六苯氧基环三磷腈的热解及其对环氧树脂的阻燃机理

采用极限氧指数仪和锥形量热仪测试了以六苯氧基环三磷腈(HPCP)阻燃环氧树脂的燃烧性能,结果显示,与纯环氧树脂相比,阻燃环氧树脂的极限氧指数值(LOI)明显提高、热释放速率峰值(pk-HRR)和总热释放量(THR)明显下降、环氧树脂的点燃时间提前以及分解速度加快.采用热失重(TGA)、热重红外联用(TGA-FTIR)、X射线光电子能谱(XPS)和热裂解气相色谱质谱联用(Py-GC/MS)研究了HPCP及其阻燃环氧树脂的热解路线和阻燃机理.结果表明,在阻燃环氧树脂过程中,一方面,HPCP分子中的苯氧基团首先解离并发生歧化反应,由此产生的苯氧基及其歧化产物的焠灭效应在环氧树脂中发挥气相阻燃作用,剩余的磷腈环和苯环基团会进一步裂解产生小分子碎片;另一方面,环氧树脂基体在HPCP的作用下提前分解,产生了基于双酚A结构的大分子碎片并在HPCP裂解产物作用下加速炭化,从而使更多的基体组分以残炭的形式被固定在凝聚相中,提高了阻燃环氧树脂的残炭产率,发挥了凝聚相阻燃作用.

Pyrolysis of hexa-phenoxyl-cyclophosphazene and its flame retardant mechanism to epoxy resin

The flame retardant properties of the epoxy resin thermosets incorporated with hexa-phenoxyl-cyclophosphazene （HPCP） were investigated via limited oxygen index （LOI） and cone calorimeter. The results show that the LOI value increased, the peak of heat release rate （pk-HRR） and total heat release （THR） decreased, the time to ignition are shortened, the temperature of onset degradation are reduced and the pyrolysis velocity of HPCP/EP thermoset are accelerated compared with that of pure epoxy resin thermoset. The pyrolysis route and mechanism of HPCP and the epoxy resin thermoset were explored via analysis of the thermogravimetric analysis （TGA）, the real time fourier transform infrared spectra （FTIR）, TGA/infrared spectrometry （TGA-FTIR）, X-ray photoelectron spectroscopy （XPS） and pyrolysis-gas chromatography mass/spectrometry （Py-GC/MS）. The pyrolysis route of HPCP is that the phenoxyl fragments were dissociated from HPCP firstly, then carded on a disproportionation reaction and subsequently the cyclotriphosphazene and benzene ring from HPCP were pyrolyzed to some smaller fragments. Meanwhile, the flame-retardant epoxy resin thermoset was decomposed earlier under the existence of HPCP and the decomposed fragments interacted with the fragments from HPCP and then the more char was produced. Therefore, the phenoxyl free radical and its disproportionated products exert the gaseous-phase flame-retardant effect and the promotion on charring of matrix implies the condensed-phase flame-retardant effect.