Reinforcement of Epoxy Resin by Lignin

Abstract

Diglycidyl ether of bisphenol A (DGEBA) epoxy resin with cycloaliphatic polyamine curing agent was modified with lignin to improve thermal and mechanical properties of of polymer composite. A systematic study of lignin loading, between 5 and 20 phr (per hundred parts resin) as compared to neat epoxy, was conducted for the reinforcement effect of epoxy resin composites. With the as-received lignin having spherical particles of 80 to 100 microns in diameter, the Tg of the epoxy-filler composites increased with a small addition of lignin up to 10 phr. Likewise, the yield stress and stiffness (Young’s modulus) of the epoxy resin-lignin composites significantly increased to a maximum value of 49.32 MPa and 2.75 GPa, respectively, with 10 phr lignin, due to the higher modulus of the filler compared to the bulk epoxy resin. Correspondingly, the storage moduli of the lignin-containing composites also increased upon filler addition up to 10 phr due to the impact of lignin. Conversely, however, the tanδ decreased in intensity with increasing lignin filler content, which reflects the dampening effect due to restricted chain mobility in thepresence of lignin particlesin epoxy systems.