A recent found that the world generated 137 billion pounds of electronic waste in 2022, an 82% increase from 2010. Yet less than a quarter of 2022鈥檚 e-waste was recycled. While many things impede a sustainable afterlife for electronics, one is that we don鈥檛 have systems at scale to recycle the found in nearly all electronic devices.

PCBs 鈥� which house and interconnect chips, transistors and other components 鈥� typically consist of layers of thin glass fiber sheets coated in hard plastic and laminated together with copper. That plastic can鈥檛 easily be separated from the glass, so PCBs often pile up in landfills, where their chemicals can seep into the environment. Or they鈥檙e burned to extract their electronics鈥� valuable metals like gold and copper. This burning, , is wasteful and can be toxic 鈥� especially for those doing the work without proper protections.

A team led by researchers at the 天美影视传媒 developed a new PCB that performs on par with traditional materials and can be recycled repeatedly with negligible material loss. Researchers used a solvent that transforms a type of 鈥� a cutting-edge class of sustainable polymers 鈥� to a jelly-like substance without damaging it, allowing the solid components to be plucked out for reuse or recycling.

The vitrimer jelly can then be repeatedly used to make new, high-quality PCBs, unlike conventional plastics that degrade significantly with each recycling. With these 鈥渧PCBs鈥� (vitrimer printed circuit boards), researchers recovered 98% of the vitrimer and 100% of the glass fiber, as well as 91% of the solvent used for recycling.

The researchers published April 26 in Nature Sustainability.

鈥淧CBs make up a pretty large fraction of the mass and volume of electronic waste,鈥� said co-senior author , a UW assistant professor in the Paul G. Allen School of Computer Science & Engineering. 鈥淭hey鈥檙e 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.鈥�

Vitrimers are a class of polymers first developed in 2015. When exposed to certain conditions, such as heat above a specific temperature, their molecules can rearrange and form new bonds. This makes them both 鈥渉ealable鈥� (a bent PCB could be straightened, for instance) and highly recyclable.

鈥淥n a molecular level, polymers are kind of like spaghetti noodles, which wrap and get compacted,鈥� said co-senior author , a UW assistant professor in the mechanical engineering department. 鈥淏ut vitrimers are distinct because the molecules that make up each noodle can unlink and relink. It鈥檚 almost like each piece of spaghetti is made of small Legos.鈥�

The team鈥檚 process to create the vPCB deviated only slightly from those used for PCBs. Conventionally, semi-cured PCB layers are held in cool, dry conditions where they have a limited shelf life before they鈥檙e laminated in a heat press. Because vitrimers can form new bonds, researchers laminated fully cured vPCB layers. The researchers found that to recycle the vPCBs they could immerse the material in an organic solvent that has a relatively low boiling point. This swelled the vPCB鈥檚 plastic without damaging the glass sheets and electronic components, letting the researchers extract these for reuse.

This process allows for several paths to more sustainable, circular PCB lifecycles. Damaged circuit boards, such those with cracks or warping, can in some cases be repaired. If they aren鈥檛 repaired, they can be separated from their electronic components. Those components can then be recycled or reused, while the vitrimer and glass fibers can get recycled into new vPCBs.

The team tested its vPCB for strength and electrical properties, and found that it performed comparable to the most common PCB material (). Vashisth and co-author , a principal researcher at Microsoft Research and an affiliate assistant professor in the Allen School, are now using artificial intelligence to explore new vitrimer formulations for different uses.

Producing vPCBs wouldn鈥檛 entail major changes to manufacturing processes.

鈥淭he nice thing is that a lot of industries 鈥� such as aerospace, automotive and even electronics 鈥� already have processing set up for the sorts of two-part epoxies that we use here,鈥� said lead author , a UW doctoral student in the Allen School.

The team analyzed the environmental impact and found recycled vPCBs could entail a 48% reduction in global warming potential and an 81% reduction in carcinogenic emissions compared to traditional PCBs. While this work presents a technology solution, the team notes that a significant hurdle to recycling vPCBs at scale would be creating systems and incentives to gather e-waste so it can be recycled.

鈥淔or real implementation of these systems, there needs to be cost parity and strong governmental regulations in place,鈥� said Nguyen. 鈥淢oving forward, we need to design and optimize materials with sustainability metrics as a first principle.鈥�

Additional co-authors include , a UW postdoctoral scholar in the mechanical engineering department; , a UW doctoral student in the mechanical engineering department; , a senior applied scientist at Microsoft Research; , a senior researcher at Microsoft Research and an affiliate researcher in the Allen School; and , a UW professor in the Allen School and the electrical and computer engineering department. This research is funded by the Microsoft Climate Research Initiative, an Amazon Research Award and the Google Research Scholar Program. Zhang was supported by the UW Clean Energy Institute Graduate Fellowship.

For more information, contact vpcb@cs.washington.edu.

The very components that make electronics fast and easy to use also make their disposal an environmental nightmare. Components of smartphones, computers and even kitchen appliances contain heavy metals and other compounds that are toxic to us and harmful to ecosystems.

As electronics become cheaper to buy, e-waste has piled up. A 2019 from the World Economic Forum called e-waste “the fastest-growing waste stream in the world” 鈥� and for good reason. That same year, people generated more than 50 million metric tons of e-waste, the U.N.’s Global E-waste Monitor. Much of it is incinerated, piled up in landfills or exported to lower-income countries where it creates public health and environmental hazards.

Three researchers in the 天美影视传媒 College of Engineering are exploring ways to make electronics more Earth-friendly. , an assistant professor in the Paul G. Allen School of Computer Science & Engineering and researcher in the UW Institute for Nano-engineered Systems, will be presenting at the CHI 2022 conference in May. , an assistant professor of mechanical engineering, is indefinitely. And , an assistant professor of materials science and engineering and researcher in the Molecular Engineering & Sciences Institute, uses biological materials, such as seaweeds and other algae, to develop alternatives to plastics that can be 3D-printed.

For Earth Day, UW News reached out to these engineers to discuss their projects.

What features do you prioritize when designing sustainable electronics?

Vikram Iyer: There are lots of important problems to tackle in designing sustainable electronics, including reducing the environmental impact of e-waste. Our groups are trying to develop creative solutions to this problem, such as using new and more environmentally friendly materials while building functional devices that don鈥檛 compromise performance. For example, the mouse we designed with a biodegradable circuit board works when you plug it into any computer.

What was the design process like for the mouse?

VI: This project was a collaboration with , a principal researcher at Microsoft, and , a UW doctoral student in the Allen School. We took several steps to make this mouse:

• We optimized our circuit design to use the fewest number of silicon chips possible, because around 80% of carbon emissions associated with manufacturing electronics comes from the energy-intensive processes used to make chips.
• We use biodegradable materials when possible. For example, the circuit board that holds and connects the chips together typically contains toxic flame-retardants, but we instead pattern our circuits on a board made from flax fibers. Also, the casing for the mouse is made out of biodegradable plastics.
• We use general-purpose, programmable chips, like microcontrollers, in our designs so that we can reuse them in new devices.
• We use software to estimate the environmental impact of each stage of production to quantify the environmental impacts and identify which stages of our design to improve next.

This is just a start, and our long-term vision is to develop new materials and methods that help us generate a production cycle for electronics in which all the materials and components can either be recycled and reused, or degraded and regenerated through the natural biological cycle.

Is it really true that the mouse’s case and circuit board dissolve in water?

VI: When we submerge our circuit board in water, the fibers start to come apart and the whole thing just disintegrates. This takes about five to 10 minutes in hot water, or a few hours at room temperature. After this we鈥檙e left with the chips and circuit traces which we can filter out. We also designed two different cases, one of these can dissolve in water and the other can be commercially composted.

Would a biodegradable mouse be as durable as a conventional mouse, especially up against the body heat and moisture we produce?

VI: There are definitely sustainable methods to ensure biodegradable components are also durable. For example, you could add a thin coating of water-repellent materials to the mouse 鈥� like chitosan, which is found naturally in the outer skeleton of shellfish. We also show that we can print the case out of polylactic acid, a material commonly used to make things like commercially compostable forks. Going forward we’re really excited to partner with researchers like Eleftheria, whose group is making new sustainable materials. And by partnering closely with researchers at Microsoft, we hope to develop solutions that are scalable and deployable for industry.

What types of new materials is the Roumeli group working on?

Eleftheria Roumeli: focuses on developing materials derived from biological matter. In addition to seaweeds and other forms of algae, this includes plant residues and microbial products. Our studies aim to further our understanding of how these natural, versatile materials can be used as composite building blocks for sustainable alternatives to plastics.

How do you manufacture sustainable components 鈥� like biodegradable parts 鈥� for electronics?

ER: The great thing is that today’s manufacturing methods can be used to create sustainable components for electronics. For example, some of the biologically derived materials my group works with can be made into inks and filaments for manufacturing parts using 3D printing. We recently published a 鈥� that鈥檚 a type of blue-green algae 鈥� both with and without cellulose fibers as a filler. Cellulose is the most abundant natural polymer, and these inks are 100% compostable in soil. There鈥檚 no special composting facility required!

What are other alternative filaments you can use for 3D printing?

ER: We can also make hybrid materials that are a blend of both biological matter 鈥� such as spirulina cells 鈥� and commercial, degradable polymers. For the polymer, we use matrix materials such as polylactic acid, which Vikram mentioned before and is the most widely available industrially compostable polymer, or polybutylene adipate co-terephthalate, a soil-compostable polymer. The particular choice of components determines the properties, performance and the compostability of our filaments.

For example, for packaging, which we usually buy and “consume” very fast and then discard immediately, a material made solely of biological components would be preferable. Then, after we use it, it could be disposed of in a backyard or landfill and it would degrade in a few weeks.

But if we want a filament for the , we would need a polymer binder to ensure that the filament meets the requirements of hot-extrusion based printing.

Are there any other new innovations for sustainable electronics?

Aniruddh Vashisth: One thing we鈥檙e working on is recyclable synthetic polymers. Unlike what Eleftheria’s team studies, these polymers are not derived from biological components. Instead, these polymers consist of an adaptive network and can be recycled and reprocessed multiple times.

Unlike other plastics, these materials do not lose their thermo-mechanical properties during reprocessing and recycling. This is exciting since you can reuse the same material again and again! This phenomenon of retaining material properties is possible because the building blocks that make up these materials can detach and reattach, just like Legos.

So when we are recycling, we are disassembling and reassembling the Legos. We have been focusing on aerospace-grade composites, but we are starting to explore other applications with a wide range of target applications.

What impact would that have on the e-waste problem?

AV: Today鈥檚 e-waste is usually a complex composite, with plastics, metal and ceramic components all in the same device. Recycling these materials is a challenging task, so they often just end up in landfills and lead to pollution.

Right now there are more than 250 million computers and 7 billion phones in the world. Most of these have polymer components. Just think if the polymers used in these devices could be recycled multiple times. That would be a great step toward sustainability! Our group has been working on how to design and characterize such recycled polymer composites for a more sustainable future.

For more information, contact Iyer at vsiyer@uw.edu, Roumeli at eroumeli@uw.edu and Vashisth at vashisth@uw.edu.