Science, Tech, Math › Science Thermal Properties of Composites Tg: The Glass Transition of FRP Composites Share Flipboard Email Print ollo / Getty Images Science Chemistry Chemistry In Everyday Life Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Todd Johnson Science Expert B.S., Business Management, University of Colorado Boulder Todd Johnson has worked on the development, commercialization, and sales sides of the composites industry since 2004. He also writes about the industry. our editorial process Todd Johnson Updated August 13, 2018 Fiber reinforced polymer composites are often used as structural components that are exposed to extremely high or low heats. These applications include: Automotive engine componentsAerospace and military productsElectronic and circuit board componentsOil and gas equipment The thermal performance of an FRP composite will be a direct result of the resin matrix and the curing process. Isophthalic, vinyl ester, and epoxy resins generally have very good thermal performance properties. While orthophthalic resins most often exhibit poor thermal performance properties. Additionally, the same resin can have vastly different properties, depending on the curing process, curing temperature, and time cured. For example, many epoxy resins require a "post-cure" to help reach the highest thermal performance characteristics. A post-cure is the method of adding temperature for a duration of time to a composite after the resin matrix has already cured through the thermosetting chemical reaction. A post cure can help align and organize the polymer molecules, further increasing structural and thermal properties. Tg - The Glass Transition Temperature FRP composites can be used in structural applications that require elevated temperatures, however, at higher temperatures, the composite can lose modulus properties. Meaning, the polymer can "soften" and become less stiff. The loss of modulus is gradual at lower temperatures, however, each polymer resin matrix will have a temperature that when reached, the composite will transition from a glassy state to a rubbery state. This transition is called the "glass transition temperature" or Tg. (Commonly referred to in conversation as "T sub g"). When designing a composite for a structural application, it is important to make sure the FRP composite's Tg will be higher than the temperature it might ever be exposed to. Even in non-structural applications, the Tg is important as the composite can change cosmetically if the Tg is exceeded. Tg is most commonly measured using two different methods: DSC - Differential Scanning Calorimetry This is a chemical analysis which detects energy absorption. A polymer requires a certain amount of energy to transition states, much like water requires a certain temperature to transition to steam. DMA - Dynamic Mechanical Analysis This method physically measures stiffness as heat is applied, when a rapid decrease in modulus properties occurs, the Tg has been reached. Although both methods of testing the Tg of a polymer composite are accurate, it is important to use the same method when comparing one composite or polymer matrix to another. This reduces variables and provides a more accurate comparison.