In the modern world, plastics are a problem. They are everywhere in consumer goods, both as the goods themselves, and as packaging. They are indestructible for the most part, and they are a large component (if not the largest part) of litter. They can be found everywhere on Earth, and they injure and kill wildlife. Through their history, plastics have made our lives easier, but they have also been revealed to cause major problems, and it would be a good idea to find a way to deal with them such that they don’t choke our landfills and oceans.
“Wait,” you think. “I recycle my plastic waste. Doesn’t that reduced plastic in the waste stream?” Well, yes, but probably not as much as you might think. The problem is that, in order for a plastic item to be recyclable in any measure, different types of plastic in said object must be separated, and even then, some of those individual plastics may not be amenable to recycling. The only two plastics that are recycled to any extent are PET (polyethylene terephthalate), from which plastic soft-drink bottles are made; and PE (polyethylene), from which milk bottles are made. This only accounts for about 20 % of the plastic waste stream. The rest is fated to end up in a landfill—or worse.
Chemists recognize this problem, a problem they themselves created by the discovery of plastics in the first place. Now they have gotten to work to try to combat the monster they’ve made.
The problem with many plastics is that different kinds of plastics are combined in products, and as yet, it is not possible to recycle mixtures of different plastics—they have to be purified first. This is done by the use of different solvents. So, for example, in a product that’s a combination of PE and PET, PE will dissolve in a fully non polar solvent like toluene, while PET, which has polar groups in it, will dissolve in more polar solvents like dimethyl sulfide (DMSO). Once the two different plastics are separated, they can be isolated and reused. Research is underway to find solvents that can be used to separate other types of plastics from each other.
Another strategy involved taking the plastic molecules apart altogether. Plastics are called polymers because they are long chains of smaller molecules called monomers. The polymers are made from chemically linking the tiny monomers together one-by-one, not unlike the links in a chain. So another way to recycle plastics is to disassemble them at the molecular level, that is to reduce them back down to the monomer level, where they can be re-reacted to make new plastic.
These are just two strategies being explored to reduce the amount of plastic litter, whose presence is continually increasing.
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