Polymers are central materials for our present and future society which have enabled us to improve the quality of all aspects of our daily life. However, our lifestyle also generates serious problems due to the ways in which we use polymers. Most polymers are discarded after use, rarely recycled, and end up in landfills, rivers, and oceans. This fate is a typical example of the current linear and fossil-based produce-use-discard value chain that causes enormous environmental pollution. Therefore, a fundamental transition is required in the field of polymeric materials from synthesis out of fossil-based feedstock and one time use to continuous re-use of polymeric products. The focus of our research is on existing polymers as well as on designing novel polymeric structures more amenable to recycling. The key is incorporation of suitable degradable functional groups or smart monomers into the polymers in their design stage. Our approach entails the use of various imine, acetal, triazine and hexahydro-s-triazine derivatives as cleavable groups within the polymer network. [1-5] Most importantly, we demonstrate chemical depolymerization, the subsequent separation and reuse of recovered building blocks, and closed-loop recycling or upcycling of novel polymers. Our studies are expected to contribute to the development of a circular plastic economy and drive research on environmentally friendly materials forward.

The global waste rubber stream is substantial, with tires comprising the largest fraction at 1 billion objects annually. Built for durability, tires feature a metal and fiber skeleton encased in vulcanized rubber with carbon black and other additives. While this ensures longevity, it also complicates recycling. Mechanical recycling is mainly limited to whole-tire reuse or crumbed filler for asphalt [1] and, until recently, sports fields. In chemical recycling, the industry favors pyrolysis for naphtha feedstock and recovered carbon black (rCB), now gaining interest for reuse in tire formulations [2].
However, we recently expanded the opportunities. We extended the lifespan of crumbed rubber fillers by developing (recycled) polyethylene and polyurethane coatings that reduce heavy metal leaching, while enabling tunable elasticity [3]. Alternatively, we tailored ozonolysis as a sustainable chemical recycling method, developing a patented work-up process [4]. This heterogeneous three-phase reaction efficiently converts tire rubbers into platform chemicals such as levulinic and succinic acid, achieving high yields (55 m% of the rubber), as shown in the figure. The remaining fillers, recovered separately, contain 16 m% ash—comparable to pyrolysis rCB but free from heavy oils and PAHs. We further studied reaction progression in different environments, solvents, and temperatures to assess the impact of solubility and solvent swelling on the ozonolysis reaction rate.
It is clear that the race for the most optimal uses of this well-defined feedstock has just begun, with several hybrid technologies to come, as discussed in this work.

Polymers play a crucial role in our modern life as no other material exists that is so versatile, moldable, and lightweight. Consequently, the demand for polymers will continue to grow with the human population, modernization and technological developments. Although polymers were never designed to be recycled, it is clear that a linear polymers economy is no longer sustainable. Of all polymers, polyolefins have the lowest life-cycle environmental impact and even outperform bio-based polymers. [1] However, polyolefins are chemically inert and reveal a low surface energy. Combining their excellent mechanical properties with the ability to adhere to other products or create nanostructured materials would widen the application window of polyolefins even more. [2]
During the presentation, of our personal account in the field of functionalized polyolefin synthesis and their application development will be presented. As the use of randomly functionalized polypropylenes is rather underdeveloped, as compared to the corresponding randomly functionalized polyethylenes, we focused on potential applications of the former material. Atactic or low crystalline hydroxyl and carboxylic acid-functionalized propylene-based co- and terpolymers form elastomers with interesting properties that can be influenced by enhancing the hydrogen-bonding within the system or by creating ionomers. Thus, the polar functionalities cluster together in domains that can host small polar molecules like for example a pH indicator affording useful sensors. The functionalized polyolefins can also be used as precursors for amphiphilic graft copolymers, undergoing self-assembly, and therefore being suitable for nanoporous membranes preparation as well as compatibilizers in various polymer blends. [3, 4]

Mussels are a sustainable and affordable protein source that naturally filters nutrients from seawater [1]. However, the accidental dispersion of plastic “socks” used for their farming on the seabed and along beaches represents a significant environmental problem. Recovery and recycling of polypropylene (PP) may represent an adequate solution for the management of plastic waste generated by mussel farming. Due to the presence on the surface of incrustation of salty biological elements and fouling, currently, a European Waste Code (CER 020104) of special waste is associated with the mussel socks: their correct disposal involves significant expenses (0.25–0.30 EUR/kg). The EU-funded LIFE MUSCLES project was established to develop a new treatment method for the recovery of polypropylene from mussel nets [2]. Through experiments performed on a laboratory scale, it was verified that it is possible to effectively remove biofilm (98%) from the polymeric material using pressurized water (25-30 bar). The spectroscopic, thermal, morphological, and mechanical characterization of the socks shredded and washed for 30 minutes demonstrated that the treatments undergone by the polymer had a non-significant impact on the PP physical properties, thus allowing its reuse in the same supply chain. In particular, the regenerated PP had an elastic modulus value (0.697±0.058 GPa) comparable to that of pristine PP (0.758±0.069 GPa). Therefore, the Life MUSCLES [3] project adopts a circular economy model, emphasizing material recycling through a mobile pilot plant capable of processing 300 kg of mussel nets daily, reducing costs for new nets and minimizing environmental impact.

We report the influence of loaded and unloaded silica particles on the ultimate behavior of polymeric blends based on 30 % mass fraction of virgin and 70 % mass fraction recycled polypropylene, (PP). The final recycled materials include a certain amount of polyethylene, (PE) because it was not fully separated from the PP in recyclates. The silica composites show greater thermal stability than the neat PP blends. A clear separation of crystallization processes of the two components, PP and PE, is noticed when cooling was performed at 2 °C/min. Moreover, a constant location is observed in the crystallization peak for the PE component with the silica content, while that for the PP shows a significant nucleating effect compared with the neat blend. This nucleation effect of the silica is also rather evident from the rheological results. Polarized optical microscopy (POM) images collected during crystallization experiments also revealed the effect of the particle amount on the crystal orientation under shear flow. The application shear flow also affects the nucleating ability, indicating that there is an obvious flow-induced crystallization (FIC) which depends on both the kind of silica and on its composition. Thus, a change from a quasi-simple to a complex rheological behavior is also deduced from the values of the frequency of crossover between the storage and loss moduli. Oxidation induction time (OIT) values show the great improvement of thermal stability of the recycled polypropylene resins by the incorporation of increasing contents of silicas at the same antioxidant concentration.

With increasing demand for sustainable packaging, post-consumer resin (PCR) high-density polyethylene (HDPE) presents challenges due to its variable performance compared to virgin HDPE. This study addresses these challenges by extensively characterising PCR HDPE resins to identify structural and performance features critical for applications in sustainable bottle packaging. Using a dataset of 24 HDPE resins (20 PCR and 4 virgin controls), our approach employs a comprehensive suite of analytical methods—including Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, rheology, colour analysis, and mechanical testing—to develop a feature-rich dataset. Data science techniques such as multivariate analysis are applied to reveal the relationships that underpin PCR quality, allowing for a detailed comparison to virgin HDPE. [1]

This research provides a robust pipeline for assessing and predicting the suitability of new PCRs as substitutes for virgin plastic in packaging. By identifying structure-property relationships, it highlights factors influencing mechanical and aesthetic properties in PCR HDPE, contributing to the advancement of circular plastic use in packaging. These insights support industry efforts to achieve sustainable material cycles by selecting and enhancing PCRs that meet the demands of high-quality applications in a circular economy framework.