Inverse vulcanization of octenyl succinate-modified corn starch as a route to biopolymer–sulfur composites

Abstract

Herein we report a route to sulfur–starch composites by the modification of corn starch with octenyl succinic anhydride (OSA, degree of substitution = 2.6%) and its subsequent reaction with elemental sulfur through an inverse vulcanization process to generate OSSx (where x = wt% sulfur, either 90 or 95). This work represents an expansion into a previously untapped biomass source for the preparation of recyclable thermoplastic materials by this process. Composites OSSx are comprized of 83–89% by mass of extractable sulfur, and have reasonable thermal stability (T_d = 214–216 °C) and T_m (DSC) of 118 °C. The starch modification strategy employed herein allowed for lower degree of substitution of the starch than was feasible for other bioploymers, leading to materials with high strength despite relatively low crosslink density relative to that in previous biopolymer–sulfur composites. The low crosslink density resulted in relatively long polysulfur catenates, thus producing materials with impressive flexural strengths (5.3–5.4 MPa) and highlighting the potential for biomass–sulfur materials to exhibit a range of mechanical properties depending on the biopolymer scaffold and modification strategy.