Abstract Graphitic structures, unlike polymers and metals, cannot be directly printed in 3D. We demonstrate here that graphitic structures can be shaped in 3D by using direct-ink writing (DIW) of lignin-graphene oxide solutions that are then dried and carbonized. Lignin is a promising precursor for the elaboration of bio-based carbon materials because of its low cost, natural availability and high carbon content. The rheology of the inks is controlled by the presence of graphene oxide (GO) in order to make the solutions viscoelastic and printable. The GO flakes are found to align during ink extrusion. This behavior is understood by considering the applied extrusion shear stress and the yield stress of the inks. By adjusting the relative fraction of GO and lignin, it is possible to change the density, the graphitic order, and thus the electrical and mechanical properties of the printed materials. In particular, GO promotes not only graphitic order but also porosity. By contrast, high amounts of lignin allow preparing denser but less ordered carbon structures. The possibility to vary density and properties offers an opportunity for the development of graphitic 3D materials with tunable properties.

中文翻译：

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用于密度可调的石墨材料的 3D 打印的木质素-氧化石墨烯油墨

摘要 与聚合物和金属不同，石墨结构不能直接以 3D 方式打印。我们在这里证明了石墨结构可以通过使用木质素-氧化石墨烯溶液的直接墨水书写 (DIW) 进行 3D 成型，然后干燥和碳化。木质素因其低成本、天然可用性和高碳含量而成为制备生物基碳材料的有前途的前体。油墨的流变性受氧化石墨烯 (GO) 的控制，以使溶液具有粘弹性和可印刷性。发现 GO 薄片在油墨挤出过程中对齐。通过考虑施加的挤出剪切应力和油墨的屈服应力，可以理解这种行为。通过调整 GO 和木质素的相对比例，可以改变密度、石墨顺序、以及印刷材料的电气和机械性能。特别是，GO 不仅促进石墨有序，而且促进孔隙率。相比之下，大量的木质素允许制备更致密但有序性较低的碳结构。改变密度和特性的可能性为开发具有可调特性的石墨 3D 材料提供了机会。