Application of chemometric tools in the QSAR development of VOC removal in plastic waste recycling.

Deodorization and, in a broader sense, the removal of volatile organic compounds (VOCs) from plastic waste have become increasingly important in the field of plastic recycling, and various new decontamination techniques have been developed. Both in research and industrial practice, the selection of VOCs has been random or unsubstantiated, making it difficult to compare studies and assess decontamination processes objectively. Thus, this study proposes the use of Statistical Molecular Design (SMD) and Quantitative Structure - Activity Relationship (QSAR) as chemometric tools for the selection of representative VOCs, based on physicochemical properties. Various algorithms are used for SMD; hence, several frequently used D-Optimal Onion Design (DOOD) and Space-Filling (SF) algorithms were assessed. Hereby, it was validated that DOOD, by dividing the layers based on the equal-distance approach without so-called 'Adjacent Layer Bias', results in the most representative selection of VOCs. QSAR models that describe VOC removal by water-based washing of plastic waste as a function of molecular weight, polarizability, dipole moment and Hansen Solubility Parameters Distance were successfully established. An adjusted-R2 value of 0.77 ± 0.09 and a mean absolute error of 24.5 ± 4 % was obtained. Consequently, by measuring a representative selection of VOCs compiled using SMD, the removal of other unanalyzed VOCs was predicted on the basis of the QSAR. Another advantage of the proposed chemometric selection procedure is its flexibility. SMD allows to extend or modify the considered dataset according to the available analytical techniques, and to adjust the considered physicochemical properties according to the intended process.

Tracing the origin of VOCs in post-consumer plastic film bales.

Volatile organic compounds (VOCs), including odors, are still a key issue in plastic recycling, especially in case of flexible packaging. Therefore, this study presents a detailed qualitative and quantitative VOC analysis by applying gas chromatography on 17 categories of flexible plastic packaging that are manually sorted from bales of post-consumer flexible packaging (e.g., beverage shrink wrap, packaging for frozen food, packaging for dairy products, etc.). A total of 203 VOCs are identified on packaging used for food products, while only 142 VOCs are identified on packaging used for non-food products. Especially, more oxygenated compounds (e.g., fatty acids, esters, aldehydes) are identified on food packaging. With more than 65 VOCs, the highest number of VOCs is identified on packaging used for chilled convenience food and ready meals. The total concentration of 21 selected VOCs was also higher on packaging used for food products (totally 9187 µg/kg plastic) compared to packaging used for non-food packaging (totally 3741 µg/kg plastic). Hence, advanced sorting of household plastic packaging waste, e.g., via tracer-based sorting or watermarking, could open the door towards sorting on other properties than polymer type, such as mono- versus multi-material packaging, food versus non-food packaging or even their VOC profile, which might allow for tailoring washing procedures. Potential scenarios showed that sorting the categories with the lowest VOC load, which corresponds to half of the total mass of flexible packaging, could result in a VOC reduction of 56%. By producing less contaminated plastic film fractions and by tailoring washing processes recycled plastics can ultimately be used in a broader market segment.

Understanding the complexity of deinking plastic waste: An assessment of the efficiency of different treatments to remove ink resins from printed plastic film.

Plastic packaging is usually heavily printed with inks to provide functional benefits. However, the presence of inks strongly impedes the closed-loop recycling of plastic films. Various media have already been studied for the deinking of plastic films, but there is little scientific insight into the effectiveness of different deinking techniques. Therefore, this study aims to obtain a systematic understanding by measuring the liquefaction and maximum solubility of 14 chemically different polymer resins in seven different media typically used in plastic deinking, such as acetone, ethyl acetate, sodium hydroxide solution, cetyltrimethylammonium bromide solution, formic acid, sulfuric acid, and N,N-dimethylcyclohexylamine. Our findings show that acid-based media are able to remove a broader range of polymer resins. Organic solvents are particularly effective against acrylics and related polymer resins. The deinking efficiency tests on pure resins are also confirmed by deinking four printed plastic films containing different classes of polymer resins. A basic cost and environmental impact analysis is given to evaluate scale-up potential of the deinking medium.