Effect of high-temperature treatment on thermochemical transformations of oxidized polyvinyl alcohol fibres

Abstract

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...

Synthesis of sorption-active polyfunctional derivatives of polycaproamide and polyglycidyl methacrylate graft copolymers

“…The formation of a new derivative of the PCA-PGMA graft copolymer containing functionally active amino and sulfo acid groups was confirmed by the data from chemical and analytical analysis and IR spectroscopy. A method was developed for obtaining a sorption-active fibrous polyampholyte containing functionally active amino and sulfo acid groups with SEC HCl = SEC NaOH = 0.895 mmole/g.The wide use of sorption processes, including use of chemisorption fibres characterized by high sorption rates and preservation of the strength properties in repeated regeneration, is one direction in comprehensively solving environmental problems [1][2][3][4].The characteristics of synthesis of polycaproamide copolymer derivatives with sulfamic acid, whose functional groups are capable of donor-acceptor and ion-exchange reactions with heavy metal ions, were investigated here to obtain fibrous polyampholytes of new composite composition.Selection of the method of obtaining polyfunctional compounds based on graft polymerization of nonionogenic monomers followed by polymer-analog conversion of the graft chains was predetermined by its high processability among existing processes [2]. We investigated polycaproamide fibre modified by grafting polyglycidyl methacrylate, the graft copolymer of polycaproamide and polyglycidyl methacrylate (PCA-PGMA) in the ratio of 56:44.…”

“…The wide use of sorption processes, including use of chemisorption fibres characterized by high sorption rates and preservation of the strength properties in repeated regeneration, is one direction in comprehensively solving environmental problems [1][2][3][4].…”