聚硅氧烷改性环氧/酚醛共混物热氧降解残留物的结构及组分演变

Structure and Composition Evolution of Polysiloxane Modified Epoxy/Phenolic Blends Under the Condition of Hot Oxygen

硅氧烷改性环氧/酚醛共混体系具有良好耐热性及韧性,研究其受热后结构及组分变化对于拓宽酚醛高温领域应用具有重要意义。以端羟基聚二甲基硅氧烷(HTPDMS)与环氧树脂缩合制得改性环氧(ES),再与酚醛共混改性获得聚硅氧烷改性环氧/酚醛共混物(ES/PF)。通过综合热分析(TGA-DSC)、傅里叶变换红外光谱(FT-IR)、扫描电镜附加能谱仪(SEM-EDS)、X射线光电子能谱(XPS)等手段研究了ES/PF的热性能和热氧降解残留物的化学结构及组分。热分析结果表明,与纯酚醛相比,ES/PF在空气中800℃残余率提高438%,且最大放热速率从21.98 m W/mg降至14.93 mW/mg,N2中残余率降低了14.3%;结合红外分析,ES/PF在430~600℃时热解形成Si-Ox杂化结构对形成炭层起稳定作用,可提高残碳率;XPS及EDS揭示硅元素在高温下赋存形态发生明显变化,430℃及以上大多转为SiO和SiO·nHO。以上结果说明热氧条件下硅元素提高酚醛残炭量对酚醛热稳定性有积极影响,N2条件下硅元素的上述有益影响受到一定程度抑制;这可能与硅氧烷基团热解具有吸氧机制有关;ES/PF的热解残留物结构及组分有利于提高材料的高温残余强度和耐烧蚀性能。

The blends of siloxane modified epoxy resin and phenolic resin have good heat resistance and toughness. The focus of structural and composition evolution of the blends under the condition of hot oxygen is of great significance to broaden the application fields of phenolic resin at high temperature. In this study, modified epoxy(ES) was synthesized by the condensation of hydroxy-terminated polydimethylsiloxane(HTPDMS) and epoxy resin, which is blended with phenolic resin to obtain polysiloxane modified epoxy/phenolic blends(ES/PF). The thermal properties of ES/PF blends and chemical structure after pyrolysis were investigated by thermogravimetric analysis(TGA), FT-IR, scanning electron microscope additional energy dispersive spectrometer(SEM-EDS) and Xray photoelectron spectroscopy(XPS). Thermal analysis results reveal that compared with phenolic resin, the residual rate of ES/PF blends is increased by 438% at 800 ℃ under air condition, the maximum exothermic rate is decreased from 21.98 mW/mg to 14.93 mW/mg, and the residual rate is decreased by 14.3% in N. Combined with infrared analysis, the hybrid structure Si-Ox formed by ES/PF pyrolysis at 430~600 ℃, which can stabilize the formation of carbon layer, delay and hinder the further degradation of the resins and improve the char yield. XPS and EDS results reveal that the occurrence form of silicon element changes significantly at high temperature, and most of them change into SiOand SiO·nHO above 430 ℃. Indicating that the introduction of silicon can increase the char yield and has a positive effect on the thermal stability of phenolic resin under thermal oxygen condition, while the beneficial effect of silicon is inhibited in N. This may be related to the oxygen absorption mechanism of siloxane group pyrolysis.The pyrolysis structure and composition of ES/PF blends are beneficial to improve the thermal residual strength and ablative resistance of the blends.