Spun silK

Eby RK et al. Production of nonwoven network of synthetically spun silk nanofibers, by electrospinning a solution containing dissolved silk fibers and hexafluoroisopropanol. University of Akron, OH... 

Spun silk is made out of damaged cocoons and any other form of waste which is broken up and no longer in continuous filaments. It is carded like cotton and then spun. It is usually made out of waste from which the sericin has been removed, but when silk which is still in the gum is spun the yarn is known as chappe. 

The properties of artifidally spun silk fibers are extremely dependent on processing conditions. Most work to create fibers from silk utilizes a wet spinning process, whereby the concentrated silk dope is extruded through an orifice on the order of 100 pm in diameter into a coagulation bath. A subsequent post-spin draw is performed, whereby the fiber is constrained in a stretched state and allowed to dry or further coagulate. 

Ramie may be combed and spun by several methods. The finest yams are produced on the spun silk system developed by the Japanese, but this system requires much labour. In Europe, Brazil and the Philippines, modification is... 

As a curiosity, spider and caterpillar silk were electrospun into nanofibers and characterized by electron microscopy [332, 333]. The diameter of these silk nanofibers ranged from about 6.5 to 300 nm, making them several orders of magnitudes smaller than the silk fibers spun by silkworms or by many kinds of spiders. Electron diffraction patterns of annealed electrospun nanofibers exhibited diffraction peaks with the molecules aligned along the axis of the fiber with a crystalline order comparable to that of naturally spun silks. 

Adapted from Mortimer, B., Guan, J., Holland, C., Porter, D., Vollrath, R, 2015. Linking naturally and unnaturally spun silks through the forced reeling of Bombyx mori. Acta Biomater. 11, 247-255. 

H.J., and Kaplan, D.L. (2006) Electro-spun silk-BMP-2 scaffolds for bone tissue engineering. J. Biomater., 27, 3115-3124. 

From 1910 onward waste filament yam had been chopped into short lengths suitable for use on the machinery designed to process cotton and wool staples into spun yams. In the 1930s new plants were built specifically to supply the staple fiber markets. During World War II the production of staple matched that of filament, and by 1950, staple viscose was the most important product. The new spun-yam oudets spawned a series of viscose developments aimed at matching the characteristics of wool and cotton more closely. Viscose rayon was, after all, silk-like. Compared with wool it lacked bulk, residence, and abrasion resistance. Compared to cotton, it was weaker, tended to shrink and crease more easily, and had a rather lean, limp hand. 

Spider Silk. Spider silks function ki prey capture, reproduction, and as vibration receptors, safety lines, and dispersion tools. Spider silks are synthesized ki glands located ki the abdomen and spun through a series of orifices (spinnerets). The types and nature of the various silks are diverse and depend on the type of spider (2). Some general categories of silks and the glands responsible for thek production are Hsted in Table 1. 

Secondary Structure. The silkworm cocoon and spider dragline silks are characterized as an antiparaHel P-pleated sheet wherein the polymer chain axis is parallel to the fiber axis. Other silks are known to form a-hehcal (bees, wasps, ants) or cross- P-sheet (many insects) stmctures. The cross-P-sheets are characterized by a polymer chain axis perpendicular to the fiber axis and a higher serine content. Most silks assume a range of different secondary stmctures during processing from soluble protein in the glands to insoluble spun fibers. 

Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis (11,28). The films, which are water soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubiUty by converting silk I to silk II in a process found usehil for enzyme entrapment (28). Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to faciUtate the conversion to silk II (29). Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to faciUtate stmctural characterization of the protein (30). ResolubiLized silkworm cocoon silk has been spun into fibers (31), as have recombinant silkworm silks (32). 

Nonabsorbable Natural Sutures. Cotton and silk are the only nonabsorbable sutures made from natural fibers that are stiH available ia the United States. Cotton suture is made from fibers harvested from various species of plants belonging to the genus Gossipium. The fiber is composed principally of ceUulose. The seeds are separated from the cotton boUs, which are carded, combed, and spun iato yams that are then braided or twisted to form sutures ia a range of sizes (Table 4). The suture is bleached with hydrogen peroxide and subsequendy coated (finished or glaced) with starch and wax. The suture may be white or dyed blue with D C Blue No. 9. 

Silk (qv) suture is made from the threads spun by the silkworm Bombjx mori. The fiber is composed principally of the protein fibroin and has a natural coating composed of sericin gum. The gum is usually removed before braiding the silk yams to make sutures in a range of sizes. Fine silk sutures may be made by simply twisting the gum-coated silk yams to produce the desired diameter. White silk is undyed. Silk is either dyed black with logwood extract or blue with D C Blue No. 9. The suture may be uncoated or coated either with high molecular weight polydimethylsiloxane or with wax. 

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... 

Acetat-kimstseide,/. = Acetatseide. -Ifisung,/ acetate solution, -seidet /. acetate silk (acetate rayon). -zellwoUet /. acetate spun rayon. 

FIGURE 19.23 Artificial spider silk can now be made in bulk. It can be spun into thin, tough thread, like that on the spools shown here, or wound into cables strong enough to support suspension bridges. 

Lazaris, A., Arcidiacono, S., Huang, Y., Zhou, J.F., Duguay, F., Chretien, N., Welsh, E.A., Soares, J.W., and Karatzas, C.N., Spider silk fibers spun from soluble recombinant silk produced in mammalian cells. Science, 295(5554), 472- 76, 2002. 

Silk is produced from the spun threads from silkworms (the larvae of the moth Bombyx mori and related species). The main protein in silk, fibroin, consists of antiparallel pleated sheet structures arranged one on top of the other in numerous layers (1). Since the amino acid side chains in pleated sheets point either straight up or straight down (see p. 68), only compact side chains fit between the layers. In fact, more than 80% of fibroin consists of glycine, alanine, and serine, the three amino acids with the shortest side chains. A typical repetitive amino acid sequence is (Gly-Ala-Gly-Ala-Gly-Ser). The individual pleated sheet layers in fibroin are found to lie alternately 0.35 nm and 0.57 nm apart. In the first case, only glycine residues (R = H) are opposed to one another. The slightly greater distance of 0.57 nm results from repulsion forces between the side chains of alanine and serine residues (2). 

Carothers decided to concentrate on the development of polyamides, as silk is also a polyamide (Houshell and Smith 1988). The best polymer should have a high enough melting point to be washed and ironed, but not too high to allow the polymer to be drawn and spun before it would decompose. The raw materials adipic acid and hexame-thylenediamine could be produced from benzene, which was plentiful, so it was the 6,6 -polyamide (nylon-66) that first went into production in 1939. Carothers committed... 

Fiber or Fibre is any tough substance composed of threadlike tissue, especially when capable of being spun or woven. Fibers may be divided into animal (wool or silk), vegetable (cotton, hemp, flax, ramie, esparto, jute, sisal etc), mineral (asbestos, glass fiber) and artificial (Rayon, Nylon, Orion, Vinyon, Saran etc)... 

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