Additive manufacturing of recyclable, highly conductive, and structurally robust graphite structures

Abstract

• Complex, electrically conductive structures with relatively high compressive strength. • Printable aqueous pastes made from graphite and cellulose nanocrystals. • Additively manufactured from sustainable and recyclable materials. • Structures made via direct ink writing (DIW) and dried at room temperature. • Minimal and controllable shrinkage of printed structures. This study investigates the design and use of a printable, sustainable, aqueous paste for room-temperature low-energy material extrusion (ME) additive manufacturing (AM) of complex structures. To this end, pastes with controlled rheology and a total solid content of ∼42% are formulated. Constituents of the pastes are commercial graphite and cellulose nanocrystal (CNC) powder, as a dispersing additive, with 91:09 and 88:12 graphite:cellulose wt.% compositions. The AM structures are dried in air at three rates (slow, medium, and fast). The structure of printed parts is characterized using electron microscopy, X-ray diffraction, Infrared/X-ray photoelectron spectroscopy, X-ray micro-computed tomography, and thermogravimetric analysis. The compressive strength of AM graphite structures reached 5.8±0.6 MPa with almost no effect from drying rates. However, samples containing more cellulose were ∼30% stronger in compression. Carbonization of the AM parts increased their electrical conductivity by more than an order of magnitude to ∼2400 S.m −1 . In addition, it enabled the fabrication of nearly pure graphite structures. The mechanical and electrical properties of samples fabricated in this study exceed the performance of previously reported AM graphite structures. Moreover, the recyclability of the printed parts was demonstrated by regenerating pastes via mixing printed parts in water and re-printing new parts with the paste. The AM graphite structures can be used in numerous applications, including but not limited to electrical discharge machining (EDM), electrochemical machining (ECM), high-temperature customized sealing, high-temperature composite tooling, and energy conversion and storage.