When you get a roll of tape, the tape is rolled and stuck on top of itself. So how does it not lose its stickiness then? And how does the stickiness instantly fades away when you stick it to something else and then peel of off?
In: Chemistry
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Everything you stick the tape to is dirty. That dirt bonds to the tape adhesive, leaving less exposed adhesive to adhere to the next thing. The top of the tape is clean when it’s rolled so there’s not schmoo on the adhesive.
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There are 2 ways in which things are considered sticky. The primary being chemical and secondary being physical. Physical is a whole other subject as it deals with low level interactions of molecules (IE Gecko Tape). The one most people are familiar with is chemical and is why tape has that very distinct “tack” when you touch it.
The tack forms due to a reaction between the glue on the tape and the surface of whatever your trying to stick it too. When a roll of tape is rolled up, the backside has been given great care to ensure its cleaned and may sometimes be coated in a way that slows down the reaction of the glue.
While this has allowed the creation of very powerful adhesives there is many downsides to making tape that adheres stuff chemically. One of the main ones being that once the reactants in the glue have been used up, the tape is nothing more than the backing that was holding the glue in the first place. Tape is considered to have a shelf life for this very reason as common things that drive chemical reactions such as oxygen, heat, and time will cause parts of the tape to break down. This results in the tape prematurely adhering to the backing, the tack being less effective and why that edge on the tape can be hard to find. The glue has reacted with the air and bonded partially to the tape backing
Also, to add to what everyone else is saying, most things you stick tape to will have some dust on them, which will make it less sticky. Even if it’s just a little bit, it’ll still effect the adhesive
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