Extrusion Printing of Electrically Conductive Polymer Composites via Immersion Precipitation

This paper describes a method to fabricate three-dimensional (3D) structures consisting of an electrically conductive polymer composite (CPC) by 3D printing assisted by immersion precipitation, using cellulose acetate (CA) and graphite microparticles (GP) as an example. Previous approaches to fabricating CA composites were primarily based on film casting and electrospinning. 3D printing of CA composites resulted in poor print fidelity because of the spreading of the ink due to (1) the low viscosity of CA ink and (2) the low vapor pressure of the solvent (such as acetone) dissolving CA. In this study, we performed embedded 3D printing of CA dissolved in acetone using a surrounding medium of water to promote the precipitation of the printed ink. The presence of water as the surrounding medium expedited the solidification of the ink via immersion precipitation, and the structure of the extruded ink was arrested without major spreading. Capillary flow analysis suggested the printability of the ink with apparent viscosities (2.3–2.7 Pa s) that were correlated with the concentration of GP (30–70% w/w) in the printing ink. Scanning electron microscopy and thermogravimetric analysis suggested the homogeneity of GP within the CPC. The electrical conductivity of the CPC was confirmed to be 5 × 10^–4–3.6 × 10 S/m for GP concentrations of 30–70% w/w, which was comparable to that of film-based CA composites prepared by casting (10^–4–10 S/m). Overall, this work demonstrated embedded 3D printing of composite materials with a high percentage of additives of up to 70% w/w facilitated by direct ink writing and immersion precipitation, which should be applicable for the prototyping of sensors, actuators, and electroanalytical devices.