State‐Of‐The‐Art Quantification of Polymer Solution Viscosity for Plastic Waste Recycling

Solvent‐based recycling is a promising approach for closed‐loop recovery of plastic‐containing waste. It avoids the energy cost to depolymerize the plastic but still allows to clean the polymer of contaminants and additives. However, viscosity plays an important role in handling the polymer solutions at high concentrations and in the cleaning steps. This Review addresses the viscosity behavior of polymer solutions, available data, and (mostly algebraic) models developed. The non‐Newtonian viscosity models, such as the Carreau and Yasuda–Cohen–Armstrong models, pragmatically describe the viscosity of polymer solutions at different concentrations and shear rate ranges. This Review also describes how viscosity influences filtration and centrifugation processes, which are crucial steps in the cleaning of the polymer and includes a polystyrene/styrene case study.