Research On Properties Of Polyisocyanurate Foams

Rigid polyurethane foam (RPUF) is a series of polymer materials with excellent comprehensive properties. It is widely used in many fields on account of its low thermal conductivity, heat resistance and excellent dimensional stability. However, it is flammable when it was not improved by flame retardants, which results of the release of toxic gases and smoke when it is burning. Hence, it is urgent to improve the flame retardancy of RPUFs.In this paper, a novel polyol containing polyisocyanurate structure was selected as a matrix resin to perpare the polyisocyanurate foam (PIRF) with excellent thermal stability, the additive flame retardants and the reactive flame retardant brominated polyol was used as flame retardant to modify the PIRFs. The related researches including the oxygen index apparatus, thermogravimetric analyzer, dynamic mechanical analysis, universal material testing machine and scanning electron microscope have been carried on by analyzing the flame retardants which affect the thermal stability, flame retardancy, dynamic mechanical properties and the morphology of char-layer. Three kinds of phosphorus-containing flame retardants, dimethyl methylphosphonate (DMMP), triethyl phosphate (TEP) and tris (1-chloro-2-propyl) phosphate (TCPP) were selected to modify the RPUFs and studied the effect of polyisocyanurate structure on the properties of RPUFs.The thermal stability of RPUFs was improved by structural modification and a novel polyol containing polyisocyanurate structure was selected as a matrix resin to perpare the PIRF with excellent thermal stability. The initial decomposition temperature was 265℃ of the PIRF, which increased about 100℃ than that of RPUF prepared by common polyether polyol. The results of DMA showed that the glass transition temperature (Tg) could reach to 182℃, indicating that the introduction of polyisocyanurate structure can dramatically improve the heat resistance of the RPUF.The flame retardancy can be improved by adding DMMP as an additive flame retardant to the system of the PIRF, and the limiting oxygen index (LOI) increased with an increase in the flame retardant content to 31.5%, increased approximately 9.5% than the PIRF without flame retardant, which illustrated DMMP can tremendously modify the flame retardancy of PIRFs. Additionally, the LOI of flame retardant PIRF was higher than the flame retardant PUFs with the same flame retardant content, illustrating that the introduction of polyisocyanurate structure can dramatically improve the flame retardancy of the RPUF.A reactive bromine-containing flame retardant was used to modify the flame retardancy of the PIRF, results showed that the Tg of flame-retardant PIRF was 209℃, which is much higher than that of the PIRF without flame retardant, and was increased with the increase of brominated polyol content. In addition, the LOI value increased 5.5% compared with the pure PIRF, indicating that the bromine-containing flame retardant can improve the flame retardancy on the basis of the comprehensive performance unchanged. The SEM illustrated that a char-layer covered on the surface of the PIRFs after burning, and increased with the increasing content of brominated flame retardant.