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

• Published in: Thermochimica acta 2019-07, Vol.677, p.131-138
• Main Authors: von Baeckmann, C., Wilhelm, H., Spieckermann, F., Strobel, S., Polt, G., Sowinski, P., Piorkowska, E., Bismarck, A., Zehetbauer, M.
• Format: Article
• Language: English
• Subjects: High-pressure crystallization; Lamellae size; Strength; γ-Polypropylene
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2019.03.007

•The strength of γ-PP is significantly influenced by the lamella thickness.•For the same lamella thickness, γ-PP is 40% stronger than α-PP.•Higher strength of γ-PP due to limited mobility of dislocations.•Mode of nucleation is not strongly influenced by the pressure. The influence of the crystallization temperature and the pressure on the crystallization kinetics, structure and compression strength of γ-polypropylene was investigated. Samples were produced in a custom-made high-pressure crystallization cell and characterized by differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). It could be shown that the strength is mainly affected by the mean lamellar thickness. The strength of γ-PP is at least 40% higher than α-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.