Microstructure and nematic transition in thermotropic liquid crystalline fibers and their single polymer composites

We describe a new single polymer composite (SPC) prepared from two liquid crystalline vectran fibers. Vectran M is the as-spun fiber while vectran HS is the high-strength version. A study of the morphology of the pristine materials shows that the two fibers have different crystal structures. The wide-angle X-ray diffraction (WAXD) data confirm the presence of the so-called pseudo-hexagonal (PH) unit cell in vectran M, while an orthorhombic structure is revealed in the vectran HS fibers. A transition to the nematic phase is observed by in situ X-ray diffraction at ∼277°C for the M fibers and at ∼315°C for the HS fibers. During the compaction process, the orientation of the reinforcing fibers is well maintained and the transition to a nematic phase seems to be delayed by processing at high applied pressure. Concomitantly, vectran M loses its orientation and the transition to the nematic phase disappears.