Reclaiming Polyethylene from Multilayer Plastic Packaging by Separating Oxygen Barrier Material Using Solvent-Based Selective Dissolution: Recycling Polyethylene for Property Characterization

Direct mechanical recycling of multilayer plastic packaging (MPP) leads to downcycling, as the costly barrier layer loses economic value and often degrades the quality of the recycled blend. In this study, a five-layer MPP film consisting of low-density polyethylene (LDPE) structural layers, maleic anhydride-grafted linear LDPE (MA-g-LLDPE) tie layers, and an ethylene vinyl alcohol (EVOH) barrier layer was treated with formic acid to selectively extract the EVOH. The effects of the solvent concentration, temperature, sample size, and solvent-to-sample ratio on dissolution efficiency were evaluated, and optimal conditions were identified and scaled in a pilot setup. The polyolefins reclaimed after EVOH extraction were reprocessed into a blend through a conventional mechanical recycling process. Mechanical testing showed that the reclaimed polyolefin blend exhibited enhanced performance compared to the MPP film blend obtained via direct mechanical recycling and demonstrated properties comparable to those of virgin LDPE. Analysis of the chemical structure and rheological behavior revealed that chemical changes of the MA-g-LLDPE tie layer via hydrolysis and ring-opening reactions played a key role in affecting intermolecular interactions and consequently the mechanical performance of the reclaimed polyolefin blend. Moreover, the thermal properties of the reclaimed polyolefin blend remained largely consistent with those of the LDPE/MA-g-LLDPE blend without dissolution treatment. These findings demonstrate that solvent-based selective dissolution is a practical and scalable method for extracting EVOH and reclaiming polyolefins, enabling subsequent mechanical recycling with satisfactory results.