Studies on the toughness and water resistance of zein-based polymers by modification

To develop novel biodegradable materials, zein was modified using polycaprolactone (PCL)/hexamethylene diisocyanate (HDI) prepolymer. The modified zein polymers, containing various PCL–HDI components (PCLH) content and plasticized by Dibutyl l-tartrate (DBT), were compression-molded. Mechanical properties, water resistance, thermal properties and morphology of the molded zein-based sheets were investigated. The toughness was improved significantly by a small amount of PCLH due to the existence of micro-phase separation structure in the sheets. In particular, zein exhibited better mechanical properties when modified by 20–50 wt% PCLH, and when the corresponding sheets were immersed in water for 24 h than when stored in 75% relative humidity. This implies an excellent water resistance. Thermal analysis indicated that the formation of physical cross-linking from PCLH segment extension, and the plasticization of water to the zein matrix, improved the water resistance of modified zein sheets. DBT had a stronger interaction with zein than with PCLH, and was considered as a compatibilizer for zein matrix and PCLH component in modified zein sheets.