Consistency of Carbopol 971-P NF gels and influence of soluble and cross-linked PVP.

A study is made of the polymerization process of polyacrylic acid, commercially known as Carbopol 971 NF, assessing its consistency as a function of the degree of neutralization at pH values from 3 to 12, approximately. Percentage concentrations ranging from 0.1 to 1.4% (w/w) were studied. The gels obtained were non-Newtonian, and pseudoplastic. As concentration and pH rise, the consistency of the gels increase to a maximum, which appears between pH 6 and 8, allowing their use as vehicles in bioadhesive formulations for mucosal application. Over the increasing viscosity interval, functions were obtained to indicate the consistency of the gel as a function of pH and concentration. Since the correlation between the theoretical and experimental results is excellent, the equation found can be used to theoretically calculate the working concentration and pH required to secure the necessary consistency for a given vehicle. The addition of soluble polyvinylpyrrolidone (PVP), and cross-linked PVP (PVPP) does not substantially modify the rheological behavior of the gels, thus permitting their addition to usual vehicles.