The Thermal Properties and Flame Retardancy of 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-Oxide (DOPO)–Mg/Polyisocyanurate–Polyurethane Foam Composites

Abstract A series of flame-retarded polyisocyanurate–polyurethane (PIR–PUR) foams were prepared using a novel phosphorus-containing flame retardant, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO)–Mg. The thermal stability and pyrolytic gases of the PIR–PUR foam with and without DOPO–Mg were detected by TG and TGA-FTIR. The results indicated that DOPO–Mg can significantly reduce the combustible gases released during decomposition of the PIR–PUR foams, such as carbonyl group containing, methyl and methylene containing flammable gas. The Py-GC-MS results proved that DOPO–Mg changed the thermal degradation process of the PIR–PUR foam and prevented a highly toxic flammable gas from being generated. The flame retardancy of the PIR–PUR foams was tested using the LOI and cone calorimeter test. The LOI and heat release rate values of the PIR–PUR sample without DOPO–Mg were 21.2% and 190.7 kW m−2, respectively. 25 phr DOPO–Mg incorporation into the PIR–PUR foam resulted in a LOI value of 23.2%. In addition, 5 phr DOPO–Mg incorporation into the PIR–PUR foam resulted in a peak heat release rate of 154.9 kW m−2. The foams with DOPO–Mg showed more compact residues. The SEM test showed that spherical material formed on the surface of the char to hinder flame and heat transmission, which can be used to explain the flame retardant effect.