Study On The Thermal Degradation Behavior And Flame Retardant Properties Of Alkyl Hypophosphite In PET

Polyethylene terephthalate(PET),as a semi-crystalline thermoplastic polyester material,has been widely used in automobile,electronics and machinery due to its excellent mechanical properties,weather resistance,chemical corrosion resistance and fatigue resistance.However,the flammability of PET greatly limits its application in the field with combustion safety requirements,so the flame retardant modification of PET material is particularly important.In this paper,two flame retardants of diisobutyl aluminum hypophosphate(APBA)and Phenylethyl bridge DOPO(DIDOPO)with P-C bond were employed to flame retardant modify PET and our afford was focused on study effect of APBA/DIDOPO compound flame retardant on thermal degradation behavior,flame retardant performance,rheological behavior of PET,and clarify the synergistic flame retardant action mechanism.Moreover,the difference of thermal degradation behavior,flame retardant performance,flame-retardant mechanism between APBA/DIDOPO and OP1230 was comparatively studied.It is believed that this study might provide theoretical guidance for designing and preparing flame retardant PET composites with high performance.The main research contents and results are as follows:1.By studying the thermal degradation behavior,flame retardant performance,rheological behavior and flame retardant mechanism of PET/APBA composites,it is found that with the addition of 15% APBA,PET composites reaches the V-0 level,the LOI value is up to 32%,the dripping of the composites is suppressed.TG,TG-IR,SEM and XPS tests showed that the addition of APBA will promote the formation of carbon layer with dense structure and high degree of graphitization during the combustion of PET composites,which can play the role of heat insulation,oxygen insulation and inhibit the volatilization of combustible substance.Meanwhile,PET/APBA materials will generate phosphorous-containing free radicals and non-flammable gases during thermal degradation,effectively play the role of free radical quenching and dilution of combustible gas density,and slow down the combustion process.Therefore,APBA can play a flame retardant role in the condensed phase and the gas phase,The flame retardancy of condensed phase is the main and gas phase is the auxiliary.2.By studying the thermal degradation behavior,flame retardant performance,rheological behavior and flame retardant mechanism of PET/DIDOPO and PET/APBA/DIDOPO composites,the results showed that :(1)PET/DIDOPO can reach UL-94 V-0 when the content of DIDOPO is 12.5%,and the LOI value increased by 56.87% compared with PET.Thermal degradation behavior analysis showed that the PET/DIDOPO composite material would generate DOPO derivative phosphorous free radicals during degradation and combustion process,which quenches the free radicals generated in the process of PET combustion to relieve the combustion,but only a small amount of carbon residue was left after the degradation,with poor barrier protection effect.Therefore,the solid phase flame retardant effect of DIDOPO in PET is weak,which is mainly manifested as the flame retardant mechanism of gas phase.(2)When the total addition amount of composite flame retardant is 10% and the ratio of APBA to DIDOPO is 1:2,the flame retardant grade of composite material can reach the UL-94 V-0 grade,and the LOI value can be increased to 30.6%.According to the thermal degradation behavior analysis,the carbon residue of the composite system is large,showing a better barrier protection effect,and the thermal degradation will generate DOPO derivatives and diisobutyl phosphates derivatives of free radicals,quenching the free radicals generated in the process of PET combustion.Therefore,the flame retardant PET composite not only maintains the good carbon forming protection of APBA,but also possesses the excellent gas phase flame retardant effect of DIDOPO,showing a good synergistic flame retardant effect.3.The thermal degradation behavior,flame retardant performance,rheological behavior and flame retardant mechanism of PET/APBA/DIDOPO and PET/OP1230 composites were compared.The results showed that: APBA/DIDOPO flame retardants can make the PET material reach the UL-94 V-0 level at a lower dosage,showing a higher flame retardation efficiency.The rheological test results show that OP1230 can increase the viscosity of the composite and inhibit the dripping,while the addition of APBA/DIDOPO can reduce the viscosity of the composite and increase the dripping,but the dripping can take away the heat and improve the flame retardant performance of the composite.The results of thermal degradation show that the two flame retardant systems can reduce the thermal degradation temperature of PET,but both could significantly increase the amount of carbon residue after combustion.In the condensed phase,the carbon forming capacity of PET/APBA/DIDOPO composites is better than that of PET/OP1230 composites,and the barrier protection effect is more obvious.In the gas phase,PET/APBA/DIDOPO composites can released compounds or groups containing phosphorus during degradation or combustion,and the flame retardant effect of gas phase will be further enhanced.However,PET/OP1230 almost no phosphorus containing substances to escape during degradation,the gas phase inhibition effect is limited.It shows that APBA/DIDOPO system has better barrier protection and gas phase inhibition effect,and has obvious synergistic flame retardant effect.APBA/DIDOPO is an ideal high efficient flame retardant system.