Resistivity and Its Anisotropy Characterization of 3D-Printed Acrylonitrile Butadiene Styrene Copolymer (ABS)/Carbon Black (CB) Composites  
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static charge dissipation, and lightning protection in electronics [8]. Those materials often require processing before being employed and 3D printing, a useful processing method for fabrication of complex shape parts, has been used to print objects with desired electrical properties. There are currently two main approaches. In one approach, the objects are fabricated to a required geometry using insulating materials, and then conductive additives are embedded in the objects to obtain electrical conductivity [9; 10; 11]. In the other approach, the objects are directly printed with conductive materials [12; 13; 14; 15; 16; 17]. The second approach is more efficient, and its application areas include electronic sensors [18; 19], paper electronics [20], light-emitting diodes [21], microbatteries [22], and electrodes [23; 24]. The conductive materials for 3D printing mainly comprise metal, carbon, and their polymer composites. The feedstock of polymer composites mixed with various forms of carbon has attracted considerable attention because carbon cannot be oxidized and then become nonconductive. In addition, the polymer composites are always thermoplastic and, thus, can be handled by fused deposition modeling (FDM), a widely used 3 Dprinting technology. For instance, [PERSON] et al. reported a method to fabricate electronic sensors using low-cost 3D FDM printing by polycaprolactone (PCL)/carbon black (CB) [18]. Although the materials appeared to have low resistivity after printing, they did not evaluate the influence of the process of FDM on the resistivity of printed parts. [PERSON] et al. revealed that the resistivity of printed parts was much higher than that of the feedstock for acrylonitrile butadiene styrene copolymer (ABS)/graphene oxide (GO) composites [15]. However, the reason why the resistivity was increased was not described in detail. To the best of our knowledge, despite the potential of these materials for various applications, few studies have specifically characterized the resistivity of 3D-printed conductive composites. Although the resistivity of the composites is mainly determined by the conductive additives, the process technique and the process parameters are also important factors that influence resistivity [25]. For example, in the traditional injection molding, the process parameters significantly influence the electrical conductivity of molded composites [26]. Additionally, in 3D printing, FDM produces 3D objects by extruding thermoplastic materials and depositing the semi-molten materials onto a stage layer by layer. Microscopically, voids inevitability exist within the model, and adjacent fibers may not be completely fused because the material is semi-molten when deposited [27]. The process parameters considerably influence the mechanical properties [28; 29; 30; 31] and the dimensional accuracy [32] of the printed parts. As the resistivity of the materials are also influenced by the inner microstructure, we hypothesize that the structural features affected by the process parameters also affect the resistivity of the printed parts. Another obvious characteristic of printed parts is structural anisotropy [33], namely the structures in horizontal direction and vertical direction of printed parts inherently are different. Structural anisotropy of the printed parts of conductive composites also produces anisotropy in resistivity [18]. Especially, considering their stacked structure, printed parts provide a complete conductive path in the horizontal printing direction of the fibers. However, perpendicular to such direction, the formation of a conductive pathway is reliant on the melting between adjacent printed fiber layers [18], which is affected by the process parameters.