Preparation Of Poly(lactic Acid)/modified ?-CD Composite Material And Study On Its Flame Retardant Performance

Due to the extensive use of petroleum-based plastics,ecological and environmental problems are increasingly aggravated,and biodegradable materials have been developed rapidly.Poly(L-lactic acid)(PLA)is a kind of bio-based material derived from renewable resources such as wheat and corn,which has excellent biocompatibility.However,PLA is highly flammable and the droplet phenomenon is serious,which seriously limits the development of PLA material.Therefore,it is of great significance to modify PLA material for flame retardancy.In recent years,bio-based flame retardants have attracted much attention.Cyclodextrin is a kind of natural polysaccharide,rich in hydroxyl structure,which can act as a carbon source in flame retardants and modify the hydroxyl on the outer side of its molecule.In this paper,a new flame retardant(?-CDCP)was synthesized by onestep substitution method from ?-CD and HCCP,and it was mixed with APP.The effects of flame retardant on thermal stability,flame retardancy and crystallization properties of composite materials were analyzed.A series of studies on its flame retardant mechanism were carried out,and the results are as follows:The chemical structure of the flame retardant ?-CDCP was verified by Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and wide-angle X-ray diffraction(WAXD),which proved the successful synthesis of the flame retardant ?-CDCP.The scanning electron microscopy(SEM)results showed that the microstructure of the flame retardant ?-CDCP was spherical.Poly(lactic acid)composites were prepared by melt extrusion method.The flame retardancy and combustion behavior of poly(lactic acid)composites were evaluated by limiting oxygen index(LOI),vertical combustion(UL-94),thermogravimetric analysis(TGA),CONE calorimetric analysis(CONE)and a series of experiments.The results showed that when the flame retardants APP and ?-CDCP were added simultaneously,The LOI of the composites increased to V-0 grade,which promoted the carbon formation.CONE results showed that PLA/5%APP/10%?-CDCP had good flame retardancy.The residual carbon was evaluated by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),Raman spectroscopy(LRS)and Fourier infrared spectroscopy(FTIR).The results show that the structure of pure PLA carbon layer is loose,but the carbon layer of the composite is dense.LRS test results show that the PLA/5%APP/10%?-CDCP integration strength value ratio is the lowest,that is,the carbon layer has the best thermal stability.FTIR results showed some phosphorous and polyphosphorous structures,which accelerated the dehydration of PLA matrix into carbon and formed a protective carbon layer.The gas products were evaluated by TGIR and PY-GC/MS.The experimental results show that the addition of flame retardants can effectively inhibit the generation of combustible gas and affect the pyrolysis process of PLA.Differential scanning calorimeter(DSC)test showed that the addition of APP and ?-CDCP could effectively promote crystallization of PLA composites.