Influence of epoxy- and polyamide-compatible carbon fiber sizings on interfacial fracture toughness and in-plane shear properties of carbon fiber reinforced polyamide-6

The fiber-matrix interaction is one of the key parameters to optimize the mechanical performance of fiber reinforced polymers. For this purpose, a sufficiently strong adhesion between fiber and matrix is necessary. This can be accomplished by employing a suitable polymeric sizing. Since conventional sizing agents, designed for thermoset composites, are usually chemically incompatible with thermoplastic matrices and do not withstand their higher processing temperatures, new customized sizings are required. In the present study, the effects of a conventional epoxy-compatible sizing and two polyamide-compatible sizing agents on micro- and macro-mechanical properties of carbon fiber reinforced polyamide-6 were investigated. On a microscopic scale, cyclic single-fiber push-out tests were performed to evaluate the interfacial fracture toughness. To determine the macro-mechanical inplane shear properties, V-notched rail shear and picture frame tests were performed. Results of microscopic push-out and macroscopic shear tests are consistent and reveal highest level of adhesion to the matrix for one of the polyamide-compatible sizings. The sample with epoxy-compatible sizing shows the lowest value of fiber-matrix adhesion. It is concluded that the customized, matrix-compatible sizing improves the fiber-matrix adhesion on microscopic scale, which in turn improves the in-plane shear properties on macroscopic scale.