Flame retardancy of dicyandiamide-crosslinked epoxy resins containing phenolphthalein structures and/or a phosphorus-containing additive

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 fir e retarding properties (OI and UL-94) of the cured epoxy were strongly impr oved by using the commercial additive resorcinol bis(diphenyl phosphate) (F YROLFLEX 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 reta rdant results. A related system where the phenolphthalein structure was bui lt into the phosphate additive rather than into the polymer backbone gave i nferior results. Thermogravimetric analysis in N-2 showed that the system of the phosphate a dditive in the phenolphthalein-extended resin gave an increased char yield. Infrared studies an the system at different pyrolysis temperatures showed that the lactone carbonyl of the phenolphthalein structure underwent reacti on during decomposition of the cured resin in the presence of the phosphate . Infrared evidence suggested that this lactone group may be involved in a crosslinking reaction forming amide links, which may lead to char enhanceme nt. The phosphate depressed somewhat both the T-g and thermal stability but the presence of the phenolphthalein structure partially overcame the T-g d epression.