This study demonstrates an open-loop recycling process of a specific post-consumer plastic waste stream. The targeted input waste material was defined as high-density polyethylene beverage bottle caps. Two methods of waste collection, informal and formal, were employed. Thereafter, materials were hand-sorted, shredded, regranulated, and then injection-molded into a flying disc (i.e., frisbee) as a pilot product. To observe the potential changes in the material throughout the entire recycling process, eight different test methods including melt mass-flow rate (MFR), differential scanning calorimetry (DSC), and mechanical tests were carried out on the various material states. The study showed that the informal collection led to a relatively higher purity in the input stream, which also appeared to have a 23% lower MFR value compared to that of the formally collected materials. The DSC measurements revealed a cross-contamination by polypropylene, which clearly affected the properties of all investigated materials. The cross-contamination led to a slightly higher tensile modulus in the recyclate, while the Charpy notched impact strength declined after processing by approximately 15% and 8% compared to those of the informal and formal input materials, respectively. All materials and the processing data were documented and stored online as a practical implementation of a digital product passport as a potential digital traceability tool. Furthermore, the suitability of the resulting recyclate to be used in transport packaging applications was also investigated. It was found that a direct replacement of virgin materials for this specific application is not possible without proper material modification.

Reintroducing recycled plastics into production processes can lead to irreversible degradation and changes in their properties, thereby limiting their recycling potential to a finite number of loops. This study investigates the impact of process-induced degradation resulting from multiple reprocessing cycles on specific material properties and aims to establish structure–property relationships. Four different polyolefins, including two polypropylenes, high-density polyethylene, and low-density polyethylene, were selected for the study. The materials underwent extrusion, pelletizing, injection molding, and milling before being reintroduced into the reprocessing cycle. This sequence of processing steps was repeated six times on each material. Various characterization techniques, including high-temperature gel permeation chromatography, melt mass flow rate, parallel-plate rheology, differential scanning calorimetry, gas chromatography–mass spectrometry, and optical defect control system, were performed to evaluate the molecular structure, rheological behavior, thermal stability, and the resulting contaminants and defects after each reprocessing step. The reprocessing of polypropylene resulted in a gradual decrease in the average molecular weights accompanied by a shift to lower viscosities and higher melt mass flow rates, whereas the polyethylene grades showed the opposite trend with a less pronounced effect in high-density polyethylene. The volatile organic compounds rose in polypropylene and sank in polyethylene after reprocessing. Additionally, all four materials exhibited an increase in degradation-related defects based on optical defect analysis. Graphical abstract

Given the rapid development of plastics recycling in recent years, the need for guidelines for sampling and material characterization is steadily emerging. However, there still exists a considerable scarcity of methods that enable proper material data acquisition. This paper consists of two parts. The first part provides a critical review of the available sampling techniques that can be utilized in the field of plastics recycling. Several sampling studies were covered in the review alongside the prominent standardization institutions. It was found that neither the literature nor the standards provide a comprehensive practice that considers the distinctive characteristics of plastic waste and applies it to different situations along the value chain. In the second part, a proposal of a sampling plan for pretreated rigid plastic waste is conceptualized based on selected information from the reviewed methods. Two variants of the proposed plan were evaluated based on the flake size distribution and the apparent density of four different pretreated polyolefin (PO) waste materials. The results of the study showed that combining stratified random sampling with composite sampling yields a good sampling technique for rigid PO waste. Moreover, the analysis of a composite sample adequately conveys the true material properties of a sublot or lot.

To assess the potential use of polyamide (PA) for solar-thermal systems applications, the effect of water with varying chlorine content on the fatigue crack growth (FCG) resistance of two PA formulations differing in their stabilizer packages was investigated at 80 °C. A commercial PA containing 30 wt % glass fibers and a standard stabilization package (PA-0) was used as the reference material. For the other formulation, the reference material PA-0 was compounded with two additional stabilizers (PA-S1). Keeping the specimen geometry and initial loading conditions the same, the total number of cycles to ultimate specimen failure was found to be reduced with an increase in chlorine content for both materials. As to the effect of the chlorine content on crack growth kinetics, the most pronounced effect in enhancing the crack growth rates or decreasing the FCG resistance was determined between 0 ppm and 1 ppm chlorine content. When comparing the relative change of FCG resistance in chlorinated water (10 ppm) to the FCG resistance in non-chlorinated water (0 ppm), the additional stabilization in the material PA-S1 appears beneficial over the stabilization in the reference material PA-0.

This study provides key insights into the extrusion of a post‐industrial feedstock primarily composed of polypropylene (PP) and reveals its influence on the property profile of the recyclate. The objective of this study was to gain a fundamental understanding of complex process‐property relationships. Therefore, a two‐part experimental design was established. The first part aimed to analyze the feedstock variability by investigating key material properties of recyclates produced under constant processing conditions. The second part aimed to systematically evaluate the effect of the screw speed, filtration setup, and degassing setup on the properties of the recyclates. An industrial‐scale recycling extrusion line was used. The material evaluation included melt mass‐flow rate (MFR), ash content, oxidation induction temperature, tensile and impact properties, degassing performance, and residual volatile organic compounds (VOCs). Higher melt temperatures led to chain scission of the PP fraction, resulting in increased MFR and higher material stiffness. Additionally, a finer filtration positively contributed to the enhanced material stiffness. Furthermore, the mechanical properties were also influenced by the levels of inorganic fillers in the material composition of the feedstock. Finally, the filtration setup had a greater impact on degassing performance and residual VOC levels than the degassing setup and screw speed.

Mechanical recycling has an important role in the recycling of plastic waste. Closed-loop recycling solutions are advantageous to produce high-quality recyclate