The construction of gradient load-bearing structure on CF surface employing novel S-PI sizing agent for interfacial and mechanical properties enhancements of CFRTPs

Abstract

The properties of carbon fiber-reinforced thermoplastics composites (CFRTPs) are heavily influenced by the quality of the interface. The sizing agent, a key component of the interface, still faces challenges such as poor thermal resistance, environmental pollution, and insufficient interfacial adhesion. In this work, a novel self-emulsifying polyimide (S-PI) sizing agent was synthesized and synergized with octa(aminopropyl)polyhedral oligomeric silsesquioxane (OA-POSS) to construct a gradient load-bearing structure on carbon fiber (CF) surface. The S-PI exhibited excellent thermal stability, with a T_{1 %} (temperature at 1 % weight loss) of 400.5 °C. Furthermore, it formed a stable water-based sizing agent via self-emulsification. The average particle size of the sizing agent was 85 nm and the sizing agent remained stable over six months of storage. The gradient load-bearing structure, which integrated of the POSS frameworks with the S-PI chains, effectively distributed the absorbed stress exerted on the composites. Compared to the commercial CF reinforced poly(ether-ether-ketone) (CCF/PEEK), the interlaminar shear strength, impact strength, and flexural strength of the SPCF/PEEK improved by 51.4 %, 60.8 %, and 43.1 %, respectively. Compared to CCF reinforced poly(ether-imide) (CCF/PEI), SPCF/PEI showed improvements of 55.8 %, 50.2 %, and 41.8 %, respectively. This approach offers new insights into the development of polyimide sizing agent and the enhancement of CFRTPs.