## 3 Results and Discussion
### Effect of CNC Lyophilization Concentrations
#### 3.1.1 Morphological Properties of CNCs Processed at Different Lyophilization Concentrations
However, the composites with CNCs processed at the high concentration showed wider sizes of CNC particles, exhibiting overall rough and uneven surfaces. For the composite with 0.5% CNCs processed at the low concentration, CNC particles of 200-300 \(\upmu\)m, which were generated during cryogenic freezing, were broken into rod-like particulates through a series of pretreatments and were present in the composite at approximately 3 \(\upmu\)m in width. However, in the case of the composites with CNCs processed at the high concentration, the deformation of the agglomerated CNCs occurred less frequently, resulting in \(>\)10 \(\upmu\)m width of CNCs on the  
Figure 5: Mechanism of the lyophilization-induced self-assembling behavior of CNCs during the freeze-drying process. 1.3 Mechanical Properties of CNC/Photopolymer Composites Processed at Different CNC lyophilization Concentrations  
The same amount of CNC incorporations into photopolymer composites resulted in higher tensile strength and tensile modulus values at a low CNC lyophilization concentration (1%) compared to a high CNC lyophilization concentration (2.2%) (Figures 10 and 11). The reason for this seemed to be due to the shapes of the added CNC particles. In the case of CNCs lyophilized at the low concentration, the condensed CNC shapes after lyophilization could be thinner and smaller, which may be easy to form more uniform and smaller CNC particles in the same pretreatment process. As a result, the CNC particles maintain smaller and more uniform size distributions when added to the composites. Importantly, it is advantageous to have a high aspect ratio to be an effective stress carrier in the composite. As shown in the SEM images of the fracture surfaces of CNC/photopolymer composites, the CNCs lyophilized at the high concentration had relatively lower aspect ratios than those lyophilized at the low concentration. Therefore, the composites with CNCs treated at the low lyophilization concentration were considered to have higher mechanical properties than the composites with CNCs treated at the high lyophilization concentration due to more efficient fracture and dispersion mechanisms. Figure 10: Tensile strength of CNC/photopolymer composites as a function of lyophilized CNC concentration and CNC loading. Figure 9: SEM images of 1.0 wt% CNC/photopolymer composites processed at a high CNC lyophilization concentration: (a) \(\times\)100 and (b) \(\times\)1000. Additionally, lower tensile strength and tensile modulus values were observed in the composite with a high CNC loading (1.0 wt%). As confirmed by the morphological characteristics, the higher the amount of CNCs added, the less effective the dispersion and destruction mechanisms of the pretreatment process, resulting in larger sizes and lower aspect ratios, and consequently lower strength values. Besides, the sizes of CNC particles dispersed in the composites with 1.0 wt% CNCs were not even. Thus, it seemed that the stress was concentrated in the CNC particles, leading to a decrease in the strength values. Therefore, the CNCs processed at the low lyophilization concentration of 1% were selected for the CNC/photopolymer composites in later experiments.