Healable ablative composites from synergistically crosslinked phenolic resin

Due to the excellent processability and high char yield, phenolic resin 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. Herein, hexamethylenetetramine (HMTA) and phenylboronic acid are applied as the co-curing agents of novolac resin. With the HMTA amount below 2.5 phr, a series of synergistically crosslinked phenolic resin (HPNR), which consist of both traditional methylene linkages and dynamic boronic ester linkages, are successfully synthesized. By tuning the ratio of the traditional/dynamic bonds, the HPNR demonstrates high char yield and controlled plasticity. Compared with its conventional counterparts, the carbon fabric reinforced HPNR matrix composites show healing capability and superior mechanical properties and ablation resistance, with an interlayer shear strength and mass ablation rate of 37.0 MPa and 0.055 g/s, respectively. The synergistic crosslinking strategy provides a promising pathway for designing and preparing healable ablative thermal protection system materials.