Flow behavior of hydroxypropyl methyl cellulose/polyacrylic acid interpolymer complexes in aqueous media

The intermolecular complexation of non-ionic polymers with weak acids having chemically complementary structures is an important approach to modify the viscosity of polymer solutions. In this study intermolecular complexation of hydroxypropyl methyl cellulose (HPMC) with polyacrylic acid (PAA) in an aqueous medium was studied. The study focuses on the factors affecting the complexation and rheological behavior of the HPMC/PAA system including the stoichiometric ratio of the two polymers, the molecular weight of the PAA, and the pH and ionic strength of the medium. Results showed that interpolymer complexation occurred between HPMC and PAA at low pH. It was attributed to hydrogen bonding between the -COOH group of the PAA and the -OH group of the HPMC. Under basic conditions (above the critical pH) the viscosity of the interpolymer complex increased accompanied by a transition from a compact interpolymer complexation structure to an extended conformation of interpolymer associates. Introduction of monovalent and multivalent salts (at > pH(critical)) decreased the viscosity of the HPMC/PAA interpolymer associates and favored the formation of interpolymer complexes between the two polymers. (C) 2012 Society of Chemical Industry