s-Triazine phosphonates as flame retardants for polyurethane and polyisocyanurate rigid foams

•s-Triazine phosphonates are halogen-free flame retardants.•s-Triazine phosphonates improve the flame retardancy of PUR and PIR rigid foams.•s-Triazine phosphonates can replace the halogenated flame retardant TCPP. The liquid flame retardant tris(2‑chloro-isopropyl) phosphate (TCPP) is widely used in polyurethane and polyisocyanurate rigid foams. However, TCPP is currently under assessment by the European Chemicals Agency ECHA and National Toxicology Program NTP, USA. For this reason, there is a high demand for new flame retardants with similarly good processing and application properties. This paper examines the influence of low-molecular liquid s-triazine phosphonates on the foaming behaviour and flame retardancy of polyurethane and polyisocyanurate rigid foams for building applications. The flame retardant investigations consisted of thermogravimetric analysis of the components and flame retardancy tests performed on the foams: limiting oxygen index, EN 13501 class E, and cone calorimetry. The newly developed class of s-triazine phosphonates are promising flame-retardant candidates with good processing and application properties.