Effect of drawing on structure and properties of a liquid crystalline polymer and polycarbonate in‐situ composite

Abstract

Fibers (strands) with various draw ratios were spun from the liquid crystalline state of a pure aromatic liquid crystalline copoly(ester amide) and the melts of its blend with polycarbonate. Scanning electron microscopy (SEMI, 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 fibers were also evaluated. I t was found that both the crystallite size and heat of fusion of the liquid crystalline polymer (LCP) increase steadily with draw ratio. However, the crystal-nematic transition temperature of the LCP is virtually unaffected by drawing. Moreover, heat of fusion of LCP is much smaller than that of isotropic condensation polymers despite the presence of very sharp dmraction peaks in WAXS measurements. These results are ascribed to the (semi)rigid rod nature of the LCP chains and the persistence of an ordered structure in the LCP melt, i.e., entropy effect. It was further observed that tensile modulus and tensile strength along fiber axis rise with draw ratio for the composite fibers. The elastic modulus of the composite fibers were found 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, respectively, with the addition of only 30 wt% LCP. This improvement in mechanical properties is attributed to fibrillation of the LCP phase in the blend and the increasing orientation of the LCP chains along the fiber axis during drawing.

Structure and morphology of the in situ composites of a liquid crystalline polymer and polycarbonate

“…The detailed blending procedures were described elsewhere (Lin et al, 1993;Lin & Yee, 1994). Blends of two different compositions (10 and 27 vol.% of LCP in polycarbonate) were prepared in the present study and the draw-down ratio was kept constant at about 12.…”

Modification of the processing window of a thermotropic liquid crystalline polymer by blending with another thermotropic liquid crystalline polymer

“…One explanation given by the authors for this behavior was that by using the dual extruder system, perhaps it was possible to orient the TLCP more effectively. In particular, Yee et al 41 extrapolated a modulus of 110 GPa for a Vectra B950 sample having complete molecular orientation. Therefore, the polypropylene (PP) matrix may have served as an insulator, allowing the Vectra B950 fibrils to be drawn further and oriented prior to solidification more than is possible when neat Vectra B950 fiber is drawn.…”

Structure–property relationship in fibers spun from poly(ethylene terephthalate) and liquid crystalline polymer blends. I. The effect of composition and processing on fiber morphology and properties

“…It has been shown that the same TLCP, which was used in this work, fibrillated in the polycarbonate matrix.6 A number of investigators reported recently in situ fibril formation during processing of biphasic blends containing a liquid crystalline polymer (LCP) component.7-9 It appears that the largest single group of self-reinforcing composites was based on polycarbonate and various LCPs, which were prepared by extrusion, compression, and injection molding or fiber spinning.1°- 13 The existence of fibrillation in blends of PET and various TLCPs was confirmed in some c a s e~'~, '~ and was inferred but not documented in other^. '^^^^ In several cases during film and rod extrusion, fibrillation of TLCP did not oc-C U~.~"~~ A wide range of morphologies and properties of PET/TLCP blends suggests that the control of the structure is a rather complex problem, influenced by a number of parameters, all of which are not readily controllable.…”