# Thermogravimetry Applicability in Compost and Composing Research: A Review
## 3 Results and Discussion
### Composting Evolution Research by Using a Variety of Techniques
#### 3.1.2 Composting Evolution Research by Thermogravimetry and Thermal Analysis  
Other authors have used thermogravimetric analyses combined with Differential Scanning Calorimetry (DSC) by which, in addition to changes in mass, endothermic or exothermic peaks --attributed to evaporations, transitions or reactions occurring in the samples-- can be shown. In this sense, endothermic peaks at <200 \({}^{\circ}\)C due to dehydration and between 600-700 \({}^{\circ}\)C attributed to thermal degradation of carbonates can be found [41]. On the other hand, two exothermic peaks at the range of 200-700 \({}^{\circ}\)C corresponding to the degradation of organic matter are also found in compost. The first exothermic peak (200-350 \({}^{\circ}\)C, part of phase II) corresponds to the combustion of carbohydrates such as cellulose and lignocellulosic and the second exothermic peak (350-700 \({}^{\circ}\)C, part of phase III) corresponds to the thermal degradation of more complex aromatic structures [42]. [PERSON] et al. [11], [PERSON] et al. [42], [PERSON] et al. [43]; [PERSON] et al. [44] and [PERSON] et al. [45] proposed the joint use of thermogravimetric analysis (TGA) and differential thermal analysis (DTA) as a technique to evaluate the grade of stabilization of composts. R1 (thermostability index) is the ratio between the weight losses associated with the second (200-350 \({}^{\circ}\)C) and third phase (350-700 \({}^{\circ}\)C) of compost thermal degradation. The relative amount of the thermally less stable organic fraction in relation to the one more stable is evaluated by this parameter. The justification for their use is that both the mineralization and, during the biological stabilization process, the conversion of organic components into humic substances and the energetic changes produced by the metabolic processes that take place during the compost maturation process are closely related. The authors mentioned above indicated that the R1 ratio should increase during composting. In this sense, [PERSON] et al. [38] demonstrated that the composting process, during the maturation phase, increases the degree of aromaticity in the resulting compounds and the results of the aromaticity index are in accordance with the thermal profiles obtained in the samples. [PERSON] et al. [46] showed, comparing the TGA curves of the compost samples, that an increase in mass that degrades above 700 \({}^{\circ}\)C occurs as the composting time increases. Moreover, [PERSON] and [PERSON] [47] showed that organic matter stabilization had been associated with an increase of water retention, and [PERSON] et al. [48] demonstrated that the parameter R1 with both humification index and degree of humification are significantly correlated during composting. The use of the TGA and the R1 parameter indicates the high sensitivity of this technique and parameter to changes induced by the composting process. However, [PERSON] et al. [49] concluded that it is necessary to test the observed trend with composts of different nature in order to analyze the relationship between thermal and biological stability. If this relationship can be found, DSC-TG thermal analysis could be taken into account among the usual methods in the characterization of composts. 3.1.3 Composting Evolution Research Studies by Combining Different Thermal and Analytical Techniques  
In addition, other authors' several combined techniques in compost characterization have been studied. In this sense, [PERSON] et al. [32], [PERSON] et al. [43] and [PERSON] et al. [50; 51] combined the traditional physicochemical parameters, Fourier transform infrared spectroscopy (FTIR), TGA and differential thermal analysis (DSC), to determine the maturity of lignocellulosic compost. The suitable correlation of these techniques in the thermal behavior of compost and its evolution (mainly by humic and fulvic acids evolution) has been demonstrated [44; 52]. Moreover, [PERSON] et al.