Thermal analysis of controlled-release elastomeric formulations. Part 2. A DSC study of the effect of sodium lauryl sulphate loading on vulcanization
Controlled release of sodium lauryl sulphate (SLS) from monolithic elastomeric pellets represents one way of achieving long-term inhibition of bacterial oxidation of pyrite. The degree of cure of elastomeric formulations influences the rate of release of SLS. Vulcanization decreases the permeability of the elastomeric matrix and results in slower release of SLS. The effect of SLS loading on the vulcanization of natural rubber and synthetic cis-1,4-polyisoprene has been studied by DSC. Dynamic temperature scans show that the heat of reaction (ΔH), which is a measure of the area of the exothermic peak, decreases with increasing SLS content. The decrease in ΔH is not very significant at SLS levels up to 15%, but is clearly noticeable at levels of 25%. In the case of formulations which contain 35% SLS, no curing exotherms are observed. It is therefore concluded that rubber formulations which contain 35% or more SLS are unvulcanized. Analysis of curing exotherms by means of the Borchardt and Daniels DSC kinetics data analysis program gives inconclusive results. It is suggested that the complex chemistry of the accelerated sulphur vulcanization of olefinic rubbers makes it difficult to obtain reliable quantitative reaction kinetics information for this particular type of reaction. © 1992.