New Anti-Waste Lining Prevents Soapy Liquids From Sticking To Plastic Packaging

(3BL Media/Justmeans) - Have you ever gotten frustrated over how much toothpaste is thrown away with the crumpled tube? Or how much shampoo is trapped inside a bottle that is all but finished? These may not be life’s most pressing questions, but it would be nice to get the full content of those containers we need for our personal hygiene.

You are not alone there. Fortunately, other people who are thinking about it are researchers who have come up with a new method that will ensure the user can get the last drop of shampoo to roll off the plastic bottle. The brains at Ohio State University have created the ideal texture inside plastic bottles so that soap products can flow freely.

This anti-waste texture is the result of a technique that includes lining a plastic bottle with microscopic y-shaped structures that cradle the droplets of soap aloft above tiny air pockets, so that the soap never actually touches the inside of the bottle.

The “y” structures are built up using tiny silica nanoparticles, or quartz, which, when treated further, won’t stick to soap.

Coatings already exist to help food pour out of their containers. But soap is not so lucky. “Compared to soaps, getting ketchup out of a bottle is trivial. Our coating repels liquids in general, but getting it to repel soap was the hard part,” Bharat Bhushan, of the research team, said in a press statement.

This is all to do with what is known as ‘surface tension’, which is the tendency of the molecules of a substance to stick to each other. Ketchup and other sauces are made mostly of water, and water molecules tend to stick to each other more than they stick to plastic.

Conversely, soap needs organic molecules called surfactants and which do the opposite of water molecules, that is, they have a very low surface tension and stick to plastic easily.

Bhushan and his research partner Philip Brown devised a method to spray-coat a small amount of solvent and ultra-fine silica nanoparticles onto the inside of bottles.

Currently, manufacturers already use solvents to change the texture of molded plastics to make their surface soften slightly. The researchers have mixed the solvent with silica to soften the surface of polypropylene (the type of plastic used to make shampoo bottles) so when the plastic re-hardened, the silica would be embedded in the surface.

These tiny structures, which have a hardness similar to that of glass, are planted a few micrometers apart. The y shape means they have tiny branches overhanging the plastic surface at an angle less than 90C, but steep enough to prevent water, oil and surfactant from sustaining a droplet shape that would fall in between the branches and touch the plastic.

Instead of spreading out on the surface of the plastic and sticking to it, the soap forms beads and rolls off the bottle.

Besides saving shampoo, the invention could boost recycling rates of polypropylene. Plastic bottles need to be rinsed clean before they are pushed to be recycled, which would no longer be necessary or at least made much easier by just turning them upside down.

The University of Ohio now hopes to license the coating technique to manufacturers of several types of plastic products that need to stay clean such as biomedical devices and catheters. They have already applied the same technique to polycarbonate, a plastic used in car headlights and smartphone cases, among other applications.

More details of the patent-pending technology appeared in the journal Philosophical Transactions of the Royal Society on June 27.

Image credit: Ohio State University