Student researchers at PTS: a closer look at the impact of adhesives and metallisations on recyclability
The students Vanessa Wortmann and Christiane Böhmer are working on their master theses in the Recycling and Digitisation department of PTS under the supervision of Lydia Tempel, Marie Geißler and Annika Eisenschmidt. The master student in Hydrosciences and Engineering, Vanessa Wortmann, came to PTS to gather experience in laboratory and general daily work routines and improve her proficiency in the German language. Before that, Vanessa was involved in the testing of everyday samples according to the recycling method PTSRH 021:2012 to help establish a broad data base and gained valuable knowledge about the paper recycling process and its assessment by examining various paper and boardbased packagings.
Moreover, she wrote her internship report for TU Dresden and has now also started her master thesis under the supervision of PTS. Her master thesis covers the impact of process parameters on the disturbance potential of adhesive particles (stickies) in paper recycling. As existing recycling test methods were harmonised to the CEPI method within the European market, it is now required to review existing data and create a new database. In this context, it is important to understand how variations of the defibration and fractionation parameters (e.g. temperature, time, pH, consistency and slot size) affect the fragmentation of macrostickies and their stickiness during paper recycling.
To achieve this goal, samples with typical adhesives used in packaging and shipping cartons (hotmelts and dispersion adhesives) were tested using the CEPI method and different variations thereof. Figure 1 shows the result of such a variation in defibration temperature: macrostickies after defibration at 40°C (left) and at 20°C (right).
Fig. 1: Difference in macrostickies due to variation in defibration temperature. Top: stained filters after fractionation in Somerville fibre fractionator, slot width 150 μm, for 10 minutes, bottom: image output of DOMAS system
The results are evaluated mainly on the basis of the analytical image data from the Domas system, the sheet glue test, as well as the coarse and fine residues. Also, a water phase analysis is planned to evaluate the influence of disturbing components such as macrostickies on the process water.
Also, Christiane Böhmer deals with disturbing components in fibre recyclates within the scope of her master thesis. After more than one year of interesting work at PTS in the Functional Products and Recycling & Digitisation departments, the student in wood science and technology is now dealing with the impact of metallisations on the recycling process. Such metallisations have a wide variety of structures and are often applied onto fibre-based packaging materials as decorative coatings or barrier coatings. Although the glittering metal particles in the pulp may have the appearance of a starry sky in microscopic images (see Fig. 2), they cause some difficulties in the recycling process. They form disturbing optical inhomogeneities that impair the quality of the secondary fibre and thus the quality of the paper products made from it.
Fig. 2: Left: Metal particles in handsheet pulp (hot embossing with aluminium), right: handsheet stained, 10x magnification by digital microscope
Scientific studies are rare regarding the separability of these particles by cleaning processes used in typical recovered- paper treatment plants in packaging paper production, as well as by means of laboratory screening methods. One reason for said lack of studies is that there is so far no standardised laboratory method for quantifying the metal particles as a result of the reflecting behaviour of the metal particles.Therefore, the subject matter of the master thesis is to check the potentials of a well-established PTS measuring method for assessing the metal particle load in the pulp.
The master thesis, similar to that of Vanessa, is focused on the new CEPI method as a recyclability test procedure. Process parameters such as screening times and slot widths are varied and different defibration times are studied in order to determine, in the accepts, their influence on the quality and quantity of the metal particles in the handsheets. Vanessa and Christiane are supported in their activities by the employees of PTS and blend in well with the friendly team climate. In August, after finalisation of their master theses, the two students wish to do further research in paper recycling and to extend their current knowledge in everyday work practice.
Fig. 3: Vanessa Wortmann (left) and Christiane Böhmer (right) at the Somerville fractionator.
Dr. Annika Eisenschmidt,