Most people believe that plastics are easy to
recycle. You just melt the plastic and reform it, right? What about the
additives in the plastics that determine their physical properties? For example, one
company may produce a plastic with a viscosity of X poise and another produces the same
plastic with a viscosity of Y poise. If you mix the two (or usually several)
plastics together when melting, you get a polymer that behaves differently from any of the
original plastics. In short, simply melting and reforming is very difficult and
certainly more expensive than producing virgin material with predetermined physical
properties. So, what recycling options do work?
Chemical recycling involves the breaking down of
polymers into their fundamental parts being monomers and raw chemicals. These
chemicals can then be purified and reused. But, like many great ideas in the
industry, it is more expensive than producing virgin material.
The other recycling option, material recycling, is what most people
think of when they hear the word "recycle". Old plastics are ground into
powder or small particles and is mixed with virgin material. A typical ratio of
recycled to virgin material may be 1:10 or 2:10. The reason that such a small
percentage of recycled plastic can be mixed with new material is that the recycled
material causes deterioration of the polymer mechanical properties. So, although
savings in raw material costs result, the product is of lower quality and may be less
valuable.
Recycling plastic is difficult, but it is done. Millions of
dollars in research are dedicated to this topic each year. As plastic demand
continues to increase, it becomes more and more imperative that an effective means of
recycling be found. Ironically, I believe that chemical recycling will ultimately be
the answer for most plastics. But first, science will have to find a way to make
chemical recycling as cost effective as producing virgin material. In order for that
to happen, researchers will have to develop better ways to breakdown the world's most
popular plastics.
