Modified Polyacrylonitrile Fiber Research Articles

Modification of polyacrylonitrile fibres to improve the properties of carbon fibres prepared from them

-- It has been found that treatment of acrylonitrile fibres obtained by the wet dimethyl formamide method before thermal oxidation with inorganic salts considerably changes the properties of the thermally oxidized fibres. -- On treatment of the fibres with an aqueous solution containing copper ion in a reducing medium, their sorptive powers are considerably impaired, the fibre diameter is increased, and the electrical conductivity is increased, plus processes of cyclization and oxidation are accelerated. -- On treatment with a solution of aluminum chloride in the presence of orthophosphoric acid, the fibre structure is made denser and its strength is increased. -- Sodium thiosulfate as a modifier considerably changes the functional composition of polyacrylonitrile fibres; thereupon, a process of structural amorphization takes place.

Preparation of high-performance carbon fibres from PAN fibres modified with cobaltous chloride

Preparations of high-performance carbon fibres have been tested and the results are reported in this article. Polyacrylonitrile (PAN) fibres modified with cobaltous chloride have increased the crystal size, the crystallinity and the orientation, and also improved the tensile strength by about 15–40% and the modulus by about 10–20% of the resulting carbon fibres, which were carbonized at 1300 °C. The oxygen content, theAI value and the density for the modified PAN fibres are smaller than those for unmodified PAN fibres. Because the formation of the ladder polymer in the modified PAN fibres is slow and gradual during the stabilization process, the resulting carbon fibres have a better modulus than carbon fibres developed from unmodified PAN fibres. The activation energy of cyclization,E a, is increased to 180.0 from 156.6 kJ mol−1 after the modification process. The modified PAN fibres do not reduce the time required for stabilization. The carbon fibres developed from the modified PAN fibres have a greater stacking size,L c, than those developed from unmodified PAN fibres. A higher stacking size, and therefore a higher number of crystalline carbon basal planes, is one of the reasons for the improved modulus of the carbon fibres.

Modification of the surface of polyacrylonitrile fibres before oxidation with a dispersion of technical carbon

-- The possibility of using dispersions of technical carbon in a medium of ethylene glycol, an aqueous solution of a binder of the “Sokrat-binder” type, or an alcoholic solution of polyvinyl butyral for the modification of polyacrylonitrile fibres before thermo-oxidation, which ensure obtaining a stable and uniform carbon-containing film on the fibre surface has been established.

Preparation of graphite fibres from a modified PAN precursor

Graphite fibres were developed from polyacrylonitrile (PAN) fibres modified with potassium permanganate. To our knowledge, this is the first time that the effect of modification on the physical properties, microstructure, elemental composition, electrical resistivity, and mechanical properties of fibres has been examined during the graphitization process. The graphite fibres developed from modified PAN fibres had a higher density, a greater stacking size,Lc, and a higher preferred orientation than those developed from unmodified PAN fibres. The graphite fibres also showed an improvement of 20%–40% in electrical resistivity and modulus.

The influence of pyrolysis on physical properties and microstructure of modified PAN fibers during carbonization

AbstractModification of polyacrylonitrile (PAN) fibers with potassium permanganate has reduced the time required for stabilization and also improved the mechanical properties of the resulting carbon fibers. In this study, the effect of modification on the physical properties, microstructure, and elemental composition of fibers during the carbonization process was examined for the first time. The resulting carbon fibers developed from modified PAN fibers had a higher density, a greater stacking size (Lc), and a higher preferred orientation than those developed from unmodified PAN fibers. The carbon fibers developed from the modified PAN fibers also showed an improvement in tensile strength from 20 to 40%. These fibers showed a radial structure in the fracture surface and were somewhat different structurally in the cross section than were the carbon fibers developed from the original PAN fibers. A model for the structure of both carbon fibers is presented. The relationship between the formation of closed pores from open pores and the variety of cumulative pore area during the heat‐treatment stage is also discussed.

Studies on flame retardancy of polyacrylonitrile fiber treated by flame‐retardant monomers in cold plasma

AbstractPlasma polymer hexamethyldisiloxane, ethyldichlorophosphate and tris(butoxyethyl)phosphate modified polyacrylonitrile fibers were examined by FTIR, XRF, and SEM and the extend of flame retardancy introduced were checked. Certain levels of concentrations of flame‐retardant elements grafted or coated at the fiber surface during plasma treatment are believed to overcome some negative effects of a number of reactions that usually are concurrent with plasma polymerization, such as crosslinking.

Microscopic study of modified polyacrylonitrile fibres

Microscopic studies have been made on polyacrylonitrile fibres which have been modified with solutions of CdSO4, ethylenediamine, and a mixture of these solutions.

The effect of modification on structure and dynamic mechanical behavior during the processing of acrylic fiber to stabilized fiber

AbstractPolyacrylonitrile (PAN) fibers pretreated with potassium permanganate have reduced the time required for stabilization, and also improved mechanical properties of the resultant carbon fibers. In this study, the effect of modification on the stabilization process and the dynamic mechanical properties of PAN fibers have been examined. The beta peak appeared at about 125°C on the loss tangent curves caused by molecular motion in the PAN fiber. Appearing at about 254°C, the alpha peak is attributed to chemical reactions and molecular motion in the formation of the crystalline phase of stabilized fibers. The alpha peak of the modified PAN fiber had lower absorption and had a smaller peak in the temperature range of 212–239°C. This indicated that potassium permanganate acts as a catalyst to lower the reaction temperature by about 20°C of the initial cyclization reaction. The dynamic storage modulus analysis indicated that modified PAN fibers have a lower initial transition temperature and that formation of the ladder polymer is gradual and steady.

Properties of polyacrylonitrile yarns which have been modified with salts of alkali metals

In modification of polyacrylonitrile fibres with alkali metal salts, a change in structure takes place, morphological nonuniformity in the transverse direction is increased, which aids in fibre crimping

Modification of polyacrylonitrile fibre with hydrolyzed wastes

Principles governing the alkaline hydrolysis of wet Nitron fibre waste and their solubilities in 51.5% aqueous sodium thiocyanate solution have been studied. It has been found that the best solubility is attained at an SEC of 0.17–0.20 meq/g. The solutions obtained on addition of these wastes are characterized by reduced viscosity, better filterability, and a reduced gel-particle content.

Modification of polyacrylonitrile fibers with hydrazine and hydroxylamine in aqueous medium

AbstractThe interaction between polyacrylonitrile (PAN) fibers and hydrazine and/or hydroxylamine in aqueous medium was investigated. The kinetics of the reaction was studied and a step‐like effect was found, testifying to a diffusion‐controlled stage. The Michaelis‐Menten kinetics was used for the description of the initial stage of the reaction. On the basis of the results and the analytical data the mechanism of the process was discussed. By studying the basic physical and physico‐mechanical indices of the fibers it was found that the chemical modification with these bases and a subsequent processing with aqueous solutions of copper salts takes place with notable changes in structure and properties of the fibers. The results obtained lead to improved methods for the production of fibers with chemical resistance and improved fire resistance.

Modification of polyacrylonitrile fibres with halogen-containing polymers

The physicomechanical and relaxation properties of fibres based on mixtures of polyacrylonitrile with halogen-containing polymers — polyvinyl chloride, chlorinated polyvinyl chloride, and Ftorlon — have been studied. It has been found that on introducing small additions of HCP, the physicomechanical properties of the fibres rise in an extreme fashion.

Use of hydrazine salts as modifying agents for polyacrylonitrile in the preparation of carbon fibres

Polyacrylonitrile (PAN) fibres are used as a raw material for the preparation of highmodulus and high-strength carbon fibres [i]. Sometimes, with the objective of cutting down the time for thermal stabilization of the fibres, they are treated in the presence of cyclization catalysts. These catalysts are substances which aid in the dehydrogenation of hydrocarbons or the dehydrogenation of hydroxyl-containing organic compounds, for example ZnCI2, AICI3, or FeCI3 [2]. Compounds of the Lewis acid type [3], acids, or alkalis can serve as catalysts [i]. In our research we used salts of hydrazine as modifiers-- the hydrochloride and the sulfate, and also combinations of hydrazine salts with caustic soda. Modification of the PAN fibres was carried out at 343°K in solutions whose concentration was from 0.5 to 20% by wt. The length of the treatment was i ho When the salt-NaOH system was used, the ratio of the components in the solution was varied from i:i to 2:1. After treatment, the fibre was subjected to oxidation in a heating chamber. The color of the fibres hardly changes if they are treated with the pure salts. Addition of alkali leads to a change in color from white to dark yellow. For comparison we carried out experiments on modification of fibres with caustic soda solutions alone. At a solution concentration greater than 0.5%, the morphological structure of the fibre is destroyed. Treatment of PAN fibres with hydrazine salts leads to an increase in the strength of the carbon fibres (Fig. i)o Treatment with salts at low concentration, 0.5-1% by wt., exerts the most important effect on the strength of the carbon fibres; the increase in their strength on treatment with 15 or 20% solutions of the salts is slight° The strength of the carbon fibres obtained by modification of PAN fibres with pure hydrazine, salts remains below the strength of the fibre obtained asa result of adding the salt--NaOH system. The difference in strength of the carbon fibres at various ratios of the components in this system is small; it is more prominent when the PAN fibres are modified with hydrazine sulfate° Within definite limits, the additions of alkali aids in raising the pH of the medium and favorably affects the quality of the carbo~ fibres, Treatment in an alkaline medium in combination with the cross-linking action of the hydrazine [4],which is liberatedondissociation of the salt, leads in the end to an increase in the strength of the carbon fibres. This fact may be explained by structural changes in the PAN fibres during the modification process. These changes are recorded on a differential scanning calorimeter, where the thermal effects of the cross-linking process are determined, which are characterized by the specific enthalpy values: Fibre AH, J/g

Antistatic effect of modified polyacrylonitrile fibres

Antistatic effect of modified polyacrylonitrile fibres

Antistatic effect of modified polyacrylonitrile fibres

Antistatic effect of modified polyacrylonitrile fibres

Modified polyacrylonitrile fibres with the properties of high-basicity anion exchangers

Modified polyacrylonitrile fibres with the properties of high-basicity anion exchangers

Modification of polyacrylonitrile fibre with organophosphorous compounds

Modification of polyacrylonitrile fibre with organophosphorous compounds

Modification of polyacrylonitrile fibre with fibroin

Modification of polyacrylonitrile fibre with fibroin