HYDROPHOBICALLY-MODIFIED URETHANE-ETHOXYLATE (HEUR) ASSOCIATIVE THICKENERS .1. RHEOLOGY OF AQUEOUS-SOLUTIONS AND INTERACTIONS WITH SURFACTANTS

The rheological properties of aqueous solutions of hydrophobically mod ified ethylene oxide-urethane block copolymers, or HEUR thickeners, of different chemical compositions have been studied. A steep increase i n viscosity with increasing thickener concentration is obtained at a c oncentration that increases with decreasing polymer molecular weight a s predicted by a simple network model. However, this model does not pr edict the efficiency of the thickener, which is greatly affected by th e hydrophobicity of the terminal hydrocarbon chains and decreases in t he order octadecyl > pentadecyl > 9-heptadecenyl. The more hydrophobic the end groups, the stronger are the cross-link points in the network , and as a consequence the more clastic is the solution. In HEUR solut ions adjusted to the low shear viscosity of 10 Pa s, 6-12% of the thic kener molecules are elastically effective in the network and the upper limit of the aggregation number is 40-60. The addition of surfactant increases the viscosity of the HEUR solutions, until, for most systems , a maximum is reached, after which the viscosity decreases. The magni tude of the variation in viscosity is dependent on the chemical struct ures of both the polymer and the surfactant. The observed differences can be explained qualitatively by stoichiometric considerations of the mixed aggregates that are assumed to be formed between the hydrophobi c chains of the polymer and the surfactant. Additional information rel ating to the HEUR-surfactant interaction was obtained from surface ten sion measurements. A non-ionic surfactant is bound by a non-cooperativ e process only to the hydrophobic aggregates of the HEUR. Sodium dodec yl sulphate is bound both to the hydrophobic domains and to the ethyle ne oxide blocks of the HEUR polymers.