Analysis of polymer crystallization by calorimetry

The assessment and control of the crystallization behavior is an important issue in polymer processing. The rate at which crystallization takes place can influence the outcome of a production line and the quality of the polymer products. Depending on the type of processing (e.g., extrusion, injection-, or blow-molding), as well as the needed properties of the finished products, polymer crystallization speed can be tailored by varying material composition or formulation, as well as through the manipulation of process conditions. For instance, the addition of nucleating or clarifying agents can accelerate the crystallization. Similarly, the processing temperatures can be varied in order to properly alter the rate of crystallization. Variations in both material formulation and processing conditions induce corresponding modifications in material properties, by affecting material crystallinity, crystal thickness and morphology, crystal structure, etc., all of which drive bulk material properties. In order to determine which changes in processing or formulation are needed to tailor the crystallization conditions, it is necessary to assess the polymer crystallization behavior. Polymer crystallization can be monitored, quantified, and modeled using several calorimetric techniques, the most common including differential scanning calorimetry (DSC), temperature-modulated differential scanning calorimetry (TMDSC), and fast scanning chip calorimetry (FSC). Calorimetry can also be coupled with additional instrumentation/methods such as X-ray diffraction, rheometry, or microscopy, to follow details of structure development. Thus, complementary relationships of crystallization kinetics, structure, and morphology can be established for a given thermoplastic polymer, which allows optimization of material formulation and processing conditions in view of the desired properties. A detailed investigation of the crystallization process is also needed for a deeper understanding of polymer structure formation, since many specifics of polymer crystallization are still under investigation.