MEMORY EFFECT AND CRYSTALLINE STRUCTURE IN POLYAMIDE 11

The memory effect in PA11 films is studied in close relation with the crystalline structure. In polyamide 11, [(CH2)10–CO–NH] n , the polarity of the amide group induces hydrogen bonds between chains that are crucial to the crystalline structure and are responsible for the memory effect. During the forming from the melt, the polyamides are sheared, which leads to persistent chain alignments due to hydrogen bonds. In the present work, the crystalline structure of PA11 films has been studied by differential scanning calorimetry and wide angle x-ray scattering. The crystalline structure at room temperature depends on the cooling rate. A quench leads to the smectic δ′ structure, whereas a slow cooling favors the formation of the triclinic α phase in addition to the smectic δ′ phase. This study also shows the influence of an annealing in the melt on the crystalline structure. With increasing annealing time in the melt, the δ phase develops and the δ′ phase progressively vanishes. It seems necessary to maintain PA11 above the melting point for a long time to totally erase the structural evidence of the memory effect.