Even if your shampoo is expensive, you probably throw some of it away. Plastic bottles–whether they’re holding shampoo or laundry detergent or lotion–are inherently terrible at squeezing out the last drops of whatever product is inside.
Researchers have a new solution: By embedding tiny nanoparticles of silica into plastic, they can make the surface of a bottle so slippery that everything comes out, without any effort.
“Currently, it is very difficult to get the last remaining portion of shampoo product out of the bottle,” says Philip Brown, a postdoctoral fellow at Ohio State University, who worked with mechanical engineering professor Bharat Bhushan on the new method, published in the journal Philosophical Transactions of the Royal Society.
“People are throwing out the bottle before using all of the product. With our coating, the shampoo is less likely to stick to the bottle, and so you can get more out before you need to replace it, reducing wastage.”
In 2009, Consumer Reports estimated that as much as 16% of liquid laundry detergent ends up in the trash because it’s so hard to get out of the bottle. As much as 25% of lotion is thrown away, and 3% to 6% of soap may stay in bottles.
That wastes money for consumers, and isn’t great for the environment. Manufacturers that are trying to reduce carbon footprints–and looking at the full life cycle of the products they make–are trying to figure out how to reduce waste. When any percentage of a product ends up in the trash, all of the resources that went into manufacturing and shipping it are also wasted.
The new bottles aren’t the first to use an extra-slippery coating. Researchers at MIT created another coating, now commercialized by a company called LiquiGlide, a few years ago, which can help get ketchup and other viscous liquids out of bottles. But it works in a different way, impregnating a surface with liquid.
The researchers from Ohio State point out that because the LiquiGlide coating is sprayed on the inside of a bottle, it could potentially detach if it sits on a shelf long enough. “Our technique is a direct surface modification of the bottle, therefore there is no coating to peel off,” says Brown. “Their technique also relies on a liquid to be added to the coating and this may leach out into the product.” (LiquiGlide says that it chooses coatings that are nonreactive so they don’t leach, and their coatings used with food use only FDA-approved materials that people eat every day).
LiquiGlide also focuses on food–which is actually somewhat easier to get out of bottles. Soaps and shampoos are a new challenge. “Soaps contain surfactants,” he says. “These molecules help soap clean, but they also make the soap stick to stuff, including the inside of the soap bottle.”
The new coating embeds microscopic heart-shaped structures into the plastic, which keeps droplets of a product from touching the sides of the bottle and spreading out. Instead, shampoo or soap just rolls out. It’s a structure that other researchers have attempted in the past, but the new technique, which is cheap and easy to do, makes it feasible.
Because the nanoparticles are made from silica–essentially sand–the researchers say that the technique shouldn’t affect whether bottles can be recycled. People may actually be more likely to recycle the new bottles, because they are easier to rinse out. They also could help recycling plants that have to deal with unrinsed bottles now. “The leftover product in bottles can cause issues during recycling,” Brown says.
Though the research focused on shampoo, the same technique could also help other products flow out of bottles. The researchers have also tested it on other types of plastic–like car headlights and smartphone cases–to keep them clean. It could also be used in food packaging, though the chemistry might be slightly tweaked. On medical devices, the slippery coating can also keep off bacteria, potentially saving lives.
The researchers hope to license the technology to manufacturers.