Zein-based polymers formed by modifications with isocyanates

Zein is a prolamine protein found in corn and has good potential in the development of industrial bioplastics. In this work, zein was modified with several isocyanates and diisocyanates in solution to evaluate its potential usage in bioplastics. The major reaction pathways were identified with the help of NMR and FTIR. For all the isocyanates employed, the surface free energy of the modified zein decreased, which phenomenon indicates decreased hydrophilicity. The moisture uptake decreased with isocyanate and diisocyanate modifications. Gel electrophoretic patterns showed that diisocyanate cross-linked a portion of zein to generate higher molecular weight species. DSC data showed single glass transition temperatures in all cases indicative that homogeneous blends were formed. The mechanical properties of modified zein were either similar to unmodified zein or reduced in some cases. Based on results from NMR and FTIR findings a reaction scheme is proposed. Our findings suggest that the reaction of zein with diisocyanates has potential usage in bioplastics formulations.

► Zein protein was reacted with isocyanates and diisocyanates.
► Reaction products were characterized by NMR, FTIR, and selected physical properties.
► The key functionalities formed were amides, ureas, and urethanes.
► The modified zein has improved water resistance and should be useful in bioplastics formulations.