Investigation of the mechanism of the thermal decomposition of cured phenolic resins by high-resolution carbon-13 CP/MAS solid-state NMR spectroscopy

Abstract

The structural changes occurring in cured phenol-formaldehyde resins when exposed to high temperatures have been investigated by high-resolution 13C solid-state NMR. The initial step in the degradation involves the loss of methylol groupings. Continued degradation results in the appearance of oxidized functionalities, with a simultaneous loss in methylene groupings. The oxidized functionalities have been identifiedas aldehydes, ketones, carboxylic acids, and anhydrides. At higher temperatures the structure becomes mainly aromatics with a few methylene linking groups. When the same resins are heated under vacuum, there is a complete loss of methylols and a reduction in the amount of methylenes along with the appearance of methyl groupings but no oxidation, and the structural and chemical integrity of the sample is largely preserved.

Effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites

“…Thermal degradation of the phenolic materials in this work occurred in five temperature-dependent stages. The first inflection around 100°C was attributed to the gradual evaporation of moisture and some volatile compounds (formaldehyde and phenol) that were trapped in the matrix during the curing reactions [31]. The following three inflections in the range 250-450°C (numbered as 2, 3, 4 in the figure) were related to the breakage of the polymeric matrix and together constituted the bulk thermal degradation stage [32].…”

Thermal and thermo-oxidative degradation of flame retardant high impact polystyrene with triphenyl phosphate and novolac epoxy resin

“…It has also been reported that polycondensates are produced from the rearrangements of phenol formaldehyde resins in their main thermal degradation and so that the flame retardancy is enhanced [7][8][9] . As well, due to the interaction between TPP and phenol resins, the evaporation temperature of TPP is elevated further [6,[10][11][12] and it could also contribute to the flame retardancy of the polymer.…”

Phenolic Resins

“…Using the much greater chemical-shift range of this technique, detailed structural information is provided for both the aliphatic and the aromatic carbons (Table 9). Current techniques provide highly reliable quantitative data and relative peak areas (19,(66)(67)(68)(69)(70) and make possible a quantitative measure of the numbers of branch points and end groups. Branching can cause early gelation in a novolak resin, and end groups usually have greater reactivity in the thermosetting reaction than do the backbone units.…”