Methanolysis of Polycarbonate Waste as a Method of Regenerating Monomers for Polycarbonate Synthesis
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ADATION OF POLYMERS
Methanolysis of Polycarbonate Waste as a Method of Regenerating Monomers for Polycarbonate Synthesis A. Ya. Samuilova, M.V. Korshunova, and Ya. D. Samuilova,* a
Kazan National Research Technological University, Kazan, Tatarstan, 420015 Russia * e-mail: [email protected] Received October 23, 2019; revised January 10, 2020; accepted January 20, 2020
Abstract—The factors affecting the methanolysis of polycarbonates catalyzed by sodium methylate are studied. The conversion rate increases with an increase in the basic properties of solvents; the rate of methanolysis depending on the amount of solvent (tetrahydrofuran) is described by an extreme dependence. Changes in sodium methylate concentration and temperature have a small effect on the methanolysis of polycarbonates. DOI: 10.1134/S1560090420030136
INTRODUCTION The mass of polymer waste in the world currently reaches 300 million tons per year [1]. Among them, polycarbonate (PC) waste is of no small importance. World production of PC in 2016 reached almost 5 million tons [2], and its production volumes are increasing from year to year. PCs obtained on the basis of 2.2bis(4-hydroxyphenyl)propane (bisphenol A) pose a special danger to the environment [3], which is due to the high toxicity of bisphenol A [4, 5] formed during the hydrolysis of PC. Therefore, the processing of PC waste by the disposal method, which is still widely used in various countries for the recycling of polymer waste [6], is completely unacceptable. A number of other methods were proposed for the recycling of PC waste, namely, the mechanical processing [7–10] and noncatalytic [11–14] and catalytic pyrolysis [15, 16]. Mechanical methods for processing PC waste lead to a significant decrease in the physicomechanical properties of recycled polycarbonates. Pyrolytic methods give rise to a complex mixture of PC degradation products and are of little use for the processing of PC waste. The hydrolysis of PC based on bisphenol A should, in principle, produce bisphenol A and carbon dioxide. This approach is complicated by the fact that PCs are completely insoluble in water; therefore, the reactions must be carried out at elevated temperatures, when PCs are in the liquid state. Many reactions proceed more efficiently in water when it is in the supercritical state [17, 18]. Supercritical water was used to implement the hydrolysis of PC. The study of the hydrolysis of PC at 430°C showed that after 1 h a mixture consisting of p-isopropylphenol, p-isopropenylphenol, phenol, and bisphenol A is formed with a yield of 88.9% [19]. When studying the hydrolysis of PC in subcritical
water [20], it was found that at 300°C the product is a mixture of bisphenol A, phenol, n-tert-butylphenol, p-isopropenylphenol, 1,2,4,5-tetramethylbenzene, and 1,2,4-trimethyl-5-isopropylbenzene. The maximum yield of bisphenol A (40%) is achieved in 30 min. An increase in the duration and temperature of the reaction entails a sharp decrease in the yield of bisphenol A [20]. The data presented indicate that the hydro
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