30 Fibre Testing – Qualitative Tests

P. Sivakumar

epgp books




  • The fibre is qualitatively tested generally under following categories.
  • The fibres are classified into natural and manmade fibres. Among the natural are sub classified into, vegetable, animal and mineral fibers (Asbestos). The manmade fibres are sub classified into regenerated, synthetic fibers and mineral fibers (Metallic, ceramic and carbon).
  • The Qualitative Analysis tests are commonly classified as non-technical and technical tests.


Non-Technical Tests:

  •  Finger sensory test
  • Burning test

Technical Tests:

  • Visual identification (Optical Microscopic ,SEM)
  • Solubility test


  1. Finger Sensory Test

The fibers exhibit varieties of behavior when they are sensed through fingers on them through senses of warmth-cool, smoothness- rough, soft- harsh, flexibility- rigidness properties. Feeling test are explained below. However, it is difficult to identify the blends of various fibres through this method.


2. Burning Test


The textile fiber behaves differently in flame based on their chemical nature and morphological structure. The natural and regenerated fibers exhibit differently in the flame based on their cellulosic and protein natures. The synthetic fibres exhibits differently based on their thermo plastic and thermoset nature. The fibers are identified through observations such as type of flame, sound and odour while burning as well as form, hardness and colour of remnant (ash or bead) at following stages of flammability test

    1.       Moving the sample slowly towards flame.

2.      During burning

3.      Immediately after being removed from the flame

4.   Post burning, sample has been cooled; the ash/bead is examined for characteristics such as amount,nature, form, hardness and colour.


The burn test should be conducted with safe ambience. Water has to be kept near the experiment place. The test should be done in a inflammable vessel or bucket made of ceramic, metalor glasspreferably withfire extinguishers like soda or even water at its bottom. . Containers made of thermoplastic materials should be avoided


General burn test procedure


Hold an unknown fiber sample of at least 1cm in length in a pair of tweezers, and slowly move it toward a small flame (candle, Bunsen burner, cigarette lighter).

  • Observe the fiber’s reaction to the flame (shrinks away, ignites before touching the flame, melts, etc.).
  • Observe the fiber’s reaction to being ignited in the flame (starts to burn but self-extinguishes, starts to burn but immediately extinguishes, melts and burns, melts but burns with difficulty, simply chars, etc.).
  • Observe the odor generated by the burning procedure like burning paper (natural cellulosics and rayons), acrid vinegar (acetates), and other various forms of plastic-like smells). Words used such as celery, sweet, sharp, etc., may be too subjective and rely too much on individual personal experiences to be useful.

Observe the remaining end of the fiber under magnification where it was burned (no bead or ash, easily crushable, soft, brownish-black, puffy bead, hard round or irregular bead of various grey to black colors, etc.). Touching the (cooled) bead end is required to determine its degree of hardness.


As for many other tests, the results should be compared with those of burn tests of a known reference fiber.




Visual appearance of fibres:


Microscope test:


Each textile fibre has its unique morphological structure and features. So the fibre can be identified easily, when it is viewed through optical microscope or scanning electron microscope. The microscopic appearance of different fibres is shown in the table.


Optical or light microscope:

  1. This is a technical test which involves identifying the fibreusing microscope with a magnification of minimum 100 x to a maximum of 4000 x and the resolution power maximum 2500 Ao or 0.25 micro meter or 250 nano meter.
  2. The fibre could be distinguished between varieties of fibers.
  3. The identification of the natural fibers is done easily as compared to MMF.
  4. Majority of synthetic fibers are similar in physical appearance and hence identification through microscope is somewhat difficult.

A scanning electron microscope (SEM):


It produces images of a sample by scanning the surface with a focused beam of electrons. The sample electrons interact with atoms in the sample, producing various signals that contain information about the sample’s surface topography and composition. SEM can achieve resolution better than 1 nanometer. Specimens can be observed in high vacuum in conventional SEM, or in low vacuum or wet conditions in variable pressure or environmental SEM, and at a wide range of cryogenic or elevated temperatures with specialized instruments.


SEM provides detailed high resolution images of the sample by rastering a focussed electron beam across the surface and detecting secondary or backscattered electron signal. An Energy Dispersive X-Ray Analyser (EDX or EDA) is also used to provide elemental identification and quantitative compositional information. The resolution power is 0.5 – 5 Ao and the magnification power is 3,00,000


Transmission electron microscope(TEM):


The transmission electron microscope (TEM) works much like a light microscope, transmitting a beam of electrons through a thin specimen and then focusing the electrons to form an image on a screen or on film. The most important difference between a transmission electron microscope and a scanning electron microscope is rather than the broad static beam used in TEM, the SEM beam is focused to a fine point and scans line by line over the sample surface in a rectangular raster pattern.

  1. Solubility or solvent Test:

The test involves treating the fibers in certain solvents for identifying them. The technical test is becoming difficult to conduct as most of the manufactured fibers and their blends are chemically similar. There is no individual chemical or solvent test for separating or identifying the fibers in combinations.




Wear nose masks to avoid harmfulness of vapors to the lungs and have hand gloves, shoes and goggles to avoid harmfulness to the body.



  • More reliable than the non-technical tests.
  • Used for both manmade fibers and natural fibers.
  • Easily conducted.


  • Certain manufacturing and finishing processes like mercerizing, affects the appearance of the fibers under the microscope.
  • Very dark colored fabrics cannot be identified under microscope.
  • Dye stuffs must be removed from fabrics.

The name of the solvents or chemicals that is used for identification through solubility test is given in the following table.

  • Distinguishing animal from vegetable fibers with an alkali :

As strong alkali destroy animal substances, a 5%of soda lye (NaOH or KOH) solution in water can be used to eliminate wool and silk fibers from a sample that contains a mixture of fiber. The vegetable fibers will not be affected by this solution.

  • Distinguishing vegetable from animal fibers with an acid

As dilute acid destroy vegetable fibers, a 2%sulphuric acid solution can be used. A drop of solution is placed on the sample, which is then pressed with a hot iron. Thespotted area will become charred if the sample is cotton linen or rayon.


The use of concentrated cold hydrochloric acid will dissolve the silk whereas the wool fiber swells.


If the fabric is thought to contain nylon, the fabric may be immersed in a boiling solution of sodium hydroxide. The nylon is insoluble in such a solution


Polyester is soluble in hot meta cresol; however,unlike acetate, it is not soluble in acetone, and unlike nylon, it is not soluble in concentrated formic acid.


Acrylic fibers will dissolve in 70 percent solution of ammonium thiocyanate at 130 degree Celsius but the other fibers will not.


Cotton and linen are immersed in a 1% solution of fuchsine FIXIN (a deep red synthetic dye used as a biological stain and disinfectant) in alcohol to give red rose color. Later ,they are washed and immersed into ammonia, linen retains the red coloration but cotton does not.


There are two specific solvents for quick identification of glass fibers, they are hydrofluoric acid and hot phosphoric acid.

you can view video on Fibre Testing – Qualitative Tests


  1. E.P.G Gohl and L.D.Vilensky, “Textile Science ”, CBS Publishers., 1987.
  2. S P Mishra, “ A Text Book of Fibre Science”, New Age Publications, 2010.
  3. https://www.textileschool.com/321/fiber-identification-tests-to-identify-a-fibre
  4. http://www.manufacturingsolutionscenter.org/fiber-analysis.html