Fabrication of high-temperature thermoplastic and highly compatible poly(amide-amide acid) salt interface via water-soluble precursor in-situ construction strategy for aerospace-grade CF/PPS composites

Interfacial failure in aerospace-grade polyphenylene sulfide/carbon fiber composites has long limited their critical applications, primarily stemming from the inherent inability of conventional thermosetting sizing agents to simultaneously achieve high thermal stability and interfacial compatibility. To address this challenge, we devised an environmentally friendly strategy involving molecularly designing water-soluble poly(amide-amide acid) (PAAAs) precursors synthesized via a one-pot aqueous polymerization. Through targeted temperature control, we achieved in-situ construction of a thermoplastic poly(amide-imide) (PAI) interface on fiber surfaces, characterized by excellent thermal resistance and compatibility. This designed interphase not only enhanced fiber–matrix integration through synergistic hydrogen bonding and π-π conjugation but also activated a unique cavitation toughening mechanism under stress. The strong interfacial interactions effectively induced cavitation within the PPS matrix, enabling substantial energy dissipation and cracked path deflection. This in-situ constructed interface significantly improved the composite’s interfacial shear strength, interlaminar shear strength, and flexural strength by 75.9%, 62.2%, and 41.4%, respectively, while transforming the failure mode from brittle interfacial debonding to ductile matrix fracture. Our molecular designed strategy for in-situ PAI interface construction successfully enabled low-viscosity sizing while resolving the long-standing compatibility and thermal resistance challenges in CF/PPS composites, establishing a new paradigm for interfacial design in thermoplastic composites.