An investigation into the novel application of high power ultrasound on the deinking of mixed office waste paper.
The current paper recycling processes are surveyed pointing out the major stages and the
variety of chemical/mechanical treatments the fibres undergo. The reduction or
replacement of chemical/mechanical treatments presents possible advantages in prolonging
The results from recycled office waste which has been treated with ultrasound show a
change in the particle size distribution of toner particles - making these particles easier to
remove using established flotation techniques. Particle size distributions were measured
using image analysis on thin (20gsm) paper handsheets. To establish the affect of
sonication on fibres, a variety of virgin fibres were obtained from UK Paper, Sittingbourne.
Results from virgin fibres which have been treated using ultrasound indicate an absence of
cutting compared to conventional techniques. Fibres were found to have the same average
length (0.6mm) after ultrasound treatment as the control sample, refined fibres were
reduced to approximately 0.3 mm in length. Freeness decreased in both virgin sonicated
and refined sonicated samples. The decrease in freeness was accompanied by an increase
in the strength properties of both categories of fibres.
Experiments with a prepared office waste furnish showed that ultrasonic treatment could
decrease the size distribution of fused toner particles. The control sample had an average
size of 80.9 um, after 1 minute sonication this was decreased to 54.9) um, decreasing further
to 46.8)um after 2 minutes sonication.
After demonstrating that ultrasound could decrease the particle distribution of the prepared
office waste a more realistic and variable furnish was used. The experiments were
conducted at room temperature, 50°C and 75°C. These temperatures were chosen to study
the behaviour of fused toners as it approaches and exceeds its glass transition point,
essentially the melting point of an amorphous polymer. It was found that the toner is easier
to remove as the glass transition temperature is approached. Ultrasound is effective in
breaking up large toner particles and detaching particles smaller than 25 microns in