Jul 6, 2017 | By Tess

A team of researchers from Texas A&M University has developed a novel method for improving the strength of 3D printed thermoplastic parts. By coating filaments with multi-walled carbon nanotubes (MWCNTs) and then exposing them to microwaves, the team found that it was able to improve a printed part’s strength by as much as 275%.

As 3D printing becomes more accessible and versatile, being used at home, in offices, and on factory floors, there are some notable challenges that persist with the technology. For instance, fused deposition modeling (FDM) 3D printing, which uses a heated nozzle to extrude melted layers of plastic and which is being used more and more to create thermoplastic components, often fails to create strong, well-fused parts.

Because the layers of a printed object are only “weakly welded together,” parts that require strength for functional applications can be hard to ensure.

As Micah Green, the lead researcher on the Texas A&M project, explained: “3D printed thermoplastic parts are usually very weak in the vertical direction because each successive layer does not weld to the layer below. Simple heating cannot solve this problem but by coating the 3D printer filaments with multi-walled carbon nanotubes (MWCNTs) that heat up when irradiated with microwaves, we can locally heat the sample at each weld and create high-strength materials.”

The research team found that by coating the filament with a MWCNT-packed polymer film, printing the desired object, and then exposing said object to microwaves, it was able to create a much stronger part. In their experiments, the researchers said they were able to localize the nanotubes at “interfaces between each filament trace,” which enabled the polymer to entangle with the thermoplastic when selectively exposed to microwave heat.

The technique, called “locally induced radio-frequency (LIRF) welding,” was even shown to increase a 3D printed thermoplastic part’s weld fracture strength by up to 275%. That is no small feat!

The Texas A&M team worked in collaboration with scientists from Essential Materials and TriFusion LLC to develop the novel technique, which consisted of using a bath coating process to coat an engineering-grade PLA filament with a thin layer of MWCNT “ink,” which is made by sonicating the MWCNT and polymer mixture in chloroform.

According to the research, similar coating results can be achieved by “coextruding a CNT melt master batch over a neat polymer core.” Using this method, the team says, could enable the technology to be scaled up significantly, even to produce industrial quantities of the material.

“Being able to print materials with increased weld strength opens up a wide range of new application areas for 3D printed thermoplastics,” said Green. “The increase in 3D printed weld strength means that MWCNT coatings on polymer filaments, followed by LIRF heating, can be used to make structures with properties approaching those made in conventional manufacturing processes, something that will allow for load-supporting structures with complex shapes.”

The research was recently published in the journal Science Advances under the title “Welding of 3D-printed carbon nanotube–polymer composites by locally induced microwave heating.” The team says it is now investigating how radio-frequency heating hardware could be integrated into a 3D printer to further streamline the process.



Posted in 3D Printing Technology



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