COMPARISON OF DYNAMIC-MECHANICAL MEASUREMENTS AND TG DETERMINATIONS WITH 2 DIFFERENT INSTRUMENTS

The results of dynamic mechanical measurements in tension, made by usi ng two commercial dynamic mechanical instruments, a DMTA (Polymer Labo ratories) and a DMA (Perkin Elmer), are compared and discussed. Differ ences in T(g) values of approximately 10-degrees-C for an unfilled and a carbon-black-filled natural rubber (NR) were obtained, the higher t emperature being associated with the DMTA instrument. For an MDPE mate rial, temperature differences of approximately 14-degrees-C for the ga mma transition and approximately 8-degrees-C for the alpha: transition were noticed. These temperature differences were apparently due to te mperature calibration errors and show the need to have an acceptable c alibration standard for this type of measurement. The modulus values s howed good agreement except for very stiff materials such as NR at tem peratures below T(g), where the modulus values obtained with the DMTA were lower than those obtained with the DMA instrument. Incorrect samp le geometry giving too stiff a structure could explain this low modulu s. Different ways to characterize T(g) by thermal analysis are also co mpared and discussed, with the-emphasis on frequency-dependence.