Rewritable paper which can be written & erased on more than 20 times- FutureEnTech | Technology, Environment, Humanity, Lifestyle

FutureEnTech | Technology, Environment, Humanity, Lifestyle

Rewritable paper which can be written & erased on more than 20 times

Despite society’s move toward a fully digital world, a good deal of business is still transacted on paper. In some estimates, it’s as high as 90 percent, with a great deal of printed paper discarded after just one-time use. That waste comes at a cost, not only for the paper but also for the ink. We shouldn’t forget the environmental effect due to cutting of trees and chemical pollution to air (to satisfy the paper requirement).

Rewritable paper that does not use ink but instead uses dyes that respond to ultraviolet light has been developed by US scientists. The dyed paper may be a solution to growing environmental problems associated with the use of regular paper. Chemists at the University of California, Riverside have now fabricated in the lab just such novel rewritable paper, one that is based on the colour switching property of commercial chemicals called redox dyes. The dye forms the imaging layer of the paper. Printing is achieved by using ultraviolet light to photobleach the dye, except the portions that constitute the text on the paper.

The new rewritable paper can be erased and written on more than 20 times with no significant loss in contrast or resolution. “This rewritable paper does not require additional inks for printing, making it both economically and environmentally viable,” said Yadong Yin, whose lab led the research. “It represents an attractive alternative to regular paper in meeting the increasing global needs for sustainability and environmental conservation.” The rewritable paper is essentially rewritable media in the form of glass or plastic firm to which letters and patterns can be repeatedly printed, retained for days, and then erased by simple heating. The study results appear online in Nature Communications.

Let’s understand the working principle of rewritable paper. The paper comes in three primary colours: blue, red and green, produced by using the commercial redox dyes methylene blue, neutral red and acid green, respectively. Included in the dye are titania nanocristals (these serve as catalysts) and the thickening agent hydroxyethyl cellulose (HEC). The combination of the dye, catalysts and HEC lends high reversibility and repeatability to the film. During the writing phase, ultraviolet light reduces the dye recovers the original colour; that is, the imaging material recovers its original colour by reacting with ambient oxygen. Heating at 115C can speed up the reaction so that the erasing process is often completed in less than 10 minutes. “The printed letters remain legible with high resolution at ambient conditions for more than three days – long enough for practical applications such as reading newspapers,” Yin said. “Better still, our rewritable paper is simple to make, has low production cost, low toxicity and low energy consumption.”

His lab is currently working on a paper version of the rewritable paper. “Even for this kind of paper, heating to 115C poses no problem,” Yin said. “In conventional printers, paper is already heated to 200C in order to get toner particles to bond to the paper.” His lab also is working on increasing the cycling number (the number of times the rewritable paper can be printed and erased), with a target of 100, to reduce the overall cost.

Given the number of different solutions now in the game for solidly readable rewritable digital text, it remains to be seen what this new development has to offer that is truly unique, but it certainly looks good and interesting, and the commercial possibilities are obvious – if no one else gets there first.

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