Developing the synergy between chemical, biochemical, and mechanical processing for enhanced recycling of multilayer plastic packaging

The food and drink industry has stringent performance requirements for product packaging, which ensures food safety, increases consumer experience and reduces food wastage. Packaging contains the product and protects against degradation during transport, storage, and display. This has led to increasing use of multi-layer packaging, which has excellent barrier properties and is thin and lightweight but also single use. The layers can be comprised of paper board, aluminium, and various types of plastic. The lack of recycling technology has resulted in part of the retail sector considering substituting multi-layer materials with single-layer materials, which are currently easier to recycle, however, this will come at the expense of packaging performance and likely increase the weight of the packaging relative to the packaged goods. We want to develop novel recycling solutions for multi layered packaging containing plastics bonded with other materials. We propose a novel integration of traditional mechanical recycling with new (bio) chemical recycling methods. For chemical recycling, we aim to selectively target glue layers to separate the main material layers by dissolving the glue through enzymatic and chemical leaching; low-cost functional ionic liquids will dissolve the glue and utilise their known propensity to extract dyes and dissolve metals. Breakdown of the glue will be catalysed by the ionic liquid itself, or, if it does not have sufficient catalytic power, by stabilised biocatalysts which will be modified to exhibit stability and hyperactivity in the liquid due to a cutting-edge stabilisation method which enables enzymes to be active at temperatures above the boiling point of water. The study of bio(chemical) recycling for multi-layer materials is accompanied by a comprehensive study of the mechanical shredding process to determine the impact of forces on material separation and the damage experienced by the various materials as they are subjected to the (bio)chemical leaching and shredding. The optimal shredded particle size will be determined leading to maximum conservation of mechanical properties of the layer materials and optimal energy use during the integrated hybrid recycling. The mechanical recycling step can be performed: (i) before the (bio)chemical process, in which case the geometry of the shredded pieces will be crucial for enhancing mixing and the reaction rate, or (ii) after the (bio)chemical process carried out with pre-swollen multi-layer materials, in which case the effect of the already degraded adhesion between the layers and lower friction due to the presence of the liquid will be exploited. We will also consider separation of the treated multi-material mixtures, such as sedimentation, flotation, anti-solvent precipitation or solvent extraction and electrodeposition of dissolved components. We will evaluate the various possible configurations of the combined mechanical, chemical and biochemical approach using a high-level technoeconomic analysis, with energy input as the key performance indicator. Although we have chosen food and drink MLP packaging as a proof-of-concept, our approach can be extended to recycling other multi-layered, multicomponent materials for a vast variety of applications, as well as unsorted plastic waste. The recycling method will allow us to continue to harness the benefits of multi-layer packaging while also enabling a much-needed circular economy, preserving economic value, which in turn will incentivise reduction of waste leakage into the environment.