Torsional braid analyzer measurements of polymer damping factors



Measurements were made in a torsional braid analyzer (TBA) and a torsional pendulum (TP) on a diglycidyl ether of bisphenol A cured with methaphenylenediamine over a broad temperature range that included the γ transition of this polymer. Based on a comparison of the results from the two instruments, we conclude that (1) the relative shear modulus measured in the TBA differs from the absolute modulus measured in the TP by a multiplicative constant that is independent of temperature in the glassy state; (2) the damping factor measured in the TBA is, at least approximately, equal to the damping factor measured in the TP, contrary to the usual assumption that only relative values are obtained from the TBA; and (3) as a result of (1) and (2), the TBA can be used to determine not only the temperature of a transition but also its activation energy.