Toner particles on top of paper fibres

Imagine a situation in which you have finished printing and reading any given document. What happens next to that sheet of paper? Does it stay resting in a shelf or a drawer for years waiting to be read again? Is it thrown away to the garbage, perhaps separated for recycling if it is lucky? Is it used to level uneven table legs? Would not it be better if you could place that piece of paper in a un-printer device, remove its text, and re-use it?

A previous PhD project undertaken at the University of Cambridge by Thomas Counsell (2007) under the supervision of Dr. Julian Allwood, estimated that paper and board consumption causes approximately 1-2% of man-made climate change gas emissions, resulting in this industry being ranked between the 3rd and 5th of the most significant causes contributing to climate change. According to this study, there are four ways to reduce these numbers: decreasing consumption, changing to carbon-neutral fuels, improving the energy efficiency of each stage in the life cycle of paper and cutting out stages in this life cycle. Our research in the Low Carbon Materials Processing Group (LCMPG) has focused on the latter option.

The typical energy demand and climate change gas emissions for each stage in the life of office paper from a tonne of typical cut size office paper are as follows (Counsell, 2007):


Un-printing and reusing office paper would cut out almost all the stages of the life cycle (only printing would remain) and their associated energy consumption and climate change gas emissions:


Because of this, current research in the LCMPG focuses mainly in using lasers, abrasives and chemical solvents to remove toner from printed paper, obtaining promising results so far:


Many challenges have been identified from these results, which need to be addressed before un-printing can be a reality:

1. Un-printing could be an effective replacement for more than 60% of new paper, consume less than 40% of the energy of recycled paper and cost less than 0.5 p per sheet only after further development. Improvements are required in terms of speed, energy efficiency and cost.

2. The abrasive process failed to produce un-printed sheets with high enough quality to act as replacements for new paper. Improvements need to be made on the print removal technique and paper damage reduction. More in depth knowledge is required in abrasive research into selective transfer and fatigue wear of polymers and into how abrasive life can be prolonged in these regimes.

3. The laser process presented two main problems: yellowing of the un-printed paper (hence, the un-printed paper cannot be used to replace new paper) and elevated cost due to the type of laser used. Further work will focus on methods to either prevent or remove the yellowing on the un-printed paper and exploring possibilities of using high-efficiency semi-conductor lasers or other ways of reducing cost. In particular, laser research should focus on how to remove material at a low enough temperature to avoid thermal conduction, as this is believed to be the cause for yellowing of the paper.

4. Regarding the solvent process, it has been concluded that this method is not environmentally preferable compared to conventional recycling.

5. All the approaches need to be tested on a wider range of prints and papers.

6. Further research needs to be done in order to understand the principles behind the removal processes and to develop predictive models of their operation.

Hence, the main research question is:

How can print removal mechanisms be improved to achieve sheets of high enough quality to replace new paper?

In particular, Counsell (2007) has shown that laser ablation removes toner, but causes paper yellowing. What is the cause of this yellowing, and can it be avoided by other laser settings?

Furthermore, Counsell (2007) showed that adhesive wear was preferable to abrasive wear. What material would most promote such adhesive wear of toner, how can the toner subsequently be removed from this material, and how affectively can toner be removed by adhesive wear?

A list of publications on our work to date on un-photocopying can be found here.