PhD defence of Clément Laügt

The aim of this work is to assess the impact of a thermo-hydro-glycol ageing on the microstructure and the mechanical behavior of an injection molded polyamide 6,6. During ageing, polyamides 6,6 are immerged in a mixture of water and ethylene glycol, at temperatures ranging from 120°C to 140°C. 

 

Concerning the microstructure, a decrease of the average molar mass of the polymer is measured by steric exclusion chromatography. This decrease results from the hydrolysis reaction. However, most of the measurements concern the crystalline phase of the polymer. Several quantities are measured, especially a crystallinity index, the lamellae thickness, the crystallites apparent size, and a crystal perfection index. A core-skin microstructural gradient is pointed out. It is the consequence of the injection molding process.

The mechanical behavior is assessed by tensile testing. The true strain fields are measured by a digital image correlation system. The loading conditions are chosen by referring to the time-temperature superposition principle. Microstructure-properties relationships are brought out.

 

Finally, the mechanical behavior is integrated in a model inspired from physics. The polymer is related to an equivalent network. This model allows the modelling of complex loading.

 

 

Keywords: PA66, thermo-hydro-glycol ageing, microstructure, mechanical behavior