Investigation of Rheological, Morphological and Mechanical Properties, Thermal Stability, Biodegradability of the Dynamically Cured Natural Rubber/Polyester Blends

Novel green biodegradable thermoplastic natural rubber (GB-TPNR) based on natural rubber and polyester blends was prepared by dynamic vulcanization. The main objective was to improve mechanical and rheological properties, thermal stability and biodegradability of the natural rubber/polyester thermoplastic vulcanizates (TPVs). Three types of natural rubber: unmodified NR, and epoxidized natural rubbers with 25 and 50 mol % epoxide (i.e., ENR-25 and ENR-50); and two polyester types: polybutylene succinate (PBS) and poly(butylene succinate-co-butylene adipate) (PBSA) were used as blend components. It was found that the dynamically cured ENR-50/PBS blends exhibited superior mechanical, rheological, thermal and stress relaxation properties relative to ENR-25/PBS and unmodified NR/PBS TPVs. This is attributed to stronger chemical interactions between the polar functional groups of ENR-50 and PBS, which caused strong interfacial adhesion and hence the smallest vulcanized rubber domains dispersed in the PBS matrix. Furthermore, stress relaxation, thermal resistance, mechanical strength and degree of crystallinity of PBS phase increased with epoxide content in the modified rubber. Moreover, the dynamically blended ENR-50/PBSA showed larger vulcanized rubber domains along with poorer mechanical, relaxation and thermal properties but easier biodegradation than the ENR-50/PBS blend.