Influences of processing on the phase transition and crystallization of polypropylene cast films

Phase transition and changes of properties of isotactic polypropylene (i‐PP) cast films with the processing conditions have been investigated by wide‐angle X‐ray diffraction, two‐dimensional small‐angle X‐ray scattering, and atomic force microscopy. It was found that chill roll temperature was a major factor, which influenced the formation of mesomorphic phase and its transition to spherulitic structure. Only mesomorphic phase was observed in the films produced under a chill roll temperature of below 40°C. When the roll temperature was increased to 60°C, mesomorphic phase coexisted with spherulitic crystal structure, and totally transformed to monoclinic structure at the roll temperature of 80°C. Differential scanning calorimetry, tensile, and optical tests were also performed on the films. The results showed that the observed structure changes were closely related to the thermal behavior, tensile, and optical properties of the PP films. The influence of die temperature on the films was also discussed, but the effect was much less than chill roll temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41100.