## 1 Introduction  
Three-dimensional (3D) printing is a technology that creates real objects by stacking appropriate materials layer-by-layer according to a three-dimensional computer-aided design [1]; 3D printing is being applied to various industries such as manufacturing, automotive, aerospace, architecture, food, jewelry, medicine and more [2, 3]. Nowadays, 3D printing is attracting attention as a highly efficient technical alternative for manufacturing products that are difficult to produce with conventional manufacturing methods or that can only be produced through complex and numerous processes [4]. It has a lot of potentials in offering a wide range of geometrically complex structures, implementing large scale and high-precision models, and combining different technologies. Hence, related research approaches have been tremendously carried out [5]. However, the materials used for 3D printing still need to be developed and supplemented in terms of their range, usability and the physical properties of the end products [6]. There are several types of 3D printing methods, depending on the processes to create the desired 3D model [5]. Representative 3D printing technologies are Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), Laminated Object Manufacturing (LOM), SLA (Stereo-lithography Apparatus), Digital Light Processing (DLP), Material Jetting (MJ), and Electron Beam Melting (EBM) [5, 7]. Among these, DLP is a state-of-the-art 3D printing technology that develops functional materials for manufacturing nanocomposites with liquid photocurable resins, allowing people to customize the properties of the final 3D printed object by simply changing the resin compositions [8]. Also, unlike SLA technology,which uses point or line light sources, DLP uses areal light sources, which can project the entire mask image at the same time. Thus, DLP 3D printers can produce final objects much faster compared to other 3D printing technologies that use point or line light sources to form layers [9]. A schematic diagram of DLP type 3D printer configuration is illustrated in Figure 1. This approach is capable of generating a variety of highly complex microscale structures with micro to sub-micrometer accuracy [10], and it is generally advantageous to fabricate smaller structures compared to locally hardening the liquid phase with point drawing [11]. Cellulose nanocrystals (CNCs), which exist only in the crystalline regions of cellulose, are crystalline cellulose nanoparticles with a diameter of 5-50 nm and a length of 100-1000 nm, obtained by removing the amorphous regions of cellulose through chemical or physical treatments [12; 13; 14]. Due to their molecular structure, rod-like CNCs have many unique characteristics, including nanoscale dimensions, easy surface modification, high surface area, unique morphology, low density, lack of toxicity, high crystallinity, low thermal expansion, excellent mechanical strength, high aspect ratio, high strength, high modulus, and dimensional stability [15]. In addition, in terms of obtaining resources from biomass, CNC has the advantages of biocompatibility, renewability, and biodegradability [16; 17]. Hence, it has attracted much attention as a functional reinforcing additive in polymer matrices [18]. As one of the strongest and stiffest natural biopolymers, particularly because of its high modulus and tensile strength, resulting from high aspect ratios and crystallinity, CNC is a suitable candidate for tailoring the mechanical properties of polymeric materials [19]. Polymer nanocomposites are a new class of composites containing nanoscale particles. The typical dimensional range of nanoscale particles used in making polymeric nanocomposites is 1-1000 nm, and they are homogeneously dispersed in polymers [20]. Polymer nanocomposites with nanoparticles, such as CaCO\({}_{3}\)[21], nanoclays [22], SiO\({}_{2}\)[23], carbon nanotubes [24], and aluminum oxide [25], have extended their functionalities for various  
Figure 1: Schematic diagram of DLP type 3D printer configuration.