Effects of Emulsifiers on the Thermal Stability of Thermoplastic Sizing Agents and the Interfacial Properties of <scp>CF</scp> / <scp>PEEK</scp> Composites

ABSTRACT In this study, anionic/nonionic (sodium dodecyl sulfonate/polysorbate‐80), cationic/nonionic (cetyltrimethylammonium bromide/polysorbate‐80), and purely nonionic (Triton X‐100) were employed as emulsifier systems, with contents of 10% to 30% to prepare a series of polyetherimide‐based emulsion sizing agents. A solution‐type sizing agent (S‐PEI) was also introduced as an ideal benchmark. The sizing agents were subsequently applied to carbon fibers. The effects of emulsifier type and content on the thermal stability of the sizing agents and the interfacial properties of carbon fiber reinforced poly(ether ether ketone) composites were systematically investigated. The results indicate that emulsifiers reduced the thermal stability of the sizing agents, with the anionic/nonionic system showing the best performance. Increasing emulsifier content progressively decreased thermal stability; above 25%, decomposition temperature fell below the composite processing temperature. Composites with the anionic/nonionic system showed the highest interlaminar shear strength (ILSS) and matrix‐dominated failure, while others mainly exhibited interfacial failure with much lower ILSS. ILSS first increased then decreased with emulsifier content, peaking at 49.1 MPa at 20%, which is 58%~60% higher than untreated and desized fibers, and is comparable to that of the S‐PEI. Failure mode evolved from interfacial to matrix failure, then reverted to interfacial failure.