Current 3D printers employ either plastic or metal and the conventional method to coat 3D plastic structures with metal is not environmentally friendly and yields poor results. Scientists have developed a metal-plastic hybrid 3D printing technique that produces plastic structures with a highly adhesive metal coating on desired areas. This approach extends the use of 3D printers to 3D electronics for future robotics and Internet of Things applications.

3D printing allows one to create arbitrarily complex 3D objects directly from their raw materials. In fused filament fabrication, the most popular 3D printing process, a plastic or metal is melted and extruded through a small nozzle by a printer head and then immediately solidifies and fuses with the rest of the piece; however, because the melting points of plastics and metals are very different, this technology has been limited to creating objects of either metal or plastic only.

The new hybrid technique can produce 3D objects made of both metal and plastic. The method is an improvement over the conventional metallization process used to coat 3D plastic structures with metal. In the conventional approach, the plastic object is 3D printed and then submerged in a solution containing palladium (Pd), which adheres to the object's surface. Afterwards, the piece is submerged in an electroless plating bath that, using the deposited Pd as a catalyst, causes dissolved metal ions to stick to the object. While technically sound, the conventional approach produces a metallic coating that is non-uniform and adheres poorly to the plastic structure.

In contrast, in the new hybrid method, a printer with a dual nozzle is used; one nozzle extrudes standard melted plastic (acrylonitrile butadiene styrene, or ABS) whereas the other extrudes ABS loaded with PdCl2. By selectively printing layers using one nozzle or the other, specific areas of the 3D object are loaded with Pd. Then, through electroless plating, one finally obtains a plastic structure with a metallic coating over selected areas only.

Because Pd is loaded in the raw material, the technique does not require any type of roughening or etching of the ABS structure to promote the deposition of the catalyst, unlike the conventional method. This is especially important when considering that these extra steps cause damage not only to the 3D object itself, but also to the environment, owing to the use of toxic chemicals like chromic acid. Lastly, the approach is entirely compatible with existing fused filament fabrication 3D printers.

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