Preparation Of Bio-based Chitosan Microsphere Flame Retardants And Their Application In Polylactic Acid

Due to the increasingly severe environmental impact of petroleum-based compounds,polylactic acid(PLA)has developed rapidly in recent years.PLA is a biodegradable thermoplastic polymer,which can be obtained by artificial chemical synthesis of lactic acid produced by biological fermentation.It has excellent processing properties,mechanical properties and high transparency,and is widely used in packaging,textile,medical,electronics and Auto parts field.However,similar to most polymer materials,PLA is highly flammable,which greatly limits the application of PLA in products requiring flame retardancy.Therefore,flame-retardant modification of PLA is a necessary means to expand its application.In recent years,researches on bio-based flame retardants have been paid more and more attention.Chitosan(CHT)is a natural polysaccharide substance,which can function as a carbon source in an intumescent flame retardant system.Its structure contains a large number of hydroxyl and amino groups,which can be modified in various ways.In addition,the addition of a flame retardant will often cause the mechanical properties of the material to decline.By designing the structure of the flame retardant,the mechanical properties of the material can be improved while improving the flame retardant performance of the material.In this paper,chitosan microspheres(CHTM)were synthesized by inverse emulsion cross-linking,and their micro-morphology and surface charge properties were studied.Bio-based expanded flame retardant with a core-shell structure was obtained by electrostatic adsorption,and flame-retardant PLA was prepared by adding forms and polylactic acid processing molding.The flame-retardant properties,mechanical properties,and biodegradability of the flame-retardant PLA were studied.A series of studies have been conducted on the mechanism,mechanical enhancement mechanism and biodegradation mechanism.The main results are as follows:(1)The surface of the chitosan microspheres is positively charged due to the hydrolysis of the amino group.The negatively charged phytic acid(cyclohexyl alcohol phosphate PA)is adsorbed on the surface of the chitosan microspheres by electrostatic force to obtain a core-shell structure.Bio-based flame retardant(PA@CHTM).The morphology and chemical structure of PA@CHTM were characterized by scanning electron microscope(SEM)and infrared spectroscopy(FTIR).PA@CHTM and PLA are obtained by melt blending to obtain flame retardant PLA composites with different flame retardant contents.The combustion performance results show that the addition of flame retardants can improve the flame retardancy of PLA.When12wt.%PA@CHTM is added,the limit oxygen index(LOI)of the composite material increases from 20.0%of PLA to 26.6%,UL-94 The vertical combustion level reached V-2;and the maximum heat release rate(pHRR)and total heat release(THR)of the composite materials decreased by 15.7%and 12.7%,respectively.The addition of PA@CHTM improved the carbon forming ability of the material.The residual carbon electron microscope showed that the carbon layer was dense and continuous,which prevented the spread of burning droplets and played a role in the condensed phase.The addition of PA@CHTM improves the crystallization ability of PLA.When 6wt.%PA@CHTM is added,the mechanical properties of the composite are improved compared to pure PLA;the flame retardant and the matrix are better compatible in the cross-section electron microscope.The addition of PA@CHTM can accelerate the degradation of PLA,and it will also undergo morphological and structural degradation.(2)Casein(CS)and PA obtain a polyelectrolyte composite through electrostatic adsorption,and cover the surface of CHTM as a shell to obtain a ternary intumescent flame-retardant CS/PA@CHTM.The morphology and chemical structure of CS/PA@CHTM were characterized by SEM,FTIR and electronic energy spectroscopy(EDS).CS/PA@CHTM was introduced into the PLA matrix by solution blending to obtain a series of flame-retardant PLAs with different flame retardant contents.CS/PA@CHTM improves the combustion performance of PLA.The LOI of PLA/5%CS/PA@CHTM composite material reaches 23.9%and the UL-94 rating reaches V-2.The cone calorimetry shows that the pHRR is from 557 kW/m2 It decreased to 450 kW/m2,and the THR decreased from 74 MJ/m2 to 64 MJ/m2,with declines of 19.2%and 13.5%,respectively.CS/PA@CHTM promotes the formation of carbon from PLA,and the carbon layer is dense and continuous with the formation of air bubbles,and the flame retardants play a synergistic role in the gas phase and the condensed phase.CS/PA@CHTM not only acts as a nucleating agent in the crystallization process of PLA,but also promotes the segment movement,thereby improving the crystallization ability of the composite;the compatibility of the flame retardant and the matrix is good,and the tensile strength of the composite Both the Young's modulus and Young's modulus increased,but the elongation at break and impact strength decreased slightly.Composite material has excellent biodegradability.