This study compares two types of methods used for the valorization of multilayer films, namely, mechanical recycling (MR) through thermomechanical reprocessing and the selective dissolution–precipitation (SDP) method, which lead to products of different nature. Both approaches were evaluated on a five-layer coextruded film composed of polypropylene (PP) (88 wt %) used as the outer layer, maleic anhydride-grafted polypropylene (PP-g-MA) (5 wt %) serving as the tie layer, and ethylene vinyl alcohol (EVOH) (7 wt %) used as the barrier layer. The comparison of the two processes was primarily based on their applicability. However, two additional criteria, namely, environmental impact and economic aspects, were also briefly addressed based on literature data. MR consisted of thermomechanical reprocessing applied over five cycles to the multilayer film by using a twin-screw extruder. The results show that MR is a promising route up to the third recycling cycle; beyond this point, the rheological and mechanical properties deteriorate. This degradation is attributed to the competition between different reaction mechanisms, namely, PP β-scission, EVOH cross-linking, and the esterification reaction generated by the interaction between EVOH and PP-g-MA. Nevertheless, according to the literature, the MR process presents a low environmental impact and a relatively affordable cost. In contrast, the SDP process consisted of a layer separation system based on the use of a solvent system. Although the SDP process successfully separated PP from EVOH, the thermal and rheological properties of the recovered materials were altered due to incomplete recovery or recovery of the interface/interphase material during dissolution, resulting from strong physicochemical interactions between the constituents (PP-g-MA/EVOH), as well as the use of solvents at elevated temperatures. Compared with MR, the SDP method is more energy-intensive and has a higher environmental impact, notably because it requires solvents and antisolvents, involving additional distillation steps for their separation. It is also more expensive due to the cost of solvents and antisolvents, as well as the equipment required for layer separation. Finally, in terms of processing time, layer separation by dissolution requires approximately 60 h, compared with 6 h for thermomechanical reprocessing.
Adam et al. (Mon,) studied this question.