The exterior cuticle cells provide a tough exterior, protecting the fibre from damage. The cells have a waxy coating, making the merino wool water repellent, but still allowing absorption of water vapour.
The molecules in this part of the fibre have fairly weak intermolecular bonds, so with prolonged wear and abrasion, they tend to break down. The weak bonds also make this area susceptible to chemical attack, such as strong alkaline conditions, which is why washing with a pH-neutral detergent is recommended.
The cortical cells also 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.
Orthocortical and paracortical cells
These cells create the crimp in wool. The 2 types of cell expand differently when they absorb moisture, causing the fibre to bend. When the cells are arranged in 2 halves, there is more crimp, and the more random arrangement in coarser fibres creates less crimp, so crimp relates directly to fibre diameter.
Inside the cortical cells are long filaments called macrofibrils. These are made up of bundles of even finer filaments called microfibrils, which are surrounded by a matrix region.
The matrix contains high sulphur proteins that readily attract and absorb water molecules. Wool can absorb up to 35% of its weight in water without feeling wet. It also absorbs and retains dyestuffs very well, helps remove sweat and absorbs odours. This region is also responsible for wool’s fire-resistance and anti-static properties.
The microfibrils in the matrix are rather like the steel rods embedded in reinforced concrete to give strength and flexibility. The microfibrils contain pairs of twisted molecular chains.
The Helical Coil
The molecular chains are protein chains which are twisted within and coiled in a helical shape. They link each coil of the helix, helping to prevent it stretching. The helical coil – the smallest part of the fibre – gives wool its flexibility, elasticity and resilience, which helps wool fabric keep its shape and remain wrinkle-free in use.