Abstract
Composites reinforced with a thermotropic liquid crystal copolyester fiber (Celanese Vectran) have been studied with regard to fiber properties and adhesion to the thermoplastic matrix. As-spun (AS) and heat-treated (HT) fibers have been characterized. Heat treatment increases the crystal-to-nematic transition by 40°C, increases the modulus by 18%, and doubles the strength. Composites made with Vectran fibers (HT) require processing at or below 275°C, since fiber properties reduce significantly above this tem perature, which corresponds to the transition for AS fibers Composites made with Vec tran fibers were found to have low transverse properties, independent of thermoplastic matrix. The matrix compositions tested were a bisphenol-A polycarbonate and liquid crys tal copolyester with the same monomers as the fiber. Small trials were also conducted with other thermoplastics. Specific fiber surface treatments, such as oxidation with ozone, did increase transverse properties, but values remained low compared to the bulk matrix. Scanning electron microscopy of transverse fracture surfaces indicates that fiber splitting occurs, especially for surface treated fibers. Poor fiber transverse properties (low inter- chain interaction), rather than fiber/matrix adhesion, thus appear to be limiting composite transverse properties, especially in composites with surface treated fibers.