Why is black plastic so difficult to recycle? © Getty Images

Why is black plastic so difficult to recycle?

Asked by: Rachel Harris, Bristol

The plastic itself is usually recyclable; the problem is the colouring. Most black plastic is pigmented using carbon. This is cheap, food-safe and provides a deep, uniform black. But as well as absorbing visible light, it also absorbs the near-infrared part of the spectrum, which has the unfortunate side-effect of making it invisible to the sorting machinery at recycling plants, which uses infrared beams to sort materials by colour and material.

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The stealthy black plastic thus passes undetected into the ‘miscellaneous’ bin at the end of the conveyor, which is destined for landfill. Charities like the Waste and Resources Action Programme (WRAP) are working with manufacturers in the UK to develop alternative black pigments that will allow black plastic to be recycled.

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