The rheological properties of carbopol gels I. Continuous shear and creep properties of carbopol gels

The effect of physical and chemical variables on consistency of Carbopol 940 and 941 gels was investigated by continuous shear rheometry. Gels provided plastic flow curves with negligible hysteresis. Continuous shear properties were not greatly affected by centrifuging, milling, temperature cycling, and ageing. Initial addition of neutralizing agent (0–6% w/w for 3% gels) markedly increased consistency; further addition caused a more gradual increase. Daylight reduced consistency. Apparent viscosities varied exponentially with concentration. Increased temperature gradually decreased apparent viscosity. Solvents had a variable effect on apparent viscosities which could not be correlated with solvent viscosity nor molecular weight. Apparent viscosities for gels neutralized with different bases were independent of type of base used.Small strain testing investigated fundamental properties of Carbopol gels and determined the effect of polymer concentration, temperature, neutralization, different solvents and neutralizers. Gels were linear viscoelastic and to a first approximation were elastic solids. Creep compliance varied exponentially with concentration and showed no correlation with solvent or neutralizer type.