Solvent-based regeneration

Solvent-based purification and depolymerization results in high grade near-virgin polymer output. An example of a solvent regeneration technique, The CreaSolv® process, is discussed in terms of POPs contaminant separation in section 6. The solvent-regenerated polymer is ready to be converted directly to plastic product without the repolymerization steps required for monomers generated from depolymerization processes. Most contaminants, coloring agents, and other additives are removed at the molecular level without affecting the target polymer structure. However, further additives may be required to replicate the target product properties as they were with the original product.

Figure 16. Small plastic/foil packages known as sachets are common in low income countries.

In general, the solvent-based purification works by dissolving the polymer in a specific solvent followed by the removal of contaminants such as additives, pigments, and non-intentionally added substances (NIAS) through filtration or phase extraction, and then precipitating the polymer using an anti-solvent in which the polymer is insoluble (Crippa et al., 2019). Nonintentionally added substances have various sources and can be grouped into side products, breakdown products, and contaminants. Side products are often formed during the production of starting substances such as monomers and all further manufacturing stages. Breakdown products of structural elements of plastic food contact materials (FCMs), such as polymers and fibers as well as additives (e.g. antioxidants, UV-stabilizers), can also contaminate plastics as a NIAS .

While the process itself can regenerate near virgin quality polymers, the forward process of producing a product with extrusion, injection, or blow moulding can induce the same thermal and stress degradation as for any polymer. In this sense, solvent regeneration is not a perpetual plastic recycling process, as the mechanistic processes of plastic production would degrade the polymer after repeated cycles. Polyolefins such as PE and PP can be regenerated using high temperature and pressure. These are two of the highest volume production polymers, and solvent recycling could be applied to increase their recycling rate while removing contaminants (such as BFRs) for further treatment or destruction. Facilities have been established in the US, EU, and Indonesia at industrial pilot scale to recycle these plastics using solvent regeneration and to process multilayer packaging23 including small sachets24 used to package foodstuffs and cosmetics. Littered sachets are a major pollution problem in many countries with virtually no recycling options and little value to waste pickers.

While it may be technically possible to separate multilayer plastic packaging polymers, the viability and economics of scaling up remain unanswered. In the past, solvent recyclers using relatively homogenous input of PVC and PS found the viability of the process challenging with relatively simple inputs compared to complex mixed-layer packaging. Key challenges for solvent regeneration of complex plastic packaging include additional solvation and separation steps, time and energy required for solvent removal, the impact of residual solvent in polymer product, and the ability to recycle solvent contaminated with extracted additives .