Understanding de-inking in packaging plastic recycling: Bridging the gap in resource conservation and establishing average hazard quotient

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 de-inking, 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.