Achieving circularity in the plastic economy predominantly depends on sourcing higher quality recyclates. Packaging plastic poses a significant challenge as it is often not prioritised for collection or recycling initiatives. The presence of additives, such as printing ink, impedes the quality of recyclates. Considering the volume of packaging plastics and the importance of branding (aesthetics and consumer information), ink removal is a critical pre-treatment step. However, the literature is limited, with only 14 studies exploring de-inking processes. Drawing parallels with the detergent laundering process, surfactants have been widely investigated in plastic deinking, with cationic surfactants proving the most effective with a de-inking efficiency of up to 100%. However, concerns exist regarding the toxic and hazardous nature of the surfactants and chemicals. The average hazard quotient (AHQ) was developed, which compares de-inking chemicals as one of the key findings. AHQ provides a quantitative proxy for the hazards and toxicities, which are qualitatively presented as part of the globally harmonised system (GHS) classification of chemicals. To drive emerging packaging plastic de-inking, including the development of green surfactants (e.g. gamma-valerolactone), this work enables an informed chemical selection minimising potential hazards (rather than creating more adverse effects in plastic recycling processes) and toxicities from plastic waste, fulfilling the objectives of cleaner plastic waste recycling.

Printing inks impede the quality and economic feasibility of packaging plastic recycling. Conventionally, different single-surfactant systems have been explored for plastic de-inking. Despite the better detergency potential, surfactant mixtures remain unexplored. This study investigates catanionic surfactant mixtures, specifically hexadecyltrimethylammonium bromide (CTAB) - sodium dodecyl sulfate (SDS) systems. A response surface methodology approach was employed to optimise key parameters: temperature (25-55 °°C), pH (10-12), and surfactant concentration (1-25 times the critical micelle concentration, CMC). Experimental results indicated that cationic-rich mixtures (Mix 2:1) achieved up to 100 % de-inking efficiency, comparable to CTAB, while anionic-rich mixtures (Mix 1:2) performed poorly. Statistically, pH was the most significant factor, with strong quadratic and interaction effects. Kinetic modelling demonstrates de-inking follows pseudo-first-order, with CTAB exhibiting a higher rate constant (k = 0.0356 min^-1) than Mix 2:1 (k = 0.0222 min^-1). Surfactant solution pre-heating improved efficiency by 34.49 %. While Mix 2:1 shows promising synergy in de-inking, the study recommends CTAB, optimised at 25°C, pH 12, and 16.5× CMC, as a viable candidate for industrial-scale de-inking. Future directions in plastic deinking should explore bio-based surfactants, solid-liquid ratio optimisation and wastewater treatment. This work advances circular economy initiatives by improving recyclate quality and reducing plastic waste contamination.