Anything that makes recylcing easier is to be lauded.
In this article from phys.org, Ohio State researchers found a way to spray coat polypropylene and polycarbonate with
a small amount of solvent and ultra-fine silica nanoparticles onto the inside of bottles. Manufacturers already use solvents to change the texture of molded plastics, because they cause the surface of the plastic to soften a little. By mixing the silica and solvent, the researchers were able to soften the surface of the polypropylene just enough that when the plastic re-hardened, the silica would be embedded in the surface.
The structures are only a few micrometers—millionths of a meter—high, and covered in even smaller branchlike projections. They look like shaggy heart-shaped pillows, but they're hard as glass.
They don't cover the inside of the bottle completely, either, but instead are planted a few micrometers apart. The main branches of the "y" overhang the plastic surface at an angle less than 90 degrees—steep enough that water, oils and even surfactant can't physically sustain a droplet shape that would fall in between the branches and touch the plastic.
"You end up with air pockets underneath, and that's what gives you liquid repellency," Brown said.
Instead of spreading out on the surface, the soap droplets form beads and roll right off.
