During the packing stage in injection molding of thermoplastics, a compressible flow under imposed pressure allows to counteract the effect of the thermal shrinkage. PVT curves are important data for the numerical simulation of this flow. They are usually obtained by measuring the volume change of a given mass of material at constant pressure and at a cooling rate usually much lower than in the process. The sharp volume decrease at crystallization may not be correctly captured. A second issue concerns the prediction of the solidified layer which grows in contact with the mold walls until full solidification. To address these two issues, we characterized the crystallization kinetics of a polypropylene either at room pressure up to a cooling rate of 100 K/min by DSC, or under pressure up to 90 MPa in isothermal conditions in the Cristapress device developed in the laboratory. This allows obtaining the crystallization temperature as a function of the cooling rates and pressure. The crystallinity ratio is used to obtain the specific volume in the crystallization range, as a function of the specific volumes of the amorphous and crystalline phases. For the no-flow criteria, instead of using a no-flow temperature, we used a criteria related to the crystallinity ratio. We performed injection molding tests and measured the pressure on three transducers located in the cavity, the mass of the molded part for different packing pressures and times. We used the Rem3D software package to test the models for the PVT data and no-flow criteria. The agreement is correct.