NMR relaxation reveals modifications in rubber phase dynamics during long-term degradation of high-impact polystyrene (HIPS)

Molecular Pathways for Polymer Degradation during Conventional Processing, Additive Manufacturing, and Mechanical Recycling

The assessment of the extent of degradation of polymer molecules during processing via conventional (e.g., extrusion and injection molding) and emerging (e.g., additive manufacturing; AM) techniques is important for both the final polymer material performance with respect to technical specifications and the material circularity. In this contribution, the most relevant (thermal, thermo-mechanical, thermal-oxidative, hydrolysis) degradation mechanisms of polymer materials during processing are discussed, addressing conventional extrusion-based manufacturing, including mechanical recycling, and AM. An overview is given of the most important experimental characterization techniques, and it is explained how these can be connected with modeling tools. Case studies are incorporated, dealing with polyesters, styrene-based materials, and polyolefins, as well as the typical AM polymers. Guidelines are formulated in view of a better molecular scale driven degradation control.

Valorization of Recycled Tire Rubber for 3D Printing of ABS- and TPO-Based Composites

Vulcanized and devulcanized ground tire rubber microparticles have been used as a minor phase in acrylonitrile butadiene styrene copolymer (ABS) and thermoplastic polyolefins (TPO) for the development of materials with desired functionalities by 3D printing. These polymers have been selected because they (i) present part of the plastic waste generated by the automotive industry and (ii) have totally different properties (ABS for its stiffness and robustness and TPO for its softness and ductility). The study aims to improve the circular economy of the automotive industry by proposing a promising route for recycling the generated tire rubber waste. In this respect, emergent technology for plastic processing such as 3D printing is used, as part of the additive manufacturing technologies for the prolongated end of life of recycled plastics originated from automotive waste such as ABS and TPO. The obtained results revealed that (i) the composites are suitable for successful filament production with desired composition and diameter required for successful 3D printing by fused deposition modeling, and that (ii) the optimization of the composition of the blends allows the production of materials with interesting mechanical performances. Indeed, some of the investigated ABS-recycled rubber tire blends exhibit high impact properties as TPO-based composites do, which in addition exhibits elongation at break higher than 500% and good compression properties, accompanied with good shape recovery ratio after compression.

MIR spectral characterization of plastic to enable discrimination in an industrial recycling context: III. Anticipating impacts of ageing on identification

Ageing of polymers entails important structural changes and degrades their functional properties, particularly their aspect. Since sorting is a primordial step in recycling to achieve acceptable mechanical properties, the use of promising technologies such as MIR-HSI (Mid-Infrared Hyperspectral Imagery), which could overcome black plastics sorting issue, has to take into account the influence of ageing on identification. As ageing strongly impacts spectra, it can create confusion between materials, especially in an automatized scheme. Based on laboratory FTIR-ATR (Fourier-Transform Infrared Attenuated Total Reflection), this work investigates spectral evolutions of natural and accelerated photodegradation of Waste of Electric and Electrical Equipment plastics (WEEE) as PE, PP, HIPS, ABS and PC to help identifying a polymer despite its ageing degree. Oxidation marks were described and retrieved within a stock of about one hundred of real waste samples, then differentiated from other sources of spectral alteration as formulation. Laboratory ageing data were found to be consistent and often more extreme than real waste samples values. Generally, styrenics showed stronger spectral alteration than polyolefins despite their respective aspects. No significant spectral alteration of PC was obtained here or observed in the waste stock. As an important oxidation marker, the carbonyl peak was also found to often enable fast identification through its wavenumber. If well taken in account, ageing should not induce confusion with other polymers, even formulated, as characteristic signals are different. Finally, the different industrial sub-ranges within MIR are not affected at the same degree, possibly influencing a technological choice for industrial sorting.