Monofilaments process

The monofilament process (Fig. 8.13) includes aspects of both the melt spinning and slit film processes. The extmder is equipped with a melt pump immediately upstream of a spinneret that extmdes relatively thick filaments ranging from 0.08 mm to 3.0 mm in diameter. The filaments are quenched in a water bath and are hauled offby godet rolls. Orientation is performed by reheating and stretching in an oven under tension applied by a second haul-off. An alternative orientation process uses heated godet rolls in place of the oven. 

Take-Up. Take-up devices attenuate the spinline to the desired linear density and collect the spun yam in a form suitable for further processing. A godet wheel is typically used to control the take-up velocity which varies from 1—2 m/s for heavy monofilaments to 10—33 m/s for fine yams. The yam can be stacked in cans, taken up on bobbins, or directiy transferred to drawing and texturizing equipment. 

Slit-Film Fiber. A substantial volume of olefin fiber is produced by slit-film or film-to-fiber technology (29). For producing filaments with high linear density, above 0.7 tex (6.6 den), the production economics ate more favorable than monofilament spinning (29). The fibers are used primarily for carpet backing and rope or cordage appHcations. The processes used to make slit-film fibers are versatile and economical. 

In selecting cloths made from synthetic materials, one must account for the fact that staple cloths provide a good retentivity of solid particles due to the short hairs on their surface. However, cake removal is often difficult from these cloths - more than from cloths of polyfilament and, especially, monofilament fibers. The type of fiber weave and pore size determine the degree of retentivity and permeability. The objective of the process, and the properties of particles, suspension and cake should be accounted for. The cloth selected in this maimer should be confirmed or corrected by laboratory tests. Such tests can be performed on a single filter. These tests, however, provide no information on progressive pore plugging and cloth wear. However, they do provide indications of expected filtrate pureness, capacity and final cake wetness. 

Processing. The process requires a monofilament carbon-fiber core which is heated resistively in a tubular glass reactor shown schematically in Fig. 19.1. PI A carbon monofilament is pre-coated with a 1 pm layer of pyrolytic graphite to insure a smooth deposition surface and a constant resistivity. 1 1 SiC is then deposited by the reaction of silane and a hydrocarbon. Other precursors such as SiCl4, and CH3SiCl3 are also being investigated. A fiber cross-section is shown in Fig. 19.2.P1... 

After the polymer is formed, the filament is produced by extrusion. The nylon can be taken directly from the polymerization process while it is still molten. Alternatively, previously dried nylon chips can be heated and melted. The molten nylon is pressed through a spinneret, which is like a showerhead with 10—100 holes. (A spinneret with a single hole produces a monofilament. Nylon monofilaments are used for fishing line and sheer... 

SiC monofilaments produced by the CVD process is generally superior to Nicalon SiC fibers in mechanical properties because of its almost 100% 6-SiC purity while Nicalon is a mixture of SiC, Si02 and free carbon. Representative properties of SiC monofilaments and Nicalon fibers are given in Table 5.15. 

In-Vivo Absorption and breaking strength retention studies. For comparing PDS monofilament in-vivo properties with copolymeric fibers, a second 90/10 PDO/glycolide copolymer (II-A) was prepared and processed following similar schemes to those used for copolymer II. 

Poly(vinylidene chloride) (XLII) and its copolymers with vinyl chloride, acrylonitrile, and acrylates, usually produced by the suspension or emulsion process, are useful as oil, fat, oxygen, and moisture-resistant packaging films (Saran wrap), containers, coatings, tank liners, and monofilaments in drapery fabrics and industrial filter cloths. 

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