EFFECT OF DRAWING ON STRUCTURE AND PROPERTIES OF A LIQUID-CRYSTALLINEPOLYMER AND POLYCARBONATE IN-SITU COMPOSITE

Fibers (strands) with various draw ratios were spun from the liquid cr ystalline state of a pure aromatic liquid crystalline copoly(ester ami de) and the melts of its blend with polycarbonate. Scanning electron m icroscopy (SEM), wide angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC) were employed to investigate the structure and properties of the resulting fibers. Mechanical properties of the f ibers were also evaluated. It was found that both the crystallite size and heat of fusion of the liquid crystalline polymer (LCP) increase s teadily with draw ratio. However. the crystal-nematic transition tempe rature of the LCP is virtually unaffected by drawing. Moreover, heat o f fusion of LCP is much smaller than that of isotropic condensation po lymers despite the presence of very sharp diffraction peaks in WAXS me asurements. These results are ascribed to the (semi)rigid rod nature o f the LCP chains and the persistence of an ordered structure in the LC P melt, i.e., entropy effect. It was further observed that tensile mod ulus and tensile strength along fiber axis rise with draw ratio for th e composite fibers. The elastic modulus of the composite fibers were f ound to be as high as 19 GPa and tensile strength reached 146 MPa with draw ratios below 40 and an LCP content of 30 wt%. Compared with the thermoplastic matrix, the elastic modulus and tensile strength of the in-situ composite have increased by 7.3 times and 1.4 times, respectiv ely, with the addition of only 30 wt% LCP. This improvement in mechani cal properties is attributed to fibrillation of the LCP phase in the b lend and the increasing orientation of the LCP chains along the fiber axis during drawing.