Fiber Formation and Structural Development of HBA/HNA Thermotropic Liquid Crystalline Polymer in High-Speed Melt Spinning.

Bo Seok Song,Wan-Gyu Hahm,Sun Hwa Jang,Jun Young Lee

doi:10.3390/polym13071134

Abstract

High-speed melt spinning of thermotropic liquid crystalline polymer (TLCP) resin composed of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-napthoic acid (HNA) monomers in a molar ratio of 73/27 was conducted to investigate the characteristic structure development of the fibers under industrial spinning conditions, and the obtained as-spun TLCP fibers were analyzed in detail. The tensile strength and modulus of the fibers increased with shear rate in nozzle hole, draft in spin-line and spinning temperature and exhibited the high values of approximately 1.1 and 63 GPa, respectively, comparable to those of industrial as-spun TLCP fibers, at a shear rate of 70,000 s−1 and a draft of 25. X-ray diffraction demonstrated that the mechanical properties of the fibers increased with the crystalline orientation factor (fc) and the fractions of highly oriented crystalline and non-crystalline anisotropic phases. The results of structure analysis indicated that a characteristic skin-core structure developed at high drafts (i.e., spinning velocity) and low spinning temperatures, which contributed to weakening the mechanical properties of the TLCP fibers. It is supposed that this heterogeneous structure in the cross-section of the fibers was induced by differences in the cooling rates of the skin and core of the fiber in the spin-line.

Highlights

Thermotropic liquid crystalline polymers (TLCPs), which exhibit liquid crystal behavior at adequate temperature, is one of the typical anisotropic polymers and represented almost exclusively by aromatic copolyesters [1,2,3]
It is expected that the change in melt structure in the vicinity of the nozzle hole owing to changes to the shear rate and spinning temperature will affect the structural development of the fibers in the spinning line and the mechanical properties of the as-spun fibers
The fiber surface was hardly affected by the draft. These results suggest that the TLCP fiber surface structure was influenced by the shear rate and temperature conditions in the nozzle hole, which could be improved by using a higher shear rate and spinning temperature

Summary

Introduction

Thermotropic liquid crystalline polymers (TLCPs), which exhibit liquid crystal behavior at adequate temperature, is one of the typical anisotropic polymers and represented almost exclusively by aromatic copolyesters [1,2,3]. Muramatsu and Krigbaum [12] conducted rheological measurements and fiber spinning for HBA/HNA (58/42 molar ratio) under the shear rates of 1~10,000 s−1 and the draft of 1~15 using a capillary rheometer and reported that the mechanical property of as-spun fibers tended to increase as the draft and spinning temperature increased. Wissbrun and Ide [13,14,15,16] reported that HBA/HNA TLCP can be processed at reduced temperatures by controlling the thermal history to improve their mechanical properties, and the control of elongational flow of the TLCP melt using small orifices during fiber spinning can contribute to enhance molecular orientation and improve product properties

Methods

Results

Conclusion