Red, yellow and orange tomatoes wrapped in clear plastic

Plastic films superior to those used as food wrappers can be made with the help of a splash of acid. Credit: Getty

Chemistry

Pointing molecules in the right direction yields a better plastic

An extra ingredient reroutes reaction, creating a sturdy plastic instead of a sticky liquid.

An inexpensive type of plastic that usually takes the form of a sticky liquid can be made as a sturdy solid — one that is good for everything from food wrappers to car bumpers — by adding acid during the production process.

A polyvinyl ether (PVE) molecule is made up of a chain of atoms with side chains branching off it in various directions. The orientation of these branches affects the molecule’s properties, and PVE usually organizes itself so that its branches point in directions that leave it a viscous fluid.

Aaron Teator and Frank Leibfarth at the University of North Carolina at Chapel Hill found that by adding phosphoric acid during synthesis, they could coax the molecule into adopting a less-preferred configuration. In batches of PVE produced with this formula, only 9% of the branches had the structure that leads to a liquid form.

The researchers converted the solid form of the material into plastic films, which proved as strong as the polyethylene used in products such as food wrappers, but were 14 times better at sticking to glass and metal.