Cured epoxy resin synthesized using acetone-soluble lignin and ligno-p-cresol obtained from steam-exploded wheat straw

The aim of this study was to synthesize a bio-based cured epoxy resin using acetone-soluble lignin, a low-molecular-weight lignin, obtained from steam-exploded wheat straw. Wheat straw, an agricultural waste, was steam-exploded at a steam pressure of 2.5 MPa (225 °C) for a steaming time of 5 min, following which it was extracted first with water and then with acetone, to obtain low-molecular-weight lignin. Lignin epoxy resin was synthesized by the reaction of acetone-soluble lignin with epichlorohydrin and then cross-linked with two kinds of curing agents, acetone-soluble lignin or petroleum-derived phenol novolac, to obtain cured lignin epoxy resins. Furthermore, ligno-p-cresol epoxy resin was synthesized using lingo-p-cresol that is made of acetone-soluble lignin and p-cresol, to improve the thermal and mechanical properties of the cured epoxy resin, using ligno-p-cresol epoxy resin instead of lignin epoxy resin. The thermal decomposition temperatures at 5% weight loss and the tensile strength of all lignin-derived bio-based curing epoxy resins obtained in this study exceeded 250 °C and 27 MPa, respectively, which are required for application in the electronic substrate material field. The cured epoxy resin synthesized from EP828 (a commercial fossil resource-derived epoxy resin) and ligno-p-cresol increased 10% weight loss and tensile strength, compared to that synthesized from EP828 and acetone-soluble lignin. Additionally, its tensile strength was almost the same as that of the fossil resource-derived cured epoxy resin synthesized from EP828 and TD2131 (a commercial fossil resource-derived curing agent). Graphical abstract