There is a debate about what is more the more responsible substance to use: cling wrap or aluminium foil. In this author’s opinion, the clear winner is aluminium foil. Why? Because it’s the only one that works. Aluminium foil is a humble but hard-working substance. Plastic wrap is an ironed-out version of the blob. It’s a confusingly clear substance that sticks to everything in sight, including one’s hands and itself, until it’s a wadded-up ball of plastic sitting next to a still-uncovered plate of brownies. How does it manage to grab onto everything so well?
Many sources say that it is static cling that keeps the wrap holding tight to everything around it. The plastic acquires a charge and sticks itself to anything with an opposite charge. Many plastic bowls carry a very slight negative charge along their surface, giving the wrap something to hang onto – or be repulsed by. But cling wrap also manages to hang on to metal – which conducts electricity and so would eliminate a difference in charge – and glass, and itself. Some plastic wrap is hydrophilic, grabbing on to any water it gets close to. Some is hydrophobic, repelling water. Water, unless it’s pure, also conducts electricity. Plus, all wraps wad up like dirty laundry, or stick on like burrs. If static electricity made them work, they would sometimes be repelled by themselves, or other substances. That would make them impractical to use. It’s materials science, not electric charge, that gives cling wrap its clinginess.
Most cling wrap is made of one of two materials; polyvinyl chloride or low-density polyethylene. Both of these are long polymers – chains of molecules. These chains cling to each other very well. In fact, the polymers in polyvinyl chloride are so bound together that they do not let water or air get through them. The military used to spray “Saran,” the early name of the chemical, on fighter planes to prevent corrosion. It was also used in upholstery. To make it suitable for home use, companies add plasticisers to make it softer and more malleable.
As time went on, both PVC and plasticisers fell out of favour – though not out of legality. PVC was thought to take up toxins, and plasticisers often came off the wrap and onto food, especially fatty foods like cheese. Companies switched to low-density polyethylene LDPE, and eliminated the plasticisers. LDPE was also cheaper to manufacture, but isn’t as much of a barrier against air and water as PVC.
The funny thing is, although both stick to themselves, neither one really sticks to other surfaces. So how do cling wraps grip? Added adhesives. Other chemicals, all minor adhesives, are added to make the cling wraps sticky enough to do their jobs. These adhesives don’t completely mix with the LDPE or PVC, so they are available to grab anything that comes by. Cling wraps stick on to things the same way a piece of tape does.
Perhaps its time to get rid of any fancy affectations and just tape food to the plate.
Republished from io9