Flame retardancy and thermal degradation mechanism of epoxy resin composites based on a DOPO substituted organophosphorus oligomer

A series of flame-retardant epoxy resins (EP) with different content of poly(DOPO substituted dihydroxyl phenyl pentaerythritol diphosphonate) (PFR) were prepared. The PER was synthesized via the polycondensation between 10-(2,5-dihydroxyl phenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-BQ) and pentaerythritol diphosphonate dichloride (SPDPC). The structure of PER was confirmed by Fourier transform infrared spectroscopy (FTIR) and H-1 nuclear magnetic resonance (H-1 NMR). The flame retardancy and the thermal stability of the EP/PER hybrids were investigated by limiting oxygen index (LOI) test and thermogravimetric analysis (TGA) in air. The results showed that the incorporation of PER into EP can improve the thermal stability dramatically. The mechanical results demonstrated that PER enhanced failure strain slightly accompanied by a decrease in tensile strength. The thermal oxidative degradation mechanisms of the EP/PER hybrids were investigated by real time Fourier transform infrared spectra (RTFTIR) and direct pyrolysis/mass (DP-MS) analysis. X-ray photoelectron spectroscopy (XPS) was used to explore chemical components of the residual char of EP and EP/PER hybrid. DP-MS analysis showed that the degradation process of EP/PER hybrid was divided into two characteristic temperature regions, attributed to the decomposition of phosphate and aromatic structure. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.