Extraction and identification of non-volatile low molecular weight compounds of recycled polymers for packaging

Multiple processing by means of successive injection cycles was applied to virgin PET in order to simulate thermo-mechanical degradation induced by mechanical recycling. The assessment of low molecular weight compounds (LMWC) that can migrate from plastics to food mainly in packaging applications relies on the performance of extraction methods. The performance of advanced extraction techniques such as Microwave-Assisted Extraction (MAE) and Ultrasound-Assisted Extraction (UAE) are assessed with the aim of substituting the traditional Soxhlet, since it is time- and solvent-consuming, despite it produces the maximum extraction yield. High-Performance Liquid Chromatography (HPLC-UV) and a statistical Design of Experiments were applied for the optimization of the operational parameters. Temperature, time and percentage of isopropanol in a polar/non-polar mixture to be used as solvent, were chosen as experimental factors. The quality effects employed for the statistical analysis were all related to the Dimethyl Terephthalate peak: Signal-to-noise ratio, Resolution, Intensity and Area of peak, as well as the differences between Soxhlet extraction and MAE/UAE for Area, Intensity and Area*Intensity. The scrutiny of the statistical results revealed the influence of the different factors, in an individual way or in combination, to the signal. DOE analysis stated that the best combination of factors for MAE were 115º and 90 minutes, and 50ºC and 30 minutes for UAE; as DOE states that no influence was made by solvent composition, a 1:1 (v:v) isopropanol and n-hexane mixture was chosen.