Solvent-Based Separation of PA6 and PET Using Solubility Data from Differential Scanning Calorimetry.

Area of Science:

• Polymer Science
• Materials Chemistry
• Chemical Engineering

Background:

• Plastic pollution necessitates circular economy solutions for polymers.
• Solvent-based recycling requires accurate polymer solubility data for efficient material loop closure.
• Separating mixed plastics like polyamide 6 (PA6) and polyethylene terephthalate (PET) is challenging but vital.

Purpose of the Study:

• To develop and validate a standardized differential scanning calorimetry (DSC) protocol for determining polymer solubility.
• To quantify the solubility of PA6 and PET in various solvents.
• To demonstrate the practical application of DSC-derived solubility data in a PA6-PET separation process.

Main Methods:

• A standardized differential scanning calorimetry (DSC) protocol was developed to measure polymer decrystallization and precipitation temperatures in solvents.
• The DSC method was applied to analyze the solubility of polyamide 6 (PA6) and polyethylene terephthalate (PET) in nine different solvents.
• Results were compared with a visual polythermal cloud point method for validation.

Main Results:

• The DSC protocol provides quantitative solubility data, including phase transition enthalpies, with high objectivity, even above solvent boiling points.
• Temperature-dependent solubility data identified methanol, ethanol, propylene glycol, dimethyl sulfoxide, and water as selective solvents for PA6 over PET.
• A proof-of-concept PA6-PET separation using methanol successfully yielded recycled polymers with near-virgin properties under mild conditions.

Conclusions:

• The standardized DSC method is a reliable tool for obtaining essential polymer solubility data for solvent-based recycling.
• Selective solvents identified can facilitate efficient separation of PA6 from PET mixtures.
• The findings support the development of low-energy, solvent-based recycling processes crucial for a circular economy in polymers.