The glass transition temperature (Tg) might be the most important parameter in polymer materials science—it determines the maximum use temperature (for structural materials) and the minimum processing temperature (for thermoplastic materials). But many engineers don't realize that the Tg value of the same material can differ depending on whether it's measured by DSC, DMA, or TMA. This isn’t a “wrong measurement”; the three methods detect different physical manifestations of the glass transition.

DSC measures Tg—changes in heat capacity. DSC determines Tg by detecting the step change in heat capacity during the glass transition. This is the most common and standardized method (ASTM E1356). Pros: simple operation, small sample amounts (5-20mg), and fast. Cons: For highly crosslinked systems, highly filled systems, or materials with subtle changes in heat capacity, DSC signals may be weak or even undetectable.

DMA measures Tg—changes in mechanical behavior. DMA determines Tg by measuring the sharp drop in storage modulus E' and the peak in tan δ. It’s 10-100 times more sensitive than DSC—weak Tg signals that DSC can’t detect are usually measurable by DMA. This is the preferred method for electronic packaging materials and high-performance composites. The tan δ peak temperature, E" peak temperature, and E' onset temperature in DMA correspond to different definitions of Tg.

TMA measures Tg—changes in dimensions. TMA determines Tg by detecting changes in the expansion rate (CTE transition point) during heating. This is suitable for films, fibers, coatings, and other sample forms that are hard to test with DSC or DMA.

Dehui Scientific Instruments (www.dehuisci.com) represents a full range of thermal analysis equipment and can recommend the best Tg measurement method based on material type. Phone: 0512-67071902.