## 2 Materials and Methods
### Results  
#### 3.1.1 3D Printing and Solvent Debinding  
It was possible to print six specimens for all the series reliably. Examples of the printed specimens with the three infill patterns (hexagonal, diagonal, and linear) at a 50% infill degree are shown in Figure 4a. The layer thickness was almost constant (the first layer was set to be twice as large as the other layers to fit the required thickness), as shown by the optical microscopy image in Figure 4b. Putting a cover on specimens significantly decreases the debinding rate in all the cases, as seen by the big difference in the loss of soluble component between specimens with and without cover during the first hours in the solvent (Figure 5). The specimens without cover can reach a debinding plateau between 3 and 6 h in the solvent. In contrast, specimens with covers reach a debinding plateau between 6 and 12 h, depending on the  
Figure 4: (**a**) Examples of bending specimens with three infill patterns at 50% infill degree (left to right: hexagonal, diagonal and linear 0/90) and (**b**) side view of a printed specimen showing the deposited layers. Figure 3: Thermal debinding and sintering profile. All heating rates were 2 K/min. 1 h debinding plateaus at 250 and 450 \({}^{\circ}\)C and 1 h sintering plateau at 1050 \({}^{\circ}\)C were used. infill grade. Adding a cover decreases the debinding rate because of the reduction of the exposed surface of the specimens, as demonstrated in several studies for powder injection moulded parts [65; 66; 67; 68; 69]. For specimens without cover, the outer surface and the surface of the infill structure are in direct contact with the solvent and most of the binder is removed in the initial steps of debinding. On the other hand, only the sides and covers are in direct contact with the solvent for specimens with covers at the beginning of the immersion. For these specimens, the solvent must go through the cover to reach the infill structure and later, the dissolved polymer must diffuse through the cover to be evacuated from the specimens. Therefore, the cover increases the diffusion distance, which slows down the debinding process, resulting in the trend observed in Figure 5.  
The only difference in the debinding rate of the specimens with different infill geometry is the higher debinding rate for the hexagonal specimens with cover compared to the diagonal and linear specimens with cover, as observed in the initial hours for the specimens with a 50% infill (Figure 5d), and especially for the specimens with a 75% infill (Figure 5e). Defects in the cover of the specimens Hexagonal 50% YES and Hexagonal 75% YES (Figure 6) are responsible for the different debinding rates. In specimens with a hexagonal infill geometry, the unsupported cover between infill structures is larger than for diagonal and linear specimens (Figure 6), which results in more unsupported material that deformed during printing, creating pores in the middle of the cover and not just only at the junction between the perimeter and the infill. During solvent debinding, the solvent can easily penetrate the specimens through these porous defects, which are also used to diffuse the dissolved polymer molecules more quickly. No effect of the infill grade on the debinding rate can be observed for the specimens without cover. For specimens with covers, the debinding rate decreases with increasing infill grade. The debinding plateau is reached after 9 h in the solvent for the specimens with an infill higher than 75% (Figure 5). Moreover, during the first hours in the solvent, the loss of soluble binder is significantly lower for the diagonal specimens with cover and higher infill grade (Figure 5b) and for Linear 0/90 100% YES compared to Linear 0/90 75% YES (Figure 5c). In the specimens with a higher infill grade, a higher fraction of material is not in direct contact with the solvent at the beginning of the immersion; thus, the diffusion path is longer, as previously described, resulting in a lower debinding rate.