Abstract
The shelf stability of uncured silicone elastomers is of fundamental interest to the silicone industry because most formulations are sold in the uncured state for further processing. An increase in viscosity of a filled silicone elastomer with time, called “structuring” or “crepe-hardening”, can pose tremendous processing problems. The macroscopic effect of crepe-hardening with time was monitored in terms of its Williams plasticity. Plasticity and its rate of change with time were shown to depend on the fumed silica morphology, fumed silica loading, and the residual surface hydroxyls on the fumed silica after treatment. The microscopic mechanisms of polymer-filler interactions that drive the observed rheological behavior were investigated using proton T2 relaxation, 29Si NMR cross polarization dynamics, and by monitoring the changes in optical properties with time. It appeared that the dominant mechanism of shelf instability was due to an increase in the thickness of the adsorbed polymer layer. There was no change in the state of dispersion of the filler as the silicone elastomer aged.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call