Viscoelastic Properties of Polyacrylic Acid Gels in Mixed Solvents

The objective of this study is to investigate the viscoelastic properties of Carbopol 934P polymeric systems in a variety of mixtures of pharmaceutical solvents. Carbopol 934P neutralized with a 1:1 equivalent ratio of triethanolamine was dissolved in various binary or ternary solvent mixtures consisting of propylene glycol, glycerol formal, and water. Dynamic moduli G and G, complex viscosities, and , and loss tangent, tan, were examined over a frequency range of 10-3 to 10 Hz using an oscillatory viscoelastic rheometer at 30°C. The results indicated that for 0.5-1.5 wt% neutralized Carbopol in ternary mixtures, G and G increased by 3-4 orders of magnitude and the phase angle decreased from 80 to 25° when the water content in the solvent mixture increased from 10 to 80 wt%. These studies also indicated that the addition of water to nonaqueous Carbopol 934P polymer systems transforms them from low-viscosity solutions to gels with significant elastic behavior involving physical interaction and entanglement of polymer segments with solvents.