MATERIALS / RECYCLING PETplanet Insider Vol. 25 No. 12/24 www.petpla.net 24 Analytics and perspectives for material fl ow-adapted melt processing by Fraunhofer LBF Material and long-term properties in recyclates The plastics industry is expected to come up with viable and practically implementable solutions that will significantly increase the share of recyclates, even in technically demanding applications.The main drivers are legal requirements at national (i.e. the German Closed Substance Cycle Waste Management Act (KrWG), including its amendments) and European level (Circular Economy Action Plan and initiatives and regulations derived from it) and legal initiatives expected in the future (e.g. the EU Single Use Plastic (SUP) Directive 2019/904). The key requirement here is the mandatory use of post-consumer recyclates in the highest possible share. While post-industrial recyclates (PIR) still have a very defined composition, the variety of possible compositions (e.g. extraneous polymers, non-plastic components, additives, adhesives, etc.) and ageing conditions of post-consumer recyclates (PCR) is very high and, not least, varies (strongly) regionally and seasonally. However, such variations of input qualities inevitably have an impact on product properties. For example, the processing and mechanical properties generally deteriorate as the proportion of PCR in the compound or the resulting product increases. The ageing resistance and thus the service life of a compound is also largely determined by its composition. The condition of the material stream used, as well as the sorting, separation and processing technologies employed, decisively determine the quality of the resulting recyclate. The compounder also has various options for further optimising the quality and properties through different measures. For example, through targeted (re-)additivation (e.g. in the case of condensation polymers such as PBT, PA, etc. through stabilisers, compatibilisers or chain extenders) or through the proportionate use of virgin material. Already the identification and evaluation of suitable extrudable secondary materials (e.g. sorted and purified flakes or regrind or regranulate) is associated with high effort. The downstream steps (e.g. characterisation or quality control, homogenisation, etc.) are also elaborate and often linked to the securing of large batches. The complexity is further increased by the variables in compounding (formulation, process). Whether the target properties (especially mechanical properties, aging resistance) are achieved as a result and whether these are also reliably controlled via other variables (such as batch-to-batch variability of the input material streams) often only becomes apparent late in the development or optimisation cycle. In many cases, this is done by the trial-and-error-method. Interdependencies between packaging, composition, compounding and application properties The joint project aims to develop and communicate extensive knowledge on the dependencies between the form of compounding (e.g. flakes, regrind, granules), the chemical composition of the input materials, influencing variables during compounding (e.g. proportion and state of recyclate, re-additives) and the resulting application properties, especially with regard to mechanical behavior and aging resistance. This is done using the example of selected condensation polymers used in technical applications, such as PA, PET, PBT or PC. The project is also intended to serve as an interdisciplinary platform of players from the entire value chain in order to develop targeted approaches to solutions for the technical problems arising around the topic of the circular economy for technical plastics. Focus & approach In the project, basic information on available (extrudable post-industrial or post-consumer) recyclates (e.g. granules, flakes, regrind, etc.) for the selected target polymers (polyamides, polyesters) will first be collected and evaluated. This includes information on availability, quality descriptions of the recyclates and sources of supply (if available). Furthermore, the main measures described in the state of the art and science (open and patent literature) for quality improvement at the compounding level (e.g. compatibilisation, chain extenders, re-stabilisation, etc.) are summarised by way of example for selected recyclates. The first project phase is rounded off by an overview of relevant and currently available additives or additive packages for optimising the mechanical properties and ageing behaviour in engineering plastics based on recyclates. The main influencing factors from the state of the art with regard to the dependencies of the mechanical properties and the ageing behaviour on the input characteristics of the recyclates are compiled and evaluated. Material and condition-specific factors are systematically considered, such as the type of polymer, the qualSamples for the analysis of additive packages to enhance the long-term properties of recyclates (Photo: Fraunhofer LBF, Raapke) MATERIALS / RECYCLING
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