In this essay we will discuss about the four main methods used for the identification of fiber. After reading this essay you will learn about:- 1. Visual Test 2. Burning Test 3. Microscopic Test for Identification of Fiber 4. Chemical Test for Fiber Identification.
Essay # 1. Visual Test:
This is a simple test which can be made by all. It is the first step of identification. Visual test is the identification of fiber from appearance and the feel of the hand. Experience and good perception can help in the identification by touch and feelings.
Procedure:
1. The edge of a piece of cloth is gasped between the thumb and the forefinger, with the thumb on the top.
2. The thumb and the forefinger are rubbed lengthwise and with a circle.
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3. Length of the fiber is to be inspected by untwisting a year. Any fiber can be made into staple length but not all can be filament length.
4. Lustre or lack of lustre in the fiber is to be perfectly looked out.
5. Body, texture, hand, soft to hard, rough to smooth, warm to cool, stiff or flexible and elasticity are to be felt by the hand and body.
Some fabrics are identified from its very appearance.
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The followings are the result of various fibers by visual test:
1. Vegetable fibers are cooler to touch than animal or synthetic fibers.
2. Cotton fiber has no lustre, if special finish is not given.
3. Linen fibers are cool and pliable.
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4. Silk fiber is very soft, lustrous, smooth and slippery surface.
5. Wool is warm and resilient.
6. If finger is placed on the sample of cotton linen and rayon fabric, the heat of the finger passes off as these fibers are good conductor of heat.
7. Rayon fabric is cooler to touch than Acetate.
Essay # 2. Burning Test:
Fibers can be identified more clearly by burning test. It is a reliable test. This test can be adopted while purchasing silk materials. It can also be used perfectly to identify cellulose, protein, minerals and synthetic fibers.
Procedure:
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1. Hold the yarn horizontally with the help of tweezers.
2. Take the fiber slowly into the edge of the flame to determine its burning characteristics.
3. Repeat the several times to check the result.
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4. Reaction of fibers while approaching flame, in flame and when it is removed from the flame the odour, colour and type are to be observed and noted in this test.
5. For mixed fibers, the warp and weft yarns are to be tested separately.
6. Difference in lustre, twist and colour will indicate that there may be two or more kinds or fibers in the fabric. In this case the yarn should be untwisted and fibers are to besepareted by the help of a magnifying glass and a tweezers and then the identification process will be started.
Burning test may be conducted along with the visual test. If some special finishing process are applied to the fabric the identification by burning test will be difficult.
The result of the burning test of different fibers can be known from the following table:
Essay # 3. Microscopic Test for Identification of Fiber:
Microscopic test with a magnification of at least 100 powers is a reliable test for identification of fibers. This is easier in case of natural fibers. Manmade fibers are sometimes more difficult to identify because some are very similar in appearance. Again a dark coloured fabric cannot be identified under the microscope because light which is necessary for identification cannot pass through a dark substance.
Method:
1. Clean the lens slide and cover-glass.
2. Place a drop of water on the slide.
3. Untwist a yarn and place the loosened fibers on the slide cover with the cover-glass and press down to eliminate air bubbles.
4. Place the slide on the stage of the microscope and focus. The fibers should be well loosened such an to enable focusing of a single fiber.
5. If the fabric contains more than one kind of fiber test each, be sure to check warp and filling yarns.
6. Observe both cross sectionally and longitudinally.
Each of the natural fibers has its own structural shape which is different from the other.
i. Cotton:
It resembles a collapsed spirally twisted tube with a rough surface. The thin cell wall of the fiber has from 200 to 400 turns of natural twist. The fiber appears flat twisted and ribbon like, with a wide inner canal (the lumen) and a granular effect.
ii. Linen:
The hair like flax fiber shows a thick cell well with a narrow central canal. There are workings or nodes at intervals of the filament.
Due to these nodes, the fiber resembles a straight smooth bamboo sticks.
iii. Wool:
Wool fiber is irregular and roughly cylindrical. It has multi-cellular structure. A cross section shows three layers, epidermis, cortex and medulla. The outer layer consists of overlapping scales in longitudinal section. It is a rod like structure with rough surface of overlapping horny scales.
iv. Silk:
Both cultivated and wild silk present different picture under the microscope. Under microscope, raw silk appears elliptical in shape. Wild or tusser silk appears flattened. It has a double rod like structure which is covered with lumps of gum, the sericin.
v. Rayon:
This fiber has a glass like luster under the microscope. It appears to have a uniform diameter. The cup ammonium shows round filaments of a bright lustre.
vi. Acetate:
The cross sectional view of acetate fiber is less irregular than Rayon. It has a bulb like appearance with indentations.
vii. Nylon:
Fibers are very fine, round and smooth. It is highly lustrous.
viii. Dacron:
Dacron fibers are straight, smooth and perfectly round.
ix. Orion:
It is flat, smooth and semi-dull.
x. Polyester:
Polyester fibers are smooth and straight. The cross section is round.
Essay # 4. Chemical Test for Fiber Identification:
Chemical tests are technical means of fiber identifications which are more accurate. The reactions of different fibers can be easily known by the solubility test with chemicals and fibers can be identified easily.
