Improvement of properties for biobased composites from modified soybean oil and hemp fibers: Dual role of diisocyanate

An environmentally friendly composite was developed from hemp fibers (HFs) and a biobased thermosetting resin that was formulated from the copolymerization of acrylated epoxidized soybean oil (AESO) and N-vinyl-2-pyrrolidone. The properties of the composites were enhanced through the incorporation of isophorone diisocyanate (IPDI). The FTIR and 13C NMR spectra reveal that the incorporated IPDI could react with the hydroxyl groups of both HFs and AESO by forming urethane connections; hence, IPDI plays two roles in composites, i.e., as a crosslinker and a coupling agent. The results show that both effects greatly contribute to increasing the tensile and flexural properties, storage modulus, and glass transition temperature of the resulting composites. However, the modification does not significantly influence the impact strength and slightly decreases the thermal stability of the composites. Further, the addition of IPDI into AESO resins results in resins with improved processability due to the lower viscosity and curing temperature.