Synthesis Of Organosilicone Containing Flame Retardant And Its Application In Polycarbonate

Polycarbonate(PC)has excellent mechanical properties,good thermal stability and high optical transparency,and is widely used in many industries such as transportation,electronics and construction.Although PC itself can pass the UL 94 V-2 testing,it cannot yet be used in some specific fields that have strict requirements for flame retardant levels.Therefore,PC must be modified to make it pass the UL-94 V-O testing.In this paper,two organosilicon flame retardants containing phosphorus and sulfur are designed and synthesized,and their effects on the flame retardant performance,combustion behavior and mechanical properties of PC are inverstigated,and the flame retardant mechanism is also explored.The main research content and results are as follows:(1)Two kinds of organicsilicon flame retardant(DPPSO and DBSSO)were synthesized through the nucleophilic substitution reaction between phenylphosphoryl dichloride or benzenesulfonyl chloride with hydroxyhydrocarbyl silicone oil,and the chemical structure and thermal stability of the two flame retardants were Characterized.(2)The results of the combustion test showed the PC/5 wt%DPPSO can pass the UL-94(3.0 mm)V-O level test,and its LOI value is 29.5%.The cone calorimetry test results show that DPPSO can effectively inhibit the heat and smoke release of the composite and also endows the composite with higher fire safety performance.Compared with pure PC,the peak heat release rate and total heat release of PC/5 wt%DPPSO decreased by 46.5%and 13.7%,respectively.The analysis of TG-FTIR and the elements composition of char residues reveals that DPPSO migrates to the surface during the combustion and decomposes into small phosphorus-containing molecules and short-chain polysiloxanes under higher temperature.Some phosphorus-containing small molecules are further decomposed into phosphorus-containing free radicals which are released into the gas phase to play the role of gas phase flame retardancy;and others remain in the condensed phase to participate in the charring formation,meanwhile short-chain polysiloxanes promote PC to form a dense and compact carbon layer,revealing that DPPSO has an effect in the condensed phase.With the addition of DPPSO and PTFE,the mechanical performance results show that the tensile strength of the composites has slight change whilst the elongation at break and notched impact strength are decrease significantly.(3)The results of the combustion test showed that the loading level of 2 wt%DBSSO alone can make the PC/DBSSO composite pass the UL-94(3.0 mm)V-O testing,and the limiting oxygen index can reach 30.3%.The cone calorimetry test results show that DBSSO can effectively inhibit the release of heat,smoke and CO during the combustion process of PC and improve the fire safety.The peak heat release rate of PC/2 wt%DBSSO is 35.2%lower than that of pure PC,and FGI is 41.1%lower than that of pure PC.DBSSO promtes the thermal decomposition of PC in advance to release H2O and CO₂ and the formation of a more expanded and condense char residues with higher graphitization.The elemental composition analysis of the residual carbon reveals the mechanism of DBSSO in the condensed phase:DBSSO migrates to the surface when the PC is burned,promoting the dehydration of the PC surface into char,and the decomposition products of DBSSO participate in char formation and form a cross-linked char layer..Although the elongation at break of the composites is decreased,the tensile and impact strength have no obvious variation as compared to the pure PC with the incorporation of DBSSO.