Shear flow of associative polymers in aqueous solutions

ABSTRACT The rheological behavior of two associative polymers in aqueous solutions, poly(vinyl alcohol) (PVA) and polyurethane (PU) was carefully investigated in steady shear conditions at different temperatures, ranging from 4°C to 80 °C. Also, dynamic light scattering measurements were carried out for rested and sheared samples and distinctive features were observed. The flow curves evidenced an associative tendency occurring in a certain shear rate range and the amplitude of this phenomenon is influenced by temperature and polymer composition. At moderate shear rates, the intermolecular interactions determine the formation of supramolecular structures that increase the viscosity of the system. Higher shear forces orient the macromolecules along the flow direction and improve the interaction of hydrophilic groups with the water molecules. On the other hand, the temperature and concentration increases allow the manifestation of hydrophobic interactions. The gelation as a function of temperature was followed in temperature sweep tests and the influence of PVA/PU composition was evidenced. The overall behavior of the system is dictated by the balance between these interactions at rest or during shear.