Physical Test of fibers

Identifying the fiber:

Identifying the fibers from textile materials mainly used physical, chemical test.

The tests for fiber identification done with the help of laboratory equipment are far more reliable than the nontechnical tests. However, technical knowledge and skill, particularly while handling chemicals, are the basic requirements for conducting these tests. The means of fiber identification can be broken down into five smaller groups or tests. They are burning, chemical, optical, staining, and density tests. Each test has its own advantages and disadvantages. Most are cheap and simple identification techniques, which is good. However, most fibers would need further analysis to be certain about the results. A burning test can help determine the class to which a fiber belongs by observing how the fiber burns. Observing how things smell and char when they are burnt are qualities than can help. However, have to be careful with burning tests in order not to over-generalize as to the type of fiber. The most important burning test pertains to flame resistance. Chemical tests are cheap and simple methods to find a number of elements, but the tests are not quantitative. Also, the number of elements that can be detected is limited. So for more accurate analysis, better and more expensive equipment is needed.

Physical test of fiber:

ü Microscope Test

ü Burn Test

Microscope Test

Microscopes having magnification of at least 100 power, can be successfully employed for testing and identifying the fiber contents of a fabric. Microscope test is very effective for testing the natural fabrics. Difficulties can be faced while testing synthetic fabrics as many of them have similar appearance. However, one must know, what the fibers look like under a microscope as many finishing processes like mercerizing and delustering, change the appearance of fibers under microscope. Apart from it, dark colored fabrics also cannot be tested with microscope as light cannot pass through dark substances. For such fabrics, either the textile dyes haveto be removed by stripping, bleaching etc. or they have to be chemically tested.

Natural fiber

Natural fibers have their own peculiar structures, spots, lines and other marks that help in identifying them. Following are some examples of natural fibers and how they look like under a microscope:

Cotton: The cotton fiber is a single elongated cell. Under a microscope, it looks like flat, spirally twisted ribbonlike tube with rough granular surface. However, mercerized cotton doesn't have natural twist. The finishing process makes them swollen, straight, smooth and round with a shining surface.

Linen: Linen fiber, under a microscope, looks like having multiple sided cylindrical filaments with fine pointed edges. The filaments show nodes at intervals. It, in fact, looks like a bamboo stick having joints that results into a little unevenness.

Wool: Wool fiber has irregular, roughly cylindrical, multi cellular structure with tapered ends. Under a microscope, three basic layers are shown- epidermis (outer layer), cortex (middle layer) and medulla (inner layer). Medulla is seen only in coarse and medium wool fibers and that too under a highly powerful microscope.

Silk: Raw silk fiber, composed of two filaments, has elliptical shape under the microscope. The two fine and lustrous filaments are shown clearly looking like transparent rods with triangular shape. Wild silk or tussah fiber has different appearance than the cultivated silk. It is flattened, coarse, thick and broader fiber having fine, wavy lines all across its surface whereas cultivated silk is narrower fiber with no marks on it.

Manmade fibers
Manmade fibers are difficult to identify through microscope because of similar appearance of many fibers. However, their certain distinguishable characteristics under a microscope have been mentioned below.

Rayons: Rayon fiber has uniform diameter with glass like shine. If delustered then rayon fiber shows marks similar to pepper, when viewed cross sectionally. Viscose fiber of rayon looks irregular when viewed cross sectionally.


Acetate: Acetate fiber looks lesser irregular than viscose rayon when viewed cross sectionally. It has indentations that look like occasional marks when viewed longitudinally.

Nylon: There are many variants of nylon fiber. However, generally it appears fine, round, smooth and translucent. Sometimes it has shiny appearance. If it looks dull, it will also be dotted under the microscope.

Aramid: If viewed longitudinally, aramid fiber looks smooth and straight. If viewed cross sectionally, it may be round or like peanut's shape.

Polyester: Generally, polyester fiber is smooth, straight. It looks round cross sectionally. However, with various finishing processes, its appearance changes in context of texture and luster.

Spandex: Spandex fiber have the outstanding characteristic of appearing like groups of fibers fused together. However, different variants of spandex show different characteristics too. The Lycra fiber looks like fused multifilaments cross sectionally. Individual fibers are dotted and in shape like that of dog-bone. If viewed longitudinally, they appear straight.

Polypropylene: When viewed cross sectionally, polypropylene fiber looks somewhat round but it looks straight and smooth when viewed longitudinally.

Glass: The glass fiber looks smooth, round, translucent, shiny and flexible.

Burn Test

To identify fabric that is unknown, a simple burn test can be done to determine if the fabric is a natural fiber, man made fiber, or a blend of natural and man made fibers. The burn test is used by many fabric stores and designers and takes practice to determine the exact fiber content. However, an inexperienced person can still determine the difference between many fibers to "narrow" the choices down to natural or man made fibers. This elimination process will give information necessary to decide the care of the fabric.
Natural fibers
Cotton is a plant fiber. When ignited it burns with a steady flame and smells like burning leaves. The ash left is easily crumbled. Small samples of burning cotton can be blown out as you would a candle.
Linen is also a plant fiber but different from cotton in that the individual plant fibers which make up the yarn are long where cotton fibers are short. Linen takes longer to ignite. The fabric closest to the ash is very brittle. Linen is easily extinguished by blowing on it as you would a candle.
Silk is a protein fiber and usually burns readily, not necessarily with a steady flame, and smells like burning hair. The ash is easily crumbled. Silk samples are not as easily extinguished as cotton or linen.
Wool is also a protein fiber but is harder to ignite than silk as the individual "hair" fibers are shorter than silk and the weave of the fabrics is generally looser than with silk. The flame is steady but more difficult to keep burning. The smell of burning wool is like burning hair.
Man Made Fibers
Acetate is made from cellulose (wood fibers), technically cellulose acetate. Acetate burns readily with a flickering flame that cannot be easily extinguished. The burning cellulose drips and leaves a hard ash. The smell is similar to burning wood chips.
Acrylic technically acrylonitrile is made from natural gas and petroleum. Acrylics burn readily due to the fiber content and the lofty, air filled pockets. A match or cigarette dropped on an acrylic blanket can ignite the fabric which will burn rapidly unless extinguished. The ash is hard. The smell is acrid or harsh.
Nylon is a polyamide made from petroleum. Nylon melts and then burns rapidly if the flame remains on the melted fiber. If you can keep the flame on the melting nylon, it smells like burning plastic.
Polyester is a polymer produced from coal, air, water, and petroleum products. Polyester melts and burns at the same time, the melting, burning ash can bond quickly to any surface it drips on including skin. The smoke from polyester is black with a sweetish smell. The extinguished ash is hard.
Rayon is a regenerated cellulose fiber which is almost pure cellulose. Rayon burns rapidly and leaves only a slight ash. The burning smell is close to burning leaves.