Flame Retardant Modification Of PC/ABS Blend

Polycarbonate/acrylonitrile-butadiene-styrene copolymer(PC/ABS)blend is an industrial plastic blend with high performance which is widely applied to mechanical areas,electrical and electronic,automobile making and other fields.The addition of ABS can reduce the flame retardancy of the blend,while the addition of flame retardant will cause the mechanical.properties of the alloy to decline.In order to improve the properties of the blend to meet the high requirements of different industries,modification of PC/ABS blend should be studied in this paper through two aspects:flame retardant modification and toughening modification.Firstly,the flame retarded and toughened PC/ABS blend was prepared by melt blending with environmental brominated flame retardant(decabromodiphenylethane,DBDPE)and compatibilizer(methyl methacrylate-butadiene-styrene,MBS).The results showed that the PC/ABS blend could reach UL 94 V-0 by adding 8 parts of DBDPE and 6 parts of MBS,and the mechanical propoties of blend could maintain a good balance of stiffness(tensile strength 44.9 MPa)and toughness(izod impact strength 31.2 kJ/m2).The phase morphology of the blend was observed by scanning electron microscope(SEM).It was found that DBDPE had poor compatibility with resin matrix,distributed unevenly in the matrix and agglomerated a little,which destroyed the continuity of the phase interface.The addition of MBS made the interface of the two phases fuzzy,the size of the dispersed phase was obviously reduced,and the compatibility of the system was improved.It was found by DMA that DBDPE blocked the movement of the chain segment and reduced the storage modulus of the blend.MBS could increase the flexibility of molecular chain and decrease the peak loss modulus of the blend.And the flame retardant toughened PC/ABS blend could still maintain good deformation resistance and high temperature resistance.Secondly,the proportion of SAN phase and PB phase in PC/ABS blend was regulated by ABS-high-rubber-powder(ABS-HRP)and styrene-acrylonitrile copolymer(SAN),and the effect of ABS phase composition on the phase interface,compatibility,mechanical properties and flame retardancy of the blend was explored.The results showed that under the condition of PC/ABS(mass ratio is 70/30),changing the phase composition of ABS had little effect on the UL 94 test results of the blend,but PB was more flammable than SAN phase,and the flame retardancy of the blend was the result of the joint action of the phase morphology and compatibility of the blend.Mechanical tests showed that SAN could act as a rigid particle to toughen and strengthen the blend at a low content(<5 phr),and SEM observation showed that too much SAN could form continuous phase and destroyed the original phase structure of the blend.In addition,ABS-HRP could improve the impact strength of the system,and the appropriate proportion of PB and SAN could make the blend maintain good rigidity and toughness at the same time.Thirdly,the flame retardant PC/ABS blend was prepared by the combination of resorcinol bis(diphenyl phosphate)(RDP)(mainly based on condensed phase flame retardant mechanism)and triphenyl phosphate(TPP)(mainly based on gas phase flame retardant mechanism),based on the fact that the flame retardant can play a role both in the gas phase and condensed phase.The results showed that the vertical combustion of PC/ABS blend could reach UL 94 V-0 with 10 RDP/TPP(mass ratio is 3:2).Cone calorimeter test data showed that RDP and TPP had synergistic flame retardant effect of gas phase and condensed phase,which not only enhanced the inhibition effect of gas-phase combustion chain reaction,but also promoted the formation of higher quality carbon layer in condensed phase.Through the analysis of the element content on the surface of the carbon residue by EDS,it was found that the content of P and O in the carbon residue increased at the same time after RDP/TPP compounding,which indicated that the formation of P-O and P-C structure phosphate was helpful to form a denser carbon layer and better played the effect of oxygen insulation.Finally,the synergistic effect of SiO2 and the effect of nano particles on the mechanical properties of the blend were investigated by using nano-SiO2 as synergistic agent and RDP as flame retardant.The results showed that 1 part of SiO2 and 10 parts of RDP could make the blend burn vertically up to UL 94 V-0.Cone test results showed that SiO2 enhanced the flame retardant effect of condensed phase and promoted the formation of continuous dense carbon layer.EDS test showed that the content of P increased from 2.54%to 7.24%and O from 18.02%to 36.71%after adding SiO2 synergism.It was speculated that the hydroxyl groups on the surface of SiO2 reacted with RDP to form cross-linked phosphide containing silicon and oxygen.This Si-O-P network structure enhanced the strength of carbon layer.Phosphorus promoted the formation of carbon layer,and silicon increased the stability of carbon layer,that is,phosphorus silicon synergistic flame retardant effect.SEM observation showed that SiO2 was distributed between the two-phase interfaces.Because SiO2 was hydrophilic and oleophobic,it has poor compatibility with the matrix,which reduced the interface binding force,made the impact section appear large pieces of falling off,and caused the reduction of blend toughness.MBS could improve the effect to some extent.