We use adhesives when we want to stick to surfaces to one another. The end by-product is the adhesive hardening. However, when adhesive is stored inside its pack, why doesn’t it harden within the pack and never come out? What makes it remain liquidic inside its packaging even after a long time?
In: Chemistry
Many adhesives contain a solvent, a liquid that can dissolve them. As long as the solvent is around, the adhesive stays soft. The adhesive “dries” when the solvent evaporates and the adhesive is left behind. So as long as the container is closed the solvent can’t evaporate. For simple white glue, the solvent is water. For rubber cement or plastic glue, it’s some kind of organic solvent.
Other adhesives contain precursor molecules that undergo a chemical reaction when they’re exposed to a catalyst (a chemical that triggers the reaction). That can be water (which is almost everything in tiny quantities), oxygen, a dedicated hardener (e.g. epoxy resin), certain metals (Loctite), etc. In thoses cases, as long as you keep them away from the catalyst then you don’t trigger the reaction.
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