The introduction of benzimidazole and ether moieties into poly(p-phenylene terephthalamide): effects on its microstructure, interactions and properties

Co-poly(p-phenylene terephthalamide) (co-PPTA) fibers containing 4,4′-oxidianiline (4,4′-ODA) and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) in terephthaloyl chloride (TPC) and p-phenylene diamine (p-PDA) were prepared via a wet spinning method, followed by water washing and drawing at a high temperature. With the addition of a new acid-binding agent, imidazole, the solution prepared by low-temperature polycondensation had suitable viscosity for spinning. Herein, the properties of six co-PPTA fibers with different contents of BIA and 4,4′-ODA segments were studied. The mechanical properties of the co-PPTA fibers were improved with the addition of BIA and ODA; they reached the optimum tensile strength of 2.45 GPa at a p-PDA/ODA/BIA molar ratio of 2/4/4, which showed a higher degree of orientation and the highest crystallinity, and the strength further increased on increasing the thermal drawing ratio. X-ray diffraction indicated that the fibers exhibited highly ordered structures, while two-dimensional wide angle X-ray diffraction showed that molecular packing regions with highly oriented structures were formed. In addition, the co-PPTA fibers exhibited excellent thermal stability when the 5% weight loss temperature was above 492 °C under nitrogen, and glass transition occurred at about 290 °C.

Co-poly(p-phenylene terephthalamide) fibers containing 4,4′-oxidianiline and 2-(4-aminophenyl)-5-aminobenzimidazole in terephthaloyl chloride and p-phenylene diamine were prepared via a wet spinning method, followed by water washing and drawing at high temperature.

Study on Crystallization Behaviors and Properties of F-III Fibers during Hot Drawing in Supercritical Carbon Dioxide

In order to obtain F-III fibers with high mechanical properties, pristine F-III fibers were hot drawn at the temperature of 250 °C, pressure of 14 MPa, tension of 6 g·d⁻¹, and different times, which were 15 min, 30 min, 45 min, 60 min, 75 min, 90 min, and 105 min, respectively, in supercritical carbon dioxide (Sc-CO₂) in this article. All the samples, including the pristine and treated F-III fibers, were characterized by a mechanical performance tester, wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and thermogravimetric analysis (TGA). The results showed that the thermal stability of F-III fibers was enhanced to some extent, and the tensile strength and modulus of F-III fibers had great changes as the extension of treatment time during hot drawing in Sc-CO₂, although the treatment temperature was lower than the glass transition temperature (Tg) of F-III fibers. Accordingly, the phase fraction, orientation factor f_c of the (110) crystal plane, fibril length l_f, and misorientation angle B_φ of all the samples were also investigated. Fortunately, the hot drawing in Sc-CO₂ was successfully applied to the preparation of F-III fibers with high mechanical properties.

Effect of Different Pressures on Microstructure and Mechanical Performance of F-III Fibers in Supercritical Carbon Dioxide Fluid

F-III fibers were treated at different pressures in supercritical carbon dioxide fluid and all samples including untreated and treated F-III fibers were characterized by a mechanical performance tester, wide-angle X-ray scattering and small-angle X-ray scattering. By studying the relationship between mechanical performance and microstructural changes of the samples, it was found that microstructural change was the main cause of variation in mechanical performance. Results revealed that the maximum tensile strength and modulus of F-III fibers were acquired at 14 MPa within the pressure range of 8 MPa to 16 MPa when the temperature, tension and time were 250 °C, 6 g·d⁻¹ and 40 min, respectively. Correspondingly, the microstructures of the samples, including the phase fraction, crystal size, orientation factor, fibril radius, fibril length and misorientation angle, have been investigated. It was fortunate that the supercritical carbon dioxide fluid could be used as a medium during the hot-stretch process to improve the mechanical performance of F-III fibers, although the treatment temperature was lower than the glass transition temperature of the F-III fibers.

In Situ Complex with by-product HCl and Release Chloride Ions to Dissolve Aramid

Because of the strong hydrogen-bond interaction among macromolecular chains, the addition of chloride salts is generally needed to offer Cl^- ions for the dissolution of aromatic polyamides. In this paper, poly-(benzimidazole-terephthalamide) which complexed with by-product HCl during polymerization (PABI-HCl) was prepared and imidazole compound as cosolvent was added into dimethylacetamide (DMAc) to dissolve PABI-HCl. Due to stronger affinity to protons, imidazole compound could in-situ complex with HCl of PABI-HCl and form imidazolium hydrochloride. Then imidazolium hydrochloride would ionize and produce much free Cl^- ions which acted as stronger hydrogen-bond acceptor to disrupt interaction among macromolecular chains. As a result, solubility of PABI-HCl in DMAc was improved significantly in existence of small amount of imidazole compound. Moreover, DMAc-imidazole mixture was utlized for synthesis of different kinds of aramids and no precipitation was observed with progress of the reaction. So the mixture was suitable to be utlized as solvent for polymerization of aramid.

Toward high-performance poly(para-phenylene terephthalamide) (PPTA)-based composite paper via hot-pressing: the key role of partial fibrillation and surface activation

Hot-pressing is in favor of fibrillation and property enhancement for para-aramid fiber based composite.