A multi-stream flow technique to obtain isotropic texture in extruded thermotropic liquid crystalline polymer melts
In this article, we present a simple method toward achieving global orientation isotropy in a capillary-extruded thermotropic liquid crystal polymer (TLCP), that is, a random copolyester of 73 mol% hydroxybenzoic acid (HBA) and 27 mol% hydroxynaphthoic acid (HNA), by passing it through porous, flow altering metal foam inserts placed in the pathway of extrusion. TLCP melt flow through foam metal inserts causes a rapid creation of large number of small streams of varying cross-section that subjects all regions of the flowing body to intense shearing leading to high orientation in individual streams. These individual streams of varying velocity and direction interact to form a structure similar to a woven rope. As a direct result of this randomization effect of these small streams, the extruded liquid crystal polymer tends toward isotropic macro properties. The degree of orientation anisotropy is evidenced by scanning electron microscopy (SEM) and micro beam wide angle x-ray diffraction (WAXD) techniques and contrasted in samples extruded with and without the presence metal foam inserts.
Polymer Engineering & Science
Boles, D.; Cakmak, Mukerrem; and Yalcin, B., "A multi-stream flow technique to obtain isotropic texture in extruded thermotropic liquid crystalline polymer melts" (2008). Polymer Engineering Faculty Research. 329.