Characterization of the Setting Process in Dental Polysulfide Rubbers

¹ Dental School of The London Hospital Medical College, University of London, London, England

The force necessary to extrude material at a constant rate increases exponentially with time. Hence the polysulfide rubbers show no clearly definable initial set. This implies that the reaction commences as soon as the lead dioxide "catalyst" paste is added. However, in the early stages of set, this reaction merely results in an increase in viscosity.

Since the extrusion force increases exponentially with time, a single parameter k (dimensions time^-1) characterizes the whole setting process. This parameter is relatively insensitive to the concentration of catalyst paste (in marked contrast to the parallel situation with silicone rubbers) but is temperature dependent with an activation energy of about 12 Kcal. per mole.