Researchers at the University of Cambridge have developed a method for removing ink from scrap paper by “unprinting” it, using lasers.

The technique involves emitting short bursts of green laser light that are sufficient to vaporise printed toner, but not so powerful as to destroy the paper. Cambridge's Low Carbon Materials Processing Group leader Julian Allwood said that the discovery could allow paper to be reused rather than recycled, reducing emissions by 20 percent.

The Cambridge team worked alongside the Bavarian Laser Centre to test 10 different laser arrangements spanning the ultraviolet, visible and infrared spectrum, using standard Canon copy paper and HP LaserJet black toner. After being exposed to the laser, the paper was analysed under a scanning electron microscope and subjected to colour, mechanical and chemical analyses.

The laser selected has a wavelength of 532 nanometres and a pulse length of 4 nanoseconds. This allows paper to be reused around three times before it becomes too thin and yellowed for further use, according to Allwood.

“What we need to do now is find someone to build a prototype,” he said. “Thanks to hand-held scanners and laser-jet printers, the feasibility for reusing paper in the office is there.”

The study states that removing ink with a laser rather than recycling allows the organisation to “remove the tree from the paper lifecycle” and eradicate emissions arising from incineration and landfill dumping.

The study further postulates that the emissions produced in the pulp and paper industry would be halved as a result of paper reuse.

“This is a significant contribution towards the cause of reducing climate change emissions from paper manufacturing, but there is modest room for improvement,” Allwood said.

Back in 2006, Toshiba started selling re-writable paper that it claimed could be erased and reprinted at least 500 times. The paper - actually thermo-sensitive sheet-plastic - required a special printer that relied on a heat-sensitive pigment in the ink. If heated above 180 degress centigrade it goes black, but if held at between 130C and 170C it turns white again.

Image credit: University of Cambridge