eli5: Glue container boasts Bonds: Metal, Plastic, Wood, Etc. So why does the plastic cap not firmly adhere to the metal tube? And why does the dried glue easily rub off the metal tube?

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eli5: Glue container boasts Bonds: Metal, Plastic, Wood, Etc. So why does the plastic cap not firmly adhere to the metal tube? And why does the dried glue easily rub off the metal tube?

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The glue needs exposure to the water vapour in the air to work, but over time the glue will cease to function. Cyanoacrylates like superglue and krazyglue stick by forming polymers when exposed to hydroxyl ions from water in their surroundings. However this does mean that the glue has a relatively short shelf life as the glue start to form these bonds in the tube. https://youtu.be/t1bHLCO1Y6Q

For glue to stick things together, it normally has to ‘dry’. Some glues literally dry out in open air, as their liquid content slowly becomes a gas and floats off. Some glues absorb water and use it to ‘dry’. Some more niche glues use other methods.