Analysis of curing process and thermal properties of phenol-urea-formaldehyde cocondensed resins

Abstract

The curing processes of resols, urea-formaldehyde (UF) resins, their mechanical blends, and phenol-urea cocondensed resins, as well as the reaction of 2,4,6-trimethylolphenol with urea were investiiated with the torsional braid analysis method. The thermal stabilities of these resins after curing also were compared. The results were as follows: (1) In the curing process of the mechanical blends under acidic conditions, it was found that the self-condensation of UF resins dominates in the initial stages, and that the curing of phenolic resin is apt to be incomplete. In alkaline curing, the blended resins require higher curing temperatures than resol, and their heat-resistances after curing generally were poor. (2) It was found that the reaction of trimethylolphenol with urea involved two stages. It was suggested that the first stage at lower temperatures is attributed to the reaction of p-methylol groups with urea residue, and that the second stage at higher temperatures is due to the reaction of o-methylol groups and urea residue. This mixture gave a resin having a great heat-resistance after completion of the reaction. (3) The curing process of the cocondensed resins also involved two stages. It was concluded that alkaline curing is better than acidic curing for these resins, and also that the heat-resistances of the cocondensed resins are superior to those of the mechanical blended resins.

Citation

Tomita, Bunchiro; Ohyama, Masahiko; Itoh, Atsushi; Doi, Kiyoto; Hse, Chung-Yun. 1994. Analysis of curing process and thermal properties of phenol-urea-formaldehyde cocondensed resins. Mokuzai Gakkaishi 40(2):170-175