Fatty acid modified zein films: Effect of fatty acid chain length on the processability and thermomechanical properties of modified zein films

The use of zein protein as a biopolymeric sustainable material is gaining interest. However, its brittle nature and inherently poor barrier properties limit its widescale applicability. In this work, the esterification of zein with fatty acid chlorides with varying aliphatic carbon chain lengths (hexanoyl chloride, decanoyl chloride, and palmitoyl chloride) were undertaken to improve its film forming and physicochemical properties. An infrared and nuclear magnetic resonance (NMR) spectroscopy confirmed the successful modifications of zein samples. The reduction in the zein's polarity due to the modifications was also noted from the change in its dispersibility and solubility in various solvents. The effect of the esterification and fatty acid grafting in improving the melt processibility of the zein was studied and reported using a polarizing optical microscope and scanning electron microscopy. Moreover, a significant improvement in the tensile properties of modified zein films was recorded. Among the studied fatty acids, the decanoyl chloride (C10) modified zein samples displayed a 500 % increase in tensile strength over its unmodified counterpart. Overall, the modified zein films exhibited significant improvement in melt processibility and mechanical properties (P < 0.05). The esterification grafting could be an appealing platform to transform zein into melt processible film for sustainable packaging or agricultural mulch film applications.