Polypropylene fiber spinning

Polymer scientists and engineers have developed a wide variety of processes by which to convert polypropylene into useable articles. These processes include fiber-spinning, production of melt blown and spun bond non-woven fabrics, film production, blow molding, and injection molding. The following sections describe these processes and the resulting properties of the product as a function of the process. 

Rank the following polypropylene conversion processes in terms of their relative sensitivity to particulate contamination, film casting, injection molding or fiber spinning. 

Polypropylene fibers. A small part of the total fibers market (and therefore at the tail end of this section on fibers) is fiber grade polypropylene. The chemistry for polypropylene fibers is the same as for thermoplastics. The spinning mechanics are the same as that for nylon. Polypropylene fibers are particularly resistant to abrasion and chemicals, and they are lightweight. However, they dont take colors very well, and the materials have low softening points and low resilience (they wrinkle). The major applications for polypropylene fibers are carpet-face fiber and backing (because its tough) and rope (because it is strong and floats in water). 

The dyeing of polypropylene fibers, being an item of research for decades, is successfully accomplished with partially stearate-modified hyperbranched polyesteramides. The long alkyl chains ensure compatibility with the polypropylene matrix. The mixing-in of hyperbranched polyesteramides via extrusion affected neither the melt spinning process nor the final polypropylene fiber properties. The modified fibers are dyeable under standard conditions as are, e.g., polyesters or cotton. They can even be used for printing for example a picture pattern on a polypropylene carpet. 

Meh Spinning. This process is used to produce a broad range of polypropylene fibers ranging from fine, dtex (one denier) staple coarse continuous filaments. Hoiuopolyiners are almost exclusive used to produce fibers, although copolymer blends are used in some special applications. Processing conditions and polymer melt flow vary with the desired fiber type. 

Fig. 14.5 Morphological model of structures developed in as-spun HDPE. Take-up velocities are (a) very low (b) low (c) medium and (d) high. [Reprinted by permission from J. E. Spruiell and J. L. White, Structure Development during Polymer Processing Studies of the Melt Spinning of Polyethylene and Polypropylene Fibers, Polym. Eng. Set, 15, 660 (1975).]...

Figure 4.7 Schematic of the melt spinning process of making polypropylene fibers.

Hollow membrane fibers are required for many medical application, e.g. for disposable dialysis. Such fibers are made by usmg an appropriate fiber spinning technique with a special inlet in the center of the spinneret through which the fiber core forming medium (liquid or gas) is injected. The membrane material may be made by melt-spinning, chemical activated spinning or phase separation. The thin wall (15-500 xm thickness) acts as a semi-permeable membrane. Commonly, such fibers are made of cellulose-based membrane materials such as cellulose nitrate, or polyacrylonitrile, polymethylmethacrylate, polyamide and polypropylene (van Stone, 1985). 

Shell PdypropylMC [ShelQ Polypropylene horiK lymers or random copolymers for inj. molding, fiber spin-... 

Radicals, generated in polypropylene fibers during irradiation as well as the transition frcan these reidicals (R ) to peroxy radicals (ROa ) are monitored by electron spin resonance spectroscopy. Experimental data exhibit an anomaly in the temperature dependence of RO, concentration, around the glassy transition temperature (Tq). The dependence of RO, concentration on temperature, around T, is described by a Hil-liam-Landel-Perry equation rather than by an Arrhenius one. Consequently, the transition consists of two steps the first is associated with diffusion processes and the second with the proper chemical reaction. 

FIGURE 3.18 Diameter fluctuations for polypropylene fibers during spinning random fluctuation and draw resonance. (From Minoshima, W. White, J.L. Spruiell, J.E. J. Appl. Polym. Sci., 1980, 25, 287. With permission.)... 

Ziabicki [187] has given an extensive review of studies of the melt-spinning process. Some derivations from this review are discussed briefly. A simple analysis for predicting the effects of process parameters on fiber orientation are also discussed before polypropylene data are presented. To summarize, the properties of spun polypropylene fiber (and other fibers as well) are primarily determined by the stress existing in the spin line at the position of the final diameter, at least at moderate spinning speeds. The stress level is determined largely by ... 

Various authors have studied the effects of spinning conditions on the basic properties of spun polypropylene fibers. Notable are the studies of Sheehan and Cole [185,108], Katayama et al. [189,112], Fung et al. [190,113], Kitao et al. [191,114], Anderson and Carr [192,110], Henson and Spruiell [193,116], Spruiell and White [85], Ishizuka and Koyama [194,117], and Nadella et al. [79]. 

FIGURE 3.53 Melting peak temperature versus heating rate for three polypropylene fibers spun at different spin-line stress levels. (From Jaffe, M. In Thermal Methods in Polymer Analysis, Shalaby, S.W. ed., Franklin Institute Press, Philadelphia, 1977, p. 93. With permission.)... 

High-shrinkage polypropylene fiber is mixed with conventional fibers in spinning to yield a fluffy yarn. The proportion of blending depends on the end-use. The blend ratio for mixed spinning generally include the following variations ... 

In summary, there is an impressive amount of research effort on various polypropylene fiber products. The developments of fine-denier spinning, dyeability modification, high fiber strength and modulus, and nanocomposites certainly appear inductive to further growth in market shares and value-in-use for propylene fibers. However, as with other synthetic fibers, the manufacturing process yield and cost, particularly spinning continuity, must not be adversely impacted by any new technology to be commercialized. This is clearly the key to the future success of polypropylene fibers. 

Spruiell, J.E. White, J.L. (1975). Structure development during polymer processing - studies of melt spinning of polyethylene and polypropylene fibers. Polym.Eng.Sci, Vol. 15, Issue 9, pp.660-667. 

High speed spinning procedures for the manufacture of high denier polypropylene fibers and yams require application of nucleating agerrls, such as dibenzylidene sorbitol, para-methyldibenzylidene sorbitol, bis-(3,4-dimethyl benzylidene) sorbitol, and sodium 2,2 -methylene-bis-(4,6-di-t-butylphenylene) phosphate. They are used in concentration of 2500-3000 ppm. ... 

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