Spin viscosity

The early methods of spinning viscose continuous filament were based upon rapid coagulation and regeneration after extrusion. This procedure is reversed in the preparation of polynosic fibres because the coagulating liquor only decomposes the xanthate slowly so that considerable stretching... 

For synthetic and regenerated fibres, the fibre production (primary spinning) is mainly made by melt spinning (polyester, nylon etc.), dry spinning (elastane etc.) or wet spinning (viscose, lyocell etc.). Lenzing AG has produced carbon footprints of viscose and lyocell fibres and compared these with other fibres (Shen and Patel, 2008 Shen et al., 2010 Terinte et al., 2014 Van der Velden et al., 2014). The production of natural fibres via agriculture or forestry has been studied elsewhere (e.g. Sandin et al., 2013). 

In 1897, Topham [117] first discovered that ripening is necessary in the preparation of a good spinning viscose and to obtain desired rayon properties. 

Second coefficient of viscosity A (Pas) Shear/bulk spin viscosity tj, A (kgms rd ) Surfactant density ps (kg/m ) ... 

Dynamic viscosity of the liquid carrier Shear spin viscosity Second coefficient of viscosity Bulk spin viscosity... 

Considerable research was undertaken into methods of improving the quality of the protein curd. Denatured soya bean protein tends to aggregate rather than crystallise so many of the modifications were intended to overcome this adhesive-like behaviour which gave rise to a variety of technical problems. US Patent 2,112,210 describes a process in which the protein was solubilised in sodium hydroxide, treated with carbon disulphide and oxidised with air. It was hoped that this method would result in a fibre with better spinning viscosity, stability and tensile strength. 

From SCRP spectra one can always identify the sign of the exchange or dipolar interaction by direct exammation of the phase of the polarization. Often it is possible to quantify the absolute magnitude of D or J by computer simulation. The shape of SCRP spectra are very sensitive to dynamics, so temperature and viscosity dependencies are infonnative when knowledge of relaxation rates of competition between RPM and SCRP mechanisms is desired. Much use of SCRP theory has been made in the field of photosynthesis, where stnicture/fiinction relationships in reaction centres have been connected to their spin physics in considerable detail [, Mj. 

Polymers owe much of their attractiveness to their ease of processing. In many important teclmiques, such as injection moulding, fibre spinning and film fonnation, polymers are processed in the melt, so that their flow behaviour is of paramount importance. Because of the viscoelastic properties of polymers, their flow behaviour is much more complex than that of Newtonian liquids for which the viscosity is the only essential parameter. In polymer melts, the recoverable shear compliance, which relates to the elastic forces, is used in addition to the viscosity in the description of flow [48]. 

To produce a spandex fiber by reaction spinning, a 1000—3500 molecular weight polyester or polyether glycol reacts with a diisocyanate at a molar ratio of about 1 2. The viscosity of this isocyanate-terrninated prepolymer may be adjusted by adding small amounts of an inert solvent, and then extmded into a coagulating bath that contains a diamine so that filament and polymer formation occur simultaneously. Reactions are completed as the filaments are cured and solvent evaporated on a belt dryer. After appHcation of a finish, the fibers are wound on tubes or bobbins and rewound if necessary to reduce interfiber cohesion. 

Because of the high melt viscosity of polyolefins, normal spinning melt temperatures are 240—310°C, which is 80—150°C above the crystalline melting point. Because of the high melt temperatures used for polyolefin fiber spinning, thermal stabilizers such as substituted hindered phenols are added. In the presence of pigments, the melt temperature must be carefully controlled to prevent color degradation and to obtain uniform color dispersion. 

Flow processes iaside the spinneret are governed by shear viscosity and shear rate. PET is a non-Newtonian elastic fluid. Spinning filament tension and molecular orientation depend on polymer temperature and viscosity, spinneret capillary diameter and length, spin speed, rate of filament cooling, inertia, and air drag (69,70). These variables combine to attenuate the fiber and orient and sometimes crystallize the molecular chains (71). 

EOY speeds are the most recent development in PET spinning (78). Properties are similar to HOY and appear to be limited by the differential cooling rate from filament surface to filament core. This leads to radial distribution of viscosity, stress, and, consequentiy, molecular orientation (75). Eiber tensde strength is limited. Nevertheless, speeds up to 7000 m /min are commercial and forecasts are for speeds up to 9000 m /min by the year 2000 (79). Speeds to 9000 m/min have been studied (68,80,81). 

In another laboratory at Kew, C. H. Steam and C. E. Topham, who had worked for Sir Joseph Swan on lamp filaments, developed the continuous filament spinning process (8) and the machinery needed to wash and coUect (9,10) the yams. A fibermaking method was outlined in 1898, and the Viscose Spinning Syndicate was formed to develop the concept into a commercial proposition. 

It is possible to add modifiers or delustrants at the dissolving stage. However, modem viscose dope plants feed several spinning machines which are often expected to make different grades of fiber. It is therefore now more common to add the materials needed to make special fibers by injection close to the spinning machines. 

The correct viscose age or ripeness for spinning varies according to the type of fiber being made. Ripeness can be assessed by estabHshing the salt concentration necessary to just coagulate the viscose dope. The preferred test uses sodium chloride (salt figure) although ammonium chloride is the basis of the alternative method (Hottenroth number). 

Permanent chemical crimp can be obtained by creating an asymmetric arrangement of the skin and the core parts of the fiber cross section. Skin cellulose is more highly ordered than core cellulose and shrinks more on drying. If, during filament formation in the spin bath, the skin can be forced to burst open to expose fresh viscose to the acid, a fiber with differing shrinkage potential from side-to-side is made, and crimp should be obtained (Fig. 5a). 

Asahi Chemical Industries (ACl, Japan) are now the leading producers of cuprammonium rayon. In 1990 they made 28,000 t/yr of filament and spunbond nonwoven from cotton ceUulose (65). Their continuing success with a process which has suffered intense competition from the cheaper viscose and synthetic fibers owes much to their developments of high speed spinning technology and of efficient copper recovery systems. Bemberg SpA in Italy, the only other producer of cuprammonium textile fibers, was making about 2000 t of filament yam in 1990. 

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