Bio-phenol formaldehyde (BPF) resoles prepared using phenolic extracts from the biocrude oils derived from hydrothermal liquefaction of hydrolysis lignin

In this work, hydrolysis lignin, as a low-value feedstock, was liquefied in ethanol/water co-solvents (50:50, v/v) at 350 °C for 30 min, with or without the use of hematite ore as the catalyst. Following this, the resulting bio-crude oil was applied as the feedstock for the preparation of neat phenol formaldehyde (PF) resole and bio-phenol formaldehyde (BPF) resoles. The net PF resole was prepared by using the whole bio-crude oil, while, the phenolic extracts from the crude oil together with 50% of phenol were employed for the preparation of BPF resoles. The results displayed that although the BPF resole contained a higher free formaldehyde and less thermally stable than neat PF resole, a lower curing temperature was adopted for BPF resole compared to neat PF resole. By analyzing their physical properties, it was observed that the dry bonding strength of BPF resoles was higher than that of neat PF resole. Most importantly, the dry and wet strengths of BPF resole met the requirements for using as an adhesive for plywood bonding. Overall, it can be concluded that the bio-crude oil-derived phenolic extracts from HTL of hydrolysis lignin is a suitable feedstock for producing value-added BPF with potential use as a wood adhesive.