How does plastic wrap work, and why does it cling to some surfaces well but not others?
The ideal plastic wrap adheres to all sorts of containers, including glass, metal, and hard plastic. The trick for manufacturers is to engineer the plastic so that it attaches well to what the consumer wants it to attach to.
Clair Hicks, professor of food science at the University of Kentucky, says that “back in the late ’80s and ’90s plastic wrap was so clingy that you first had to work hard to find the edge on the roll. Then when you successfully ripped off a piece it would immediately fold back on itself, so it was really hard to work with.” Eventually, consumers dictated the evolution of plastic wraps, using their dollars to purchase those that had less aggressive cling, and manufacturers developed formulas that made their products easier to handle.
Plastic wraps are generally made from a vinyl or polyvinylchloride molecular configuration, which gives the material its “clingy” characteristic. Plasticizers add stretchiness. The level of clinginess depends on a mix of factors, for example the electrical charge the wrap carries, plus the charge the container carries.
“Glass, as well as some plastics, has a net negative charge on its surface, so a wrap that has an opposite charge is going to cling quite well to these surfaces,” says Hicks, though of course it’s unlikely that you would know what charge your container carries. A plastic wrap that carries the same charge as the container will not adhere as well.
Plastic films can also be hydrophobic (meaning they repel water) or hydrophilic (they attract water). Hydrophobic wrap is better at stretching across the tops of bowls and wrapping deli meats.
Hicks thinks that Saran wrap is your best bet for cling. It’s also one of the most expensive brands on the market, probably in large part due to the barrier film included in its formula, according to Hicks. Barrier film keeps the smells from leaking out of a wrapped product.
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