Electrically conductive CNT-composites could be produced using standard commercial 3D printers, according to Italian researchers.
In the past five years, additive manufacturing (AM) has gone from a tool used exclusively in industry for rapid prototyping, to a new, widepsread approach to developing high-value products. The automotive, aerospace and architecture sectors are all also exploring its potential for use in printing composite materials. But a growing number of research groups, including one at the Polytechnic University of Turin, are interested in using it to produce polymer nanocomposites. In a paper published in a recent issue of Polymer [DOI: 10.1016/j.polymer.2016.12.051], this team, led by Prof Marco Sangermano, have shown that it may be possible to tap into the electrical properties of carbon nanotubes (CNTs), in order to make conductive composites on a standard commercial printer.
What’s colloquially called 3D printing could refer to any one of up to eight different techniques, but what they all have in common is that they build 3D objects layer-by-layer. Sangermano and his colleagues chose digital light processing (DLP), a technique that uses photopolymers that react with a specific light source, to cure in precisely-defined locations, forming a 3D object.
The team blended two polymers – PEGDA and PEGMEMA – to form the matrix material, and mixed multi-walled carbon nanotubes into it. Rheological tests were performed on a number of different formulations that varied ratio of the polymers and the concentration of the nanotubes within it. With the viscosity optimised for printing, they used an unmodified DLP printer to produce a series of objects – 3mm cubes, submillimetre films, and centimetre-scale hexagonal structures and a circuit model – to test the mechanical and electrical properties of the CNT-polymer.
They found that the addition of CNTs to the formulation causes a slight decrease in crosslinking density, which reduces its mechanical performance. But electrical tests showed that the addition of just 0.1 wt% CNTs increased the conductivity by almost three orders of magnitude, with higher concentrations improving it even further. The team believe that they could retain this electrical performance while improving the mechanical properties by using a more intense light source in the DLP printer. For those interested in printing conductive composites, this results are rather promising.
G. Gonzalez, A. Chiappone, I. Roppolo, E. Fantino, V.Bertana, F. Perrucci, L. Scaltrito, F. Pirri, M. Sangermano. Development of 3D printable formulations containing CNT with enhanced electrical properties” Polymer 109 (2017) 246-253. DOI: 10.1016/j.polymer.2016.12.051