## 3 Results and Discussion
### Carboxymethylcellulose Characterization
#### 3.1.2 Physical Characterization  
All CMC samples were characterized in terms of moisture content, purity degree, degree of substitution, and molar mass distribution, since these parameters may have an impact on the CMC biological properties. The data obtained are reported in Table 1.  
Regarding sample purity, the results obtained showed that all CMC samples were highly pure (ranging from 97.23 to 99.61%) with no statistically significant differences (\(p>0.05\)) being found between samples. The specification sheet of CMC2 reports the carbohydrate content of 93 \(\pm\) 3% and the results obtained come in line with this information as they showed it possessed a purity degree of 97.23 \(\pm\) 0.55%. Since no statistical differences (\(p>0.05\)) were obtained among the samples and taking into consideration that the specification sheet of CMC2 (the CMC sample which showed the lowest purity) indicates that it complies with the regulation for purity requirements according to the commission directive 96/77/EC, BGBIL.S.230 and BGBIL.S.2082 standards, and FAO 1992, it was considered that all CMCs can be used for cosmetic, food, or pharmaceutical applications. In terms of moisture content, no statistical differences (\(p>0.05\)) were found between CMC3 and CMC4  
Figure 2: Structural characterization of CMC samples by (**a**) scanning electron microscopy, (**b**) Fourier-Transform Infrared Spectrometry, and (**c**) powder X-ray diffraction analysis. (5.09 and 5.97% respectively). On the other hand, CMC1 exhibited a statistically significantly lower (\(p<0.05\)) moisture content (3.67%) and CMC2 a significantly higher (\(p<0.05\)) moisture content (11.74%). The higher moisture content observed for CMC2 can be associated with the statistically higher (\(p<0.05\)) \(M_{w}\) of this sample (i.e., 471.7 kDa) (Table 1) and the largest aggregates observed (Figure 1), which can bind more water molecules. It has been described as a proportional relationship between water absorption and \(M_{w}\) for cellulose derivative samples [28]. Another factor that can also contribute to the moisture protection is the crystallinity of CMC samples (Figure 2c), as materials with a higher crystalline state will typically have less water vapor sorption than the amorphous state, due to the reduction in free energy, void space, and/or surface area [29]. In this case, it was not possible to establish a clear relationship between the crystallinity degree and the moisture content of CMCs, and thus the \(M_{w}\) factor appeared to have a higher impact on the CMC water absorption. These factors may also explain why CMC2 presented the largest particle aggregates in SEM imaging (Figure 2a). The product data sheets of samples CMC 1-2 reported a maximum moisture content of 10%, which was not experimentally verified, thus leading to a non-conformity, while the information available for CMC 3 reported a maximum of 8%. In the case of CMC4, we found a lack of information regarding this parameter. In the specific case of CMC1 and CMC3, it was possible to assess the certificates of analysis, where the values of moisture content of 2.9 and 6.3% were described, respectively. These values are in the line with those experimentally determined here, and thus in conformity with the maximum values defined. This parameter provides information about the water affinity of a material or its capacity to absorb water during powder processing and storage and thus is an important parameter to have in consideration since it significantly impacts the product's long-term stability and performance (e.g., compressibility, flowability, cohesion, caking, and density) [29]. The DS constitutes a pivotal property of CMC because it not only influences its solubility but also the solution characteristics, thus directly affecting the CMC physicochemical properties. By definition, DS is the average number of carboxymethyl groups per anhydroglucose unit.