Bamboo fibers grafted with a soybean-oil-based monomer for its unsaturated polyester composites

A soybean-oil-based monomer, acrylated epoxidized soybean oil (AESO), was grafted onto bamboo fibers (BFs) using 1,6-diisocyanatohexane (DIH) as a linker to facilitate the formulation of a hydrophobic layer on the fiber surface and to impart the fibers with active functional groups that can form chemical connections with unsaturated polyester (UPE) resin. The reaction mechanism of BFs with AESO and DIH and its surface chemical characteristics were investigated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) analyses. These analyses confirmed that the AESO reacted with the DIH and then the resultant AESO-DIH oligomer was covalently bonded onto the BFs via urethane linkages. The grafting of BFs with AESO-DIH resulted in improved tensile and flexural properties, storage modulus, and thermal stability of the BF–UPE composite samples. There were also reductions in the water uptake rate and the diffusion coefficient due to the surface chemical changes of the fibers and thus the enhanced fiber-matrix interface of the composites.