Thermal decomposition of fire retardant brominated epoxy resins cured with different nitrogen containing hardeners

Epoxy systems frequently have to meet a flame retardancy grade which can be accomplished by incorporating brominated reactive compounds, like tetrabromobisphenol A (TBBA) cured by a number of hardeners. A few brominated epoxy resins (BERs) have been prepared by curing a mixture of diglycidyl ethers of bisphenol A (DGEBA) /and diglycidyl ethers of tertabromobisphenol A (DGETBBA) and different hardeners: dicyandiamide (DICY), 4,4’-diaminodiphenyl sulphone (DDS) and polyethylene polyamine (PEPA). The use of different hardeners strongly affects the thermal degradation behaviour of the BER. The main volatile products of pyrolysis characterized by Pyrolysis-Gaschromatography (PY-GC-MS) at 423°C were phenol, isopropyl- and isopropenylphenol, mono- and di-brominated phenols, bisphenol A, mono-, di-, tri- and tetra-brominated bisphenol A. No nitrogen containing volatile products or HBr were evolved whereas SO2 is formed from BER cured with DDS (BER-DDS) and bromoethylene from BER cured with PEPA (BER-PEPA). Differences of 30-60°C in thermal stability of epoxy network have been found in dependence of the hardener. The experimental evidences point out at a cooperative action of bromine and nitrogen in chain scission of epoxy resins. In particular the ability of the hardener in fixing HBr, evolved from TBBA units, seems to depend on the base power of the N atom of the hardener: the lower the base power, the lower the scavenging effectiveness and consequently the higher the thermal stability.