Use of recycled polyethylene in extrusion coating
Santahuhta, Venla (2024)
2024
Materiaalitekniikan DI-ohjelma - Master's Programme in Materials Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2024-08-15
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202407157619
https://urn.fi/URN:NBN:fi:tuni-202407157619
Tiivistelmä
The purpose of this work was to find out what are the current ways to recycle polyethylene (PE) and how commercially available polyethylene is recycled. In addition, it was investigated whether it is possible to use recycled polyethylene in the extrusion coating. In the thesis, the structure, and properties of different polyethylenes are reviewed in more detail. In addition, different polyethylene recycling methods and the effect of recycling on the structure of polyethylene are discussed. The theory of extrusion coating is also studied.
At the beginning of the experimental part, commercial recycled polyethylenes that could be suit-able for extrusion coating were searched for. All materials selected for the research were mechanically recycled. Polyethylene granules were studied in different ways. Melt flow rates, purity, crystallinity, and volatile compounds in the headspace were determined from the granules. In addition, the volatile compounds produced during the processing of recycled plastic were investigated. Materials for the extrusion coating pilot line were chosen based on preliminary studies with cast film extrusion line. The coating weight of the coated paperboard was measured, and the adhesion between coating and paperboard was determined. In addition, the coated paperboards were examined for pin-holes, their heat sealability and their water vapor transmission rate.
The research found that the recycled materials were not always what the material suppliers had declared. In some materials, polypropylene (PP) or other polyethylenes were detected in addition to the indicated polymer. In addition, the recycled material could be very variable. The granules from the same batch may vary in color and size. There was also great variation between different batches of the same material.
The recycled polyethylenes in this research were not fully suitable for extrusion coating. In extrusion coating, problems were caused by gels, pinholes, impurities and the material's poor melt strength, which caused the film to tear. However, perfect adhesion was achieved with recycled plastics and almost all of them achieved the desired coating amount. The water vapor transmission rate of the recycled materials did not differ from the virgin material. The heat sealing properties of the recycled materials were worse than the virgin material.
At the beginning of the experimental part, commercial recycled polyethylenes that could be suit-able for extrusion coating were searched for. All materials selected for the research were mechanically recycled. Polyethylene granules were studied in different ways. Melt flow rates, purity, crystallinity, and volatile compounds in the headspace were determined from the granules. In addition, the volatile compounds produced during the processing of recycled plastic were investigated. Materials for the extrusion coating pilot line were chosen based on preliminary studies with cast film extrusion line. The coating weight of the coated paperboard was measured, and the adhesion between coating and paperboard was determined. In addition, the coated paperboards were examined for pin-holes, their heat sealability and their water vapor transmission rate.
The research found that the recycled materials were not always what the material suppliers had declared. In some materials, polypropylene (PP) or other polyethylenes were detected in addition to the indicated polymer. In addition, the recycled material could be very variable. The granules from the same batch may vary in color and size. There was also great variation between different batches of the same material.
The recycled polyethylenes in this research were not fully suitable for extrusion coating. In extrusion coating, problems were caused by gels, pinholes, impurities and the material's poor melt strength, which caused the film to tear. However, perfect adhesion was achieved with recycled plastics and almost all of them achieved the desired coating amount. The water vapor transmission rate of the recycled materials did not differ from the virgin material. The heat sealing properties of the recycled materials were worse than the virgin material.