STICKIES AND CONTAMINANTS
Stickies are probably the main concern of papermakers involved in recycling. Tacky matter present in the recycled pulp is the result of various contaminants introduced into the recycling process. The problems caused by these materials are numerous: defects in the paper produced, breaks, formation of deposits in various parts of the papermachine, reduced productivity.
Within the framework of an overall approach to the phenomena, the goals are multiple.
Better removal of primary stickies by improving screening, cleaning and flotation. Previous studies in the field of screening have led to a better understanding of the probable screening mechanisms. The effects of the main parameters were investigated and a screening model is under development. Slot width is not the only criterion, especially with soft particles such as pressure sensitive adhesives. The specific behaviour of stickies in screens and cleaners will be investigated in relation to the properties of adhesive material. Flotation, as a promising means of removing micro-stickies, will be studied in a new project which will include developing basic knowledge about adhesive floatability in relation to deinking chemistry.
Better understanding of the mechanisms involved in deposit formation so as to propose preventive solutions for controlling the stickies phenomena, particularly the deposits in the drying section. Recent work on this topic showed the primary origin of deposit potential to reside in recycled pulp. Based on this knowledge, various solutions were imagined to reduce the deposition phenomena. To evaluate some of these solutions, industrial trials will be performed with the help of a new sensor recently developed at CTP: the clogging measurement device, which gives on-line measurements of the clogging rate of papermachine drying fabrics.
Collaboration with adhesive manufacturers, additive suppliers and converters will be sought in order to help them to develop adhesives and additives less detrimental to paper recycling. This approach has provided positive results in previous research projects. A method has been established for testing the behaviour of adhesives and has been used to evaluate recycling friendly adhesives developed by adhesive suppliers.
Finally, as reduction of losses is an important concern for papermakers, a study aimed at determining the treatments to be applied on rejects at the different process steps in order to selectively recover most of the materials which can be reused in the paper, while maintaining the quality of the pulp, will start in 2004.
