The non-isothermal and isothermal crystallization of different types of commercial polypropylenes (PP) are investigated by fast scanning calorimetry and wide-angle X-ray scattering. Typically, PP shows two different crystallization processes: below 55 °C the mesophase formation and at higher temperatures the α-phase formation. Here we report the first observation of an additional crystallization process in some PP-types. It is observed between 45 °C and 75 °C, and is understood as a consequence of an additional nucleation of α-phase crystals.
KEYWORDS: Polymers, Crystal size