Ah yes, this is very similar to the paint-drying-in-the-tin question! Basically most glues require oxygen or an air source to help undergo the chemical reaction required to become sticky! If the glue is in a sealed tube with no air supply, then it won’t undergo any reactions, and therefore won’t become sticky!
Nice one Karen! It’s true, most glues require air to become sticky, which is why your glue will get stickier if you leave the cap off of the bottle or as the glue bottle empties (since air has replaced the liquid that was emptied out of your bottle). But some types of glue require a chemical other than those found in air and these types of glues won’t stick to the bottle even if you leave the cap off. Glue is an interesting and useful material… superglue for example, can hold a two ton truck in the air with only a few drops! cool hey! Great question Shauna 🙂
And there are some even more interesting glues that only become sticky when an electric current is passed through them! So you could literally turn the glue on and off! Pretty dangerous when there’s a truck stuck to the roof….