PA612 double bubble tubular film process - Processability and structure development

Biaxially oriented Polyamide 612 (PA612) films made by double bubble tubula r film extrusion were characterized. The processing characteristics of the polymer in the double bubble process were investigated. The development of crystallinity and orientation in the films was clearly considered. First bu bble PA612 films showed a low level of crystallinity (X = 7.7 %). Different ial scanning calorimetry (DSC) indicated that the first bubble PA 612 films experienced a considerable increase in glass transition temperature (T-g), cold crystallization temperature (T-c) and crystallinity during aging at r oom conditions. The second bubble films were more highly, crystalline (X = 22 to 28 %) with poorly grown beta unit cells. The WAXD and SAXS patterns s howed that the crystallites of double bubble PA612 films became more perfec t by annealing in a boiling 20 % formic acid solution, resulting in a well- developed triclinic a crystals coexisting with minor proportion of beta pha se. The WAXD and SAXS patterns indicated that crystallographic planes and l amellae in the second bubble films were oriented depending on SBUR X SDDR ( second blow-up ratio x second draw down ratio). White-Spruiell biaxial orie ntation factors were calculated with the WAXD pole figure data. The hydroge n bonding (0k0) planes of biaxial double bubble films were found by WAXD to be aligned parallel to the sheet surface before and after annealing.