New pro-environmental technologies for the de-inking of wastepaper

VTT Technical Research Centre of Finland has developed new technologies for further use of wastepaper in an optimal and environmentally acceptable way. The particular problem in this process was the mixing of digitally printed paper and normal household wastepaper in the collection phase, which deteriorates the de-inking result. The new technologies improve the recyclability of fibres and decrease the amount of unexploitable fibre. These alternative technologies can make the conventional de-inking processes more efficient and even replace them.

The new technologies, high-power ultrasound processing and magnetic separation, enable printing ink to be separated from fibres with lower amounts of chemicals in comparison to current technologies. This environmentally friendly process saves fibres, improves the recyclability of them and decreases the amount of unexploitable fibres, the so-called zero fibres.

Conventional methods, generally flotation and/or washing, are well-suited to the processing of household wastepaper for the time being. However, increased amounts of digitally printed paper in household wastepaper will significantly change the situation in terms of both ink composition and adhesion. In de-inking it is essential that the size of printing ink particles, or the non-uniformity of ink, is correct when de-inking is performed by flotating.

Digitally printed ink detaches in large particles, but high-power ultrasound can be used for splitting ink particles into a size suitable for the process and promoting the detachment of ink from the fibres. On the other hand, several printing ink qualities of office wastepaper contain ferromagnetic, or iron-bearing, components and these are thus easily separated from the de-inked pulp through magnetic separation and lower amounts of chemicals.

Two patent applications have been filed for the technologies developed in the project. The development of pilot-scale equipment is now being continued as part of the factory process, and the objective of this work is a low chemical and energy saving de-inking process for office wastepaper, applying the magnetic separation and ultrasound treatment technology. The analysis methods developed in the project are also well-suited to the quality control of the de-inking process and de-inked pulp.

The high-power ultrasound equipment and magnetic separator will bring distinct quality improvements, particularly in the manufacture of soft tissues. Thanks to these new technologies, it will be possible for equipment manufacturers to launch new products on the market and de-inking plants will be able to improve their de-inking process according to changing raw materials.

VTT’s co-operation partners in this project have been , TEKES, Metso Paper, Raisio Chemicals (currently CIBA Speciality Chemicals), UPM, MetsaeTissue, Paperinkeraeys, SICPA, PQ Finland, Norem Magnets, Finnsonic, and other players in the forest cluster.

VTT co-ordinates Finnish participation in the EU’s COST E46 project called “Improvements in the Understanding and Use of De-Inking Technology”.