Flammability of Novolac epoxy cured with aromatic diamines

• Published in: Thermochimica acta 2024-11, Vol.741, p.179870, Article 179870
• Main Authors: Silveira, Mauro R.S., Moritz, Vicente F., Ferreira, Carlos A., Ferry, Laurent, Lopez-Cuesta, José-Marie
• Format: Article
• Language: English
• Subjects: Aromatic diamine; Chemical Sciences; Flame retardancy; Material chemistry; Novolac epoxy; Organophosphorus compound
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2024.179870

•Organophosphorus compound improves self-extinguishing properties in fire tests.•Thermo-oxidative results show varied performance of modified Novolac by hardener.•The increase in the limiting oxygen index indicates effective flame retardancy.•Phosphorus-rich samples exhibited high flame retardancy in vertical burning tests. The modification of Novolac epoxy with the organophosphorus compound 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide (DOPO) to reduce flammability and its influence on curing reactions has been investigated. Three aromatic diamine curing agents were used, namely 4,4′-diaminodiphenylmethane (DDM), 4,4′-diaminodiphenylsulphone (DDS), and diethyltoluenediamine (DETDA). The thermal stability and dynamic-mechanical behaviour of the cured resin depend on interactions of the curing agent with DOPO. The onset degradation temperature decreased with increasing phosphorus content, indicating the influence of DOPO on thermal stability. The DDM 3 %P sample exhibited the highest glass transition (Tg) of 136 °C, while DDS-crosslinked simples displayed the highest Tg of 147 °C among all samples. An improvement in the reaction of Novolac epoxy to fire was achieved by incorporating DOPO compound, as indicated by cone calorimetry results, showing up to a 67 % reduction in the peak heat release rate (pHRR) and 53 % reduction in total heat release (THR) for DDM 3 %P. The modified samples containing DOPO presented a self-extinguishing performance, displaying a UL-94 V-0 rating and a limiting oxygen index (LOI) values reached a maximum of 37.1 % for DDM 3 %P, with less flame propagation than for neat Novolac epoxy.