Developments in melt spinning

Melt spinning is not limited to the production of conventional polymeric filaments various developments in terms of type of filaments, structure-property relationships, introduction of nano materials, and advances in process characterization have evolved in the last few years. Some of these developments are briefly discussed below. 

Hooshmand et al. (2011) blended polypropylene/polyamide with carbon nanotubes (CNTs) and melt spun to as-spun and drawn filaments. Thermal analysis showed that increasing the polyamide content decreased the degree of crystallinity in the blends. Characterization of the filaments demonstrated 

The volume throughput was controlled by an adjustable piston speed and was kept constant at 0.755 cm /min. The melt-spun monofilaments were collected on a winder. The take-up velocity was set to 20, 50, and 100 m/min. The researchers found that the liquid sensing properties of the filaments were strongly influenced by both the MWNT content and the take-up velocity. Both yielded decreased relative resistance changes. It is interesting to note that multi-walled carbon nanotubes had reasonably good macroscopic dispersion and distribution within the PLA as evidenced by the microscopy image shown in Fig. 4.6 (Potschke P et al., 2010). 

5 Piston-type spinning device for production of monofilaments (Potschke P et al., 2010) 

6 Light transmission microscopy image of a PLA fiber with 3.0 wt.% MWNT (as extruded) illustrating the high degree of macroscopic MWNT dispersion (Potschke P et al., 2010). 

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A cartoon of this model of morphology and molecular chain topology development in melt spinning of PET is shown in Figure 1.6. 

FIGURE 1.5 Morphology development in melt spinning as a function of key spinning parameters. 

Choi, C.H. White, J.L. (1998). Comparative study of structure development in melt spinning polyolefin fibers. Intem.Polym.Proc., Vol.l3, Issue 1, pp. 78-87. 

Choi, D. White, J.L. (2000). Structure development in melt spinning syndiotactic polypropylene and comparison to isotactic polypropylene. Intern.Polym.Proc., Vol.15, Issue 4, p>p. 398-405. 

Melt spinning was developed in the 1930s. In melt spinning the polymer is melted or extruded, clarified by filtration, and pumped through a die having one or more small holes. The die is called a spinneret. The number, shape, and size of the hole can vary considerably. The number of holes ranges from several to several thousand. For continuous filament formation, the... 

Because of its extremely low solubility in low-boiling and inexpensive organic solvents, nylon 66 required a new technique for converting the solid polymer into fibers hence the development of melt spinning, the third basic method for producing manufactured fibers. The following description refers essentially to nylon 66 because it was the first to use the method, but the process applies, in general, to all melt-spun manufactured fibers. 

Although Sumitomo had first introduced a PAN hydrate melt spun fiber in 1948, it was not until about 1969 that American Cyanamid had developed their melt spinning process [106-108], which was later sold to BASF, who continued further developments [109-113]. 

It is interesting to note the developments in the spinning designs of bi-component spinning. One of the hrst patents in bi-component spinning went to Okamoto from the US Pat. No. 3531368. As seen in Rg. 6.5, the melt-ers 41 and 42 are for two different polymers through metering pumps 61 and 68. IVansfer pipes 57 and 59 transfer dual streams from the left hand pump to the spinneret assembly, from where the bi-component fibres are extruded. 

Finally, the manner in which individual molecules crystallize depends on the nature of the polymer molecule and the conditions under which crystallization takes place (see Fig. 5.18). It is worth noting at this point the work of Dees and Spruiell (1974) concerned with the structure development during melt spinning of HDPE fibers. Figure 9.9 presents their morphological model based on crystallite orientation factors and some other information. At low take-up speeds... 

Similar to molecular orientation, the development of ciystalhne stractnre plays an important role in melt spinning. In general, the crystallization of polymers occurs between the glass transition temperature T and melting temperatnre TJ. Literature reports show the crystallization conld occnr above the melting temperature, especially under high molecnlar orientation. However, the amount of such crystallization is small and has no apparent effect on the final stractuie and properties of most melt-sprm fibers, and hence this chapter will only address the crystallization below T. ... 

In previous paper [8], we reported that a small amount of PP could obviously decrease the orientation of ethylene butene copolymer (EBM) in melt spinning. In this study, the phase morphology development of PP/EBM blends in extrusion and melt spinning is studied. The dispersed PP droplets were also found to form encapsulation layer in both high speed extrusion and melt spinning. The encapsulation phase morphology was found to affect the birefringence of the blends. 

In the spunbond process, the fiber is spun similarly to conventional melt spinning, but the fibers are attenuated by air drag appHed at a distance from the spinneret. This allows a reasonably high level of filament orientation to be developed. The fibers are directly deposited onto a moving conveyor belt as a web of continuous randomly oriented filaments. As with meltblown webs, the fibers are usually thermal bonded or needled (53). 

Mechanical Properties. Polyester fibers are formed by melt spinning generally followed by hot drawing and heat setting to the final fiber form. The molecular orientation and crystalline fine stmcture developed depend on key process parameters in all fiber formation steps and are critical to the end use appHcation of the fibers. 

Reservoir or coaxial fibers can be produced from the glycolide/ lactide polymers (53,55). Two different methods have been investigated. Dunn (53) utilized a melt-spinning technique in which the drug was introduced during the spinning process as a suspension or solution in a suitable lumen fluid. Eenink (55) developed a dry-... 

Hollow fiber membrane(s), 70 766 76 1-31 additional types of, 76 24 advantages of, 76 3 categories of, 76 2-3 in desalination, 76 22 development of, 76 1 extractors, 70 787 fiber treatment for, 76 12-18 future prospects for, 76 26-28 glass and inorganic, 76 23-24 handling and unit assembly of, 76 15-18 interpenetrated wall matrix in, 76 15 low pressure, 76 24-26 macrovoids in, 76 12 materials associated with, 76 18-24 melt spinning of, 76 9-10... 

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