Reaction of jute fiber with isocyanate component for the production of plant fiber-reinforced polyurethane composites

It is thought that hydroxyl groups of plant fiber may react with isocyanate groups during the preparation of plant fiber-reinforced polyurethane composite, resulting in good interfacial bonding. In this work, jute fiber was reacted with polymethane polyphenyl isocyanate (pMDI) under different conditions, and the degree of reaction was evaluated using Fourier transform infrared spectroscopy and elemental analysis. The degree of reaction largely depended on the accessibility of the hydroxyl groups of the jute fibers and it increased with the reaction time and temperature. Thus, to obtain good interfacial bonding sufficient reaction time and a proper high temperature should be provided for the reaction of plant fiber with an isocyanate component in the preparation of plant fiber-reinforced polyurethane composites. The activity of catalyst also had a significant effect on the reaction of jute fiber with pMDI. The alkali-treated jute fiber presented clearly lower reactivity to pMDI than the raw fiber for the hydroxyl groups of the former fiber were less assessible. When pMDI reacted with the raw fiber, isocyanate groups primarily reacted with the hydroxyl groups of hemicellulose covering its surface, which might result in interfacial debonding between the hemicellulose molecules bonded to matrix and those adhered by van der Waals forces in raw fiber-reinforced polyurethane composite. When jute fiber reacted with pMDI at room temperature with no catalyst, the reaction rate was extremely low.