Chemistry 439

Fiber analysis

Objectives:

    1. Determine whether or not an unknown fiber matches one of the known samples.
    2. Learn how to collect and present comparison data.
    3. Learn what data to collect that will best demonstrate a difference between two objects.
Background:
It is impossible to prove conclusively that two fibers or two paint chips came from the same source. However, it is possible to demonstrate to a reasonable person that it is likely that they did. Therefore, this experiment is aimed at collecting data most likely to convince that reasonable person that the unknown is the same as one of the known samples.
Recall that the scientific proof requires that:
    1. A hypothesis is stated that is proposed to explain the observations.
    2. The hypothesis is then tested with a risky experiment.
    3. The resulting data are evaluated and the hypothesis is revised as appropriate if necessary.
    4. The process is repeated until the hypothesis fully explains all experimental observations.
Note that step 2 calls for a risky experiment. This is an experiment where traditional thinking would predict the incorrect results but the hypothesis will predict the observed results if it is correct. An experiment where the observations are predicted by many hypotheses is not a risky experiment. Risky experiments are very convincing and are therefore favored when collecting data to be used to convince a reasonable person that your position is the correct position.

Any property that might be different between fibers or paint chips may be used in this experiment so the procedures are general. These properties include:

Several of the tests available for students in this class are described below. Other tests, such as a microscopic examination, are usually completed in addition to the tests we will run but they are not part of this class. For this experiment, each student will run one known fabric and the unknown fabric and will report their data to all other students. Each student must then compare the unknown to all known fabrics for which data are available.

I. Stripping the Dye from a Fiber (Fabric)
Fabrics may contain dyes, fillers, softeners, brighteners or antistatic agents that can be used to establish similarities or differences. They must be removed to examine the "cleaned" fabric fibers (see below). Procedures to "strip" these materials from the fabric are described below.

    1. Obtain a piece of the unknown and a known fabric and cut it into six 1 cm x 1 cm pieces. Put each piece in a small beaker.
    2. Add 2 drops of 1% ammonium hydroxide and 0.5g of sodium hydrosulfite to beaker #1. Add 10 ml of 5% sodium hydrosulfite, 1 ml of 1% sodium hydroxide and 15% butyl carbitol to beaker #2. This is a general stripper but it will not work on animal fibers or cellulose acetate. It is a basic reducing agent.
    3. Add 10 ml of 5% acetic acid.
    4. Add 10 ml of 1.0% ammonium hydroxide
    5. Add 10 ml of 0.1M sodium hypochlorite and adjust the pH to 10-11 with sodium hydroxide.
    6. Add 10 ml of 2% sodium hypochlorite and adjust the pH to 5 with acetic acid. If ClO2 fumes are released during heating, add a small amount of hydrogen peroxide. This is used to strip black dyes.
Bring all solutions to a boil and continue until the dye is removed or it becomes obvious that nothing else is being removed. Record your results and use the stripped fibers for additional tests as described below.

II Burning Test
Take a fiber from each piece of fabric and observe how it burns using a small burner. Record your results.

III. Solubility Test
Fibers are soluble in some solvents but not in others. Below are a list of solvents and the fibers that are soluble in them. Generally, the way to run the test is to place a fiber in a melting point capillary filled about ¸ full with the solvent, seal the capillary and heat the capillary for about 15 minutes in a boiling water bath.

    1. Acetone-(at room temperature)-acetate, Arnel, Dynel, vinyon and (in boiling water) Verel.
    2. Acetic Acid (100%)-acetate, Arnel, nylon
    3. m-cresol-Arnel, vicose, silk, orlon, nylon, Fortisan, vinyon, Dynel, Saran
    4. 90% phenol-acetate, Fortisan, Arnel, Dynel, nylon, Dacron, vinyon, polyvinyl chloride & viscose.
    5. Calcium Thiocyanate-Acrilan, Creslan, orlon, Darvan
    6. Monochlorobenzene-vinyon, Saran
    7. 5% Sodium hydroxide-cultivated silk, hair, wool, Darvan
    8. 45% Sodium Hydroxide-cultivated silk, Tussah silk, hair, Darvan, Arnel, acetate,
    9. 5.25% Sodium hypochlorite-protein fibers, hair, silk, wool
    10. 50% hydrochloric acid-nylon
    11. 70% sulfuric acid-cotton, linen (they are not soluble in 60% sulfuric acid)
    12. 67% zinc chloride-cotton, viscose, acetate, Arnel, silk, Acrilan, Orlon, Creslan and cupra.
IV. Dying a fabric
    1. Place 20 ml of 1% TIS stain in a small beaker and warm on a hot plate.
    2. Wet the test fabric with distilled water and then place it in the hot TIS solution for 3-5 minutes.
    3. Remove and wash well with distilled water.
V. Chemical Composition
Evaporate the solvent from the dyes and other chemicals stripped from the fibers in step I above carefully using a stream of nitrogen. Dissolve the residue in a small amount (10 ul) of the appropriate solvent and obtain a FTIR spectrum and/or analyze by TLC as described in other experiments in this manual.

Report:
Summarize all of the data and include an estimate of the probability that the unknown fabric is similar to one of the known fabrics and is not like the other known fabrics. What is the probability that the tests "just happened" to come out the way they did?