Progress towards composition-based inline sorting and recycling of multilayer polymer packaging

Two-dimensional plastic packaging films provide vital protection during transport and storage of food and other goods, offering significant economic benefits compared to other materials. However, their usage results in a considerable amount of packing waste including multi-materials and multilayer films made of various polymer layers, which are exceptionally difficult to recycle into high-value products. To promote sustainable material usage, efforts towards recycling of these two-dimensional materials are essential. This work presents a proof of concept for composition-based mechanical sorting of multilayer plastic films. The use of transflectance near-infrared (NIR) hyperspectral imaging data collected on a laboratory scale sorting line and principal component analysis (PCA) allowed a composition-specific distinction. Besides the separation of multilayers from monolayers, several multilayer classes according to their two major polymer components were identified. In case of two commonly used multilayers, polyethylene-polyamide (PE/PA) and polyethylene-polyethylene terephthalate (PE/PET), further NIR based classification was found and investigated using Raman and attenuated total reflectance Fourier transform infrared (FTIR-ATR) imaging spectroscopy. Cross-section analysis showed that only certain classes within PE/PA multilayers contain ethylene vinyl alcohol, whereas classes within PE/PET showed the presence of polyvinyl alcohol layers and different number of layers. This composition-based sorting method could enhance the recycling potential of multilayer packaging films.