# Stability Study of Erythrhitol as Phase Change Material for Medium Temperature Thermal Applications
## 3 Results and Discussion  
### Mass Loss  
The measured time-dependent mass loss percentages were fitted in a linear regression based on the least squares method. Mass loss rates were represented as the slope of the linear regression, while the uncertainty of each rate was described as the standard error of the given slope. Figure 2a shows the results of all tests.  
Figure 2: (**a**) Percentage of mass loss per hour at 121 \({}^{\circ}\)C, 131 \({}^{\circ}\)C and 141 \({}^{\circ}\)C for short-term tests. (**b**) Percentage of mass loss at 141 \({}^{\circ}\)C for long-term test.  
Samples of pure erythroid under air registered the highest mass loss rates along the short-term heating treatment: 0.0063 \(\pm\) 0.0008%/h, 0.0082 \(\pm\) 0.0007%/h and 0.0136 \(\pm\) 0.0014%/h at 121 \({}^{\circ}\)C, 131 \({}^{\circ}\)C and 141 \({}^{\circ}\)C, respectively. An upward trend in the percentage of mass decrease regarding heating temperature for both groups of short-term tests under air was registered. The use of antioxidant helped to diminish the temperature effect on the mass content loss of samples under air as seen in Figure 2a. When heated at 141 \({}^{\circ}\)C and after 935 h (long-term test) erythroid with antioxidant under air lost nearly 5% of its mass. However, it seems that the antioxidant was consumed during the first 600 h, since after 597 h its mass loss rate tripled the initial one, as shown in Figure 2b.  
Regarding samples under argon atmosphere, a mass loss rate increase was also recorded. Temperature, however, had a lighter impact on these results in comparison with the registered values of the samples under air. In addition, adding antioxidant did not have a major impact on the samples under Argon. Vials were weighed before and after filling them with argon, as well as after the heating procedure. As a result of the argon purge, vials were not completely sealed anymore due to the use of cannulas on the lids. Thus, by the end of the experiment it was not possible to assure that the registered mass loss was related only to the sample itself and not to a loss of argon during the heating treatment.  
Erythritol mass loss could be associated to oxidation and dehydration reactions. During oxidation, several fragmentation products can be formed (see Section 3.4). Fragmentation produces low molecular weight products with high vapor pressures. Fragmentation products may then evaporate, increasing the mass loss rate. In addition, dehydration of erythroid yields 1,4-erythritane, which can be further dehydrated to form carbonyl compounds also affecting the mass loss ratio. Samples of pure erythroid were more susceptible to oxidization due to the higher oxygen availability in comparison to samples with antioxidants or argon. Dehydration reactions may also have followed. Therefore, mass loss rates of pure erythroid at the three tested temperatures were also the highest. On the other hand, mass loss of both types of samples under argon is more likely related to dehydration reactions of erythroid. [PERSON] et al. (2015) claimed that the degradation of erythroid depends on oxygen concentration. In addition, as it is known, increasing the temperature at which a reaction takes place generally speeds up the rate of reaction. These last two statements can also be confirmed in Figure 2a.