Thermoset recycling is coming.

Thermoset Recycling Is Coming

SMC auto parts back to oil? Not easy, but doable.

Behind-the-scenes efforts to meet the challenge of recycling thermoset automotive parts came out into the open at the recent SPI Composites Institute Annual Conference in Washington, D.C. Spokesmen for General Motors, the largest user of automotive composites, and the SMC Automotive Alliance, an SPI group that includes 25 of the largest SMC molders and material suppliers, reported the results of two years of feasibility studies on SMC recycling. What they reported was that SMC can indeed be recycled--all the way back to oil--but a lot more work will be needed to make that technically and economically feasible.

In a series of trials between June 1988 and January 30 of this year, both GM on its own and members of the Alliance investigated pyrolysis as the most promising avenue for disposing of SMC manufacturing waste and old car parts. Pyrolysis is a decades-old technology for decomposing organic materials at high temperature (1400 F, in this case) in the absence of oxygen. It's being evaluated by the tire and rubber industry, and the trials were conducted at a pilot facility near Seattle that was designed for reclaiming tires.

The investigators found that pyrolysis could be made self-sustaining by feeding back the resulting off-gas into the process as an energy source. Pyrolysis also yielded oil that could be used as boiler fuel. The third byproduct was a friable mass of filler, glass fibers and carbon char.

Unquestionably, the biggest question remaining is how to chop SMC efficiently. SMC is tough stuff, and defeats most grinding machinery. General-purpose waste-shredding equipment had the undesirable effect of breaking the fibers away from the matrix resin, producing the result seen in the left-hand photo above. The most promising device was a peculiarly nasty-looking contraption called a "universal refiner," devised for tire shredding. It produced small chunks at close to the target rate of 1 ton/hour. The second problem is what to do with the solid residue. The investigators tried milling it to a 20-micron powder, which preliminary results suggest could be used as a filler in other SMC or BMC, or perhaps in concrete or asphalt.

Speaking for the Alliance, Donald R. Norris, general manager of molding materials for Eagle-Picher Plastics Div. in Grabill, Ind., concluded that pyrolysis may turn out to be a usable disposal method in two to five years. Now that the thermoset guys have picked up the gauntlet thrown down by their thermoplastic competitors, it remains to be seen whether "recyclability" will have any future effect on the selection of automotive body materials.

PHOTO : Ground SMC, when pyrolized

PHOTO : yields oil for fuel

PHOTO : and glass, filler and carbon filler.