Synthesis And Flame Retardancy Of Siloxane Functionalized Polyethylene

Polyethylene（PE）is the most widely used polymer material.However,polyethylene contains only C and H elements,and its high flammability limits its application in many fields.Silicon flame retardants have the characteristics of high thermal stability,low toxicity and environmental friendliness,and can produce a layer of insulation and protection to inhibit the spread of fire during combustion so as to achieve the purpose of flame retardant.In this paper,two simple synthetic routes of siloxane functionalized polyethylene were designed to effectively improve the flame retardant performance of polyethylene material.The grafted siloxane could not only replace the inorganic silicon filler in the traditional blending flame retardant system and solve the compatibility problem between the polyethylene matrix and inorganic filler,but also showed the synergistic flame retardant effect with magnesium hydroxide（MH）and expandable graphite（EG）in the condensation phase,which rendered the polyethylene composite with excellent flame retardant performance.The specific research contents are as follows:（1）A synthesis method of siloxane functionalized polyethylene was designed by coordination polymerization method.First,chlorosilane graft PE was synthesized by the coordination copolymerization of ethylene with chlorosilane alkyl group（F₁ or F₂）over a typical Ziegler-Natta catalyst.Then,at the end of polymerization,hydroxyl silicone oil（DMS）was immediately added and chlorosilane PE was grafted with efficient reaction to achieve the purpose of DMS grafting.Finally,siloxane functionalized PE with adjustable DMS content ranging from 0.03 to 0.58 mol%was successfully synthesized.By TGA test,siloxane functionalized PE can produce 1.9-20.8 wt%residue at 650℃.The effect of siloxane functionalization on the combustion behavior of PE composites was studied by cone calorimeter（CCT）.After adding siloxane to graft PE,the morphology of combustion residue of LDPE composites changed greatly compared with that of ordinary blends.The grafted DMS in-situ generated 50-100 nm nano-sized silica particles,which adhered uniformly to the surface and edge of the Mg O crystal plate and bonded with amorphous carbon to form a dense carbon layer,which could provide protection for the underlying material.（2）A more simple and convenient synthesis method of siloxane functionalized polyethylene was designed by using the reaction processing method.Using commercial polyethylene,vinyl trichlorosilane（VTC）,DMS as raw materials,using free radical grafting method,directly in the process of polyethylene melting modification.By adjusting the amount of VTC monomer and DMS,siloxane graft PE with adjustable DMS content ranging from 0.21to 0.66 mol%could be obtained.By TGA test,siloxane functionalized PE can produce residues of 1.4～7.0 wt%at 650℃.The siloxane functionalized PE was blended with LDPE/MH/EG to make the composite.After CCT combustion test,it was found that after adding siloxane functionalized PE,the THR value of LDPE composite decreased slightly,LOI increased and the structure of carbon layer changed greatly.Different from polymerization,the particle size of nano-silica generated after combustion of functionalized PE obtained by reaction processing method is 10-20 nm,and the silicon-carbon protective layer with a certain rigid and porous skeleton structure can be formed together with Mg O and EG,which can inhibit droplet generation.The results show that there is an excellent synergistic flame retardant effect between siloxane functionalized polyethylene and flame retardant MH and EG.