A simple method for calibrating the temperature in dynamic mechanical analysers and thermal mechanical analysers

Abstract

An intrinsic requirement in reliable dynamic mechanical analysis (DMA) or thermal mechanical analysis (TMA) is the precise determination of the sample temperature. In this work a straightforward method is proposed and implemented that allows correction of the average sample temperature for a variety of probe geometries (flexural, tensile and compression). Hydrophilic polymeric-based matrices, with geometries similar to the sample to be tested, are swelled with a pure liquid (in this case water) and placed in the correct testing place of the equipment; a static force is applied at low temperature and the probe position is monitored in a temperature scan, where the melting of the standard is clearly detected and compared with the expected melting temperature. This allows the average sample temperature to be obtained, using a sample that exhibits similar thermal resistance to the sample to be tested, instead of probing specific locations inside the furnace, as it is usually proposed in calibration routines with pure metals. For the specific configurations analysed, a strong and similar dependence of the thermal lag on the scanning rate was found for both flexural and compression modes that also depends weakly on the sample dimensions. More complicated dependence of the thermal lag on the scanning rate is found for the tensile mode, probably due to the complex thermal environment existing inside the furnace with this arrangement. However, the results indicate that there is a significant contribution from the thermal resistance of the sample in the temperature correction. It is suggested that the proposed method may be employed in other situations such as isothermal and non-isothermal creep/stress relaxation experiments or in rheometers.