The effect of topochemistry on polymer-analog transformations of graft copolymers of polycaproamide, hydrated cellulose, and polyvinyl alcohol with polyglycidyl methacrylate under the effect of different amines was established. The amine-containing sorption-active fibres exhibit high activity with respect to heavy metals and platinum-group metals.Chemisorbents, in particular, sorption-active fibres, play an important role in solving environmental problems (treatment of gas--air emissions and wastewaters from industrial enterprises, separation and concentration of valuable metals) and problems in occupational safety (creation of devices for protecting the respiratory organs) [1][2][3]. These fibres are a promising alternative to granulated ion-exchange resins due to the developed specific surface.The Chemical Fibre Technology Department at Moscow State Textile University has developed a large group of sorption-active fibres of different composite and chellfical composition based on graft copolymers [4, 5] using ionogenic monomers and polymer-analog transformations of highly reactive o~-oxide groups of graft polyglycidyl methacrylate (PGM) in amination and sulfonation reactions (Scheme 1).An efficient graft polymerization process has not yet been developed due to the specific features of polymerization of ionized monomers. For this reason, the method based on graft polymerization of nonionogenic monomers and chemical transformations of the graft polymer is preferred in industry. The method of initiation utilizing the CUk--H202 redox system proposed for these purposes, which allows fixing the copper complex in the fibre and subsequently formation ofa macroradical, makes it possible to synthesize graft copolymers of the fibre-forming polymers listed above with PGMA with a degree of conversion of 95-97% and without formation of homopolymer; this makes this stage of production of chemisorption fibres highly efficient.In studying the characteristics of graft polymerization, a topochemical effect was found. According to electron microscopic data, the layer of graft polymer almost does not touch the central part ofpolycaproamide (PCA) fibre even for an almost 100% PGMA content in the fibre, while in grafting of GMA to hydrated cellulose (HC) fibre, the graft polymer is distributed over the entire section, as indicated by the absence of a cavity in the fibre after etching. This distribution of the graft polymer affects both the occurrence of the reactions of chemical transformations of PGMA and the sorption activity of the fibre chemisorbents obtained.We used a large group of nitrogen-and sulfur-containing compounds for incorporation of sorption-active groups. The systematic studies of the chemical transformations of graft PGMA in different polymer matrices and under the effect of a broad spectrum of nitrogen-and sulfur-containing compounds were directed toward revealing the characteristics of this process and formulating fundamental scientific premises which would allow more successfully solving practical problems in cre...

Scientific concepts concerning the characteristics of graft polymerization to oriented polymeric materials and p~lymer-anal~g transf~rmati~ns ~f the graft p~lymer were elab~rated based ~n systematic studies. The principles of fabrication of sorption-active fibre materials Of different ~,pes based on graft copolymers and the most important directions of their use were formulated.The consequences of human technological activity has sharply worsened the environmental situation, making environmental protection an urgent modern problem. One direction in the complex solution of these problems is to develop highly efficient processes for scrubbing of industrial gas-air emissions and cleaning ofwastewaters. Sorption materials, used to prevent further environmental pollution and ensure rational resource management, are playing an important role in the creation of such processes.These materials include chemisorption fibres with a developed specific surface area which is more than one order of magnitude greater than the surface area of granulated sorbents. A comparison of the geometric surface area of fbres and granules gives an idea of the advantage of fibre sorbents over granulated sorbents, manifested by a higher rate of chemisorpticn and greater completeness of removal. In addition, the variety of forms of use of fibre sorbents favors the rational organization of technological processes.The analysis of the scientific and technical literature on fabrication of chemisorption fibres revealed the following methods:-spinning of fbres from blends of fibre-forming polymers with nonfibre-forming polymers containing ionogenic groups;-synthesis of fibre-forming copolymers containing functionally active groups and fabrication of fibres from them; -incorporation of functionally active groups in the fibre via reactions in the polymer chains; -modification of fibres by graft polymerization of ionogenic and nonionogenic monomers with subsequent polymeranalog transformations of the graft chains.Spinning of chemisorption fibres from polymer blends is a relatively simple method. However, the difficulties of obtaining stable spinning solutions from blends of fibre-forming and nonfibre-forming polymers and the possibility of washing out the sorption-active component of the fibre make it necessary to conduct an additional operation of formation of a threedimensional spatial network in the fibre [1,2]. Moreover, this method can be used together with other variants for production of sorption-active materials.The method of spinning fibre chemisorbents from copolymers with chemically active groups in the main chain has been widely used in fabrication of chemisorption fibres of the VION group [3,4]. In this case, acrylonitrile is usually usedas the fibre-forming component, and the composition of the ionogenic comonomers responsible for incorporation of sorptionactive groups in the structure of the fibre is relatively varied. This concerns methylvinylpyridine (MVP), vinylimidazole, sodium p-styrenesulfonate, and others [3,[5][6][7][8]. The fibres...

A. V. Tolkachev, T. V. Druzhinina, and L. A. Nazar'ina UDC 677.494.745.32.021.125.56 The thermal properties of polyvinyl alcohol in the presence of phosphorous-containing and other inorganic compounds were investigated. The catalytic role of a phosphorus-containing fireproofing compounddiammonium phosphate --in thermooxidative decomposition of PVA was revealed. It was found that dehydration of PVA is intensified, the activation energy of decomposition of PVA increases, and its cokeforming power also increases in the presence of (NH4)2HPO 4.

Carbon fibre materials (CFM) for sorption applications are increasingly widely used in different areas, making it necessary to expand the assortment of carbon fibres [1][2][3]. For this reason, and also because file group of carbomzable fibreforming polymers is small, the use of nontraditional raw materials and determination of the correlation between the conditions of high-temperature treatment and the properties of the materials is of great interest for fabrication of carbon fibres. The effect of high-temperature treatment of polyvinyl alcohol (PVA) fibres in nonoxidizing medium on the composition and properties of CFM fabricated from them are examined in the present article.Since PVA fibre is a thermoplastic polymer material, converting it to the nonmelting state is a necessary condition for fabrication of CFM. This can be done by thermooxidation of the fibre in the presence of compounds that intensify dehydration and cross-linking of the macromolecules of the polymer. We used diammonium phosphate (DAP), whose efficacy in dehydration and cross-linking of PVA fibres is relatively high, as such a compound [4, 5]. Thermooxidation was conducted in air medium at 200~ for 16 h [5].Thermooxidized samples of PVA fibres were treated with heat in the 500-900~ range in nitrogen medium with a temperature elevation rate of 3~ and subsequent holding of the samples at the given temperature for 30 min. Selection of the temperature was dictated by the boundaries at which the basic physicochemical processes of formation of the carbon structure evolve. A number of methods (thermogravimetric, elemental, chemical) were used to characterize the thennochemical transformations of PVA fibres containing DAP during high-temperature treatment. The effect of the treatlnent temperature on the yield of carbonized product, the change in the concentration of double bonds, the elemental composition, and sorption of iodine was investigated.High-temperature treatment is associated with an important change in the elemental composition of the polymer. Elemental analysis of the products of carbonization (Table 1) indicates enrichment of PVA fibres with carbon (its concentration increased from 64.6 to 96%) and a decrease in the concentration of hydrogen (from 3.8 to 0.4%) and oxygen (from 30 to 1.5%). The concentration of carbon in CFM increased by approximately 6% when the temperature was increased from 500 to 900~ The ratio of the concentration of hydrogen to the concentration of carbon is the most important index of the composition of the products of heat treatment of the polymer. As the data m Fig. 1 show, when the temperature was increased from 500 to 900~ the H:C ratio decreased by 6 times.In heat treatment in the 600-700~ region, the elemental composition of the carbonized fibres is almost identical despite the 100~ difference in temperatures. A similar picture is also characteristic of the 800-900~ temperature region.In the temperature range investigated, the most important changes in the elemental composition of carbonized PVA fibres thus t...

No abstract

The oxidation temperature-time regime that results in carbon fibre materials (CFM) The study of deep thermal transformations of polymer fibres is of both scientific and practical interest. From a scientific point of view, despite the publication of a number of generalizing studies [1][2][3], it must be acknowledged that some characteristics of the processes that take place in thermolysis of polymers have not yet been sufficiently investigated. Such characteristics in particular include the features of the effect of inorganic additives on thermal transformations of the polymer. From a practical point of view, fabrication of carbon fibres (CF) with interesting new properties can in this way be hypothesized [4].Thermal oxidation of polyvinyl alcohol (PVA) fibres in the presence of inorganic salts --mono-and diammonium phosphate -is examined in the present article. Loss of thermoplasficity by the fibre, the yield of CF in carbonization, and the elasticity of the carbon fibre materials (CFM) obtained were the criteria in selecting the parameters of the oxidation process, i.e., the temperature and duration which ensure the most complete occurrence of dehydration and cross-linking of the polymer.The phosphorus-containing compounds were applied on the fibre by impregnation with 2-5 % aqueous solutions of the salts with subsequent wringing out of the fibre in a padding machine to a 100% degree of wringing. After wringing, the fibre was dried in air at room temperature for 24 h. Thermooxidation was conducted while heating from 20"C to the selected temperature at a temperature elevation rate of 2*C/rain and subsequent holding for the def'med time. Before thermooxidation, the fibre samples were dried at 110-115~ for 4-5 h to eliminate the possibility of destructive oxidative processes under the effect of moisture.Carbonization was conducted on a laboratory setup in a nitrogen current with a rate of heating from 20 to 450~ of 3~ and from 450 to 900~ at the rate of 10*C/rain. The holding time at 900"C was 30 rain. The thermal properties of the oxidized fibres were investigated by differential thermal (DTA) and thermogravimetric (TGA) analysis while heating the sample in air medium and the characteristic products of decomposition at a temperature elevation rate of 10*C/min on a Paulik-Paulik-Erdey derivatograph and by elemental analysis on an EA 1108 CHNS-0 instrument from Carlo Erba Instruments.The IR spectra were made on a Specord M 80 Carl Zeiss Jena spectrophotometer in the 200-4000 era-1 spectral range. The concentration of double bonds in the polymer was determined by the chemical method based on the "bromine number."As indicated in [3], PVA fibres are oxidized beginning at a temperature of --180"C. The data in Fig. 1 show that in the presence of phosphorus-containing compounds, significant weight loss of the polymer begins at 170"C and becomes more intense when the temperature is increased to 200"C. A comparison of curves 2 and 3 indicates that diammonium phosphate is a more effective agent in this case, since it cause...

No abstract

No abstract