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Towards recycling friendly adhesive products for the paper chain (EURO-STICKIES)


In co-operation of institute PTS and CTP an assessment scheme for the classification of the recycling behaviour and disturbing potential of adhesives was established, which takes the recovered paper treatment conditions of packaging papers and graphic papers into account. This classification scheme has been proved as a useful approach to assess the recycle-friendliness of the adhesives. Lab scale studies of the adhesives for recyclables, 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 (PTS was in charge of lab, CTP was in charge of the pilot-scale tests). The procedure can obviate the need for expensive and time-consuming analytics to determine the microsticky content or depositing behaviour. The adhesive capture rate after pulping is an adequate indicator of the quantity of microstickies produced. Experience has shown that the disturbing potential of the adhesive is the pulping process produces the greater the more microstickies. 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 plants of recycle mills may be predicted.
To study the deposition behaviour of adhesives Pira stickie deposition test method which measures both primary and secondary stickies was extensively assessed with adhesives and compared with the results from CTP’s ‘plugging of the wire’ method which measures the deposition of secondary stickies. A hybrid test method was developed by combining Pira Tack test and CTP’s ‘plugged wire method’ to study the behaviour of stickies under different test conditions. The new (hybrid) stickie tackiness method involved destabilisation of micro or colloidal stickie forming adhesive components into secondary stickies followed by assessing its propensity to cause deposits on machine wires under different process chemistries. The test method was also used to investigate the effect of a range of typical papermaking additives on the deposition characteristics of the main types of pressure sensitive adhesives and an EVA based hot melt adhesive.
In the framework of the project a large amount of different adhesives were studied regarding their behaviour in the recycling process. The individual adhesives behaved differently and some of them showed a poor recycle-friendliness as determined by the selected criteria. Knowledge was gained regarding the behaviour of the adhesives and to what extent they form stickies during recovered paper treatment processes (in particular by PTS in lab-scale testing, by CTP in pilot-scale testing and by PIRA regarding the potential to form secondary stickies). Know-how was derived from: - Information about sticky formation during different recovered paper treatment processes (both in the process steps of treatment of brown recovered papers for the production of packaging papers and in the treatment of white recovered papers to obtain DIP for printing paper production) - Information about interactions between stickies and various chemical additives - Information about fundamental mechanisms for the deposition of secondary stickies. This knowledge forms the basis to develop and design new products or modify adhesives in order to produce recycling-oriented products and to market the newly designed products. Know-how is usable for consultancy.
In close co-operation with Bostik Findley, Smurfit tested the newly formulated PVA adhesive (Findtack 30) in comparison to commonly used commercial products for their processing and usage properties to manufacture regular boxes made of corrugated board. In industrial trials, boxes were manufactured on a RTA case maker with an output of 5000 boxes per minute. For each adhesive the runnability of the machine, the quality of the bonding and the mechanical strength of the boxes were evaluated. At the laboratories of Smurfit, tests were performed to quantify the bonding obtained with each adhesive. Specifically, the tests identified the delamination of the bond (measurement of fibre pick), the burst of the box (balloon test) and the box compression. The trials carried out confirmed the good performance of the new adhesive developed by BOSTIK-FINDLEY for the production of standard boxes. The individual values obtained in the tests resembled each other. The behaviour of the newly formulated adhesive on the machine is equivalent to the commercial products. Favourably, the new Findtack 30 did not affect the mechanical properties of the box. The bonding is correct and no particular problem appears during the production. Moreover, the recycling behaviour of these boxes were studied at pilot plant scale. The results obtained confirm the better recycling compatibility of Findtack 30 compared to conventional adhesives tested in similar conditions.
Results achieved by BOSTIK FINDLEY: In the framework of the project BOSTIK FINDLEY covered packaging adhesives based on polyvinyl acetate dispersions. Based on the experience gained in testing commercial products, a new product was formulated - named Findtack 30 - with a better performance in terms of separability by screening. In this context, two non-plasticized polyvinyl acetate dispersions were formulated in a first step. After their recycling characteristics had been identified, one of these dispersions was considered a suitable starting material for a new adhesive with superior recyclability. The newly designed product gave good results in terms of runnability, viscosity, setting time and open time. The new adhesive showed good performance for the production of standard boxes. Favourably, the new Findtack 30 did not affect the mechanical properties of the box. Regarding the behaviour in recycling process, it was possible to remove 80 % of the adhesive by 0.2 mm screening compared with 40 % for conventional commercial adhesives. Findtack 30 seems very promising, because it meets the specifications in terms of recyclability, performance and price. Results achieved by BASF:
Based on the knowledge of the recycling properties of current BASF products, new pressure sensitive adhesives with potentially improved recycling friendliness were formulated and coated in the BASF pilot coater under conditions which are nearly equivalent to industrial-scale coating. One development area dealt with water based pressure sensitives. Based on the idea that higher cohesion (''inner strength'') of the polymer material will prevent redispersing of the PSA films during the pulping step and thus lead to bigger adhesive particles with improved removability, PSA dispersions with higher shear strength were selected from a big series of lab scale samples and formulated for pa-per label application. Pilot samples of these emulsion polymers with increased cohesion and fully competitive application properties, which were tested, did not give a substantial improvement in sticky removal rates. The other development area was devoted to acResin® products (UV crosslinkable hot melt PSAs). UV-crosslinkable liquid acrylic polymers, which can be applied at 120 - 140 °C with commercial hotmelt technology and reach their PSA application properties by subsequent UV-C irradiation on the web, are sold under the trade name acResin®. To evaluate the properties of this new product class a formulation was developed which exhibits competitive properties for general purpose permanent paper labels. A mixture of the commercially available polymer acResin A 203 UV and Foral® 85 (East-man, formerly Hercules) shows sticky removal rates which were significantly higher than those of water based systems. The application properties of the coated adhesive are - as determined by BASF tests - competitive with market standard adhesives for general purpose permanent paper labels.
In the framework of the project RAFLATAC developed different new pressure sensitive adhesives, which were submitted for testing. Among these pilot adhesives, one product showed either in lab-scale and pilot-scale testing a significantly improved recyclability. This product is water based acrylic adhesive with increased cohesion through cross-linking, but also with a high level of hydrophobic properties (good water resistance). Lab and pilot testing were carried out in order to evaluate the suitability of this particular adhesive to production process and to different end applications for self-adhesive labels. The coatability and other processing properties seem to be all right. The adhesive properties are somewhat limited. It would be possible to use this adhesive as a special grade for applications where recycling properties are important. In addition, the cost structure of this adhesive was evaluated. It turned out that the current price would be more expensive than RAFLATACs’ current adhesives. This difference is not so big that it would make further progressing impossible. Specific actions (e.g. improving the production efficiency through larger scale production) will probably not eliminate the whole price difference, but a significant part of it, which will make it possible to introduce it for wider use than just special applications.