Effect of Crosslinking Structure on the Mechanical Properties of Biomass Epoxy Resin Cured with an Aromatic Amine Containing a Biphenyl Group

Abstract

To reduce the environmental impact of insulation materials, a biomass epoxy resin with an aliphatic structure was cured with an aromatic amine containing a biphenyl group at different equivalent ratios, and the effect of the crosslinked structure on mechanical properties was evaluated. The formulation with twice the chemical equivalent of curing agent (1/2 eq) showed the highest flexural strength (198 MPa), about 1.3 times higher than that of the equivalent formulation (1/1 eq). This formulation also maintained a higher storage modulus up to elevated temperatures, and its flexural strength at high temperature was also higher then that of the 1/1 eq. The glass transition temperature was 192°C, which was about 80°C higher than that of the equivalent system. Polarized optical microscopy revealed multiple orientation domains of several hundred micrometers, presumed to result from the orientation of planar biphenyl groups. It is considered that the optimization of the formulation ratio promoted dense biphenyl orientation in addition to the crosslinking, and the suppression of molecular motion up to high temperatures improved mechanical properties.