Spinneret hole

Although the cross-sectional shape of the spinneret hole direcdy affects the cross-sectional shape of the fiber, the shapes are not identical. Round holes produce filaments with an approximately round cross section, but with crenelated edges triangular holes produce filaments in the form of a "Y." Different cross sections are responsible for a variety of properties, eg, hand, luster, or cover, in the finished fabric. Some fibers may contain chemical additives to provide light-fastness and impart fire retardancy. These are usually added to the acetate solution before spinning,... 

Fig. 13. Cross sections of cellulose acetate fiber from (a) circular and (b) triangular spinneret holes.

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

The dark blue solution containing 5—10% of cellulose with a DP of 1000—2000 is filtered through a series of plate-and-frame filter presses using fine mesh metal screens to remove any particles that might block the spinneret holes. It is then deaerated under vacuum and stored ready for spinning. Unlike viscose dope, the cuprammonium cellulose [9050-09-3] solution is relatively stable. 

Liquid crystals, due to the presence of the ordered domains, are optically anisotropic, i.e. birefringent. This can be easily verified by observing the liquid crystal, e.g. aramid and sulfuric acid solution, at rest between crossed polarizers. The parallel arrays of polymer chains in liquid crystalline state become even more ordered when these solutions are subjected to shear as, for example, in extruding through a spinneret hole. It is this inherent property of liquid crystal... 

Fiber Formation. Solutions were extruded from a wet spinning apparatus (Bradford Univ. Research Ltd., equipped with a six hole spinneret, hole diameter 0.23 mm) by wet or air-gap spinning. Methanol was the coagulant. Alternatively, fibers were extruded from a syringe into methanol through a 2.5 cm air-gap. 

A number of phenomena, such as extradate swell and melt fracture, depend on blend composition and, in turn, affect the process. Melt fracture obviously puts limitations to the production rate. Swelhng of fibers at the exit from spinneret holes was reported to be a non-linear function of the blend composition for a number of systems [Han and Yu, 1972]. 

The system of equations shown in Figure 4 are those of Seorge(2), except for the addition of the spin-line deflection terras, S, the slope of the spin line with respect to the vertical, and Y, the distance from the vertical axis through the spinneret hole. Both these terms are illustrated in Figure 3. 

Historically, temperature and velocity profiles have been shown as functions of position, as in Figures 5 and 6. It is instructive to plot these profiles as functions of time, as in Figures 7 and 8. From this type of plot, we gain a sense of the time involved and the magnitude of the rates of change. The time plotted in these two figures starts at the Instant an element of polymer leaves the spinneret hole and ends when the freeze point is reached. Typically, this transit time is a few hundred milliseconds but, as can be seen... 

Fitzgerald and Knudsen [286] have described the mechanics of crimp development in bicomponent yams. The extent of crimp development will depend on (1) the shrinkage differential between the components, (2) the distribution of components in the fiber, and (3) the translational restraints that may inhibit crimp development. Obviously, the maximum crimp would be developed when the fibers were comprised of equal parts of each component and these components were separated and located on opposite sides of the fiber. On the other hand, if the cross section revealed a distribution in which one polymer was separated into two regions, each on one side of the center slice, then any differential shrinkage forces would be neutralized and no crimp would be developed. In practice, many different distributions of the two components may be observed depending upon the technique used to mix the two polymer dope streams and deliver them to the spinneret hole [287-290]. 

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