Silk Fibre Processing

Figure 13 Cross-sections of silk fibres (a) cartoon of a native silk fibre and (b) scanning electron micrograph of a fractured, processed textile fibre (10 pm across)...

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. 

For centuries silk is a synonym for luxury garment. It describes a woven textile made of natural protein fibres sptm by the larvae or caterpillars of the domesticated silk moth, Bombyx mori. In this context, spinning does not refer to the textile process of fabricating a yam from a bulk of single fibres by warping and but rather describes the process of transforming an aqueous protein solution into an insoluble protein filament (Kerkam et al., 1991). Thus, silk fibres ate filaments that are spun at the point-of-delivery from feedstock, which can differ widely in detail but are protein based (Vollrath and Porter, 2009). 

Figure 12.6 Silk processing. Schematic of common silk material fabrication methods. Silk materials are made starting from either silk cocoons (a) or silk fibres (b), both must be boiled to remove sericin. Cocoons are solubilised while fibres are left intact before final processing to form different silk materials.

Spinning process [17,18], as well as on tuned dopants in the polymer feedstock [19]. Several factors may contribute to the toughness of a spider silk fibre ... 

The average volume of an amino-acid in silk is 2.4 x m, and the volume of 1 cm of a silk fibre is 8.66 x 10 m. Therefore there are approximately 360,000,000 molecules per cm length and this number added per second per fibre. The fibres are actually hollow, so a minimum dimension for the fibre has been used. Fibre dimensions vary from 0.023 to 0.009 mm during the spinning process... 

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... 

Metallisation of fibres is not only a physical process determined by absorption capacity of the fibres for the metal and diffusion capacity of the metal in the fibre structure, but also depends on chemical parameters such as chemical structure of the fibres, presence of functional groups, reactivity of the fibre and the metal, oxidation state of the metal and the presence, necessity and reactivity of supporting chemicals (e.g. reducing agent). Therefore, it was necessary first to study metallisation at different types of fibres in order to investigate which structure is most useful for further research. In this respect, viscose, cotton, natural silk and polyacrylonitrile fibres were investigated because of their different structure and properties and their availability in the New Independent States of the former Soviet Union (Uzbekistan, Kazakhstan, Kyrgyzstan). 

Rayon is made from cellulose. Count Chardonnet made the synthetic fibre from mulberry leaves. Chardonnet was studying the diseases of the silkworms. He was inspired by the silkworm spinning silk to find a way to make artificial silk. He made artificial silk from the cellulose he obtained from mulberry leaves by a complex process. 

In man-made fibres, any stretching will irreversibly alter the crystallinity and there is no control of the lateral size of polymer crystals. Semicrystalline polymer networks typically consist of platelet type crystals whose width exceeds their thickness by several order of magnitudes because only the thickness is controlled by the chain folding [61]. In contrast to synthetic fibres, spider silk does not need any mechanical treatment by external forces the constituents self-assemble directly during the spinning-process. These examples clearly demonstrate the need for more detailed control of the mesoscopic structures for further development of man-made materials. 

Conducting polymers have also been prepared as coatings on both natural and synthetic fibres and fabrics. For example, silk and wool [143,144] or nylon [145] have been coated. The Milliken Corporation developed the first commercial process for producing conducting polymer coated fabrics [146]. 

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