DMA testing of epoxy resins: The importance of dimensions

Abstract

Dynamic mechanical analysis is commonly used to characterize thermoset polymers at temperatures ranging from well below to well above their glass transition temperatures. Many sample fixtures are available; however, the best clamp and best sample dimensions for a given material are not often readily apparent. Five different epoxy amine networks with glass transitions spanning over 1008C were characterized on three-point bending, dual cantilever, and single cantilever clamps with both constant thickness and constant span-to-thickness. Glassy modulus values were accurately measured on all clamps provided span-to-thickness ratios >10 were maintained. Thermal expansion and decreasing sample stiffness with increasing temperature greatly affect measurements in the rubbery region resulting in single cantilever clamps being best suited to measure rubbery data.

Preparation and Characterization of Highly Bio‐Based Epoxy Amine Thermosets Derived from Lignocellulosics

“…MW c data were calculated using the minimum value of the storage modulus for the thick samples using the theory of rubber elasticity (Equation ) where ρ is the cured resin density, R is the gas constant, T E ′min is the temperature at which the storage modulus is minimized, and E ′ min is the minimum value of the storage modulus. Only the thick samples were stiff enough to ensure reliable modulus data in the rubbery regime …”

“…Overall, the thermomechanical properties and thermal stability exhibited by the cured resins produced in this study were similar to comparable thermosets reported in literature, but consisted of much greater bio‐based content. In particular, these bio‐based polymers had properties higher than that of EPON828‐Jeffamine systems, while lower than that of EPON828‐PACM . This bioderivation alone makes these tunable‐property thermosets of immediate and significant value as replacements for less‐sustainably sourced and more hazardous incumbent resins.…”

“…Due to span‐to‐thickness ratio induced effects in DMA analyses, samples were prepared of two uniform dimensions, 17.5 mm × 12 mm × 2.9 mm (thick samples) and 17.5 mm × 12 mm × 1.6 mm (thin samples). Samples with lower span‐to‐thickness ratios display more accurate rubbery region data, whereas samples with span‐to‐thickness ratios > 10 are useful for accurate measurements of glassy region data (i.e., storage modulus) . Samples were run using single cantilever clamp geometry at a 1.0 Hz frequency, a set Poisson's ratio of 0.35, and a deflection amplitude of oscillation of 7.5 µm with a heating ramp of 2 °C min −1 from 0 to 200 °C.…”

“…Samples were run using single cantilever clamp geometry at a 1.0 Hz frequency, a set Poisson's ratio of 0.35, and a deflection amplitude of oscillation of 7.5 µm with a heating ramp of 2 °C min −1 from 0 to 200 °C. The T g of each sample was taken to be the peak of the loss modulus ( E ″) curve as a more conservative estimate of T g compared to using the peak of the tan δ . The temperature of the inflection point of the storage modulus ( E ′) curve also coincides more closely with that of the peak of E ″ than with the temperature for the peak of tan δ.…”

Kinetics studies and characterization of poly(furfuryl alcohol) for use as bio‐based furan novolacs

“…The samples were tested at 1 Hz and amplitude of 2.5 µm, while subjected to a temperature ramp from −20 to 200 °C at a rate of 2 °C/min. DMA can be used to determine the glass transition temperature of a polymer through three methods . Storage modulus ( E ′) is one method where the inflection point is considered the T g .…”