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The effect of hygrothermal aging on the mechanical behaviour of polyamide 6 (PA6) material filled with 10 wt % multi-walled carbon nanotubes (MWCNTs) has been investigated experimentally. Young's modulus and flexural modulus of the materials are decreased by more than 30% for the conditions of 25°C/85% RH, compared to the reference conditions of 25°C/55% RH (RT), while the flexural strength by 6-17%. The decrease is larger for the conditions of 40°C/85% RH, which reveals that the effect of combined elevated temperature and moisture is more severe. The decrease in the properties is smaller for the MWCNT/PA6 specimens, which shows that the presence of MWCNTs mitigates the effect of hygrothermal aging. Finally, it is observed that the increase in the properties of the MWCNT/PA6 material is so large, for the specific MWCNT concentration, that it compensates the negative effect of hygrothermal aging.

The tensile behaviour of the polypropylene (PP) material reinforced by multiwalled carbon nanotubes (MWCNTs) was characterised by mechanical testing. Two different MWCNT weight ratios, namely 2 and 5%, were considered. The strains were measured using strain gauges and a digital image correlation system. The results from mechanical tests were evaluated using scanning electron microscopy (SEM). An increase in the average Young's modulus of 20?29 and 25?19% and in average maximum stress of 26?13 and 33?31% was obtained for the 2 and 5 wt-% MWCNT/PP specimens respectively. The Young's modulus and maximum stress of the MWCTN/ PP specimens show a considerable scatter, which is attributed to the varying dispersion and agglomeration size. For specimens with mechanical properties lower than the average values, SEM interpretation revealed poor dispersion and formation of large agglomerations.

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