酚醛树脂基纳米多孔材料的制备及结构调控

酚醛树脂基纳米多孔材料（Phenolic Resin-based Nanoporous Materials，PNM）是满足新一代航天飞行器轻质、高效隔热需求的新型热防护材料，传统制备方法中需使用超临界干燥技术，制备周期长、成本高。本研究通过两步法，即先合成线性酚醛树脂，再进行溶胶-凝胶的方法，实现了常压干燥PNM的制备。系统研究了固化剂含量、固化温度和固化时间对材料结构的影响和调控作用，分析了影响材料收缩率和热稳定性的因素。结果表明，PNM的微观纳米结构的变化会影响材料干燥后的收缩率，制备大颗粒、大孔径的微观结构更有利于降低材料的收缩率。而PNM的热稳定性主要受交联反应过程形成的化学结构的影响，通过优化固化剂的含量可提高PNM的热稳定性。当固化剂含量为10%，固化温度提高至150℃，固化时间延长至48 h的条件下，获得的PNM有最高的热稳定性（900℃下的残碳率为54.2%）、最发达的孔结构（比表面积为264.0 m²/g、孔容为2.67 cm³/g、平均孔径为40.0 nm）和最小的收缩率（0%）。此PNM制备方法简单、性能优异，在未来航天飞行器上有广阔的应用前景。

Preparation and structure control of phenolic resin-based nanoporous materials

Phenolic resin-based nanoporous material (PNM) is a new kind of light-weight and efficient thermal protection material that meets the demand of new-generation aerospace craft. Traditionally, its fabrication requires supercritical drying technique which is costly and time-consuming. In this work, PNM is fabricated via a two-step approach including the synthesis of novolac resin and the sol-gel process, making the ambient pressure drying of PNM possible. The effects of curing agent amount, curing temperature, and curing time on the structure were systematically investigated. And the factors affecting shrinkage and thermal stability were also identified. The results show that the change of nanoporous structure of PNM can affect the shrinkage of PNM after drying. Larger particles and larger pores contribute to smaller shrinkage. The thermal stability of PNM is mainly influenced by its chemical composition and molecular structure. Higher thermal stability is expected when the addition of curing agent was optimized. When the curing agent amount is 10%, the curing temperature is elevated to 150℃, and the curing time is extended to 48 h, the obtained PNM has the highest thermal stability (char yield of 54.2% at 900℃), highly developed nanoporous structure (surface area of 264.0 m²/g, pore volume of 2.67 cm³/g and average pore diameter of 40.0 nm), and the smallest shrinkage after drying (0%). This kind of PNM is promising to be used in future aerospace crafts for its easy fabrication and excellent performance.