Silk fiber properties

Qiana, introduced by Du Pont in 1968 but later withdrawn from the market, was made from bis(4-aminocyclohexyl)methane and dodecanedioic acid. This diamine exists in several cis—trans and trans—trans isomeric forms that influence fiber properties such as shrinkage. The product offered silk-like hand and luster, dimensional stabiUty, and wrinkle resistance similar to polyester. The yam melted at 280°C, had a high wet glass-transition temperature of - 85° C and a density of 1.03 g/cm, the last was lower than that of nylon-6 and nylon-6,6. Qiana requited a carrier for effective dyeing (see Dye carriers). 

Resistance to axial compressive deformation is another interesting property of the silk fibers. Based on microscopic evaluations of knotted single fibers, no evidence of kink-band failure on the compressive side of a knot curve has been observed (33,35). Synthetic high performance fibers fail by this mode even at relatively low strain levels. This is a principal limitation of synthetic fibers in some stmctural appHcations. 

Thermal Properties. Spider dragline silk was thermally stable to about 230°C based on thermal gravimetric analysis (tga) (33). Two thermal transitions were observed by dynamic mechanical analysis (dma), one at —75° C, presumed to represent localized mobiUty in the noncrystalline regions of the silk fiber, and the other at 210°C, indicative of a partial melt or a glass transition. Data from thermal studies on B. mori silkworm cocoon silk indicate a glass-transition temperature, T, of 175°C and stability to around 250°C (37). The T for wild silkworm cocoon silks were slightly higher, from 160 to 210°C. 

Nevertheless, despite our rapidly increasing knowledge about silk protein sequences, very little is known about the part played by gene design (Tatham and Shewry, 2000) in the stability and solubility of the prespun silk and in the final property of silk fibers across a wider variety of spiders and insects. 

The / -transition is a key feature and trademark in silks (Craig, 2003), whether the final product (Fig. 7) will be a high-performance fiber or will have other functions (Craig, 1997). The role, functionality, and diversity of each silk raise the interesting question whether selection pressures on the final fiber properties are mirrored (at, ultimately, the molecular level) in the precursor liquid proteins. Figure 8 shows SRCD spectra of six of the... 

The early work focused on a particular silkworm, Bombyx mori, that lives on mulberry bushes. There are other silkworms each with its own special properties, but in general most silk is still derived from the original strain of silkworm. Crystalline silk fiber is about four times stronger than steel on a weight basis. 

The attractive properties of silk fibers as a natural, sustainable product have inspired researchers to look for options to fabricate such fibers without the use of worms or spiders. Furthermore, these natural polymers, silk proteins (both fibroin and spidroin), allow for adjustable mechanical properties, thermal resistance (Drummy et al., 2005 Motta et al., 2002), as well as biomedical compatibility (Vepari and Kaplan, 2007). 

Overall Table 3 indicates that the properties of artificial silk fibers cannot match those of native fibers (Table 2 and Figure 4). 

Work, R.W. "Dimensions, birefringences, and force-elongation behavior of major and minor ampullate silk fibers from Orb-Web-Spinning Spiders - Effects of wetting on these properties". Text. Res. ]. 47(10), 650-662 (1977). 

The thermal degradation of textiles is influenced by the environment in which they exist as well as by impurities, additives, and finishing agents in the fiber. Damage to all fibers by heat and secondary influences such as ultraviolet light and biological attack occurs more rapidly in humid atmospheres. Cotton and silk can withstand higher temperatures than can wool without adverse effects on their fiber properties. 

Wool and silk. Wool is animal hair from the body of sheep. Silk is a lustrous, tough elastic fiber produced by silkworms. Both wool and silk fibers are protein substances with both acidic and basic properties. The building blocks for these fibers are amino acids. The a amino acids... 

In all of the varieties of artificial silk which we have mentioned the product is probably in the form of hydrates or oxidized hydrates of cellulose. This cellulose compound is obtained as fine filaments by spraying the solution of the cellulose, in one of the various solvents, into a coagulating solution. The filaments are then spun into thread and converted into other forms desired. Whether as fiber, thread, cloth or other material the product possesses silk-like properties both as to luster, feel and ability to react with dyes. It thus has many advantages over ordinary cotton. All of the varieties of artificial silk are, however, inferior to silk itself in strength, especially when wet,... 

Johnson et al. [27] report that polysulfone and poly(vinyl acetate) show enhanced low-temperature -loss transitions in proportion to the unclustered water. Clustered water in poly(vinyl acetate) has no effect on Tg, although shifts with increasing amount of unclustered water. Fuzek [3T] found that water absorbed by synthetic fibers and silk at room temperature and 65% RH substantially lowers Tq s, the effect being reflected in several different fiber properties. Wet soaking has an additional effect. 

---