Rheological behaviour of a commercial TGDDM-DDS based epoxy matrix during the isothermal cure

The change of the viscosity profile during the isothermal cure of a commercially available epoxy system commonly used as a matrix for high performance composites, TGDDM-DDS from CIBA, has been obtained by means of both a constant shear rate viscometer and a dynamic one. The range of temperature investigated varied from 120 up to 180°C. The increase of the molecular weight during the cure reaction is reflected on a macroscopic level in a progressive linear increase of the logarithm of the shear viscosity up to a critical point, near gelation, where an upturn is observed. The values of the time and viscosity at the critical point have been used to normalize the experimental data in a single generalized curve of the cure-viscosity profile. The William, Landel and Ferry equation has been found to adequately describe the temperature dependence of the viscosity for systems in the range of temperatures where the cure reaction did not occur. The apparent activation energy of the cure reaction, 19.7 Kcal/mole, obtained from the critical times, is consistent with calorimetric determinations. © 1984 Steinkopff.