Heterocoagulation of Inorganic Pigments for Solvent-Based Recycling of Polystyrene

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Pigment removal is crucial for high-value plastic recycling.
• Current methods can impact mechanical properties and circularity.
• Solvent-based recycling offers potential but requires efficient pigment separation.

Purpose of the Study:

• To investigate heterocoagulation as a solid-liquid separation technique for inorganic pigments in solvent-based plastic recycling.
• To evaluate the effectiveness of different heterocoagulants and solvents on pigment removal.
• To assess the impact of polymer concentration on pigment separation efficiency.

Main Methods:

• Investigated heterocoagulation of carbon black, red, and yellow pigments using polystyrene (PS) in xylene and cyclohexanone.
• Tested cationic polyacrylamide, poly(ethylene glycol), and sodium dodecyl sulfate as heterocoagulants.
• Measured turbidity reduction to quantify pigment removal efficiency at various polymer concentrations.

Main Results:

• Achieved over 99% turbidity reduction with optimal heterocoagulants (cationic polyacrylamide, poly(ethylene glycol), sodium dodecyl sulfate).
• Successfully removed red and yellow pigments (>90% turbidity reduction) at 5 wt% PS concentration.
• Efficiently separated carbon black (up to 98% turbidity reduction) at 1 wt% PS concentration.
• Demonstrated selective recovery of heterocoagulants via water washing.

Conclusions:

• Heterocoagulation is an effective technique for removing inorganic pigments in solvent-based plastic recycling.
• The choice of heterocoagulant and solvent, along with polymer concentration, influences separation efficiency.
• This method enhances plastic circularity by improving recyclate quality and enabling heterocoagulant recovery.