Characterization of the glass Transition Using a Microindenter.
CORNELL UNIV ITHACA NY SCHOOL OF CHEMICAL ENGINEERING
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The microindenter described here requires a very small sample c. 10 mg, can be used with heating rates comparable to those in DSC ie., 10 C minute, and gives a large, clearly defined change at the glass transition. The essential features are a needle probe and a linear variable differential transformer LVDT. By suitably controlling the force on the needle, the rate of heating, and the sample thickness, reproducible results can be obtained. The small sample size permits a relatively fast heating rate. Most mechanical tests often using oscillating stress and strain require large samples with a corresponding long time for temperature equilibration to take place ASTM D 4065. Another indentation test, the Vicat Softening Temperature ASTM 1525 also uses a thick 3 mm sample. Like the Vicat test, the present procedure is best suited to amorphous polymers. The application to plasticized samples of polymethyl methacrylate illustrates the utility of the method.
- Physical Chemistry