Beyond Traditional Phenolics: Disulfide Bonds for Performance Enhancement of Aerospace Ablation-Resistant Materials...

As a key material of solid rocket motor nozzles, phenolic resins (PR) possessing high char yield, good processability, and efficient repairable performance are strongly desired for advanced ablation materials. Achieving these requirements simultaneously is challenging for traditional PR or for dynamically cross-linked polymers. The present study proposed a strategy to reconcile the thermal stability and reprocessability of ablation materials based on a resole-type PR bridged with disulfide bonds (HPDS). The aromatic disulfide bonds conferred outstanding performance in resin processing, composite molding, application, and recycling. During processing, the partial dissociation of S─S bonds ensured effective control of the resin's viscosity, allowing for fitting to multiple pre-impregnated processes. During molding, dissociation and re-bonding of S─S bonds enabled effective network reconstruction, yielding a repairable resin matrix and allowing high-value carbon fiber recycling. During the ablation stage, the cleavage of S─S bonds produced long-lifetime thiyl radicals that captured radicals, protecting carbon-containing species that participate in char formation. The cured HPDS (CHPDS) exhibited a char yield of 64.7% at 800°C, and its carbon fiber-reinforced composites are stable to oxyacetylene ablation at 2800°C. From processing to application, from thermal stability to recyclability, the dynamic S─S bonds unleash the renewed vitality of phenolic resins.