A synthesis of styrene-grafted starch accompanied with reaction condition optimization and microstructural and macroscopic property analysis

Abstract

Styrene grafting is efficient to alter starch macroscopic property. Nevertheless, reaction mechanism, condition and products structure and properties are blurry. A deep exploration is necessary. Herein, K2S2O8 and styrene were chosen for corn starch modification. Reaction conditions involving K2S2O8 and styrene amounts, temperature and period were explored. Concurrently, microstructural and macroscopic properties of modified starches were explored via FT-IR, XPS, 13C NMR, GPC, XRD, SEM, TGA, DSC, CA and water dispersibility analysis. Main results reveal that K2S2O8 and styrene amounts, temperature and period as 3 and 200 wt%, 50 °C and 3 h is an optimized condition for starch grafting styrene, achieving a grafting yield (GY) as 45.8 wt%. GPC, XPS and 13C NMR analysis certified successful grafting and grafting mainly occurred at C-3 site OH within glucose unit. This variation converted starch crystalline shape transformation from A-typed to V-typed accompanied with crystallinity, thermal-stability and swelling characteristic decrease and surface hydrophobicity elevation. With GY increased from 0 to 45.8 wt% crystallinity decreased from 38.7 to 15.1%, thermal-decomposition temperature decreased by 10 °C, gelatinization temperature and CA increased by 50 °C and 70°, respectively. It seems a small amount styrene grafting can alter starch macroscopic property such as hydrophilicity efficiently, readily to manufacture hydrophobic starch. This hydrophobic starch might have a potential use in plastic industry, enlarging starch use application, meaningful.