Uniform Dyeing of Polyester with Supercritical CO2

Significance of the Topic

Supercritical carbon dioxide (scCO2) dyeing addresses environmental challenges and resource demands of traditional water-intensive textile processes. With global investments exceeding one billion dollars for wastewater reduction, scCO2 offers a sustainable alternative that eliminates water use, reduces effluent treatment, and lowers operational costs while delivering uniform and high-quality polyester dyeing.

Objectives and Study Overview

This study evaluates the feasibility of using scCO2 to uniformly dye polyethylene terephthalate (PET) packages with disperse dyes. Goals include assessing color uniformity, optimizing process parameters (pressure, temperature, dye concentration), and demonstrating the tunability of scCO2 to achieve desirable shade depth without water-based rinsing steps.

Methodology and Instrumentation

Methodology:

• PET packages loaded into a 40-L high-pressure dye vessel.
• scCO2 introduced and maintained at supercritical conditions (120 °C, 4200 psi) with a recirculation rate of 5 kg/min.
• C.1. Disperse Blue 79 dye dissolved in circulating CO2 for 40 minutes to achieve uniform penetration.
• System depressurized to collect any excess dye in a recovery vessel.

Used Instrumentation:

• Applied Separations Spe-ed™ Supercritical CO2/Dye Pilot Plant.
• Industrial-grade CO2 supply with dip tube for fluid transport.

Main Results and Discussion

The scCO2 process produced uniformly dyed PET fibers, confirmed by weaving dyed packages into a test fabric (sock) and evaluating color consistency. The absence of residual dye on fabric surfaces indicates complete uptake by fibers, eliminating the need for post-dye washing. The tunable density of scCO2 enabled precise shade control by adjusting pressure without chemical modifiers.

Benefits and Practical Applications

• Eliminates water usage and related effluent treatment costs.
• Reduces energy consumption associated with drying and dye removal steps.
• Enables precise color control through pressure-and-temperature tuning.
• Recovers and recycles unabsorbed dye, improving material efficiency.

Future Trends and Opportunities

With ongoing advances in high-pressure equipment design and process automation, scCO2 dyeing is poised for broader industrial adoption. Future research may explore co-solvent modifiers to extend compatibility with a wider range of dyes and fiber types, as well as scale-up studies for continuous processing in textile mills.

Conclusion

Supercritical CO2 dyeing of polyester offers a viable, eco-friendly alternative to conventional water-based methods, combining uniform dye uptake, tunable processing conditions, and significant environmental benefits. This technology has the potential to revolutionize textile dyeing by minimizing waste and optimizing resource use.

References

• Kaziunas A., Maxwell R. Optimization of Flow Conditions for the Uniform Dyeing of PET Packages with Supercritical CO2. AATCC Show, Oct 1999.