The Synergistic Flame Retardancy Effect Of MOFs/Phosphorous Flame Retardant In Poly (L-actic) Acid

Poly(L-actic acid)(PLA)is an ideal green polymer material,which is biodegradable and regenerated.It has been used in plastic packaging and electronic products widely.However,poly(L-actic acid)has poor flame retardancy and is easy to burn,which limits the further application and development of PLA to a certain extent.In this paper,phosphorous flame retardants and metal organic framework were used together to prepare PLA composite materials by means of melt blending,which not only reduced the amount of phosphorous flame retardants,but also improved the flame retardancy of samples in the same time.The detailed contents as follows:(1)The catalytic Ni-MOF and ammonium polyphosphate(APP)were used in combination to prepare the PLA/APP/Ni-MOF composite material to improve the flame retardancy of PLA.As the results of flame retardancy test,the best result of composites was achieved when the total flame retardants was 14wt% and the Ni-MOF was 2 wt%.The limit oxygen index value(LOI)was 36.6%,the phenomenon of dripping in the UL-94 test was inhibited and reached V-0 level.In addition,continuous and dense stable carbon layer could be formed in the cone calorimetry test,and the peak heat release rate(PHRR)was reduced by 60.4% compared with pure PLA.(2)In order to improve the dispersion of flame retardants in the PLA matrix,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO)was grafted onto the surface of Fe-MOF,and the PLA/MOF(Fe)-g-DOPO composite materials were prepared.LOI test results showed that when the addition of MOF(Fe)-g-DOPO was 2 wt%,the LOI value was 21.9%,and the PHRR value decreased by 13.9% in the cone calorimetry test.It can be found from the SEM images that the morphology of residual char has changed,which is helpful with the flame retardancy of the materials.(3)PMo-MOF composite was synthesized in one step by solvent-thermal method,which were synergistic with PLA/IFR system.The results showed that when the addition of PMo-MOF was 0.5 wt%,the LOI value of the composites reached 35.0%,and the PHRR value decreased 59.7%.The catalysis of PMo-MOF promoted the formation of carbon residue and improved the flame retardancy of the composites.