Methodenübergreifende Charakterisierung der thermo-oxidativen Stabilität von Polyamid 66

Polyamide 66, as a technical thermoplastic, is often used as a material for high-performance components that are exposed to extreme thermal, mechanical and chemical stresses. Under these conditions, accelerated ageing can occur, particularly due to thermo-oxidative processes that can cause chain degradation, embrittlement and premature failure of components. The evaluation of thermo-oxidative stability is therefore crucial for estimating the service life and safety of such components. The aim of this master's thesis is to systematically investigate the thermo-oxidative resistance of polyamide 66 for different processing conditions and thermal pre-treatments. Structure-property relationships for granules, standardised test specimens and real components are determined and the influence of processing on ageing behaviour is evaluated. In addition, the methods are compared in terms of time required and efficiency. Polyphthalamide is used as a validation material to test the transferability of the correlations found to other polyamide materials. For this purpose, samples of different processing and material states (granules, test specimens and components) were subjected to oven ageing at different temperatures over a period of up to eight weeks. This was followed by an analysis of chemical changes, rheological properties and mechanical characteristics, as well as an examination of the microstructure using light and scanning electron microscopy. The results show that ageing is strongly dependent on temperature, geometry and surface morphology. Thin-walled components age the fastest, test specimens are the most resistant and granules show intermediate behaviour. With increasing storage time, the carbonyl index, which indicates chemical degradation in IR spectroscopy, and the flowability increase, while the elongation at break and the notch impact strength decrease. This illustrates the qualitative correlation between chemical, rheological and mechanical characteristics. The investigations at the granulate and test specimen level provide initial indications of age-related molecular changes and their effects on mechanical properties. However, transferability to component behaviour is only possible to a limited extent. Tests on real components, which also take into account processing-related influencing factors, provide the most meaningful results. FTIR spectroscopy is an efficient, highly sensitive method for characterising ageing. Measurements on the validation material confirm the observed trends.