DEVELOPMENT AND EVALUATION OF SURFACE TREATMENTS TO ENHANCE THE FIBER-MATRIX ADHESION IN PAN-BASED CARBON-FIBER LIQUID-CRYSTAL POLYMER COMPOSITES .2. ELECTROCHEMICAL TREATMENTS

Various electrochemical surface treatments, designed to improve the fiber-matrix adhesion, were applied to commingled as-received continuous AS4 carbon reinforcing fiber/liquid crystal polymer (LCP) matrix fibers. Unidirectional composite plates (nominally 60 vol% carbon fiber) were fabricated and short beam shear (SBS) tests were conducted to provide an indication of the effect of the treatments on AS4 carbon fiber-LCP matrix adhesion. The mean SBS strength of the as-received AS4/LCP system was 49 MPa. Three electrochemically polymerized coatings-poly-para-phenylene (PPP), polyphenylene oxide (PPO), and polyaniline (PA) -were applied. Only the PPO coating, however, had a beneficial effect on the composite shear strength. This coating enhanced the shear strength by 14% relative to the as-received AS4/LCP system. Scanning electron microscope (SEM) observations of the PPO treated shear failure surface indicated the presence of a strong fiber-matrix bond. That is, the failure location was in the LCP matrix material.