Synthesis of biobased phenolic resins/adhesives with methylolated wood-derived bio-oil

Bio-oil from the hydrothermal liquefaction of Eastern White Pine (Pinus strobus L.) sawdust was methylolated with formaldehyde in the presence of sodium hydroxide. The obtained methylolated bio-oil (MB) was used to synthesize methylolated bio-oil-phenol formaldehyde (MBPF) resol resins with a phenol substitution ratio of up to 75 wt %. All of the resins were used as wood adhesives for the production of a three-layered plywood. The MBPF resol resins were comprehensively characterized for their physical, chemical, thermal, and mechanical properties (e.g., viscosity, nonvolatile content, shelf life, free formaldehyde level, molecular weight and distribution, curing temperature, bonding strength) when used as plywood adhesives. All of the MBPF resins contained similar nonvolatile contents as the reference pure phenol formaldehyde (PF) resin but had higher viscosities and shorter shelf lives, depending on the amount of MB in the MBPF. All of the MBPF resins displayed a lower curing temperature than the reference PF resin, with the main curing peak around 140°C, which was similar to that of the pure PF resin. According to thermogravimetric analysis, the methylolation treatment of bio-oil improved the thermal stability of the MBPF resins compared to the bio-oil-PF resol resins, which used untreated bio-oil. The dry/wet bonding strengths of the plywood specimens glued with the MBPF resol resins with up to 60 wt % phenol substitution exceeded or were comparable to those of the conventional PF resol resin. © 2012 Wiley Periodicals, Inc.