Tensile tests of polymers at low temperatures in the environmental scanning electron microscope: an improved cooling platform.

The investigation of the fracture behavior of polymers in the environmental scanning electron microscope (ESEM) can provide information about the correlation between the microstructure of a specimen and the macroscopic stress-strain characteristic. As the mechanical properties of polymers change dramatically at the glass transition temperature, cooling of the specimens during the tensile tests can yield very valuable information about the influence of individual components of polymer blends on the fracture behavior of the material. A serious problem in this connection is the poor heat conductivity of polymers. A commercially available cooling platform, which can be mounted on the tensile stage used for the tests was substantially modified to both enhance the heat transfer between platform and specimen, and to minimize the temperature gradient along the specimen. The first experiments on modified polypropylene specimens already delivered some unexpected results. Fibril-like structures appeared at the crack tip that would not be expected at temperatures below the glass transition temperature of the polymer blend.