Compatibilization and reinforcement of PHB/PBAT bends via sequential blending of surface-modified cellulose

Polyhydroxybutyrate (PHB) is a natural and biodegradable polymer generated by bacteria. While its applications to potentially replace petroleum‐based plastics are severely limited due to its brittleness and notoriously low thermal stability. In this work, biodegradable composites of PHB/poly(butylene‐adipate terephthalate) (PBAT) and cellulose are prepared via reactive melt‐processing with a chain extender of epoxy‐functional polymer. The effects of blending sequence on the morphology, rheological and mechanical properties of the composites are investigated. Commercial cellulose fiber is pre‐modified with stearic acid to improve its compatibility with the polymers. The melt‐processing conditions of PHB/PBAT (70/30 w/w) blend were first optimized by minimizing PHB thermal degradation. Then two processing methods were conducted, (i) one‐step batch blending of PHB/PBAT/cellulose, and (ii) sequential blending of PBAT/cellulose, then blending with PHB. It is found that the sequential blending method facilitated the dispersion of PBAT/cellulose in the PHB matrix and improved the toughness of the composite without compromising the elongation, as compared to the one‐step blended counterpart. The preferential location of cellulose fiber in PBAT effectively facilitates energy dissipation of the toughening PBAT phase. This work demonstrates an avenue to optimize the mechanical properties and thermal stability of polymer blends and composites by carefully altering the blending sequence without the need of excessive additives.