Investigation of Recycled Expanded Polyamide Beads through Artificial Ageing and Mechanical Recycling as a Proof of Concept for Circular Economy.

Car manufacturers are currently challenged with increasing the sustainability of their products and production to comply with sustainability requirements and legislation. One way to enhance product sustainability is by reducing the carbon footprint of fossil-based plastic parts. Particle foams are a promising solution to achieve the goal of using lightweight parts with minimal material input. Ongoing developments involve the use of expanded particle foam beads made from engineering plastics such as polyamide (EPA). To achieve this, a simulated life cycle was carried out on virgin EPA, including mechanical recycling. The virgin material was processed into specimens using a steam-free method. One series was artificially aged to replicate automotive life cycle stresses, while the other series was not. The mechanical recycling and re-foaming of the minipellets were then carried out, resulting in an EPA particle foam with 100% recycled content. Finally, the thermal and chemical material properties were comparatively analysed. The study shows that the recycled EPA beads underwent polymer degradation during the simulated life cycle, as evidenced by their material properties. For instance, the recycled beads showed a more heterogeneous molecular weight distribution (an increase in PDI from two to three), contained carbonyl groups, and exhibited an increase in the degree of crystallization from approximately 24% to 36%.

Comparison of Mechanical Properties of Steam-Free and Steam-Based Specimens Made of Expanded Polypropylene Beads.

Reducing the CO2 emissions of plastic parts is crucial in terms of sustainable product and process designs. Approaches include the use of recycled materials and reducing the energy demands of processes through more efficient technologies. In this context, this study shows the potential of the steam-free processing of particle foam beads into thin-walled moulded parts. Expanded polypropylene (EPP) particle foam beads have been processed in both a steam-free and steam-based process. For this purpose, specimens with different part densities and thicknesses were produced, the mechanical properties were investigated, and the surface quality was discussed. Specimens made of EPP with a part thickness of 5 to 20 mm and part densities of 60 to 185 g/L were produced steam-free. Lower part thicknesses and higher densities increase the mechanical properties. As the density increased, the homogeneity of the surfaces of the steam-free specimens also increased. In comparison, specimens with a thickness of 10 mm and part densities of 35 to 90 g/L were produced on a steam-based process. The results of the mechanical test were compared with those of the steam-free specimens. The steam-based specimens showed higher mechanical properties for the same density.

Influence Analysis of Modified Polymers as a Marking Agent for Material Tracing during Cyclic Injection Molding.

Injection molding (IM) is already an established technology for manufacturing polymer products. However, in the course of the increased use of recyclates for economic and ecological reasons, its application capability has been confronted with new requirements for reliability and reproducibility. In addition, the IM process is confronted with regulations regarding a verifiable recycling degree in polymers. With regard to the material identification and storage of manufacturer-, process- or product-related data in polymers, the implementation of a material-inherent marking technology forms a potential answer. The IM process combined with modified polymers (MP) as a marking technology turns out to be a feasible approach to manufacturing reproducibly and offers a high quality based on increased process awareness and fulfilling the required traceability. Therefore, this work focuses on the trial evaluation of MP within the IM process. The influence of MP on the material process behavior and mechanical and thermal component properties, as well as the influence of the IM process and recycling on MP traceability, are investigated. No discernible influences of MP on the investigated properties could be identified, and the traceability from the initial material to a recyclate could be confirmed. MP is suitable for monitoring the aging state of polymers in IM.

Investigations for Material Tracing in Selective Laser Sintering: Part ΙΙ: Validation of Modified Polymers as Marking Agents.

Selective laser sintering (SLS) is currently in transition to the production of functional components. However, the ability to apply it is confronted with new requirements for reliability and reproducibility. Therefore, an in-depth understanding of aging processes in polymers is essential. Regarding material traceability as well as defective component identification with subsequent cause tracing, the application of a material-inherent marking technology represents a solution. SLS in combination with modified polymers as a marking technology proves to be an efficient opportunity to produce reproducible and high-quality components due to an increased understanding of the process. Based on a selection of modified polymers for use in SLS, which were characterized in part I of the study, this work focuses on the experimental validation of the result. The influence of modified polymers on materials and component properties and the SLS process's influence on the traceability of modified polymers are examined. Intrinsic and extrinsic material properties as well as mechanical properties, surface quality and sinter density are analyzed. No discernible influences of the modified polymers on the investigated properties could be observed and the traceability of the modified polymers could also be confirmed in the aged powder and component using mass spectroscopy.

Investigations for Material Tracing in Selective Laser Sintering: Part Ι: Methodical Selection of a Suitable Marking Agent.

Selective laser sintering (SLS) with polymers is currently at the transition stage for the production of functional components and holds great potential to revolutionize conventional production processes. Nevertheless, its application capability is confronted by newly imposed requirements regarding reliability and reproducibility. To safeguard these requirements, a deeper process understanding of material aging mechanisms in polymeric materials is needed. In order to enable the traceability of the materials as well as the identification of defective components with subsequent tracing of the cause, the use of a material marking process represents an alternative. SLS in combination with material marking is proving to be an efficient option for reproducible, high-quality manufacturing based on an increased understanding of the process. In this study, the idea of a marker-based traceability methodology for the purpose of process optimization is presented. Fundamental to the subsequent experimental investigation of the marking agent suitability, this work first focuses on the systematic selection of a suitable marking agent for use in SLS. Based on an analysis of the sinter material to be marked and a set of marking technologies, as well as using the selection methodology, the modified polymer marking technology was evaluated as the most suitable marking technology.

Finite Element and Finite Volume Modelling of Friction Drilling HSLA Steel under Experimental Comparison.

Friction drilling is a widely used process to produce bushings in sheet materials, which are processed further by thread forming to create a connection port. Previous studies focused on the process parameters and did not pay detailed attention to the material flow of the bushing. In order to describe the material behaviour during a friction drilling process realistically, a detailed material characterisation was carried out. Temperature, strain rate, and rolling direction dependent tensile tests were performed. The results were used to parametrise the Johnson-Cook hardening and failure model. With the material data, numerical models of the friction drilling were created using the finite element method in 3D as well as 2D, and the finite volume method in 3D. Furthermore, friction drilling tests were carried out and analysed. The experimental results were compared with the numerical findings to evaluate which modelling method could describe the friction drilling process best. Highest imaging quality to reality was shown by the finite volume method in comparison to the experiments regarding the material flow and the geometry of the bushing.