Preparation And Properties Of Halogen-Free Flame Retardant ABS Composites

“The directive on the restriction of the use of certain hazardous substances in electricaland electronic equipment”(RoHS directive) required new electrical and electronic productsshall not contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls,polybrominated diphenyl ethers of six hazardous substances in the EU market after July1,2006. People have paid more and more attention to preparing halogen-free ABS by usinghalogen-free flame retardants and flame retardant mechanism.In this paper, the decomposition products of ABS in the different stages were analyzedby the thermogravimetry-gas phase chromatography-mass spectrum, which provided areasonable basis for the selection of flame retardant. There are many halogen-free flameretardant methods for the ABS. The widely used intumescent halogen-free flame retardant toplastic was applied in this article. Organic hypophosphite and charring agent(TPU or PBT),blending with ABS to prepare halogen-free flame retardant composite materials. Limitingoxygen index (LOI) and UL94V-0was used for characterizing flame retardant performanceand flame retardant mechanism was preliminary discussed by thermogravimetric analysis(TG), tapered calorimeter (CONE), scanning electron microscopy (SEM). In addtion, theinfluence of flame retardants and carbonforming agent on the mechanic properties ofcomposite was also studied in the paper.The previous heat and oxygen can both accelerate the degradation of ABS, and carbonresidue can further cause the oxygenolysis completely. So, the phosphoru flame retardant,which was heat insulated and oxygen insolated, can restrain hot oxygen degradation of ABS,which can improve the carbon residue during the oxygen degradation process of ABS. So ithelps to reduce the mass loss rate and smoke density when burning ABS, then the heat releaserate will also reduce. ABS thermal degradation belongs to incomplete combustion and a largenumber of benzene and olefin-class small molecule volatile compounds generated. ABSthermal degradation primarily arised from300℃to400℃, so in order to play a goodflame-retardant effect the selected flame retardants must play a role in about300℃. When thecontent of flame retardants and TPU is respectively25%and20%, the limiting oxygen index of ABS composite materials is28.5, which increases by50%than pure ABS. Furthermore, theUL94V-0(1.5mm) is qualified. When the content of flame retardants and PBT is25%and30%repectively, the limiting oxygen index of ABS composite materials is27.0, whichincreases by42.1%than pure ABS, and can reach the level of UL94V-0(1.5mm). Organichypophosphite can flame retardant both from condense phase and gas phase. When the TPUwas used as a charring agent, the carbon layer was more compact, and condense phase flameretardant was more efficient; When the PBT was used as a charring agent, gas phase flameretardant was more efficient. The flame retardant property of ABS/A8307/TPU compositematerial meet the level of UL94V-0(1.5mm), the bending performance and impactperformance can’t satisfy requirements of electrical shell simultaneously. The flame retardantproperty of ABS/A8307/PBT composite material meet the level of UL94V-0(1.5mm), and theimpact strength is20J/m, which can’t meet the electrical appliances shell requirements. TheTPU with hardness of80A and85A can improve the impact performance of ABS/A8307/TPUcomposite material, but it also has a negative impact of the bending strength. Compared withTPU with hardness of90A, TPU with hardness of80A or85A can improve the heat releaserate of the ABS/A8307/TPU composite materials, at the same time, the content of carbamicacid ester groups reduced, causing low efficiency of charring. Therefore, it delays the processof extinguish.