Following HPMC gelation with a piezoelectric quartz crystal

The reversible thermal gelation of HPMC is the basis for many applications. A simple, fast and low-cost thermal characterization is important for manufacturers in order to choose the appropriate thermal conditions for each purpose and to avoid undesired changes in rheological properties when HPMC solutions are subjected to temperatures above that of gelation. In this work, a simple piezoelectric quartz crystal, without any coating, was used to monitoring the changes in the physical properties of several HPMC solutions when submitted to different thermal conditions. The technique allowed to follow the gelation process from its beginning. Submitting the HPMC solution to consecutive thermal cycles allowed to conclude on the reversibility of the overall process and of the physical changes induced by temperature. Inductance and resistance measurements are strongly dependent on the absolute value of temperature, above or below gelation, and reflect the changes on the properties of the HPMC solution.