Empirical Modeling of the Effect of Water Content on the Tensile Modulus of Polyamide‑6

This work aims to model the effect of water content on the stiffness of polyamide-6. Our empirical model developed earlier was used to model stiffness. The tensile modulus is calculated from parameters of the crystalline structure obtained by calorimetry. The model was fitted to modulus data estimated after conditioning standard specimens in desiccators at different but constant relative humidities to change the water content over the widest range. The mechanical properties were studied by standard tensile tests, and the parameters of the crystalline structure were studied by calorimetry. The calculated modulus values are in good agreement with the experimentally measured data, indicating that the prediction of the modulus is accurate. The effect of water content was also described accurately, and one of the iterative parameters of our model showed a strong correlation with the water content of the sample. We assumed that this parameter weighs the intermolecular interactions of the polymer. According to the results of this study, the stiffness of any polyamide-6 grade can be calculated at any water content if experimental data are recorded at a single water content, which makes it possible to model the tensile modulus of a polyamide-6 specimen under realistic outdoor conditions.