Oxidative Chemical Recycling of Polyethylene

Abstract

To reduce the environmental burden of plastic waste, it is essential to develop better methods for the recycling of plastic wastes. This dissertation focuses on the chemical recycling of polyethylene, the most widely used plastic, through oxidation. In this approach, the plastic reacts with oxygen to form high-value molecules (dicarboxylic acids) that can be used in applications such as textiles, including nylon. The first part of this dissertation focuses on the development of analytical methods to gain a deeper understanding of the oxidation reaction. By combining multiple analytical techniques, key reaction intermediates in the conversion of polyethylene to dicarboxylic acids were identified. This insight is crucial, as it enables reaction development based on mechanistic understanding rather than a trial-and-error approach. The knowledge gained led to a significant improvement in reaction performance. By adding copper and vanadium metal salts in the presense of O2/NO, the yield of dicarboxylic acids was increased to over 50%. In addition, it was demonstrated that similar yields can be achieved using heavily contaminated post-consumer plastic waste, highlighting the robustness and practical relevance of the method. In the final chapter, we show that the produced dicarboxylic acids can be used directly as mixtures in polyester synthesis. This is attractive because it reduces purification requirements and therefore saves energy. Together, these results underline the potential of oxidative chemical recycling of polyethylene as a sustainable route to valuable materials.