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  • The oldest glue in the world is over 8,000 years old and comes from a cave near the Dead Sea.

  • Ancient people used this glue, made from a mixture of animal bone and plant materials, to waterproof baskets and construct utensils.

  • And for thousands of years after, plants and animals were the glue that held human civilization together.

  • Today, we have enough types of tape and glue to build and repair almost anything.

  • But what gives glue and tape their stickiness?

  • And is one stronger than the other?

  • Adhesives can be made from synthetic molecules or natural proteins and carbohydrates like the vegetable starch dextrin,

  • the milk protein casein, and the terpenes in tree resin.

  • In order to work, glue and tape need both adhesive bonds and cohesive bonds.

  • Adhesive bonds occur between an adhesive's molecules and the molecules of whatever it's sticking to.

  • Cohesive bonds happen between a glue or tape's own molecules, holding it together.

  • Most glues consist of adhesive polymers dissolved in a solvent that prevents them from sticking to the inside of the bottle.

  • The strong smell of many glues comes from the solvent, which evaporates when exposed to air.

  • Some glues use water as a solvent, but others use chemicals that can be harmful to inhale.

  • Glues with two or more components that chemically react instead of just drying can create stronger bonds.

  • Both the adhesive and cohesive bonds of glue are strong, but the drying process makes them irreversible.

  • This is why, if a glued surface is broken after it dries, it can't be reattached without new glue.

  • By contrast, when tape is applied to a surface, it forms weaker, reversible bonds, so you can peel a piece of tape off a surface and use it again.

  • These weak bonds, called Van der Waals forces, can occur between any two materials, but only if they're extremely close together, closer than the naked eye can see.

  • Tape usually consists of a backing coated with a combination of a rubber or rubber-like "stretchy" component, and a compound called a tackifier.

  • That's the "sticky" component.

  • A tape's stickiness is determined by the proportion of elastic component and tackifier,

  • the thickness of adhesive spread onto the backing, and the type of backing material.

  • No chemical reaction occurs when tape is pressed onto a surface.

  • Instead, the soft adhesive flows into the cracks and grooves of the surface.

  • This ability to slide into cracks and then stay in place is called viscoelasticity.

  • Once the viscoelastic adhesive fills these microscopic crevices, it is close enough to form Van der Waals forces.

  • So what's the world's strongest adhesive?

  • Well, there's no one answer.

  • In terms of absolute strength of adhesive bonds, glue is stronger than tape, but no single adhesive works well in all circumstances.

  • Of the glues, cyanoacrylates, or super glues, may form the strongest bonds,

  • but two-component epoxy glues have much higher resistance to heat and shearing, and are compatible with a wider range of surfaces.

  • So, if you wanted to dangle an anvil in the air, super glue might be your best bet.

  • But if you're doing so over an active volcano, you'd want an epoxy instead.

  • And in order to work at all, glues need enough real estate where surfaces touch.

  • If for some reason you wanted to make a chain of bowling balls, duct tape would be better.

  • Engineers weigh similar, if less absurd, factors all the time.

  • Choosing the right glue to withstand the heat inside an engine is a matter of life and death.

  • And though the strength of duct tape's adhesive bonds can't compete with those of epoxy glues,

  • tape does have the advantage of instantaneous stickiness in an emergency.

  • Glue may be necessary to get a rocket to space, but when it comes to extraterrestrial repairs, stick to duct tape: liquid glues don't work in zero gravity.

The oldest glue in the world is over 8,000 years old and comes from a cave near the Dead Sea.

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B2 US TED-Ed adhesive glue tape epoxy solvent

Which is stronger: Glue or tape? - Elizabeth Cox

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    Evangeline posted on 2021/04/30
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