Synthesis of Phosphaphenanthrene-modified Cardanol-based Polyol and Its Performance as Flame Retardant in Rigid Polyurethane Foams

A phosphaphenanthrene-modified cardanol-based polyol (P-Cardanol-Polyol) was synthesized from cardanol and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and its structure was characterized by H-1 and P-31 nuclear magnetic resonance (NMR)spectra. Subsequently, P-Cardanol-Polyol was used to prepare a series of flame-retardant rigid polyurethane foams (RPUFs). The effects of P-Cardanol-Polyol on the morphology, density, thermal conductivity, compression property, thermal stability and flame-retardant properties of RPUFs were investigated. The results showed that P-Cardanol-Polyol had a negligible effect on the density of RPUFs;with the increased amount of P-Cardanol-Polyol, the average pore size and the thermal conductivity of flame-retardant RPUFs decreased gradually. The maximum heat release rate and total heat release of the unmodified RPUF were 390 kW/m(2) and 31.9 MJ/m(2), respectively, while those of flame-retardant RPUF were reduced to 340 kW/m(2) and 24.6 MJ/m(2). In addition, the compressive strength of flame-retardant RPUF was about 13% higher than that of unmodified RPUF. The results of char analysis showed that P-Cardanol-Polyol can promote the formation of a continuous and dense char layer with good thermal-oxidative resistance,which is conducive to reducing the escape of combustible gases during combustion,so as to improve the flame-retardant performance.