TEXTILE FIBRES-Fibre Identification (Burning Test)-3.2.1

Fibre Identification

Fibre Identification : 

The identification of textile fibres is a very important part of the study of textile science. At one time,
simple fibre identification was a relatively easy task; most consumers could tell by appearance and hand whether a fabric was cotton, wool, silk, or linen. Once the first manmade fibres were introduced, the process became a bit more difficult. Consumers usually could identify the fibre composition of fabrics made of 100 percent rayon or acetate, but blends of some fibres were difficult to identify. As more fibres were introduced, the task became progressively more difficult. Today, sophisticated techniques are usually required for accurate fibre identification.

The purpose of the Textile Fibre Products Identification Act was to provide information on fibre
content of textiles at the point of sale. Consumers were at once relieved of the responsibility to
identify fibre content of items they purchased; however, professionals working with textile
products still must be able to identify fibres accurately. Such individuals include retailers who
suspect some textile products they bought for resale have been labeled inaccurately; customs
officials who must identify imported fibres; dry cleaners who must clean an item from which all
the labels have been removed; extension home economists who are asked to help solve a
consumer's problem with a textile product; and forensic scientists who must use a textile
sample to help solve a crime.

For most individuals, the only information needed is a qualitative analysis of fibre content: what
fibre or fibres are present in this product? For others, a quantitative analysis of the product is
also important: in what percentages are the fibres present? With the numbers of fibres
available today and the variety of blends being produced, neither analysis is easy.
Methods for qualitative identification of fibres include such procedures as burning tests,
microscopy, density determination, moisture regain analysis, dye staining, chemical solubility,
melting point determination, infrared spectroscopy, and chromatography. Simplified versions
of the first six procedures are relatively easy to perform in most laboratories. They require the
use of a drying oven, an analytical balance sensitive to 0.005 gram, a compound light
microscope capable of 200 x magnification, laboratory glassware, and a supply of chemicals.

Methods for qualitative identification of fibres include such procedures as burning tests,
microscopy, density determination, moisture regain analysis, dye staining, chemical solubility,
melting point determination, infrared spectroscopy, and chromatography. Simplified versions
of the first six procedures are relatively easy to perform in most laboratories. They require the
use of a drying oven, an analytical balance sensitive to 0.005 gram, a compound light
microscope capable of 200 x magnification, laboratory glassware, and a supply of chemicals. 

  

A. Burning Test:   The burning test is a good preliminary test for categorizing fibres. Observation 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 fibre, but it
provides valuable information that may be used with other evidence to make a positive
identification of an unknown fibre.

Blends of fibres are difficult to test using this procedure. The reaction of the predominant
fibre may mask the presence of a second fibre, which could have entirely different burning
characteristics. Finishes, especially flameretardant finishes, can also give misleading
information. Although the test is easy to perform, it does involve the use of an open flame, making it
necessary to observe certain safety precautions. Use a small flame source in an area where
there is no danger of igniting other materials. A candle in a stable base or a small alcohol
lamp is preferable to a hand-held match. A nonflammable pad should be used under the
burning material to provide protection from molten drip and smoldering ash. Do not touch
ash or tweezers while they are still hot.

Procedure:   The sample to be tested should be in fibre form. A single yarn from a woven or knitted
fabric should be untwisted to produce a tuft of fibres for testing. Use the following
instructions, and observe the reactions of the burning fibre very carefully.

1. Hold the tuft of fibres with a pair of tweezers.
2. Move the tuft close to the side of the flame; do not place the fibres above or below
   the flame. Observe carefully to see if the fibres melt, shrink, or draw away from the
   flame.
3. Slowly move the fibre 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 fibre 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 fibre is removed from the flame, does it continue to burn, or does it self
   extinguish?
4. If the material is still burning when it is removed from the flame, blow out the flame.
    Note the odor and colour of the smoke, or note that no smoke was produced when
    the fibre was removed from the flame.
5. Observe the residue remaining after burning. Does a residue drop from the
    tweezers? Does that residue continue to burn? How much residue is left? Does the
    residue remain red, indicating that it is still very hot? What colour is the ash that
    remains? Is the ash the shape of the fibre, light and fluffy, or is it bead-shaped?
6. After it cools off, touch the residue or ash. Is it soft or brittle? Can it be crushed
   easily between the fingers, or is it hard to crush?

Results:  Typical fibre reactions for the major natural and manmade fibre types are given in the
following table. When interpreting results, remember:
1. It is difficult to detect the presence of blends with a burning test. One fibre in a
    blend may completely mask the proper ties of another fibre.

2. Dyes and finishes affect test results. Flame-retardant finishes are especially
    misleading.

3. Coloured fibres, especially those produced with pigments, may retain the colour in
    the ash or residue. 

Table for burning characteristics of fibre

Fibre	Approaching Inflame	In Flame	Remove from flame	Odor	Residue
Cotton & flax	Does not shrink away; ignites on contact	Burns quickly	Continues to burn; afterglow	Similar to burning paper	Light, feathery; Iight to ch areoa gray in colour
Rayon	Does not shrink away; ignites on conta with flame	Burns quickly	Continues to burn; afterglow	Similar to burning pape	Light, fluffy ash; very small amount
Polyeste	Fuses; melts & shrinks away from flame	Burns slowly & continues to melt; drips	Self-extinguishes	Chemical odor	Hard, tough gray or tawny bead
Acrylic	Melts & fuses away from flame; ignites readily	Burns rapidly with hot flame & sputtering drips, melts	Continues to burn; hot molten polymer drops off while burning	Acrid	Irregularly shaped, hard black bead
Nylon	Melts away from flame; shrinks, fuses	Burns slowly with melting, 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 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	Usually self-extinguishes	Similar to singed hair	Crushable black bead(unweighted)  Shape of fibre or fabric (weighted)
Spandex	Fuses but does not shrink away from flame	Burns with melting	Continues to burn with melting	Chemiool odoc	Soft, sticky,gummy mass