The Science of Everyday Life by Marty Jopson

Author:Marty Jopson [Jopson, Marty]
Language: eng
Format: epub, pdf
Publisher: Michael O'Mara Books

Scaly wool fibres and smoother alternatives

We now turn to the dried keratin scales found on the surface of the wool fibres. All hair, wool and fur fibres have a coat made of overlapping dried-up cells. As you might have seen in hair care commercials, they are a bit like the tiles on a roof, but in wool the scales don’t lie particularly flat. The edges stick up a bit and tend to get caught on one another. And now we finally get to the reason that woollen clothes shrink.

If you place wool in hot, soapy water, the fibres absorb some of the water, and swell a little bit. You don’t actually need the water to be hot or soapy, but the swelling is much more pronounced if it is. As the wool swells, the edges of the scales push up even further than usual. If you begin to agitate the wool, perhaps by swirling it back and forth in a washing machine, the fibres ratchet together as the scales lock onto each other. What’s more, the hot water relaxes the spring in the fibres a little bit. This allows the scales to pull the fibres together with less elastic resistance. When the wool subsequently dries and cools, the spring returns and the fibres tighten up, locked together by their own scales. You have now successfully shrunk your sweater. In fact you are partly on the way to making felt, which is just wool that has been heated and pounded until all the fibres are tightly locked and held together by the spring of the wool. While felt is a valuable and useful material in its own right, it’s much less flexible and comfortable to wear, so this is not something you want to do to your sweater.

Since wool can shrink even in cold water, this science would indicate that sheep should suffer the same fate in cold rain. But they don’t, because there is another component of a sheep’s fleece to take into account.

Lanolin is a yellow, waxy substance secreted by the skin of sheep that can account for up to a quarter of the weight of a single fleece. It’s a substance analogous to the sebum secreted by our skin that makes hair gradually become greasy (see here). Lanolin not only gives the wool its unique sheepy smell, but also provides a waterproof coating. The lanolin prevents the fleece from becoming soaked with water so that the wool never gets particularly wet. What’s more, waxy lanolin covers the keratin scales on the surface of the wool strands, so that the wool can’t lock itself together. It’s lanolin that prevents the wool on a sheep’s back from shrinking.

In theory you could make your woollen garments shrink-proof by drenching them in lanolin, but I fear, even if you could put up with the smell, that those around you would object. Fortunately, technology has come to the rescue with machine-washable wool for some garments, although please do check the label before you chuck your favourite sweater in the washing machine.

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