A team of researchers from Shandong University of China, the University of California, Riverside and the Lawrence Berkeley National Laboratory of the USA have developed a printable paper with light that can be printed with ultraviolet light, and erased when heated to 120 ° C . Thus, it can be rewritten up to 80 times.
The secret of printing with light lies in a chemical process of color change in nanoparticles, with which conventional paper can be easily coated. In this way, the paper becomes printable with light, informs Physorg .
Scientists hope that the system has enormous economic and environmental advantages for modern society, since currently the production and disposal of paper has a great negative impact on the environment: it is one of the main sources of industrial pollution, waste paper is an important component (approximately 40%) of landfills, and even paper recycling contributes to pollution due to the process of ink removal. Not to mention the issue of deforestation that papermaking causes.
One possibility to solve this problem is to take advantage of the ability to change the color of certain chemicals when exposed to light. However, in the past this approach had not been developed, due to factors such as its high cost or the difficulty in applying the coating to paper, an extremely porous material.
But the new printable paper with light has overcome these obstacles and could have many practical applications, such as the printing of temporary information (newspapers, magazines, posters, etc.).
The new coating developed consists of two types of nanoparticles. On the one hand, some made of Prussian blue, a dark blue pigment often used in painting, and which was formerly used in drawings. This pigment is not toxic and becomes colorless when it gains electrons.
The other nanoparticles in the coating are titanium dioxide (TiO2), a photocatalytic material that accelerates chemical reactions after exposure to ultraviolet light.
When the Prussian blue and TiO2 nanoparticles are uniformly mixed and coated, the paper, unprinted, appears blue. To print text or images on it, the paper is exposed to ultraviolet light, which photoexcites TiO2 nanoparticles. These nanoparticles then release electrons that are collected by the adjacent prussian blue nanoparticles, which thereby become colorless.
Thus the paper is left with a white background and the words in blue on it. Once printed, the paper retains its configuration for at least five days, and then slowly turns blue completely again, through oxidation under ambient conditions. If you want to erase more quickly, you can warm up for about 10 minutes.
Researchers predict that printable paper with light will be cheap when produced on a commercial scale and, therefore, that it can be competitive.