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ScreenClean
Optimisation of screening and cleaning technology to control de-inking pulp cleanliness

The purpose of the project is to improve the technology in paper recycling to solve the critical problem of 'stickies', relating to when adhesive enters the de-inking process. The approach is to optimise the adhesive size and shape at the pulping step in order to remove them completely by pressure screening and centrifugal cleaning. The basic mechanisms of pulping and fundamentals of screening hydrodynamics, including numerical flow simulation, will be studied with respect to the rheological properties of adhesives. New pulping, screening and cleaning technology will be developed. Flotation and a new pressure filtration technology will be studied to clean the pulp and the process waters further. Optimised strategies for the removal of stickies in de-inking lines and basic knowledge towards recycling friendly adhesives will be established.

Objectives
The main objective of the project is to develop new solutions to the problem of stickies in de-inking mills, which is far from being completely solved, despite the recent progress in de-inking technology and the efforts engaged towards recycling friendly adhesives. This will be achieved by:
1) further understanding of the basic phenomena of stickies production and removal
2) development of a new and improved stickies removal technology and strategy
3) elaboration of basic criteria for new, recycled, friendly, adhesive products.
The project also aims at increasing the cost effectiveness and eco-efficiency of the de-inking process and will help to produce high quality graphic papers containing significant amounts of recycled fibres.

Progress to Date
The project is focused on the study of the production and removal mechanisms of pressure sensitive adhesives particles (PSA stickies) in the following de-inking process steps: pulping, pressure screening, centrifugal cleaning, flotation and pressure filtration. The project includes fundamental and applied research at pilot and industrial scale and the development of new technologies. The research during the first year has been concentrated on pulping, screening and cleaning as planned, as well as on the development of common stickies control methods. Further to stickies analyses in mills, which showed that most of the stickies transferred to the paper were colloidal/molecular and micro-stickies, it was decided to increase the effort on flotation, the most promising technology to improve the removal of micro-stickies.

Results
Two reference PSA products, a water-based acrylic and a hot-melt rubber adhesive, were selected. Stickies control methods were developed or improved: laboratory-screening equipment based on European standard to determine macro-stickies, and analyses of micro-stickies including a new DMF extraction method.
Pulping: basic parameters, including special chemistry and optimised pulp flow, were identified to promote the agglomeration of stickies and remove them by screening.
Screening: fundamental aspects were studied to understand the extrusion of stickies through slots: numerical flow simulation, rheological tests on adhesives, visualisation.
Cleaning: high-density cleaners showed a potential to remove some small stickies, which were not removed by screening, with the most common acrylic adhesive product.

Classified in NON-FOOD PRODUCTS

Scientist responsible for the project

Dr FRANÇOIS JULIEN SAINT AMAND
Domaine Universitaire Box 251
38044 Grenoble CEDEX 9
France - FR

Phone: +33 4 76 15 40 25
Fax: +33 4 76 15 40 16
E-mail: Francois.Julien-Saint-Amand@ctp.inpg.fr

References

Project ID QLRT-2000-00619
Organisation Centre Technique de l'Industrie des Papiers, Cartons et Celluloses
Area 5.3.2
Start date 01 April 2002
Duration (months) 36
Total cost 1 619 972 €
Total EC contribution   809 986 €
Status Completed

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