The burning test is a good preliminary test for categorizing Textile fibers. Observations of burning provides information on behavior in a flame, smoke generation, odor during burning, and ash or residue. It never should be used as the only method of identifying a fiber, but it provides valuable information that may be used with other evidence to make a positive identification of an unknown fiber.
Fiber Burning Test Procedure
The sample to be tested should be in fiber form. A single yarn from a woven or knitted fabric should be untwisted to produce a tuft of fibers for testing. use the following instructions, and observe the reactions of the burning fiber very carefully.
- Hold the tuft of fibers with a pair of tweezers.
- Move the tuft close to the side of the flame; do not place the fibers above or below the flame. Observe carefully to see if the fibers melt, shrink, or draw away from the flame.
- Slowly move the fiber tuft into the flame to observe its burning behavior, and then slowly and carefully remove the tuft from the flame to observe the reaction once the flame source is no longer present. Careful observation provides an answer to these four questions –
a) When introduced to the flame, does the fiber burn rapidly or slowly, or does it show no sign of ignition?
b) Does the material begin to melt?
c) Does the material produce a sputtering flame, a steady flame, or no flame at all?
d) When the fiber is removed from the flame, does it continue to burn, or does it self extinguish?
- If the material is still burning when it is removed from the flame, blow out the flame. Note the odor and color of the smoke, or note that no smoke was produced when the fiber was removed from the flame.
- Observe the residue remaining after burning.
a) Does a residue drop from the tweezers?
b) Does that residue continue to burn?
c) How much residue is left?
d) Does the residue remain red, indicating that it is still very hot?
e) What color is the ash that remains?
f) Is the ash the shape of the fiber light and fluffy, or is it bead-shaped?
- After it cools off, touch the residue or ash. Is it soft or brittle? Can it be curshed easily between the fingers, or is it hard to crush?
Results of Fiber Burning Test
Typical fiber reactions for the major natural and man made fiber types are given in the following table.
|Fiber Name||Approaching Flame||In Flame||Remove From Flame||Odor||Residue|
|Cotton & Flax||Does not shrink away; ignites on contact with flame.||Burns quickly||Continues to burn; afterglow||Similar to burning paper||Light, feathery; light to charcoal gray in color.|
|Rayon||Does not shrink away; ignites on contact with flame.||Burns quickly||Continues to burn; afterglow||Similar to burning paper||Light, fluffy ash; very small amount.|
|Polyester||Fuses; melths and shriknks away from flame.||Burns slowly & continues to melt; drips||Self-extinguishes||Chemical odor||Hard, tough gray or tawny bead.|
|Acrylic||Melths & fuses away from flame; ignites readily||Burn rapidly with hot flame & sputtering; drips, melths||Continues to burn; hot molten polymer drops off while burning||Acrid||Irregularly shaped, hard black bead|
|Nylon||Melts away fro flame; shrinks, fuses||Burns slowly & continues to melt; drips||Self-extinguishes||Cooking celery||Hard, tough gray or tan bead.|
|Olefin||Fuses; shrinks & curls away from flame||Melts, burns slowly||Continues to burn||Chemical odor||Hard, tough gray or tan bead.|
|Wool||Curls away from flame||Burns slowly||Self-extinguishes||Similar to burning hair||Small, brittle black bead|
|Silk||Curls away from flame||Burns slowly & sputters||Self-extinguishes||Similar to singed hair||Curshable black bead. Shape of fiber or fabric.|
|Spandex||Fuses but does not shrink away from flame||Burns slowly & continues to melt||Continues to burn with melting||Chemical odor||Soft, sticky, gummy mass.|
It is worth mentioning that, Dyes and Finishes affect test results. Flame-retardant finishes are especially misleading.
Colored fibers, especially those produced with pigments, may retain the oclor in the ash or residue.
It is difficult to detect the presence of blends with a burning test. One fiber in a blend may completely mask the proper ties of another fiber.