Measuring the Glass Transition Temperature of EPDM Roofing Materials: Comparison of DMA, TMA, and DSC Techniques

Two ethylene-propylene-diene monomer (EPDM) roofing membranes were aged at 100°C for 7 and 28 days. The Tg of these membranes was then determined by dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), and differential scanning calorimetry (DSC) and the results compared. It was found that: (1) Tg data can be obtained easily using the DMA and TMA techniques. The DSC method requires greater care due to the broad step change in the baseline which is associated with heavily plasticized materials. (2) The closest correspondence between techniques was for TMA and DSC (half-height). The latter, within experimental error, yielded the same glass transition temperature before and after heat-aging. (3) The peak maxima associated with tanδ and E“ measurements should be cited with Tg values as significant differences can exist. (4) The Tg(E") values were closer to the Tg(TMA) and Tg(DSC) data than were the Tg(tanδ) values. Data obtained at 1 Hz (or possibly less) should be used when making comparisons based on various techniques. An assessment of Tg values indicated that EPDM 112 roofing membrane is more stable than the EPDM 111 membrane. The Tg for EPDM 112 did not change significantly with heat-aging for 28 days at 130°C.