The Strange Behavior of a Bouncing Modeling Putty
“Horst die Hüpfknete” is the German name for a make of bouncing modeling putty used as a toy for children. The material exhibits two quite different types of behavior at room temperature: On the one hand, it can be easily shaped and stretched and flows like a viscous liquid. In contrast, if it is rolled into a ball and allowed to fall to the ground, it behaves elastically and bounces back up like a tennis ball.
Introduction
How can this most unusual behavior be explained? – In this article, we will try to answer this question.
DSC Measurements
The putty was first measured by DSC using a METTLER TOLEDO DSC 1 equipped with an FRS5 sensor and a liquid nitrogen cooling system. The measurement results are shown in Figure 3.
The DSC heating curve shows a steplike change at about –120 °C, which we interpret as a glass transition. At about –79 °C, there is a small exothermic peak followed by an equally large endothermic peak at –54 °C.
These two effects correspond to the crystallization and melting of part of the sample. This behavior is typical for silicone rubber. Comparison of the step height of the glass transition of the putty with the step height of pure silicone rubber (see small inset diagram) shows a difference of about 10%.
This indicates that the putty consists not only of silicone rubber but also contains another compound that does not produce any detectable effects on the DSC curve.
The DSC experiment does not of course provide any information about the mechanical behavior of the putty. For this reason, we decided to perform several different DMA experiments.
DMA Measurements
The viscoelastic behavior of the putty was investigated using a METTLER TOLEDO DMA /SDTA861e dynamic mechanical analyzer. The measurements were performed in the shear mode using the shear sample holder for liquids. The sample thickness was 1 mm...
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Summary and Conclusions
In this article, we studied the strange behavior of a bouncing modeling putty. At room temperature, the putty exhibits both flow properties and excellent elastic properties.
A DSC measurement indicated that the putty consisted of silicone rubber (about 90%) and another component (about 10%)
This second material was directly detected by DMA measurements and had an unusually broad glass transition of about 40 K. DMA measurements at different frequencies clearly demonstrated why the putty exhibits both elastic and flow properties at room temperature.
The measurements showed that, at low frequencies, the loss modulus was significantly greater than the storage modulus. This explains the flow properties of the putty. At higher frequencies, the storage modulus was considerably greater than the loss modulus and the putty behaves elastically.
The pronounced frequency dependence of the complex modulus can be easily be measured using a DMA/SDTA861e and is crucial for understanding of the behavior of the material.
The Strange Behavior of a Bouncing Modeling Putty | Thermal Analysis Application No. UC372 | Application published in METTLER TOLEDO Thermal Analysis UserCom 37