1998 Volume 26 Issue 3 Pages 157-162
Rheological behavior was examined for suspensions of PMMA powder/associating polymer solution. Hydrophobically modified ethoxylated urethane (HEUR) was used as the associating polymer. Suspensions showed non-Newtonian flow at lower HEUR concentrations. Flocculation and sedimentation of PMMA powder was induced by the addition of HEUR polymer in this concentration range, suggesting that associating thickners also act as flocculant. Suspensions showed Newtonian flow at higher HEUR concentrations. In this concentration range, aqueous solutions of HEUR showed linear viscoelastic behavior which was caused by networks of hydrophobically associated HEUR polymers. Frequency dependence of the storage modulus and the loss modulus of HEUR solutions and PMMA/HEUR suspensions showed almost straight lines with slopes of 2 and 1, respectively. The relaxation time of HEUR aqueous solutions estimated from master curves was independent of the polymer concentration. The relaxation time of PMMA/HEUR suspensions was almost the same as that of HEUR aqueous solutions. These results imply that the dispersed particle does not affect the lifetime of intermolecular junction. Viscosity and relaxation time of HEUR aqueous solutions showed Arrhenius type of dependence on temperature, but a deviation occured above a certain critical temperature. Flow curves of suspensions changed from Newtonian to non-Newtonian and frequency dependence of moduli yielded a shoulder at this critical temperature even in the higher HEUR concentration range. It is deduced that the association of hydrophobic groups was destroyed by increasing temperature, and resulted in the flocculation of the particles. This temperature-induced flocculation was thermoreversible, because the shoulder in frequency dependency of moduli disappeared with decreasing temperature.
