Properties of polyurethane coatings based on linseed oil phosphate ester polyols and expandable graphite

Abstract

The effect of two grades of expandable graphite (EG 096 and EG 290) on the thermal decomposition and flammability of polyurethane (PU) coatings, based on two kinds of linseed oil phosphate ester polyols, was studied. Thermogravimetric analysis (TGA) and the cone calorimeter test at a heat flux of 35 kW/m2 were used for this purpose. The chemical structure of the synthesized polyols was identified by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (31P NMR) spectroscopy. The content of EG was varied from 0 up to 25%. For all characteristics of PU coatings, the maximum effect was reached at 25% of EG. It was found that PU coatings filled with EG 096 had higher char residue at thermal decomposition under nitrogen. The flame retardancy of the PU coating filled with EG 290, which generated more blowing gases at thermal decomposition and therefore had a higher expansion volume, was higher than the flame retardancy of the coatings filled with EG 096. The best characteristics were shown by filled PU coatings based on the polyol, which was phosphorylated in the presence of isopropyl alcohol and which, besides phosphate mono- and diesters, had phosphate triester and pyrophosphate monoester.