Effect of Heat Treatment on Molecular Mass and Thermal Properties of Thermotropic Liquid Crystal Polyesters

Abstract

The thermotropic liquid crystal polyester(TLCP) fiber is an increasingly important strategic high-performance fiber.In this paper, the TLCP was prepared by two-step melt polymerization using 4-hydroxybenzoic acid(HBA) and 6-hydroxy-2-naphthoic acid(HNA) as comonomers at a molar ratio of 7∶3.The structure of TLCP was confirmed by the Fourier transform infrared(FTIR) spectrometer and nuclear magnetic resonance(NMR) spectrometer.The thermal and rheological properties of TLCP before and after heat treatment were analyzed systematically by the differential scanning calorimeter(DSC), dynamic mechanical analyzer(DMA) and high-temperature rotational rheometer.The results revealed that the melting temperature, glass transition temperature and melt viscosity of the TLCP increased significantly after heat treatment.It indicates that the crystallization of the TLCP is perfect, and solid-phase condensation occurs during heat treatment, which increases its molecular mass.In conclusion, heat treatment at a temperature below but close to the melting temperature can effectively regulate the structure and properties of the TLCP, and the results of this study can provide a reference for the high strengthening of TLCP fibers.

Keywords

thermotropic liquid crystal polyester(TLCP) / heat treatment / viscosity / thermal property

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Funding

National Key Research and Development Program of China(2021YFB3700105)