The influence of hydrogen peroxide on the rheological behaviour of Ultrez-21 gels

Abstract

Objectives. The aim of this study was to analyse the influence of hydrogen peroxide (H2 O2) and its concentrations on the rheological characteristics of Ultrez-21 1% gel, in order to develop and optimize formulations easy to prepare in the pharmacy, for various pharmaceutical or cosmetic applications. Material and methods. A series of gels containing 5-29.5% H2O2 were analysed and compared to the gel base in terms of rheological properties induced by the action of forces applied either with constant intensity (adhesiveness, consistency, extensibility, viscosity) or with variable intensity (viscous structural flow, thixotropy). Perhydrol has been selected as a source of H2O2, as it is a product commonly used in pharmacy, and which, being a concentrated solution (30% m/mH2O2), can be very easily diluted by mixing with water to obtain the desired concentration in gels. Outcomes. Even if the presence of H2O2 causes changes in adhesiveness, consistency, extensibility and viscosity of gels, they do not correlate with the H2O2 contents, each gel having its own specific behaviour. The gels have a lower flow threshold when are sheared at D = 0.33 s-1 than the gel base. Differences between shear flows are statistically significant both in terms of the deviation from linearity (Runs test) and the deviation from zero value (F test). The slopes of the regression lines have positive values in all cases, but statistically different (p 15% H2O2 decrease the thixotropic capacity of the Ultrez-21 gel with comparable values (32, 38, 35 and 28%). Conclusions. All the studied gels have a plastic-thixotropic behaviour which changes both with the presence and the concentration of hydrogen peroxide. The differences in consistency, adhesion and extensibility between the gels cannot be attributed to the viscosity, but rather to the degree of homogeneity and / or strength of the dispersed system formed by hydrogen peroxide in the Ultrez-21 gel. The flow behaviour of the gels correlates with the variation of pH, consistency and adhesiveness, and less with the spreading properties.

Keywords

• hydrogen peroxide
• ultrez-21
• carbopol gels; structural viscosity
• share flow
• tixotropy