Reduction of Organic Compounds Leached to Extractive Media from Polymers through Improved Polymer Processing

Keck, Klaus (2022) Reduction of Organic Compounds Leached to Extractive Media from Polymers through Improved Polymer Processing. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

This research work was sparked by the initial publication of Professor Eric Arvin for the Department of Environmental Engineering of the Technical University of Denmark in Lyngby in 2002. He reported several organic fragments in drinking water which is transported via “plastic” pipes. The fragments seemed to originate from protective chemicals present in the organic pipe substrate. In the last 20 years several other publications have reported similar fragments. Whilst these studies have been useful in identifying this issue, there has not been a systematic approach to the polymeric substrate and its intentionally added ingredients. This study intends to add the knowledge on which conditions cause protective chemicals in polyolefins (stabilisers, antioxidants, modifiers) to produce specific structures and concentrations of water-extractable fragments It further examines how factors other than protective chemicals in a PO determine water-extractable fragments. PO (as a thermoplastic material) cannot be melt-processed at ~250°C without the formation of a very high concentrations of oxidised-aliphatic fragments. Addition of protective chemicals to suppress these fragments, results in additional fragments of an oxidised-aromatic nature. The total number and concentration of fragments, as well as the ratio between oxidised-aliphatic and oxidised-aromatic fragments, is an optimum function between the two opposing effects. Optimum stabilisation packages to reduce water-extractable fragments optimum can be identified by this systematic approach, by clustering the different fragments based on their mechanism of formation. Five different mechanisms of leading to fragments are proposed, which require different strategies to inhibit them. The strategies proposed in this study have shown that a significant reduction in fragments, in the range of ~90%, can be achieved. The extraction temperature has a major impact on type, number, and concentration of fragments. A temperature of approximately 40°C has been chosen as characteristic of extraction in service-life applications for water containment (e.g., pipes and packaging). Different migration behaviour of organic fragments above and below this temperature has been examined.