Lignocellulosic ethanol residue-based lignin–phenol–formaldehyde resin adhesive

Phenol–formaldehyde (PF) adhesive is usually used to bond exterior grade plywood for high bonding strength and water resistance. However, all components are based on petrochemicals, nonrenewable materials from fossil fuel. Lignocellulosic ethanol residue (ER), as the by-product of lignocellulosic ethanol production, is rich in activated lignin and usually treated as waste. In this work, the ER was used as a renewable and valuable resource to partially replace phenol in the range of 10–70% to prepare lignin–phenol–formaldehyde (LPF) adhesive. The composition, functional groups and molecular weight of the ER were characterized. The result revealed that ER, with rich hydroxyl group and less methoxyl group as well as lower molecular weight, was suitable for the synthesis of LPF adhesive. The synthesis process parameters of ER-modified PF (ERPF) adhesives were optimized. It was found that the phenol could be replaced by ER for 50% at most, without much free formaldehyde and free phenol in the ERPF adhesives and the performance of plywood bonded by ERPF adhesives met the requirement of exterior grade according to the Chinese National Standard (GB/T 9846.3-2004). FT-IR, solid state 13C-NMR and TGA were used to characterize the PF and ERPF adhesives. FT-IR and solid state 13C-NMR spectra of the adhesives showed structural similarity between them. With the increase of substitution rate, the content of aliphatic OH group in the ERPF adhesive increased. Thermal stability of ERPF adhesives was better than that of PF adhesive in the initial thermal degradation. After scale up production, the industrial feasibility of preparing ERPF adhesives had been confirmed.