Adhesive tricks to recycle old computers

August 21, 2000

WASHINGTON, D.C.-- A barrier to 100 percent recycling of outmoded computers has been overcome with the development of an environmentally friendly adhesive.

Detailed studies of an epoxy compound developed at Cornell University and dubbed Alpha-Terp (or, more formally, (-Terpineol epoxy monomer), have revealed precisely the time and temperature required to make the seemingly indestructible adhesive "fall apart" during recycling of an outmoded computer or the remanufacturing of a usable one.

Materials scientists from Cornell and the State University of New York (SUNY) at Binghamton reported on the development today (Aug. 22) at the 220th national meeting of the American Chemical Society (ACS) at Washington Convention Center, Washington, D.C.

"This epoxy seems to have all the attributes for an environmentally sensitive design that calls for an adhesive that can be easily removed and cleaned up," said John Jir-Shyr Chen, a graduate student of materials science in Cornell's College of Engineering. "If this material is adopted in the manufacturing process of computers, their circuit boards will be a lot easier to disassemble for reuse and recycling."

Chen presented a report at the ACS meeting titled "Reworkable Thermosets: Enabling Disassembly of Microelectronic Components." He is supervised in his studies by Christopher K. Ober, the Cornell professor of materials science and engineering who first developed Alpha-Terp, and Mark D. Poliks, research associate professor of chemistry at SUNY Binghamton.

Displaying a snapshot of all his obsolete personal computers -- stacked in his driveway for Earth Day -- Poliks, who also is manager of materials development in IBM's microelectronics division, described a kind of PC paradox that has long vexed materials scientists: "Computers don't break down when we want them to," Poliks said. "Long after you have moved on to a more powerful computer, your old machine continues to contain components and materials that could be reused and recycled."

In 1998, more than 20 million computers became obsolete and unwanted in America, according to a study by the National Safety Council. At that rate, by 2005, some 55 million computers a year could be discarded in landfills.

In fact, a few companies have been remarkably successful at "asset recovery," as the process of breaking down computers into reusable parts and recyclable materials is known. Computer asset recovery facilities have processed more than 120 million pounds of scrap material, Poliks noted, and more than 95 percent of those materials, by weight, were reused or recycled.

One of the toughest nuts to crack, in terms of asset recovery, is the computer circuit board, where components worth hundreds of dollars apiece are soldered in place then further secured with a protective adhesive, such as an epoxy compound. Loosening the solder is easy enough -- a little heat will handle that -- Poliks noted. But the presence of nearly indestructible epoxy adhesives around the components and their soldered connections has made disassembly so difficult that an estimated 77 percent of printed wire circuit boards cannot be reused.

"Epoxy compounds in electronics applications have to be super tough because they serve so many functions," Chen explained. "They must form a hermetic seal to isolate components and connections from the environment and prevent corrosion and contamination. They have to be an electrical insulator. And they have to offer stress relief and enhance the general resilience of the product. Part of that function is coefficient-of-internal-expansion management, because different materials that are located next to each other will expand or shrink at different rates as the product heats and cools.

"Furthermore, the glue and all the components have to survive the manufacturing process, which is beyond what the user would subject the computer to," Poliks said. He noted that epoxy also is sandwiched into multi-layer devices. "And when something goes wrong with one of these precious chips, we want to be able to get the chip off to replace it. What we really need is a reworkable glue that falls apart when we want it to."

That is exactly what Alpha-Terp does, according to Chen, who studied the material's performance with a variety of analysis techniques, including NMR (nuclear magnetic resonance) spectroscopy, while applying more and more heat. At 190 degrees Celsius (374 degrees Fahrenheit) the epoxy's chemical bonds begin to break -- it falls apart -- and the glue can be dissolved with a common industrial solvent.

"The only other way to break an epoxy's grip is to smash it with a hammer," Chen commented, "and that's kind of tough on those delicate components. If it proves to be cost effective, safe and can be widely adopted, this material should go a long way toward making computers 100 percent recyclable."
Funding for the epoxy study was provided by the Semiconductor Research Corp. and IBM.

Cornell University

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