Preparation And Properties Of Flame-Retardant Silane-Crosslinked Polyethylene For Cable Material

Silane cross-linked polyethylene has gradually replaced ordinary polyethylene andpolyvinyl chloride as new materials of wire and cable for its good mechanical properties, heatresistance, weather resistance and electrical insulation. However, silane cross-linkedpolyethylene is still a kind of flammable materials, which is accompanied by dropletsandleaves the flame spread while burning. Therefore, to improve the flame-retardant properties ofsilane cross-linked polyethylene is important to expand its application in wire and cableaswell as other aspects.Silane cross-linked polyethylene is generallyprepared and formed by blending silanegrafted polyethylene masterbatch (material A) with catalyst polyethylene masterbatch(material B), cross-linked by bathing inthe water with high temperature. The silane thatgrafted onto the polyethylene chain can be seemed as a reactive group.9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) is a kind of novelphosphorus-containing flame retardant and reaction intermediate, whose derivatives arewidely used as flameretardant in a variety of polymer materials, mainly the reactiveflame-retarded thermosetting polymer.In this paper, two methods were used to improve the flame-retardant properties of silanecross-linked polyethylene.A. Using the halogen flame-retardant master batch. Decabromo diphenyl ethane(DBDPE)and antimony oxide were used as flame retardant, which was blended with low-densitypolyethylene(LDPE) to prepare flame-retardant master batch. The flame-retardant silanecross-linked polyethylene was prepared by blending the material A, B with theflame-retardant master batch and bathing in the hot water. The suitable content of flameretardant in master batch was confirmed. The influence of flame retardant content on theflame-retardant properties, tensile properties, thermal stability, crystallization properties,rheological properties and crosslinking degree of silane cross-linked polyethylene wasdiscussed. The influence of anti-dripping agent on the flame-retardant properties and tensileproperties of the composite was also discussed. The results indicate as follows. The suitable content of flame retardant in the master batch is70wt%; When the content of flame retardantis24wt%, the limited oxygen index of the composite can reach29and the flammability canachieve UL-94V-0rating, while the tensile strength and elongation at break of the compositeis15.2MPa and115%, respectively, decreased by5.6%and20%compared to the origin; Theflame-retardant master batch slightly increases the crosslinking degree of silane cross-linkedpolyethylene, has little influence on its crystallization properties and postpones thepre-crosslinking between material A and B while blending; The anti-dripping agent combinedwith the master batch makes the flame-retardant properties of the composite decrease on thecontrary.B. Using the non-halogen reactive flame retardant. Two kinds of DOPO derivatives,ODOPM with hydroxyl and DA25with alkoxysilane, were synthesized. The chemicalstructure of the DOPO derivatives was characterized by Fourier transform infraredspectrometer(FTIR) and nuclear magnetic resonance spectrum(1H-NMR,13C-NMR,31P-NMR). The reactive flame-retardant silane cross-linked polyethylene was prepared byblending DA25or ODOPM with material A and B, respectively, and bathing in the hot water.The influence of DOPO derivatives on the flame-retardant properties, tensile properties andthermal stability of the composites was discussed. It shows that when30wt%ODOPM isadded in silane cross-linked polyethylene the limited oxygen index of the composite increasesfrom19to25and the flammability achieves UL-94V-0rating. While30wt%DA25cannotmake the composite flame-retarded. Both two DOPO derivativescause the tensile propertiesof composite greatly decline and the thermal stability slightly decline. The influence ofODOPM on the crosslinking degree, crystallinity and dynamic mechanical properties of thecomposite was studied. The flame-retardant mechanism of ODOPM to the silane cross-linkedpolyethylene was also simply analyzed. The test shows that the crosslinking degree of thecomposite decreasesand the crystallinity increasesas the content of ODOPM rises to30wt%.It can be inferred through DMA that the dehydration between ODOPM and silane occursbefore water bathing, and then ODOPM is dissociated as time goes by. The TG-FTIRindicates that ODOPM shows gas-phase flame-retardant mechanism.