Prevention of Hydrosilation Cure Inhibition in a Polysiloxane Adhesive by Surface Oxidation

For a variety of reasons epichlorohydrin-ethylene oxide (ECO)-based compounds, in the form of rain erosion boots or sleeves, are bonded to aircraft radomes using a hydrosilation-cured RTV polysiloxane adhesive. Unfortunately, cure of the adhesive can be completely inhibited by unreacted vulcanizing agent and/or ECO cure by-products. We have earlier shown that this inhibition can be prevented by treating the ECO surface with hydrogen peroxide to oxidize the hydrosilation catalyst poisons to a harmless state. In this study we have used spectroscopic techniques to monitor the hydrosilation reaction kinetics and in turn to identify the poison, define the poisoning level and monitor the poison removal by hydrogen peroxide treatment. The degree of poison removal is also correlated with adhesive bond strength using a 180°; peel test. The critical poison in the system was excess ECO vulcanizing agent which can be completely removed from the surface using a 30 vol. % H₂O₂ treatment for 30 minutes as long as the initial vulcanizing agent concentration is 1 p.p.h. or less.