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Which is stronger: Glue or tape? - Elizabeth Cox

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    The oldest glue in the world
    is over 8,000 years old
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    and comes from a cave near the Dead Sea.
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    Ancient people used this glue,
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    made from a mixture of animal bone
    and plant materials,
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    to waterproof baskets
    and construct utensils.
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    And for thousands of years after,
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    plants and animals were the glue
    that held human civilization together.
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    Today, we have enough types of tape and
    glue to build and repair almost anything.
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    But what gives glue
    and tape their stickiness?
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    And is one stronger than the other?
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    Adhesives can be made
    from synthetic molecules
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    or natural proteins and carbohydrates
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    like the vegetable starch dextrin,
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    the milk protein casein,
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    and the terpenes in tree resin.
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    In order to work, glue and tape need
    both adhesive bonds and cohesive bonds.
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    Adhesive bonds occur between
    an adhesive’s molecules
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    and the molecules
    of whatever it’s sticking to.
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    Cohesive bonds happen between
    a glue or tape’s own molecules,
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    holding it together.
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    Most glues consist of adhesive polymers
    dissolved in a solvent
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    that prevents them from sticking
    to the inside of the bottle.
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    The strong smell of many glues
    comes from the solvent,
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    which evaporates when exposed to air.
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    Some glues use water as a solvent,
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    but others use chemicals
    that can be harmful to inhale.
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    Glues with two or more components that
    chemically react instead of just drying
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    can create stronger bonds.
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    Both the adhesive and cohesive bonds
    of glue are strong,
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    but the drying process
    makes them irreversible.
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    This is why, if a glued surface
    is broken after it dries,
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    it can’t be reattached without new glue.
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    By contrast,
    when tape is applied to a surface,
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    it forms weaker, reversible bonds,
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    so you can peel a piece of tape off
    a surface and use it again.
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    These weak bonds,
    called Van der Waals forces,
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    can occur between any two materials,
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    but only if they’re
    extremely close together,
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    closer than the naked eye can see.
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    Tape usually consists of a backing coated
    with a combination of a rubber
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    or rubber-like "stretchy" component,
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    and a compound called a tackifier.
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    That’s the "sticky" component.
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    A tape’s stickiness is determined
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    by the proportion of elastic component
    and tackifier,
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    the thickness of adhesive spread
    onto the backing,
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    and the type of backing material.
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    No chemical reaction occurs
    when tape is pressed onto a surface.
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    Instead, the soft adhesive flows into
    the cracks and grooves of the surface.
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    This ability to slide into cracks and then
    stay in place is called viscoelasticity.
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    Once the viscoelastic adhesive fills
    these microscopic crevices,
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    it is close enough to form
    Van der Waals forces.
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    So what’s the world’s strongest adhesive?
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    Well, there’s no one answer.
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    In terms of absolute strength
    of adhesive bonds,
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    glue is stronger than tape,
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    but no single adhesive
    works well in all circumstances.
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    Of the glues, cyanoacrylates,
    or super glues,
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    may form the strongest bonds,
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    but two-component epoxy glues have much
    higher resistance to heat and shearing,
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    and are compatible
    with a wider range of surfaces.
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    So, if you wanted
    to dangle an anvil in the air,
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    super glue might be your best bet.
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    But if you’re doing so
    over an active volcano,
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    you’d want an epoxy instead.
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    And in order to work at all,
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    glues need enough real estate
    where surfaces touch.
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    If for some reason you wanted
    to make a chain of bowling balls,
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    duct tape would be better.
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    Engineers weigh similar,
    if less absurd, factors all the time.
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    Choosing the right glue to withstand
    the heat inside an engine
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    is a matter of life and death.
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    And though the strength
    of duct tape’s adhesive bonds
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    can’t compete with those of epoxy glues,
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    tape does have the advantage of
    instantaneous stickiness in an emergency.
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    Glue may be necessary
    to get a rocket to space,
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    but when it comes
    to extraterrestrial repairs,
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    stick to duct tape:
    liquid glues don’t work in zero gravity.
Title:
Which is stronger: Glue or tape? - Elizabeth Cox
Description:

View full lesson:

The oldest glue in the world is over 8,000 years old and comes from a cave near the Dead Sea. 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? Elizabeth Cox explores the world of adhesives.

Lesson by Elizabeth Cox, animation by Sinbad Richardson.

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Video Language:
English
Team:
closed TED
Project:
TED-Ed
Duration:
04:51

English subtitles

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