It’s one of life’s little annoyances: that last bit of shampoo that won’t quite pour out of the bottle. Or the last bit of hand soap, or dish soap, or laundry detergent.
Now researchers at The Ohio State University have found a way to create the perfect texture inside plastic bottles to let soap products flow freely.
The technique involves 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 much smaller nanoparticles made of silica, or quartz—an ingredient in glass—which, when treated further, won’t stick to soap.
It works for “polypropylen” a common plastic used to package foodstuffs and household goods.
Polypropylene isn’t the most common plastic bottle material, but 177 million pounds of it were made into bottles and bottle lids in the United States in 2014 alone. Aside from shampoo, soap and detergent bottles, it’s also used for yogurt tubs, ketchup bottles and medical bottles, single-serve coffee pods and Starbucks iced beverage cups.
Polypropylene is classified as a “number 5” plastic by the Resin Identification Coding System. A recent ACC report found that recycling of number 5 plastics is on the rise, increasing from 44.2 million pounds in 2013 to 45.6 million pounds in 2014.
The Ohio State invention could actually aid recycling. Before plastic bottles can be recycled, they have to be rinsed completely clean.
With further development, the university hopes to license the coating technique to manufacturers—not just for shampoo bottles, but for other plastic products that have to stay clean, such as biomedical devices or catheters. They have already applied the same technique to polycarbonate, a plastic used in car headlights and smartphone cases, among other applications.
