Concurrent improvements in crosslinking degree and interfacial adhesion of hemp fibers reinforced acrylated epoxidized soybean oil composites

Abstract Biocomposites with high performance and biobased contents were prepared from renewable feedstocks, i.e., hemp fibers (HFs) and acrylated epoxidized soybean oil (AESO). Two bifunctional isocyanates, i.e., isocyanatoethyl methacrylate (IEM) and 3-isopropenyldimethylbenzyl isocyanate (TMI), were used as reactive diluents for AESO, respectively. The incorporated IEM or TMI carrying both C C bonds and isocyanate groups not only crosslinked with the C C bonds of AESO by a free-radical polymerization, but also reacted with the –OH groups of both AESO and HFs to concurrently improve the unsaturation level of AESO monomers and the interfacial adhesion between HFs and AESO matrix, which was verified by FTIR and DSC analyses. Both IEM-AESO and TMI-AESO resins exhibited favorable viscosities and curing temperatures for the production of HFs-reinforced composites while without the emission of hazardous air pollutants. The composite with 15 wt% IEM modified AESO (based on the total weight of IEM-AESO blend) had comparable tensile and flexural strengths with the composite from 30 wt% styrene; while the 15 wt% TMI resulting composite obtained higher tensile strength and modulus as well as flexural strength and modulus than the composites from 15 wt% IEM or 30 wt% styrene. This indicated that TMI has a higher reinforcing efficiency on the composites than IEM. Significant improvements in storage modulus, glass transition temperature, and water resistance were obtained for the composites from IEM or TMI relative to the composite from pure AESO resin, which is attributed to the simultaneously improved crosslinking density and interfacial adhesion of the composites as confirmed by SEM analysis.