Crystallinity and microstructure in injection moldings of isotactic polypropylenes. Part II: Simulation and experiment

The injection moldings of isotactic polypropylenes with various molecular w eights were simulated using finite difference method. in the simulations, t he unified crystallization model proposed in our previous paper was applied . The prediction of crystallinity and microstructure development in the mol dings was based upon the crystallization kinetics and the "competing mechan isms" for introducing various microstructure layers in the moldings. Extens ive injection molding experiments were carried out. The pressure traces dur ing the molding experiments were recorded. The crystallinity distribution i n the moldings was determined using differential scanning calorimetry. The measurements on the microstructure embedded in the moldings were performed, including the thickness of the highly oriented skin layer and the gapwise distribution of the spherulite sizes. The measured data for the crystallini ty and microstructure in the moldings were compared with the simulated resu lts. The effects of molecular weight and processing conditions on the devel opment of crystallinity and microstructure in the moldings were elucidated. Theoretical predictions were found to be in a good agreement with experime ntal measurements.