA: PP and PLA: LDPE) at 30 and 40 wt% to fabricate high-biopolymer content wood-plastic composites (WPCs). The entire composite was then subjected to up to five recycling cycles to elucidate the effects of recycling on different systems. The simulated recycling process induced crosslinking reactions in the case of LDPE, evidenced by an increase in melt viscosity and changes to the zero-shear viscosity ratio of the blended polymers. In the case of PP, recycling led to reduced viscosity likely attributed to temperature and shear mediated chain scission inducing changes in both the matrix and dispersed phase’s viscosity. The study provided valuable insights into the behavior of the materials and composites undergoing through recycling.