No matter how science-savvy you think you are, there’s always room for surprise in this business. For example, imagine our surprise when — in the process of researching this blog — we discovered a debate rages around plastic wrap and what makes it sticky. On one side, some say it’s static electricity. Another camp argues molecular structure. The debate between the two sides is every bit as polarized (see what we did there?) as the mostly settled controversy over climate change!
Being polymer scientists, we’re going to come down on the side of molecular structure. Here, in a nutshell, are the two schools of thoughts on what makes plastic wrap stick.
The static cling camp
The act of peeling plastic wrap off a roll (heaven help you if you lose the end of the film in the wrinkles on the roll), you create a static charge. The plastic picks up the charge, and since plastic bowls often have their own minutely negative charge, the positive charge in the plastic wrap makes it stick to the plastic bowl. Or so the theory goes.
The problem with the static-cling argument is that plastic wrap also clings just as well to metal and glass, two materials that conduct electricity and would thereby eliminate any difference in charge between the bowl and the wrap — and any stickiness. In fact, plastic wrap actually clings better to glass and metal than it does to plastic!
The molecular structure philosophy
Science is really on the side of the opposing camp that holds plastic wrap’s molecular structure accounts for its stickiness. Originally, plastic wrap was made of polyvinylidene chloride (PVDC). Today, most brands of cling wrap are made of PVC/polyvinyl or low-density polyethylene (LDPE) — two long polymers with very tightly bound and coiled chains of molecules. The tight molecular bond and spring-like quality of the chains are why plastic wrap made from these polymers sticks really well and does a good job of blocking moisture and odors.
These polymers are sticky in their own right and don’t need an additional static charge to make them better at adhering, although it’s not uncommon for plastic wrap makers to incorporate stickiness-enhancing additives to the base PVC or LDPE formulae.
A case of corporate responsibility
Remember we mentioned what plastic wrap used to be made of?
Dow Chemical accidentally discovered Saran Wrap all the way back in 1933, began marketing it to the public 20 years later, and sold it to SC Johson in 1998. At that time, Saran Wrap contained PVDC, which imparted superior performance for their product.
In 2004, after realizing PVDC could be bad for the environment, SC Johnson decided to replace the polymer with a safer alternative that, CEO Fisk Johnson, admits doesn’t perform as well.
In 2015, Johnson told the The Journal Times of Racine, Wisconsin: “PVDC, or polyvinylidene chloride, was a substance responsible for two of Saran Wrap’s product benefits that no other plastic wrap could claim — an impenetrable barrier to odor and superior microwavability. But when products containing any kind of chlorine, including PVDC, end up in municipal incinerators, they can emit toxic chemicals into the environment.”
“Once we learned about the possible toxic chemicals PVDC emitted from landfills, we never really considered retaining the original formulation,” Johnson told the paper. “Doing the right thing for customers is always the right thing for us.”
So in the end, the tale of the great plastic wrap debate is one of static, molecules and corporate responsibility!