Investigation Of Synergistic Flame Retardant And Smoke Suppression For EVA/PAPP System

Ethylene vinyl acetates（EVA）were widely used in the fields of wire and cable and automotive interiors due to excellent chemical resistance and easy processing.However,EVA was easily flammable and generated massive smoke during combustion which restricted the application.Therefore,it was essential to improve the flame retardant and smoke suppression properties of EVA composite.Intumescent flame retardants（IFR）exhibited positive flame retardant properties for EVA,but the flame retardant efficiency and smoke suppression properties should be improved.Piperazine pyrophosphate（PAPP）possessed high phosphorus content and excellent self-carbon formation performance.Meanwhile,suitable fire retardant co-efficient were selected to effectively enhance the fire safety performance of EVA,which was of important scientific significance and practical application value for the preparation of high-performance flame retardant EVA materials.The inorganic synergist contributed to the enhancement of the carbon layer,while the Boehmite（BM）decomposed during the heating process to release non-combustible gases.Therefore,in this thesis,BM was firstly selected as a synergist and then mixed in a certain mass ratio with PAPP for EVA flame retardant modification.When 17 wt%PAPP was added,EVA composites passed UL-94 V-1 grade during vertical combustion test with a limiting oxygen index（LOI）of 26.9%.When PAPP was mixed with BM at a mass ratio of 95:5 with 17wt%loading,the EVA/PAPP/BM achieved UL-94 V-0 rating with a LOI value of 28.2%.Cone calorimetry tests showed that the total heat release（THR）and total smoke production（TSP）of EVA/PAPP/BM composites decreased from 132.8 MJ·m^-2 and 11.5 m² for EVA/PAPP to 122.6MJ·m^-2 and 9.9 m²,respectively.It indicated that the addition of BM improved the flame retardant efficiency of EVA composites and reduced the amount of heat and smoke released during the combustion.BM was an inorganic filler.In order to improve the dispersion and compatibility of the synergists in EVA matrix,the organic-inorganic polymer polycarbonate silane（PCS）was selected as a synergist and formulated with PAPP for the flame retarding of EVA.When the mass ratio of PAPP:PCS was 95:5 and the total addition was 17 wt%,the material passed UL-94 V-0 grade with a LOI value of 29.3%.The THR and TSP values of the EVA/PAPP/PCS composites were reduced by 19.1%and 19.3%,compared with EVA/PAPP,and the maximum smoke density was reduced by 17.6%.The thermogravimetric-infrared test indicated that the gas phase products of EVA/PAPP/PCS composites during pyrolysis process were significantly reduced,and the addition of PCS promoted the formation of a denser and more high-strength carbon layer of PAPP during the combustion,which exhibited a superior barrier effect and further improved the flame-retardant and smoke-suppression properties of EVA.It was difficult to combine PCS with PAPP uniformly due to its small specific surface area and high packing density,which influenced the synergistic flame retarded effect to some extent.Metal organic framework（MOF）was used for flame retardant polymers with high specific surface area,excellent compatibility with polymers and catalytic carbon formation by metal ions.In this paper,metal organic framework containing cerium ions（Ce-MOF）was synthesized and used for the synergistic flame retardancy of EVA/PAPP systems.When PAPP:Ce-MOF=97:3 were mixed,the residual carbon at 800 ^oC increased by 49.7%compared with PAPP added alone.When the total addition was 17 wt%,the composite passed UL-94 V-0grade with a high LOI value of 31.3%.Compared with PAPP added alone,the EVA/PAPP/Ce-MOF composite exhibited a significantly higher self-extinguishing ability,and the values of THR and TSP decreased by 25.6%and 36.5%,respectively.According to X-ray photoelectron spectroscopy（XPS）test of the char layer,the phosphoric acid and polyphosphate produced by the decomposition of PAPP cross-linked with the cerium ions of Ce-MOF,which left phosphate with higher thermal stability in the condensed phase.A high quality intumescent char layer was formed,which effectively inhibited the emission of smoke and combustible gases to improve the fire safety performance of the EVA composites.