Structure-Property Relationship in Isotactic Polypropylene Under Contrasting Processing Conditions

Polypropylene (PP), owing to its favorable physical, thermal, and mechanical properties, and excellent processability, has become one of the most widely used synthetic polymers. It is known that the overall properties of semicrystalline polymers, including PP, are governed by the morphology, which is influenced by the crystallization behavior of the polymer under particular conditions. Among various types of polypropylene, isotactic polypropylene (iPP) remains the most significant for the industry and has been extensively studied for its polymorphic nature and crystallization behavior over the past five decades. Due to its regular chain configuration, iPP belongs to the group of polymers with a high tendency for crystallization. The rapid quenching of molten iPP fails to produce a totally amorphous polymer, but rather leads to an intermediate crystalline order. In contrast, the slow cooling yields a material with high crystalline content. The processing conditions that occur in practice and industry typically lie between these two extremes and, in some cases, approach either limit. Therefore, the investigation of limits in processability and extreme preparation conditions on morphology, structure, thermal, and mechanical properties can be of great importance, and is the main focus of this research. Two sets of samples were prepared: the first set was obtained by rapid quenching (Qs samples), and the second by very slow cooling from the melt to room temperature (SCs samples). Characterization of samples was performed by optical microscopy (OM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic dielectric spectroscopy (DDS), and mechanical measurements. The obtained results were analyzed and discussed in depth, thus providing a detailed insight into the structure-property relationship.