The cure time is less than a minute, ACC Plastics Division auto team Chairwoman Sandra McClelland said during the Center for Automotive Research’s Management Briefing Seminars last month.
The substance involves nanoparticle balls of iron dust inside of a polymer, according to a video from the ACC’s plastics arm shown at the conference. Applying electric current causes them to vibrate and reach temperatures between 320-800 “within seconds” — but “not so much the adjacent materials,” according to the film. The polymer melts and debonds the parts without harming the substrates being joined.
“Turn off the current, and it hardens within seconds,” the video states.
“We call it ‘magic glue,'” McClelland said July 31, and said it had applications in “safe and economical repairs,” recycling of aged cars, and in an OEM factory — for it cures “within the 1 minute automotive assembly time requirement.”
And here’s the real kicker — the rebonded joint can be even stronger, the research indicates, according to McClelland.
A carbon-fiber frame could be fixed to greater strength after a collision, and a frame replacement on an aged car could make a vehicle “better than new,” McClelland said.
The substance “could stand the automotive notion of joint fatigue on its head,” she said.
Asked during a panel discussion how the bond could be stronger, McClelland said that the heating of the nanoparticles gives off energy, leading to the thermoplastic adhesive melting and becoming more crystalline.
“A more crystalline polymer has better strength,” she said.
Testing has shown it to work in joining metal to metal, metal to composite, and composite to composite — but “avoiding damaging the composite fibers and increasing joint stress resistance.” (The video pointed out that fasteners like rivets can weaken carbon fiber during the bonding.)
The researchers think it’s economically viable, and “we are working to demonstrate that,” McClelland said.
Asked by a moderator if the fastener would still be necessary during the curing process to hold the part together, McClelland pointed to the sub-minute cure time. “At that point, do you really need the fastener?” she asked.
Society of Collision Repair Specialists Education Committee Co-Chair Toby Chess has observed the low shear strength of structural adhesives can demand a collision repairer use glue in combination with another form of joining.
Asked about this by Repairer Driven News, McClelland said it just required thinking of the car as a “total system.”
“We have used the same joints for many, many years,” she said. “… You change the design of that joint, and then you don’t have that issue.”
Researchers continue to test different substrates at MSU, McClelland said.
“They’ve had success with all the substrates that they’re using,” McClelland said. “So, I think they’re available for OEMs to look at.”
Oak Ridge National Laboratory Manufacturing Systems Research Group leader Lonnie Love, who spoke at the conference about 3-D printing factory tooling but had experience with nanoparticles, noted that a scientist could “dope” the nanoparticle with a different metal to control the curing temperature.
McClelland in an interview after the panel said both the particles and adhesive can be engineered to activate at a specific temperature. This would seem ideal for a collision repairer, who must avoid exposing substrates like aluminum and higher-strength steels to excessive heat.
You can “tailor these particles,” said Love, who called McClelland’s adhesive “the coolest thing” he’d seen at the conference that day.
Michigan State University and the American Chemistry Council are working on reversible joining of multiple substrates. (Courtesy Michigan State University and American Chemistry Council)
Michigan State University and the American Chemistry Council working on reversible joining of multiple substrates using nanoparticles in a polymer. (Courtesy Michigan State University and American Chemistry Council)
Michigan State University civil and environmental engineering assistant professor Mahmood Haq is working on reversible joining of composite materials. (Provided by MSU; photo by Harley Seeley)