مرکز منطقه ای اطلاع رساني علوم و فناوري -

چكيده لاتين :

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 gelation temperature. The shear rate dependency of the reactive mixture was also studied in linear and non-linear viscoelastic domains. The viscosity of the reacting formulation exhibited shear thinning behaviour in both viscoelastic regions. By superimposing the curves of shear viscosity in non-linear viscoelastic domain and the complex viscosity in linear viscoelastic region, it was found that the formed network-like structure remained intact under the shear rate in non-linear viscoelastic region. Moreover these results showed that by progression of the reaction the shear viscosity deviated to higher values with respect to complex viscosity. This was attributed to the effective role of convective movements in non-linear viscoelastic regime. Convective movements led to mobility increase of functional groups at high viscosities where the Brownian motions are drastically retarded.