Plasticized starch-based biocomposites containing modified rice straw fillers with thermoplastic, thermoset-like and thermoset chemical structures

Abstract

In this work, rice straw (RS) as an abundant biomass was applied to prepare some renewable thermoplastic materials by using soda-pulping and benzylation processes. The obtained RS products including untreated RS, RS pulp, benzylated RS pulp and pulping liquor as well as benzylated RS were incorporated into the thermoplastic starch through a twin-screw extrusion process to obtain all green composites. The successful thermoplasticization reaction of RS products was confirmed by spectroscopy results and morphological observations. The interfacial adhesion between the plasticized starch matrix and the RS products is enhanced by the chemical modifications, which confirmed by investigating through the morphological observations and linear rheological responses. The partial phase miscibility of the plasticizer/starch mixtures is improved by adding the benzylated RS and RS pulp. The RS pulp having cellulosic microfibers enhances the Young modulus and tensile strength of the plasticized starch even more than untreated RS. However, their thermoset and thermoset-like structure leads to the brittle failure mode of the starch biocomposites, similar to the common natural fiber biocomposites. The thermoplasticization reaction changes the failure mode and significantly improves the toughness of the plasticized starch/RS product biocomposites owing to better phase miscibility.