Examining interfacial interactions in a range of polymers using poly(ethylene oxide) functionalized carbon fibers

It is commonly assumed that a higher oxygenated content on the surface of carbon fibers will lead to high interfacial adhesion. Thus, carbon fibers are exposed to oxidizing treatments to increase surface polarity. Here, we examine the interfacial interactions of a range of thermoset and thermoplastic polymers with carbon fibers that have a grafted polyethylene oxide (PEO) chains to their surface. This provides an extremely hydrophilic surface, without potential degradation of the fiber via chemical oxidation. We find that high surface polarity does not always correlate to high interfacial adhesion; in some instances, unsized hydrophobic carbon fibers possess equal or better fiber-to-matrix adhesion than treated hydrophilic carbon fibers. The most notable example is in vinyl ester resin, in which the presence of an alkyne group, able to participate in the radical polymerization process, provides significant improvements in interfacial shear strength (IFSS) compared to a larger, and polar, PEO chain.