Melt spinning polypropylene

In melt spinning, polypropylene in powder or pellet form is heated above the melting point and then is extruded through fine orifices of a spinneret into the air. Below spinneret in the air thin streams are intensively cooled and subjected to an intense stretching. During cooling the liquid streams sohdify. Finally, solidified filaments are taken by final take-up device. 

Yu, Y. White, J.L. (1999). Structure development in melt spinning polypropylene-EPM blends and dynamically vulcanized polyolefin TPEs. lntern.Polym.Proc., Vol.l4, Issue 2, pp. 159-167. 

Mini-fibers have also been observed by Liang et al. [159] on melt spinning polypropylene/polyamide blends. The diameters of the dispersed polyamide 6 phase mini-fibers are tens of microns and more. This is clearly due to the large interfadal tension in this system (polypropylene/polyamide 6) as compared to polyethylene/ polystyrene blends of Min et al. (Table 1.1). 

Improvements in melt spinning techniques and film filament processes have made polypropylene accessible for fiber production. Low-cost fibers made from polypropylene are replacing those made from sisal and jute. 

P.O.72 is used for melt spin dyeing of polypropylene, in which 1/3 SD (1% TiOz) affords 0.2% pigment. The lightfastness of PP colorations with 0.3%... 

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. 

J.J. Kim, T.S. lang, Y.D. Kwon, U.Y. Kim and S.S. Kim, Structural Study of Micro-porous Polypropylene Hollow Fiber Membranes Made by the Melt-Spinning and Cold-Stretching Method, J. Membr. Sci. 93, 209 (1994). 

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). 

The filaments of polypropylene fibre are produced from propylene using special catalysts. The polymerisation process involved is addition, as the double bond is broken in the propylene molecule, the monomer or single molecules join or add together. The filaments are produced by the melt-spinning process in a similar manner to polyester. The repeat unit of polypropylene is... 

The same authors studied polypropylene samples PP-H-N, PP-H-R-B, PP-M-N, and PP-M-B in low-speed isothermal melt-spinning experiments at 180°C [93]. The apparent viscosities measured in that experiment are given in Figure 3.9. As seen, the viscosities are larger than those measured in simple elongational flow. Also, all the viscosities decrease with elongation rate, although those of the narrow samples do not decrease as rapidly as those of the broad-distribution samples. 

FIGURE 3.9 Apparent melt-spinning elongational viscosity as a function of elongational rate for polypropylene. (From Minoshima, W. White, J.L. Spruiell, J.E. J. Appl. Polym. ScL, 1980, 25, 287. With permission.)... 

The manufacture of large monofilaments, certainly larger than 100 denier, must be carried out in a water-quench process because of the inherent limitation of forced convective heat-transfer with gases. Conventional screw extruders are used for melting and conveying the polypropylene resin, just as in the case of the melt-spinning processes described above. Often, however, there are no metering pumps used in the process. 

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 ... 

For the formation of polypropylene textiles different techniques were developed. The common method used for the formation of mono- and multifilaments is classical melt spinning. 

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