Preparation Of Acidified Kaolin And Its Effect On The Properties Of Intumescent Flame Retardant In Ethylene-vinyl Acetate Copolymer

Ethylene vinyl acetate copolymer(EVA)is an excellent elastomer material,which is widely used in the fields of wire cable and functional films.However,it is easy to burn and generate lots of dripping and smoke during combustion,which will bring great risks to people and its property.Therefore,it is very necessary to study the flame retardant and smoke suppression of EVA materials.Recently,intumescent flame retardants(IFR)were widely used in EVA,however its development is restricted due to its high addition,low flame retardancy and poor compatibility.Therefore,using inorganic nanoparticles to synergistically flame-retardant EVA/IFR system has important research significance for further improving the flame retardancy.In this paper,the kaolinite(Kaol)was modified by surface grafting or preacidification and surface loading,which was added into EVA composites by melt blending with IFRs to obtain a synergistic flame retardant system.What's more,the flame retardant mechanism was also explored.The main research results were as follows:(1)By grafting organic acid phytic acid(PA)on the surface of Kaol obtained modified Kaol(PA-g-Kaol),which was synergistic flame retardant with IFR in EVA composites.The results showed that when 2wt%PA-g-Kaol were added to the EVA/18IFR composites,the limited oxygen index(LOI)of EVA composites was promoted to 23.7%and the drippings of the composites were also greatly reduced compared with EVA/20IFR sample.Meanwhile,the peak heat release rate(pHRR)was reduced 34.6%.Moreover,The PA-g-Kaol promoted the formation of char and improved the thermal stability for EVA composites.(2)The pre-acidified Kaol by sulfuric acid was further dealt with TiO2 loading and Zn doping to obtain Zn/TiO2@AKaol to improve the flame retardancy and smoke suppression of EVA/IFR composites.The results showed that the addition of 1wt%Zn/TiO2@AKaol improved the flame retardancy and reduced the smoke release of EVA/IFR composites.The total smoke production in the CCT test was decreased from 18.4 m2 to 13.5 m2,and in building materials smoke density test it was decreased from 63.91%to 33.39%.It was proposed that Zn/TiO2@AKaol not only promoted the production of P· in advance,but also increased a cross-linked structure char in the condensed phase to achieve flame retardancy and smoke suppression of EVA composites.(3)The "sandwich" structure of GO@TiO2@AKaol was prepared by loading graphene oxide(GO)and TiO2 on the surface of AKaol.The results showed that the LOI value was achieved 31.4%for EVA/23IFR/2GO@TiO2@AKaol composites,and it completely suppressed drippings and the vertical burning test according to UL-94 was achieved V-0 rating.Moreover,due to the introduction of GO and TiO2,the denser and more stable carbon layer was formed in the condensed phase to prevent the transfer of heat insulation and combustible gases.