| In recent years,with the gradual implementation of plastic bans around the world,polylactic acid(PLA)has developed rapidly as a popular degradable plastic.The annual growth rate of the global market has reached about 20%,and the production capacity is about 330,000tons/year.The domestic market demand is also increasing year by year,and the development prospect is broad.It has been widely used in medical,food,home textiles,3D printing and other fields.However,PLA itself is a non-flame retardant material,and the macromolecular chain composed of hydrocarbon and oxygen components is extremely unstable at high temperature.Droplets with flame will expand the fire range and bring immeasurable losses.In order to reduce the fire risk,the flame retardant research of degradable materials has become a hot topic.A large number of experimental data show that the introduction of additive flame retardants will bring a series of thorny problems.In addition to high load,incompatibility,high cost and difficult degradation,the anti-melt drop effect is always poor.Based on the advantages of high efficiency and environmental protection of phosphazene flame retardants,combined with the characteristics of toughening and high thermal stability of methyl MQ silicone resin,flame retardant PLA composites were prepared to completely solve the melt drop problem of PLA materials.CP-DDS microspheres flame retardant system: CP-DDS(cyclotriphosphazene-co-4,4'-diaminodiphenyl sulfone)microspheres were prepared by high temperature copolymerization of hexachlorocyclotriphosphazene and 4,4'-diaminodiphenyl sulfone.SEM and TEM images showed that the diameter of CP-DDS microspheres was 0.5-4 ?m.N2 adsorption test showed that there were a certain number of micropores on the surface of the microspheres,and gas products such as NH3 and SO2 were detected by Py-GC/MS.The results showed that the limiting oxygen index(LOI)of PLA/7.0 FR composites with 7wt% CP-DDS was 26.8%,and the vertical burning V-1 grade was obtained.In addition,the peak heat release rate(p HRR)of PLA/FR7.0 composites decreased by 23.02%,the total heat release(THR)decreased by 20.85%,and the average effective combustion heat(av-EHC)decreased by 14.24% compared with PLA.The tensile test results showed that the tensile strength of PLA/FR7.0 composites decreased slightly,and the elongation at break increased by about 40% compared with PLA.TG-IR,Raman and XPS analysis confirmed that the gas released inert gas and condensed phase formed dense coke residue.PZS,CP-DDS and methyl MQ compound flame retardant system: PZS(cyclotriphosphazene-co-4,4'-sulfonyldiphenol)polyphosphate microspheres were prepared by ultrasonic copolymerization of hexachlorocyclotriphosphazene and 4,4'-dihydroxy diphenyl sulfone.SEM images show that the diameter of PZS microspheres is 600-900 nm,thermogravimetric analysis shows that the decomposition temperature is about 400 °C,and the thermal stability is excellent.After the introduction of 5wt% PZS microspheres,the LOI value of PLA/5.0 PZS composites reached 24.8%,and the vertical combustion test passed V-1 grade.The2wt% MQ,3wt% PZS and 3wt% CP-DDS were compounded respectively,and the results showed that PLA/3.0PZS/2.0MQ and PLA/3.0CP-DDS/2.0MQ could pass through the V-0 level.The droplet phenomenon completely disappeared,and the peak CO2 production decreased by about10.8%.Tensile test showed that the mechanical properties decreased seriously.The residue of coke increased significantly.SEM showed that the outer surface of coke was more compact,and there were many micropores inside.XPS technology detected that there were phosphorus and silicon elements.This special siliceous carbon layer structure could prevent the release of pyrolysis volatiles and slow down the transfer of heat and oxygen.The presence of PO2· was detected by thermogravimetric-infrared analysis.PO2· combined with oxygen free radicals to achieve quenching effect and played a key role in gas phase flame retardant. |
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