Identification of Textile Fibers - The Textile Journal

Why is the identification of textile fibers necessary?

Understanding textile fibers is a core element of our textile science journey. Back in the day, discerning fibers was a simpler task, where folks leaned on sight and touch to recognize cotton, wool, silk, or linen. Yet, as synthetic fibers entered the scene, things got slightly more tangled. Even though identifying fabrics made entirely of rayon or acetate remained doable, pinpointing blends became a puzzle. With the ongoing arrival of fresh fibers, the act of identification has woven itself into a more intricate tale. Today, achieving accurate fiber recognition frequently calls for sophisticated techniques.

What is the objective of conducting tests on textile fibers?

The Textile Fiber Products Identification Act was crafted to reveal the fibers present in textiles at the time of sale. This aids buyers, removing the need for them to identify the fibers on their own. However, individuals in the textile industry, such as retailers scrutinizing for incorrect labels, customs officials inspecting imports, dry cleaners handling unlabeled items, home economists assisting with textile issues, and forensic scientists unraveling crimes with textiles, still require a deep understanding of fibers. Some simply seek to discern the types of fibers present, while others demand precise percentages of each fiber. This proves challenging due to the abundance of fibers and diverse blends.

Testing Methods for Textile Fibers

Non-technical tests

Feeling test
Burning test

Technical tests

Microscopic test
Solubility test
Melting point test

Non-technical tests

Feeling test

Various fibers display unique characteristics when laid upon your hand. This falls within the technical testing, where fiber identification is done by feeling the fabric. It demands a deep understanding gained through years of hands-on experience. However, this test poses challenges when trying to distinguish and compare fabrics with diverse fiber contents.

Feeling test characteristics of fiber:

Cotton: Cool to the touch, with a soft and inelastic feel.
Linen: Cool sensation on the hand, smooth and lathery feel.
Jute: Cool to the touch, smooth and leathery texture.
Silk: Warm to the touch, exhibiting elasticity and a smooth feel.
Wool: Warm to the touch, with an elastic and springy texture.
Rayon: Cool to the touch, smooth, lacking elasticity, and possessing a lustrous appearance.
Acetate Rayon: Warm to the touch, smoother, more elastic, and resilient compared to regular rayon.
Nylon: Very smooth feel, lightweight, elastic, and lustrous.
Polyester: Very smooth and stiffer in texture.
Acrylic: Resembles wool in feel, but is lightweight and slippery.

Burning test

The burn test is a starting point for sorting fibers. When we watch the burn, it shows how the flame acts, the smoke, the scent, and what remains as ash. It’s not the only way to figure out a fiber, but when combined with other clues, it helps recognize an unknown one. Trying this with blends of fibers is tricky. The way the main fiber reacts could hide a second one with different burning qualities. Also, some finishes, especially the flame-resistant ones, might give the wrong signals. The test is simple, but it involves an open flame, so caution is key. Use a small flame in a safe place where it won’t catch other things on fire. A stable candle or a small alcohol lamp is better than a match. Place something non-flammable under the burning material to stay protected from hot ash. Don’t touch the hot ash or tweezers.

Process of burn test:

To figure out the fibers in an unfamiliar fabric, grab a little piece, roughly 1 inch long, forming a triangle no wider than ¼ inch.
Hold that fabric scrap with a pair of tweezers above a dish, letting it meet the flame directly until it catches fire.

Burning characteristics of fiber:

Cotton, Flax, Viscose Rayon, Linen

1. 1. Approaching flame: Do not shrink.
  2. In flame: Burn readily without melting.
  3. Outside the flame: Continue to burn afterglow.
  4. Smell: Burning hair, paper or wood.
  5. Residue: Small amount of light grey ash.

Acetate

1. 1. Approaching flame: Melts before contact.
  2. In flame: Melts burn with yellow flame.
  3. Outside the flame: Melts.
  4. Smell: Burning paper and vinegar.
  5. Residue: Hard dark bead.

Wool, Silk

1. 1. Approaching flame: Curl away.
  2. In flame: Burn slowly, sputter.
  3. Outside the flame: Self-extinguishing.
  4. Smell: Burning hair.
  5. Residue: Easily crushable blackhead.

Polyester

1. 1. Approaching flame: Shrinks away from the flame.
  2. In flame: Melts burns slowly, drips.
  3. Outside the flame: Burns may be extinguished because of dripping.
  4. Smell: The sweet smell of ester.
  5. Residue: Hard, tough, and grey bead.

Nylon

1. 1. Approaching flame: Shrinks away from the flame.
  2. In flame: Melts burns slowly, drips.
  3. Outside the flame: Burns, may be extinguished because of dripping.
  4. Smell: Pungent burning beans.
  5. Residue: Hard, tough, light color bead.

Polypropylene

1. 1. Approaching flame: Shrinks away from.
  2. In flame: Melts, burns slowly, drips.
  3. Outside the flame: Continue to burn.
  4. Smell: Burning plastic.
  5. Residue: Hard, tough, tan bead.

Acrylic

1. 1. Approaching flame: Shrinks away from the flame.
  2. In flame: Burns readily sputters.
  3. Outside the flame: Burns may extinguish because of dripping.
  4. Smell: Acrid or harsh.
  5. Residue: Irregular, hard black bead.

Asbestos (fireproof)

1. 1. Approaching flame: Does not shrink.
  2. In flame: Does not burn glows.
  3. Outside the flame: Retains shape.
  4. Smell: None.
  5. Residue: Same as original.

Technical tests

Microscopic test

This belongs to the world of technical testing, using a projection microscope with a 100-power magnification to spot fibers. When it comes to this method, it’s easier to recognize natural fibers, but spotting synthetic ones is tricky because they look alike, and there are a whole bunch of different types.

Microscopic test characteristics of fiber:

Cotton

1. 1. Longitudinal Appearance: Flat, irregular convoluted ribbons Mercerized cotton is Smoother and less irregular.
  2. Cross-sectional appearance: Bean or peanut shape with a lumen running through the length.

Linen

1. 1. Longitudinal Appearance: Smooth and Bamboo with cross marking nodes, narrow lumen.
  2. Cross-sectional appearance: Sharp polygonal shape with straight sides. Immature oval shape with a large lumen.

Jute

1. 1. Longitudinal Appearance: Cylindrical with uneven in diameter, a lumen is broad.
  2. Cross-sectional appearance: Rounded polygonal with a central lumen.

Hemp

1. 1. Longitudinal Appearance: Smooth and cylindrical, broad lumen.
  2. Cross-sectional appearance: Partly polygonal.

Ramie

1. 1. Longitudinal Appearance: Irregular and broad with cross marks irregularly distributed.
  2. Cross-sectional appearance: Oblong shape.

Cellulose acetate

1. 1. Longitudinal Appearance: Distinct longitudinal striations that are uniform in width.
  2. Cross-sectional appearance: Irregular and serrated.

Viscose Rayon

1. 1. Longitudinal Appearance: Striated, smooth.
  2. Cross-sectional appearance: Irregular with a serrated outline, oval.

Wool

1. 1. Longitudinal Appearance: Rough surface with scales protruding out, irregular.
  2. Cross-sectional appearance: Nearly round, the medulla present in coarse fibers is concentric and irregular in size.

Silk

1. 1. Longitudinal Appearance: Smooth with distinct length-wise striations.
  2. Cross-sectional appearance: Mostly triangular and irregular.

Nylon

1. 1. Longitudinal Appearance: Smooth, rod-like.
  2. Cross-sectional appearance: Regular, circular.

Polyester

1. 1. Longitudinal Appearance: Smooth, regular, rod-like.
  2. Cross-sectional appearance: Circular.

Acrylic

1. 1. Longitudinal Appearance: Rod-like, irregular striations.
  2. Cross-sectional appearance: Irregular, dog bone shape.

Solubility test

This fits into the non-technical testing path, where we identify fibers by treating them with certain solvents. This way gives us a careful analysis for figuring out fibers. Spotting manufactured fibers and their mixes is tough using this test because of how similar they are chemically. There isn’t a chemical test to pull apart or figure out fibers when they’re all mixed.

Cotton, viscose rayon (Soluble in): 70% H2SO4.
Viscose rayon (Soluble in): Sodium zincate.
Wool, silk (Soluble in): 0.25-0.50% sodium hypochlorite solution.
Wool (Soluble in): 5% NaOH at room temperature.
Silk (Soluble in): 5% NaOH(hot), 70% H2SO4.
Cellulose triacetate, cellulose diacetate (Soluble in): Cold acetic acid or glacial acetic acid.
Cellulose triacetate (Soluble in): Chloroform, methylene chloride, methylene dichloride.
Nylon 6, Nylon 66 (Soluble in): m-cresol, 85% formic acid.
Nylon 6 (Soluble in): Boiling dimethyl formamide (DMF).
Acrylic (Soluble in): Cold DMF.
Polyester (Soluble in): Ortho chlorophenol, meta cresol at 75°c.
Polypropylene (Soluble in): Carbon tetrachloride, boiling xylol.
Asbestos, and glass (Soluble in): Do not dissolve in common organic or inorganic solvents.

Melting point test

Identifying fibers is possible by considering their melting points.

Cotton: It does not melt Decomposes at 149°C. Deterioration takes place at 246°C.
Viscose rayon: Does not melt. Decomposes at 150 °C.
Silk: Does not melt. Decomposes at 320 °C.
Polyester: 265°C.
Nylon 6: 218°C.
Nylon 66: 265°C.
Acrylic: 320°C.
Polypropylene: 165°C.
Polyethylene (low density): 115°C.
Polyethylene (high density): 135°C.
Aramid (Kevlar): 500°C.
Asbestos: 1482°C.
Glass: 1713°C.

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Identification of Textile Fibers

Why is the identification of textile fibers necessary?

Table of Contents

What is the objective of conducting tests on textile fibers?

Testing Methods for Textile Fibers

Non-technical tests

Technical tests