The Research On Crystallization Behavior Of Isotactic Polypropylene

Polypropylene(PP) is a kind of polymer materials that have been widely used over world because of it’s excellent performance and low price. Generally, PP extensive used is often a kind of PP with high isotactic degree, and the crystal process would influence the forming and application at a large extent, thus, studying the crystallization behavior of polypropylene would be important for the forming and application design. At present, the study on the crystallization behavior of polypropylene was mostly focused on the effect of crystallization behavior with different temperature fields under static conditions. But the crystallization behavior of polypropylene was always undertaken under the conditions of stress field, which meant the study result under static conditions could not be used to direct the design of forming and application.Thus, study the crystallization behavior of polypropylene under both static and dynamic condition systemically, and comparing similarities and difference between them become urgently. In this paper, the crystallization behavior of the polypropylene under static condition and dynamic condition had been researched, and following contents were concerned.1. The crystallization behavior of polypropylene under the static isothermal condition was studied by hot stage polarizing optical microscope, and results showed that: a) Crystallization temperature had a significant effect on the crystallization behavior, the effect of molecular weight on the crystallization behavior was weaker than the crystallization temperature; b) Nucleation rate and crystal growth rate of isotactic polypropylene decreased at the same time with the increase of the crystallization temperature; c) Nucleation rate and crystal growth rate of isotactic polypropylene decreased while molecular weight increased.2. Rotational rheometer was used to research the crystallization behavior of isotactic polypropylene under dynamic shear stress conditions and results showed that: a) Under slight dynamic stress conditions, the crystallization temperature was still the most important influence factor to the crystallization behavior of isotactic polypropylene,slight oscillating shear stress played an important role in both of isotactic polypropylene nucleation and spherulite growth rate; b) The frequency increase of the shear stress on the crystallization played a role in promotion nucleation. c) The increase of strain could promote the crystal nucleation, decreased time of the crystallization induction, and promoted the crystallization.3. Due to the different evaluation criterion of nucleation and the different characterization parameters, result of nucleation under the static and dynamic conditions could not be compared. However, evaluation criterion of crystallization growth were same under both static and dynamic conditions,so results obtained under both static and dynamic conditions could be used to study the effect of the shear stress field on the crystallization behavior, and as the result could be compared. After comparing the crystallization behavior of isotactic polypropylene under the static and dynamic conditions, the result that the shear stress could accelerate the crystallization growth could be arrived.