In the wash

ImageDe-inking used paper is a major step towards making recycled paper, but can established de-inking processes keep up with advances in printing technology?

There is a generally accepted principle that it is better to recycle as much paper as we can, rather than cutting down trees to make paper from virgin fibres.

Recycled paper can be put to many uses, including tissue paper and cardboard. But contaminants within the mass of paper to be recycled, including the inks that have been used on it, can cause the resultant recycled paper to be discoloured or grey. Such paper is not really suitable for graphic arts use, where there is a preference for a white appearance. One obvious solution is to bleach the paper white, but there is a trend against bleaching, which is not seen as the most environmentally friendly option.

A better solution is to de-ink the paper first, removing as many of the contaminants as possible to get a paper pulp clear enough to produce white paper suitable for graphic arts use. There are two established methods for de-inking paper, known as washing and flotation. De-inking by washing involves mixing the paper in a pulper to produce a slurry. From this, waste objects such as staples are filtered out, and then the water, together with most of the ink, is drained away, leaving the paper fibres which may be rinsed again. This method can be very effective at recovering paper fibre, but uses lots of water, which then needs to be treated, somewhat undermining the environmental benefits of recycling the paper.

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