In a recent article in Science (August 2009) there was a long discussion of new ways to polymerize olefins (ethylene, propylene etc.) using different catalysts that join the polymers in all different ways to achieve many different properties.

In that article, it was taken for granted that “…Finding the balance between performance and price is critical to commercial success, as the customer will always adopt the cheapest solution that meets the performance criteria…”

While no one can doubt the importance of price, there is no mention anywhere in the article about the ability of the polymer to be reused. This simply does not enter into the author’s consciousness. If all of the polymer made by these newly developed methods is used once and then discarded into a dump, this is not seen to be of any importance. This is not considered to be part of the “greenness” equation. All that goes into greenness, according to the article, is whether the raw material comes from petroleum or sugarcane, no matter how soil is degraded or energy is squandered. In the chemical field, discussions of green chemistry have been driven by the most conventional markers (frequently only toxicity and reduced solvent usage) but are not tied in important ways to planetary preservation.

So what path should polyolefin design take to address reusability? Of course, the best way to reuse a plastic part is to reuse it in its highest, complex function. A pump housing should be used in another pump as the same kind of housing. But plastic materials are also highly complex molecular assemblies in their own right, aside from the kind of parts they are made into. It is incomparably better to maintain molecular complexity than to break down materials to carbon dioxide or other simple molecules, such as by burning them.

Plastic polymer chains are susceptible to many design parameters. Polyolefins are not necessarily made from long chains that are identical, length after length. They can be combined with other kinds of monomers so that a long run of polymerized olefins then give way to a run of a completely different kind of monomer (such as styrene or urethanes). The chains are separated into blocks. By combining blocks of different properties and different lengths, the properties of the macroscopic plastic can be fine tuned. This gives us a key way to build in one kind of reusability, as I will explain.

While polyolefin chains are very difficult to break apart chemically, that is not true of all chains. For example, polyester chains can be broken apart fairly easily (there are factories based on this easy reaction). So if we want to be able to break apart polyolefin chains so that we can purify and reuse them, we could add in even a single polyester bond in the middle of a very long polyolefin chain and break the chain apart by the same methods used to break apart polyesters.

The neat part of doing this is that the small presence of the polyester will be so diluted in all the polyolefin that it will change the polyolefin properties almost not at all. Thus we can build in a major reuse capability without changing the plastic properties. Is this a win-win situation or what?

A very important place to apply this kind of modification would be in polyvinyl chloride design. The manufacturers proudly claim that their plastic cannot be reused. Certain environmentalists have proudly repeated this claim because they think it supports their campaign to ban all PVC entirely. But reusability will certainly never be designed into anything while the dump is always welcoming. Smugness will not solve any problems. PVC research needs to be bent toward reuse in every way possible.