Fiber spinning rheometer

Figure 3-25 A Spin-Line or Fiber-Spin Rheometer for Extensional Viscosity Measurement (Redrawn from Bames et al., 1989).

Understanding the rheology of the fiber-spinning dope solutions is important to enable the fabrication of the polyaniline fibers with reproducible electrical and mechanical properties. In our studies, a Brookfield RVDV-III cone and plate rheometer was used to measure the viscosity of the concentrated EB solutions. The gelation studies of these solutions were conducted at 25°C and a constant shear rate of 0.8 using cone spindle (CP-52) with a semivertical cone angle of 87°. Figure 2.10 illustrates the viscosity... 

Another area of current research deals with combining the earlier work on production of polymer blends in the elastic melt extruder and the observation of the maximm in melt elasticity as a fimction of composition as fo md in the orthogonal rheometer studies on blends. It would be expected that as the melt elasticity increased the forces required for melt orientation would also increase. This has been confirmed in current studies of melt tension in fiber spinning experiments. The important point is that the composition of the blend can be used to control the molecular orientation. 

These working equations, along with the limitations and utility of fiber spinning measurements, are summarized in Table 7.5.1. The major problem is that typically is not constant, so the force, which is measured over the entire fiber, is an integration of stresses due to various strain rates and even the upstream shear histmy in the die. For these reasons, the fiber spinning experiment is not a true rheometer, but gives only an iq>paient uniaxial extensional viscosity. 

The other important commercial design for extensional measurements on low viscosity fluids is the opposed nozzle device shown in Figure 8.5.2 (Fuller et al., 1987 Mikkelsen et al., 1988). In addition to the opposed-nozzle configuration, if the arm G is turned 90°, the device can also be operated as fiber spinning and tubeless siphon rheometers (Cai et al., 1992). 

Two series of PBTA/PI block copolymers were synthesized in this study and solution processed into molecular composite fibers via dry-jet wet-spinning. The unique rheological properties of liquid-crystalline PBTA homopolymers and PBTA/PI block copolymers were studied with a cone-and-plate rheometer. For block copolymers, the critical concentration decreased with an increase in PBTA content. The flow curves of isotropic and anisotropic solutions could be described via the power-law model and Carreau model, respectively. Copolymer fibers possess tensile strength and modulus located between those of PBTA fibers and PI fibers. Moreover, the tensile strength and modulus of Col fibers increase with an increase in PBTA content. Besides, increasing the draw ratios would give rise to an increase in the mechanical properties of copolymer fibers... 

The polymer solution used for the production of the PAN I filaments discussed in this chapter was a 15% w/ w DMPU/PANI spin dope having a viscosity of 2l,0(K) cP at a shear rate of 1.5 s at a temperature of 25°C. A Brookfield cone-and-plate rheometer was used for the viscosity determination. The polymer solution is placed in the spin dope tank and pressurized with N2, providing a steady flow of the spin dope to the gear pump. The solution is then pumped through a 0.1 mm circular spinnerette (L/D = 2.0) into a coagulation bath consisting of NMP and water. The fiber is continuously taken up... 

Schematic diagram of the Carri-med Spin Line Rheometer (Jones et al., 1987). Air pressure, A forces test liquid the reservoir B through tube C to the spinning nozzle D, where it is drawn down by the rotating drum E. Liquid is scraped from the drum by F and falls into the beaker G. The feed tube C also acts as a force spring, whose deflection is measured by LVDT, H. Fiber diameter is reccxrded with a video camera near J. The whole apparatus is contained in an environmental chamber.

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