Effect of polar solvents on the crystalline phase of polyamides

We investigate the effect of absorption of polar solvents (water and ethanol) on the structure of amorphous and semi-crystalline copolyamides containing aromatic entities. Different length scales of structural organisation are probed using a combination of Small angle X-ray scattering and neutron/X-rays diffraction. Crystallisation in the presence of solvent, characterised by very slow kinetics, is observed in the originally amorphous material, as a combined effect of a rearrangement of the hydrogen-bond distribution and plasticization. The steady-state crystalline structure is reached on a timescale much longer than the absorption kinetics, and is similar but not identical to that of processed semi-crystalline materials. In semi-crystalline polyamides water absorption induces a swelling of the spacing of the lamellar stacking but also modifications of the unit cell structure, which suggest a moderate but significant rearrangement of the hydrogen bond structure in the crystalline phase.