Chemical modification of zein by bifunctional polycaprolactone (PCL)

Prepolymer was synthesized by use of PCL and hexamethylene diisocyanate (HDI), and then used to prepare modified zein-based polymers (ZPs). Solid-state 13C NMR results showed that at least four amino acids (Glu, Gln, Tyr and His) reacted with the prepolymer, and urea–urethane links were prominent. Thermal analysis indicated that micro-phase separation formed between zein matrix and PCL–HDI (PCLH) component in ZPs. With the increasing PCLH content, the melting point of PCL in ZP decreased, and the Tg of zein reduced due to plasticizer role of PCLH. The breaking elongation of modified zein containing 10% PCLH content, increased about 15 times while its strength at break only reduced by about 2 times than that of commercial zein. In addition, with the increasing PCLH content, the flexibility of modified zein sheet improved dramatically with negligible reduction in strength. This indicates that PCL was an elastic fraction in ZPs. Therefore, it is an effective way to improve the mechanical properties of zein by modification with PCL, showing a potential in the field of biodegradable polymers.