The Strongest Glue in the World

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Hint: It’s not what usually comes in these bottles

This was my answer to a question on Quora that was quite popular.

I think it would depend on what you are trying to glue together, but from an all around perspective in terms of general adhesive strength (I’m guessing metals) you would either want to pick a polyurethane or an epoxy resin thermoset.

If you are looking for something with very good thermal properties (high Tg, high thermal stability) epoxy resins are a good choice, but they are kind of expensive and a little challenging to work with due to the need to mix in an appropriate cross linker. The auto industry is already using epoxy resins to glue together car parts near the engine where thermal resistance is essential.

Polyurethanes are typically cheaper and easier to work with, but they probably won’t have the same thermal resistance as an epoxy resin. I’m not as familiar with polyurethanes, but they are very prevalent as an adhesive as well.

The more aromaticity in your glue (phenyl/phenol) groups such as an epoxy resin based on a bisphenol the stronger the resin.

To answer your question in terms of strength that can depend on how thick and well prepared your sample is, but for tensile strength easily over 1000 MPa for youngs modulus and probably over 50 MPa for tensile strength (at break) for an ASTM type IV tensile mold. Numbers are kind of meaningless unless you attach specific dimensions to the sample being tested.

But the strength of the glue shouldn’t necessarily be your biggest concern. Adhesion should be the most important aspect as that can be a likely source of failure. So surface chemistry of what you are trying to glue together is extremely important.

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Writer of The Polymerist newsletter. Talk to me about chemistry, polymers, plastics, sustainability, climate change, and the future of how we live.

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