Toughening And Organic/Inorganic Hybrid Halogen-free Flame Retardant Modification Of Polyethylene Used For Optical Cable Sheath Materials

High-density polyethylene(HDPE)is often used as the outer protective layer(sheath material)of fiber optic cables due to its excellent dielectric,corrosion resistance and mechanical properties.However,the high modulus of HDPE and the poor thermal strength of the shielding layer of metal plastic composite belt lead to the slippage under the action of external force,which affects the pavement and service life.On the other hand,HDPE is flammable,which will cause secondary fire,so it must be modified.However,the traditional halogen-free flame retardants can not be widely used because of the toxic gases released by combustion,while the halogen-free flame retardants have the problems of poor compatibility with the matrix resin,large amount of sacrificing material mechanical properties and so on.In this paper,linear low density polyethylene(LLDPE)and metallocene linear low density polyethylene(m-LLDPE)with excellent flexibility,which are similar to HDPE,are selected to toughen and modify HDPE for directly buried or pipeline fiber optic cable sheathing materials.HDPE/LLDPE and HDPE/m-LLDPE series blends are prepared through melt blending.The sealing strength between HDPE/LLDPE,HDPE/m-LLDPE blends,MDPE and aluminum-plastic tape,as well as the mechanical properties,relaxation behavior and compatibility between the components of the blends were studied by dynamic rheological analysis,differential scanning calorimeter,small angle X-ray diffraction(SAXS)and contact angle test etc.The results show that the comprehensive properties of HDPE/LLDPE blends are better than that of HDPE/m-LLDPE.With the increase of LLDPE content,the tensile strength and modulus of HDPE/LLDPE decrease,and the elongation at break increases.And the HDPE/LLDPE(70:30)blends(A70)has the best compatibility,the most overlapping of the molecular interface,and the best adhesion with the aluminum plastic strip interface.The tensile strength,elongation at break,modulus of elasticity of A70 and the heat-sealing strength of its aluminum plastic strip are 26.3 MPa,1057%,442 MPa and 27.2 N/cm,respectively,which are superior to the MDPE used by the current enterprises.For the sheathing material of overhead or high-level fiber optic cable,polyethylene glycol(PEG)is used as the surfactant of aluminum hydroxide(ATH),aluminum trihydroxide(ATH)core composites with a styrene-ethylene-butadiene-styrene block copolymer grafted with maleic anhydride(MAH-g-SEBS)shell phase,and P-N flame retardant as a synergistic agent,were prepared through an interface design,The product was then blended with HDPE.The effects of PEG content,core-shell structure on the interfacial interaction,flame retardant properties and mechanical properties of composite materials were studied by dynamic rheological analysis,microscale combustion calorimetry,and limiting oxygen index(LOI)etc.The results show that the toughness of HDPE/ATH/PEG(3%)/MAH-g-SEBS/P-N(abbreviated as HDPE/MH3/M-g-S/P-N)is significantly improved,and the elongation at break is increased from 21% to 558% compared to HDPE/ATH.At the same time,HDPE/MH3/M-g-S/P-N showed excellent flame retardant performance,the LOI increased from 17.5% to 27.5%,and total heat release per unit mass(THR)decreased from 45.6 kJ/g to 26.7 kJ/g.Compared with HDPE/ATH,the increase of the thickness of HDPE/MH3/M-g-S/P-N interface layer shows that ATH has good compatibility between polymer matrix and high strength of interface bonding layer,which is conducive to polymer carbon formation and effectively improves resin Flame retardant properties.