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Name: Max D.
Status: student
Grade: 6-8
Location: HI
Country: USA
Date: N/A


Question:
How does glue stick to skin? Is there a way to create a glue that sticks to everything else but not skin? how?


Replies:
Max,

Most glues work on the principle that a fluid is able to fit into the microscopic cracks and crevices of a surface. This fluid, under the action of oxygen, heat, or some other molecule will then form more chemical bonds and harden. Think of a bunch of rubber bands. As a loose grouping, the rubber bands can penetrate into small holes, or fit themselves into tight spaces (the microscopic cracks on the surface of what it is you are trying to glue together). However, let us say you then took a flame or a heat gun to the rubber bands so that the pieces melted into each other. Now, because the bands are linked to each other, they do not move as much. But if these pieces of rubber were initially already partly found in cracks and crevices, than they will be very difficult to pull out since they are no longer as mobile once they have been melted together.

So the problem is that skin is very much a rough surface, full of crevices and cavities in which the fluid glue can penetrate. Once the glue hardens, the individual molecules of the glue bond to each other, then the hardened glue is difficult to remove from the crevices in the skin where it penetrated.

It might be possible to develop a glue that works on a different principle. A glue could be made that would dissolve the surface of the object(s) that has to be glued together. Then, when the glue evaporates, the dissolved material will harden once again but the two pieces will be penetrating into each other. The glue can then be made such that it does not dissolve skin, but can dissolve some other material. This is not economically feasible however as one would have to develop a glue that can dissolve a wide variety of objects (otherwise it would have limited use) while making sure that it does not dissolve skin. Both because it is difficult to find such a substance, and because it would have to be tailored to the specific object to be glued - I don't think it would be a commercially successful product.

Greg (Roberto Gregorius)


Glue sticks to skin (or any other material) if it forms some sort of chemical bond to the material. This bond may be strong or weak depending upon the chemical nature of the glue and the material. One way to prevent the glue from sticking to the material is to apply a thin layer of a coating that either does not stick to the glue, or to the skin, or both. In the case of skin, a thin layer of Vaseline, or mineral oil works well. Even some water based hand creams also prevent sticking to the skin. You may have noticed that if you try to apply a piece of adhesive tape to skin that is "sweaty" that it won't stick. The principle is the same, but the weak sticking layer is oil from your skin. You can use any "weak sticking" film of any sort. For example, the Teflon "goop" plumbers apply to pipe threads so that the pipe will not freeze up over time is the same principle.

So the choice of the glue is less important that the barrier film applied to the skin. Some examples: epoxy, Elmer's glue, and "Crazy" glue all stick to skin very aggressively -- as well to most other materials except maybe polyethylene. So the strategy for keeping the glue from sticking to skin is to apply a lotion or cream before exposing the skin to the glue. Note: it doesn't take much to do the job, just a couple of drops rubbed into the skin very thoroughly.

Vince Calder

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