What you have in common with your cat and the world’s astronauts

The instant you react to a spill by reaching for something as simple as a handful of kitchen paper to mop it up, you’ve become an organic chemist, because you’re creating the circumstances for a controlled reaction to take place.

The principle is the same no matter what everyday material you use to absorb the liquid that’s been spilled. It’s a principle relied on by astronauts travelling in space (who don’t have conventional toilets; enough said), domestic cats travelling no further than the litter tray, and you, every time you reach for a towel after a bath or shower.

It’s all about cellulose, which makes up about a third of all vegetable matter, with the proportion rising to 50% of wood and 90% of cotton. Cellulose is the most common organic polymer on the planet, and has a complicated chemical structure involving carbon, hydrogen and oxygen – the same elements found in sugar – and absorbs liquid very readily.

AbsorbentAnd there’s the magic. We all know how readily sugar dissolves in water (or coffee or tea). Cellulose is a kind of sugar, so draws liquid into its molecules, which happens when you mop a spill. Kitchen paper, commercially-available absorbent granules, or cotton Terry towelling all contain cellulose, and work in the same way to achieve the same objective in different scenarios. The thicker the fabric (if fabric is being used) the more moisture can be absorbed, simply because there are more fibres to do the work.

The same principle takes place when wood rots. The cellulose in the timber absorbs water over a long period, which eventually destroys the cells from within. Timber treatments are geared to prevent that absorption, and make your shed, decking or fence last longer.

The older readers amongst us will be familiar with Terry nappies for babies; the younger ones will be more familiar with disposables. The latter are based on another polymer with even greater capacity to absorb liquids. That’s called sodium polyacrylate, which can absorb more than 200 times its own weight of liquid.

Finally, if cellulose is sugar, why can’t we eat it? The answer is that we can, but the human digestive system can’t break it down, so its only value is as dietary fibre. Animals such as cows, sheep and goats have similar problems, but they digest it with the aid of bacteria found naturally in their digestive systems.

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