Mechanical recycling of printed flexible plastic packaging: The role of binders and pigments.

Low-density polyethylene (LDPE), extensively employed in flexible plastic packaging, often undergoes printing with inks. However, during the mechanical recycling of post-consumer waste, these inks act as contaminants, subsequently compromising the quality and usability of recycled material. To understand better exactly which ink components cause which effects, this study comprehensively assesses the thermal behavior of three organic pigments and two commonly utilised binders, correlated with the impact on the mechanical recycling of LDPE-based flexible plastic packaging. In this regard, the study focuses on four pivotal factors: processability, mechanical properties, aesthetic attributes, and volatile organic compound profiles. The results indicate that nitrocellulose, used as a binder, degrades during reprocessing, resulting in film discoloration and the emission of potentially odorous compounds. Conversely, pigments are found to be dispersed within droplets of polyurethane binder in LDPE recyclates, whilst reprocessing printed samples detrimentally affects film properties, notably dart drop impact resistance, strain at break, and the number of inclusions. Additionally, it is shown that both inks comprise components that emit volatile compounds during reprocessing: non-thermally stable components, nitrocellulose and pigment yellow PY13, as well as low-molecular weight molecules from polyurethane and by-products from wax, plasticisers, and additives.

Technical and market substitutability of recycled materials: Calculating the environmental benefits of mechanical and chemical recycling of plastic packaging waste.

Most plastics are today mechanically recycled (MR), whereas chemical recycling (CR) is an emerging technology. Substitutability of virgin material is vital for their environmental performance assessed through life cycle assessment (LCA). MR faces the reduction in the material's technical quality but also the potential market because legal safety requirements currently eliminate applications such as food packaging. This study presents a data-driven method for quantifying the overall substitutability (OS), composed of technical (TS) and market substitutability (MS). First, this is illustrated for six non-food contact material (non-FCM) applications and three hypothetical future FCM applications from mechanical recyclates, using mechanical property and market data. Then, OS results are used in a comparative LCA of MR and thermochemical recycling (TCR) of several plastic waste fractions in Belgium. For mechanical recyclates, TS results for the studied non-FCM and FCM applications were comparable, but OS results varied between 0.35 and 0.79 for non-FCM applications and between 0.78 and 1 for FCM applications, reflecting the lower MS results for the current situation. Out of nine application scenarios, MR obtained a worse resource consumption and terrestrial acidification impact than CR in six scenarios. MR maintained the lowest global warming impact for all scenarios. This study contributes to an improved understanding of the environmental benefits of MR and TCR. Inclusion of other criteria (e.g. processability, colour, odour) in the quantification of the overall substitutability for MR products should be further investigated, as well as the environmental performance of TCR at industrial scale.

A step forward in quantifying the substitutability of secondary materials in waste management life cycle assessment studies.

Life Cycle Assessment (LCA) is a widespread tool used to guide decision-makers towards optimal strategic choices for sustainable growth. A key aspect of LCA studies of waste management systems where recycling activities are present is to account for resource recovery and the related substitution effects. Although multiple scientific papers assume a 1:1 substitution ratio between similar materials/products, this is often incorrect as the actual ratio is likely to vary. The focus of this paper is on the calculation of the substitutability coefficient for secondary materials based on technical characteristics. A state of the art literature review showed that many different calculation procedures were applied, which led to a wide variety of substitutability coefficients (sometimes provided under different terminology). In this perspective, the objective of this paper is to provide guidelines on the procedure to be followed to calculate the substitutability coefficient for secondary materials, based on technical characteristics. These guidelines are then applied to two waste management case studies, one dealing with bottom ashes from incineration and the other with plastic waste. In total, sixteen technical substitutability coefficients are given for ten secondary materials, based on state of the art and presented case studies. The paper thus represents a step forward in quantifying the substitutability of secondary materials in waste management LCA studies. The guidelines presented may allow other case studies to enrich the list of coefficients, useful for all LCA practitioners in a harmonized way allowing a more correct evaluation of the environmental impacts associated with recycling activities.