Comparative study on flame retardancy and thermal degradation of phosphorus- and silicon-containing epoxy resin composites

Epoxy composites containing phosphorus and/or silicon were prepared using polyphenylmethoxysilicone (PPMS) and microencapsulated ammonium polyphosphate (MFAPP) as modifiers. Siliconized epoxy copolymer (EPMS) was obtained via the polycondensation of PPMS and diglycidyl ethers of bisphenol A (DGEBA) type epoxy resin. Then MFAPP was added into EPMS or DGEBA based hybrids respectively to improve their flame retardancy further. Thermal and flame retardant properties of EPMS/MFAPP and DGEBA/MFAPP composites were evaluated by Limited Oxygen index (LOI), UL-94 test and thermogravimetric analysis (TGA). The higher LOI value and UL-94 rating confirmed that MFAPP was an effective flame retardant in DGEBA compared with EPMS. A remarkable synergistic effect of phosphorus and silicon on flame retardation of EPMS/MFAPP was not observed. The reason was that the flame retardancy of epoxy composites containing phosphorus was based on solid phase. FTIR spectra of the char residue showed that when MFAPP was added, without sufficient O-H groups in EPMS/MFAPP, an effective insulative layer which protects underlying materials can’t form during combustion.