Synthetic polymer fibres process

As a result of the manufacturing process, the molecules of synthetic polymer fibres are more or less oriented along the axis of the fibre. The degree of orientation affects the physical properties of the fibres. Just as in the case of drawn... 

The third main class of separation methods, the use of micro-porous and non-porous membranes as semi-permeable barriers (see Figure 2c) is rapidly gaining popularity in industrial separation processes for application to difficult and highly selective separations. Membranes are usually fabricated from natural fibres, synthetic polymers, ceramics or metals, but they may also consist of liquid films. Solid membranes are fabricated into flat sheets, tubes, hollow fibres or spiral-wound sheets. For the micro-porous membranes, separation is effected by differing rates of diffusion through the pores, while for non-porous membranes, separation occurs because of differences in both the solubility in the membrane and the rate of diffusion through the membrane. Table 2 is a compilation of the more common industrial separation operations based on the use of a barrier. A more comprehensive table is given by Seader and Henley.1... 

In terms of nanocomposite reinforcement of thermoplastic starch polymers there has been many exciting new developments. Dufresne [62] and Angles [63] highlight work on the use of microcrystalline whiskers of starch and cellulose as reinforcement in thermoplastic starch polymer and synthetic polymer nanocomposites. They find excellent enhancement of properties, probably due to transcrystallisation processes at the matrix/fibre interface. McGlashan [64] examine the use of nanoscale montmorillonite into thermoplastic starch/polyester blends and find excellent improvements in film blowability and tensile properties. Perhaps surprisingly McGlashan [64] also found an improvement in the clarity of the thermoplastic starch based blown films with nanocomposite addition which was attributed to disruption of large crystals. 

Typical materials include woven fibres, metal screens or fabrics, pressed felt or cotton batting, sheets of synthetic polymers, paper, sand, coal, silica porcelain and many more. Filtration equipment is equally diverse for both batch and continuous processing [23]. 

The above discussion of silk fibres produced by spiders due to Viney, indicates how liquid crystalline order can be a precursor to the formation of the more ordered crystalline structures that become load bearing. We can see in nature combinations of the processes that are sometimes seen to occur individually in synthetic polymer systems. 

Textiles, as a woven cloth or a nonwoven fabric, are probably the most common industrial filter medium, and are made from natural (cotton, silk, wool) and synthetic fibres. Wire cloths and meshes are also widely used in industrial filtrafions, produced by weaving monofilaments of ferrous or non-ferrous metals the simpler plain weave is used for sieving and sizing operations, and the more complex weaves such as Dutch twills are used on pressure and vacuum filters. At the small scale, particularly for laboratory use, filter papers are common, made from fibrous cellulosic materials, glass fibre or synthetic polymers these papers are made using developments from conventional paper manufacturing processes. 

In many practical applications of synthetic polymers molecular orientation is produced by the fabrication process to give improved properties, especially with regard to stiffness and strength. Well known examples are textile fibres such as Terylene or nylon, polypropylene packaging films and polyester bottles. Most natural materials such as silk and cotton fibres, muscle and bone also show significant molecular orientation. All these synthetic and natural materials are anisotropic, i.e. their properties are different in different directions. 

The strength of a fibre can be increased by drawing, this process being discussed in Section 2.4.4 and illustrated in Fig. 2.12. Common synthetic polymers used to produce fibres are generally polyamides, polyesters or polyacrylics. The class of nylons are the most familiar polyamides. For example, the structure of nylon-6,6 (here the numerals refer to the numbers of carbon atoms between successive amide groups in the repeating unit) is shown in Table 2.1. An example of a polyester is poly(ethylene terephthalate) (PET) (Table 2.1), known commercially in fabrics as tery-lene or dacron (this polymer is also used in PET plastic drink bottles). A well-known polyacrylic used to make fibres is poly(acrylonitrile) (Table 2.1). 

The membrane processes that have just been briefly described can be implemented, in principle, with any material (ceUulosic, synthetic polymer or inorganic) or in any format (hollow fibre, spiral wound, etc.). The system design process selects the most appropriate material and format according to the process operating parameters. 

These polymers, typical of polyamides with fewer than four main chain carbon atoms in the repeating unit, decompose before melting and have to be processed from solution. Several of the polymers may, however, be spun into fibres. Over thirty years ago Courtaulds produced silk-like fibres on an experimental commercial scale from poly-(L-alanine) and from poly-(a-methyl-L-glutamate). The latter material is also said to be in use as a synthetic leather in Japan. The... 

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