Curing mechanism of resole phenolic resin based on variable temperature FTIR spectra and thermogravimetry-mass spectrometry

To solve the problem that the curing mechanism evolution of phenolic resin catalyzed by Ba(OH)(2) remained unclear, the p-p methylene index, o-p methylene index, o-o methylene index, hydroxymethyl index, and ether index were introduced to quantitatively investigate the chemical structure of resin in the curing temperature range of 90-230 degrees C. The chemical structures were investigated by variable temperature FT-IR. The gas products released with the increase of curing temperature were characterized by Thermogravimetry-Mass Spectrometry. The curing mechanism from 90 degrees C to 230 degrees C was concluded finally. The results show that the main reaction is the formation of the p-p methylene group in the range of 90-120 degrees C. It is difficult to form the o-p methylene bridge at this stage. In the range of 120-160 degrees C, the main reaction is the formation of the p-p methylene group. From 160 degrees C to 190 degrees C, the main reactions are the breaking of the ether bond, the formation of the carbonyl group and the propyl bridge. Above 190 degrees C, the main reactions are polycondensation reaction among phenolic hydroxyl groups, and the formation reaction of carbonyl groups. The ether bond breaks completely above 230 degrees C. This work provides a new method to investigate the curing mechanism. It is a benefit for the rational design of the curing process of phenolic resin-based composites.