Determination of the cure index of B-stage phenolic and cresolic resol resins in laminating materials by infrared spectroscopy

This investigation reveals that the most available cure index for socalled B-stage phenolic and cresolic resol resins in laminating materials is the ratio of the absorbance at 1000 cm-1 and the absorbance at 1610 cm-1 as a parameter. B-stage resins in laminating materials containing paper and glass fiber fillers are extracted with anhydrous acetone. The sample concentration is about 100 mg per 1 ml acetone and a rock salt cell with a 0.1 mm path length is used. The peak intensity method and the baseline method are used for the calculation of the absorbance. The reproducibility is about 3 per cent. The apparent activation energy of the curing reaction determined by this cure index method is about 17 kcal/mole and is in good agreement with that obtained by a chemical method. This cure index is not applicable to the determination of the curing of A-stage resins because of the absorption interference at 1610 cm-1 by a free monomer.