Grafting soyprotein isolates with various methacrylates for thermoplastic applications

Soyprotein isolates were grafted with four different methacrylates and compression molded into films with good dry and wet tensile properties. Soyprotein isolates are obtained as coproducts during soybean processing, have unique properties and have been widely studied for various industrial applications. Although films with properties suitable for various applications have been developed from soyproteins by solution casting, attempts to obtain thermoplastics from soyproteins with high strength and stability under aqueous environments have not been successful. In this research, soyproteins were grafted with methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA) and hexyl methacrylate (HMA) and the grafting conditions were optimized. Influence of grafting conditions on % monomer conversion, % grafting efficiency and % homopolymers were studied. Grafted samples were analyzed for their thermal behavior using thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) and grafting was confirmed using nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR). Grafted samples were compression molded into films and the influence of % homopolymers on tensile properties was investigated. It was found that increasing length of alkyl chains decreased grafting efficiency but improved the thermal behavior and provided films with better properties. At high humidity (90%), HMA grafted soyprotein films containing 25% homopolymers retained about 73% of their dry strength, had elongation of 16.5%, better than thermoplastic films previously developed from soyprotein isolates. (C) 2014 Elsevier B.V. All rights reserved.