TEXTILE FIBRES-Fibre Identification (Chemical Solubility Tests)-3.2.3

C. Chemical Solubility Tests:  Chemical solubility tests are necessary to identify most manufactured fibres. They areusually performed after burning tests and microscopic examination of the fibres.
Preliminary burning tests usually provide some information about the specific fibres that
may be present or the fibres that are definitely not present, and microscopy provides
information on the number of fibres to be identified and the predominant fibres in a blend.
The solubility procedure described in this section is based on the chemicals specified in the
AATCC (American Association of Textile Chemists and Colourists) qualitative identification
test method. In some instances, the term solubility is a misnomer as the material does not
dissolve, but merely degrades. A material that dissolves in a solvent can be recovered from
that solvent, whereas a material degraded by a solvent breaks apart but does not dissolve,
and so cannot be recovered from the solvent. When observing solubility tests for fibres, it is
not always possible to determine whether a fibre has actually dissolved or has merely
disintegrated.

All chemical tests should be conducted in a room with proper ventilation and chemical
safety protection devices. The required Material Safety Data Sheet (MSDS} for each
chemical should be posted in areas where the chemical is used. Although only very small
amounts of chemicals are needed for testing, accidents sometimes happen. Adhere to
chemical safety rules in performing fibre identification tests. Wear protective eye goggles
when using chemical solvents. Organic solvents and heated liquids should be used only in a
fume hood! Follow local laboratory regulations for disposing of used solvents and fibres. 

Procedure:  The following Chemicals used for solubility test table lists the chemicals and test conditions used in chemical solubility testing. When there is no prior knowledge of the fibres that may be present, the material should be tested in the solvents in the or.der presented in the table.
Once a positive identification is made, solvent testing may be terminated. Where prior
information indicates that certain fibres may be present, test the unknown fibre only in
those solvents required for its identification. The general procedure for solvent
identification follows.

1. When solvents are used at room temperature, the tests may be performed in a
watch crystal, a 50-ml beaker, or a small test tube. Place a small amount of the fibre
in the container and add the solvent. Use about 1 ml of solvent for 10 mg of fibre.

2.  Tests performed at the boiling point of the solvent require the use of a ventilated fume hood. Pour the solvent into a small beaker and place the beaker on a hot plate inside the fume hood. Adjust the temperature of the hot plate to maintain a slow boil. Add the fibre to the boiling liquid. Watch the reaction carefully to make surethe solvent does not boil dry. Never add additional solvent to the heated beaker!

3. For tests conducted at intermediate temperatures, heat a beaker of water on a hot plate under the fume hood, and adjust the temperature using a thermometer. Place the fibre and solvent in a test tube, then set the test tube in the beaker of heated water.

4. Watch the fibre in the solvent carefully to observe the speed with which it breaks down and the amount of the material dissolved. Note whether the material actuallydissolves, degrades into small pieces, or forms a plastic mass. If all fibres are not dissolved in a specific solvent, carefully remove the undissolved fibres. Rinse them in water, and attempt to dissolve them in another solvent.

Results: The following Solubility of Fibres table provides fibre solubility test results. Compare the
results to identify a fibre. Some of the chemicals in the table are commonly found in the home. Other household products containing similar solvents will also damage or dissolve fibres. Acetone is often a component of nail polish, nail polish remover, paint thinners, and paint removers. Amyl acetate, a similar chemical, may damage acetate, modacrylic, and vinyon fibres. Vinegar is a dilute solution of acetic acid; it does not dissolve fibres, but it may damage the same fibres that are dissolved by glacial acetic acid. 

 

Sodium hypochlorite, which has about 5 percent available chlorine and a pH of about 11, is
the active ingredient in undiluted household chlorine laundry bleaches. Some laboratories
use undiluted bleach as the chemical reagent in fibre solubility tests instead of mixing a 5
present sodium hypochlorite solution.

Cresol is sometimes a component of household disinfectants and antiseptics. It is not Present  in a sufficiently high concentration to dissolve fibres, but it may damage acetate, acrylic, modacrylic, nylon, nytril, polyester, spandex, and vinyon fibres