Abstract
In order to measure the temperature dependence of the dynamic modulus in crystalline high polymers at definite frequency, an apparatus was constructed, which was found to be very useful for analysis of temperature-dispersion curve of dynamic modulus, due to its high accuracy and rapid operation for measurements, adding to the advantage of constant frequency.
Both ends of sample fiber or high polymer film are fixed to two strain gauges of unbonded type, one of which is used to transform the sinusoidal displacement into electrical quantity proportional to the displacement and the other is transducer of generated force. Absolute values of these electrical vectors representing force and displacement are adjusted to unity (full scale of voltmeter) and vector reduction are conducted by changing the connection of the output circuit of two strain gauges. By this operation the value of tanδ can be directly read off by the voltmeter. Regulation of the magnitude of vector is conducted conveniently by controling the input of strain gauges. Dynamic modulus, G', can also be calculated from the ratio of the input voltages of strain gauges, E2/E1, when the output voltages of them are regulated to be equal,
G'=K(E2/E1),
where K is a constant relating to the dimensions of samples and strain gauges.
The main structural feature of this apparatus exists in that the vector reduction is conducted without amplifying the respective electrical output from two strain gauges proportional to force and displacement respectively. By this method the possibility of introducing experimental error based on the phase shifting effect from amplifier could be avoided. However, in order to make this possible, it was necessary to amplify very small output voltage (less than one micro volt) by using selective amplifier of the highest sensitivity.
Another advantage of this apparatus must be cited: the reading of the output voltages of strain gauges is not necessary in absolute values but the relative values of them are satisfactory for determination of both values of tanδ and G'. This makes the measuring operation so rapid that the long time stability of the amplifier is not so serious, and high reproducibility of data can be realized.
The measurements of tanδ and G' at one temperature need only several tens seconds. The temperature characteristics of viscoelasticity of several fibers over a wibe temperature range were measured with heating rate of 1°C/min., with high precision and reproducibility.
