Advantages of wool fibre structure
In addition to the particular tensile and other properties, the special features of structure of wool ﬁbre 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 fibre and their specific role in terms of performance are shown in Figure below.
The advantages of wool fibre structure are explained briefly as under.
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 fibre 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 fibre 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 fibre 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 fibre. 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 fibre 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.
The recovery behaviour of wool fibre structure is unique and completely different than other polymers. Most of the polymers do not have recovery from yielding. In wet condition the wool fibre has complete recovery from extension up to 30%. The recovery behavior is an important structural feature of wool fibre. The composite structure of wool fibre 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
Wool structure helps in air cleaning
The complex chemistry of wool fiber enables it to bind pollutant gasses including formaldehyde, sulfur dioxide, nitrogen dioxide and others chemically into its structure. It has been estimated that wool carpets can continue purifying indoor air for up to 30 years. Researchers, using a controlled environment chamber have demonstrated that wool carpet can reduce high levels of introduced formaldehyde to virtually zero within four hours. Studies by the US Gas Research Institute which compared 35 building and furnishing materials showed that wool carpets have one of the highest removal rates of nitrogen dioxide of any of these materials. The UK Atomic Energy Research Establishment has shown that large amounts of sulfur dioxide are also irreversibly absorbed by wool carpets. Wool is a highly complex fiber that has been created by nature over thousands of years. It is simply not possible to get the benefits of wool from any man-made fiber.