Utilization of Steam-Treated and Milling-Treated Lignin from Moso Bamboo as Curing Agent of Epoxy Resin

Low-molecular weight lignin was used as a curing agent to synthesize a bio-based cured epoxy resin. The low-molecular weight lignin was extracted from moso bamboo using steam treatment at 10-40 atm for 5 min followed by milling treatment for 10 s and then water and acetone extractions. The number and weight average molecular weight of low-molecular weight lignin, i.e. acetone soluble component, were 554-698 and 1460-3240, respectively. Furthermore, the hydroxyl equivalent of low-molecular weight lignin were 111-169 g-lignin/eq. The lignin-cured epoxy resin was made from EP828 (a commercial diglycidyl ether bisphenol A epoxy resin) with the low-molecular weight lignin as a curing agent. The decomposition temperature at 5% weight loss (Td(5)) of lignin-cured epoxy resins were 298-327 degrees C and the maximum value, i.e. 327 degrees C, was obtained using a low-molecular weight lignin at 30 atm. Though Td(5) varied with the steam pressure, all values satisfied the thermal stability property required for soldering resistance in the electronic substrate field, i.e. beyond 250 degrees C. The tensile strengths of lignin-cured epoxy resins were 44-59 MPa and these values satisfied the tensile strength of commercial cured epoxy resins, i.e. beyond 27 MPa.