Thermochemical characterization of phenolic resins - Thermogravimetric and pyrolysis-GC studies

Phenol-formaldehyde resins (I and II), synthesised at a monomer feed ratio of F/P=1.0 and 1.5, were cured at 130 degrees C for 48 h without any catalyst (Ia, IIa), with 0.1% ferric acetyl acetonate (Ib, IIb) and with 0.1% p-toluenesulphonic acid (Ic, IIc). Thermogravimetric studies indicate that the decomposition of the cured products takes place in two distinct stages: The first stage (T=340-480 degrees C; alpha=0.045-0.16; Delta E-1=140+/-10-239+/-24 and 60+/-3-65+/-2 kJ mol(-1) for series I and II respectively) was attributed to the predominant cleavage of formal linkages. The main stage decomposition (T=460-640 degrees C; alpha=0.114-0.393; Delta E-2=115+/-8-169+/-8 and 91+/-6-103+/-7 kJ mol(-1) for series I and II respectively) was attributed to reactions leading to graphitisation. Delta E-2 values were correlated to the extent of cure as measured by IR spectroscopy and pyrolysis-GC. The effect of catalysts on the extent of cure and on the activation energy was evaluated.