Synergistic Effects Of Rare Earth Phenylphosphonates And Brominated Flame Retardants On Polycarbonate

Polycarbonate(PC)is one of the most widely used thermoplastic engineering plastics which has a large production amount every year.The application of PC is spread in various areas such as electrical&electronic devices,household articles,construction materials,cars,aircrafts and medical instruments,etc.PC has an inherent fire resistance,and usually has a rating of V-2 in UL94 vertical burning test and its limiting oxygen index(LOI)is approximately 25%.However,better flame retardant properties are demanded when it is used in specific cases.Brominated flame retardants(BFRs)have been long been used because of their high efficiency and mature technology.But their use is gradually being prohibited as people lay more and more care on environment and human safety.What's more,the traditional bromine-antimony compound system is not suitable for PC,which leads to a higher additive amount of BFR.Rare earth is one of the most important strategic resources of the 21st century.China's reserve of rare earth ranks first in the world,while the rlated researches and applications are not sufficient at present.Rare earth compounds could lead to excellent properties when they are applied to modify materials.Its use in polymer flame retardant is drawing more and more attraction in recent years.In this research,two kinds of rare earth phenylphosphonates(ReHPPs)were incorporated with BFRs into PC.Their effects on the thermal stability and flame rtardancy of the composites were investigated.And the synergistic mechanism was analyzed.Firstly,the cerium phenylphosphonate(CeHPP)and the lanthanum phenylphosphonate(LaHPP)were synthesized through solution reflux and hydrothermal methods.Transmission electron microscope(TEM)graphs showed that both CeHPP and LaHPP dispersed well in the PC matrix,while the dispersion of LaHPP was more evenly and meticulous than CeHPP.They were separately incorporated into the PC/decabromodiphenyl oxide(DBDPO)composites.TG-FTIR analysis showed that both CeHPP and LaHPP could improve the thermal oxidative stability of PC/DBDPO composites,while CeHPP performed better than LaHPP at the initial degradation stage.The results of LOI and UL94 vertical burning tests revealed that a small amount of ReHPP could improve the flame retrdancy dramatically.But higher ReHPP additive amounts leaded to a worse performance conversely.Cone calorimetry demonstrated that the incorporation of ReHPP brought about a decrease in heat and smoke release during combustion.LaHPP contributes to a lager reduction in the peak heat release rate(PHRR),while CeHPP performs better in the inhibition of smoke production rate(SPR)and total smoke release(TSR).The study on chars and analysis of the synergistic mechanism revealed that ReHPP promotes the procedure of cross-linking and char fonnation.The flame retardant efficiency relies on the synergistic effects between DBDPO and ReHPP.Secondly,brominated polystyrene(BPS),which is a relatively environmental friendly BFR,was chosen to incorporate with LaHPP into PC.TG-FTIR analysis showed that the incorporation of LaHPP could improve the thermal oxidative stability of PC/BPS composites,but it failed to reduce the release of volatilized degradation products.Flammability tests also revealed that LaHPP had little influence on the LOI and UL 94 rating of the composites.Cone calorimetry indicated that although LaHPP leaded to an increase in char residue,it did not help to decrease the release of heat and smoke.Comparing the results to PC/DBDPO composites,it was deduced that the overall flame retardancy depends on the synergism between BFR and ReHPP.The gaseous effects of BFR played the main role in the fire resisting procedure,while ReHPP acted as a synergistic agent to enhance the char layers,which provided more space and time for BFR to perform abundantly.The whole efficiency is mainly dependent on the gaseous performance of BFR and the additive amounts of ReHPP.