Development of polyvinyl acetate based packaging adhesive less detrimental to paper recycling

First of all, this work describes the behaviour of different polyvinyl acetate dispersions, used as main constituent in packaging adhesive formulations, during recycling processes simulated at laboratory and on pilot plant scale. One dispersion (dispersion C) has been found to be very sensitive to fragmentation during the pulping step. Indeed, this product leads to the formation of very small adhesive particles (roughly I μm diameter) which are trapped in the fibre network. Thus, this makes this dispersion impossible to remove either by screening, or cleaning. Moreover, this study has shown that these small particles can be deposited at a later stage in the papermaking process, particularly on the surface of the drying devices.This important drawback makes this kind of product unsuitable for the recycling. Another dispersion (dispersion A) behaves totally differently. Indeed, this product is much more resistant to the fragmentation and consequently leads, after disintegration, to a majority of particles large enough to be removed by screening. On laboratory scale, more than 80% of the product introduced can be removed by a screening step using a 0.2mm slotted screen. On pilot plant scale, 70% of the dispersion A introduced in the paper may be removed by a 0.2mm screening stage performed in an industrial pressure screening device. It has also been shown that since this product is well removed by a screening step, its contribution to the formation of deposits in the drying section of the papermachine is reduced. Thus, on the basis of these results, BostikFindley has formulated an experimental commercial adhesive formulation based on the use of dispersion A. This product was then tested regarding its recycling behaviour at laboratory and on pilot plant scale. A comparison with a commercial existing product was also carried out. The results of this part of the study clearly show a much better removal ability of the experimental adhesive formulation compared to the conventional one. The commercial existing product is only partially removable : indeed at the end of a recycling process simulated at pilot plant (including 0.2 mm screening and cleaning) only 45% of the introduced adhesive is removed. On the other hand, the experimental formulation is much better removed by the process: more than 80% of the adhesive introduced is removed by the recycling sequence simulated (screening + cleaning). Finally, to validate this work an industrial trial was performed: the experimental adhesive was produced on large scale (and named FINDTACK 30).Then it was used to produce corrugated boxes in a converting mill. The recycling behaviour of these boxes was then assessed on the CTP recycling pilot plant. A comparison with boxes manufactured with 2 conventional adhesives was carried out. The results of these trials performed with industrial raw materials entirely validate those obtained previously: indeed, the FINDTACK 30 adhesive appears much less sensitive to the fragmentation during pulping, when compared to the conventional formulations studied. This leads to a significantly better removal ability of this adhesive during the screening step which takes place in the recycling process. Moreover, FINDTACK 30 presents an excellent processability for disc and nozzle applications.