CHEMORHEOLOGY OF A HIGHLY FILLED EPOXY COMPOUND

Based on measurements of the dynamic viscosity, a strategy is proposed to find an expression that relates the viscosity of an epoxy compound during curing, to the temperature, shear rate, and degree of reaction . It appeared that the dynamic viscosity is a unique function of the e ffective shear rate (i.e. the product of frequency and strain) over a wide range of frequencies and strains after being corrected for the te mperature. The effective shear rate dependence of the viscosity is des cribed with a power law with an exponent that depends on the conversio n. The effect of temperature is described with an Arrhenius-type equat ion with conversion dependent parameters. Differential scanning calori metry is applied to determine the kinetic equation that is used, in co mbination with the thermal history, to obtain the conversion during th e rheological measurements. The description of the viscosity gives a g ood prediction of the measured viscosity in the region behveen melting and gelation of the compound. The theories proposed in the literature to detect the gel point from dynamic experiments are examined. It is found that neither the G'-G '' crossover, investigated by e.g. Tung an d Dynes (i), nor the frequency-independence of tan(delta), described b y Winter (2, 3), can be used to determine the gel point of the given m aterial. In contrast, the curves of G' against conversion for measurem ents performed at equal strain but with different thermal histories ap pear to converge at a conversion of similar to 18%,which agrees with t he gel point determined through extraction experiments.