Verkenning maximaal haalbarekwaliteiten gerecyclede PET uit schalen: Praktische studie naar de maximaal haalbare kwaliteit van mechanisch gerecyclede PET uit schalen

A technical exploration study has been executed to define the maximal achievable quality of recycled poly(ethylene terephthalate) (rPET) that can be made from PET trays with a standard mechanical recycling process. PET is a versatile packaging material used to package multiple fresh food products such as meat, fish, cheese, salads, nuts, etc. Multiple recycling processes have been developed for PET bottles that deliver food-grade rPET. For the larger market of PET trays this has not been successful, yet, on an industrial scale, despite multiple attempts by various companies. The attempts to process the sorted product PET trays into recycled PET have failed because of low mass yields for the PET product, large volumes of waste being generated and insufficient quality of the final product. Sorted PET trays are a complicated feedstock. It is heterogeneous in size, colour and composition. Moreover, PET trays are composed of multiple components and materials. This translates in quality issues with the recycled PET material, which limit the applicability of the PET material largely. To determine the maximum achievable quality of rPET that can be made from trays, four types of trays were studied. It involved PET trays that were composed of only PET, but also PET trays with a sealing layer on the flange, PET trays with a PE coating on the inside and PET trays with sealing layers and residues of top-film. All these trays were separately comminuted, dried, extruded and injection moulded into test specimen. The material properties of the mechanically recycled PET trays were studied in relation to the composition of the feedstock trays. This revealed that recycled PET made from pure PET trays, to which no seal medium has been added, is transparent and hardly coloured. The intrinsic viscosity of this type of recycled PET is unfortunately too low, which results in a brittle material. This material will first have to be subjected to a solid-state post-condensation process. This will make the material stronger, easier to process and wider applicable. An additional and alternative option to increase the intrinsic viscosity is to mix with virgin PET. In case the feedstock contains a seal medium or a residue of top-film the rPET turns grey and hazy. Although the intrinsic viscosities of these types of rPET were slightly better, they are still too low to process the material smoothly. Also these types of rPET will need to be subjected to solid state postcondensation. For these types of recycled PET there is currently no market of significance. These results show that the desired quality of transparent recycled PET can only be obtained from PET trays that are solely composed of PET and to which no other material has been added. This implies that PET trays that are designed for mechanical recycling are only allowed to be composed of PET and the packaging components (such as labels) should be removed during recycling with very high separation efficiencies. The removal efficiency of packaging components during the washing step of the recycling process was not analysed, as this fell outside the scope of this study. According to this study the mechanical recycling should be possible for the subset of PET trays that does not rely on a gas tight closure of the trays, such as clam shells for grapes, tomatoes, soft fruit, nuts, etc. For PET trays used in modified atmosphere packages, that hence need to be sealed hermetically (meat, fish, cheese, cured meats, meat replacements, etc.), first a sealing system is required that is either compatible with PET or can be completely removed during recycling. To progress with the mechanical recycling of PET trays, further research into such a sealing system, including its removal during a mechanical recycling process, is paramount. In the meantime, only a limited amount of PET trays can be mechanically recycled, provided that a sorting technology is developed that can sort out pure PET trays from a mixture of PET trays. Besides these challenges, also the limited mass yield of the mechanical recycling process for PET trays has to be resolved.