In co-operation with the participating institutes (PTS, CTP and PIRA) a classification system has been elaborated to assess the recycle-friendliness of the adhesives. Based on the testing of selected adhesives (commercial products - typical representatives of their grade classes) for their sticky potential both in laboratory and pilot tests, basic requirements on the behaviour of adhesives in paper recycling operations were formulated.
For adhesives to be recycling-friendly they should meet the following criteria:
- high shear resistance of the adhesive film in the pulping process to ensure minimal fragmentation;
- completely separable by screening (cleaning and flotation);
- non-redispersible (no generation of microstickies and secondary stickies).
Based on these results the participating adhesive producers developed new adhesives or modified some of their products with a view to enhancing the separability of adhesives in recovered paper treatment plants. The types of adhesives produced and studied were weighted to reflect the composi-tion of the Consortium. Compared to packaging and bookbinding adhesives, priority was given to pressure sensitive adhesives.
The newly designed adhesives coming within the product categories of pressure sensitive adhesives and packaging adhesives (based on polyvinyl acetate dispersions) were compared with commonly used commercial products in terms of their recyclability. This comparison indicates that targeted product development in the adhesives area has in fact substantially reduced the disturbing potential of the adhesives during recovered paper treatment and in paper production processes. This may be concluded from both lab-scale tests and in near-practical pilot tests. Additionally, both adhesive sup-pliers and paper converters have evaluated the newly formulated adhesives for their convertibility, functionality and cost. The majority of the new adhesives tested during the project and rated as recy-cle-friendly can be considered an initial basis for marketable industrial products. In some cases, their future use may be restricted to special applications for reasons of performance or cost. The project has further demonstrated that the classification scheme elaborated to assess the recycle-friendliness of the adhesives is a useful approach. Lab-scale studies of the adhesives for recyclability which, in the case of favourable results, were followed by pilot-scale studies gave the combined benefits of low-cost laboratory investigations plus field orientation. The combined lab and pilot-scale tests enable a systematic approach to meaningful, detailed and practically relevant evaluations of the disturbing potential of different adhesives during papermaking. Accordingly, the behaviour of the adhesives in industrial treatment plant of recycle mills may be predicted.
Over the past decade recycled fibre has become the dominant raw material of the European paper industry. Striving to achieve a further increase in waste paper inputs, mill managers are using waste paper furnishes for higher-grade papers, too. This strategy is, however, restrained by non-paper components entering the manufacturing process together with waste papers. As a result of increasing circuit closures that are being implemented for economic and ecological reasons, accumulating contaminants of this kind tend to cause production failures, which lead to productivity and quality losses. In modern mills the so-called stickies have become the most critical problem recently. Conventional screening systems can only remove stickies of particle size ranges that fit the available mesh sizes, but even if the stickies have the right size the screening result is still dependent on efficiency values. This project is aimed at studying a selection of commercial adhesives and coating binders for evaluation of their sticky forming potential and sticky sizes.
For simplicity, the collective term 'adhesive products' will be used for both adhesives and coating binders in the following. Based on the project findings, criteria will be elaborated which allow recycle friendly adhesive products to be developed. The stickies formed by products of this kind are expected to be separable from recycled furnishes by screening and fractionation or else to leave the paper manufacturing process undisturbed. The project will be handled in steps as follows: - Evaluation of representative products, latest know-how and State-of-the-Art - Selection and establishment of test methods for macrostickies, microstickies and secondary stickies - Establishment of basic test parameters and treatment conditions - Lab- and pilot-scale testing of products for their sticky potential - Assessment of critical adhesives and systems - Formulation of experimental recycling-oriented products and testing of their tendency to form stickies - Final assessment of adhesives BE97-4903
Funding SchemeCSC - Cost-sharing contracts
3201 JX Leiden
KT22 7RU Leatherhead