Carbonisierung von Polyacrylnitrilfasern mittels Diodenlaserstrahlung
Aachen (2020) [Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (III, 199 Seiten) : Illustrationen, Diagramme
In comparison to other commercial reinforcement fibres, carbon fibres are superior in terms of mechanical properties such as specific tensile strength and specific Young’s modulus. Being used in carbon fibre reinforced polymers they show great potential to reduce moving masses in applications like aerospace, automotive and mechanical engineering. The manufacturing of carbon fibres is typically accomplished by stabilization and carbonization of polyacrylonitrile (PAN) precursor fibres via ovens. Due to the fast dynamics with respect to time and space, laser-based processes offer a greater degree of freedom in inducing the temperature-time profile during the carbonization in comparison to conventional carbonization methods via ovens. In contrast to CO2 laser radiation, there is in academic literature as well as in industrial developments no systematic research available that covers the carbonization of stabilized polyacrylonitrile fibres via energy efficient diode laser radiation. The main objective of this thesis is the theoretical and experimental investigation of influencing factors for the discontinuous carbonization using diode laser radiation. The associated technical objective includes the manufacturing of carbon fibres according to the industrial relevant HT classification with a tensile strength of at least 3 GPa. To achieve these goals, simulation studies are performed to identify factors that influence the temperature of the filament bundle. Additionally, influencing factors for the process efficiency of the carbonization via laser radiation are investigated using the derived process model. Based on theoretical insights from literature and the conducted simulations a suitable experimental set-up is designed, assembled and tested to allow for the experimental investigation conducting experiments on the discontinuous carbonization using diode laser radiation. In the next step the findings from the simulation studies are experimentally validated and the critical process parameters for the tensile strength are determined. Based on the experimental results, a carbonization process of carbon fibres via laser radiation is developed and compared to the industrially used manufacturing process using ovens. The maximum carbonization temperature plays - analogous to the carbonization via oven - a decisive role for the tensile strength during the laser-based carbonization. In contrast to the carbonization via oven, the width of the filament bundle has a significant influence on the temperature of the filament bundle during the carbonization via laser radiation which is shown in simulation studies as well as in experiments. To ensure a constant maximum carbonization temperature during the experiments a control concept using the laser power as actuated variable is implemented in the experimental set-up during the process development. Different temperature time profiles and a varying counterweight have a major influence on elongation-time profiles but the tensile strength is not affected significantly. The key result of the investigations is that carbonization by means of diode laser radiation can produce carbon fibres with a tensile strength of at least 3 GPa. This is the basis for developing energy-efficient and compact systems for laser based carbonization in future work.