THE STRUCTURE OF WOOL
Mention the word wool and the first thing that springs to mind is most likely what grows on the sheep’s back, or maybe a ball of wool for knitting. But have you ever stopped to think about what it is that makes wool such an incredible and versatile fibre?
Wool’s range of unique properties make it a desirable and irreplaceable material for a variety of purposes: from fashion to fire-resistant work wear and durable carpets. Wool is a complex biological fibre consisting of proteins, which provide flexibility and excellent performance qualities. Something the simple composition of a synthetic fibre cannot match when it comes to performance and functionality.
By learning more about wool’s cellular structure and how the different elements work you can better understand why wool fibre has so many valuable properties.
Wool belongs to a group of proteins known as keratins. It has a heterogenous composition where the protein is made up of amino acids and acidic carboxyl groups. Without delving further into the chemical complexity, this is what is responsible for its flexibility, elasticity, resilience, and good wrinkle recovery properties. It’s also what allows it to absorb both moisture and dyes so well.
In addition to its chemical complexity, wool also has a complex physical structure. The surface is made up of overlapping cuticles. Place it under a microscope and you see a scaly surface, which is very different from the smooth surface of synthetic fibres. These scales protect from dirt and are what enable felting to occur.
Lanolin is the waxy coat produced by glands surrounding the cuticle. It protects sheep from the elements and repels water while allowing water vapour absorption. When wool is processed, lanolin is removed. It’s then sold as a wool by-product.
Wool’s interior is intricate being made up of membrane, cortex, cortical cell, microfibril, matrix, microfibril, and the twisted molecular chain and helical coil.
Schematic diagram of wool fibre structure.
Membrane – dyes and moisture can penetrate the membrane and it’s this which enables fibre to absorb humidity.
Cortex – comprises 90% of the fibre. Millions of cells bind together to create cortical cells.
Cortical cells – fine wool contains two main types are para-cortical and ortho-cortical and each has a unique chemical composition. Basically, these cells put the crimp in wool.
Macrofibril – these are the long filaments found inside the cortical cells. In turn, these are made up of microfibrils.
Matrix – This makes wool absorbent, fire-resistant, and anti-static. The high sulphur proteins attract water molecules allowing wool to absorb up to 30% of its weight in water.
Microfibril – think of these twisted molecular chains as supporting structures providing strength and flexibility.
Twisted molecular chain and helical coil – these protein chains work much like springs and give wool its flexibility, elasticity, and resilience so that it can keep its shape free of wrinkles.
Wool has been intensively studied and we can’t hope to do justice here to the full science behind its complex structure. If you’d like to learn more about nature’s wonder fibre, see the suggested reading list below.