Comprehensive Introduction to Textile Fibers: Classification, Structure, and Properties

Fundamental Textile Terminology

• Textile: Originally defined as a woven fabric. Currently, the term applies generally to the following categories:

  • Staple fibers and filaments suitable for conversion into yarns, or for preparing woven, knitted, or nonwoven fabrics.
  • Yarns produced from natural or manufactured fibers.
  • Fabrics and manufactured products derived from the aforementioned fibers and yarns.
  • Garments and articles fabricated from these materials that retain the characteristic flexibility and drape of the original fabrics. The word is derived from Latin.

• Textile Materials: A general term encompassing fibers, yarn intermediaries, yarn, fabrics, and products made from fabrics. These materials must retain, more or less completely, the strength, flexibility, and other typical properties of the original fiber or filaments.

• Textile Fiber: A material primarily derived from natural or synthetic sources used to manufacture yarns and fabrics (woven, knitted, or nonwoven).

• Yarn: A generic term for a continuous strand of textile fibers, filaments, or material in a form suitable for knitting, weaving, or intertwining. Forms include:

  • Spun Yarn: A number of fibers twisted together.
  • Zero-Twist Yarn: Filaments laid together without twist.
  • Twisted Filament Yarn: Filaments laid together with a degree of twist.
  • Monofilament: A single filament with or without twist.
  • Narrow Strips: Materials such as paper, plastic film, or metal foil used in textile construction.

• Staple Fiber: Non-continuous fibers of relatively short length that must be twisted together to form continuous yarn. They are typically natural.

  • Short Staple Fibers: Maximum length of $60\,mm$.
  • Long Staple Fibers: Length exceeding $60\,mm$.

• Filament Fiber: Long, continuous fibers. These are usually synthetic, though silk is a natural filament fiber.

Classification of Textile Fibers by Source

• Natural Fibers:

  • Plant (Cellulosic):
    • Seed Fibers: Cotton, Kapok.
    • Fruit Fibers: Coir, Areca.
    • Stem / Bast Fibers: Linen (Flax), Hemp, Banana, Ramie, Jute.
    • Leaf Fibers: Pina, Sisal, Abaca, Manila Hemp.
  • Animal (Protein):
    • Wool/Hair: Wool (Sheep), Alpaca, Camel, Yak, Rabbit, Goat.
    • Secretion: Silk (Mulberry, Tussah, Eri, Muga), Spider Silk.
  • Mineral: Asbestos.

• Man-Made Fibers:

  • Regenerated Fibers:
    • Cellulosic: Viscose Rayon, Modal, Bamboo, Lyocell, Acetate, Cuprammonium. Sources include wood pulp, cotton linters, and paper.
    • Protein: Milk (Curd-Casein), Soya, Rubber.
    • Mineral: Glass, Ceramic, Carbon, Metal (Gold, Silver, Copper, Steel).
  • Synthetic Polymer Fibers: Polyester, Nylon (Polyamide), Acrylic, Modacrylic, Polypropylene (Poly-hydrocarbon), Elastane/Elastomeric (Polyurethane), Teflon, Rubber.

Microscopic Structures of Textile Fibers

• Cotton:

  • Cross-Section: Mature fibers show a lumen (central canal), primary wall, and thick secondary wall.
  • Longitudinal View: Appears as a twisted ribbon or collapsed tube.

• Linen (Flax) and Banana:

  • Cross-Section: Features micro-fibrils, lumen, middle lamella, primary wall, and secondary wall. These are polygonal in shape.
  • Longitudinal View: Characterized by nodes or bamboo-like joints and an orientation angle.

• Wool:

  • Cross-Section: Comprised of the epidermis (outer layer/scales), cortex, and sometimes a central medulla in coarse fibers.
  • Longitudinal View: Distinguished by overlapping surface scales (cuticles).

• Silk:

  • Cross-Section: Features two fibroin filaments held together by a protein coating called sericin. Cultivated silk (B. mori) is more triangular with rounded corners.
  • Longitudinal View: Raw silk appears irregular due to sericin; degummed silk is smooth, translucent, and rod-like.

• Man-Made Fibers (Standard Types):

  • Viscose Rayon/Modal/Bamboo/Lyocell: These often show a serrated or "cloud-shaped" cross-section with longitudinal striations, though Lyocell is more circular.
  • Acetate Rayon: Typically shows a multi-lobed or "popcorn" cross-section.
  • Synthetic Fibers: Often manufactured with specific cross-sections including circular, trilobal, hexagonal, or hollow.
    • Nylon/Polyester: Usually smooth and rod-like longitudinally; often circular in cross-section.
    • Acrylic: Can be dog-bone or lima-bean shaped in cross-section.
    • Modacrylic: Often has a kidney-bean or flattened cross-section.

Bicomponent Fiber Variants and Cross-Sections

• Specialized Man-Made Cross-Sections: Hollow fiber, ribbon fiber, trilobal fiber, hexagonal fiber.
• Bicomponent Fiber Types:
  • Side-by-Side: Split $50/50$ or $20/80$.
  • Sheath-Core: Concentric or eccentric; includes conductive core types.
  • Matrix / Islands-in-a-Sea: Multiple small components within a larger fiber matrix.
  • Segmented Pie: Divided into wedge-shaped segments.
  • Tipped: Trilobal with different components at the tips.
  • Mixed: Mixed deniers, colors, or components (e.g., striped).

Burning Characteristics and Identification

Physical and Mechanical Properties

Chemical Properties and Solubility

• Reaction to Acids:

  • Cotton/Linen/Banana/Viscose/Lyocell: Attacked by hot dilute and concentrated mineral acids.
  • Wool/Silk: Attacked and decomposed by hot concentrated acids.
  • Acetate: Decomposed by concentrated acids.
  • Nylon: Affected by hot concentrated acids.
  • Elastomeric: Attacked by concentrated acids.

• Reaction to Alkalies:

  • Cotton/Linen/Banana: Excellent/Good resistance.
  • Wool: Sensitive to alkalies.
  • Silk: Attacked by concentrated alkalies.
  • Viscose/Modal/Lyocell: Good resistance to dilute alkalies; attacked by strong alkalies.
  • Polyester: Good resistance except to ammonia and its derivatives.
  • Natural/Synthetic Rubbers: Generally good resistance to alkalies.

• Chemical Dissolving Solvents:

  • Cotton / Bast Fibers: Cold concentrated or hot dilute mineral acids.
  • Wool: Concentrated alkalies.
  • Silk: Cold concentrated Hydrochloric Acid ($HCl$).
  • Viscose / Modal / Bamboo / Lyocell: Concentrated Sulphuric Acid ($H_2SO_4$) and Hydrochloric Acid ($HCl$).
  • Acetate Rayon: $80\%$ solution of Acetone.
  • Nylon: Concentrated Formic Acid, Phenol, or Cresol.
  • Polyester: Hot Metacresol.
  • Acrylic: Ammonium Thiocyanate.
  • Modacrylic: Dimethyl Formamide.
  • Polypropylene: Toluene or Xylene.
  • Elastomeric: Cold concentrated Hydrochloric Acid ($HCl$).

Thermal Properties and Environmental Effects

• Cotton: Yellows at $120^{\circ}C$, decomposes at $150^{\circ}C$. Gradual strength loss from sunlight.
• Linen / Banana: Highly heat resistant; discolors at $120^{\circ}C$. Deteriorates in moisture.
• Wool: Decomposes/yellows at $130^{\circ}C$, chars at $300^{\circ}C$. Sunlight develops a harsh feel.
• Silk: Withstands heat to $140^{\circ}C$, decomposes at $175^{\circ}C$. Sun causes decomposition.
• Viscose / Bamboo / Lyocell: Loses strength at $150^{\circ}C$, decomposes at $185 - 205^{\circ}C$.
• Polyester: Melts at $290^{\circ}C$. Highly resistant to age and sunlight.
• Nylon: Yellows and loses strength above $150^{\circ}C$. Melts at approximately $205^{\circ}C$.
• Polypropylene: Softens at $150^{\circ}C$ and melts at $160 - 170^{\circ}C$.
• Elastomeric: Hardens and loses strength at $140^{\circ}C$. Softens then turns hard/brittle above $350^{\circ}C$.

Microbial Resistance and Comparative End Uses

• Insects and Microorganisms:

  • Natural Plant Fibers: Resistant to insects; attacked by fungi/bacteria (mildew) in damp conditions.
  • Natural Animal Fibers: Sensitive to moths and insects; poor bacteria resistance when damp.
  • Regenerated Fibers: Generally resistant to most insects but attacked by silverfish. Bamboo has unique high resistance to microbes.
  • Synthetic Fibers: Mostly resistant to both insects and microorganisms.

• Common End Uses:

  • Cotton: Apparel, upholstery, medical and technical textiles.
  • Linen / Banana: Sacks, packaging, geo-textiles, furnishings.
  • Wool: Carpets, insulators, apparel.
  • Silk: Lingerie, upholstery, premium apparel.
  • Viscose / modal: Tyre cords, embroidery threads, sewing threads, protective clothing.
  • Nylon: Swimwear, socks, parachutes, ropes, nets, tyre cords.
  • Polyester: Floor coverings, belts, sewing threads, apparel.
  • Polypropylene: Diapers, mattress covers, wet wipes, geo-textiles.
  • Elastomeric: Contour garments, stretch fabrics, footwear, intimate wear.
  • Acrylic / Modacrylic: Fake fur fabrics, sweaters, knitwear, carpets.