General characteristics of chemical and structural transformations of polyvinyl alcohol fibre in conditions of high-temperature treatment

Abstract

The role of phosphorus-nitrogen-containing pyrolytic additives in formation of polyunsaturated threedimensional structures in polyvinyl alcohol which stimulate coking in different stages of heat treatment is established. The possibility of obtaining unactivated carbon-fibre materials with high sorption activity from PVA fibre was demonstrated.Research on obtaining carbon-fibre materials with unique properties is one of the scientific directions in the Department of Chemical Fibre and Nanomaterials Technology at A. N. Kosygin Moscow State Textile University. This direction began with development of the theoretical principles of carbonization of polymer systems and creation of competitive domestic carbon fibres [1,2] under the direction of Professor Aleksandr Arsen'evich Konkin.The Department's research in this area was basically directed toward investigating the Thermochemical transformations of nontraditional precursors of carbon fibres (CF) and searching for ways of controlling pyrolytic processes to obtain carbon materials with a given structure.Of the nontraditional precursors, polyvinyl alcohol (PVA) fibres should be considered very promising based on the structure and tendency of the polymer to form structures with a high carbon content and the possibility of fabricating carbonfibre sorbents and an assortment of reinforcing CF based on PVA fibres from ultrahigh-molecular-weight polymer.As shown in [1-4], thermochemical transformations of certain classes of organic polymers are the basis of the technology for manufacturing carbon materials. The specific features and complexity of the technology for fabrication of fibre materials consist of conducting rigorously controlled pyrolysis of an organic polymer to remove heteroatoms from it and structural transformations of the polymer, including carbon.One effective direction in creating new technologies that enhance the process and change the structure and properties of carbon fibre materials is treating the precursors with organic or inorganic compounds that play the role of catalysts of pyrolysis and change the mechanism of the thermochemical transformations, which enhances carbonization and usually increases the yield of final product. Using pyrolytic additives again predetermines the necessity of formation of a spatially cross-linked polymer in the early stages of heat treatment to preserve the fibre form and consequently the status of the CF precursor for thermoplastic PVA fibres. In carbon-fibre sorbent production technology, the ability to form a pore structure in the carbonized fibres is another important function of pyrolytic additives.Phosphorus-nitrogen-containing compounds were basically used in studying the characteristics of thermochemical transformations of PVA fibres in conditions of heat treatment corresponding to production of CF, since they cause dehydration of the polymers and in many cases the properties of fireproofing compounds appear, which is very important for stimulating cross-linking and carbonization of hydroxyl-containing polymers. In ...