ANDREA CABANES

Cabanes, A.; Valdés, F.J.; Fullana, A.
Plastic demand is continuously growing and, with it, the amount of plastic waste. The packaging industry is by far the largest source of single-use plastic products that, after use, end up in landfills and oceans. Mechanical recycling is the solution most widely implemented in the global industry and its effectiveness and reliability have been demonstrated for processing post-industrial plastic scrap. The recycling of post-consumer plastic waste, however, requires an upgrade in the current technology to achieve complete decontamination and removal of malodorous substances embedded in the polymer. This review explores the state-of-the-art technology currently employed in the mechanical recycling of plastic waste, focusing on the progress made for the removal of volatile organic compounds emitted from recycled materials. Followed by a review of the analytical techniques that have been applied for the identification of volatile organic compounds, including, in particular, the techniques used for the identification of odor-active substances. Finally, this review gathers from literature all the volatile organic compounds and odor-active substances identified in virgin and recycled polymers, aiming to evaluate whether there is a notable difference between them based on the chemical structure of the emitted VOCs. As a result, 437 volatiles were gathered, which show the difference between post-consumer recycled plastics and the other plastic waste sources. A larger number of volatile organic compounds, especially flavor and fragrances-based substances as well as oxygenates, appear in post-consumer plastic waste compared to virgin and post-industrial plastic scrap.

Horodytska, O.; Cabanes, A.; Fullana, A.
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.

Cabanes, A., Strangl, M., Ortner, E., Fullana, A., Buettner, A.
The establishment of recycling systems aiming at high-quality recyclates from post-consumer plastic waste are essential to avoid the waste of resources. One main impediment for introducing recyclates into the market is their unwanted odor. For this reason, this study aimed at determining if the collection strategy affects the odor profile of post-consumer LDPE bags. Furthermore, the effect of hot water washing, inspired by the conventional mechanical recycling procedure, on the odor of post-consumer LDPE bags was screened. More than 60 odorants were detected in LDPE bags collected in a separate plastic fraction as well as in LDPE bags from the non-separated collection by means of gas chromatography-olfactometry, and 37 of them were unequivocally identified using two-dimensional gas chromatography-mass spectrometry/olfactometry. The sensory results revealed that the type of collection affects the overall odor intensity, the hedonic tone of the odor and the odor profile. Namely, cheesy and fecal smelling odorants were predominant in the waste that had not been separated at source, whereas odorants with earthy and moldy smells showed mostly higher intensity ratings in the waste separated at source. Short chain carboxylic acids, likely originating from microbial spoilage of organic waste, were found with higher dilution factors in the mixed fraction, and could, accordingly, contribute to the observed differences. Additionally, we could show that the hot washing procedure, applied to the LDPE sample from the separate collection system, significantly reduced the overall odor intensity from 8 to 6.3 (0–10 scale). However, the washed waste still showed high smell intensity ratings.

A. Cabanes, A. Fullana
While the annual European demand for polyolefins is 25 million tonnes, only 3 million tonnes of recycled polyolefins find their place in the market, despite collecting 15 million tonnes of post-consumer polyolefins every year. Brand owners of care products are showing their interest in using post-consumer recycled plastics for their packaging. However, there is a general concern in using these materials, as recycled polymers can contain unwanted substances that may expose the consumer to health risks or make the packaging unattractive. Accordingly, the presence of these contaminants narrows the market opportunity of recycled plastics to applications with low-quality requirements and in which the product is not in direct contact with the consumer.

Though mechanical recycling is the most widespread solution presents limitations in terms of decontamination, as only superficial substances are removed. Thereby, the volatile organic compounds (VOCs) migrated to the polymer matrix remain inside. Consequently, there is a need to find a solution to purify recycled plastics and increase their market share.

This study focuses on removing VOCs from post-consumer recycled HDPE through two innovative methods applied for the first time in this field, steam stripping and polyethylene glycol (PEG) extraction. The methodology implemented to analyze the volatile organic compounds in HDPE was HS-SPME-GC/MS. Both methods showed a decrease above 70 % in the VOCs content compared to extrusion-degassing. Moreover, these were compared to hot air stripping, a new technology developed at an industrial scale for the removal of VOCs. As a result, steam stripping improved efficiency in reducing the overall VOCs compared to hot air stripping. The PEG extraction method lowered the volatile polar compounds further than using hot air stripping. Additionally, none of these technologies modified the HDPE melting flow index.