Crystallization of amorphous polyamides from the glassy state

The general crystallization behavior of amorphous polyamides during heating treatment was measured by wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) to get information on (1) the temperature range where the crystallization in an anisothermic process takes place and (2) the type of the crystalline phases (alpha or gamma) considering the Brill transition and the state of order in the alpha-crystal. Various polyamides (PA 6, 6.10 and 6.6) were quenched and cooled to 200 K and then heated until they melted. During heating from the glassy state the crystallization starts rapidly at the glass transition temperature and then the crystallinity slowly increases until the melting point. The crystallinity was calculated on the basis of the separation of the amorphous and crystalline scattering by profile fitting. The angular position of the amorphous halo and so the density of the amorphous phase is higher in the presence of the crystalline phase compared to the completely amorphous state. The crystalline structure (alpha or gamma), which is difficult to distinguish at higher temperatures due to the Brill transition, was determined by quenching the samples from elevated temperatures to room temperature after heating. The perfection of the alpha-crystal, i.e. the crystal perfection index, increases with temperature during continuous heating.