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Rheological properties, structure and thermal behavior of liquid crystalline copolyester

Levchenko A. A., Abdullaev K. M., Antipov E. M., Kulichikhin V. G., Stamm M.

Applied Mechanics and Engineering

1999

Vol. 4, no spec.

289-296

Rheological properties and thermal behavior of a copolyester (CPE) prepared as high oriented fibers from PET, hydroxybenzoic, terephthalic acids and hydroquinone (40:20:20:20 mol %) in a temperature range of 30-350oC have been investigated by capillary viscosimetry, WAXS, SAXS and DSC. The copolyester under study can be characterized by an existence of two temperature regions with various shapes of flow curves. Different values of flow activation energies in the low and high temperature regions were determined. This material revealed a prominent dependence of viscosity on a residence time at 240oC and its absence at higher temperatures. It has been found that the non-crystalline structure of as-spun fibers can be identified as a LC smectic state with non-periodic layers. The crystalline phase (~8 %) coexists with LC one. A first-order phase transition takes place at 220oC, related to a presence of block sequences of PET that can be formed during the synthesis. The remaining part represents solid crystalline phase melting at 293oC. This phase plays role of net junctions that prevent the actual flow of soften CPE. Therefore, in a temperature range 240-250oC a pure slippage and a superposition of the flow and slippage ( 255-280oC) take place. Only at T>290oC a real flow proceeds.