Development of a closed-loop solvent-based recycling process for dyed denim waste

Area of Science:

• Textile Chemistry
• Sustainable Materials Science
• Chemical Engineering

Background:

• Indigo-dyed denim waste presents significant recycling challenges due to dye stability and fiber adhesion.
• Current textile recycling methods often struggle with effective indigo removal and dye recovery.
• Developing closed-loop systems is crucial for sustainable textile waste management.

Purpose of the Study:

• To develop a closed-loop recycling process for indigo-dyed denim waste.
• To investigate the use of dimethyl sulfoxide (DMSO) for efficient indigo stripping and dye recovery.
• To assess the recyclability of the solvent and the quality of the stripped cellulose substrate.

Main Methods:

• A closed-loop process utilizing dimethyl sulfoxide (DMSO) for color stripping was designed.
• Optimized process parameters including solvent composition (100% DMSO), treatment time, temperature, and material-to-liquor ratio.
• Evaluated indigo extraction efficiency, cellulose mechanical properties (tensile strength), and lightness of stripped denim.
• Assessed the recyclability of DMSO over multiple stripping cycles.

Main Results:

• 100% DMSO achieved superior indigo extraction (up to 98% color removal) compared to aqueous systems.
• Optimized conditions maximized stripping efficiency while preserving cellulose integrity (approx. 98% tensile strength retention).
• Stripped denim showed high lightness values (L* > 81), suitable for re-dyeing or as a white feedstock.
• Recovered DMSO demonstrated excellent recyclability, maintaining performance over at least five cycles.

Conclusions:

• A closed-loop recycling process using DMSO is effective for indigo-dyed denim waste.
• The method allows for high dye removal, preserves cellulose quality, and enables solvent reuse.
• This approach supports circular economy principles and advances sustainable textile recycling.