Chemorheological Analyses of a Reaction Injection Moulding Polyurethane Formulation

Investigation on rheological properties of a reaction injection moulding polyurethane formulation was performed during the formation reaction. The effect of reaction temperature on the gelation time was studied in a wide temperature range covering temperatures below and above the gelation temperature. The gelation temperature and gel times were determined using the results of temperature sweep and time test experiments by employing rheological criteria. The results indicated that a noticeable increase has been occurred in the activation energy of gelation process at gelationtemperature. The shear rate dependency of the reactive mixture was also studied inlinear and non-linear viscoelastic domains. The viscosity of the reacting formulationexhibited shear thinning behaviour in both viscoelastic regions. By superimposing thecurves of shear viscosity in non-linear viscoelastic domain and the complex viscosityin linear viscoelastic region, it was found that the formed network-like structureremained intact under the shear rate in non-linear viscoelastic region. Moreover theseresults showed that by progression of the reaction the shear viscosity deviated to highervalues with respect to complex viscosity. This was attributed to the effective role ofconvective movements in non-linear viscoelastic regime. Convective movements ledto mobility increase of functional groups at high viscosities where the Brownianmotions are drastically retarded.