08 Jun 2020
From pasting pictures of your family onto an A4 coloured paper titled “Family Tree” for a project in primary school to creating animal faces by cutting and sticking small pieces of paper together to even spreading it across your hand and then peeling it off, the white pasty substance of glue has been constant throughout all your childhood experiences.
Glue stuck things together (and helped us bind, or bracket, several of your childhood experiences together in the last line!), but never stuck to its own bottle – why is that so? While that is a question that has confounded many, the short answer lies in the “driving force of all nature” – water (note that this post addresses only commonly-used white glue).
To understand this better, let’s look at the composition of glue. Glue is made up of polymers, which are long stretchy molecules helping the glue to stick, and water, which acts as a solvent and keeps the glue in a liquid state while it is in its bottle.
Now, take a step back and think about why glue is not in a liquid state after you put it on a piece of paper: when you take glue out of its bottle, you expose the water in the glue to the air, following which the water evaporates. As the water dries out, the glue only has those stretchy polymers left, so it dries and hardens without a solvent.
Therefore, glue doesn’t stick to it its own bottle, because when it is inside the bottle, it is not exposed to enough air to allow the water to evaporate and make the glue adhesive enough to stick to the bottle. This may also help you understand why glue dries out when you don’t put a cap on its bottle.
So, while glue doesn’t ordinarily stick to its bottle, it’s not entirely impossible – so, remember to close your glue bottles off from next time!