Sorption studies of amorphous polyamides.

Abstract

The crystallinity of polyamides has a great influence on their mechanical and physical properties, and this has important implications in their applications. When applying methods such as X-ray diffraction and differential scanning calorimetry to determine the degree of crystallinity of semi-crystalline polymers, one may experience complications such as tedious data interpretation and a prior knowledge of the properties of pure crystalline samples. The objective of this project is to determine the ratio of the number of NH groups in the amorphous phase of polyamides to the number of sorbed acetone molecules. If this ratio always exists as a constant, sorption of acetone can be an alternative technique to characterize the crystallinity of polyamides. This ratio was determined through the investigation of the sorption behavior of two amorphous polyamides, poly(hexamethylene isophthalamide) (PA6I) and poly(trimethyl hexamethylene terephthalamine) (PA6-3-T), in acetone solvent. The study revealed that PA6I absorbed 1.40 wt% of acetone at equilibrium, i.e. 33.8 NH groups to one acetone molecule. For PA6-3-T (where the results were close to equilibrium), the corresponding numbers are 14.6 wt% and 2.79 respectively. The results from this sorption study imply that sorption method could still be a potential alternative to determine the crystallinity of polyamides. This should be confirmed by extending the sorption studies to a particular polyamide with different crystallinities. The results from the sorption studies should then be verified with the results from conventional crystallinity determination methods, such as X-ray diffraction and differential scanning calorimetry.