Response surface methodology optimisation of catanionic surfactant mixtures in de-inking packaging plastic waste

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Printing inks hinder plastic recycling quality and economic viability.
• Single-surfactant systems are conventionally used for plastic de-inking.
• Surfactant mixtures offer potential but remain largely unexplored for de-inking applications.

Purpose of the Study:

• To investigate the efficacy of catanionic surfactant mixtures, specifically hexadecyltrimethylammonium bromide (CTAB) - sodium dodecyl sulfate (SDS) systems, for plastic de-inking.
• To optimize de-inking parameters including temperature, pH, and surfactant concentration using response surface methodology.
• To evaluate the performance of different surfactant mixture ratios and compare them with single surfactant systems.

Main Methods:

• Utilized a response surface methodology to optimize temperature (25-55°C), pH (10-12), and surfactant concentration (1-25× CMC).
• Investigated catanionic surfactant mixtures of CTAB and SDS at various ratios.
• Performed kinetic modeling to determine de-inking reaction order and rate constants.

Main Results:

• Cationic-rich mixtures (Mix 2:1) achieved up to 100% de-inking efficiency, comparable to CTAB alone.
• Anionic-rich mixtures (Mix 1:2) demonstrated poor de-inking performance.
• pH was identified as the most significant factor influencing de-inking efficiency, with strong quadratic and interaction effects.
• Pre-heating surfactant solutions increased efficiency by 34.49%.

Conclusions:

• Catanionic surfactant mixtures, particularly cationic-rich formulations, show synergistic potential for effective plastic de-inking.
• Optimized CTAB (25°C, pH 12, 16.5× CMC) is a viable option for industrial-scale de-inking.
• Future research should focus on bio-based surfactants, optimizing solid-liquid ratios, and integrated wastewater treatment for enhanced circular economy initiatives.