Epoxidized Novolac Modification in Resol Phenolic under Open Mold Heat Curing for Microvoid Reduction

Resol phenolics were generally cured by temperature assisted compression molding. In this study, resol phenolic was modified using epoxidized novalacs (EN) and cured by heat assistance without pressure to find the influence of EN on the reduction of microvoids in cured resol phenolics. Epoxidized phenolic novolac (EPN), epoxidized p-cresol novolac (EPCN) and epoxidized o-cresol novolac (EOCN) were synthesized and used for modification of resols. The modification led to reduction in both the size and number of voids and increase in the tensile strength, flexural strength and impact strength of the resol phenolics. Epoxidized novolacs with phenol: formaldehyde ratios 1:0.7 and 1:0.9 exhibit comparatively better results for the resols. The decrease in the % soluble matter in the cured resin and FTIR spectrum show the incorporation of epoxidized novolacs to the resol phenolics. The dynamic mechanical analysis (DMA) confirms better damping properties of the modified resols. Thermogravimetric analysis shows improved thermal properties for the resol samples modified with EPN and EPCN. The optimum amount of epoxidies novolacs required for the modification was ~7.5-10%.