Don't you just hate leaving all that unused ketchup in an otherwise empty bottle? No matter how much tapping, shaking or squeezing you do, you'll always leave some behind. It's the same with other foods that stubbornly stick to the sides of their containers. And that's not only wasteful but also means tedious rinsing before recycling.
Doctor Michaela Muller is trying to solve this problem. As a polymer chemist, she's working on an applied research project at the Fraunhofer Institute for Interfacial Engineering and Biotechnology in Germany. Another Fraunhofer institute -- Process Engineering and Packaging IVV -- is also involved, along with industrial partners and the Munich University of Technology. The project was initiated by the food manufacturing firm Nestle.
Although finding non-stick surfaces for packaging isn't new, Muller's approach involves plasma coating the insides of bottles. While it's possible to make coatings using other methods, the resulting layers would be too thick.
"We need a very thin coating and only plasma processes will give these very thin coatings in the range of nanometers," Muller says.
The method is remarkably simple. Muller places the bottle to be coated inside a vacuum chamber with an electrode inside the bottle and another electrode outside it. She then introduces a polymerizable gas and switches on an electric current. As the plasma glows, it forms an ultra-thin film of polymer on the inside of the bottle within seconds. By adjusting time, gas flow and current, films of around 20 nanometers or less are deposited.
Although Muller is secretive about the composition of this luminous gas, she says that it contains precursor molecules for the plasma polymerization process.
"If the coating is only nanometers thick, the adhesion is very strong to the substrate," Muller says.
Not only is the polymer inert -- it does not react with foodstuffs -- but the amount used is tiny.
So what keeps the ketchup from sticking? This isn't nanotechnology, but chemical interactions between the food and the polymer, which is designed to repel specific food groups. At the same time it's hydrophobic, which allows water to run off easily, but overall this isn't the same as water-repelling clothing or self-cleaning glass.
"Mainly it's the chemistry," Muller says. "We choose the right chemical groups that have very low interaction forces with other molecules. The food group composition strongly influences the emptying properties."
Over the next two years, Muller will perfect the formula for the polymer coating to more than halve leftover traces. Two or three different types of coatings may be needed for different food groups. Her fellow scientists are looking at issues such as mechanical stress resistance, temperature fluctuations and contact with acids or alkalis.
It's not just going to be ketchup lovers who'll enjoy the results. Cosmetics, chemicals and motor oils, along with anything else that's sold in a container and leaves wasteful residues, will benefit. And because the process could be applied to foils, much larger containers may be possible too.
Philip Barlow is the scientific and technical adviser to the Food Innovation Research Centre at Sheffield Hallam University. He points out that consumers have already seen a change from glass to squeezy plastic bottles, making it easier for a product such as ketchup to slip out.