Synergistic Effect Of SBA-15 And Intumescent Flame Retardant On Preparing Halogen-free Flame Retardant Poly(lactic Acid)

Polylactic acid(PLA)is a kind of bio-based degradable plastic with excellent mechanical properties,biological compatibility and processing properties.PLA is widely used in biological,food packaging,3D printing and other fields.However,PLA is highly flammable,with an extreme oxygen index(LOI)of only 19%and serious droplets during combustion,which limits its application in electronics,cables,and automobiles.In order to improve the flame retardant performance of PLA,adding intumescent flame retardant(IFR)is a simple and environmentally friendly method in industry.IFR has the advantages of being cheap,practical and environmentally friendly,but traditional IFR has the disadvantages of poor thermal stability and low flame retardant efficiency compared with halogen flame retardants.In this paper,the catalytic and adsorption properties of the mesoporous molecular sieve SBA-15 are utilized.The flame retardant efficiency of IFR was improved through the synergistic effect of SBA-15 and IFR,and the synergistic flame retardant mechanism of SBA-15 and IFR was further study as well.The obtained results are shown as below:Firstly,the synergisitic effect of 1 wt%SBA-15 and different addition of IFR on flame retardant of PLA was studied.It was found that when the addition of IFR was 15 wt%and SB A-15 was 1 wt%,PLA/15IFR/1 SBA-15 showed the best flame retardant properties.Compared to the PLA compisites with merely adding 16 wt%IFR,the LOI of PLA/15IFR/1SBA-15 increased from 26.0%to 31.0%,and the UL-94 rank V-0,the peak heat release rate(PHRR)and total heat release(THR)also decreased from 148.3kW/m2 and 45.2 MJ/m2 to 127.2 kW/m2 and 41.3 MJ/m2 respectively,and it shows excellent flame retardant performance.In addition,SBA-15 has a significant smoke suppression effect in PLA/IFR system,with the addition of SBA-15,the peak smoke release rate(PSPR),total heat release(TSR,mean yield of CO2(Mean-CO2Y)and mean yield of CO(Mean-COY)of PLA/IFR system were significantly decreased by 54.5%?37.6%?8.9%and 60.6%,respectively.SBA-15 promoted the esterification reaction between ammonium polyphosphate(APP)and pentaerythritol(PER)as a catalyst,which accelerated the formation of more expanded carbon.Meanwhile,SBA-15 promoted the decomposition of PLA matrix into small molecular chain segments at lower temperatures,which was beneficial to form more carbon and to provide a level of fire resistance.Secondly,in order to achieve efficient synergistic effect of IFR and SBA-15 on flame retardancy of PLA,the dispersion of SBA-15 in PLA/IFR system was improved by modifying SBA-15 with silane coupling agent.Modified SBA-15 was synthesized by using 3-glycidyloxypropyltrimethoxysilane and triethoxy(octyl)silane.The synergistic effect of different modified SBA-15 and IFR on flame retardant properties of PLA were investigated.It was found that SBA-15 modified with 3-glycidyloxypropyltrimethoxysilane(E-SBA-15)had the best synergistic effect with IFR on flame retardancy of PLA.Compared with PLA/15IFR/1SBA-15,the LOI of PLA/15IFR/1E-SBA-15 increased to 32.0%,and its PHRR and THR decreased to 127.1 kW/m2 and 37.1 MJ/m2,but the smoke suppression effect of SBA-15 decreased slightly due to the blockage of the pores after modified.Compared to pristine SBA-15,E-SBA-15 has a better dispersion in PLA/IFR system.E-SBA-15 improves the stability of residue char in high temperature and promotes the migration of silicon to the surface of the carbon layer.Finally,in order to further improve synergistic effect between SBA-15 and IFR on flame retardancy of PLA,and don't affect the smoke suppression effect of SBA-15.Al-SBA-15 was prepared through post-synthesis.The highly efficient synergistic effect with IFR on flame retardancy and smoke suppression effect of Al-SBA-15 was achieved.The synergistic effect of IFR and Al-SBA-15 with different Si/Al ratio on flame retardancy in PLA was studied.Compared to SBA-15,Al-SBA-15 has a better synergistic effect on flame retardancy with IFR in PLA.Furthermore,Al-SBA-15 with a Si/Al ratio of 5(Al-SBA-15-5)has the most significant synergistic effect with IFR.Compared with PLA/15IFR/1SBA-15,the LOI of PLA/15IFR/1Al-SBA-15-5 increased to 37.4%,and its PHRR and THR decreased to 75.6 kW/m2 and 6.9 MJ/m2,It also has self-extinguishing effect in the combustion process which decreased the smoke release,with the addition of Al-SBA-15-5,PSPR,TSR and Mean-CO2Y of PLA/IFR system were significantly decreased by 70.6%?60.0%and 31.4%,respectively.Al-SBA-15-5 promotes the esterification reaction of IFR,which accelerates the formation of more expanded carbon.Meanwhile,Al-SBA-15-5 promotes the small molecules containing carbonyl compounds(small molecule of PLA)to participate in the formation of carbon.