The effect of silicon sources on the mechanism of phosphorus-silicon synergism of flame retardation of epoxy resins

The effect of silicon source on the mechanism and efficiency of silicon-phosphorus synergism of flame retardation was studied. The studied systems composed of a phosphorus-containing epoxy resin and various types of silicon additives including nanoscale colloidal silica (CS), tetraethoxysilane (TEOS), and diglycidylether terminated polydimethylsiloxane (PDMS-DG). Thermal stability and degradation kinetics of cured epoxy resins, elemental analysis of degraded residues, and evolved gases analysis of degradation reactions were conducted with a thermogravimetric analyser, energy-dispersive X-ray spectrometry, and gas chromatography-mass spectrometry, respectively. Addition of silicon compounds showed significant effect on enhancing the thermal stability and char yields of the cured epoxy resins. During thermal degradation, TEOS and PDMS-DG exhibited silicon migration to sample surface and CS did not. Self-degradation of PDMS-DG resulted in a silicon loss for PDMS-DG-containing epoxy resin. From the results it was concluded that using TEOS as an additive for epoxy resins and formation of epoxy-silica hybrid structure through sol-gel reactions was a good approach for achieving phosphorus-silicon synergism in flame retardation.