According to the U.S. Environmental Protection Agency, more paper is now recovered for recycling than almost all other materials combined. While this saves energy, water, landfill space and greenhouse gas emissions, even more waste could be avoided if consumers could reuse paper many times before recycling or trashing it.
Scientists have now developed a low-cost, environmentally friendly way to create printed materials with rewritable paper. The material, which is made out of tungsten oxide and a common polymer used in medicines and food, avoids use of the toxic, expensive organic dyes associated with other such products under development.Researchers led by Ting Wang and Dairong Chen, of the School of Chemistry and Chemical Engineering at Shandong University, created a film by mixing low-toxicity tungsten oxide with polyvinyl pyrrolidone. To “print” on it, they exposed the material to ultraviolet light for 30 seconds or more, and it changed from white to a deep blue.
To make pictures or words, a stencil can be used so that only the exposed parts turn blue; to erase them, the material can simply sit in ambient conditions for a day or two. To speed up the erasing, the researchers added heat to make the color disappear in 30 minutes. Alternatively, adding a small amount of polyacrylonitrile to the material can make designs last for up to 10 days.
Testing showed the material could be printed on and erased 40 times before the quality started to decline.