Fiber-forming polymers properties

Fiber stmcture is a dual or a balanced stmcture. Neither a completely amorphous stmcture nor a perfectly crystalline stmcture provides the balance of physical properties required in fibers. The formation and processing of fibers is designed to provide an optimal balance in terms of both stmcture and properties. Excellent discussions of the stmcture of fiber-forming polymers and general methods of the stmcture characterization are available (28—31). 

Table 2. Thermal Properties of Olefins and Other Fiber-Forming Polymers...

The properties of elastomeric materials are also greatly iafluenced by the presence of strong interchain, ie, iatermolecular, forces which can result ia the formation of crystalline domains. Thus the elastomeric properties are those of an amorphous material having weak interchain iateractions and hence no crystallisation. At the other extreme of polymer properties are fiber-forming polymers, such as nylon, which when properly oriented lead to the formation of permanent, crystalline fibers. In between these two extremes is a whole range of polymers, from purely amorphous elastomers to partially crystalline plastics, such as polyethylene, polypropylene, polycarbonates, etc. 

PET is not strictly Newtonian, or else it could not be fiber-forming. Polymers with the latter property develop increasing tension due to retraction forces as they become oriented, so that localized necks do not grow and become discontinuities. At high shear rates, molecular orientation will also reduce the resistance to shearing. 

In a previous section, data and plots were given showing the rapid rise in consumption and production of manufactured fibers at the expense of natural fibers. The principal reason for this has been the wide range of manufactured fiber variants that can be produced from a single fiber-forming polymer. The wide range of polymers available, each with its particular properties, adds yet another dimension. This is not to say that there is only one type of cotton, wool, silk, or asbestos fiber there are many varieties of natural fibers, but their supply is limited by natural factors such as climate and genetics. The relative availabilities of manufactured fiber types can be altered by controlled chemical-process... 

Synthetic fibers are generally made from polymers whose chemical composition and geometry enhance intermolecular attractive forces and crystallization. A certain degree of moisture affinity is also desirable for wearer comfort in textile applications. The same chemical species can be used as a plastic, without fiber-like axial orientation. Thus most fiber forming polymers can also be used as plastics, with adjustment of molecular size if necessary to optimize properties for particular fabrication conditions and end u.ses. Not all plastics can form practical fibers, however, because the intermolecular forces or... 

There are many different bioresorbable polymer systems based on different degradation mechanisms and having a range of physical and mechanical properties. However, the scope of our review will be restricted to only fiber-forming polymers. Those that are hydrolytically sensitive are discussed in this chapter, while enzymatically catalyzed bioresorbable polymers are presented in Chap. 6. Table 4.1 shows the classification of fiber-forming hydrolytically sensitive bioresorbable polymers. 

Thus, the 2nd fiber category encompasses carbon and carbonized polymers. The foundation materials of this group are the heat convertible, fiber forming polymers, the most common of which today is PAN (polyacrylonitrile). Others are rayon, PBI, and pitch tar. One of the earliest to report results of PAN pyrolysis was Goodhow, et. al.(5i) in 1975. Later, in 1979, Fischbach and Komaki(5 and Brehmer, et. al.(di) in 1980 reported on the electrical properties of carbon fibers made fi om various polymers and described a dependency of resistivity upon the heat treat temperature (HTT) employed to carbonize the fiber which is now well known. The studies by Swift, et. al(52) in 1985 and more recently reported herein were undertaken to expanded upon this base of knowledge and to initiate studies of the stability of the electri properties of fibers made on commercially viable platforms. These studies have led to a launch point for what is believed to have been the first, relatively large scale, commercial application for partially carbonized PAN fibers(50), as resistive carbon fiber based static eliminator brushes. 

Work in our own laboratories has shown, however, that in the presence of conventional flame retardants, nanoclays can promote additive and synergistic effects in PA6, PA6,6 Aims that have been used as models for respective fibers. This work has provided evidence that significant reductions in flame retardant additive concentrations may be achievable, as has been noted for other polymers in Section 11.3.1. Normally, minimal flame retardant additive contents of about 15 to 20% w/w are required, which are too high for inclusion in conventional synthetic fibers. This is because for fusible fiber-forming polymers snch as PA6, PA6,6, PET, and polypropylene, flame retardant property trends versns concentration are not linear but follow an S-shaped curve. " This phenomenon is believed to be a consequence of the need to generate a threshold char level having an extended coherence throughout the polymer. It follows that this will... 

Heat Resistance n A property of certain fibers or yams whereby they resist degradation at high temperature. Heat resistance may be an inherent property of the fiber-forming polymer or it may be imparted by additives or treatment during manufacture. Also see Heat Stabilized. 

By blending the liquid crystal polymers (LCP) with conventional fiber forming polymers it is possible to obtain fibres reinforced at the molecular level. By incorporating a LCP component with high strength and high modulus into fibers with poor thermal stability (such as PO), the thermal properties can be improved. 

The molecular weight and its distribution are also important for fiber-forming polymers. If the molecular weight is too high, the fiber-making process becomes difficult. On the other hand, if the molecular weight is too low, the resultant fibers would have insufficient mechanical properties. 

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