Investigation of the degradative impact of multiple reprocessing loops on the rheological behavior of different polypropylenes
Sprache des Vortragstitels:
37th INTERNATIONAL CONFERENCE of the POLYMER PROCESSING SOCIETY
Sprache des Tagungstitel:
Mechanical recycling has an important role in the recycling of plastic waste. Closed-loop recycling solutions are advantageous to produce high-quality recyclates. However, the return of the material into the production processes affects the polymers negatively. This can lead to irreversible degradation in the material properties, thereby limiting the recycling potentials to a finite number of rounds.
To investigate the influence of the multiple recycling loops on the material degradation and the resulting property profile, a reprocessing cycle was designed. The material was extruded and granulated, injection molded, and then milled to be re-introduced into the cycle. To simulate the recycling loops of drinking cups, two polypropylene (PP) grades were processed six times according to the above-mentioned cycle. Melt flow rate (MFR), parallel-plate rheology, and gel permeation chromatography (GPC) tests were performed to determine the impact of the reprocessing steps on the rheological behavior as well as the molar mass of the materials.
Both PP grades showed a significant increase in the MFR values after each re-processing step. A similar trend was observed in the results of the parallel-plate rheology tests. This behavior was accompanied by a corresponding decrease in the weight average molar masses. Therefore, the results of this study are in agreement with usual degradation mechanisms, namely, chain-scission in PP materials.