Evaluation of the Rheological Properties of Various Kinds of Carboxyvinylpolymer Gels

Abstract

The rheological properties of carboxyvinylpolymer (CVP) hydrogels were evaluated using various methodologies. As CVPs, the series of Hiviswako (HVW) 103, 104, and 105 (denoted as H₁₀₃, H₁₀₄, H₁₀₅, respectively), and Carbopol (CP) 934, 940, and 941 (denoted as C₉₃₄, C₉₄₀, C₉₄₁, respectively) were used. The rheological measurements were carried out by the capillary tube method, oscillation method, and continuous shear method (Ferranti-Shirley viscometer). These measurements were mainly performed on the HVW series because their properties are not as well established as those of CPs.In the HVW series, the order of magnitude of intrinsic viscosities obtained by the capillary tube method was H₁₀₅>H₁₀₄>H₁₀₃ at all pH values examined This order agreed with that of the viscoelastic parameters obtained by the oscillation method and that of the viscosity obtained by the continuous shear method when the gels were in a non-neutralized state. However, the orders were reversed when they were partially neutralized by adding alkali.From these results, the gel structure of each polymer was presumed to be as follows. In the case of H₁₀₃, the polymer is rich in side chains or cross-links and takes a compact form in the nonneutralized state. When alkali is added to H₁₀₃, side chains are extruded into the water phase by the electric repulsive forces between carboxyl groups, and the polymer molecules become entangled with each other, so that the gel shows larger viscoelastic values. On the other hand, in the case of H₁₀₅, the polymer is poor in side chains and the addition of alkali has less effect on the viscoelastic properties than in the case of H₁₀₃ or H₁₀₄, due to the lack of entanglement of side chains. The viscoelastic properties measured in glycol solutions and the swelling rate for the HVWs supported the above hypothesis.As regards CP, C₉₄₁ showed almost the same properties as H₁₀₅. C₉₃₄ and C₉₄₀ showed similar properties to H₁₀₃ and H₁₀₄ respectively, although some differences were observed among them.