Wool fiber – Mother Nature at its best

Wool and other hair fibers have the most complicated structures of all textile fibers. Wool is composed of a complex blend of proteins and other chemical substances. The thermal and mechanical responses of the fibers are determined by a variety of inter-atomic and inter-molecular bonds and a variety of structural forms. The wool fiber has a slightly and imperfectly elliptical cross section. In this blog, for my readers I intend to write briefly about the vital few advantages of wool fiber over other fibers.

Advantages of Wool Fiber

In addition to the particular tensile and other properties, the special features of structure of wool fiber are crimp, which leads to high bulk and softness, and scales, which lead to felting. Good recovery properties are also beneficial, and especially the regeneration of properties by washing. The structural elements of wool fiber and their specific role in terms of performance are shown in Figure.

The structural elements of wool fiber and their specific function.

The complex interior structure creates flexibility and absorbency

The cortical cells in the wool structure have a complex interior structure. The smallest component within these cells is a spring like structure which gives wool its flexibility, elasticity, resilience and wrinkle recovery properties. This spring like structure is surrounded by a matrix which contains high Sulphur proteins that readily attract and absorb water molecules. Wool can absorb up to 30% of its weight in water without feeling wet. It also absorbs and retains dyestuff very well, helps remove sweat and absorbs odors. The matrix also creates wool’s fire resistant and anti-static properties.

  • Crimp in wool structure

The crimp in wool fibers makes it soft and springy to touch. It also adds bulk and traps a large volume of air between the fibers, giving it good insulation properties. Finer fibers with more crimp such as merino gives good draping properties. The natural crimp of the wool fiber also contributes to the overall elasticity.

  • Scales of surface and directional frictional effect

The wool fiber has the unusual feature of a directional frictional effect due the existence of scales. Scales are exposed edges of the cuticle cells point towards the tip of the fiber creating a jagged edge. This allows fibers to slip over one another easily in one direction but not the other and giving wool the ultimate ability to felt. Felt is created when wool fibers are agitated in water they slip over one another and the scales interlock preventing the fiber from returning to its original shape eventually, a highly interlaced and self-locking felt is produced. The process can be controlled to create very dense fabrics such as felt and wool blanket and jacket fabrics.

Absorbency creates comfort

When wool absorbs moisture it produces heat so if you go from a warm room into a cold damp night wearing a wool jersey the wool picks up water vapor from the air keeping you warm. The reverse occurs when you go back into the warm room the moisture in your jersey passes into the atmosphere cooling you down. Tiny pores in the cuticle cells allow water vapor to pass through the wool fiber. This makes wool comfortable to wear in both warm and cool conditions.

  • Water repellent and strong surface

The cuticle cells provide a tough exterior, protecting the fiber from damage. The cells have a waxy coating, making wool water repellent, but still allowing absorption of water vapor. The water-repellent surface makes wool garments naturally shower-proof and also reduces staining because spills don’t soak in easily.

Wool fiber-wonders of mother nature
  • Elastic recovery

The recovery behavior of wool fiber structure is unique and completely different than other polymers. Most of the polymers do not have recovery from yielding. In wet condition the wool fiber has complete recovery from extension up to 30%. The recovery behavior is an important structural feature of wool fiber. The composite structure of wool fiber is treated as a fibril with helical chains in parallel with an amorphous matrix, with the two linked at intervals to give a series of zones. The links correspond to the IF keratin tails which are cross-linked to the matrix. When the wool fiber is extended these zones open up and after removal of stress all the extended zones of fibril matrix composite will contract together without any critical factor until they disappear and the initial stress strain curve is rejoined. The elastic recovery of wool decreases with increasing imposed extension. The viscoelastic nature of wool fiber results in reduced stress as rate-of-extension is decreased, in creep under constant load, in stress relaxation at constant extension and in changes in dynamic properties. The rate of creep decreases with time and, on a linear time scale, appears to become asymptotic to a constant value. Creep is faster at higher temperatures. The creep, or stress relaxation, in wool will show up as higher extensions at a given stress in load extension testing.

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