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Closed loop (film to film) recycling of PE-based flexible film is made challenging by a significant amount of non-PE that inevitably comes into the recycling stream. Other polymer types like PET, PA are part of multilayer structures for example. The other polymer types are considered large-scale contaminants (several percent) and their effect are being understood in ongoing research. The challenge is now shifted to understanding the effects of smaller-scale contaminants, which are present it much lower amounts. Examples include labels, adhesives, inks and barrier layers.
One focus of such small-scale contaminants is adhesives, which are often PU-based. There is a trend to change multilayer structures (like PET-PE) to “full PE” structures for better recyclability. However, this still involves different layers of PE, for example a MDO (machine direction oriented) HDPE for stiffness and a LDPE for sealability. In production, these layers are laminated together with an adhesive. This adhesive is typically PU based. It is our objective to identify the recyclability of such adhesives, meaning what effects do they have on the recycling of these structures? And what is the relation between the chemical structure of the adhesive and the quality of recycling. The PhD student is not responsible for making the new chemical formulations of the adhesive (we do this with a company, global market leader), but for the assessment of recyclability and the fundamental understanding of how all these materials interact together.
As a baseline, a PU adhesive built on standard building block (one adhesive ref) and PU based on new building block (one adhesive ref) will be investigated. Objective of this step is to understand the influence of the adhesive (chemical functions, molecular weight, polymer structure) in the PE recycling stream (miscibility, number and size of gels, rheology, film mechanical properties…). The further research will keep the same focus and will allow to dig in adhesive formulation. We will characterize the polyester backbone used in the PU adhesive synthesis as well as the PU backbone itself and will check their properties in the PE stream.
What are the key parameters, in the adhesive formula, which could support a better performance vs PO recycling stream: hydroxyl index, NCO/OH ratio, molecular weight, Mw distribution, …? The expected conclusion is to get a clear mapping about raw material-adhesive structure and formula vs the PO recycling stream.
The PhD research will not be limited to just these adhesives (but will keep focus on minority components in PE film recycling), but for the sake of the required research plan, may be considered as such.
The topic is highly relevant to industry and part of several projects with industrial partners. The results will also be coupled in to the group's larger work on Recycling Quality (RQ). This PhD topic is meant to go deep into the polymer science, to then be translated to the more applied nature of the RQ work (not necessarily by you).
Located in the heart of Europe, UM is the most international university in the Netherlands with half of our students and one third of academic staff coming from abroad. In total, UM has around 22.000 students and almost 5.000 employees and represents 100 different nationalities. Maastricht University is a stimulating environment where research and teaching are complementary, where innovation is our focus and where talent can flourish. Research is characterized by a multidisciplinary, thematic, and collaborative approach, and with education, forms the core of UM.
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Faculty of Science and Engineering
The Faculty of Science and Engineering (FSE) is home to several outstanding departments and institutions covering education and research in Science, Technology, Engineering and Mathematics (STEM) as well as the liberal arts and sciences.
The Circular Plastics research group is part of the newly created Department of Circular Chemical Engineering in the Faculty of Science and Engineering at Maastricht University. Our research group is uniquely situated in the heart of the Dutch chemical industry at the Brightlands Chemelot campus, 20 km north of Maastricht. Our strong links with industry give excellent opportunity to build collaborations and partnerships, giving good prospects for a future career in industry. Our group has a strong expertise in plastics recycling, polymer processing, characterization and multi-scale structure-property-processing relationships in plastics. The chair is widely recognized as a European leader in plastics recycling research. We have excellent international connections with esteemed laboratories, and we therefore expect the applicant will have the opportunity to work abroad during their PhD.
To learn more about our department, please visit our website: https://www.maastrichtuniversity.nl/research/circular-chemical-engineering
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