The Truth About Saran Wrap Page The answer to what really makes this material stick to itself.
After battling a particular stubborn piece of Saran wrap one day I got to wondering about what made it, or any plastic wrap for that matter, stick to things and in particular to itself. I figured the answer would be found easily on the Internet.
I figured wrong.
An hour's cruising the net turned up many pages that explained Saran wrap's stickiness using one of two theories:
The first theory claimed that the plastic picked up a static electric charge either during its manufacturing or when peeled off its roll. Just like a balloon rubbed against hair will cause it to cling to a wall, so the static on the plastic caused it to cling to itself and other objects.
The second theory was that Saran wrap, and in fact any plastic wrap, consists of a mixture of hard, high-molecular weight plastic and soft, low-molecular weigh plastic. The hard plastic gives Saran wrap its gross mechanical properties while the soft plastic acted like a weak adhesive. In essence this second theory stated that Saran and other cling wraps were nothing more than glorified Scotch tape, except that the glue was mixed into the main plastic instead of just coating one side and that it wasn't nearly as sticky.
The number of pages supporting both were about equal so obtaining a consensus wasn't possible. Which was the correct theory?
What I needed was a simple test anyone could perform to determine the truth for themselves.
I found it.
The difference between the static electric theory and the glue theory is that the static theory demands that two plastic sheets should be attracted to each other across a distance because the charge on each of them radiates outward, whereas the glue theory claims they only stick together after coming in contact; there isn't any attracting force.
To test both theories I taped a sheet of Saran wrap to a kitchen cabinet so that it hung down loosely. Then I took a second sheet and moving very slowly so that air currents wouldn't effect the sheets' movements, I positioned the second sheet so that it was next to the first. Did they immediately rush together as the static theory claimed? Did they just hang there as the glue theory suggested? The answer is...
... they just hung there.
They hung as shown in the photo above for several minutes as their weight very slowly dragged them down, forcing the air between them out. Had there been any static electric attractive force they would immediately have been drawn together from the top down. Even when they both hung straight down they only clung together where they accidentally happened to touch.
So, the static theory is dead.
In fact there were a couple of problems with it. If Saran wrap had been manufactured with a charge it would have to be the same charge everywhere and since like charges repel it would repel itself rather than stick to itself. Second, a static charge can't be created by peeling a plastic off itself. The process, called contact electrification, only takes place between two materials with different electrical properties.
But what about the electrical popping noises we hear when pulling apart a tangled piece of Saran wrap? Isn't that from sparks like quickly pulling a bedspread down a bed?
The popping sound heard when untangling plastic wrap is the mechanical snapping back of the plastic as two areas in contact are stretched before breaking loose and snapping back into shape.
hope you found this page useful and as interesting I found
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