Sizing Spinneret

Quench. Attempts have been made to model this nonisotherma1 process (32—35), but the complexity of the actual system makes quench design an art. Arrangements include straight-through, and outside-in and inside-out radial patterns (36). The optimum configuration depends on spinneret size, hole pattern, filament size, quench-chamber dimensions, take-up rate, and desired physical properties. Process continuity and final fiber properties are governed by the temperature profile and extension rate. 

Melt spinning was developed in the 1930s. In melt spinning the polymer is melted or extruded, clarified by filtration, and pumped through a die having one or more small holes. The die is called a spinneret. The number, shape, and size of the hole can vary considerably. The number of holes ranges from several to several thousand. For continuous filament formation, the... 

A variation on this approach used multifilament coextrusion, so-called microfabrication by coextrusion (MFCX) . A limitation of the single-filament process is the size of the filament. The rheological properties of the polymer/ ceramic blends make spinning fibers smaller than 250 pm very difficult. Additionally, spooling fine-diameter fibers is quite challenging. The MFCX is shown schematically in Fig. 1.3. The setup is the same as that used to spin fibers except that the spinneret is replaced with an extrusion die with a diameter between 1 mm and 6 mm. Two separate extrusion steps are used. In the first step, coarse primary filaments are extruded from the feedrod (Fig. 

Female lobsters carry their e s (known as berries) beneath their abdomen, attached to stractures called spinnerets. The number of eggs is related to the size of the female, and is typically about 5,000 eggs for a 10 in (25 cm) long female, and 40,000 for a 14 in (36 cm) lor aitimal. However, one 17 in (43 cm) long female had 63,000 e, and another slightly larger one had 97,000. 

Some methods adhere to the principle of closing the incident drop by fusion. A thin film of a polymer material is formed on the surface of a spinneret with a small orifice size. Microdrops of a liquid Cl are forced periodically through the orifices. When squeezed the drop makes contact with the film... 

The processes that occur in the spinline, between the exit of the polymer from the spinneret and the point of stress isolation on the first godet or roller at the base of the spin line, involve the changing of this fluid network to the solid-state molecular chain topology of the filament. Within a distance of 3 5 m, and under the influence of an applied force (take-up tension) and quench media, at speeds in excess of 100 miles per hour—less than 0.01 sec residence time—the fiber is transformed from a fluid network to a highly interconnected semicrystalline morphology, characterized by the amount, size, shape, and net orientation... 

The spin pump (metering pump) delivers the molten polymer to a spin pack, which consists of a top cap and a breaker plate to distribute polymer evenly, then into a filtration media and out of the spinneret. The filtration media contains either different layers of special sand, layers of different size of stainless steel screens, or sintered metals. In addition to removing the foreign particles, gel particles and undesirable conglomerate additives, filtration may also improve the polymer melt homogeneity due to its torturous path and high shear of the filtration media. 

The spinnerets are made of stainless steel or other suitable metals. Selection of material for spinnerets is made on the basis of resistance to corrosion by the solvent system and ease of machinability. The spinneret material must be readily machinable to close tolerances because each hole of a spinneret is precision-made to the specific size and shape. 

FIGURE 12.39 Shear rate dependence of jet swell. Spin-bath conditions are same as in Figure 12.38. Symbols indicate different spinneret sizes. See original reference for specific values. (From Paul, D.R., J. Appl. Polym. Sci. 12, 2273, 1968.)... 

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