Natural Protein Fibers: Wool & Silk

Natural Protein Fibers: Wool & Silk

• Protein fibers are animal-based, including wool and specialty wools (animal hair), and silk (insect secretion) and spider silk.
• Animal sources for hair include sheep, vicuna, alpaca, camel, llamas, cashmere goats, angora goats, and angora rabbits. Silk comes from silkworms.
• Protein fibers are made of amino acids (carbon, hydrogen, oxygen, and nitrogen). Keratin is the protein in hair fibers; fibroin is the protein found in silk.
• Wool is a short, fluffy undercoat on wild sheep, initially used as a covering.
• Domestication of sheep likely stemmed from the need to use the fleece effectively, even matted, to create coverings.
• Modern sheep fleece is primarily soft downy undercoat, due to selective breeding.
• Wool is prized for warmth, moisture absorption, heat retention, resilience, water repellence, flame resistance, and felting ability.
• Australia, New Zealand, England, Russia, Argentina, Uruguay, South Africa, and the US are major sheep-breeding countries.

Processing of Wool

• Wool quality depends on the sheep's breeding, climate, food, care, and health.
• Shearing sheep annually removes the fleece using power shears (or chemical methods) for continuous pieces.

Classification of Wool

• Wool classification can be done by the type of sheep or by the fleece type.
• Sheep classifications:
  • Class I (Merino): Short (1-5 inches), strong, elastic fibers with high crimp and scale count, ideal for high-quality clothing.
  • Class II: Longer (2-8 inches), strong, fine, elastic, with a good crimp and scale count, suitable for good-quality clothing.
  • Class III: Intermediate (4-18 inches), coarse, few scales, smoother, suitable for clothing.
  • Class IV (Mongrels): Coarse, hair-like, fewer scales and crimp, used in carpets, rugs, blankets, and lower quality clothing.
• Fleece classifications: based on age (e.g., lamb's wool, hogget wool, wether wool), whether pulled (after slaughter), or from dead animals (dead wool), and whether matted/damaged (e.g., cotty wool, taglocks).

Types of Wool

• Lamb's wool: First shearing from 6-8 month-old lambs, fine quality, tapered ends, soft fabric.
• Hogget wool: First shearing of 12-14 month-old sheep, fine, soft, resilient, tapered ends.
• Wether wool: Sheared from sheep over 14 months, variable quality, may contain dirt/soil.
• Pulled wool: Pulled during slaughter, inferior quality.
• Dead wool: From accidentally killed sheep, lowest grade.
• Cotty wool: Damaged/matted wool, inferior quality.
• Taglocks: Torn/ragged fleece parts, inferior quality.

Physical Structure of Wool

• Wool fibers have a complex structure: cuticle (outermost layer with scales, contributing to water repellence and felting), cortex (main part made of cells with melanin for color), and medulla (in coarse wool only, honeycomb like with air spaces for insulation).

Properties of Wool

• Length & Diameter: Varies from 1.5 to 16 inches and 10-50 microns in diameter.
• Microscopic View: Uneven structure that tapers to the tip, with overlapping scales.
• Strength: Weakest of natural fibers, loses strength when wet.
• Elasticity: Good elasticity, stretches up to 25-30% of its length. Resilient (quickly returns to shape).
• Drapability: Excellent drapability due to flexibility, elasticity, and resilience.
• Heat Conductivity: Poor conductor, keeping the body warm.
• Absorbency: Initially water repellent but absorbs water, drying slowly.

Chemical Composition

• Primarily keratin, made of carbon, hydrogen, oxygen, nitrogen, and sulfur; with 18 different aminos acids.

• Wool has natural cross-links (cystine/sulfur linkages).

Biological Properties

• Mildew resistance: Wool can be affected in high moisture conditions.
• Insect resistance: Generally resistant to moths and carpet beetles, but should be stored with protection (i.e. neem leaves).

Uses of Wool

• Apparel, blankets, rugs, carpets. Can be blended with other fibers.