Silk, artificial natural

Synthetic Spider Silk Fibers Natural i/s Artificial Spinning Strategies... 

Synthetic Spider Silk Fibers Natural vs Artificial Spinning Strategies 174... 

When brought near to a flame, natural (ordinary and wild or tussah) silk bums with an odour of burnt hom and leaves a spongy carbonaceous residue (except with heavily weighted silk) artificial silks with a cellulose basis bum rapidly, almost without odour or residue, while " strengthened " 1 silks leave an ash in the form of the fibre artificial silks with a gelatine basis (A. Millar s silk, Vandura silk) bum like animal fibres. 

The structural differences between natural and man-made silk materials determine the property differences. Even minor changes in the chemical structures give rise to a wide range of variability in mechanical properties (Porter et al., 2005). How this happens is both a challenge to understand and to control when fabricating silk artificially. 

The overall performance difference between the artificial fibroin silk and natural silk is induced by many factors. Composition of the spinning dope is critical but not the only factor. Important to understand is that the spinning process which determines the condensed structure of silk is crucial. It suggest that knowing the spinning process details it should be feasible to produce high-performance silk artificially and "design" silk. 

The structures of some natural protein-based materials, such as silk and wool, result in strong, tough fibers. Spiders and silkworms use proteins as a structural material of remarkable strength (Fig. 19.22). Chemists are duplicating nature by making artificial spider silk (Fig. 19.23), which is one of the strongest fibers known. 

The first fibers used by humans were probably those that occur naturally as tissues or excretions of either vegetables or animals (see Table 87). At much later times, after metals had been discovered, humans also learned to manufacture - from some of the ductile metals, mainly gold, silver, and their alloys - thin filaments (not fibers, however), which have since been used to decorate textile fabrics. It was only during the twentieth century, after synthetic plastics were discovered, that it became possible to make artificial human made fibers. The great majority of the natural fibers, such as cotton and wool, occur as staple fibers, short fibers whose length is measured in centimeters. Silk is different from all other natural fibers in that it occurs as extremely long and continuous filaments several hundred meters long. 

Natural fibers go back to prehistoric days. Probably one of the early applications was the conversion of a fiber (possibly wool or cellulose) into thread or rope strong enough to be used in a snare, net, or cage. Literature as far back as the 17th century notes that people attempted to make fibers out of something other than cotton, wool, or flax. The first man-made fiber, known as artificial silk, was made in the 19 th century, when wood pulp was treated with nitric acid. The result was known chemically as cellulose nitrate and (eventually) commercially as Rayon. The commercial name referred to the sheen that has the brilliance of the sun. ... 

Sheets also play an important role in the construction of peptide-based functional nanohbrous materials. /3-sheets are preferred over a-helices as molecular building blocks in the fabrication of artificial nanostructured materials perhaps because of the growing interest in understanding the self-assembly of two types of namral /3-sheet products silk protein and amyloid-Uke /3-sheets. Furthermore, extended /3-sheet conformation is relatively easy to achieve. Indeed, preventing their formation, particularly in high concentration or at high temperature, can be difficult in both synthetic and natural constructs. 

Although fibers can be classified in numerous ways, in terms of present-day technology, they are fundamentally classified as(l) natural libers, and (2) synthetic libers. The principal natural fibers are cotton, wool. and. to a much lesser extent, silk. liax. and mohair. Synthetic tihers have made inroads into the use of all natural fibers, bul the greatest impact has occurred in connection with the latter three libers. Cotton continues to be a major textile fiber, measured in terms of billions of pounds used per year. Colton is one of the most versalile of all libers and blends well with synthetics. This is also true of wool, bul lo a somewhat lesser extent. Synthetic Fibers. Introduced in 1910 as a substitute for silk, rayon was the first artificial or synthetic fiber. Rayon, of course, differs completely in chemical constitution from silk. Rayon typifies most reconstituted or synthetic fibers, which perform almost as well and. in a number of respects, far better than their natural counterparts Some of the more recently developed synthetic libers have lilile if any resemblance to naturally available fibers and thus enlirely new types of end-producls with previously unobtainable end-qualities are available,... 

Distinction between Natural and Artificial Silk and between the different Artificial Silks (A. Solaro). 

A portion of the sample is immersed in the cold in concentrated hydrochloric acid or in sulphuric acid of 58° Baumd ordinary non-weighted, natural silk dissolves readily, heavily weighted silk and wild natural silk more slowly artificial silks dissolve after some time, those with a gelatine basis first softening and then dissolving in about two hours. 

Mixed fabrics containing natural silk and artificial silk based on either cellulose, or nitrocellulose or viscose. 

Where natural and artificial silks are present together, use is made of the property exhibited by 10% caustic potash solution and by Ldwe s solution, in the conditions already mentioned, of dissolving natural silk and leaving artificial silk undissolved. 

A. Mixed fabric containing cotton, wool, natural silk and artificial cellulose, nitrocellulose or viscose silk. 

Until the 20th century mankind was limited to natural fibers such as wool, cotton, linen, and for the rich, silk. The first man-made fiber was artificial silk rayon (1910), which was based on cellulose. The big jump came with the invention of nylon by Wallace Carothers, with commercial production starting in 1939, followed in the 1950s by acrylics (which, when mixed with cotton, produced the wash-and wear textiles), polyesters, and many others. 

Natural fibers such as cotton can be chemically modified to form rayon or acetate. Rayon was first called artificial silk. In the viscose process, cellulose is dissolved in sodium hydroxide, pushed through spinnerets, and treated with acid to harden. Treatment with copper compounds and ammonia is used to form hosiery yams. Acetate (or cellulose acetate), produced by treating cotton with acetic acid and acetic anhydride, is also used in production of clothing. 

Substantially more work is done on the elucidation of properties of regenerated silk, compared to film materials in view of the difficulty to fabricate uniform films. From Table 3, it can be concluded that the mechanical properties of man-made silk materials are inferior to the natural ones. This can be attributed to the fact that the final properties are greatly affected by the structural hierarchies. Typically, the "artificial" materials do not contain the controllable microstructure and supramolecular structure that natural ones possess. 

Accordingly, major hurdles will need to be overcome to achieve required performance including overcoming inherent weaknesses of natural silk such as super-contraction and fabrication consistency (Hakimi et al., 2007). To date, film, sponge-like silk, and nonwoven mat materials can artificially be made from silk solution, as mentioned in previous section (Vepari and Kaplan, 2007). 

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