The Effect of Fiber-Matrix Interphase Properties on the Quasi-Static Performance of Thermoplastic Composites

A number of concerns about carbon-fiber adhesion to thermoplastic- matrix systems have been raised. As a result, the effect of the fiber-matrix interphase on the mechanical performance of thermoplastic composites was investigated. The interphase condition was altered by an electrochemical fiber surface treatment and addition of an unreacted epoxy sizing of PAN-based carbon fibers. The AU4, AS4, and AS4CGP fibers were embedded in an amorphous thermoplastic polymer, J2, and formed into laminates. The meso-indentation technique was used to quantify the interfacial quality and indicated only a 22 % increase in interfacial strength over the AU4 fiber composite. The mechanical properties of these composites in the fiber direction were shown to be insensitive to the in terfacial quality as were the transverse and shear moduli. The transverse and shear strengths of AS4/J2 and AS4CGP/J2 composites were increased by more than 50 % when compared to the AU4/J2 composites. Scanning electron microscopy of the failure surfaces showed clean fiber in the AU4/J2 composites, whereas matrix remained on the fiber surface of the AS4/J2 and AS4CGP/J2 composites.