|MadSci Network: Physics|
?Basil: 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: http://www.bostikfindley.com.au/pdf/msds/bostik_blu_tack.pdf 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.
Try the links in the MadSci Library for more information on Physics.