Preparation and Rheological Characterization of Phenolic/Glass Prepregs

Phenolic/glass prepregs are widely used in manufacturing of structural composites. In this work, four types of glass/phenolic prepregs, each with a resin content of about 40 wt% were prepared by using resole and novolak phenolic resins and satin glass fibre fabric. They were B-staged or pre-cured at 100°C, 110°C and 120°C in a laboratory-scale prepreg production machine at different processing conditions. The manufactured prepregs were characterized in terms of their volatile content, resin content, conversion or the degree of pre-cure, tack and flow behaviour to provide qualitative and quantitative assessments of prepreg processing, structure and properties. The optimum processing conditions were determined and the results show that the level of pre-cure or conversion was in the range of 2 to 55% having significant effect on tack and flow properties of the prepregs. The resole prepreg containing 15% novolak resin (Re15N) showed the maximum tack of 19.8 kPa which was found to be at 6.5% of pre-cure. Nonetheless, the volatile content of prepreg was very critical and had a dual effect on tack and processing condition. We studied the rheological properties of these prepregs by using a parallel plate rheometer. The novolak prepreg displayed a distinct rheological behaviour and by using a mixture of both resole and novolak resins a suitable processing condition was achieved.