MadSci Network: Physics

Re: How does Blu -Tak work, and what is it made of

Date: Wed Jan 22 16:07:48 2003
Posted By: Joseph Weeks, President
Area of science: Physics
ID: 1039784005.Ph


Good question.  Blu-Tack (note the correct spelling) is manufactured by 
BostikFindley, a company that specializes in adhesives.  And like most 
trade secrets, they don't want to share their secrets either.  So we have 
to kind of guess what makes Blu-Tack work.  The first thing I did was
look for a material safety data sheet.  The MSDS sheet at least will tell 
you the chemical composition for the material.  The Blu-Tack MSDS can be 
found at: 
The useful thing that we learn from the sheet is that the composition of 
Blu-Tack is: Mineral Fillers-60 to 100%; Mineral Oil-1 to 10%; Hydrocarbon 
Polymers-1 to 10%; Pigment-0 to 1%.

Hydrocarbon polymers is the adhesive component in Blu-Tack.  Polymers tend 
to be pretty sticky; they are long chained hydrocarbons that have lots of 
hydrogen on the surface that tend to form physical bonds with anything 
that they come in contact with.  Hydrocarbon polymers include most glues, 
the resin in paint, the glue in fiber glass.  So the hydrocarbon polymer 
in Blu-Tack is the part that makes it sticky.

Probably the real trick is how to limit the stickiness of Blu-Tack; you 
want something to stick or hold in place, but to be removed cleanly when 
you pull it off the wall.  The mineral fillers and hydrocarbon oil 
probably both combine to limit the stickiness of the Blu-Tack.  Both of 
them probably tie up some of the sticky sites on the polymer so that the 
polymer only has a fraction of its real adhesive strength for bonding.  If 
a batch of Blu-Tack is too sticky, probably a bit of additional mineral 
oil or filler will bring the stickiness down.

The mineral filler also has one other important function.  Except for the 
mineral filler, Blu-Tack is a liquid.  The filler gives the mixture 
structure, otherwise the Blu-Tack would gradually distort and flow down 
the wall given time, just like Silly Putty.  We want Blu-Tack to flow and
mold when we apply pressure, but to set up and remain relatively solid 
when we stop molding it. Such a fluid is called a Bingham plastic.  
Bingham plastics are great for fluids like toothpaste or anything else you 
don't want to drip out of a tube when the cap is left off.  Depending on 
the size, shape, and quantity of mineral filler, the properties of the Blu-
Tack can probably be changed a lot.

Finally there is the pigment.  You like the blue color, don't you?

So, that is my theory on how Blu-Tack works, involving a bit of polymer 
chemistry, surface chemistry, and fluid mechanics.  Until Bostik opens 
their lab door a bit wider, maybe we just have to make do with an educated 
guess.  Hope there is enough information to settle your argument.

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