Polyethylene terephthalate based multilayer food packaging: Deterioration effects during mechanical recycling

Abstract

Modified atmosphere packaging (MAP) comprises a multilayer structure of polymers and adhesives offering excellent protection to food products. While this widely used structure improves shelf life, its recyclability is restricted by polymer incompatibilities and difficulty separating individual layers during sorting, which limits the viability of this prominent waste stream for 2030 European Union (EU) reuse and recycling targets. This study assessed the recycling potential of MAPs by system part and functional layer based on composition, component miscibility and temperature and incompatibility induced changes in physical and mechanical properties. Lids and trays alone exhibited similar compositions, but when combined their PET (polyethylene terephthalate)-PE (polyethylene) ratios varied considerably resulting in embrittlement and reduced toughness indicating limited compatibility and recyclability. Although PET-PE immiscibility resulted in phase separation causing inhomogeneity induced loss in ductility and toughness, barrier structures exhibited better phase adhesion and more homogeneous morphologies. Nonetheless, the PET dictated processing temperature, greatly exceeding that of PE, promoted cross-linking effects. The barrier and carrier layers of current MAPs must be delaminated within waste sorting processes to be recyclable. More economic and ecological recycling of MAPs to meet EU targets will require designs with more compatible polymer components.