Novel solutions to new problems in paper deinking

Purpose ‐ This paper aims to describe and evaluate the traditional methods for effective ink removal during the recycling of printed papers. Additionally, novel techniques for dealing with the newer "difficult to deink" inks such as toners from photocopiers, UV-cured ink films and liquid toner suspensions or Electroinks® are to be evaluated. Design/methodology/approach ‐ High intensity ultrasound was applied to pulps derived from papers printed with these newer inks in order to evaluate its effectiveness in detaching the inks from paper and establishing the resultant ink particle size distributions. Findings ‐ When exposed to ultrasound at a frequency of 20?kHz, it was found that "difficult to deink" pulps did exhibit significant ink detachment. In the case of toners, temperature did have an effect on particle breakdown with larger numbers of particles produced at temperatures well below the softening point which was attributed to a greater brittleness of the toner at lower temperatures. Electroinks® can be effectively de-inked by exposure to ultrasound coupled with washing under neutral conditions. With all the inks investigated, exposure to ultrasound resulted in the detached ink having particle size distributions that can be removed by conventional flotation and washing techniques. Research limitations/implications ‐ The exposure of the pulp to ultrasound was only carried out using a batch-wise process. A future development would be to use a continuous flow system incorporating an annular ultrasound horn. Practical implications ‐ Introducing ultrasound exposure into a conventional deinking plant, all post-consumer printed waste paper could be deinked without the use of deinking chemicals. Originality/value ‐ The findings are of interest to those in paper recycling.