Amphiphilic terpolymer sizing enabling an interfacial toughening layer for enhanced interfacial and mechanical properties of CF/EP composites

The surface of carbon fibres (CF) was modified by chemical oxidation to introduce carboxyl and hydroxyl functionalities. A polymerization-induced self-assembly (PISA) approach based on reversible addition–fragmentation chain transfer (RAFT) polymerization was adopted to prepare a functional amphiphilic terpolymer, poly (hexyl methacrylate-co-acetoacetoxyethyl methacrylate-co-[2-(methacryloyloxy)ethyl]trimethylammonium chloride) (PHAM), by adjusting the monomer feed composition. The resulting PHAM was subsequently used as a sizing agent for carbon fibre/epoxy (CF/EP) composites. Leveraging the cooperative effects of hydrophilic and hydrophobic moieties, the PHAM sizing layer constructs a stress-buffering interphase with enhanced toughness at the fibre/matrix interface. This hierarchical structure facilitates efficient load transfer through chemical bonding while promoting energy dissipation via the physical entanglement of flexible polymer chains, thereby improving the interfacial properties and the macroscopic mechanical performance of the composites. Contact-angle measurements of carbon fibres with different degrees of modification in polar and nonpolar liquids indicate that oxidation of CF, together with the introduction of the highly polar PHAM, enhances chemical compatibility within the interfacial region and consequently increases the overall surface energy of the CF. As a result, the flexural strength and impact strength of the CF/EP composites were improved by 26% and 44.5%, respectively .