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Fate of Plastics and Their Additives in Alkaline Solution at Different Temperatures

Abstract : In France, storage in a deep geological layer is conceivable as the final destination for radioactive wastes of long live intermediate-level activity (ILW) (Andra, 2005). In this context, the organic wastes should be in contact with infiltrated water, which is become highly alkaline in contact with cement (pH≃13; Berner, 1992) and they can release new hydrophilic organic products (Glaus et al., 1999 ; Colombani et al., 2009). These produced molecules can play major roles in the complexation of radionuclides present in the disposal packages (Wieland et al., 2012), and can therefore facilitate their migration in the environment. Among these organic wastes, degradation of some products like cellulosic compounds were well studied in the literature (van Loon and Glaus, 1997; Glaus et al., 1999). However, the fate of some polymers, like “plastics” under alkaline conditions are less documented. PVC (polyvinyl chloride) and PE (Polyethylene) are present in these packages. Specific adjuvants are added to the formulation, in order to obtain specific PVC and PE properties. The study of the degradation of these plastic polymers and their adjuvants is an important prerequisite in monitoring the diagenetic evolution of these organic compounds and the molecules resulting from their degradation as well as their possible behaviour in radioactive waste storage. The objective of this work is to identify the molecular behaviour of plastic polymers and their additives against alkaline degradation under different temperatures. Three types of PVC (PVC1, PVC2 and PVC3) and one PE with varying additive concentrations have been studied. Soft PVC formulations were previously well investigated in the literature (Colombani et al. 2009 and references there in). We focused therefore our study on hard PVC formulations. Alkaline degradation experiments were performed at different temperatures (22°C and 90°C) under aerobic and anaerobic conditions. The leaching solution has a pH = 13 and it is prepared from NaOH 10-1 M. The experiments with pure PVC and PE (without additives) were realized under the same conditions in order to compare their respective behavior. Triplicate experiments were carried out in glass vessels equipped with silicon septum. After 1 day, 15 days, 1 month, 3 months and 6 and 12 months of reactions, gases were sampled, the liquid and solid fraction were separated. Eh and pH were directly measured in the reacting solutions. Determination of the organic products released in the liquid fraction by alkaline hydrolysis and their quantification are carried out by measuring the Total Organic Carbon (TOC) by gas chromatography coupled with mass spectrometry (GC / MS) and ion chromatography. Gases were analyzed by gas chromatography. Solid residues were analyzed by infrared spectrometry. And their dichloromethane extracts were derivatized and analyzed by GC/MS. Analyses of the initial products (PVS and PE) reveal the presence of additives. With respect to previous studies on PVC (Colombani et al., 2009), the different nature of the material (hard instead of soft) implies modifications in the nature and the proportion of the additives. In our case, we note a depletion in the proportion of phthalates (Diethylhexyl Phthalate, Diisononyl Phthalate, Dioctyl Terephthalate …). On the other hand, we detected the presence of n-C14 to n-C40 alkane chains. Such molecules are specific from hard PVC and are used as lubricant in the production process. In the room temperature experiments the evolution of the dissolved organic fraction after one year duration is very limited. The gas production do not display significant evolution and the organic dissolved fraction remains below the quantification limits. On the other hand, concentrations in organic carbon measured from the leaching experiments at 90°C display a gradual increase over time. This increase is consistent with the evolution of the gas concentrations. For the experiments carried out on PVC1, an increase in the concentration of organic carbon is observed after one month at 90°C in contact with an alkaline solution. Under these same conditions, the PE showed an increase in hydrogen and a decrease in oxygen. A kinetic rate could be retrieved from the experiment analyses, which essentially represents the gradual release of the additives from the main solid fraction. This work presents preliminary results concerning the release of organic ligands from plastics under alkaline hydrolysis, activated by temperature. In a further step, those results will be compared with similar experiments performed under γ radiation in order to assess radiation influence over the organic ligand release rates. References: Andra, Evaluation de la faisabilité du stockage géologique en formation argileuse, dossier 2005 Argile. 2005. Berner, U.R., 1992. Evolution of pore water chemistry during degradation of cement in a radioactive waste repository environment, Waste Management, 12, pp. 201-219. Colombani, J., Herbette, G., Rossi, C., Joussot‐Dubien, C., Labed, V., Gilardi, T., 2009. Leaching of plasticized PVC: effect of irradiation. Journal of applied polymer science, 112, pp. 1372-1377. Glaus, M.A., van Loon, L.R., Achatz, S., Adcura, A., Fisher K., 1999. Degradation of cellulosic materials under the alkaline conditions of a cementitious repository for low and intermediate level radioactive waste part I: Identification of degradation products. Analytica Chimica Acta, 398, pp. 111–122. Van Loon, L.R., Glaus, M.A., 1997. Review of the kinetics of alkaline degradation of cellulose in view of its relevance for safety assessment of radioactive waste repositories. Journal of Environmental Polymer Degradation 5, pp. 97-109. Wieland, E., Tits, J., Dobler, J.P., et Spieler, P., 2002. The effect of α-isosaccharinic acid on the stability of and Th(IV) uptake by hardened cement paste.Radiochimica Acta. 90. pp. 683-688.
Keywords : GEOF Degradation PVC
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Submitted on : Monday, January 24, 2022 - 3:44:10 PM
Last modification on : Wednesday, August 3, 2022 - 4:05:54 AM

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Hela Ben Zeineb, Claude Le Milbeau, Philippe Blanc, Patrick Ollivier, Laurent André, et al.. Fate of Plastics and Their Additives in Alkaline Solution at Different Temperatures. 30th International Meeting on Organic Geochemistry (IMOG 2021), Sep 2021, Online, France. pp.1-2, ⟨10.3997/2214-4609.202134198⟩. ⟨insu-03541375⟩

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