For approximately 3,000 years China successfully held the secret of silk and sericulture and held a virtual monopoly on the silk industry. About AD 300 Japan learned the secret of raising silkworms and reeling the filaments from the cocoons.
Throughout history, silk has maintained a position of great prestige and is considered a luxury fiber. It is often called the “queen of fibers”. Perhaps one of the most important contributions silk has made in the history of textiles is that it was responsible for investigation into the possible production of man-made fibers. Scientists observed how the silkworm spun the fibers and believed that people could duplicate the art.
Silk is one of the strongest natural fibers used in creating textile products. It has a tenacity of 2.4 to S. 1 grams per denier when dry. Wet strength is about 80 to 85 percent of the dry strength. Silk has good elasticity and moderate elongation, when it is dry, the elongation varies from 10 to 25 percent; when wet, silk will elongate as much as 33 to 35 percent. At 2 percent elongation the fiber has a 92 percent elastic recovery.
Silk has medium resiliency. Creases will hang out relatively well, but not so quickly or completely as for wool.
The density of specific gravity of silk is cited as 1.25 to 1.34 grams per cubic centimeter, depending on the resource used. Because of the nature of silk, it is possible that the density varies among fibers as well as between the various types of moths that form the fiber. Another source of variation may be due to methods used in determining density. In any case, the density results in the formation of lightweight but strong filaments, yarns and fabrics.
Silk has a relatively high standard moisture regain of 11 percent. At saturation the regain is 25 to 35 percent. This relatively high absorption is helpful in applying dyes and finishes to silk; however, unlike many fibers, silk also absorbs impurities such as metal salts. These contaminants tend to damage silk by weakening the fiber or causing actual ruptures to occur when the fabric is not handled properly.
Silk will ignite and continue to burn when there is another source of flame. After removal from the source, it will sputter and eventually extinguish itself. It leaves a crisp, brittle ash and gives off an odor like that of burning hair or feathers. It bums similarly to wool.
Like other protein fibers, silk has a lower thermal or heat conductivity than cellulosic fibers. This factor coupled with certain methods of construction, creates fabrics that tend to be warmer than comparable fabrics of cellulosic fibers.
Silk is damaged by strong alkalis and will dissolve in heated caustic soda (NaOH); however, silk reacts more slowly than wool, and frequently the identity of the two fibers can be determined
by the speed of solubility in NaOH. Weak alkalis such as soap and ammonia cause little or no damage to silk unless they remain in contact with the fiber for a long time.
Silk protein, like wool, can be decomposed by strong mineral acids. Medium concentrations of hydrochloric acid will dissolve silk, and moderate concentrations of other mineral acids cause fiber contraction and shrinkage. The molecular arrangement in silk permits rapid absorption of acids but tends to hold the acid molecules, so they are difficult to remove. This accounts for some of the acid damage to fibroin that does not occur to keratin. Organic acids do not damage silk and are used in some finishing processes. Some authorities maintain that the scroop of silk – a rustling or crunching sound which used to be considered a natural characteristic, is actually developed by closure to organic acids.
Silk has been the queen of fabrics for centuries. As in the past, it is still used for luxury fabrics and for high-fashion items. It is frequently considered to be a sensuous fabric because of its smooth and soft feel, or hand.
Dry cleaning is the preferred method of care for silk fabrics and products. If handled carefully, however, silk fabrics can be laundered. A mild soap or synthetic detergent in warm, not hot, water should be used, and minimal handling is recommended. Thorough rinsing is required, and the best method for extracting water is to roll the garment in a towel and then hang it in a cool place, out of the sun, to dry. Tumble drying should not be attempted unless a care label specifies that such procedures are acceptable. Silk should be ironed or pressed at medium to low temperatures; steam is acceptable.
When silk requires bleaching, hydrogen peroxide or perborate bleaches must be used, as chlorine bleaches may destroy the silk.
One problem with silk is that body perspiration tends to weaken the fibers and frequently will alter the color. Many deodorants and antiperspirants contain aluminum chloride, which damage silk. It is advisable to wear protective dress shields if perspiration is a serious problem.
Several factors are involved in the demand for silk. It offers an incredible variety in fabric and yam structure. Through dyeing, many beautiful fabrics can be produced. Probably no other fiber is so widely accepted and suitable for various occasions. It is versatile and can be used in almost any type of apparel and in a wide variety of fabrics for home furnishings.
Many silk fabrics cost considerably more than similar fabrics for man-made fibers. However, the consumer who has formed an attachment to silk is willing to pay the high price. Because silk combines strength, flexibility, good moisture absorbency, softness, warmth, luxurious appearance, and durability, choice products for the discerning consumer are made of this fiber. Its use, however, is limited primarily to apparel and home furnishings such as draperies and accessories.