Why does glue not dry up in a bottle?

Glue is an essential item used to bond various types of things. It is widely used in homes, offices, schools, manufacturing, medical industry, and forensics. The utmost importance of glue traces back ancient history. Prehistoric people utilized glue for the tools they used for their survival and even used them to repair pots and other items using glue from tree saps.

The pasty substance surely sticks nearly anything together. But, what is intriguing is why it doesn’t dry up or bond to its bottle?

Well, it’s all about polymers and water. The regular white glue that you often use at school or at home is made of an array of chemicals regarded as polymers, the same compound used for resins and plastics. Polymers are generally large molecules composed of smaller particles linked together. Other familiar household items that use polymers include nylon in fabrics and textiles, Teflon on your non-stick pans, PVC in plumbing, and Bakelite for electrical items.

But, polymers used on glue can be either stretchy or sticky. With the right blend of these polymers, manufacturers are able to produce different types of adhesives. Glue also contains water, which serves as a solvent to keep the glue’s fluidity until you decide to use it.

When you use glue on a piece of cardboard or paper, water or the solvent is exposed to air. It causes the water to evaporate, leaving only the polymers in the material and freeing it to do its function. It leads to mechanical adhesion, and the glue dries up or hardens, bonding two things together.

Now, why doesn’t glue dry up or stick inside the bottle?

It boils down to the amount of air present. There is not enough air present inside the bottle that may cause water’s evaporation and reinforce mechanical adhesion. With that, the glue doesn’t harden or dries up. The bottle actually serves as the glue’s protection from the air, keeping it runny and available for use when you need it. With that, never ever left the cap off the glue bottle as it can cause the glue to dry up.

But, what about the super glue? You may have observed that they dry out or harden in its medium quicker than white glue does.

It stems down to the component instead. Super glue is composed of a chemical regarded as cyanoacrylate instead of using polymers. Cyanoacrylate is a strong, biodegradable adhesive that quickly polymerizes and adheres well to porous surfaces. The compound quickly bonds stuff together as it reacts with the water vapor present in the air, reinforcing a process called chemical adhesion.

You may think that the air is dry, but there is actually a certain amount of water vapor lurking in the air. So, super glue must be kept in a tightly-sealed vessel to keep it from drying out. Through hat, no water vapor can enter and react with the super glue.

Basically, water is responsible for why both white and super glue dries out. However, the water works on them in opposite ways. On white glue, water serves as the solvent keeping the glue runny, sticky, and available for use. Meanwhile, for super glue, water vapor acts as the culprit why it quickly hardens. So, whichever glue you are using, store them based on how they interact with water!

More Readings:

Adhesive (Wikipedia)

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