Classical curing of epoxy modified lignin with polyamine for new Epoxy-Polyimine composite

Abstract

Lignin, which is the most abundant aromatic polymer in nature was used as a green substitute for the toxic bisphenol A. Here we synthesized the epoxy agent from lignin by reacting lignin with epichlorohydrin. Further this product was reacted with the lignin-amine to give the new epoxy-polyimine composites. This study evaluated the curing of bio-based epoxy resins derived from lignin with aromatic and an aliphatic amine. The thermal stability of the cured lignin-based epoxy samples was evaluated. Epoxidation is an interesting way to develop new uses and applications of lignin. Lignin-based epoxy resins were obtained by the epoxidation reaction using the lignin recovered directly from pulping liquor. For the epoxidation reaction it was optimized the influence of the lignin:NaOH (w/w) ratio, temperature and time of the reaction on the properties of the prepared epoxidized lignin. The structures of lignin-based epoxy resins were evaluated by epoxy index test and FTIR spectroscopy. Optimal conditions were obtained for lignin-based epoxy resin produced at lignin/NaOH = 1/3 at 80 °C for 3 h. Thermogravimetry analysis (TGA) revealed that epoxidation enhances the thermal stability of lignin and may allow a wider temperature range for various applications.