Preparation and characterization of bark-derived phenol formaldehyde foams

Bark-derived oils produced by hydrothermal liquefaction of outer and inner white birch bark in an ethanol-water (1 : 1, w/w) mixture were utilized for the synthesis of bio-based phenol formaldehyde (BPF) foamable resole resins with different levels of phenol substitution ratios (25 wt% and 50 wt%). Then BPF foams were successfully produced by mixing a blowing agent, a surfactant and a curing agent with the synthesized BPF resoles. The FT-IR analysis showed that BPF foamable resoles and BPF foams both have a very similar structure as a conventional phenol formaldehyde (PF) resole resin and foam. The obtained BPF foams displayed satisfactory compressive strength, elastic modulus, and thermal conductivity. The inner bark-derived oil was found to be more suitable than the outer bark-derived oil for the production of BPF foams, as the former resulted in foams with lower densities and tinier cell structure.