Ways to decrease the effect of thermal degradation of WEEE plastics during mechanical recycling
Kangashaka, Iida (2022)
Kangashaka, Iida
2022
Materiaalitekniikan DI-ohjelma - Master's Programme in Materials Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2022-03-09
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202202282227
https://urn.fi/URN:NBN:fi:tuni-202202282227
Tiivistelmä
As the world moves towards a more circular economy the recyclability of different materials becomes an increasingly pressing issue. The EU has created a strategy that aims to push the European plastic industry towards circularity, and this also includes significantly increasing the recycling rates of all plastic products. However, some plastic fractions are harder to recycle than others. An example of such a plastic fraction are the plastics in waste electrical and electronic equipment. Part of the reason why this material stream is difficult to recycle are those bromine-containing fire retardants, which are harmful, and which have been used in older electrical and electronic equipment, but are no longer allowed in new products, so they must be removed during recycling. Another problem facing plastic recycling is the degradation that occurs during re-processing, which lowers the plastic’s molecular weight.
The ALL-IN for Plastics Recycling project, which this thesis is a part of, aims to help actors in the plastic industry to discover better recycling systems for challenging plastic streams, such as plastics from waste electrical and electronic equipment. This thesis aims to find if the effects of the degradation during processing can be prevented by adding certain additives into the bromine-free plastics from waste electrical and electronic equipment, and if the resulting recycled plastics can be used in new electrical and electronic equipment.
The work begins with a literature review section, where the current state of the waste electrical and electronic equipment plastic recycling is mapped. Additionally, the theory of how the polymers degrade during processing, how it affects the properties, and how the additives can be used to prevent this are discussed. The studied plastics are polypropylene, polystyrene, acrylonitrile-butadiene-styrene, and polycarbonate/acrylonitrile-butadiene-styrene recycled from waste electrical and electronic equipment. The chosen additives are antioxidants, chain extenders, and graphene nanoplatelets grafted with maleic anhydride. The antioxidant products are Irganox 1010 and Irganox 1076, the chain extender products are Joncryl ADR 4400 and Joncryl ADR 4468, and the graphene nanoplatelets grafted with maleic anhydride are produced in the laboratory. The study is done by performing tensile tests and by measuring the viscosity curve with rotational rheometer experiments for the plastics with and without the additives. These results are then compared to the section in the literature review, that explained how the changes in the molecular weight affect the properties to see how well the different additives prevent degradation. Additionally, oxidation induction times are determined for the samples with antioxidants to evaluate their ability to prevent oxidation.
Based on this analysis it seems that the additive type that worked the best at preventing degradation for polypropylene are the antioxidants, the most effective additive for polystyrene are the graphene nanoplatelets grafted with maleic anhydride, and the best additive type for acrylonitrile-butadiene-styrene and polycarbonate/acrylonitrile-butadiene-styrene are the chain extenders. The rheological and mechanical properties seem to be quite a reliable way to assess degradation caused by thermal oxidation in plastics. In addition, the mechanical properties of the recycled plastics are high enough to be used in new electrical and electronic equipment.
The ALL-IN for Plastics Recycling project, which this thesis is a part of, aims to help actors in the plastic industry to discover better recycling systems for challenging plastic streams, such as plastics from waste electrical and electronic equipment. This thesis aims to find if the effects of the degradation during processing can be prevented by adding certain additives into the bromine-free plastics from waste electrical and electronic equipment, and if the resulting recycled plastics can be used in new electrical and electronic equipment.
The work begins with a literature review section, where the current state of the waste electrical and electronic equipment plastic recycling is mapped. Additionally, the theory of how the polymers degrade during processing, how it affects the properties, and how the additives can be used to prevent this are discussed. The studied plastics are polypropylene, polystyrene, acrylonitrile-butadiene-styrene, and polycarbonate/acrylonitrile-butadiene-styrene recycled from waste electrical and electronic equipment. The chosen additives are antioxidants, chain extenders, and graphene nanoplatelets grafted with maleic anhydride. The antioxidant products are Irganox 1010 and Irganox 1076, the chain extender products are Joncryl ADR 4400 and Joncryl ADR 4468, and the graphene nanoplatelets grafted with maleic anhydride are produced in the laboratory. The study is done by performing tensile tests and by measuring the viscosity curve with rotational rheometer experiments for the plastics with and without the additives. These results are then compared to the section in the literature review, that explained how the changes in the molecular weight affect the properties to see how well the different additives prevent degradation. Additionally, oxidation induction times are determined for the samples with antioxidants to evaluate their ability to prevent oxidation.
Based on this analysis it seems that the additive type that worked the best at preventing degradation for polypropylene are the antioxidants, the most effective additive for polystyrene are the graphene nanoplatelets grafted with maleic anhydride, and the best additive type for acrylonitrile-butadiene-styrene and polycarbonate/acrylonitrile-butadiene-styrene are the chain extenders. The rheological and mechanical properties seem to be quite a reliable way to assess degradation caused by thermal oxidation in plastics. In addition, the mechanical properties of the recycled plastics are high enough to be used in new electrical and electronic equipment.