Removal of impurities from low-density polyethylene using supercritical carbon dioxide extraction

Degradation of low-density polyethylene by the bacterium Rhodococcus sp. C-2 isolated from seawater

Low-density polyethylene (LDPE), which accounts for 20% of the global plastic production, is discharged in great quantities into the ocean, threatening marine life and ecosystems. Marine microorganisms have previously been reported to degrade LDPE plastics; however, the exploration of strains and enzymes that degrade LDPE is still limited. Here, an LDPE-degrading bacterium was isolated from seawater of the Changjiang Estuary, China and identified as Rhodococcus sp. C-2, the relative abundance of which was dramatically enhanced during PE-degrading microbial enrichment. The strain C-2 exhibited the degradation of LDPE films, leading to their morphological deterioration, reduced hydrophobicity and tensile strength, weight loss, as well as the formation of oxygen-containing functional groups in short-chain products. Sixteen bacterial enzymes potentially involved in LDPE degradation were screened using genomic, transcriptomic, and degradation product analyses. Thereinto, the glutathione peroxidase GPx with exposed active sites catalyzed the LDPE depolymerization with the cooperation of its dissociated superoxide anion radicals. Furthermore, an LDPE degradation model involving multiple enzymes was proposed. The present study identifies a novel PE-degrading enzyme (PEase) for polyethylene bioremediation and promotes the understanding of LDPE degradation.

Recycling of polypropylene by supercritical carbon dioxide for extraction of contaminants from beverage cups. A comparison with polyethylene terephthalate and polylactic acid

BACKGROUND

EU policies towards a circular economy address plastic packaging as one of the significant concerns and sets ambitious recycling targets. Polyolefins (POs) cannot be recycled for food contact using conventional polyethylene terephthalate (PET) recycling approaches. Thermal degradation prevents the use of high temperatures and, consequently, decontamination of POs may be insufficient when using lower temperatures. Polypropylene (PP) beverage cups were decontaminated using supercritical fluid extraction with carbon dioxide (scCO₂ ). Decontamination efficiencies (DEs) of selected markers were determined in challenge tests following European Food Safety Authority guidelines. The effects of time (10-60 min) for PET, polylactic acid (PLA), and PP and temperature (60-80 °C) for PP were studied at constant pressure. The physical properties, sensorial properties, and overall migration of treated scCO₂ PP were analysed and compared with virgin PP.

RESULTS

PP showed the highest average DE, and PET the lowest, for all the surrogates and in all time conditions. A relative increase in the DE with the increase in process time, particularly for PET and to some extent for PLA, was seen. For PP, no significant impact of time and temperature was observed under the conditions tested. The DE of volatile surrogates was higher than that of semi-volatiles. Results indicate that the scCO₂ treatment did not affect the physical and sensorial properties, nor the overall migration of PP, although it contributes to a considerable reduction in extractable n < C24 alkanes.

CONCLUSIONS

Results indicate that scCO₂ can be used to decontaminate post-consumption PP beverage cups with higher DEs than those for PET and PLA, applying mild processing conditions. © 2022 Society of Chemical Industry.

Coloration Modeling and Processing of Commodity Plastic Buttons in Supercritical Carbon Dioxide

We examined the color processing of the commodity plastic buttons made of acrylic, polyester, nylon, and casein with scCO₂. The buttons' dyeing color depth (K/S) was measured over a wide range of scCO₂ and correlated accurately with the response surface method. Moreover, we measured the solubility of C.I. Disperse Red 22 in scCO₂ to formulate a dye-sorption model for the K/S value in the color processing of the plastic buttons. Finally, the dye-sorption model for the K/S value combining the dye solubility in scCO₂ with the dye diffusion inside the buttons successfully represented the color processing of the buttons.

Characterization of refuse derived fuel samples prepared from municipal solid waste in Vellore, India

The objective of this work was to explore an alternative way to manage the non-biodegradable and non-recyclable fraction of municipal solid waste (MSW) in Vellore city, India. Refuse-derived fuel (RDF) samples with different proportions of plastic, thermocol, foam and jute straw were formulated. The RDF samples were characterized in the form of heating values (proximate and ultimate analysis), surface properties through X-ray diffraction (XRD) and thermal stability through thermogravimetric analysis (TGA). The measured higher heating values (HHV) of four RDF samples varying between 6032 and 6168 kcal/kg were effectively modelled using various empirical models for the prediction of HHV based on their elemental analysis. Higher absolute weight loss in TGA was evident in samples with jute straw while the highest rate of weight loss was noted in samples with a higher proportion of thermocol. Results from this preliminary investigation of RDF samples prepared from non-biodegradable and non-recyclable fractions of MSW warrants an exhaustive analysis of a larger pool of samples to project appropriate RDF composition for better energy recovery.

Non-intentionally added substances (NIAS) in recycled plastics

The demand for high quality recycled polymers in the European plastic industry is on the increase, likely due to the EU's Plastic Strategy intended to implement the circular economy model in this sector. The problem is that there is not enough recycled plastic in the market. In terms of volume, post-consumer plastic waste could be key to meet the current and future demand. Nevertheless, a high level of contamination originated during the product's life cycle restricts its use. The first step to change this must be identifying the undesired substances in post-consumer plastics and performing an effective risk assessment. The acquired knowledge will be fundamental for the development of innovative decontamination technologies. In this study, 134 substances including volatile and semi-volatile compounds have been identified in recycled LDPE and HDPE from domestic waste. Headspace and solvent extraction followed by GC/MS were used. The possible origin of each substance was studied. The main groups were additives, polymer and additives breakdown products, and contamination from external sources. The results suggest that recycled LDPE contains a broader number of additives and their degradation products. Some of them may cause safety concerns if reused in higher added value applications. Regarding recycled HDPE, the contaminants from the use phase are predominant creating problems such as intense odors. To reduce the number of undesired substances, it is proposed to narrow the variety of additives used in plastic manufacturing and to opt for separate waste collection systems to prevent cross-contamination with organic waste.