Analysis of citrates and benzoates used in poly(vinyl chloride) by supercritical fluid extraction and gas chromatography

Recycling PVC with scCO2: From Soft to Rigid PVC

This study explores using extraction with supercritical carbon dioxide to remove plasticizers from poly(vinyl chloride) (PVC), with the aim to enhance recycling processes. Experiments were performed at 100 to 500 bar with temperatures varying from 75 to 110 °C. The results show that continuous supercritical carbon dioxide efficiently removes bis(2-ethylhexyl) phthalate (DOP) from PVC with extraction efficiencies of more than 98% which resulted in PVC samples with over 99.5% purity. A process model based on the Sovová model accurately describes the extraction process. The impact of the extraction process on polymer properties and associated molecular structures like viscosity, morphology, and mechanical properties was also evaluated using gel permeation chromatography, rheology, tensile test, and scanning electron microscopy.

Assessment of Supercritical CO2 Extraction as a Method for Plastic Waste Decontamination

Due to the lack of advanced methods to clean plastic waste from organic contaminants, this study aimed at evaluating supercritical extraction as a decontamination method. Oil-adhesive high-density polyethylene (HD-PE) oil containers were subjected to supercritical extraction using supercritical carbon dioxide. The extraction was conducted at 300 bar, applying various temperatures (i.e., 70, 80 and 90 °C). The study assessed the impact of temperature on the decontamination efficiency. The variation in the samples’ quality was first analyzed using near infrared (NIR) spectroscopy. An analysis of the content of polycyclic aromatic hydrocarbons (PAHs) was followed. Samples treated at 70 and 80 °C showed higher extraction efficiencies, in spite of the lower extraction temperatures. The NIR analysis showed that the plastic specimens did not experience degradation by the supercritical decontamination method. Moreover, the NIR spectra of the extracted oil showed the presence of a wide range of compounds, some of which are hazardous. This has been confirmed by a GC-MS analysis of the extracted oil. Based on the provided assessment, the quality of the decontaminated HD-PE plastic samples—from a contamination point of view—is enhanced in comparison to untreated samples. The level of PAHs contamination decreased to be within the allowed limits defined by the REACH regulation, and also met the specifications of the German Product Safety Committee. This study proved the effectiveness of the supercritical extraction using CO₂ in extracting organic contaminants from plastics, while maintaining their quality.

Purification of pharmaceutical excipients with supercritical fluid extraction

Supercritical fluid extraction (SFE), with carbon dioxide as the solvent, was tested for its ability to remove common reactive impurities from several pharmaceutical excipient powders including starch, microcrystalline cellulose (MCC), hydroxypropylcellulose (HPC), polyethylene oxide (PEO), and polyvinylpyrrolidone (PVP). Extraction of the small molecule impurities, formic acid and formaldehyde, was conducted using SFE methods under conditions that did not result in visible physical changes to polymeric excipient powders. It could be shown that spiked, largely surface-bound, impurities could be removed effectively; however, SFE could only remove embedded impurities in the excipient particles after significant exposure times due to slow diffusion of the impurities to the particle surfaces. Attempts at hydrogen peroxide extraction were hindered by its low solubility in CO2, thereby effectively precluding SFE for removal of hydrogen peroxide from excipients. This work suggests that SFE will only be commercially useful for removal of low molecular weight impurities in polymeric excipients when migration of the impurities to the particle surfaces is sufficiently rapid for extraction to be completed in a reasonable time frame.