Preparation Of LDPE/SEBS Crosslinked Cable Material And Study On Halogen-free Flame Retardant Modification

With the development of national industrialization,China's electric power related industries continue to develop and grow,the position of wire and cable are increasingly prominent,the demand continues to expand.Low density polyethylene(LDPE)and styrene-ethylene-butylene-styrene block copolymerization(SEBS)are important raw materials for wire and cable.Combined with the properties and structural characteristics of LDPE and SEBS materials,both materials are melt-blended together by a mixer,and the obtained LDPE/SEBS composite material is used as the cable base material.In order to prepare cables in line with industry standards,the LDPE/SEBS composite was crosslinked by bis(1-(tert-butylperoxy)-1-methylethyl)-benzene(BIBP)and flame retarded by halogen-free flame retardants.In summary,this paper focuses on the following three aspects:(1)Study on Processing and Properties of LDPE/SEBS CompositesThe LDPE/SEBS composite was prepared by melt-blending method in an internal mixer with a total of 100 parts of LDPE/SEBS as cable base materials.The mechanical properties,retention rate of mechanical properties after thermo-oxidative aging,processing technology,melt index,thermal properties and microstructure of the composite materials with different amounts of SEBS were studied.The study found that when the amount of SEBS was 50 parts,the tensile strength of the composite was 21.37 MPa,and the elongation at fracture was 685.82%,and the mechanical properties reached a better value.After thermal and oxygen aging,the tensile strength retention rate of the composite was 91.36%,and the elongation at fracture retention rate was 96.38%,and the mechanical properties retention rate reached the maximum.The mechanical properties of LDPE/SEBS(50/50)composites was the best when the internal mixer temperature was 180? and the mixing time was 10 min.The melt index,crystallization temperature,melting temperature and melt enthalpy decrease with the increase of SEBS content.It can be seen from the electron microscope photos that with the increase of SEBS content,partial SEBS in LDPE gradually changes from "flaky" to small particles,and another part of SESB always penetrates with LDPE,showing an interpenetrating network structure.(2)Study on BIBP Crosslinking Modified LDPE/SEBS CompositesBIBP was used as a cross-linking agent,and the cross-linked modified LDPE/SEBS composites were prepared by an internal mixer and an open mixer.At the same time,the effects of BIBP on mechanical properties,microstructure,gel content,thermal properties,crystal content and rheological properties of LDPE/SEBS/BIBP(50/50/0.9)composite was investigated.The study found that the mechanical properties of the composite reached the best after adding 0.9 phr of BIBP,with tensile strength of 26.22 MPa and elongation at fracture of 732.27%.It can be seen from the electron microscope photos that with the increase of addition of BIBP,the interfacial compatibility of LDPE and SEBS is improved,the interpenetrating network structure gradually disappears,and the two gradually combine into a whole.In the gel content test,it was found that the gel content of the composite increased rapidly from 0 to 79.24%after adding 0.3 phr BIBP,but the increase rate of gel content slowed down after continuing to add BIBP.In addition,with the increase of BIBP addition,the viscosity value and storage modulus of the composites increase,and the crystallization temperature,melting temperature,melting enthalpy,crystallinity and loss modulus of the composites decrease.(3)Study on Halogen-free Flame Retardant LDPE/SEBS CompositesThe flame retardant formulation was designed with magnesium hydroxide(MH)as the main flame retardant and hydrotalcites(LDHs),microencapsulated red phosphorus(MRP)and organic montmorillonite(OMMT)as synergistic flame retardants.The effects of different flame retardant formulations on composite oxygen index,flame retardant grade and mechanical properties were investigated by orthogonal experiments.Then,the effects of maleic anhydride grafted polyethylene(PE-g-MAH)on the mechanical properties of the composites and the effects of synergistic flame retardant on the thermal stability,thermal properties,rheological properties,dielectric properties and carbon layer morphology of the composites were studied.Finally,the cable standard data were compared with the measured data.The optimal flame retardant formula was determined by orthogonal experiment,that is,45 phr of MH,20 phr of LDHs,8 phr of MRP,10 or 14 phr of OMMT.The maximum elongation at fracture reaches 294.77%when 6 phr of PE-g-MAH are added.It can be seen from the electron microscope photos that the addition of the synergistic flame retardant can make the carbon layer of the composite more compact,and the large "carbon block" will gradually change into small particles.With the addition of synergistic flame retardants,the carbon residue,viscosity,storage modulus,loss modulus and dielectric constant of the composites increase,while the thermal weight loss rate,crystallization temperature,melting temperature,melting enthalpy and dielectric loss of the composites decrease.By comparing the measured data and standard data of cable materials,it can be seen that the performance of cable materials has met the enterprise's standards.