February 27, 2005

Recycling Myths 2 

This is to continue the essay I began a few days ago.

In addition to the problems I presented in the first part, there is the fact that commercial plastics often contain other materials: plasticizers, fillers - which are most often pulverized minerals like calcium carbonate, but also glass powder/short fibers; even sawdust or starch. The most strange I've seen was plastic loaded with iron powder, for some special application. Then there are reinformcement materials, which can be natural, synthetic or mineral fibers. The presence of these materials must be taken into account when thinking about the recycling of plastics, and it can make things considerably more complicated.

From an economic standpoint, the recycling costs for consumer plastics are more or less equal to the production costs - this means that recycling is hardly profitable. But, often governments adopt regulations which make recycling more profitable - for example, with subsidies or tax reductions. In the extreme case, governments can make recycling mandatory.

But from an environmental standpoint, I remain rather skeptical about recycling of consumer plastics. The fact that production and recycling costs are almost equal means that the amount of energy and resources required for the two processes is similar.
In the end, the extent of separation and cleaning required depends strongly from the end-product specifications: if the end product must meet strict specifications, more in-depth selection and cleaning are required, thus consuming more energy and resources.
On the other hand, if the end product does not have to be of a high quality (for example, greenish recycled PE instead of the white virgin one), the selection and cleaning processes can be more superficial. One interesting point is that, when for example separating PVC from PET, for each kilo of pure PET we will obtain a certain amount of a mixture of say, 1:2 PVC-PET, which is good for nothing; it may be further processed to separate its components, or disposed of. It must also be noted that if undifferentiated plastics are just re-melt together, the resulting material will be ill-looking, have scarce mechanical properties, and generally be good only for very low-grade applications. (As usual, things are not so clear-cut: there are special high-shear processes of grinding that can render compatible plastics which normally are not compatible. But this is a feature that hardly counts for cheap consumer plastics).

I don't see putting the burden of differentiation on citizen's shoulders as a good solution for these problems. That differentiation cannot really be trusted because for an array of reason like lazyness, ignorance or malice is going to be less thorough than required (especially for something quite delicate like PET); at best, home differentiation can reduce the extent of differentiation that has to be done at the recycling plant (or some intermediate selection facility). Not to mention that our plastic bottle, as I wrote in the first article, is already made of two or three types of plastic. Nor I see home cleaning as a solution for the cleaning problems: again, it cannot be really trusted. In second place, that will only shift the resources and energy consumption from the plant to a number of households, but will not eliminate it (actually, for scaling reasons, I think that industrial-scale cleaning will be more efficient).

Things are quite different for engineering plastics, the likes of ABS (acrylonitrile-styrene-butadiene resins, a high performance category of polymers), polycarbonate (PC), nylon and other polyamides, hi-impact PS, polyurethanes (PU) and polyolefins; engineering plastics are used to produce the casings of electronic devices, domestic appliances, furniture, tools, parts of buildings and vehicles etc. These plastics have high mechanical (and in the case of PC also optical) properties, and are much more expensive than consumer plastics, so recycling is a considerably more interesting idea. There is another point about engineering plastics, and it's that often they can be collected in relevant quantities at one single site: car bumpers are made mainly of polyolefins, and a junkyard can easily collect hundreds of kilos of old bumpers in a month, and all this will be quality plastic, with no extraneous materials and little contaminants. Likewise, facilities for the dismantling of scrap electronic equipment already exists (electronic devices like mobile phones and computers contain small amounts of very expensive materials, and it's already a bargain to recycle those) or can be easily built. The concentration of "raw materials" means less energy spent to transport the plastic to the recycling plant, compared to the energy required for a doo-to-door recyclables collection.

To end, there are plastics that cannot be recycled, because of their chemical composition or a number of other reasons, but these plastics are mainly used in small amounts for special applications and thus they not represent a real concern.

All this discussion regards primary recycling, where old plastics are used to produce new plastics of the same kind. But there are also secondary and tertiary recycling, when old plastics are used to produce other chemicals or energy. But of those, I will eventually write in another article.

Much of the information presented here is taken from the book "Polymer Recycling: science, technology and applications", John Scheirs, Ed. Wiley 1998, Chichester; ISBN 0471970549 m.


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