Zhejiang University researchers have come up with a thrilling discovery that could make resins much more sustainable. In a paper for Science, “Circular 3D printing of high-performance photopolymers through dissociative network design,” they explained how they can reverse a photo-click reaction. This could, in subsequent cycles, enable the same performance from reused resin again and again.

The research team came to their results through a completely unexpected reaction of two reagents. A thiol reagent was added to aldehydes and a reaction occurred under light and without heat, which usually doesn’t happen. The team then made dithioacetal bonds that they could associate and disassociate, which would then separate a part into its original constituent materials.

Corresponding co-author Xie Tao, from the College of Chemical and Biological Engineering, said that if 3D printing materials were “infinitely” recyclable, waste and costs would both be cut, which would be “a win-win for both industry and the environment.”

“It’s like disassembling Legos. The printed object can be recovered at the molecular level and reprinted again and again,” he explained.

“Our research has successfully overcome the longstanding trade-off between mechanical performance and closed-loop recyclability in photocurable 3D printing materials at the molecular level.By establishing a light-responsive dynamic dithioacetal chemistry system, we offer a novel molecular design strategy, providing meaningful insights for advancing sustainable manufacturing technologies.”

Similar work in thiol-aldehyde chemistry at Anhui University has been shown to be reversible. Now, this team is looking at creating new flexible, rigid, and crystalline materials that work in the same way with the same chemistry. Potentially, this is a fundamental breakthrough in materials science and additive manufacturing. Through having one class of recyclable materials, we could easily recycle all support and misprints. At the same time, old parts could perhaps be recycled and turned into new things in a very easy way. This could make 3D printing, especially vat polymerization, much more sustainable. At the same time, this could really lower costs for operators. Recycling all your waste and supports could make everything much more efficient. And looking beyond this, if we can reverse these reactions, can we do so locally? Then, can we maybe make supports that are digital, and could be reversed once the part is done? Could we remove surface inaccuracies this way?

But, we don’t yet know the costs of this chemistry, and if it can be made at attractive volume and prices. What kind of equipment would you need to do this, and how safe would it be? Could we use current 3D printers well enough to make this stuff? That would greatly improve the adoption process. But, new machines, procedures, post-processing steps, or investments would make it all take longer. At the same time, the thiol aldehyde chemistry they’re playing with here is potentially harmful. What gasses or other noxious materials are released during this reaction, and how can it be made safe? Lung diseases and cancers could be caused by aldehyde thiol chemistries in flux, as both thiols and aldehydes are skin, eye, and respiratory irritants. Thiols are also super stinky, and I’m not sure if the parts or process will be stinky as well.

The idea is excellent, and this sounds like a hugely beneficial technology for us all. But, will it actually work in the field? How dangerous will it be? And how will it be dangerous? We also don’t know the costs of implementing this, or the costs of these materials. As a vision, however, this is completely compelling. Perhaps it will not be this chemistry, but someone somewhere else will be inspired to develop something similar. Reversible click or other dissociative chemistry holds a lot of promise generally. For additive specifically, it could promise methods that can save time or money. Wholly new ways of looking at material management could also result. Or you could find a way to very chemically 3D print using this technology, or something similar. Vat polymerization has looked like an end of life technology since the 2010s. Every time, it looked like an amazing technology for the previous time period. it was great for prototypes but would never be used for end-use parts. Then Invisalign becomes a huge application, using it for intermediates. Formlabs then puts tens of thousands of machines in offices and labs. Then Carbon and Henkel revolutionize the materials space and make many more elastomeric materials possible. Phrozen and others then make the $200 DLP machine a reality. Vat polymerization has repeatedly, in wholly surprising ways, evolved itself to not only remain relevant, but also grow. Perhaps this could be the next big leap forward.