Structure-charring relationship in phenol-formaldehyde type resins

The thermal behaviour in nitrogen and in air of phenol-formaldehyde, m-cresol-formaldehyde and p-cresol-formaldehyde resins having different levels of crosslinking is reported. The steps of degradation are studied by FTIR analysis of the residues. The different structures and crosslinking levels induce different thermal stabilities. In nitrogen the more crossinked novolacs have a lower stability up to about 300 °C, whereas after 500 °C their residue is more stable. In contrast, in air the resins that are more crosslinked are oxidised at temperatures of about 50 °C lower.