The effect of formaldehyde to phenol ratio on the curing and carbonisation behaviour of resole resins

Two resole-type phenol formaldehyde resins were synthesised with a formaldehyde to phenol (FP) molar ratio of 1.2 and 1.8 and their structure on curing examined by 13C CP-MAS solid state NMR. The FP=1.8 material was considerably more complex than the FP=1.2 material. This has been interpreted as due to the formation and subsequent cleaving of ethers in the FP=1.8 system. The structural changes in each resole after heating were observed by 13C CP-MAS NMR up to 500°C, and their surface areas after carbonisation at 1000°C were measured using N2 and CO2 gas adsorption. The FP=1.2 material was found to possess narrower micropores than the FP=1.8 material. These results are significant for those industries where the high-temperature behaviour of phenol formaldehyde materials is important.