Viscoelastic behavior of dehydroabietic acid

Abstract

The viscoelastic behavior of a rosin derivative, dehydroabietic acid, DHAA, has been determined with shear creep and recovery measurements at temperatures between 43 and 88 °C. The viscosity measurements extended up to 162 °C. The glass temperature Tg (0.2 °C/min cooling) was estimated to be 43.3 °C. Earlier measurements on a commercially produced dehydrogenated rosin called Galex, which was thought to be relatively pure DHAA, had a Tg of 7 °C. A steady-state recoverable compliance, JS, of 2.2×10−7 cm2/dyne was extracted from a reduced shear compliance curve. Our measurements on highly purified DHAA showed JS of 1.4×10−10 cm2/dyne. However an unmodified rosin does show large recoverable compliances that are comparable to those found in Galex. We have concluded that rosin and Galex are dilute polymer solutions. All of the common viscoelastic functions have been calculated from the retardation spectrum determined, the glassy compliance Jg, and the viscosity of DHAA. It is believed that such a complete description of the viscoelastic behavior of an organic nonpolymeric glass former has not previously been presented. At Tg the retardation spectrum was found to be the same as that of all other amorphous glass formers at times between 0.1 and 1000 s within experimental uncertainty.