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.