The influence of crystallization conditions on the macromolecular structure and strength of γ-polypropylene

The influence of the crystallization temperature and the pressure on the crystallization kinetics, structure and compression strength of gamma-polypropylene was investigated. Samples were produced in a custom-made highpressure crystallization cell and characterized by differential scanning calorimetry (DSC), wide angle X-ray scattering (WARS) and transmission electron microscopy (TEM). It could be shown that the strength is mainly affected by the mean lamellar thickness. The strength of gamma-PP is at least 40% higher than alpha-PP at the same mean lamellar thickness. This confirms the hypothesis that the arrangement of non-parallel chains restricts the number of possible slip systems so that almost no mobile dislocations are generated. The mode of nucleation is only slightly affected by the crystallization pressure. The Avrami coefficient is n = 2.5 +/- 0.1 at the beginning of crystallization and largely independent of pressure.