Melt spinning processes

Synthetic Fiber and Plastics Industries. In the synthetic fibers and plastics industries, the substrate itself serves as the solvent, and the whitener is not appHed from solutions as in textiles. Table 6 Hsts the types of FWAs used in the synthetic fibers and plastic industries. In the case of synthetic fibers, such as polyamide and polyester produced by the melt-spinning process, FWAs can be added at the start or during the course of polymerization or polycondensation. However, FWAs can also be powdered onto the polymer chips prior to spinning. The above types of appHcation place severe thermal and chemical demands on FWAs. They must not interfere with the polymerization reaction and must remain stable under spinning conditions. 

Tensile Properties. Tensile properties of nylon-6 and nylon-6,6 yams shown in Table 1 are a function of polymer molecular weight, fiber spinning speed, quenching rate, and draw ratio. The degree of crystallinity and crystal and amorphous orientation obtained by modifying elements of the melt-spinning process have been related to the tenacity of nylon fiber (23,27). 

The melt-spinning process used to convert mesophase pitch into fiber form is similar to that employed for many thermoplastic polymers. Normally, an extruder melts the pitch and pumps it into the spin pack. Typically, the molten pitch is filtered before being extruded through a multi-holed spinnerette. The pitch is subjected to high extensional and shear stresses as it approaches and flows through the spinnerette capillaries. The associated torques tend to orient the liquid crystalline pitch in a regular transverse pattern. Upon emerging from the... 

A very unusual characteristic of mesophase pitch is the extreme dependency of its viscosity on temperature [19,34,35]. This factor has a profound influence on the melt-spinning process (described above), as a mesophase pitch fiber will achieve its final diameter within several millimeters of the face of the spinnerette, in sharp contrast to most polymeric fibers. 

Vapor grown carbon fiber (VGCF) is the descriptive name of a class of carbon fiber which is distinctively different from other types of carbon fiber in its method of production, its unique physical characteristics, and the prospect of low cost fabrication. Simply stated, this type of carbon fiber is synthesized from the pyrolysis of hydrocarbons or carbon monoxide in the gaseous state, in the presence of a catalyst in contrast to a melt-spinning process common to other types of carbon fiber. 

The process competes with the traditional method of fiber production in which the precursor material is melted, usually in an arc furnace, then drawn through spinnerets and spun or impinged by high pressure air. The melt-spin process is not well suited to materials with high melting points such as zirconia, silicon carbide, or pure alumina. 

The melt spinning process used for PET fibers is clean and economical. 

Figure 12.7 Schematic of the melt-spinning process used to produce PET fibers...

The melt spinning process for PET fibers can be divided into three regions of take-up speed, as follows ... 

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. 

The usual shear measurements on polymer melts are performed as steady-state experiments in which a stationary state of shear deformation is maintained. A steady-state experiment on tensile deformation, however, means an imitation of a melt spinning process. This type of experiment has several disadvantages ... 

Spinnability is the ability of a polymer to be transformed into long continuous solid threads by a melt-spinning process. Therefore a spinnable polymer must conform to three requirements ... 

Sulfar fibers are extruded from polyphenylene sulfide) or PPS by the melt-spinning process. The first PPS polymer was made in 1897 by the Friedel-Crafts reaction of sulfur and benzene. Researchers at Dow Chemical, in the early 1950s, succeeded in producing high-molecular weight linear PPS by means of the Ullmann condensation of alkali metal salts of p-bromothiophenol. 

Polylactic acid also has many potential uses in fibres and non-wovens. It is easily converted into a variety of fibre forms using conventional melt-spinning processes. Spunbound and meltblown non-wovens as well as monocomponent, bicomponent, continuous (flat and textured) and stable fibres are all easily produced. 

Figure 15 Two selected methods for metallic glass preparation (a) in the melt-spinning process the molten alloys are projected against a spinning wheel (b) in the twin-roUer quenching technique the melt is cooled between two rotating wheels. In both processes, the aim is to achieve ultrafast cooling...

The process of cellulose regeneration in the form of lyocell fibers is significantly simpler than that of the viscose rayon process. It is illustrated in O Fig. 16. A solution containing 14% cellulose, 10% water, and 76% NMMO plus stabilizers is extruded at a temperature slightly above 100 °C into an aqueous NMMO-bath from which cellulose is precipitated [74,75]. The extrusion has been described as a melt-spinning process that has recently made it possible to manufacture cellulosic self-bonded meltblown nonwovens as well [76]. 

In addition to these process, special processes are known, particularly for the manufacture of thin metal fibers the continuous filament process, melt spinning processes and the Taylor process. 

In melt spinning processes a metal melt is forced through dies as a thin jet into a liquid medium so quickly that the solidification rate is faster than the rale of disintegration of the jet into droplets. 

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... 

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