Fully biobased composite made with epoxidized-lignin, reinforced with bamboo fibers

In this study, we entirely replaced petroleum-based bisphenol A (BPA) with unmodified kraft softwood lignin in epoxy resin formulation. Epoxidized lignin was prepared by reacting lignin with biobased epichlorohydrin (ECH) made from glycerol, and the formation of epoxide rings was confirmed by measuring the epoxy content of the epoxidized lignin using titration and Fourier-transform infrared spectroscopy (FTIR). A fully biobased epoxy resin was then prepared by mixing the epoxidized lignin with a biobased curing agent derived from chew nutshell (from Cardolite Co.). Pre-impregnated composite sheets were fabricated by impregnating unidirectional bamboo fibers with the developed water-dispersion epoxy resin. The properties of the biobased composite samples were measured using a dynamic mechanical analyzer (DMA), scanning electron microscope (SEM), and a universal testing machine. The flexural strength of the lignin-based epoxy composite was found to be 36% lower (14 MPa) compared to commercial epoxy (22 MPa). However, when bamboo fibers were added to the lignin-based biocomposite (containing 25 wt.%), a higher flexural strength (116 MPa) was observed, representing an increase of 11% compared to the biocomposite made with EPON and bamboo fiber (104 MPa). Similarly, the addition of bamboo fibers to the lignin epoxy resulted in an increase in the flexural modulus by 1255% (from 0.42 to 5.69 GPa), while the flexural modulus of commercial epoxy was increased by only 736% (from 0.58 to 4.85 GPa). This was attributed to the higher compatibility of bamboo fiber with lignin, which is known to act as a natural glue in plants.