Rheological study on lower critical solution temperature behavior of organo-soluble cyano-substituted p-aramid in isotropic phase

• Published in: Korea-Australia rheology journal Vol. 36; no. 2; pp. 89 - 97
• Main Authors: Kim, Hyo Jeong, Thanakorn, Yeamsuksawat, Jung, Dae Eon, Eom, Youngho
• Format: Journal Article
• Language: English
• Published: Seoul / Melbourne Korean Society of Rheology, Australian Society of Rheology 01.05.2024; Springer Nature B.V; 한국유변학회
• Subjects: Aramid fiber reinforced plastics; Aramid fibers; Characterization and Evaluation of Materials; Chemistry and Materials Science; Complex Fluids and Microfluidics; Cyano groups; Dimethyl acetamide; Dipole interactions; Food Science; Heterogeneity; High temperature; Lithium chloride; Materials Science; Mechanical Engineering; Original Article; Polymer Sciences; Rheological properties; Soft and Granular Matter; Sulfuric acid; Temperature; Viscosity; 공학일반; Poly(2-cyano; Lower critical solution temperature; Isotropic phase; phenylene terephthalamide
• ISSN: 1226-119X; 2093-7660
• DOI: 10.1007/s13367-024-00088-z

Poly(2-cyano- p -phenylene terephthalamide) (CY-PPTA) has garnered significant interest as a promising precursor for super p -aramid fibers because of its organosolubility in N , N -dimethyl acetamide/lithium chloride (DMAc/LiCl) while conserving the superior properties of the resultant fibers. However, CY-PPTA has been reported to exhibit abnormal phase behavior owing to the strong dipole–dipole interactions induced by the cyano groups. Herein, we rheologically study the isotropic phases of CY-PPTA/DMAc solutions with respect to the concentration and temperature and compare them with those of CY-PPTA/sulfuric acid (H 2 SO 4 ) solutions. In the isotropic region, the CY-PPTA solutions yield a higher power-law exponent of the dynamic viscosity ( η' ) versus concentration of 6.0 ( ηʹ  ~  c 6.0 ) in the DMAc system than that in H 2 SO 4 ( ηʹ  ~  c 3.2 ). Moreover, the CY-PPTA/DMAc solutions exhibit a lower critical solution temperature (LCST) behavior with increasing temperature, in contrast with the upper critical solution temperature in H 2 SO 4 . Consequently, the viscosity and exponent of the CY-PPTA/DMAc solutions increase at elevated temperatures. As shown by the Cole–Cole plot, the heterogeneity in the DMAc system becomes worse. The LCST of the CY-PPTA solution is ascribed to the intermolecular interactions between the highly polar cyano groups, which are negligible in H 2 SO 4 .