Roles of organically-modified montmorillonite and phosphorous flame retardant during the combustion of rigid polyurethane foam

The improvement of the flame retardancy of rigid polyurethane foam (RPUF) has been attracted much attention, and addition of phosphorus flame retardants and/or nanomaterials is one of good methods. Two systems have been adopted to improve the flame retardancy of RPUF in this work. Firstly, the phosphorus flame retardant system of ammonium polyphosphate (APP) and triphenyl phosphate (TPP) is introduced to promote the char-forming property of RPUF during its combustion. Thermogravimetric analysis (TGA) results show that the thermal stability and the char yield of RPUF have been extremely improved by addition of APP-TPP system. Secondly, organically-modified montmorillonite (OMMT), possessing of its particular nano-layer structure, is incorporated as an additional filler in the APP-TPP/RPUF system to further improve the flame retardancy of RPUF. The CONE combustion tests indicate that 5% OMMT/8% APP-4% TPP/RPUF (ATO-845) exhibit the longest combustion duration time, slowest heat release rate and lowest total smoke production among pure RPUF (ATO-000), 5% OMMT/RPUF (ATO-005), 8% APP-4% TPP/RPUF (ATO-840), and ATO-845 samples. The extraordinary flame retardant performance of ATO-845 is attributed to the synergy effect between OMMT and APP-TPP system in forming a mass of integrated, stable and tight charred layers during the combustion of RPUF.