Reaction of products of thermal and thermal oxidative degradation of polyvinyl chloride with barium hydroxide

Abstract

The reaction of products of thermal and thermal oxidative degradation of polyvinyl chloride with barium hydroxide was studied. The degree of binding of chlorine and carbon atoms from polyvinyl chloride in reactions of barium hydroxide with hydrogen chloride and carbon dioxide formed by degradation and oxidation of the polymer was studied in relation to the hydroxide/polymer weight ratio and temperature. The activation energies of the reaction and the specifi c rates of formation of barium chloride and carbonate were calculated.Utilization of polymer wastes, of which materials based on polyvinyl chloride (PVC) make a signifi cant fraction, involves certain problems, because in the course of the commonly used incineration polyvinyl chloride releases toxic compounds, in particular, extremely hazardous dioxins. There are two ways to reduce the amount of chlorine released in PVC incineration. The fi rst way is a decrease in the chlorine content in PVC formulations. To this end, PVC should be used as a blend with other, chlorine-free components or as a copolymer with halogen-free monomers [1]. The second way is the use of relatively small amount of fi llers that can effi ciently take up HCl in the course of PVC degradation or incineration. As reported in a patent [2], lithium-containing compounds (LiOH and Li 2 CO 3 ) are more effi cient than CaCO 3 in binding of the released HCl. However, LiOH is hygroscopic and is a strong base, which complicates its use as PVC fi ller. Li 2 CO 3 , on the contrary, is fairly stable in air, which allows its use in large amounts. Other patents describe procedures for reprocessing halogenated compounds, including solid polymeric materials containing halogens, by fi nely dividing them, mixing with calcium, magnesium, and barium oxides or hydroxides, and heating these mixtures with the formation of the corresponding halides and carbonates [3,4].This study deals with the reaction of polyvinyl chloride degradation products with barium hydroxide. Our goals were to determine the product composition and the kinetic parameters of the reactions occurring in the process and to elucidate the effect of various factors on the completeness of binding of chlorine and carbon from the polymer into environmentally safe products (ВаCl 2 , BaCO 3 ). EXPERIMENTALIn our study we used E-6250Zh emulsion PVC powder and barium hydroxide Ва(ОН) 2 ·8Н 2 О, which was thoroughly dehydrated at 120-150°C before each experiment. Because Ва(ОН) 2 absorbs СО 2 from air to form barium carbonate, in calculation of the degree of PVC carbon binding into ВаСО 3 we took into account the carbonate percentage in barium hydroxide [ω(ВаСО 3 ) = 11%]. The reaction kinetics was studied under isothermal conditions. A mixture of the polymer and hydroxide in a defi nite weight ratio was placed in a crucible heated to a preset temperature. The samples were prepared by thorough mixing of a suspension of the components in acetone in an agate mortar. The furnace with the quartz crucible placed in it was brought to a constant temperature. T...