Study On Preparation And Performance Of Low-smoke Halogen-free Flame Retardant Vinyl Polymer Materials

Wires and cables are important equipment for transmitting electrical energy,transmitting information and manufacturing various equipment.The wire and cable industry is an important supporting industry for our country's economic construction and is widely used in energy,transportation,information,petrochemical and other fields.Due to the special working environment,if short circuit,overload and other problems occur during use,it is easy to cause the wire and cable to overheat,which may cause the sheath material to burn and cause a fire.Improving the flame-retardant performance of wire and cable sheathing materials is a necessary condition to ensure the safety of people's lives and property and economic development.The research of efficient,safe,and environmentally friendly flame-retardant wire and cable materials has always been a common technical concern in the field of wire and cable.Vinyl polymers(such as polyethylene,ethylene-vinyl acetate copolymer,etc.)are widely used as sheath materials for wires and cables due to their excellent comprehensive properties,but because of their chemical composition,they have high flammability.This paper developed a series of ethylene-vinyl acetate copolymer(EVA)/linear low-density polyethylene(LLDPE)-based low-smoke halogen-free flame-retardant polyolefin material for use in wire and cable sheathing materials.At the same time,the effects of main flame retardants,synergistic flame retardants and processing methods on their comprehensive performance are also studied.First of all,this article has developed two flame retardant vinyl polymer flame retardant materials of aluminum hydroxide(ATH)/magnesium hydroxide(MH)and aluminum hydroxide/mixture of huntite and hydromagnesite(HH).The effects of the type and ratio of the main flame retardant on the mechanical,thermodynamic and flame retardant properties of the two flame retardant materials are studied.The study found that with the increase in the content of the mixture of magnesium hydroxide and the huntite and hydromagnesite,the mechanical properties and thermal stability of the two flame-retardant materials have been improved;meanwhile,the flame retardant performance test of flame retardant materials shows that there is a synergistic effect between ATH and MH/HH flame retardants.When the total amount of flame retardant added is 150 phr,and the filling ratio of ATH to MH and HH is 1:1 and 1:3,respectively,the synergistic flame retardant effect of flame retardant materials is the best.At this time,the limiting oxygen index of the flame-retardant material is relatively high,and the UL-94 level has reached the V-1 level.Subsequently,this article uses magnesium hydroxide sulfate hydrate(MHSH)whiskers as a synergistic flame retardant for flame-retardant composite materials,and studies the effects of two processing methods on flame-retardant materials by twin-screw extruder and twin eccentric rotor extruder.The study found that the comprehensive performance of the flame retardant material prepared by the twin eccentric rotor extruder was significantly enhanced.When the content of MHSH whiskers reached 30 phr,the tensile strength of the composite material reached 13.37 MPa,and the limiting oxygen index reached 37.9%,and UL-94 rating reaches V-0 level.The results prove that MHSH whiskers still maintain a fibrous structure after burning,which can strengthen the carbon residue.Meanwhile,for the one-dimensional structure of MHSH whiskers,the tensile flow field of the twin eccentric rotor extruder can better disperse it in the polymer matrix and retain its fibrous structure,thereby enhancing the synergistic flame retardant ability of MHSH whiskers.Afterwards,this article also uses organic montmorillonite(OMMT)as a synergistic flame retardant for flame-retardant composite materials,and uses twin-screw extruder and twin eccentric rotor extruder to prepare ATH/MH/OMMT composite materials.Comparing the performance of materials prepared by the two kinds of processing equipment,it is found that the twin eccentric rotor extruder can effectively reduce the amount of OMMT and improve its synergistic flame-retardant efficiency.Data shows when only adding 7.5 phr of OMMT,the composite material can reach a LOI of 38.5%,and the UL-94 rating can reach V-0.According to the scanning electron microscopes of the combustion residues and the X-ray diffraction results of the composite materials,OMMT will form a special lamellar structure after burning,this structure can effectively hinder the exchange of materials and energy inside and outside the carbon residue;at the same time,under the action of the stretching flow field brought by the biaxial eccentric rotor extruder,OMMT has peeling and intercalation in the polymer matrix,which is of great help to improve the flame retardant properties of composite materials.