Purification of post-consumer polyolefins via supercritical CO2 extraction for the recycling in food contact applications

• SCCO2 extraction has great potential for purification of post-consumer polyolefins.
• Wide range and large size of contaminants can be extracted by SCCO2 from polyolefins.
• SCCO2 extraction from polyethylene is more effective than that from polypropylene.
• Extraction rate can be improved by reducing of matrix size or increasing temperature.
• SCCO2 extraction is better than MeCl2 extraction in terms of efficiency and speed.

Throughout their lifecycle or first use, polyolefins can be exposed to contaminating media which limit their recyclability, especially in food industry, such as packaging. Supercritical carbon dioxide (SCCO2) extraction in dynamic mode is studied as a possible method to purify post-consumer polyolefins. As a first approach, the strategy was to remove the well-known conventional additives (i.e., antioxidant) which are already present in food grade polypropylene (PP) and linear low density polyethylene (LLDPE). The extraction yields and kinetics have been obtained by gas chromatography. A systematic study of the influence of the shape (pellets or films) and the thickness of the materials shows that it is possible to increase the speed of extraction with a thinner material: high yields (100%) are obtained with films at 300 bar, 50 °C and 5 min of extraction. Finally, the potential of SCCO2 extraction was compared to that of traditional liquid extraction with methylene chloride.

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