Determination of moisture gradients in polyamide 6 using StepScan DSC

Polyamides are known to absorb and desorb water to establish an equilibrium with their environment. Water uptake by diffusion leads to a drastic reduction in the strength and stiffness of the material, which is referred as the water-induced plasticizing effect. This effect leads to a shift of the glass transition region towards lower temperatures what can be determined by differential scanning calorimetry (DSC). However, a determination of the glass transition temperature T-g is not accurate in samples with inhomogeneous moisture distribution before an equilibrium is reached by diffusion and T-g is superimposed by water-specific effects. It is shown that the glass transition can be measured by StepScan DSC even with inhomogeneous moisture distribution within the sample. In addition, a method is developed and validated which uses the low thermal conductivity and the shift of T-g to detect a water-saturated sample boundary layer in inhomogeneously conditioned PA 6 samples.