Investigation of the influence of sorting quality on the properties of film recyclates

Sustainability and in that sense recycling of polymer waste has gained attention and importance over the past years. To reach the European Unions (EU) postulated recycling and recycling content targets for plastics packaging, an increase in recycling rate has to be achieved and a certain recyclate quality has to be aimed for. A significant portion of plastics packaging waste in Austria is comprised of large and small films, whose potential for material recycling due to challenges such as for instance separation of multilayer materials and low bulk density still goes largely unused.
The objective of this thesis is to investigate the effect of sorting quality on the properties of polymer film recyclate. For this purpose, four waste fractions of post-consumer film waste of different sorting quality have been processed on lab-scale to recyclate granules and films. To be able to better compare the obtained results, an analysis of three commercially available post-consumer polyethylene low-density/polyethylene linear low-density (PE-LD/PE-LLD) recyclates as well as of virgin grade PE-LD has been performed additionally.
The characterization of the materials was performed on granule and film level. The melt mass-flow rate (MFR), density, oxidation temperature (Tox) and the ash content were determined at granule level. The MFR of the lab recyclates showed a lower level than of the commercial recyclates and virgin material. Also, in the lab recyclates, with one exception, increased sorting resulted in a lower MFR. The observed differences in MFR might be explained by variations in input materials and different levels of PE-LD degradation. The density of the lab recyclates showed a downward trend with decreasing sorting quality. All recyclates showed a lower Tox than virgin material, the commercial recyclates also lower than the lab recyclates. This may be caused by the absence or different remaining levels of stabilizers from the input material and different levels of degradation. With one exception, the ash content increased when sorting quality decreased. With the produced films, inclusion and transparency measurements were performed as well as tensile and puncture tests. A relatively high average number of inclusions per square meter smaller than 300 μm were recorded for all recyclates. The higher the size of inclusions, the lower the average abundance. The lab recyclates show the trend of lower sorting quality leading to a higher number of inclusions. In terms of transparency, all recyclates presented a lower transparency than the virgin material, yet no trends were observable. The observed differences could be caused by the different coloration of the films caused by the input materials as well as different crystallinities. The tensile stress and strain at break were analyzed in both machine and transverse direction. A trend of decreasing tensile stress and strain at break in both directions, for both the lab and commercial recyclates is recorded, indicating an influence of the sorting quality on these tensile properties. The puncture test resulted in a maximum puncture force and displacement at maximum puncture force within a close range, suggesting no significant effect of the sorting quality on this property.