Natural fiber composites have gained increasing attention due to sustainability considerations. One often neglected aspect is the potential for the mechanical recycling of such materials. In this work, we compounded injection-molded polypropylene (PP) and polylactic acid (PLA) short cellulose fiber composites with fiber shares up to 40 percent by weight. Both matrix materials were reinforced by the addition of the fibers. We investigated a trifold full recycling process, where we subjected the materials produced in the first place to compounding, injection molding, testing, and shredding, and then repeated the process. Although the materials’ properties assigned to degradation were found to decrease with progressive recycling, attractive mechanical properties could be preserved even after the third reprocessing cycle.

Silicone rubber is a widely used elastomer, with a broad range of applications across many industries. Injection moldable liquid silicone rubbers (LSR) are one type of silicone with high production quantities, and hence production waste generated. Nevertheless, there are few efforts to recycle silicones and LSRs in particular. Reported approaches mainly focus on chemical recycling, whereas mechanical recycling, which is well established for thermoplastic materials, is completely neglected in LSR production and only scarcely published, even though mechanical recycling, which, for example, encompasses the shredding and reintroduction of sprues and runners in the injection molding production process, is the higher value reutilization compared to chemical recycling, where the materials need to be further broken down even to a molecular level. In our study, we investigated a mechanical recycling approach of LSRs by introducing ground particles as filler to silicone matrix material. We examined the influence of Shore A hardness, degree of shredding, and amount of filler used. LSRs with Shore A hardnesses of 30, 50, and 70 were used. The particle sizes were varied from 1.0 down to 0.2 mm, and the amount of filler added to LSR was between 10 and 30 wt%. Our results reveal good mechanical properties, differing from the original properties only to a small extent, and no consistent trends regarding the influence of the particle size were found. Even if there are still obstacles to overcome in industrial processes, our study could encourage consideration of mechanical recycling of production scraps also for silicones as a way to contribute to waste reduction.

Plastic recyclates can be contaminated with a variety of impurities due to their previous life, which cannot always be perfectly separated in recycling pretreatment steps. Hence melt filtration is an important step in reprocessing plastic recyclates to achieve material of sufficient purity, but it also leads to more stress on the material due to higher pressures and longer processing times. In our study, we investigated the influence of typical particulate impurities as may occur in recyclate on the mechanical and rheological properties of ABS. Even low amounts of contaminations lowered the key properties. Melt filtration of post‐consumer ABS recyclate with different mesh size melt screens showed little improvement of mechanical properties, but longer idle times and loss of material. Damage to the material caused by finer filtration could be shown by thermal measurements.Highlights: Determination of properties of ABS contaminated with 0.5–2.0 wt.% of selected impurities (wood and rubber particles). Melt filtration of post‐consumer ABS recyclate with different melt screens. Investigation of process and properties of filtered ABS recyclate.

Continuous-fibre-reinforced thermoplastics are attractive materials for industries to cut down on weight in structural components. Recycling these parts or trims generated during production is difficult due to the reduced properties in materials intended for high-performance applications. Our study investigates the recyclability of short-fibre-reinforced compounds made from shredded organosheets. The fibre share was varied by the addition of virgin polypropylene, and three recycling rounds via a reduced injection-moulding process and a full thermomechanical recycling process including a compounding step were compared. Organosheet cuttings were found to be able to be applied as a short-glass-fibre source for the production of composites with varying fibre shares. Up to 14,000 MPa of elastic modulus and 80 MPa of tensile strength could be achieved at a fibre content of 45 vol%. Fibre length was reduced with progressive processing, less so for lower fibre shares, and in the reduced process without the shear and stress of the compounding step. Fibres from organosheets might be present in bundles and disperse in the matrix with progressive processing, which is particularly the case without compounding processes and can also influence the mechanical properties.

Liquid silicone rubbers (LSR) are thermoset elastomers, with a wide range of use across many industries and applications. Their crosslinked structure made them rather unattractive for material recycling up to now. In previous studies, mechanical recycling via the introduction of ground LSR particles was shown to be generally possible, but it has not yet been investigated what happens when the recycled LSR is recycled over again. In our study we investigated four consecutive mechanical recycling cycles of liquid silicone rubbers by adding 10, 20, and 30 wt% recycled content repeatedly. Mechanical tests showed that such a reprocessing of LSR is possible without significant loss in material performance. Thermal degradation tests revealed that the addition of ground particles has no negative effects on thermal stability. The properties of the recycled silicones were almost independent of the recycled content and the recycling round.

Increasing amounts of textile waste require rapid implementation of novel recycling technologies. Biocatalytic degradation via enzymatic hydrolysis can be used to separate blends, which are otherwise inaccessible. However, the complex nature of the substrate and narrow operating window of the reaction necessitates process optimization but also complicates computational approaches. The reaction is performed in aqueous suspension at ambient pressure and temperatures well below boiling. Due to the gentle process conditions, preliminary assessment of ideal stirrer geometries can be performed in water under ambient conditions, using stirrers produced from commodity plastics using material extrusion-based 3D-printing at both bench (2 L) and semi-pilot (30 L) scale. Eight geometries were assessed using suspension activity (via cloud height), mixing energy consumption, and mixing time assessment via tracer addition at the bench scale. Four of these geometries were chosen for scale-up in a 30 L conical vessel. While large, especially close-clearance mixing equipment performed well at both sizes, an increase in performance of the pitched-blade turbine was observed at 30 L. This highlights the necessity of experimental scaleup procedure as well as optimized stirrer geometries for enzymatic hydrolysis.