Water accessibility in aliphatic polyamides by NIR and FT-IR spectroscopies

Abstract

The capabilities of FT-IR and NIR spectroscopies to analyse water absorption mechanisms in aliphatic semi-crystalline polyamides (PA) are presented. This work was carried out on PA6, PA11 and PA12 and was divided into three parts: (1) assignment of the NIR absorption bands of PA11; (2) comparison of FT-IR and NIR results on water accessibility; (3) comparison of solubility values given by gravimetric and spectroscopic methods. Primarily, the water accessibility for the polyamides tested can be estimated by FT-IR as well as by NIR. The NIR technique is more appropriate for melt processed samples, as film casting (for FT-IR) can induce structural modifications. The scheme of water incorporation in polyamides is confirmed. The complete hydration of some regions of the polymer is proved by correlation between gravimetric and NIR data. Finally, a concept for intrinsic solubility is suggested to take into account spatial and structural distributions of water molecules in the amorphous phase of polyamides. This parameter remains constant with temperature.