Solution dry spinning

Dry Spinning. On a worldwide basis, about 90% of all spandex fibers are produced by various adaptations of dry spinning (15,16). The solution dry spinning process is illustrated in Figure 5. The polymer spinning solution is metered at a constant temperature by a precision gear pump... 

Four different processes are currently used to produce spandex fibers commercially melt extrusion, reaction spinning, solution dry spinning, and solution wet spinning. As shown in Figure 5, these processes involve different practical applications of basically similar chemistry. If the diol or diamine(s) reaction with the prepolymer is carried out in a solvent, the resulting block copolymer solution may... 

Process 3 can be achieved mainly by three procedures melt spinning, solution dry spinning, and solution wet... 

Extrusion Processes. Polymer solutions are converted into fibers by extmsion. The dry-extmsion process, also called dry spinning, is primarily used for acetate and triacetate. In this operation, a solution of polymer in a volatile solvent is forced through a number of parallel orifices (spinneret) into a cabinet of warm air the fibers are formed by evaporation of the solvent. In wet extmsion, a polymer solution is forced through a spinneret into a Hquid that coagulates the filaments and removes the solvent. In melt extmsion, molten polymer is forced through a multihole die (pack) into air, which cools the strands into filaments. 

Pure PVA dissolves in water but does not fluidize by melting. Commercial production of PVA fiber is therefore carried out by wet spinning or dry spinning, utilizing aqueous PVA solution. In either case, purified PVA is dissolved in hot water and the solution is extmded through fine holes of a spinneret the extmded streams are coagulated to form continuous filaments, which are then heat-treated to have adequate mechanical properties. 

Copolymers of acrylonitrile are sensitive to heat, and melt spinning is not used. Solution spinning (wet or dry) is the preferred process where a polar solvent such as dimethyl form amide is used. In dry spinning the solvent is evaporated and recovered. 

Acetate A general name for processes for making cellulose acetate fibers. Cellulose is acetylated, dissolved in acetone, and spun into fibers by injecting through orifices into heated chambers. Cellulose mono-acetate is made by acetylating with a mixture of acetic acid, acetic anhydride, and sulfuric acid as the catalyst. Cellulose tri-acetate is made in a similar fashion, but using perchloric acid as the catalyst, and dry-spinning from a solution in ethanol/ methylene chloride. Cellulose tri-acetate fibers were first made commercially by Courtaulds in London in 1950. 

Elastomeric fibres based upon both polyester-urethane and polyether-urethane structures followed. The early work by Bayer led to the use of highly polar solvents such as dimethyl formamide. Formation of fibres by reactive spinning, where the isocyanate-ended polymer is extruded into an aqueous solution of a chain-coupling agent, was described in 1949 [75] and by dry-spinning a solution of the chain-coupled polymer in 1951 [76], However, Bayer did not immediately use their technology to produce commercial fibres [77],... 

Solution blends of 20-25% by weight were formed in DM Ac, with conventional dry spinning and film casting techniques used to produce blend fiber and film, respectively. Blend powders were prepared by precipitating the dope with a non-solvent (water). All materials were extensively washed in methanol or water to reduce residual solvent to less than 1 wt %. Neat resin tensile bars and plaques were compression molded from both powder and fiber. 

Cellulose Acetate and Triacetate Fibers. Polymer solutions arc convened into fibers by extrusion. The dry-extrusion process, also called dry spinning, is primarily used lor acelate and triacetate. 

There are three conventional synthetic liber spinning methods that can he applied to the production of hollovv-liher membranes melt spinning, solution (well spinning, and a combination of these lirst two methods, dry-jet vvei spinning... 

---