以商业酚醛树脂为原料,介绍了一种工艺简单、制备周期短、低成本的低温溶胶-凝胶聚合和常压干燥工艺制备酚醛树脂气凝胶的方法。使用三种酚醛树脂(低粘度钡酚醛、普通热塑性酚醛和硼酚醛)在醇溶剂中制备了三个系列的凝胶。应用扫描电子显微镜(SEM)、比表面积及孔隙率分析仪和红外光谱(FT-IR)分析了所制备气凝胶的骨架结构和孔结构以及合成机理。所制备的多孔纳米酚醛树脂气凝胶密度低至0.17~0.23 g/cm3、压缩强度为0.68~0.80 MPa,热导率为0.039~0.046 W/m.K。研究表明,酚醛树脂与醇溶剂之间有较强的选择匹配性,轻质多孔的钡酚醛树脂气凝胶只能在乙醇中合成,热塑性酚醛树脂在正丙醇溶剂得到的气凝胶结构更均匀。然而,硼酚醛树脂由于固化温度过高,难以通过该方法获得气凝胶材料。这种低成本、简捷的气凝胶制备工艺对实现酚醛树脂气凝胶的大尺寸制备和产业化发展具有重要意义。
A facile, rapid, low-cost and low temperature sol-gel polymerization and atmospheric drying process was developed using commercial phenolic resin as raw material. Gels were prepared from three different phenolic resins (Low viscosity barium phenolic resin、thermoplastic phenolic resin and boron phenolic resin) using ethanol and n-propanol as solvents, respectively. Scanning electron microscope (SEM), automatic specific surface area and porosity analyzer, Fourier transform infrared spectrometer (FT-IR) were appllied to analyse the synthesis mechanism, skeleton and pores structure of aerogels. The prepared aerogels had the density of 0.17~0.23 g/cm3, the compressive strength of 0.68~0.80 MPa and the low thermal conductivity of 0.039~0.046 W/m·K with porous nano structure. Results showed that there was strong selective matching between phenolic resin and alcohol solvents. Low-density barium phenolic resin aerogels could only be synthesized in etanol while homogeneous thermoplastic phenolic resin aerogels were easier to be prepared in n-propanol solvent. However, it was difficult to obtain boron phenolic resin aerogels for its high curing temperature via this method. This low-cost and facile aerogel preparation process is of great significance, which can promote the large-scale preparation and industrialization of organic phenolic aerogels.