Multiscale analysis of the thermal degradation of polyamide 6,6: Correlating chemical structure to mechanical properties

International audienceIn this paper, the thermal oxidation of polyamide 6,6 between 140°C and 200°C is evaluated. The aim of this study is to correlate the modifications of the polymer properties on scales ranging from molecular to macroscopic. Chemical structure changes are monitored by infrared and UV-visible spectroscopies. The modifications of the microstructure are evaluated using DSC while molar mass evolution is determined by SEC measurements. Vickers µ-hardness is used to assess the mechanical properties. Although the carbonyl index is frequently used to measure the extent of oxidation, this article employs the overtone of the amide II band (3080 cm−1) as a more relevant criterion to quantify the oxidation of polyamide. This criterion allows for an earlier detection of the thermo-oxidation of polyamides and is well-correlated with modifications of the polymer properties. Direct correlations are observed between changes in the chemical structure, modification of the microstructure and the thermal/mechanical properties, regardless of the measurement scale. It is shown that the variations in the intensity of this band fit well with the changes in the crystallinity, molar mass, molecular mobility and micro hardness, validating the multiscale characterization model