What properties necessitate the seemingly endless array of adhesives available? It seems like one good glue should be fine for everything. Can someone help me break them down into categories?

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I do construction and the number of adhesives is mind boggling. Really, the only glue that seems to bond anything is plumbers goop.

I guess I somewhat understand the concept of “solvent welding” in that certain glues melt some of the parts their bonding. But often, say with general construction adhesive, it’ll just not stick to plastics at all and you can peel it off after it dries.

Is there an easy way to understand all these things without pouring over the fine print of all the sundry tubes of stuff?

In: Chemistry
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I don’t think you will get a simple sum up. Adhesives are in active research and got a lot better in recent years. We discover more and more well working formulas each with their own advantages and disadvantages.

What surface they are good with depends on effects on the molecular level, so you won’t really find a one-size-fits-all solution or even simple categories.

Alone the molecule size in relation to each other can determine if it tends to crack at the interface when drying, causing a bunch of seemingly random compatability issues.

The main problem with plastics is that though we classify them as “plastics” in general there are a ton of different varieties. For eg. PVC,PC,PPE,etc and these are just the families with varieties existing inside them as well. Plus some applications use blends of two or more different plastics. What works for one particular material doesn’t always work for others. Generic ones which claim to work on all usually only manage a very weak bond and hence you see the peeling off often

There are many variables to the question „which glue should I use“.

There is material which, you already mentioned it, determines the types of chemical or physical reactions a glue needs to perform. How well it sticks to a certain material is called adhesion.

Then you have flexibility: if you use glue that gets very hard and stiff, the connection might break e.g. because of vibrations, but if the consistency is more „chewy“ (for lack of better wording), it might for example not hold a heavy item stuck onto a wall for it might just slowly slide down. In both cases it might stick to both materials (adhesion) but wont stick to itself (cohesion).

Another one is longevity, because sometimes it’s even wanted for the glue to not last forever to make disassembly easier.

Then there is resistance against environmental factors like temperature, uv radiation and moisture that change the properties of the glue.

Last but not least you always have to consider the costs of the components of the glue, and the technology that’s needed to make it.