Pressurized liquid extraction and GC/MS determination of model contaminants in HDPE - Application to recycling of post-consumer polyolefins using limonene

Abstract

A pressurized liquid extraction and gas chromatography-mass spectrometry (PLE-GC/MS) method is developed for the quantification of seven model contaminants in post-consumer and recycled high-density polyethylene (HDPE). Chloroform, toluene, chlorobenzene, methyl salicylate, phenyl cyclohexane, benzophenone, and methyl stearate were selected as model contaminants according to the European Food Safety Authority (EFSA) and the Food and Drug Administration (FDA) recommendations. The GC/MS method presented limits of detection (LOD) under 0.5 µg L^-1 for all contaminants except toluene and methyl stearate (18 µg L^-1 and 310 µg L^-1 respectively). Repeatability and intermediate precision were studied at two concentration levels, with the former presenting relative standard deviations under 10 % and the latter under 17 % in almost all cases. The PLE method was optimized by means of a central composite design (CCD), studying the extraction temperature and time. The selected conditions were three extraction cycles with acetone at 100 °C for 6 min at 1500 psi. Accuracy, repeatability and intermediate precision were stablished for the whole PLE-GC/MS method. Accuracy values were close to 100 % for most of them. Repeatability and intermediate precision were good for most of the model contaminants, with RSD values less than 11 and 17 %, respectively. The PLE-GC/MS method was applied to evaluate, via a challenge test, a novel HDPE recycling method based on the dissolution and precipitation of the polymer using limonene. The recycling method was shown to have high cleaning efficiencies, proving its potential in recycling of HDPE, as well as the utility of the PLE-GC/MS method to carry out challenge test evaluations.