Question: What packaging materials do you recommend for reactive adhesives and sealants that are sensitive to moisture or the atmosphere?
Answer: Packages are chosen based on performance and cost. Specialty materials like anaerobic adhesives need oxygen to maintain their stability and shelf life. These materials were traditionally packaged in low-density polyethylene tubes or bottles to allow air diffusion into the package. However, with modern stabilizer systems, many are now packaged successfully in high-density polyethylene containers like cartridges.
Other materials, such as cyanoacrylates, silicones or polyurethanes, need protection from atmospheric moisture to maximize their shelf life. Cyanoacrylates intended for consumer use have often been packaged in aluminum tubes, although one prominent manufacturer used a small polyethylene tube inside an overpack that contained a desiccant tablet to absorb moisture. More modern packs use thick-walled polyethylene bottles, as do products for industrial use.
Storage at low temperatures also maximizes shelf life. One-component silicones and polyurethanes are not quite as sensitive to moisture as cyanoacrylates and polyethylene tubes; hence, cartridges are usually adequate. In the case of silicones, premature thickening and curing is the danger, whereas in polyurethanes (whether one- or two-component), excessive moisture generates carbon dioxide gas that causes foaming and expansion of the adhesive or sealant. These sealants are also often formulated with sacrificial moisture absorbers.
Testing is, of course, essential to estimate shelf stability. Air permeability increases at high test temperatures, and moisture-sensitive products are tested in humidity cabinets at temperatures above ambient.