Recycling of plastics is not only desired, but also required in the Netherlands starting from 2027 as 15% of new plastic products should consist of recycled plastics [1]. Polyvinyl chloride (PVC) recycling is specifically challenging due to its low thermal stability as elevated temperatures cause the release of hydrochloric acid (HCl). Furthermore, the European Commission has regulated the amount of so-called legacy additives which are allowed to be present in PVC recyclate [2]. Phthalate plasticizers and heavy metal-based stabilizers in particular are of concern and require removal from PVC waste in order for PVC to be able to be recycled.
In this work an interesting avenue for addressing the problem of legacy additives is discussed, namely supercritical CO2 (scCO2). As a supercritical fluid, scCO2 is capable of harnessing both the diffusivity of a gas, whilst also retaining fluid-like density [3]. Moreover, it can dissolve into polymers such as PVC, meaning that scCO2 can extract apolar compounds such as phthalates. It was found that temperature and pressure both improved the extraction efficiency (EE) with pressure having the greatest impact. Above 300 bar the improvement in EE is marginal, whereas there is reason to believe that temperatures above 110 °C can improve EE further, which is currently being investigated along with different modes of operating the extraction equipment. Furthermore, plate-plate rheology is being investigated under super critical conditions to gain a more fundamental insight in the interaction of PVC and scCO2.