The synthesis of DOPO-g-ESO and its effect on the properties of phenolic foam composites

In order to improve the properties of phenolic foam (PF), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was introduced into the structure of epoxidized soybean oil (ESO), and DOPO-grafted ESO (DOPO-g-ESO) was obtained to modify phenolic resin (PR) and to prepare modified PF (DEMPF). The structures of ESO and DOPO-g-ESO were verified by Fourier transform infrared spectroscopy and nuclear magnetic resonance. In comparison with ESO, DOPO-g-ESO shows slightly worse thermal stability; the initial decomposition temperature (T_i) and residual carbon (600°C) decreased by 18.3 and 5.57%, respectively. DOPO-g-ESO-modified PR (DEMPR) shows a slightly higher decomposition temperature in comparison with PR. The carbon residues (600°C) of DEMPR decreased with the increase in the DOPO-g-ESO/phenol (P) content. Moreover, with the increase in the DOPO-g-ESO/P content, the activation energies of DEMPR gradually increased, and the reaction orders were all non-integers. Compared with PF, when the dosage of DOPO-g-ESO/P was less than or equal to 10%, the mechanical properties of DEMPF improved and then deteriorated. However, the flame retardancy of DEMPF decreased slightly, but not too much. In addition, the cell sizes of DEMPF gradually increased. Using comprehensive analysis, the optimal dosage of DOPO-g-ESO/P was found to be about 10%.