Effects of initial phenol-formaldehyde (PF) reaction products on the curing properties of PF resin

Differential scanning calorimetry (DSC) was used to study the effects of varying NaOH concentrations on the thermochemical curing properties of 2,4-dimethylol phenol (2,4-DMP), and 2,6-dimethylol phenol (2,6-DMP). Analysis of the DSC curves showed significant differences in the thermochemical curing behavior of these compounds with increasing NaOH:DMP molar ratios, in terms of the peak shape, position of the reaction peaks, (T-p), along the temperature scale and energy of activation, E. The curves consisted of either a single, two or three exothermic peaks which indicated the occurrence of multiple reactions. One of these peaks was observed for the entire range of NaOH molar ratios, and is attributed to the self-condensation reaction. For the 2,4-DMP, NaOH had the effect of lowering the T-p of curing from 212 degreesC in the uncatalyzed state to 135 degreesC between 0.15-0.75 molar ratios. The lowest value of E, however, was 111 kJ mole(-1), only through 0.45-0.60 molar ratios and this combined with the above, points to this concentration range as the optimum NaOH level. Similarly, the T-p of curing for the 2,6-DMP was lowered from 211 degreesC in the uncatalyzed state, to a minimum of 116 degreesC at the NaOH:2,6-DMP molar ratio of 0.45. At this ratio, E also had the lowest value of 117 kJ mole(-)1 and this suggests that 0.45 molar ratio is the optimum NaOH level.