Preparation And Properties Study On Conductive Flame Retardant Poly Lactic Acid Composites

Poly lactic acid（PLA）is one of the important biodegradable aliphatic thermoplastic polyester,and has a broad commercial application prospect and is receiving increasing attention.However,PLA is an insulating material that is extremely flammable,and is severely limited in the fields of household appliances,transportation,and electronic industry.Solving this problem is extremely urgent.In this paper,Graphene（GR）as a conductive filler to prepare conductivity modified PLA,and then mixed with polyphenoxy diphenyl phosphate（PBPP）/melamine（Mel）to prepare flame retardancy modified PLA.The GR mixed poly（2-10-hydrogen-9-oxa-phosphaphenanthrene hydroquinone phenyl phosphate）（POPP）to prepare flame retardancy modified PLA.The synergistic effects of conductive filler and flame retardants on the electrical conductivity,flame retardancy,thermal stability,and enhancement mechanism of electrical conductivity and flame retardancy of PLA were studied.The main tests results and analysis as follows:Firstly,Graphene is added to the PLA matrix,and electrical conductivity PLA composites are prepared by two different methods,namely,melt blending hot-compression method and slurry method,to improve the electrical conductivity of PLA.Graphene as a conductive filler effectively improves the electrical conductivity of PLA composites,and the electrical conductivity of composites added with 4wt%GR is1.340×10^-4S/m.By adding GR/PBPP and GR/PBPP/Mel synergistically to PLA,and preparing PLA composites by melt blending hot-compression method,the electrical conductivity and flame retardancy of the composites are significantly improved compared to pure PLA.However,the synergistic effect of electrical conductivity and flame retardance of GR/PBPP system is better than GR/PBPP/Mel system.GR and POPP are synergistically modified to PLA materials by melt blending hot-compression method.The results show that the addition of conductive fillers can significantly improve the electrical conductivity of PLA composites,and the physical barrier effect formed by the synergy of GR and POPP significantly improves the flame retardancy and thermal stability of PLA composites.The electrical conductivity of the GR/POPP composite is up to 1.688×10^-4 S/m,with LOI value of 36.5%,and it reaches a UL-94 V-0 rating.Compared with pure PLA,the smoke production rate（SPR）and total smoke production（TSP）of GR/POPP-6composites decreased by 55%and 46.67%,respectively,inhibiting the release of smoke and improving the fire safety of PLA to a certain extent.The results of char residues after cone calorimeter and thermal degradation behavior analysis reveal that the unique network structure of GR enables PLA composites to have excellent electrical conductivity and flame retardancy at the same time,and the enhancement mechanism lies in the synergistic effect of gas phase and condensed phase.In order to compare with electrical conductivity of PLA composites,the highest electrical conductivity of PLA/GR composites were prepared by slurry method is 0.239 S/m.In order to improve the flame retardancy of PLA composites,Graphene and PBPP/Mel were added to the PLA matrix to improve its flame retardancy.When a certain proportion is added,there is a synergistic effect to improve the flame retardancy and thermal stability of PLA.The electrical conductivity of the PLA/GR-PBPP composite prepared by the slurry method is up to2.725×10^-4S/m,GR/PBPP/Mel composite has a maximum electrical conductivity of 3.186×10^-4S/m,with the vertical burning test（UL-94）of V-0 and the limiting oxygen index（LOI）of 28.2%.Compared with pure PLA,the T_5%,T_10%,and T_50%of GR/PBPP/Mel-20 composite are 298℃,322℃and 373℃,respectively,which are lower than pure PLA by40℃,36℃and 10℃.The char residues of PLA/GR-PBPP6composite significantly increased from 0 to 20.37%at 600℃,effectively promoting the carbon formation effect of PLA composites,increasing their carbon residue,and effectively improving the thermal stability of PLA materials.Adding GR and PBPP/Mel to the PLA matrix,using melt blending hot-compression method and slurry method to prepare PLA composites,and using melt blending hot-compression method to blend graphene and POPP cannot improve its electrical conductivity very well.Preparation of GR/POPP composites by slurry method,that modified of PLA with electrical conductivity and flame retardant properties.When a certain amount of GR/POPP is added,the cross-linking of GR and PLA forms a good network structure,to transform the PLA composites from an insulating to conductive material,and the maximum electrical conductivity of its composite reaches 45.91 S/m.At the same time,the PLA/GR-POPP composites have a LOI value of up to 33.1%,and it reaches a UL-94 V-0 rating.Due to the layered morphology of GR,it acts as a barrier to gaseous and volatile products after degradation.The barrier effect of GR promotes the generation of more char residues in the PLA by GR/POPP,isolating the transfer of oxygen and heat,inhibiting the release of smoke,and effectively improving its flame retardancy and smoke suppression.Besides,the addition of GR/POPP effectively improves the carbon forming ability and graphitization degree of its composites,forming a more dense carbon layer structure with a physical barrier effect,playing a synergistic effect in the condensed and gaseous phases,and improving the fire safety of PLA composites.In summary,the slurry methods bring GR/POPP into the PLA matrix.When 20wt%GR/POPP is added,the electrical conductivity of the composites can reach up to 45.91 S/m.The LOI value of PLA/GR-POPP composite material has been increased from 16.3%of pure PLA to 33.1%,it reaches a UL-94 V-0 rating,and effectively improve the carbon forming ability and graphitization degree of its composite,thereby improving the electrical conductivity and flame retardancy of PLA material.