Properties of Silk Presentation

7/28/2019 Properties of Silk Presentation

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PROPERTIES OF SILK

Evaluating Silk Fabrics: In spite of itshigh cost, silk has been one of the mostpopular fabrics because of its unique

properties. Soft, supple, strong & lighterin weight than any other natural fiber,silk is prized for its lightness withwarmth, sheerness with strength &

delicacy with resiliency.


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Strength: Silk is the strongest natural fiber. Thecontinuous length of the filaments in thrown yarns

provides a factor of strength above what is possiblewith short natural fibers. The smoothness of the silkfilament yarns reduces the problem of wear fromabrasion. The inherent strength of silk along with itsfine diameter & lightness has made it a highlydesirable fiber for sheer yet durable fabrics. Thestrength of silk fabric is also affected, of course, by its

construction as well as its finish.

Spun silk yarn, though strong, is weaker than thrownsilk filament yarns. The quality of spun silk dependsupon the source of the staple. Douppioni & pierced-cocoon silk are generally stronger than the other silk

staple, which tend to be less uniform.


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Elasticity: While silk is an elastic fiber, itselasticity varies, as may be expected of anatural fiber. Silk fiber may be stretchedfrom 1/7 to 1/5 its original before breaking.It returns to its original size gradually &

loses little of its elasticity. Thischaracteristic means less binding &sagging, thus contributing to the wearerscomfort. It should be kept in mind that theelasticity of the yarn and the fabric is

affected by the kind of yarn used (thrownor spun), the construction of the fabric &the finish that it is given.


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Resilience: Silk fabrics retain

their shape and resist wrinklingrather well. This is particularlytrue of the fabrics made frompure-dye silk and from wild silk.Fabrics that contain a largepercentage of weighting or aremade from short-staple spun silk

have less resilience.


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Drapability: Silk has a pliability andsuppleness that, aided by its

elasticity and resilience, give itexcellent drapability.


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Heat Conductivity: Like wool, silk is a protein fiber,therefore, it is also a non-conductor of heat. Because silkprevents body heat from radiating outward, it is desirable forwinter apparel, including scarves. Thin silk fabrics are alsocomfortable warm when used for lingerie, pajamas, robes &linings. The warmth giving quality is lessened by weightingbecause the metallic content causes the fabric to become aconductor of heat.

A question often raised is why silk is used for summer fabricswhen it is a nonconductor of heat. The answer is that silk,

being fine and strong, may be made into very fine yarns andwoven into very sheer fabrics this permits the body heat andthe air to pass freely through the open construction of suchcloth.


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Absorbency: The good absorptiveproperty of silk also contributes to itscomfort in a warmer atmosphere. Silk fiber

can generally absorb about 11 percent ofits weight in moisture, but the range variesfrom 10 percent to as much as 30 percent.This property is also a major factor in silks

ability to be printed and dyed easily.


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Cleanliness and Washability: Silk is a hygienic materialbecause its smooth surface does not attract dirt. When dirt doesgather, it is given up readily by washing or dry cleaning. Careshould be exercised in laundering silk-always use a mild soap.

Wringing or strong agitation in the washing machine should beavoided, as silk weakens slightly when wet.

All silks water-spot easily, but subsequent washing or drycleaning will restore the appearance of the fabric, unless it has

a special finish. Taffeta, for example, may be given a finish thatcould be permanently stained by water. Dry cleaning ispreferable for weighted silks, but wild-silk and spun-silk fabricsmay be washed.


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Reaction to Bleaches: Strong bleaches

containing sodium hypochlorite willdeteriorate silk. A mild bleach of hydrogenperoxide or sodium perborate may be usedwith normal caution.


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Shrinkage: Because of the straightness of thefilament, smooth-surfaced silk fabrics have only

a normal shrinkage, which is easily restored byironing. Crepe effects shrink considerably inwashing, but careful ironing with a moderatelyhot iron will restore the fabric to its original size.


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Effect of Heat: Silk is somewhat sensitiveto heat. It will begin to decompose at 330F

(165 C); therefore, it should be ironed whiledamp with a warm iron.


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Effect of Light: Continuous exposure to light

weakens silk faster than either cotton or wool.Raw silk is more resistant to light thandegummed silk and weighted silk has the leastlight resistance. Silk drapery and upholstery

fabrics should be protected from direct exposureto the light.


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Resistance to Mildew: Silk will not

mildew unless left for some time in a dampstate or under the extreme conditions oftropical dampness.


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Resistance to Insects: Silk may beattacked by the larvae of clothes moths or

carpet beetles and it may be destroyedwhen blended with wool which is attackedby these insects.


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Reaction to Alkalies: Silk is not assensitive as wool is to alkalies, but it can

be temperature are high enough. Use amild soap or detergent in lukewarm waterwhen laundering.


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Reaction to Acids: Concentrated mineralacids will dissolve silk faster than wool.

Organic acids do not harm silk.


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Affinity for Dyes: Silk has a very good affinity for dyes. Itreadily absorbs basic, acid and direct dyes. Prints on silkare taken so well that the color on the back of the fabric

often differs only slightly from the face.

Dyed silk is colorfast under most conditions, but itsresistance to light is unsatisfactory. The resistance ofweighted silk is particularly poor; therefore, silk is not

recommended for window curtains. Pure-dye silks may beredyed by the consumer, provided a suitable commercialdye is used and the directions on the container arefollowed.


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Resistance to Perspiration: Silk fabricsare damaged by perspiration. The silkitself deteriorates and the color isaffected, causing staining. Garments wornnext to the skin should be washed or

otherwise cleaned after each wearing.


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SILK BLENDS

Silk is blended with many fibers. When itis to be blended with any of the natural

fibers, silk noil is used. This makesblending and spinning possible becauseall of the fibers are of staple length. Theresultant properties depend upon the

ratio of the fibers blended.


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Silk and cotton: When silk is blendedwith cotton, silk contributes a soft, smooth

hand, lightness of weight with strength,resilience, comfort and good colorpossibilities. Cotton provides body and

lower cost.


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Silk and Linen: Silk is not regularlyblended with linen. Such a blend

frequently includes other fibers as well.Silk and lined both provide strength andabsorbency. Silk reduces weight and adds

good hand. Linen provides body. Both andprestige.


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Silk and Wool: Silk and wool are usuallyblended on a worsted system, producing a

fine, strong yarn. The fabrics may have asoft sheen. They are lightweight, resilient,durable and drape well. Silk/wool blends

are used for such apparel as suits,particularly summer weights.


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CHEMICAL TEST:

Distinguishing Animal from Vegetable Fibers withan Alkali: As strong alkalis destroy animal substances, a5 percent so-lotion of lye in water (1/2 teaspoon of lye in

a glass of water or 5 milliliters [ml] in 100 [ml] can beused to eliminate wool and silk fibers from a sample thatcontains a mixture of fibers. The action of this chemical(also known as caustic soda or sodium hydroxide) ishastened by boiling the solution before the sample is

immersed. The wool and silk fibers will be completelydissolved. The vegetable fibers will not be affected;therefore, another test is necessary to identify thosefibers.


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Distinguishing Vegetable from AnimalFibers with an Acid: As dilute acids

destroy vegetable fibers, a 2% solution ofsulfuric acid may be used to distinguishvegetable from animal fibers. A drop of thesolution is placed on a sample of the fabric,

which is then placed between two blottersand pressed with a hot iron. The spottedarea will become charred if the fabric iscotton, linen or rayon.


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Distinguishing Linen from Cotton: Before any chemical test is made todistinguish linen from cotton, all surface dressings should be removed from thesamples by boiling them for a few minutes in a solution of dilute sodiumhydroxide, about 1/2%. Then any of the following tests can be made:

Immersing cotton & linen samples in a 1 percent solution of fuchsin in alcoholproduces a rose-red color in both samples. After the samples have beenwashed and then immersed in ammonia, linen retains the red coloration, butcotton does not. This test is sometimes made with a 1 percent solution of

magenta, a red dyestuff. Cotton fibers are weakened more than linen fibers if samples are immersed in

concentrated sulfuric acid for two minutes. After the samples are rinsed andimmersed in weak ammonia, the cotton fibers dissolve, leaving the linen fibersunaffected.

When cotton and linen sample are immersed in a solution of iodine and zincchloride (Herzbergs stain), cotton is stained reddish purple and linen is stainedblue to purple.

When samples are immersed in a caustic soda solution, cotton remains whiteand linen turns yellowish.


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Distinguishing Silk from Wool: If the fibersin a sample are known to consist of silk

and wool and identification of each isdesired, the use of concentrated coldhydrochloric acid will dissolve the silk and

cause the wool fiber to swell.


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Questions:

1. Describe the life cycle of the silk worm.

2. Describe the degumming process and its effects on versions types ofsilk fabrics.

3. What characteristics does silk contribute to the blend with (a) Cotton(b) Linen (c) Wool, or how is silk blended with the natural fibres?

4. List the essential qualities of silk & show the effects of each quality onfinished good.

5. Why is silk not recommended for window curtains?

6. For what purpose would you select silk rather than other fabrics?Why?


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Properties of Silk Presentation