Synthesis And Properties Of A Novel Boron-containing Phosphonate Flame-retardant And Its Fire-retardance For SEBS-bssed Thermoplastic Elastomers

Styrene-ethylene/butylene-styrene block copolymer (SEBS) is an excellent thermoplasticelastomer material with comprehensive performance, the investigations involved SEBSmodified by rubber extender oils are drawing more and more attentions.However, the range ofapplications of SEBS and its blends are restricted by their flammability. halogenated flameretardants were widely used in SEBS, but the release of toxic gases in the combustion causegreat harm to the environment, facing the fate of being replaced. Halogen-free flame-retardantpolymer materials producing non-toxic and low smoke during burning have became a trendfor environmental protection requirements. Magnesium hydroxide [Mg (OH)2, MH] has beenone of existing commercial flame retardants due to the good smoke suppression, loading andlow cost. But the efficiency is low when MH is used as a single flame retardant, usually needmore than65%in order to achieve UL94V-0rating, and has poor compatibility with thethermoplastic elastomer because of the surface polarity, resulting in the sharp decline of theprocessability and mechanical properties of the flame retardant material.In this paper, the intermediate product of boron phenolic resin (FB)was synthesized bysalicylaldehyde alcohol and boric acid, then FB and BPOD occured dehydrochlorination, andfinally capped with phenol, at last get a new boron-containing phenyl phosphonic ester flameretardants BPP; the optimal synthesis conditions of BPP were: The ratio of FB, phenylDichlorine and triethylamine as acid binding agent is1:2:2, the toluene solution of FB andtriethylamine were joined in the four flask, toluene solution of phenyl Dichlorine through theconstant pressure dropping funnel slow titration flask, finished in2h, refluxing for10h, thereaction temperature at room temperature, and finally got the BPP with phenol terminated.FTIR, NMR proved the successful synthesis of the BPP, the thermal stability and meltingtemperature of BPP were evaluated by TG and DSC. The results showed that the initialdecomposition temperature of BPP in nitrogen is219°C, the melting temperature is77.1℃.The blends of SEBS modified by Paraffin oil (O-SEBS) as matrix, BPP as flameretardants, the mixtures of O-SEBS and BPP were processed in a twin-screw extruder.Theeffects of BPP content on the combustion was studied. Scanning electron microscopy (SEM)and thermal gravimetric analysis (TGA) test were used to investigate the fire retardantmechanism. The results showed that the BPP can significantly contribute to the charring effect,but when BPP added to40wt%, the total carbon residue is still less, and the carbon layer is notenough dense, so there is no apparent flame-retardance effect to O-SEBS.MH and BPP as Retardants of O-SEBS, the effect of MH and BPP content on the combustion performance、thermal stability and mechanical were studied; the synergistic flameretardant mechanism of MH and BPP was investigated by scanning electron microscopy(SEM) and thermal gravimetric analysis (TGA). The results showed that58wt%MH and5wt%BPP was required to make the complexes achieve UL94V-0rating. Its tensile strength,elongation at break, tear strength and Shore hardness are5.04Mpa、278%、25.7kN/m and71,compared with and thecomposites filled with65wt%MH which reached UL94V-0rating,thetensile strength, tear strength were increased by460%,73.6%, while the hardness decreasedby5.The BPP has good synergistic effects, it can increase the oxygen index and char yield ofthe system, by shortening the burning time of the compound to reduce the total heat release ofthe system,and the gas and condensation mechanism play a role together.To keep the total flame retardants for65wt%,5wt%BPP、 RDP and BDP replaced thesame amount MH, the combustion performance、thermal stability and mechanical werestudied.The results showed that, complex with BDP and RDP can not achieve UL94rating,complex with BPP can achieve UL94V-0rating; the combustion of the complex and theintensity of complex from largest to smallest are RDP、BPP、BDP.Combined with TGA analysis, precisely because of the release of more decompositionproducts of BPP increased the combustion risk, the gas mechanismof BPP is dominant. WhenBPP、RDP and BDP instead of part of the MH complex, the complex mechanical propertieswere improved.