Cellulose, a major component of organic matter present in low and intermediate level radioactive wastes undergoes degradation through both hydrolytic and radiolytic processes under both storage and disposal conditions. In the highly alkaline cementitious environment of a disposal system, hydrolytic degradation of cellulose will lead to the formation of many soluble degradation products, with the two diastereomeric forms of isosaccharinic acid (ISA), namely alpha ISA and beta ISA, as the main compounds. Especially the alpha form is well known for its complexing effect with radionuclides, which may facilitate their migration from the waste to the biosphere. The present study aims to identify degradation products formed in cellulosic tissues when subjected to alkaline degradation following irradiation. Such tissues represent a real case study since this type of tissues have been widely used in the nuclear facilities. The identification of the degradation products was performed using Electrospray ionisation time-of-flight mass spectrometry (ESI-ToF MS) technique. Given the acidic nature of these degradation products, negative ionization mode and a 0.1% formic acid solvent were used for the analysis. The analyses of the solutions from long-term degradation experiments were optimised using pure degradation products known from literature. This served as a basis for developing a methodology for the interpretation of the complex spectra of degraded solutions of cellulose. In addition to the expected deprotonated ion form, various aspects originated from the analyses of the pure compounds, such as occurrence of adduct formation with formic acid and presence of oligomers. These aspects were considered while interpreting the complex spectra of the solutions of degraded cellulose. Furthermore, the choice of solvent played a key role, particularly in the identification of low molecular weight organic pure compounds, which posed a challenge. These molecular weight organic compounds were difficult to detect, and another method may be needed. The MS spectra of the solutions from degradation studies are complex and therefore difficult to interpret. However, the current interpretation suggests that hydrolytic degradation of cellulosic tissues under alkaline conditions primarily leads to the formation of ISA. The intensity of the m/z peak corresponding to the deprotonated molecule of ISA together with the m/z peak presumably linked to its lactone form, varied depending on the test conditions, i.e., their intensity increased with absorbed dose during pre-irradiation and with hydrolysis time. Another peak consisting to the presence of one 13C in the deprotonated molecule of ISA was observed in all the spectra accompanying the ISA peak. Additional peaks observed in the ESI MS spectra suggested the presence of xyloisosaccharinic acid (XISA), lactic acid as well as low-intensity peaks of unidentified compounds. The origin of the latter needs further investigation. ESI-ToF MS proved to be a promising semi-qualitative analytical technique for the identification of cellulose degradation products. However, further investigations are required to confirm the identified compounds and to have an understanding of the molecular mass or unidentified compounds. Combining ESI-ToF MS with complementary techniques would enhance the characterization of the unknown degradation products. The presence of additional products with potentially strong complexing properties highlights the need for further investigation of cellulose degradation products. In conclusion, this study provides a valuable insight into the degradation products formed in tissues undergoing radiolytic and hydrolytic degradation at alkaline pH. Further research is necessary to fully understand the nature and properties of these degradation products, and the integration of multiple analytical techniques would facilitate their comprehensive identification and characterization.
|Qualification||Master of Science|
|Date of Award||3 Jul 2023|
|State||Published - 3 Jul 2023|