One method that breaks down plastics almost instantly is, burn them clean. That is, burn the plastics so that every molecule is combusted.

Plastics are made from, basically, hydro carbons - petroleum, and plant based oils - often containing chlorine, but also many other components. See: https://en.wikipedia.org/wiki/Plastic.

A business might be evolving where a person could develop a scoop-ship to scour the oceans for the plastics, and present them back to nations for burning in furnaces especially made for them. This could provide heat for homes in winter, and heat for anything that industry might need heat for.

At the present, this would probably not be a viable business, because there isn't a big enough concentration of plastic in the oceans,yet. But if we start planning now, we will be ready for the future when the concentration makes it a paying business.

Imagine touring the world in a ship that gets its fuel from filtering the plastic out of the oceans... all the while doing mankind the favor of helping to save the planet.