Klaus Bernreitner

Crystallinity and mechanical properties of PP-homopolymers as influenced by molecular structure and nucleation

The evolution of crystallinity and mechanical properties of two different series of PP-homopolymers (RE grades coming directly from the polymerization reactor and CR grades priorly subjected to a defined degradation process) as influenced by the molar mass and heterogeneous nucleation was investigated, including one highly isotactic material to check the tacticity influence. In principle, the effects seem explainable by differences in the number of nuclei and the spherulithic growth speed, which were determined separately. The nucleation effects are similar for all materials, but strongly dependent of the molar mass of the materials. Apart from the bulk material properties, also the development of shearinduced structures is strongly influenced by molar mass and nucleation, contributing additionally to mechanics.

Correlation between molecular structure and rheological behaviour of polypropylene

Abstract Using data from different types of polypropylene (reactor-grade, peroxide-degraded and technical types), various correlations between parameters of the molar mass distribution, the storage and loss modulus and the steady shear viscosity are investigated. Most assumptions turn out to oversimplify the real, complex relations between molecular structure and rheological properties. Nevertheless they appear to be useful for first estimations in screening tests and production control.

Influence of molecular structure on crystallization behaviour and mechanical properties of polypropylene

Abstract Two series of polypropylenes with different molar mass—reactor grade (RE) and peroxide-degraded (CR) types—were investigated with respect to mechanical and crystallization parameters. A significant influence of the production process on mechanical parameters was found, which can be attributed to differences in the crystallization behaviour, mainly to the number of nuclei per unit volume. At a comparable average molar mass, RE types crystallize faster and exhibit higher levels of stiffness, combined with lower levels of impact strength, than CR types.

Characterization of modified polypropylene by scanning electron microscopy

Characterizing the morphology of modified multiphasic polymer systems, as are often applied for improving the impact strength, is normally a complicated and tedious task. Nevertheless, knowledge about the volume fraction and particle-size distribution of the elastomer phase is important for the specific development of high-impact systems. Direct production in the reactor enables only indirect control of these two quantities. Computer-controlled scanning electron microscopy in combination with image processing allows an automated measurement of both all the necessary particle parameters (size distribution, shape, orientation, etc.) and the elastomer content of the material. Since bulk materials are used for the investigation, additionally, three-dimensional information about the structure of the material can be gained by simply varying the electron energy, without the necessity to resort to multiple slices. This information is especially important in the case of particles with extremely irregular shapes, as obtained, for example, by strong agglomeration of the modifier particles. The mathematical routines used for calculation of the particle-size distributions from the measured profile-size distributions cannot be applied in such cases. The method was tested for several materials with significantly different compositions, both immediately after molding and also after a subsequent thermal relaxation.

Application of interconversions to viscosity measurements of polystyrene

Abstract Empirical and theoretically based numerical interconversions between viscoelastic material functions are used to compare results of two different measuring techniques for polymer melts. The methods compared are the magnetoviscometer and a dynamic-mechanical apparatus. For the case of two technical polystyrenes results are given which show the possibility of determining the zero shear viscosity and, using an empirical conversion, more of the flow curve from results of the magnetoviscometer. In general, the results of both techniques are in good accordance.