Surface Modification Of Phosphorus-containing Flame Retardants And Synergistic Flame Retartant ABS

Aluminum hypophosphite(AHP)is a new type of phosphorus-containing flame retardant which has excellent flame retardant and thermal stability.However,AHP also has some defects including moisture sensitivity and poor compatibility with ABS matrix.So in this paper,different microencapsule shell materials were selected to be modified surface of aluminium hypophosphite.The microencapsulation of flame retardant by designing various molecular structure could not only improve water resistance of flame retardant,it also increases the flame retardancy of polymer.Then the influence of char structure and formation process of the flame-retardant ABS composites were studied systematically.(1)Aluminum hypophosphite has been microencapsulated by polystyrene(PS-AHP)via free radical polymerization.FT-IR spectra and SEM images suggested that a lot of spherical polystyrene particles with dimensions of about 20 to 300 nm were attached to the surface of PS-AHP.TG results showed that the Tmax2 of PS-AHP increased 48.3?,and the char yield increased from 72.5% to 77.2% at 800?.The water solubility test results showed that the solubility of PS-AHP prepared by suspension system was the lowest,decreasing by 58.1%,49.1% and 40.8% at 25?,50? and 75? respectively.The vertical burning rate of the ABS composite with 22wt% PS-AHP achieved V-0.(2)Phenyl silicone resins microencapsulated AHP(Ph-SiAHP)were prepared via the condensation polymerization by phenyl trimethoxy silane.FT-IR spectra and SEM images suggested that a lot of irregulary silicone resin were coated with the surface of the AHP.The water solubility showed the water solubility of Ph-SiAHP significantly decreased by 66% at 25?.TG results showed that the char yield of Ph-SiAHP increased by 1.6% at 800? and the thermal stability was improved.The vertical burning rate of the ABS/Ph-SiAHP composite achieved V-0 with 22wt% Ph-SiAHP.(3)Microencapsulated AHP(PN-SiAHP)were prepared via the condensation polymerization of phenyl trimethoxy silane and N-(b-aminoethyl)-?-aminopropylmet--hyldimethoxy silane.FT-IR spectra and SEM images suggested that a lot of irregulary silicone resin were coated with the surface of the AHP which thickness of approximately 30 to 80 nm.The water solubility results showed that the water solubility of PN-SiAHP decreased by 28.8%,29.7%,35.8% at 25?,50? and 75? respectively.TG results showed that the char yield of PN-SiAHP increased by 4.6% at 700? and the thermal stability was improved.The vertical burning rate of the ABS/PN-SiAHP composite achieved V-0 rating with 22wt% PN-SiAHP.(4)The peak heat release rate(pHRR)value of the ABS/22wt%PS-AHP composite were decreased by 19.4%,compared to those of the ABS/22wt% AHP composite.Moreover,the total heat release(THR)and the total smoke production(TSR)values of the ABS/PS-AHP composites were all lower than those of the ABS/AHP composites.The char yield of ABS/22wt%PS-AHP composite increased 48.7% compared to the ABS/22wt% AHP composite.The residue of the ABS/PS-AHP composites exhibited a denser and more compact surface char layer structure than that of the ABS/AHP composite.The pHRR values of the ABS/24wt%Ph-AHP and ABS/24wt%PN-SiAHP composites were decreased by 10.8% and 18.7%,and char yield increased by 17.4% and 62.1%,respectively.The compact surface char layer structure suggested silicon improved flame retardant of ABS composites.The efficiency of PN-SiAHP was higher than Ph-Si AHP because of synergistic effect of P-N in PN-SiAHP.(5)The influence of char structure and formation process about ABS composites by staged combustion was studied.The results suggested compact char suface structure was formed in the early stages of combustion,and the thickness growed as the burning time prolonging.The char of half-burnt ABS composites were seperated thin skin layer and the thick porous layer and melten layer.Less pores in the skin layer and its physical property was good,the porosity of the porous layer was big and numerious,having the effect of expanding char.It improved the flame retardant of ABS composites.TG results showed skin layer was stable and weight loss was small.The porous layer was protected by skin layer,weight loss was high due to incomplete carbonized things decomposition.The analysis of mechanism suggested the decomposition of AHP promoted formation of char structure,silicon compounds migrated to the surface because of its low suface energy and the char containing P,C,Si elements has been formed combining with phosphorus compounds.The char structure inhibited heat and oxygen into inner of composite and improved flame retardant.