One of the main challenges in closed-loop recycling of plastics is the presence of contaminants that can cause problems related with the existence of odors and color, making it difficult to obtain a high product quality. Solvent-based recycling, sometimes referred to as physical recycling, is a promising approach to tackle these difficulties, as it allows the cleaning of the plastic waste. Whilst the polymer is dissolved, contaminants as well as additives can be removed with a separation process after the dissolution of the polymer. However, one crucial factor for the economic balance of this technique is the amount of solvent used to dissolve the polymer. High amounts of solvent leads to low concentrated solutions but requires also huge amounts of antisolvent, typically used to precipitate the polymer. On the other hand, saving on solvent induces highly concentrated polymer solutions, causing an increase in viscosity. This creates difficulties in handling, especially during the cleaning steps.<br/>In this work, the rheological behavior of polymer solutions is reviewed and an evaluation of the existing models for the prediction of polymer solutions rheology is carried out with a view on dissolution-based recycling. Additionally, the influence of the viscosity of polymer solutions on separation processes for the removal of pigments from plastic waste is assessed with a case study on a polystyrene (PS) solution. The results show that the pressure drop in filtration increases by 7 times with a concentration increase from 6 to 9 wt%. Furthermore, the experimental determination of the rheological behavior of PS solutions in different solvents (including bio based solvents), concentrations and temperatures is studied and the most promising viscosity models are applied. The results show that in the studied shear rate range, the solutions show Newtonian behavior (Fig.1) and the viscosity seems to be dependent on the solvent viscosity. To conclude, both the polymer solutions viscosity and solvent-polymer ratios are important aspects in the effectivity of the cleaning steps and on the cost-efficiency of the overall solvent-based recycling technique.

Influence of the rheological behavior of polymer solutions on solvent-based recycling

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.