Materials

Almost 100%-recyclable circuit board turns to jelly for disassembly

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From left to right is a vitrimer-based printed circuit board, a sheet of harvested glass fibers, chunks of gelatinous vitrimer polymer that have been removed from a board, and harvested electrical components
Mark Stone/University of Washington
From left to right is a vitrimer-based printed circuit board, a sheet of harvested glass fibers, chunks of gelatinous vitrimer polymer that have been removed from a board, and harvested electrical components
Mark Stone/University of Washington
Agni K. Biswal, a University of Washington postdoctoral scholar in mechanical engineering, uses a heat press to laminate a vitrimer printed circuit board
Mark Stone/University of Washington

A new type of printed circuit board (PCB) could drastically reduce the amount of electronic waste that ends up in landfills. Although most PCBs are difficult to recycle, such is not the case with this one, which partially turns into a reusable jelly when necessary.

Among other components, PCBs typically incorporate a layer of non-conductive fiberglass which serves as a substrate for electronic parts such as chips, resistors and transformers. The fiberglass is in turn made up of two ingredients – woven glass fibers and epoxy resin – which are very difficult to separate from one another.

Because this substrate material can't be easily broken down, retrieving the electronics for reuse is labor-intensive and time-consuming. Sometimes the fiberglass is burned away in order to harvest the electronics, but this process is environmentally-unfriendly plus it may damage the very components that it's freeing up.

That's where the experimental new PCB comes in.

Created by scientists from the University of Washington, it replaces the resin in the fiberglass with a polymer known as a vitrimer. As long as the PCB is in use, that vitrimer remains strong, rigid and non-conductive, allowing the substrate to function just like one made of traditional fiberglass.

Agni K. Biswal, a University of Washington postdoctoral scholar in mechanical engineering, uses a heat press to laminate a vitrimer printed circuit board
Mark Stone/University of Washington

Once such a "vPCB" (vitrimer printed circuit board) has reached the end of its use, it will be sent to a recycling facility and immersed in an organic solvent which has a relatively low boiling point. When that solvent boils, it causes the vitrimer to swell and become gelatinous.

All of the glass fibers and electronics – which remain completely undamaged – can then be easily plucked out for reuse. Additionally, lab experiments have shown that 98% of the vitrimer itself can be reused, along with 91% of the solvent.

And importantly, vPCBs can be manufactured at existing facilities, plus they can be recycled over and over again. In fact, the scientists estimate that the use of recycled vPCBs could entail a 48% reduction in global warming potential and an 81% reduction in carcinogenic emissions as compared to traditional PCBs.

"PCBs make up a pretty large fraction of the mass and volume of electronic waste," says Asst. Prof. Vikram Iyer, co-senior author of a paper on the research. "They’re constructed to be fireproof and chemical-proof, which is great in terms of making them very robust. But that also makes them basically impossible to recycle. Here, we created a new material formulation that has the electrical properties comparable to conventional PCBs as well as a process to recycle them repeatedly."

The paper was recently published in the journal Nature Sustainability. And as an interesting side note, some of the same scientists previously used vitrimers in a more easily repairable and recyclable type of carbon fiber.

Source: University of Washington

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3 comments
paul314
I wonder what manufacturers would do with the recovered components -- recycle or just return to the supply chain (perhaps in lower-spec uses).
Treon Verdery
It would be wonderful if the organic solvent that the vitrimer PCBs turned to jello in was cheap and physiologically harmless. They have methyl ethyl Keytone (MEK) at the gallon can at the hardware store, that or the related acetone would be very cheap, MEK might or might not be bad for people. Acetone is actually made at small amounts at the human body, so looks pretty plausible. Actually the body produces many keytone variation molecules, perhaps the most hamless or even beneficial of those could be utilized as a solvent for a chemical variation of Vitrimer PCB material. What would be really nice is if a C16 carboxylated alkane like edible food palm oil could be used as the jello making solvent. That sounds unlikely, but consider the effect of putting the palm oil/food oil solvent with the PCB boards at an ultrasonic cleaner bath that also had some micrometer or millimeter particulates like reusable sharp edged glass or mineral or metal fragments at it. The microparticulates would continuously abrade the PCB surface so fresh surface was always available to the food oil, MEK, or acetone solvent. The ultrasound, depending on the energy of the ultrasound could cause an order of magnitude, or orders of magnitude faster PCB jelloization. That means that dozens or hundreds greater amounts of PCB boards can be treated per actual machine, generating dozens or hundreds of times greater revenue per machine.
Troublesh00ter
Regarding the non-conductivity of the circuit board, my question is: just HOW non-conductive? I used to work for a company where measurements in the nanoampere and picoampere ranges were regular occurrences. Even using FR4 board material, additional board design techniques had to be used to deal with current leakage issues.

That said, if this new material had similar insulating specs to FR4, this innovation would potentially be a game-changer.