Polylactic acid(PLA)as a biobased degradable plastic has increasingly become a research hotspot.However,PLA's application in packaging and electrical appliances is limited due to its high combustibility.In order to solve the above problem,lignin containing silicon-nitrogen synergistic(Si-NLig)was synthesized by modifica-tion of alkali lignin(Lig),and its TGA results showed that the temperature corresponding to mass loss 5wt%of material(T5%)increased by 20℃and the high temperature residue increased from 2.3%to 25.5%in air.And Si-NLig was used as a charring agent,and compounded with ammonium polyphosphate(APP)to prepared flame retardant polylactic acid(Si-NLig-APP/PLA)by melt blending and hot-press molding,and the PLAs'flame retardant proper-ties,mechanical properties,and combustion behavior,were investigated.The results showed that addition of 10wt%Si-NLig-APP with the mass ratio 1∶4 made Si-NLig-8%APP/PLA reach the limiting oxygen index(LOI)value of 27%and the vertical burning UL-94 V-0 level,while the LOI value of Lig-8%APP/PLA with Lig as charring agent at the same condition was 26%and the vertical burning UL-94 only passed V-2 rating.Meanwhile,the peak heat release rate(PHRR)reduced by 27%compared to Lig-8%APP/PLA.Raman spectroscopy was used to charac-terize the structure of the residual char after cone calorimeter testing,it was found that the degree of graphitization of Si-NLig-8%APP/PLA increased by 36.7%compared to that of Lig-8%APP/PLA,which provides a theoretical basis for its good flame retardancy.Introduction of Si-NLig led to the enhancement of mechanical properties of the flame retardant PLA with tensile strength increasing by 21%.It can be seen that Si-NLig has potential application prospect in the field of halogen-free flame retardant PLA.
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