Abstract
The effect of phenylphosphonic acid (PPOA) on polyurethane (PU) thermal stability was studied through Fourier transform infrared spectroscopy and Thermogravimetric analysis. To synthesize PPOA-modified PUs (PPOA-PUs), polyether-type diols (Mw=62, 106, 190, 419, 605) were chemically modified with PPOA and then reacted with 4,4′-dicyclohexylmethane diisocyanate (H12MDI) and 4,4-diphenylmethane diisocyanate (MDI). During thermal decomposition in air, the PPOA embedded in the PUs formed intumescent phosphocarbonaceous char. Below 400°C, PPOA-H12MDI-PUs were more unstable, as PPOA decomposed at lower temperatures than phenyl groups and aliphatic ethers. Above 550°C, the thermal stability of PUs followed this order: PPOA-MDI-PUs > PPOA-H12MDI-PUs > MDI-PUs > H12MDI-PUs. At 700°C, unmodified PUs had no residue, while the PPOA-MDI-PU residue was 4.4~23.0 wt.% and the PPOA-H12MDI-PU residue was 1.5~17.5 wt.%. The enhanced thermal stability of PPOA-MDI-PUs at high temperatures can be attributed to the synergetic effect of PPOA and phenyl groups on the formation of phosphocarbonaceous char.
Keywords: Thermal stability;polyurethane;phenylphosphonic acid;intumescent char barrier;phosphocarbonaceous char