Polar Wrap

February 5th, 2008 admin Leave a comment Go to comments

Polar Wrap
Anyone good at science? PLEASE HELP?

Plastic wrap is made of nonpolar molecules and is able to stick well to polar surfaces, such as glass, by way of dipole-induced dipole attractions. Why does plastic wrap also stick to itself so well?

I found a page which does a decent job of explaining it. It, in turn, refers to a second page which actually explains it. I've included both links, below.

Here's what I think is the key concept, from the second post:

"Scientists had to find some way to make PVdC and LDPE cling to itself and discovered that certain other LOW molecular weight polymers that weren't quite compatable with the host would do the trick. The two most commonly used today are polyisobutylene and poly[ethylene-vinylacetate] or PIB and EVA, for short.

Unlike magnetism, in which like poles repel each other, in adhesive chemistry like materials attract each other. When the low molecular weight additives are put into a high molecular weight host of different composition, they tend to not mix [they form seperate phases]. When the film of PVdC or LDPE contacts itself, the PIB or EVA in the one film seeks out and associates with PIB or EVA in the second film surface. Since the additives are low in molecular weight, they are much more mobile than the host polymer. Higher mobility leads directly to the rapid development of an association that is perceived as 'cling'."