Effect of Temperature on the Storage Life of Polysulfide Sealants
MATERIALS RESEARCH LABS ASCOT VALE (AUSTRALIA)
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The storage performance 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 Semkit form, has been surveyed. The sealants were separately maintained at temperatures of -16, 2, 13 and 25 C and changes in viscosity of the polymer base compound, cure rate, peel strength and application life were monitored over 26 months. Concurrent changes in thiol content of the liquid polymer in the base compound and concentrations of ManganeseIV or ChromiumVI in the cure pastes were also determined. Variations in activity of cure pastes with time were assessed using LP-32 as a standard polymer and changes in polymer base compounds were monitored by measuring cure rate with laboratory prepared reference cure pastes. Low temperature storage extended storage life significantly. After maintenance at temperatures of 2 degs and below, the canned sealants still performed satisfactorily after two to three years storage. Most materials were procured several months after manufacture and with reduction of acquisition time further extension of the low temperature storage life could be expected. No significant storage differences between PR-1750 and PR-1422 sealants or the A or B classes were noted. Dichromate-based cure pastes were prone to lose solvent at higher storage temperatures and some dried pastes resulted. The main cause of failures was oxidation of the polymer base compound which led to surface skinning and was accompanied by a gradual drop in thiol content. Peel strength was unaffected by storage and the concentrations of MnIV and CrVI were little changed.
- Adhesives, Seals and Binders