A novel eco-design approach to enhance the recyclability of polystyrene-based multilayer films: Effect of melt rheological properties of coexisting components on the morphological and mechanical performances
Résumé
Due to the recent updates of the international legislation on plastic waste, research on polymer recycling is speeding up to reuse plastics otherwisetargeted for landfills in order to reduce the environmental impacts of post-consumer products. More particularly, multilayer polymer foils representan important part of produced packaging films. Many works devoted to the recycling of multi-component materials showed that recyclate fromsuch films are heterogeneous compounds, producing secondary materials with poor properties making them more difficult to use for thedevelopment of new valuable products. In this study, a novel eco-design approach for the valorization of polystyrene-based multilayer films wasevaluated. To simplify their recyclability, the films were prepared with a limiting number of constituents by avoiding the use of tie layers. Theforced assembly coextrusion technology was used to produce polystyrene (PS)/polyethylene (LLDPE) (90/10 vol%) multi-micro/nanolayerarchitectures having different initial morphological and rheological properties (i.e. different viscosity and elasticity ratio between the polymerconstituents). The effect of multiple reprocessing cycles on the evolution of phase morphology, thermal and mechanical properties wasinvestigated. It was found that under certain rheological conditions, the initial multi micro-nano-layered structure was transformed into a multimicro-nanofibrillar or lamellar morphology which made it possible to have recycled films with a good compromise between stiffness and ductility.On the other hand, it was highlighted that the Young's modulus increased when the number of layers increased (from 32 to 2048 layers) and theoverall mechanical performances were maintained or improved throughout recycling cycles. The obtained results demonstrated that the eco-designof multi-nanolayer structures can be used as a promising economically strategy to improve recyclability of complex structure packaging films by direct melt blending.