This study investigated the dissolution of virgin EVOH in DMSO, reclamation of dissolved EVOH and its subsequent thermo-mechanical processability using extrusion. By examining the thermal, rheological, and spectroscopic properties as well as color changes of the virgin, recovered and extruded materials, this research provides key insights into solvent based recycling and subsequent processing strategies for multilayer plastics. Multilayer plastics have transformed packaging by offering excellent barrier properties, mechanical strength, and versatility, making them essential for preserving food, pharmaceuticals, and other perishable items. These materials typically consist of multiple polymer layers—such as polyethylene (PE), polypropylene (PP), and ethylene-vinyl alcohol copolymer (EVOH) each contributing specific functional property. However, even when multilayer packages are deemed recyclable, the higher value barrier layer is diluted in the polyolefin stream. Solvent extraction has emerged as a promising recycling method to selectively dissolvepolymers from multilayer structures. In particular, dimethyl sulfoxide (DMSO) has shown effectiveness in dissolving EVOH, a high-cost barrier material valued for its superior gas impermeability, from within multilayer polyolefin packages. During dissolution, solvent molecules penetrate and swell the polymer, leading to chain disentanglement and eventual dissolution. This process may also remove additives such as plasticizers or stabilizers, altering the polymer’s properties and influencing its behavior during processing. Despite chemical recycling’s potential, limited research exists on how solvent extraction affects the processability of recovered EVOH.
This study compared the properties of EVOH that had been dissolved in DMSO, recovered, and extruded in a Haake MiniLab with the properties of the same type of EVOH that had simply been extruded at the same conditions. The results showed that solvent extraction had a minimal effect on the polymer's thermal properties, crystallinity, and microstructure. Interestingly, the recovered material did not show as much color change as the virgin material after extrusion. Time resolved rheology in the linear viscoelastic region was found to be the most sensitive method for discerning how the extraction process affected EVOH’s stability. The rheological behavior of extracted EVOH differed noticeably from virgin EVOH post extrusion. Unlike many polymers, EVOH degrades by cross-linking. The viscoelastic properties of the virgin material increased significantly after extrusion which is consistent with cross-linking. Unlike virgin EVOH, which exhibited a significant increase after extrusion due to EVOH’s sensitivity to mechanical and thermal stresses, the extracted EVOH’s viscoelastic properties remained stable regardless of extrusion or its duration, suggesting its longer chains are less prone to degradation. High-frequency data, reflecting shorter chains, showed no significant property change over time for virgin EVOH, though extruded virgin EVOH displayed a slight increase, while extracted EVOH remained unchanged before and after extrusion. It is hypothesized that the difference in EVOH stability during extrusion was the result of cross-linking that occurred during processing and additive loss during extraction. Nuclear Magnetic Resonance (NMR) spectroscopy and ICP-OES analysis revealed phosphorus and boron based additive loss during solvent extraction. The lowering of viscoelastic properties of the recovered EVOH was attributed to loss of additives. Future work will further explore how the solvent extraction from multilayer consumer packaging affects the properties of EVOH including its barrier properties.
