Studies on phenol formaldehyde gel formation at a high temperature and at different pH

Gel formation characteristic of dilute phenol-formaldehyde solution in water is studied at an elevated temperature near 140° C. It is experimentally found that at temperature range of 135° C to 140° C a solution containing 3.0% phenol with the phenolformaldehyde mole ratio 1.0: 3.5 forms gel in a range of pH values of 9.6 to 12.0. The minimum gelling time is observed at a pH value of 10.4. The gel formation is found to be strongly depending on the pH at this elevated temperature. An explanation for the gelling behavior is presented which is based on an optimum ion concentration of Na ⁺ to initiate the tri-methylol formation. It is hypothesize that subsequent gel formation begins when concentration of tri-methylol phenol attains a minimum threshold concentration value. The kinetics analysis provides a rationale for the proposed hypothesis. The observed dependence of gelling time has been explained.