Temperature fiber spinning

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. 

Polymer Solvent. Sulfolane is a solvent for a variety of polymers, including polyacrylonitrile (PAN), poly(vinyhdene cyanide), poly(vinyl chloride) (PVC), poly(vinyl fluoride), and polysulfones (124—129). Sulfolane solutions of PAN, poly(vinyhdene cyanide), and PVC have been patented for fiber-spinning processes, in which the relatively low solution viscosity, good thermal stabiUty, and comparatively low solvent toxicity of sulfolane are advantageous. Powdered perfluorocarbon copolymers bearing sulfo or carboxy groups have been prepared by precipitation from sulfolane solution with toluene at temperatures below 300°C. Particle sizes of 0.5—100 p.m result. 

Melt spinning is not used for polyacrylics because they are sensitive to high temperatures. They actually begin to decompose before they reach melting temperature. Solution spinning is used instead. The dried polymer is dissolved in a polar solvent like acetone or dimethyl formamide (DMF). The spinning mechanics are otherwise the same, except the solvent is recovered as it vaporizes, immediately after the extrusion through the spinneret. Most acrylics are sold and used in the form of staple fiber. 

A fiber spinning dope is prepared by mixing the polysulfone, solvent and a nonionic surfactant. A preferred solvent is di-methylformamide (DMF) a preferred surfactant is an alkylaryl polyether alcohol. The dope is prepared such that its bulk viscosity is typically between 9000 and 12000 poises. Successful dopes demand control of the mode of addition, degree of polymer comminution, the temperature protocol and agitation rate. The dope is typically filtered through a 10 micron filter under pressure prior to spinning. 

The polystyrene simulation followed the experiments of Bell and Edie (12) with good agreement. Figure 14.8 shows the simulation results for fiber spinning nylon-6.6 with a draw ratio of 40. The figure demonstrates the wealth of information provided by the model. It shows the velocity, temperature, axial normal stress, and crystallinity fields along the threadline. We see the characteristic exponential-like drop in diameter with locally (radially) constant but accelerating velocity. However, results map out the temperature, stress, and crystallinity fields, which show marked variation radially and axially. 

Tg and melting temperature of PP are lower than that of the HKL. Further, the fiber spinning temperature for PP is approximately the same as that of HKL. This, combined with the fact that the blends are immiscible and do not exhibit any specific interactions, makes it difficult to increase the heating rate of thermostabilization beyond that of the HKL fibers. 

Motionless mixers were a new class of mixing devices that were introduced in the late sixties. These devices are placed in line and give radial mixing to a stream to homogenize composition and temperature (50). They are used in extrusion, injection molding, and fiber spinning to achieve a radially homogeneous stream. 

Barmag 3DD torpedo mixer is a foreraimer of this category of mixers. The unit was designed to improve the temperature homogeneity of the film and fiber spinning extrusion lines. The device is... 

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