Fiber Identification Methods: Burn, Bleach & Strength Test

by Elizabeth / Friday, 17 February 2017 / Published in Silk Identification, Textile Knowledge

The number of different fibers used in the textile industry is quite large. Identification of these fibers is frequently difficult since it is usually not possible to distinguish one fiber from another merely by touch or sight. Other tests must be performed. There are advantages and disadvantages to each. Some are easy, quick and relatively inexpensive，but do not allow clear distinctions to be made between fibers with the same characteristics. For example, a burning test will not differentiate between flax and cotton since both have the same burning properties. Others enable positive identification, but require much more time and more sophisticated testing apparatus (e. g. chemical analysis).

Burn test

The burning test is a good preliminary test. It provides valuable data regarding appropriate care and will help place a fiber into a specific category. It is not, however, a test that can be used alone to provide exact identification of specific fibers. In the case of yarns composed of two or more fibers, the test will usually give the reaction of the fiber that burns most easily; if a fiber is heat-sensitive，it will tend to melt or withdraw from the flame, leaving the flammable fiber to burn. Burning Characteristics of Textile Fibers

Fiber	Burn or melt	Shrinks from flame	Odor	Residue	Other properties
Cotton	Burns only	No	Burning paper, leaves or wood	Fine, feathery, gray ash	/
Flax, hemp, jute, ramie, etc.	All burning characteristics same as cotton
Rayon	All burning characteristics same as cotton
Wool, mohair, cashmere, alpaca，etc.	Burns only	Yes	Very strong odor of burning hair	Black, hollow irregular bead which crushes easily to a gritty, black power	Self – extinguishing
Silk	Same as wool, except odor is not so strong and may smell like charred or burning meat ( no sulphur content like wool)
Acetate	Burn & melt	Yes	Combination of burning paper and vinegar	Dark, hard, solid bead	/
Acrylic	Burn & melt	Yes	Broiled fish	Hard, irregularly shaped bead	Flame gives off black smoke
Aramid	Burn & melt	Yes	Sweet	Hard, black bead	Self – extinguishing
Glass	Melt only	Very slowly	No odor	Hard, whitish bead	Flame resistant fiber； heat from match will not cause fiber to melt
Modacrylic	Burns and melt	Yes	Chemical	Hard, black irregular bead	Self – extinguishing
Nylon	Burns and melt	Yes	Celery	Hard, cream – colored bead. If fibers are overheat， bead will become dark	drops of melted fiber may fall from heated portion of sample
Olefin	Burns and melt	Yes	Chemical	Hard, tan bead	Flame gives off black smoke
Polyester	Burns and melt	Yes	Sweet chemical	Hard，cream — colored bead. If fibers are overheat, bead will become dark	Drops of melted fiber may fall from heated portion of sample; flame gives off black smoke
Spandex	Burns and melt	Yes	Chemical	Soft, black ash	/
Vinal	Burns and	Yes	Paraffin – like or Chemical	Hard, tan bead	/

Remember that the burning test is a preliminary test indicates general grouping or categories only. The test is relatively simple but must be used with care to avoid injury and guard against fire.

Microscopic evaluation

Most fibers provide different view of both their lengthwise and crosswise. Natural fibers have their specific shape in their cross- section，and man-made fibers are similar in their microscopic appearance.

Chlorine bleach test

For silk or wool fibers，they will be wet with liquid chlorine bleach，these fibers turn yellow and after a while disintegrate from the action of the chemical.

Dry and wet strength test

The strength of many fibers is affected by the amount of water they contain, a few fibers get a little stronger when wet, such as cotton fibers; some retain about the same in strength; and others get weaker.