Question

Why does the glue does not stick to its own tube??

Answer 1

this process is called mechanical adhesion. when white glue is inside a bottle there is not enough air inside it to cause the water to evaporate to make the glue sticky.
basically the bottle protects the glue from the air and keeps the glue runny.if you have ever left the top off a glue bottle for a while you may have noticed that the glue has dried up

Answer 2

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As the water evaporates, the glue dries and hardens. All that's left are the sticky polymers that hold things together. ... When white glue is inside a bottle, there's not enough air inside the bottle to cause the water to evaporate to make the glue sticky.