Microscopic Analyses of Polymer Materials
Apart from mere research purposes, microscopic analyses are carried out for quality assurance, as well as failure analysis. They may explain relations between a polymer material’s structure and its mechanical properties, as well as detect the impacts exerted by processing parameters, or damages that lead to failures. While investigating recycled materials, proof and identification of polymeric and other soiling are of particular interest. Optical microscopy is performed at transmitted and incident light, in addition to surface examinations by a scanning electron microscope.
To carry out transmitted light investigations, a slide or rotation microtome cuts thin sections out of thermoplastic materials. If the plastic is very soft, the specimen must be cooled down. To conserve the section permanently, it may be embedded into acrylic resin, on an object plate. Reinforced plastics are embedded into an epoxy resin that cures at room temperature, then carefully grinded and polished. To analyze cracks, the embedding material is added a fluorescent coloring agent. In order to examine the matrix structure of a fiber-reinforced plastic material under transmitted light, or in case the thermoplastic specimen has an unfavorable geometry, a microsection is made. To avoid electric charging in the sputter, the specimens submitted to examination by a scanning electron microscope are coated with gold or carbon.
Thin sections of pure plastics are transparent. Altering the ray’s course in an optical microscope, a contrast may be generated, enabling the user to investigate a variety of tasks:
|Transmitted Light||Bright field||Soiling|
|Polarization||Spherolithe structure, orientations|
|Phase contrast||Polymer mixtures|
|Incident Light||Bright-, dark field||Soiling, cracks|
|Differential Interference Contrast||Fiber distribution|
Thanks to its high resolution, the scanning electron microscope is used, e.g. to analyze crack interfaces. The institute has developed a micro-scale tensile testing equipment designed for microscopic investigation of thin sections during tensile testing.
At regular intervals, the Institute of Polymer Technology offers a seminar concerned with preparation and optical microscopic analysis on polymer materials. Here we give you an introduction of techniques and their applications, in theory and practical use.