Making and analysing more recyclable multilayer polymer packaging films

Most polymer films used in food packaging are multilayer laminates of very different polymers or metal films, due to the wide range of properties which need to be satisfied and balanced. Unfortunately, such mixed materials are extremely difficult or impossible to recycle, reducing the overall sustainability of polymer packaging. In addition, the polymers are mostly made from non-renewable sources and are non-degradable. Approaches to these challenges include: (a) producing laminates that can be separated for recycling by "debonding on demand" with an external chemical or physical trigger, allowing the material layers to be separated; (b) producing films and laminates from renewable sources which can be degraded at end-of-life. Such innovations will be key for decreasing polymer waste and enabling recycling and the circular economy for plastics. However, characterization of multilayer polymer films, and other polymer films which have through-thickness variation in chemistry (e.g. resulting from degradation or small molecule uptake) is challenging.

This main objective of this project is to develop a new analysis capability - infrared spectroscopic ellipsometry (IRSE) - for the in-situ analysis of multilayer polymer laminates and polymer films with through-thickness variation in chemistry. This optical technique is fast, non-destructive and can be used with measurement cells for heating, solvent or vapour exposure, allowing dynamic processes such as curing, drying, swelling, degradation and delamination to be observed in-situ. Commercial IRSE systems are not widely available and the technique has been rarely applied to polymer challenges. We will use the new IRSE capability within the Henry Royce Institute Sustainable Materials Innovation Hub at Manchester to develop this key enabling technology for polymer innovation.

The student will measure model multilayer polymer samples (including real polymer packaging samples and in-house fabricated films) by IRSE and develop the necessary analytical methods using model samples to characterize these multilayer stacks. Through-thickness chemical profiling will be demonstrated and applied to understanding polymer curing, drying, swelling, degradation and delamination. Results will be correlated to other techniques including various microscopies, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and mechanical testing.

Finally, the insight and expertise gained into the characterization of multilayer polymer films and buried layers will be applied in initial experiments towards developing new adhesive layers for multilayer packaging films than can respond to an external trigger and allow the laminate to be separated and recycled. The response of these new laminates to simulated real-world usage conditions will also be investigated. In addition to characterization work, the student will also gain hands-on experience of "wet chemistry" laboratory work for sample preparation and new materials synthesis and formulation, in addition to some practical polymer processing for film fabrication.



Suggested EPSRC Research Area: Polymer Materials