Synthesis and melt spinning of fully aromatic thermotropic liquid crystalline copolyesters containingm-hydroxybenzoic acid units

Annealing effect of thermotropic liquid crystalline copolyester fibers on thermo-mechanical properties and morphology

A series of thermotropic liquid crystal copolyesters (Co-TLCPs) was prepared by melt polymerization using 2,5-diethoxyterephthalic acid (DTA), 2,7-dihydroxynaphthalene (DHN), and p-hydroxybenzoic acid (HBA) monomers, where the HBA content was varied (0-5 mol). At 3 mol HBA, the Co-TLCPs formed nematic mesophases, while below this concentration, the liquid crystalline phase did not appear. The Co-TLCP sample with 3 mol HBA was subjected to melt spinning and heat-treated under various conditions (temperature and time) to investigate their effect on the thermo-mechanical properties and degree of crystallinity. The objective was to determine the critical heat treatment condition that can maximize the properties of the spun Co-TLCP fibers. The microstructure of the heat-treated fiber was investigated using scanning electron microscopy, and the optimal annealing conditions were confirmed based on the morphology of the fiber, which exhibited a skin-core structure owing to the varying heat and pressure conditions applied during spinning.

Influence of hydroquinone content on thermotropic liquid crystalline copolymers and nanocomposites: thermo-mechanical properties and morphology

Thermotropic liquid crystalline copolyesters (Co-TLCPs) were synthesized by varying the hydroquinone (HQ) molar ratio from 1–5 with respect to the 2,5-diethoxyterephthalic acid (ETA) monomer. The thermal properties and liquid crystalline mesophases of the synthesized Co-TLCP were investigated. All of the Co-TLCPs synthesized using a HQ molar ratio of 1–5 showed a nematic liquid crystalline phase. Among the Co-TLCPs obtained using HQ in various molar ratios, the most stable physical properties and a clear liquid crystalline phase were obtained when HQ was 4 mol. Among the various Co-TLCPs synthesized, hybrids were prepared using Co-TLCP synthesized with a 1 : 4 = ETA : HQ ratio and organoclay. A 1–10% loading of the organoclay Cloisite 93A was employed per weight of TLCP, and the clay was dispersed using the melt intercalation method. Among the Co-TLCP hybrids, the morphology and thermal properties of the hybrids were investigated according to the changes in the Cloisite 93A in the 1–10 wt% range. In general, the thermal properties were superior when the organoclay loading was 3 wt% and were inferior when the organoclay amount was 5 wt% or more. This result was confirmed by the dispersibility of the clay through transmission electron microscopy.

Thermotropic liquid crystalline copolyesters (Co-TLCPs) were synthesized by varying the hydroquinone (HQ) molar ratio from 1–5 with respect to the 2,5-diethoxyterephthalic acid (ETA) monomer.

Thermotropic liquid crystalline copolyester fibers according to various heat treatment conditions

Thermotropic liquid crystal copolyester (TLCP) was synthesized using a melt polymerization method, with a molar ratio composition of 2,5-diethoxy terephthalic acid (ETA), hydroquinone (HQ), and p-hydroxybenzoic acid (HBA) of 1:1:3. TLCP exhibited nematic liquid crystalline mesophase and maintained nematic textures under all heat treatment conditions applied. The synthesized TLCP was processed into fibers using a capillary rheometer. The liquid crystalline mesophase, thermo-mechanical properties, and morphology of TLCP fibers obtained under various heat treatment conditions were investigated. The thermo-mechanical properties of the heat-treated fibers were improved compared to those of the as-spun fibers. The best results were obtained for TLCP fibers annealed at 230 °C for 9 h. The heat-treated fibers showed a well-developed microfiber morphology compared to the as-spun fibers. In the spun fibers, a skin–core morphology was observed regardless of the heat treatment conditions, and a well-developed fiber morphology better than the core area was observed in the skin area. The diameter of the fiber heat-treated at 230 °C for 9 h was approximately 60–110 nm.

Pre-drawing induced evolution of phase, microstructure and property in para-aramid fibres containing benzimidazole moiety

Copoly(p-phenylene-benzimidazole-terephthalamide) (PBIA) fibre was spun by wet-spinning and drawn in a coagulating bath with different pre-drawing ratios (R).

Synthesis and properties of aligned all-aromatic liquid crystal networks

A series all-aromatic main-chain liquid crystalline (LC) polymers based on 6-hydroxy-2-naphtoic acid (HNA), biphenyl-4,4′-dicarboxylic acid (BA), resorcinol (RS), and a cross-linkable ethynyl functionality, 4,4′-(1,2-ethynediyl)bisbenzoic acid (EBA) were synthesized using a one-pot melt condensation method. In contrast with reactive LC oligomers where reactive functionalities were placed at the chain terminus, the reactive ethynyl group is now used as a cross-linking functionality placed in the polymer main-chain. Differential scanning calorimetric analysis reveals that these polymers can be cured at temperatures above 350°C in the nematic melt and exhibit excellent thermal properties, that is, temperature at 5% weight loss > 465°C, and reaches a maximum after cure glass transition temperature ( Tg) of 167°C. When only 5 mol% of BA was replaced with EBA, a slightly cross-linked nematic network, HNA/BA/RS/EBA-5, was obtained and thin films thereof could be stretched by 400% strain above Tg in four consecutive steps. A maximum order parameter [Formula: see text] of 0.54 could be achieved, and this moderately aligned LC network displays a room temperature storage modulus ( E′) of 29 GPa, a tensile strength of 330 MPa, a tensile modulus of 7 GPa, and an elongation at break of 7%. Cross-linking also improved the transverse properties of the nematic films. E′ of HNA/BA/RS/EBA-5 is 1.0 GPa at 150°C after being stretched by 400% versus 0.16 GPa for the non-cross-linked reference polymer. An affine deformation model was used to calculate E′ using [Formula: see text], and the predicted values are in close agreement with the experimental results.