## 3 Results and Discussion
### Density, Contamination, and Magnetic Properties  
The average values of density, carbon, and oxygen content of the Nd-Fe-B parts produced with the different binder systems are reported in Table 2. Feedstocks A, B, and C had the same density level. In contrast, feedstock D had slightly lower values, which could be produced by defects during compression molding or worse densification during sintering, resulting from powder binder separation since feedstock D had the lowest SA content, as corroborated by the pressure stability curve in Figure 5. On the other hand, the highest density (6.94 g/cm\({}^{3}\)) was obtained for feedstock C, which had the highest SA content. It is important to remember that SA acts as a surfactant; thus, SA reduces the surface tension between the binder and the particle and increases the wettability of the binder; therefore, SA helps stabilize the dispersion of the Nd-Fe-B particles in the polymer [72]. As such, higher SA content seems beneficial for achieving a higher density. However, as discussed in the previous sections, high SA content leads to very low viscosity, which causes problems during compounding and molding. Therefore, a lower SA content was used. All feedstocks had an acceptable range of oxygen and carbon contamination, with feedstock B having the lowest oxygen content but the highest carbon content. These results are directly attributed to its binder composition. The relatively high content of SA in feedstock B chemically adsorbs onto the surface of the alloy particles [72], limiting oxygen pickup. However, feedstock B also has a higher LLDPE content that must be removed during thermal debinding, leading to higher carbon residues compared to feedstocks C and D, which have lower LLDPE contents (Table 1). In this regard, [PERSON] et al. [73] achieved a \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Feedstock** & **Density (g/cm\({}^{3}\))** & **Oxygen (ppm)** & **Carbon (ppm)** \\ \hline A & 6.83 & 6097 \(\pm\) 922 & 1356 \(\pm\) 63 \\ B & 6.85 & 4468 \(\pm\) 292 & 2012 \(\pm\) 182 \\ C & 6.94 & 5121 \(\pm\) 1345 & 1949 \(\pm\) 91 \\ D & 6.61 & 4966 \(\pm\) 587 & 1165 \(\pm\) 104 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average values of the density, carbon, and oxygen contamination content of sintered parts for different feedstock formulations at 55 vol.% powder loading. Figure 6: Representative apparent viscosity versus apparent shear rates for different powder loadings. lower amount of carbon (800 ppm) by using the same LLDPE (61 vol.%) as the backbone in their binder system. This lower C content could be attributed to the higher powder content (i.e., 61 vol.%), resulting in the decreased binder amount and, consequently, lower carbon contamination. However, the oxygen level was higher (5360 ppm) than all samples in the current study. Thus, there should be a balance between the binder ingredients to prevent oxidation and carbon residues. According to [PERSON] et al. [43], using HDPE as the backbone results in high carbon residue (5000 ppm) in the samples with 50 vol.% NdFeB powder loading, which indicates that employing LLDPE in this study is the reason lower carbon contamination was observed. On the other hand, the magnetic properties of remanence, coercivity, and maximum energy product were less for the specimens produced with feedstock C than those of feedstock B (Table 3) because feedstock C has a greater variability in the oxygen content after sintering than feedstock B. Meanwhile, feedstock A had the lowest magnetic properties because it had the highest oxygen content after sintering, even though it had low carbon content. These results corroborate that oxygen contamination is more critical than carbon contamination for achieving strong magnetic properties, as has already been mentioned in the literature [39]. In conclusion, and considering these results, careful adjustment of each component of the binder system can increase the densification rate, lower oxygen and carbon contamination, and increase the magnetic properties.