Eco-design of polymeric adhesives for sustainable packaging development

Packaging represents most of plastic waste and it often has a multilayer structure, which is not recyclable because the separation the different layers at the end of life is neither obvious nor cheap. This is due to the use of adhesives that are used to bond dissimilar materials together. This study aims to contribute to the improvement of multilayer packaging recyclability through a design for recycling strategy. The focus is on the eco-design of polymeric adhesives, from three different perspectives. The first chapter of the study deals with the development of a multilayer structure with enzyme-containing adhesives. Enzymes are very interesting for their ability in degradation of tie layers and adhesives, but their application on an industrial scale is hindered by their poor resistance to harsh conditions. To overcome this, a thermal protection system is developed. The protected enzyme can be incorporated into adhesives without losing activity. As a result, the adhesive can be degraded, and the single layers can be recovered and recycled. The second chapter focuses on the synthesis of polymers with labile bonds. Specifically, a polyacetal is prepared via a polyaddition reaction in acidic conditions, without any solvents. Since the acetal bond is known to break under mild acidic conditions, degradation tests are performed at different pH levels. This sustainable synthesis could be used in the future for the development of adhesives that could degrade under controlled acidic conditions. The third chapter focuses on the mechanical recycling of mono-material multilayer packaging containing different adhesives. Indeed, the presence of adhesives can negatively affect the quality of the recyclates. The study uses a simple structure based on LLDPE and BOPE, laminated using different commercial adhesives. The laminates are re-granulated and re-extruded into films, and the properties of the recyclates are evaluated to determine how different adhesives affect their quality.