Surface Modification Of Magnesium Hydroxide Flame Retardant And Its Optimization Application In Ethylene-Vinyl Acetate Copolymer Resin

Wires and cables are widely used in modern society,from aerospace,industrial production and transportation to home lighting,and their use occasions are complex and diverse.Wires and cables are made up of a metal core and polyolefin resins covered in an outer layer,the main base resins being polyethylene(PE),polypropylene(PP)and ethylene vinyl acetate copolymer(EVA).Such matrix resins,like most polymers,suffer from high flammability,heat and smoke emissions,and some emit toxic gases,limiting their applications.In order to expand the application of polyolefin materials,flame retardants are usually added to modify polyolefin cable materials to give them good flame retardant properties.Inorganic flame retardant magnesium hydroxide has become one of the most commonly used flame retardants for polyolefin cable materials because of its low cost,green environment and excellent smoke suppression effect.However,the surface of magnesium hydroxide flame retardant(MH)has a high surface energy and strong hydrophilic,easy to agglomerate within the lipophilic polymer,and its compatibility with the substrate is poor,the direct application effect is not ideal.In particular,EVA for wire and cable industry requires a MH mass fraction of 60%or more to meet its flame retardant needs,the use of this filler volume leads to a decline in the mechanical properties and processing properties of EVA resin.Therefore,in order to solve this problem,this study used surface modification methods for MH to alleviate the trend of deterioration of mechanical and processing properties of EVA resins filled with high amounts of MH.The main details of this paper are as follows:(1)Oleic acid(OA)and dodecyltrimethoxysilane coupling agent(KBM3103)were used as modifiers to prepare a modified magnesium hydroxide flame retardant(ZF-83-D)compounded with KBM3103 organosilane coupling agent through a dry modification process.The water contact angle results showed that the water contact angle of ZF-83-D was 55.67°,with some decrease in hydrophilicity.MH.5wt%vinyltriethoxysilane coupling agent(A151)and MH,ZF-83-D were filled into EVA resin to prepare MH-filled EVA resin and EVA resin filled with modified MH respectively.Dispersibility evaluation experiments,SEM images and dynamic mechanical thermal analysis showed that the modified MH could effectively enhance the dispersion of MH in EVA resin and improve its compatibility with the substrate.When the MH filling amount reached 60%by mass fraction,the overall performance of EVA resin filled with modified MH was improved in comparison with that of MH-filled EVA resin.The equilibrium torque of EVA resin filled with 5wt%A151 and MH(oxygen index 35.6%)and EVA resin filled with ZF-83-D(oxygen index 37.0%)were reduced by 0.3N·m and 0.7N·m,and the tensile strength was improved by 20.89%and 24.06%,respectively,while maintaining better flame retardant properties.(2)The modified magnesium hydroxide flame retardant(SPUA-MH)with polyurea resin as the wall material and MH as the core material was synthesized by in situ polymerization method using MH,deionized water and toluene-2,4-diisocyanate as raw materials.The results of Fourier transform infrared spectrometry tests,scanning electron microscopy results,energy dispersive X-ray spectrometry results and transmission electron microscopy results showed that SPUA-MH was successfully prepared by in situ polymerisation with a water contact angle of 93.05° and the surface changed from hydrophilic to hydrophobic.X-ray photoelectron spectroscopy results showed that the polyurea resin on the surface of SPUA-MH was bonded to the hydroxyl groups on the surface of MH in a carbamate bond.Ball milling of SPUA-MH revealed that the polyurea resin on the surface of SPUA-MH was well maintained,indicating that the carbamate bond formed between the polyurea and the hydroxyl groups on the surface of MH was relatively stable and therefore the mechanical forces had less effect on the modified MH during the subsequent processing.(3)SPUA-MH was filled into EVA resin to prepare SPUA-MH filled EVA resin.The results of dispersion evaluation experiments,SEM results and DMA tests showed that the dispersion of SPUA-MH in EVA resin and its compatibility with EVA resin were better.When the MH filling amount reached 60%by mass fraction,the overall performance of the EVA resin filled with SPUA-MH was improved in comparison with the EVA resin filled with MH.While maintaining a high level of flame retardancy,the equilibrium torque of SPUAMH-filled EVA resin(oxygen index 38.0%)was 13.1N·m,a decrease of 2.6N·m;the maximum thermal weight loss temperature of the third decomposition stage was 484.55℃,an increase of 14.66℃,and the residual mass fraction after thermal decomposition increased by 1.66 wt%;the tensile strength was 8.07 MPa,an increase of 50.56%.