From model systems to post-consumer waste: towards sustainable strategies for recycling multilayer plastic packaging

Multilayer plastic packaging (MPP) combines two to twelve polymeric and non-polymeric layers to provide barrier, mechanical, and functional properties unattainable with a single material [1]. However, this structural complexity limits the effectiveness of conventional mechanical recycling, causing most multilayer plastic packaging waste (MPPW) to be incinerated or landfilled. Delamination, defined as the selective separation of layers through dissolution or degradation of an internal layer, has emerged as a promising strategy for recovering individual polymer fractions [2].

This study evaluates the effectiveness of organic acids as delamination agents for MPP. Monocarboxylic, dicarboxylic, and tricarboxylic acids were investigated under systematically varied operating conditions, including acid concentration (0.25–1 M), temperature (50–80 °C), and treatment time (1–4 h). A multilayer film consisting of polyethylene (PE) coated with poly(vinylidene chloride) (PVDC) and bonded to poly(ethylene terephthalate) (PET) through a polyurethane (PU) adhesive layer was used as a model system. Delamination efficiency was assessed gravimetrically, while the chemical integrity of the recovered fractions was evaluated by FTIR-ATR spectroscopy. Organic acids successfully promoted delamination under the studied conditions, consistently achieving separation efficiencies above 90 %. FTIR-ATR spectroscopy confirmed the chemical integrity of the recovered PE and PET fractions after treatment. Nevertheless, PU adhesive residues remained on the PE surface, and the PVDC coating was not completely removed, highlighting limitations in obtaining clean polyolefin fractions.

The best-performing conditions identified for the model system were subsequently applied to post-consumer MPPW, consisting of a light fraction (~60 wt%) containing PE, polypropylene (PP), and poly(ethylene-co-vinyl acetate) (EVA), and a heavy fraction (~39 wt%) composed of PET, polyamide (PA), and polystyrene (PS). Delamination was evaluated indirectly through changes in the light-to-heavy fraction mass ratio before and after treatment. Results showed that delamination strongly depends on material composition and waste heterogeneity.