Thermal analysis of controlled-release elastomeric formulations. Part 1. Determination of the solubility limits of sodium lauryl sulphate in elastomers by differential scanning calorimetry
Controlled-release formulations for attaining long-term inhibition of bacterial oxidation of pyrite and the concomitant acid mine drainage were prepared from natural and synthetic rubbers used as binding matrices and sodium lauryl sulphate (SLS) as the active ingredient. The kinetics of release of an active agent from a polymeric matrix depend on several solute-dependent and solute-independent variables. This study focuses on one of the solute-dependent variables, namely, the solubility limit. Since no data on the solubility limits of SLS in natural and synthetic rubbers could be traced, techniques for determining these solubility values were investigated. In this study natural rubber (SMR 20) and synthetic cis-1,4-polyisoprene (IR-80) formulations containing from 0 to 35% SLS were analysed by differential scanning calorimetry (DSC). The thermograms obtained show the appearance of a characteristic melting endotherm when the solubility limit of SLS is exceeded, and this allows the amounts of dissolved and dispersed SLS in the controlled-release formulations to be estimated. The results of the study demonstrate the usefulness of DSC as a convenient and reliable method for determining the solubility limits of solids in elastomers. © 1992.