Teacher education in Germany is a complex system comprising various phases, training institutions, and stakeholders. Throughout their training, prospective teachers form social relationships with a wide range of people. With some, they have official training relationships (e.g., instructors, practicum supervisors). Others are not official trainers of the student teachers, yet they are still part of their daily training routine (e.g., fellow students or student teachers). These official and unofficial training stakeholders form a social network of relationships that significantly influence the professionalization of prospective teachers. These training actors, the social relationships with them, and their influence on professionalization have already been identified to some extent as subjects of research. However, there has been a lack of a network-analytical perspective that examines 1) the formation and change of networks and 2) the interaction among actors with regard to professionalization. This dissertation study focuses on the second phase of teacher education and aims to examine the social networks of student teachers during their practical training. The goal is to analyze how these social networks form and evolve over the course of the training, as well as the professionalization effects resulting from relationships and interactions with training stakeholders. To this end, as part of a qualitative longitudinal study, 15 student teachers were accompanied during their practical training, and network interviews were conducted at three different time points. These were evaluated using a combination of content-structuring qualitative content analysis and qualitative structural analysis. The results show that the formation and transformation processes of social networks among student teachers can be explained by five factors: perceived freedom of action, perceived professional support, perceived emotional and social support, perceived network burdens, and perceived function/role of training stakeholders. Furthermore, the professionalization effects could be explained using the two mechanisms of social learning and social pressure. For both mechanisms, different types of reactions and coping strategies were also identified, which can lead to effects that either promote or inhibit professionalization.

In the context of the transition from a linear to a circular economy, this dissertation investigates the pyrolysis of scrap tires as a technically and environmentally viable recycling option. The primary objective is to quantify the substitution potential of the pyrolysis products coke and oil, as well as carbon black produced from pyrolysis oil, in comparison to conventional carbon black. In addition, the feasibility of pyrolysis as a complementary technology for expanding urgently needed recycling capacities is assessed from a technical, economic, and environmental perspective alongside established recovery pathways, including mechanical recycling, thermal treatment, and retreading. As existing approaches to the environmental assessment of tire pyrolysis are not standardized and involve considerable uncertainties, an integrated modeling framework was developed that links a technology-specific process model of pyrolytic conversion with a life cycle assessment model. Based on validated primary data from semi-industrial experiments conducted in a rotary kiln at the :metabolon Institute of TH Köln, the assessment shows that pyrolysis coke can reduce greenhouse gas emissions by approximately 80 % compared to conventional carbon black. Carbon black produced from pyrolysis oil processing achieves a 3 % emission reduction compared to fossil-based carbon black and, due to its enhanced product quality, offers greater circularity potential than pyrolysis coke. From a recovery perspective, pyrolysis demonstrates the most favorable climate performance compared to mechanical recycling and thermal treatment, surpassed only by the hierarchically preferred retreading process. The modeling results further indicate that a complete substitution of conventionally produced carbon black with pyrolysis coke could, in the long term, reduce the global emission level of the carbon black industry by up to 80 %. However, achieving this potential requires overcoming existing quality differences between pyrolysis coke, carbon black derived from pyrolysis oil, and conventional carbon black, which are already being addressed through targeted post-treatment processes for pyrolysis coke. In the interim, the use of blends comprising all three materials provides a practical strategy to significantly improve the overall greenhouse gas balance. The developed integrated model provides a transferable methodological framework that demonstrates how the coupling of process and life cycle assessment models can serve as a basis for the environmental optimization of industrial systems within the circular economy.