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Science corner

Ray Oliver suggests ways of testing the strength of paper

We don't usually think of paper as a strong material but it is an ideal choice for strength tests. Anyone who has found a paper wasps' nest at home will realise how robust it can be.

Wasps' nests are built of plant fibres, often wood, moulded into shape with a natural paste. With the invention of paper, the insects got there first. The earliest edition of Encyclopaedia Britannica, from 1771, describes papers made from papyrus, tree bark, cotton and rags. Children can assemble a range of papers for testing, such as newspaper, kitchen towel, greaseproof paper, file paper and glossy magazine pages (the shiny paper needed for high-quality colour-printing has a filler, often china clay, to produce the ultra-smooth surface required). Cut circles of each type of paper and stretch over the open end of an empty soup tin, with elastic bands holding them in place. Set up a metre rule vertically, next to the tin.

For the burst test, drop an object on to the stretched paper from progressively greater heights until the paper breaks. Children will be surprised how difficult it is to break some of the samples. A suitable object for this test is a large nail, or a ballpoint pen, weighted with plasticine.

This investigation can be extended by making repeat measurements with fresh paper to see the variability of results. Since some papers are said to have wet strength, moisten the paper first and compare the results with the dry version.

Children can also try stretching paper until it breaks. Cut rectangular samples of each paper type. Clamp one end securely between two thin pieces of wood. At the lower end, use a punch to make a hole and strengthen around the hole with ring reinforcements. Suspend a weight hanger, adding 10g or 50g weights each time. Or you could use a plastic cup, adding quantities of sand until the paper breaks.

Ask children to think of other ways to test paper strength. These might include twist strength and resistance to tearing.

You could also try laminating paper using glue.

Ray Oliver teaches science at St Albans Girls' School, Hertfordshire.

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