Qualitative Identification of Textile Fibers by Five Experimental Methods

I. Fiber Identification by Burning Method

1. Scope of Application

This method is applicable for the preliminary identification of various types of fibers. It is not suitable for fibers that have undergone flame-retardant treatment.

2. Principle of the Experiment

The fiber type is identified based on its behavior when approaching, contacting, and leaving the flame, the odor produced during combustion, and the characteristics of the residue left after burning.

3. Experimental Materials

A variety of commonly used known fibers (cotton fiber, viscose fiber, silk fiber, wool fiber, polyester, acrylic, nylon, vinylon) and unknown fiber samples.

4. Experimental Instruments

Alcohol lamp, matches or lighter, scissors, tweezers, petri dish, magnifying glass.

5. Experimental Procedure

(1) Twist the fiber into a bundle. Use tweezers to hold one end of the fiber bundle, and slowly bring the other end close to the flame. Observe and record the changes in the sample when heated (e.g., melting, shrinking).

(2) Move the sample directly into the flame and allow it to burn fully. Observe and record the burning behavior in the flame (e.g., burning rate, smoke generation) and smell the odor of the burning gases.

(3) Remove the sample from the flame. Observe and record the burning behavior after removal (e.g., whether it continues to burn or self-extinguishes).

(4) Place the sample in an evaporating dish. When the flame goes out, smell the odor and record your observations.

(5) After the sample has cooled, observe the condition of the residue. Lightly pinch the residue with your fingers and record the findings.

6. Experimental Report

The experimental report should include: sample information, observation records from each stage of the experiment, and a judgment of the unknown fiber type. The entire observation process can be recorded in Table 1.

Table 1. Burn Characteristics Observation Table

II. Microscopic Identification of Fibers

1. Scope of Application

This method is applicable for the identification of various types of fibers.

2. Experimental Principle

By observing the longitudinal and cross-sectional morphology of fibers under a microscope and comparing them with standard fiber images and morphological descriptions, the fiber type can be identified.

3. Experimental Materials

Various commonly used known fibers (cotton fiber, viscose fiber, silk fiber, wool fiber, polyester, acrylic, nylon, vinylon) and unknown fibers.

4. Reagents

Anhydrous ethanol, glycerol, ether, liquid paraffin, collodion, paraffin for sectioning.

5. Instruments and Equipment

Optical microscope, Herzberg microtome, glass slides, cover slips, blades, tweezers, scissors, fine glass rods.

6. Experimental Procedure

(1) Observation of Longitudinal Morphology

① Take a small bundle of fibers, straighten and evenly spread them loosely on a glass slide. Add a drop of glycerol and cover with a cover slip (avoid air bubbles), then place it on the microscope stage.

② Select a suitable magnification, generally between 100× and 500× (eyepiece 10×, objective lens starting from 10–15×, gradually adjusting to 40×), and observe the longitudinal morphology of the sample.

③ Capture images of the fiber's longitudinal morphology and record the observations.

④ Compare with standard images or descriptions of common fibers to determine the type of unknown fiber.

(2) Observation of Cross-Sectional Morphology

① Turn the fixing screw of the Herzberg microtome counterclockwise to raise the lower end away from the slit. Loosen the screw, remove the positioning pin, rotate the screw base 90°, and pull out the metal tongue from the slit base.

② Take a small bundle of fibers, remove the short fibers, align them neatly, and clamp them tightly into the slit base. Lock the bundle using the metal tongue base (tightness should allow slight movement of fibers when gently pulled). Trim any exposed fiber ends with a sharp blade. Rotate the screw base back to its original position, insert the positioning pin, and tighten the fixing screw.

③ Use a fine glass rod to apply a thin layer of 5% collodion solution to the fibers below the slit. Let it sit until the collodion solidifies. Then, slightly turn the graduated screw clockwise to expose the fiber bundle slightly. Keeping the blade as close to the base as possible, carefully slice the fiber cross-section.

④ Place the fiber cross-section on a glass slide, add a drop of glycerol, and cover with a cover slip (avoid air bubbles), then place it on the microscope stage.

⑤ Select an appropriate magnification to observe the cross-sectional morphology of the sample.

⑥ Capture images of the fiber's cross-sectional morphology and record the observations.

⑦ Compare with standard images or descriptions of common fibers to identify the unknown fiber type.

7. Experimental Report

The experimental report should include: sample information, longitudinal and cross-sectional observation records, and the identification result of the unknown fiber type. The full observation process can be recorded in Table 2.

Table 2. Fiber Morphological Characteristics Recording Table

III. Identification of Fibers by Chemical Dissolution Method

1. Scope of Application

This method is applicable for the identification of various types of fibers.

2. Principle of the Experiment

The identification of fiber types is based on their solubility characteristics in different chemical reagents at various temperatures.

3. Experimental Materials

Various commonly used known fibers (cotton, viscose, silk, wool, polyester, acrylic, nylon, and vinylon) and unknown fibers.

4. Reagents

Hydrochloric acid, sulfuric acid, nitric acid, formic acid, glacial acetic acid, hydrofluoric acid, acetone, phenol, cyclohexanone, m-cresol, tetrachloroethane, sodium hydroxide, sodium hypochlorite, dimethylformamide, etc. All reagents should be of analytical grade or chemically pure.

5. Experimental Instruments

Beakers, tweezers, graduated cylinders, test tubes, test tube holders, glass rods, watch glasses, Erlenmeyer flasks, thermometers, hydrometers, alcohol lamps, water baths, electronic balances, and enclosed electric heaters.

6. Experimental Procedure

(1) Prepare the various solutions required for the experiment.

(2) Take approximately 100 mg of fiber and place it in a test tube or beaker. Add about 10 mL of the prepared solution (the ratio of sample to solution should be at least 1:50). Stir with a glass rod at room temperature for 5–10 minutes, observing the dissolution of the fiber during stirring, and record the results.

(3) For fibers that are difficult to dissolve at room temperature, perform a heated boiling test. Heat the test tube or beaker containing the sample and solution to boiling and maintain for 3 minutes. Observe the dissolution of the fiber and record the results.

(4) Conduct the experiment on two samples of each fiber. If the dissolution results differ significantly, repeat the test.

7. Experimental Report

The experimental report should include: sample information, observation records of the dissolution process, and judgment on the type of unknown fiber. The entire observation process can be recorded in Table 3.

Table 3. Fiber Dissolution Observation Record Sheet

IV. Fiber Identification by Chemical Reagent Staining Method

1. Scope of Application

This method is applicable for the preliminary identification of various types of fibers.

2. Experimental Principle

This method distinguishes fiber types based on their differing dyeing behaviors when exposed to specific chemical reagents. The dyeing characteristics of commonly used fibers are listed in Table 4.

Table 4. Dyeing Characteristics of Common Fibers

3. Experimental Materials

Various known fibers (cotton, viscose, silk, wool, polyester, acrylic, nylon, vinylon) and unknown fiber samples.

4. Reagents

Iodine, potassium iodide, anhydrous zinc chloride, HI-1 fiber dye (5 g/L).

5. Apparatus

Beakers, tweezers, test tubes, test tube clamps, glass rods, watch glasses, alcohol lamp, iron stand, asbestos net.

6. Experimental Procedure

(1) Iodine–Potassium Iodide–Zinc Chloride Staining Method

① Weigh 50 g of potassium iodide and dissolve it in 100 mL of distilled water.

② Weigh 20 g of iodine and add it to the potassium iodide solution. Stir thoroughly and keep the solution protected from light for more than 24 hours.

③ Weigh 50 g of anhydrous zinc chloride and add it to the prepared iodine–potassium iodide solution. Stir well to obtain the iodine–potassium iodide–zinc chloride staining reagent.

④ Take a small bundle of fiber and place it on a watch glass. Add the staining reagent dropwise (enough to fully soak the fiber).

⑤ Let the fiber soak for about 1 minute, then immediately rinse thoroughly with clean water.

⑥ After air-drying, observe and record the staining condition of the sample.

(2) HI-1 Fiber Dye Method

① Pour approximately 10 mL of HI-1 fiber dye into a beaker and heat it over a low flame until boiling.

② Use tweezers to place a small bundle of fiber into the beaker and boil-dye it for about 1 minute.

③ Remove the fiber and rinse thoroughly with clean water.

④ After air-drying, observe and record the staining condition of the sample.

7. Experimental Report

The experimental report should include: sample information, observation records of the staining results, and judgment on the type of unknown fiber. The full observation process may be recorded in Table 5.

Table 5. Fiber Staining Observation Record Sheet

V. Identification of Fibers by Chlorine- and Nitrogen-Based Color Reaction Method

1. Scope of Application

This method is suitable for the preliminary identification of fibers containing chlorine or nitrogen elements.

2. Experimental Principle

Fibers that contain chlorine or nitrogen produce characteristic color reactions when subjected to flame tests or acid-base detection methods. These color changes can be used to distinguish fiber types.

3. Experimental Materials

A variety of commonly known fibers (cotton, viscose, silk, wool, polyester, acrylic, nylon, vinylon) and unknown fibers.

4. Reagents

Sodium carbonate.

5. Instruments

Copper wire, scissors, tweezers, test tubes, test tube holders, alcohol lamp, fine sandpaper, red litmus paper.

6. Experimental Procedure

(1) Chlorine Test:

① Take a clean copper wire and remove the surface oxide layer using fine sandpaper.

② Heat the copper wire in a flame until red hot, then immediately touch it to the fiber sample.

③ Place the wire back into the flame and observe whether the flame turns green (a green flame indicates the presence of chlorine). Record the observation.

(2) Nitrogen Test:

① Cut a small amount of fiber into pieces and place in a test tube. Add a suitable amount of sodium carbonate to cover the sample.

② Heat the test tube over an alcohol lamp and place red litmus paper at the mouth of the test tube.

③ Observe whether the litmus paper turns blue (a blue color indicates the presence of nitrogen). Record the observation.

7. Experimental Report

The report should include: sample information, observed color changes, and identification of the unknown fiber type. The entire observation process can be recorded in Table 6.

Table 6. Fiber Color Reaction Observation Record

For laboratories, manufacturers, and researchers seeking reliable third-party testing for textile materials, Alfa Chemistry offers comprehensive textile testing services tailored to garments and upholstery applications. Our services are designed to meet international standards and ensure product performance, safety, and compliance. Contact us to learn how we can support your testing protocols.