Rheological properties of liquid-crystalline solutions of poly(p-phenylene terephthalamide) and behavior of the jet in spinning through an air space

Abstract

LC solutions of PPTA behave like liquids with a power law of flow and n = 0. 65-0. 78 Liquid-crystalline (LC) sulfuric acid solutions of poly(p-phenylene terephthalamide) (PPTA) with a concentration of 19-20% heated to 80-95"C are used to fabricate high-strength fibres by spinning through an air space [1]. In optimum conditions, the air space is usually small, 4-20 ram, and the diameter of the spinneret chapels is 0.05-0.08 ram. Orientational drawing of the jet in the space with a ratio of 4-8 is used (calculated as the ratio of the fibre take-up rate to the rate of extrusion of the solution through the channel without consideration of spinneret expansion of the jets). The fibre take-up rate is 70-400 m/min and its range can be wider. Water and aqueous solutions of sulfuric acid in low and moderate concentrations with preferred temperatures of O-10*C are used as the spinning bath (SB). These are "harsh" polymer precipitators, since the liminal concentration of PPTA corresponds to a solvent composition with an approximately 10% concentration of water in the sulfuric acid [2]. The possibility of conducting high-speed spinning indicates formation of the structure of the high-strength fibre directly in the SB.It was interesting to study the rheological properties of the solutions and the behavior of the jets in conditions of real spinning of high-strength fibres.We used 19% LC solutions of PPTA in 99.6% H2SO 4 at 82"C with a viscosity of 120-200 Pa-see, determined on a Hoeppler rheoviscometer with shear stress of 200 Pa. The intrinsic viscosity [77] of the polymer, determined in 96 % H2SO 4 at 25~ was 6.0-6.5 dl/g. Standard cup spinnerets made of a precious metal with a 12.5 mm cup diameter and 0.3 mm wall thickness were used. The spinneret channels had a capillary with diameter D from 0.06 to 0.17 and 1.0 mm, ratio of length to diameter L/D equal to 1.0 (0.3 for D = 1.0 mm), and an entry conical part with an angle at the apex of 22"C (except for the channel with D = 1.0 mm). The number of channels in the spinnerets ranged from 18 to 40 and was 1 for the spinneret with D = 1.0 mm. Mono-and .complex filaments were spun through an air space up to 20 mm in size, heated by hot air feed or unheated, into a water SB with a temperature of 10*C, as described in [3]. The flow curve of a LC solution of PPTA with a viscosity of 120 Pa-sec through channels 0.08 mm in diameter is shown in Fig. 1. The shear stress a was calculated as a = DPI4L, where P is the pressure of the solution in the spinneret, and the real shear rate on the wall of the channel 5',o was calculated with the Weissenberg Rabinovich equation:Terlon Industrial Association, Mytishchi.

Comparison study of the effect of blending method on PVDF/PPTA blend membrane structure and performance

“…1(a) and (b). It can be seen that both casting solutions synthesized by in situ polycondensation and solution blending methods exhibited the typical shear thinning behavior of pseudo-plastic fluid and the viscosities greatly increased with the increasing of PPTA concentration (Kiya-Oglu et al 1997). Higher viscosity emerged in casting solution synthesized by in situ polycondensation method.…”

Dynamic Rheological Studies of Poly(p-phenyleneterephthalamide) and Carbon Nanotube Blends in Sulfuric Acid

“…Such strong molecular arrangement is attributed to the extreme anisometry of rigid PPTA and disruption of intermolecular hydrogen bonds in PPTA caused by the super-acidity of H 2 SO 4 . Nematic sulfuric acid LC solution of PPTA, referred to as PPTA-H 2 SO 4 , with a weight concentration range of 19–20% when heated to 80–95 °C has been used to fabricate high-strength fibers by dry-jet wet-spinning process [ 4 – 6 ]. The unusual rheology phenomena of PPTA-H 2 SO 4 LC solution have been reported [ 7 – 11 ], including strong shear-thinning, long relaxation time, and high viscous activation energy.…”