Flame Retardancy of Dicyandiamide-Crosslinked Epoxy Resins Containing Phenolphthalein Structures and/or a Phosphorus- Containing Additive

Abstract

The feasibility of producing halogen-free epoxy moldings having a UL-94 V-0 flammability rating has been further supported. We have shown that the fire retarding properties (OI and UL-94) of the cured epoxy were strongly im proved by using the commercial additive resorcinol bis(diphenyl phosphate) (FYROLFLEX RDP) but not improved merely by reacting phenolphthalein into the resin as a chain extender. However, a combination of the phosphate with the phenolphthalein as a chain extender gave substantially enhanced flame retar dant results. A related system where the phenolphthalein structure was built into the phosphate additive rather than into the polymer backbone gave inferior re sults. Thermogravimetric analysis in N2 showed that the system of the phosphate ad ditive in the phenolphthalein-extended resin gave an increased char yield. Infrared studies on the system at different pyrolysis temperatures showed that the lactone carbonyl of the phenolphthalein structure underwent reaction during decomposition of the cured resin in the presence of the phosphate. Infrared evi dence suggested that this lactone group may be involved in a crosslinking reac tion forming amide links, which may lead to char enhancement. The phosphate depressed somewhat both the Tg and thermal stability but the presence of the phenolphthalein structure partially overcame the Tg depression.