Converting adhesives entering the papermaking cycle through the recycling of recovered papers lead to numerous “stickies” problems including deposits on the paper machine, optical defects in the paper and printing problems due to adhesive spots. Despite considerable progress in deinking technology and efforts engaged to develop recycling friendly adhesives, “stickies” problems are far from being solved.

The main objectives of the ScreenClean project (1) are to develop new solutions to the “stickies” problems in deinking mills, by the following approaches:

- The development of the understanding of the basic phenomena involved in the production and removal of stickies in the paper recycling process.
- The development of new and improved deinking technology and strategies for the removal of stickies.
- The elaboration of basic criteria for the development of new recycling friendly adhesive products.

The project also aims at increasing the cost effectiveness and eco-efficiency of the deinking process and will help to produce high quality graphic papers containing significant amounts of recycled fibres.
(1) Optimisation of Screening and Cleaning Technology to Control Deinking Pulp Cleanliness EU Project: QLK5-2001-006119 – Duration: April 2003 to March 2005 – Budget: 1.6 M€

The project is focused on the study of the production and removal mechanisms of pressure sensitive adhesives (PSA) in the deinking process. Indeed, due to their inherent physical properties, the solid adhesive particles, or “primary stickies” produced during the re-pulping of the recovered papers are very difficult to remove from the pulp even with the latest deinking technology. In addition some components of the adhesive material are soluble under conventional deinking conditions and contribute to increasing loads in process waters of dissolved and colloidal material (DCM), which are liable to form “secondary stickies”.

The project aims at improving the size and shape of the stickies at the pulping step, to remove them early in the process by screening and cleaning. The rheological properties of the adhesives, which are decisive in this approach, and new analysis techniques will be studied. The efficiency of flotation and process water filtration will be evaluated with respect to the removal of micro-stickies. The project includes fundamental and applied research at pilot and industrial scale and the development of new technologies.
- Pulping: basic parameters, study of a new kind of agglomeration techniques, optimisation and comparison to drum pulper technology, up-scaling and evaluation of the new technology in a deinking mill.
- Pressure screening: numerical flow simulation, basic parameters, optimisation of screen plate design, screening model and development of a new high consistency fine screening technology with rotary basket.
- Cleaning: basic parameters, effect of cleaner construction material, new cleaners and optimisation of the rotary cleaner technology at high consistency.
- Flotation: basic parameters and assessment of practical stickies removal efficiencies.
- Pressure filtration: study of a new technology for the removal of micro-stickies in process waters.
- Stickies removal strategies: optimisation and implementation of new technology in deinking mills.
A wide range of adhesives will be produced in various forms and studied at the different process steps, in order to establish guidelines for the development of completely removable adhesives.

The partnership has been elaborated to provide the basic scientific skill and the test facilities required for the study of all the relevant recycling techniques. It includes 3 paper research institutes (CTP, ICP and PTS) for the papermaking trials, an adhesive supplier (Avery Dennison Jackstädt) for the production of different types of adhesives, an equipment supplier (AFT) for the design and manufacture of screen plates, and a university (LEGI) for the numerical simulation of the flow in screens.