## 3 Results and Discussion  
For the development of stable NLC formulations, the evaluation of the degree of crystallinity and polymorphism of the lipid matrices is instrumental to ensure that the matrix remains in the solid state at room temperature. Besides, it is possible to predict polymorphic changes and the degree of miscibility between the solid lipid and the liquid lipid during recrystallization [35; 44]. As for the NLC production, the methods usually require heating and the volatility of carvacrol compromises the success of its loading in the lipid matrices. TG analysis can be useful to determine the mass change after the tempering process. Figure 1 shows the mass change (%) of selected solid lipids (SA, BW and CW) and their respective binary mixtures containing 10, 25 and 50% of carvacrol, as a function of temperature. Figure 1: Thermogravimetric curves of the stearic acid (SA, upper left), beeswax (BW, upper right) and carnauba wax (CW, bottom) in comparison to their binary mixtures containing 10%, 25% and 50% of carvacrol (see Table 1 for composition). Two mass loss events were identified in the differential thermogravimetric (DTG) curve of stearic acid (SA, Figure 1), the first being within the temperature range of 161 and 306 \({}^{\circ}\)C (\(\Delta\)m\({}_{1}\) = 79.63% T\({}_{\text{peak}}\) DTG \(\sim\) 267 \({}^{\circ}\)C), which is typical of the SA decomposition, and the second within the range of 306 and 410 \({}^{\circ}\)C, attributed to the elimination of carbonaceous material [45; 46]. The TG curves of beeswax (Figure 1, upper right) and carmauba wax (Figure 1, bottom) depict only one mass loss event within the temperature range of 180-480 \({}^{\circ}\)C (\(\Delta\)m\({}_{1}\) = 99.5% T\({}_{\text{peak}}\) DTG \(\sim\) 396.7 \({}^{\circ}\)C) and 250-500 \({}^{\circ}\)C (\(\Delta\)m\({}_{1}\) = 98.5% T\({}_{\text{peak}}\) DTG \(\sim\) 426.1 \({}^{\circ}\)C), respectively. The analysis of the binary mixtures shows the detection of carvacrol during the progressive mass loss with the increasing concentration of the oil and over the course of the experiment. It was interesting to see that the first mass loss event observed for all samples was within the range of the percentage of carvacrol (10%, 25% and 50%) in each of the binary mixtures (Table 2). Despite the volatility of the monoterpene [47], the results shown in Figure 1 demonstrate that when mixing carvacrol with the three solid lipids in the selected ratios, no mass change was recorded within the range of temperatures below 100 \({}^{\circ}\)C. This result assures the possibility of producing NLCs for the loading of carvacrol, since the production methods do not make use of temperatures above 100 \({}^{\circ}\)C. Carvacrol is an oil at room temperature (melting point of 1 \({}^{\circ}\)C, boiling point of 237.7 \({}^{\circ}\)C). No chemical degradation of carvacrol is thus anticipated from the thermal stress during the production of the melted mixtures. DSC analysis provided information about the physical state of the melted lipids and their mixtures with carvacrol, degree of crystallinity, melting temperatures and respective enthalpies [48]. Figure 2 shows the DSC curves for the selected solid lipids (SA, BW and CW) and their binary mixtures containing 10%, 25% and 50% of carvacrol. As seen in Figure 2 (left panel), SA showed an endothermic event between 40 \({}^{\circ}\)C and 65 \({}^{\circ}\)C (with the T\({}_{\text{peak}}\)\(\sim\) 57 \({}^{\circ}\)C), which is related to the melting point of the solid lipid [45; 46]. The melting point of beeswax was recorded at T\({}_{\text{peak}}\)\(\sim\) 63 \({}^{\circ}\)C (middle panel) and that of carnauba wax was recorded at T\({}_{\text{peak}}\)\(\sim\) 82 \({}^{\circ}\)C (right panel). The adding of monoterpene to the bulk lipids resulted in a slight shift down to lower temperatures, i.e., from 57 \({}^{\circ}\)C down to 56.34 \({}^{\circ}\)C, 54.9 \({}^{\circ}\)C and 50.2 \({}^{\circ}\)C, for stearic acid with 10%, 25% and 50% of carvacrol, respectively (Figure 2, left).