Molecular Mechanisms Underlying Surfactant-Based Plastics De-Inking

Area of Science:

• Polymer Science
• Materials Chemistry
• Surface Science

Background:

• Surfactant-mediated binder removal is crucial for effective plastics recycling.
• Understanding the molecular mechanisms of surfactant performance in de-inking is limited.

Purpose of the Study:

• Investigate interactions between surfactants and polyether urethane (PEU) binder on polyethylene (PE) surfaces.
• Elucidate molecular mechanisms governing surfactant performance in plastics de-inking.
• Guide the design of improved surfactant formulations for recycling.

Main Methods:

• All-atom (AA) and coarse-grained (CG) molecular dynamics (MD) simulations.
• Alkaline surfactant washing experiments.
• CG umbrella sampling to calculate binder desorption free energy barriers.

Main Results:

• De-inking efficiencies varied from <25% to >95% based on surfactant properties.
• Charged surfactants achieved stable coverage, while nonionic surfactants aggregated.
• Simulations showed up to a 52% reduction in binder desorption free energy barrier.
• A strong correlation (R2=0.92) was found between computed free energy changes and experimental de-inking efficiencies.

Conclusions:

• Charged surfactants are more effective than nonionic surfactants for de-inking.
• Three regimes of surfactant de-inking processes were identified based on PEU desorption and aggregation.
• Molecular insights can optimize surfactant design for enhanced plastics recycling.