**4. Results and discussion**

354 Thermoplastic Elastomers

a certain uniaxial extension to the sample. A high quality signal amplifier in combination with a high resolution AD-converter is used to detect and digitize the analogue signals of the high-resolution force transducer and the thermocouple. In order to detect the current temperature the thermocouple is placed near the centre of the sample. All signals are transferred to a personal computer. A special software program is used for treatment and evalua-

The test procedure starts with placing the sample in the electrical heated test chamber, which is controlled at the initial temperature T0 of 23 °C. After the initial strain of 0 = 50% is applied, the isothermal relaxation period starts, whereas the temperature remains constant at 23 °C within +/- 0.1 °C. During this time most of the short time relaxation processes occur and the sample reaches a quasi equilibrium state. Then the sample is heated linearly at a constant rate of β = 2 K/min, until the stress relaxation has been fully completed or rupture

From the obtained force – temperature curve certain characteristic quantities such as T10, T50, T90 and the TSSR index RI can be calculated. The temperature Tx stands for the temperature at which the force ratio F/F0 has decreased about x% with respect to the initial force F0. The TSSR index RI is a measure of the rubber like behaviour of the material and is calculated from the area below the normalized force – temperature curve, as represented in Figure 5 and given by Eq. (9). Additionally, the temperature coefficient and the relaxation spectrum H(T) are calculated from the initial slope and the derivative of the stress–temperature curve,

tion of the data as well as for the control of the test procedure.

2. Step: Isothermal relaxation

1. Step: Initial strain is

3. Step: Temperature scan with constant heating rate

at T0 = 23 °C for 2 hrs

<sup>0</sup> = 50%

applied at 23 °C

β = 2 K/min

Fig. 4. TSSR instrument and test procedure

of the sample has occurred.

23 °C 180 – 300 °C

respectively, as described in chapter 2, in more detail.
