This article describes how rheological experiments can be used to simulate the application of sealant coatings and to determine their in-use performance. This has considerable value in assessing the applicability and effect of particular fillers, and in optimizing formulation of the product. A number of experiments were performed on sealant samples containing stearic acid modified magnesium carbonate as a filler, and the ability of rheological testing to discern differences between samples of similar composition was shown.
In many systems, the filler makes up a significant proportion of the weight of the formulation - as much as 40%. As a result, it exerts considerable influence on the rheological properties of the system. Materials used as fillers range from expensive, highly effective fumed silica to cheaper but less-effective natural products such as carbonates and silica. There has been a recent trend toward the use of coated precipitated carbonates; these not only offer effective performance, but are also intermediate in price. The usual coating material is stearic acid, which anchors to the precipitated carbonate as the calcium or magnesium salt during processing.