Poly(dimethylsiloxane) as Interphase in Carbon Fiber-Reinforced Epoxy Resin: Topographical Analysis and Single-Fiber Pull-Out Tests

Covalently bonded poly­(dimethylsiloxane) on carbon fibers presents a low-friction, elastomeric interphase in carbon fiber-reinforced plastics. Poly­(dimethylsiloxane) is a well-known material in terms of low friction and its use as a slip additive. Using poly­(dimethylsiloxane) as an interphase in composites decreases frictional sliding and reduces interface abrasion. Different poly­(dimethylsiloxane) polymers were used and analyzed concerning reaction yield, functional groups, molar masses, and molecular structures. The polymer grafting created characteristic nanoscaled patterns on the carbon fiber surface, which depend on the structure of the poly­(dimethylsiloxane) species, and were analyzed with atomic force microscopy. The change in polarity from unsized carbon fibers to poly­(dimethylsiloxane)-coated fibers was observed via contact angle measurements: increases in hydrophobicity up to 120° were noted. Furthermore, the fiber resin interactions were directly influenced by the poly­(dimethylsiloxane) coating and led to a decrease in interfacial shear strength from 10.3 ± 2.0 to 4.3 ± 1.5 MPa.