Microwave-based post-treatment for FDM 3D printing: CNT coating improves layer adhesion

One of the biggest weaknesses of fused deposition modeling (FDM) is the limited adhesion between the individual layers. Annealing is often recommended to improve mechanical strength. An alternative approach was published by researchers at Texas A&M University in Science Advances in 2017. They developed a method using PLA filament coated with carbon nanotubes (CNTs). These CNTs are mainly concentrated in the boundary layers between the individual print layers.

The key advantage of this coating is that CNTs are sensitive to microwave radiation. They absorb the radiation and convert it into heat. Instead of annealing the entire component in an oven, this process enables localized heating directly at the layer boundaries. The researchers refer to this approach as Locally Induced RF Heating (LIRF).

Compared to conventional annealing methods, LIRF offers several advantages. The component dimensions hardly change, as the heating is limited to the interfaces between the print layers. The process is also faster and more energy-efficient than conventional heat treatment. According to the study, the resulting strength of the layered joints is very similar to that of injection-molded components.

Despite its promising potential, this technology has so far found little practical application. Both single-walled and multi-walled CNTs as well as microwave devices are readily available. More information can be found in the paper “Welding of 3D-printed carbon nanotube-polymer composites by locally induced microwave heating”.