Fabrication of 3D Shapes of Carbon By Origami
Authors: Islam Monsur , Flach Joshua Paul , Martinez-Duarte Rodrigo 
Published: February 2020

We present preliminary experiments leading to a novel approach to manufacture 3D complex shapes of thin carbon using origami. Origami is an ancient art of paper folding, where a 3D complex shape can be fabricated by folding planar paper along the creases. Paper is generally a random network of cellulose fibers. Cellulose decomposes to carbon upon heat treatment around 900 °C in inert atmosphere. The cellulose derived carbon resembles to glass-like carbon and possesses interesting properties such as low density, high electrical conductivity, biocompatibility, and high resistance to high temperature and corrosive environment1,2. Here, we aim to demonstrate the capability to manufacture 3D complex origami structures of carbon by heat treating the precursor paper origami structures. These complex 3D structures of thin cross section carbon have huge potentials as multifunctional material in different applications such as tissue engineering scaffold, catalyst support and biomedical devices.
We used Fisherbrand pure cellulose chromatography paper (Sigma Aldrich, Cat. No. 05-714-1) because of its cellulosic nature and minimal impurity. A cutting plotter machine (Graphtec CE6000-40, USA) was used to pre-crease the paper. The pre-creasing method started with generating CAD models to define the location of the creases. CAD models for the creases on both sides of the paper must be created separately. Registration marks were printed on the both sides of the chromatography (CG) paper by a laser-jet printer for accurate alignment during pre-creasing. The CG paper was fed to the cutting plotter machine and pre-creased with a ball-point pen mounted on the cutting plotter machine using specific equipment parameters. Once pre-creasing is done on one side, the CG paper was flipped and creased on the other side. Excess portion of the paper was then trimmed and folded manually along the creases to obtain paper origami structures. The paper origami structures were carbonized in a tube furnace (TF1400, Across International, Japan) at 900 °C for 75 minutes in a nitrogen atmosphere. This process was repeated for three different origami tessellations, which are Miura-ori, Waterbomb-base and Yoshimura in descending order of complexity. SEM and XRD were performed to characterize the effect of carbonization on the microstructure and the material composition of the carbonized sample respectively. The compressive strength of the carbonized Miura-ori was characterized by compression test.
Figure 1 shows the origami tessellations before and after carbonization. The carbonized samples retained the original precursor origami structure during the heat treatment, although surface wrinkling could be observed for the carbonized structures. Around 90% weight loss occurred during the carbonization. A significant shrinkage was also observed for the carbonized origami structures. Although the overall shrinkage was dependent on the complexity of the origami structures, around 75-90% shrinkage was observed in the fibril structures when compared the microstructures of CG paper and carbonized samples as shown in Figure 2a and 2b respectively. Our hypothesis is escape of the gaseous substances from the cellulose during the carbonization results in the weight loss and the shrinkage. The XRD pattern of the carbonized sample as shown in Figure 2c confirms the formation of amorphous carbon during the carbonization process. The compressive strength to weight ratio of the carbon Miura-ori was measured to be 96.4 ± 0.48 kPa/g, which is over 5 times that of paper Miura-ori as shown in Figure 2d.
Ongoing work is on characterizing the scalability of this manufacturing process; infiltrating the paper origami structure with metal precursor to obtain metal impregnated carbon origami structure through carbothermal reduction reaction for structural electrode or sensor application; and infiltrating the carbon structure with bio-epoxy to increase the strength of the carbon origami structures.
References:
1. L. A. Pesin, J. Mater. Sci., 37, 1–28 (2002).
2. O. Ishida, D. Kim, S. Kuga, Y. Nishiyama, and R. M. Brown, Cellulose, 11, 475–480 (2004).

Figure 1