Multiphase polymers specimen preparation methods

There are multiphase polymers where OM and SEM techniques cannot fully describe the microstructure due to a combination of small particle size (less than 0.5 /xm) and good adhesion between the dispersed phase and the matrix. Additionally, broad particle size distributions are often encountered, and in these cases a combination of techniques is required to describe the microstructure. TEM requires ultrathin specimens, about 50-500 nm or less in thickness, which are prepared by film casting or ultrathin sectioning. Films formed by casting or dipping methods provide a much easier specimen preparation method than ultrathin sectioning of bulk plastics. However, a major question in such studies is always whether the microstructure is the same as in bulk polymers of industrial interest. Specific stains are often required to provide contrast between the dispersed phase and the matrix pol)m[ier. 

Different specimen types yield a range of results upon ion or plasma etching. Multiphase polymers generally etch differentially, enhancing the contrast. Melt crystallized polymers can be etched to reveal the spherulites. Surface protuberances and particulate fillers can and do form cones or ridges when etched. Oriented semicrystalline polymers, on the other hand, appear to be the most controversial with respect to the resulting surface textures. Clearly, in such cases the specimen should be prepared by other methods for comparison, and control experiments are essential. There are problems in the industrial laboratory that can be solved, in part, by microscopy of surfaces prepared by etching techniques however, these are far fewer than those addressed by other specimen preparation methods. 

Determination of dispersed phase morphology is most often conducted by SEM of fractured specimens. Fractures are prepared by manual methods, after immersion in liquid nitrogen, or by standard physical testing procedures. The microstructure of the homopolymers should be examined for comparison with the multiphase polymer. SEI of an Izod fracture surface of a POM/PP copolymer is shown in Fig. 5.42. The two phases are incompatible, i.e. they are present as two distinct phases. The dispersed phase particles range from less than 0.5 to 2[xm in diameter. The sample fracture path follows the particle-matrix interface and holes remain where particles have pulled out of the matrix, showing there is little adhesion between the phases. 

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