Here we present the results for fabrication of 3D complex shapes of cellular carbonaceous materials using origami. Cellular carbonaceous materials, particularly carbon and carbide, possess interesting properties including low density, high surface area, high chemical inertness, high oxidation resistance, adjustable electrical conductivity, and high mechanical properties. Due to such properties, they find their use in different applications such as high temperature filters, catalytic support, thermal insulators and structural materials [1,2]. The current state-of-the-art to manufacture cellular carbonaceous materials includes direct foaming method and template method. However, 3D complex shapes, especially with thin cross-sections, are challenging to fabricate in these current techniques. Here we postulate origami-inspired manufacturing to fabricate 3D complex shapes of carbonaceous material. These complex shapes are good candidate for multifunctional materials, as the origami-inspired manufacturing integrates the structural properties of the origami structures to the intrinsic properties of the materials. Furthermore, the potential for scalable manufacturing makes this origami-inspired manufacturing suitable for industry-level production.

Our initial target was to fabricate origami structures of glassy carbon and tungsten carbide (WC). Although theoretically numerous shapes can be possible to fabricate, we demonstrated our process using a traditional Miura-ori shape. Here we used Fisherbrand pure cellulose chromatography paper (Sigma Aldrich, Cat. No. 05-714-1) because of its cellulosic nature and minimal impurity. For automatic pre-creasing, we generated CAD models to define the location of the creases. CAD models for the creases on both sides of the paper must be created separately. The chromatography paper was pre-creased using an empty ball-point pen mounted on a cutting plotter machine (Graphtec CE6000-40, USA) using specific equipment parameters. The creasing on the both sides of the paper were automatically aligned by the registration marks generated by the cutting-plotter software and printed on the paper. Figure 1a illustrates an example of a pre-creased paper. Once the pre-creasing was done, the paper was folded manually along the creases to obtain paper origami structures (Figure 1b). The paper origami structure was carbonized at 900 °C for 75 minutes with a heating rate of 5 °C/min in nitrogen environment to obtain origami structures of glassy carbon (Figure 1c). For WC, the paper origami structure was infiltrated with aqueous solution of 20 wt% ammonium metatungstate (AMT). The AMT infiltrated origami shapes were heat-treated at 1300 °C for 3 hours with a heating rate of 2.5 °C/min in vacuum environment to obtain WC origami shape (Figure 1f). In both the cases, the Miura-ori pattern was preserved, although a significant shrinkage occurred during the heat treatment. The heat-treated samples were characterized by x-ray diffraction (XRD) spectroscopy to determine the composition of the material. Scanning electron microscopy (SEM) was used to characterize the microstructures of the precursor paper, carbon and WC origami shapes.

The XRD pattern of the carbonized paper (Figure 1d) show weak and broad peaks centered around 2θ = 24° and 2θ = 43°, which corresponds to (022) and (100) reflections of amorphous carbon. Carbonization of the cellulosic paper results in a porous fibril network of glassy carbon as seen in Figure 1e. The fibers feature an average diameter of 5.26 ± 2.53 µm. The pore size distribution among the fibers are random leading to macroporosity with pore diameter ranging from 1.56 µm to 21.71 µm. The results from the XRD of the heat-treated AMT infiltrated paper (Figure 1g) shows the formation of WC, along with a small amount of W₂C. The average diameter of fibers forming the fibril matrix of WC is 10.88 ± 2.05 µm (Figure 1h) and the macro-pores caused by the random distribution of the fibers range from 1.04 µm to 28.34 µm.

Ongoing work is 1) optimization of WC synthesis process by implementing Taguchi design of experiment; 2) characterization of the mechanical properties of carbon and WC origami shapes; 3) understanding the effect of the microstructures on the mechanical properties of the origami shapes; and 4) use paper a scaffold obtain 3D complex shapes of different other materials such metal impregnated carbon or oxides.

References:

[1] M. Inagaki, J. Qiu, Q. Guo, Carbon foam: Preparation and application, Carbon N. Y. 87 (2015) 128–152. doi:10.1016/j.carbon.2015.02.021.

[2] L. Borchardt, C. Hoffmann, M. Oschatz, L. Mammitzsch, U. Petasch, M. Herrmann, S. Kaskel, Preparation and application of cellular and nanoporous carbides, Chem. Soc. Rev. 41 (2012) 5053. doi:10.1039/c2cs15324f.