European process makes sturdy posts from `dirty' plastic
STURDY plastic posts driven into the sand form barriers along West Germany's north coast, in an experiment designed to arrest accelerating beach erosion there. If successful (and early indications are that they will be), many similar barriers will be placed along the coast - and a mountain of mixed, dirty plastic will be removed from the German waste scene.
In Switzerland, vine stakes made of such waste are being tried. If acceptable, they will help that almost squeaky-clean nation to become cleaner still.
What is significant about both the erosion barriers and the stakes is that they shouldn't even exist, according to a long-popular belief about plastics. These products were made from mixed post-consumer plastic - unsorted, dirty waste that contains some paper and glass as well as soft metals like aluminum and copper. Until recently, blending these diverse wastes was considered impossible.
The standard reasoning was that - apart from undesirable contaminants like oils, paints, traces of congealed milk, and so on - the differing chemical components of various plastics salvaged from the waste stream made them incompatible. Only by costly separation of the types would effective plastics recycling be possible.
But Mike Baele (pronounced Bahl), an engineer at a Swiss-Belgian company with an English name, Advanced Recycling Technology Ltd., refused to accept the negative view.
``Where is the [scientific] literature showing where someone tried and failed?'' he would ask. No one could show him any, other than the facts that various resins melt at different temperatures and react differently when heat is applied.
This meant that conventional melting of the plastic would not be acceptable. So his company came up with an alternative heating system considered the key to mixed-plastics recycling: A screw-type feeder uses friction to heat the waste just enough to homogenize it before it enters the extruder.
No one is certain what happens to the finely ground plastic in the feeder, but the theory is that softer, film-type plastics melt completely, while harder types soften almost to the point of becoming liquid, so that all the resins combine to form a solid piece when extruded.
``We don't yet know how the resins bond together, all we know is that they do,'' Mr. Baele says. Extrusions can be made in various profiles - rectangular, round, even star-shaped.
Items with critical structural requirements could not be made from a mix that might vary from batch to batch. But a range of products, from fence posts and stakes to pier poles and bench planks, is possible.
Some of the first fence posts and lumber fabricated show no sign of degradation after more than five years in use. In effect new plastic with a short life span is being recycled into plastic with an indefinite life span.
The product can be nailed, sawed, screwed, and glued just the way wood is. Coming as it does from mixed plastic, it is not quite as smooth and good looking as the lumber being made from pure, high-density polyethylene (milk-jug plastic) in Chicago (see Ideas page, Oct. 4). But it is cheaper to make and usable where appearance is less critical. In lumber-short Europe, agricultural applications are thought to be particularly appropriate for the plastic extrusions.
Like the polyethylene lumber, it will not conduct electricity, which makes it useful for electric cattle fences. It won't rot, animals don't chew on it, and termites ignore it. It resists chemical spills and urine, which makes it particularly good for pig-farrowing pens. And it won't absorb water.
The advantage of the latter was readily shown on a recent visit to Baele's firm here. After a morning of rain, beads of water covered a park bench until a quick rub with a cloth left it dry to the touch - something that could never happen so speedily on a wooden bench.
But to Baele the real beauty of the bench was that it was salvaged from the waste stream, contaminants and all, and turned into a product that should last for decades.
``Dirty waste does not matter,'' he says. Plastic buckets with dried paint on the sides are acceptable. Buckets with what looked like a quarter-of-an-inch of putty on the bottom were about to be processed when I toured the factory. Electric cable (copper wire surrounded by thick plastic) was waiting in line as well. Paper labels and aluminum bottle tops, I was assured, were also a breeze to put throught the system as well.
On the other hand, plastic heavily contaminated with organic waste is not acceptable. The process can accept greasy wrapping, ``but not with all the bacon still inside!'' Baele says. Inert contaminants such as glass and aluminum can account for nearly 30 percent of the mix.
Slowly knowledge of Advance Recycling's mixed-plastics technology is spreading, and extruders are being exported around the world, principally to West Germany but as far afield as Australia. In the United States, three machines are now in operation, one of them at New England CRInc in Billerica, Mass. Since March of this year the machine has been turning out 10-foot lengths of 2- and 4-inch-thick lumber in a range of widths.
Steven Katz, a recycling development officer with CRInc, describes the system as an ``effective disposal solution that also turns out a very useful product,'' which is currently is being marketed for ``non-load-bearing applications.'' The plastic lumber is competitive in the US with pressure-treated lumber; in Europe even with untreated lumber, which accounts for its ready acceptance in West Germany. There, Stadtereinigung Nord of Flensburg has produced an innovative line of products ranging from garden stakes and compost bins to picket fences.
Plastic lumber is more flexible than wood, which is seen as a drawback. But this could be an advantage in the vine stakes being tested in Switzerland: The automatic grape harvester frequently splinters the more rigid wooden stakes. If the plastic stakes measure up in all other respects, they will replace wooden stakes by the millions throughout Switzerland, Baele says. After all, he says,``Why should the Swiss import wood when they can make a better product from their own dirty waste?''