Bio-oil-based phenol–formaldehyde resin: comparison of weight- and molar-based substitution of phenol with bio-oil

Abstract

The objectives of this study were (i) to synthesize bio-oil-based phenol–formaldehyde resin to be used for the wood products industry, and (ii) to investigate the effect of phenol substitution (molar-based vs. weight-based) with bio-oil on the properties of resulting PF resin. Bio-oil was produced by hydrothermal liquefaction (HTL) process using sweetgum hardwood, and utilized as a bio-based phenolic feedstock as an alternative for petroleum-based phenol in the synthesis of PF resin. Phenol was substituted with bio-oil (both as weight- and molar-based). The resulting PF resin was noted as BPF-W and BPF-M when bio-oil was used to replace 50% of phenol in weight- and molar-based, respectively, and then compared with neat PF resin in terms of free formaldehyde content, gel time, pH of the resin, solid content, bond strength and thermal stability. Results showed that BPF-M resin had less free formaldehyde content and longer gel time than BPF-W resin. No significant difference in pH and solid content was observed between bio-oil-based PF resins. Moreover, molar-based substitution resulted in a resin with higher bonding strength than that of weight-based substitution, and both BPF-W and BPF-M showed higher bonding strength then neat PF resin. TGA analysis of the resin revealed that substitution of phenol with bio-oil lowered the thermal stability of bio-oil derived PF resins. However, molar-based substitution of phenol with bio-oil could enhance the thermal stability.