Thermal degradation performance of bark based phenol formaldehyde adhesives

• Neat PF and BPFs all went through typical three stages degradation.
• Bio-crude reduced the thermal stability of BPFs to a greater extent than extractives.
• Bio-crude improved auto-oxidation resistance of the resulted BPFs.
• Xylenol not yielded during neat PF degradation was evolved during BPFs degradation.
• Reaction mechanisms for BPFs degradation were proposed.

Neat phenol formaldehyde adhesive (neat PF), bark bio-crude synthetic bio-based phenol formaldehyde adhesive (bio-crude synthetic BPF) in which 50% phenol was substituted by bio-crude during synthesis, bark bio-crude formulated bio-based phenol formaldehyde adhesive (bio-crude formulated BPF) that was prepared through direct blending of aqueous bio-crude with neat PF at the weight ratio of 50:50, and bark extractives synthetic bio-based phenol formaldehyde adhesive (extractive synthetic BPF) in which 50% phenol was substituted by alkali extractives during synthesis were characterized by thermogravimetry analyzer coupled to Fourier transform infrared spectroscopy (TGA/FTIR), to investigate the stability, thermal degradation kinetics, structure change and the evolved gaseous products. It was found neat PF and BPFs all went through typical three stages degradation. Introduction of bio-crude into BPF reduced the thermal stability for the resulted BPF to a greater extent than extractive introduction. With respect to residual weight after degradation at 800 °C, adhesives thermal stability followed the order: neat PF > extractives synthetic BPF ≫ bio-crude formulated BPF > bio-crude synthetic BPF, which is consistent with the activation energy for the adhesives degradation in the main degradation stage. Auto-oxidation occurred during all the adhesive thermal degradation. But bio-crude based BPFs are more auto-oxidation resistant than neat PF or extractive synthetic BPF. Gaseous products evolved from neat PF degradation mainly consisted of water, phenol, cresol, CO2, CH4, CO and carboxylic acids. During BPFs degradation, CH4, phenol, cresol were yielded at lower temperatures than neat PF degradation. Besides, xylenol not yielded during neat PF degradation was evolved from BPF degradation.