Effect of temperature on the storage life of polysulfide aircraft sealants

The storage performance from −16° to 25°C of a range of PR-1422 PR-1436G and PR-1750 two-part polysulfide aircraft sealants of A and B classes, packaged both in cans and injection kits, has been surveyed. Changes in viscosity of the base compound, cure rate, peel strength and application life were monitored over 36 months together with the thiol content of the polymer and concentrations of Mn(IV) or Cr(VI) in cure pastes. Variations in activity of cure pastes and polymer bases were assessed by using a reference polysuflide and laboratory prepared cure pastes, respectively. Low temperature storage extended sealant life significantly: at 2°C and below, canned sealants performed satisfactorily after 2 to 3 years' storage. All failures were due either to oxidation of the polymer, which led to surface skinning or solvent loss from dichromate based curatives. Peel strength was unaffected and the concentrations of Mn(IV) and Cr(VI) were little changed. The shelf life of injection kits could also be extended at low temperatures, but it was essential to use a sheath of low permeability to prevent ingress of air.