A multidisciplinary team from Virginia Tech’s Macromolecules Innovation Institute (MII) is pioneering a new additive manufacturing process specifically for processing the material Kapton—arguably one of the most sought-after materials in the aerospace and electronics industries.
Kapton is king
The process makes it possible to 3D print structures out of Kapton, a polyimide that showcases exceptional thermal and electrical properties. Among its most desirable properties are that it possesses a degradation temperature of about 550° C, it doesn’t dissolve in solvents, it’s an excellent electrical insulator and it is resistant to ultraviolet irradiation. Further, because the material’s molecules are all-aromatic, meaning they contain rings that restrict rotation, Kapton is overall a very stable material.
Timothy Long, a professor of chemistry and the director of MII, explained: “[Kapton] can withstand all kinds of harsh environmental insults: radiation, high temperature, chemical reagents. It’s one of these molecules that is the ultimate in terms of performance.” Up until recently, however, the only way to work with Kapton was to deal with thin 2D sheets, making it suitable for some applications (like wrapping around a satellite for insulation) but limiting its overall potential.
Last year, professor Long and other researchers from the College of Science and the College of Engineering made a breakthrough with the material, using a stereolithography process to 3D print Kapton.
Excitingly, the researchers have announced a second way of 3D printing Kapton: a process they call direct ink write (DIW). This second process, which was recently described in an article in ACS Applied Materials & Interfaces, offers the research team more versatility in producing Kapton structures.
“If you think of caulking a bathtub or decorating a cake with icing, [DIW is] a very similar process,” elaborated Daniel Rau, one of the co-authors of the study and a PhD student in the DREAMS Lab. “Because it’s so simple, [DIW] gives us incredible flexibility on the ink, synthesis, and the properties it has.”
Using the DIW process, parts printed from Kapton demonstrated properties similar to those of commercial Kapton film. More precisely, the printed material showcased similar mechanical properties up to 400°C and a degradation temperature of 534°C, only a handful of degrees less than Kapton film.
Two processes with distinct advantages
It is worth noting that the new DIW process is not meant to replace stereolithography—as both Kapton 3D printing processes offer their distinct advantages. For instance, stereolithography is better for producing whole parts from Kapton, while DIW is well suited for printing multiple materials side-by-side or for printing on existing materials, including curved surfaces. In other words, both methods showcase the versatility of working with Kapton and AM.
“As soon as we were able to print Kapton, people asked us about applications,” said Christopher Williams, director of the DREAMS Lab and associate director of MII. “The answer we often gave was printed electronics, but that’s challenging to do in stereolithography. This new technique could really enable that as we look towards simultaneous printing of conductive materials and this excellent insulator.”
In developing DIW, the multidisciplinary team from Virginia Tech had to re-adapt the Kapton resin that had been synthesized for stereolithography. Despite initial beliefs that this modification would be simple enough, the researchers quickly found that the original resin required quite an overhaul to be suitable for DIW.
“Often times, I synthesized a resin and studied its rheological properties, and Danny tested if it performed in the printer as we predicted,” explained Jana Herzberger, a postdoc in the Long Group. “It was a new experience for me to work with engineers, and I think we learned a lot from each other and improved our communication skills quite a bit.”
In other words, the journey to developing a suitable resin for the DIW process took a joint effort from various faculties and team members. “My group makes macromolecules and Chris’ group puts them into unique geometric shapes,” Long added. “It’s almost like one group working together to solve really complex questions like this.”