In a report published in the ACS Applied Materials & Interfaces, scientists describe an environmentally friendly, low-cost method to create printed materials with rewritable paper. The material is made out of a common polymer used in food and medicines, and tungsten oxide. In a world that still depends on paper and ink, most of which ends up in recycling centers or landfills, this will go a long way to reduce this waste.
In the USA, recycling efforts have been increased for years in an effort to reduce paper waste. The Environmental Protection Agency recently reported that more paper is now recovered for recycling than almost all other materials combined. The result is a saving in water, energy, greenhouse gas emissions and landfill space. Waste could be further reduced if consumers were able to reuse paper many times before trashing or recycling it. Products under development are often made with expensive, toxic organic dyes. Dairong Chen, Ting Wang and their colleagues set out to provide a better solution.
A film was created by mixing polyvinyl pyrrolidone with low toxicity tungsten oxide. To “print” on it, the material is exposed to ultraviolet light for 30 seconds or more, resulting in it changing from white to a deep blue. Words or pictures can be created by using a stencil so that only the parts that are exposed turn blue. Simply allowing the material to sit in ambient conditions for a day or two erases whatever is on it. The researchers added heat to speed up the erasing. This makes the color disappear in 30 minutes.
When a small amount of polyacrylonitrile is added to the material, designs can last for up to 10 days. Experiments have shown that the quality only starts to decline once the material has been printed on and erased 40 times.