Biodegradable toughened polymers from renewable resources: blends of polyhydroxybutyrate with epoxidized natural rubber and maleated polybutadiene

Abstract

Polyhydroxybutyrate (PHB) is a biodegradable bacterial polyester emerging as a viable substitute for semi-crystalline synthetic non-biodegradable polymers. Novel toughened polyhydroxybutyrate (PHB) based green materials were successfully developed through reactive extrusion of PHB and functionalized natural rubber followed by injection molding. Natural rubber and epoxidized natural rubber were investigated as impact modifiers. Significant differences in the melt viscosity of PHB and the rubber phase established the need for a compatibilizer to improve the toughness. Theoretical modeling of the blend behavior by Takayanagi models also ascertained the positive effect of a compatibilizer. Maleated polybutadiene with high grafting and low molecular weight was determined to be an efficient compatibilizer for the PHB–rubber blend system thereby improving the toughness of PHB by 440%. The toughened PHB materials were characterized through thermo-mechanical analysis and differential scanning calorimetry showing the influence of the elastomer in reducing the PHB crystallinity. Morphological analysis through polarized optical microscopy, environmental scanning electron microscopy and atomic force microscopy also confirmed the ability of the compatibilizer to successfully reduce the rubber particle size and to create interphase bonding. The resultant toughened PHB exhibited impact strength (124 J m⁻¹) superior to a specific grade of thermoplastic polyolefin (TPO) and a high-impact polystyrene (HIPS).