# Stability Study of Erythrhitol as Phase Change Material for Medium Temperature Thermal Applications
## 3 Results and Discussion
### Chemical Degradation
Sample browning was also not observed in erythroid-antioxidant under argon and all samples solidified at room temperature. Unlike pure erythroid, all erythtritol-antioxidant samples under air solidified at room temperature. [PERSON] et al. [40] reported that Irganox 1098, a hindered phenolic antioxidant, acted as a nucleating agent in a thermoplastic vulcanizate blend. [PERSON] et al. [41] claimed that in hindered phenols with a symmetrical structure the formation of hydrogen bonds is high, which leads to agglomeration and crystallization of the system where it is used. Since Irganox 1010 has a high symmetric molecular structure, it may have promoted the crystallization of erythroid. However, further investigation to confirm this latter point is advised. Figure 7: Samples of pure erythroid under air for short term at (from left to right) 121 \({}^{\circ}\)C, 131 \({}^{\circ}\)C and 141 \({}^{\circ}\)C.  
It is assumed that erythroid may undergo oxidation and dehydration reactions. In the presence of air and according to the proposed mechanism of oxidation of erythroid based in reactions already reported in the literature [42; 43; 44; 45], hydrogen abstraction either from the carbon chain (Pathway A) or from a hydroxyl group (Pathway B) could take place. Pathway A leads to the formation of carbonyl groups by adding oxygenated functional groups to the carbon chain. In pathway B the resulting alkoxy radicals are decomposed via C-C bond scission, generating fragmentation products, as shown in Figure 9. The former case increases vapor pressure by approximately 1 order of magnitude, while the latter may increase volatility by a much larger degree by reducing the carbon number of the product molecules [42]. Irganox 1010 is a primary antioxidant, known as a h-donor and as radical scavenger. In accordance with the mechanism of oxidation of erythroid under air, two different alkyl radicals (R\(\bullet\)) can be formed in pathway A, which in turn react with molecular oxygen to produce their corresponding peroxy radicals (ROO\(\bullet\)). As mentioned before, oxidation of pathway B also produces alkoxy radicals (RO\(\bullet\)). Primary antioxidants terminate oxidation by scavenging R\(\bullet\), ROO\(\bullet\) and RO\(\bullet\) radicals. In oxygen-rich conditions alkyl radicals react too fast with molecular oxygen and hence their lifetime is shortened enormously, which makes that alkyl radical scavenging become less important [46]. Irganox 1010 (ArOH) converts peroxy and alkoxy radical into inactive products and phenoxy radicals (ArO\(\bullet\)). Phenoxy radicals are less reactive; however, they still can react with other ROO\(\bullet\)/RO\(\bullet\) yielding non-radical products (ROO/ROArO). These non-radical products can rearrange once to regenerate the phenolic antioxidant group, allowing further radicals to be scavenged [46; 47]. However, once the antioxidant is fully consumed erythroid will begin to degrade as in the case of the long-term test under air. Figure 8: DSC (**a**) cooling and (**b**) heating scans of pure erythroid samples as received (iii), after 50 h (ii) and after 78 h (i) at 141 \({}^{\circ}\)C.  
It has been reported that erythroid, as polyol, undergoes neither Maillard browning nor caramelization [48; 49; 50]. Even though some authors have suggested that the browning of sugar alcohols (D-mannitol) may be related to caramelization reactions [37; 51], they have not detected sugar caramelization products, such as hydroximethyl furfural (HMF) and hydroxacetylfuran (HAF), but \(\alpha\), \(\beta\)-unsaturated carbonyl groups. However, these latter compounds may also be produced during dehydration reactions of polyols. Conjugated ketones, also known as enones, are a type of \(\alpha\), \(\beta\)-unsaturated carbonyl, which are found to be responsible for the color change in various systems. Conjugated ketones may have contributed to the brown coloration of a commercial pentaerythitol tetraester oil [52].