Due to the excellent processability and high char yield, phenolic resin (PR) plays a pivotal role in ablative thermal protection systems for the aerospace industry. However, internal defects in conventional phenolic resin matrix composites could potentially scrap the entire thermal protection system and cause devastating safety hazards to the spacecraft. Dynamic crosslink networks could endow the PR and its composites with good healability. But the development of healable and ablative PR materials still remains a challenge. Recently, researchers from the Joint Innovation Center of Thermal Protection Materials (JICTPM) of Xi’an Jiaotong University reported a series of novel PR-based materials. By introducing the crosslinks of hexamethylenetetramine (HMTA) and phenylboronic acid (PBA), the synergistically crosslinked PR with high stability and excellent processability was obtained. Compared with its conventional counterparts, the dynamic boronic ester linkages in the synergistic crosslinks not only offer good processability, but high char yield as well. Thanks to its reversibility, the dynamically crosslinked PR composites could be manufactured at a lower cost and higher efficiency. More importantly, the composites could be repaired, reprocessed, and recycled. The oxy-acetylene ablation data showed that the synergistically crosslinked PR composites possess excellent ablative properties and could be potentially used for thermal protection parts in solid rocket motors.

   The first author of the paper is Dr. Xiaolong Xing.

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酚醛树脂以其良好的工艺性和高成炭率被广泛应用于航天热防护复合材料，然而，这种复合材料常常会由于内部缺陷而造成安全隐患或产品报废。虽然通过动态交联可以实现树脂及其复合材料的可修复和消除内部残余应力，但是，开发可用于可修复耐烧蚀复合材料的基体树脂仍然是一个严峻的挑战。近日，以“热防护材料联合创新研究中心”（JICTPM）为依托，研究人员为了协调酚醛树脂基复合材料的可修复性能和耐烧蚀性能，通过引入苯基硼酸(PBA)，与传统的固化剂六次甲基四胺(HMTA)相结合，实现了热塑性酚醛树脂的协同交联。通过传统共价键(亚甲基)和动态共价键(硼酸酯基)的协同运用，得到了兼具稳定性和动态性的酚醛树脂基体。与基于亚甲基交联的酚醛树脂相比，协同交联的酚醛树脂中的动态硼酸酯基在赋予树脂基体良好的动态性的同时，又能保证树脂具有较高的成炭率。由于树脂化学结构上的动态可逆性，不仅能够通过更加高效低成本的成型工艺制造复合材料，还可以实现复合材料的修复、加工和再生。氧-乙炔烧蚀试验表明，协同交联的酚醛树脂基复合材料具有优良的耐烧蚀性能，在固体火箭发动机关键热防护部件方面具有重大的应用价值。

论文的第一作者是刚刚取得博士学位的行小龙同学。