Improvement of Manufacturing Technology for Ultrastrong and High-Modulus Carbon Fibres

1. The quality of CF, their strength and modulus of elasticity in particular, can be increased by the following methods: reducing the porosity of the initial PAN fibres by selecting the optimum conditions for spinning, plasticization drawing, finishing, and drying; decreasing the nonuniformity of the fibre diameter due to suppression of deformation resonance during spinning by selecting the jet formation and hardening conditions; decreasing the fibril and crystallite size by reducing the precipitator and solvent concentration gradient in the precipitation zone (spinning into mild baths); creating optimum conditions for mesophase self-ordering of the material at 450–550° C during precarbonization; increasing the cohesive energy by increasing the density to 1.8–2.1 g/cm³. 2. Replacing convective tempering of PAN twists in thermooxidative treatment by conductive tempering reduces the treatment time by 3–4 times. __________ Translated from Khimicheskie Volokna, No. 5, pp. 11–15, September–October, 2005.     

Nanotechnologies and chemical fibres

The features of nanotechnologies and possibility of applying them in research and industrial practice in the chemical fibres sector are examined. Structural elements 1–100 nm in size are the objects of nanotechnologies. The cross sections of fibrils and their crystalline sections (large periods) whose structure determines the mechanical and physical properties of the fibres fall in this range. In the initial stage, the chemical fibres were improved, especially with respect to increasing the strength, by orientation drawing, which corresponded to the nanotechnology principle of “top-down” processing. The wide use of the more progressive “bottom-up” processing principle by regulating the fibrillar structure by selecting the optimum conditions of spinning the fibre was recently supplemented by the method of self-ordering on the molecular level through the liquid-crystalline state. Fibre strength of 500–600 kgf/mm² was attained with this method. The energetic mechanism of transition of a substance into the liquid-crystalline state was substantiated. To attain a high degree of ordering of the fibrils before spinning, it is necessary to destroy the structural network of linkages in the spinning solutions and melts as completely as possible. __________ Translated from Khimicheskie Volokna, No. 1, pp. 26–30, January–February, 2008.     

Structural and mechanical characteristics of aramid fibres for bullet-proof vests

The following conclusions can be drawn from an analysis of the data reported in the present article: SVM and Armos fibres are now the most promising for use in bulletproof materials; increasing the elongation to 5–6% while preserving the strength at the level of 400–450 kgf/mm ² allows increasing the efficiency of use of fibres for bulletproofing; the method proposed here allows rapidly and efficiently conducting comparative tests and initial selection of materials and the pack structure of the energy-absorbing polymer support; new types of bulletproof fabrics must be developed to increase the efficiency of manifestation of the energy-absorbing properties of fibres. Translated from Khimicheskie Volokna, No. 6, pp. 37–40, November–December, 1997.     

Development of electroconductive polyacrylonitrile fibers through chemical metallization and galvanisation

The paper describes the modification of PAN fibres with metallic nickel in order to give the fibre electroconductive properties. This is achieved by two consecutively executed processes. The first process is chemical metallization, involving the immersion of the PAN fibres in a bath containing 0.5 mol l⁻¹ NiCl₂ and 1.5 mol l⁻¹ Rongalite at pH = 5.5 and T=288–293 K. Ni(II) is absorbed in the structure of the fibre and adsorbed at the surface through a complex reaction with the cyanide and carboxylic acid groups present in the PAN chemical structure and the Rongalite reduces the adsorbed Ni(II) to metallic Ni. The second process is galvanisation of the Ni-containing PAN surface (the Ni particles present at the surface form a “seed” layer) in an electrolyte bath using an electrolyte with 150 g l⁻¹ of NiSO₄ at pH 5–6 and room temperature. The resulting fibre showed a specific electrical resistance of the order of 10⁻⁶ Ω m, which is a promising result.     

Polypropylene fibres and yarns in the current state of development

Polypropylene (PP) production capacities in 2010 will exceed 60 million tons and by 2020, 90 million tons at an average annual growth rate of 8% in 2005–2010 and 4% in 2010–2020. Consumption of PP in 2010 will be 53 million tons, more than half of which will be in Asia, where 2/3 of production capacities are concentrated. World production of PP textile materials is slightly over 7 million tons, which is approximately 10% of natural and chemical fibres. Film fibres, staple fibre, carpet twist, and different kinds of nonwovens are the basic consumers of PP in the textile sector. In Russia, manufacture of PP for fibre applications is 7%, versus 11–12% in world practice. In 2007, production of PP fibres and yarns reached 24,300 tons (8.7% higher than the preceding year), and 56.4% was for manufacture of film fibres, 20.7% was for staple fibre, and 12.5% was for spunbond. Moscow Office of Coltech, Canada. Translated from Khimicheskie Volokna, No. 5, pp. 3–8, September—October, 2008.     

Intensification of thermooxidation of polyacrylonitrile fibres

It was found that in thermooxidation of PAN fibres in air by the conductive (contact) method, the density of 1.38–1.40 g/cm³, required for subsequent high-temperature treatment, is attained in 30–60 min. The chemical composition and equilibrium sorption of the PAN fibre oxidized by convective tempering do not differ significantly from the fibre fabricated in industrial conditions in convective tempering. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna. No. 6, pp. 22–24, November–December, 1999.     

Carbonization of polyacrylonitrile fibre modified with polyphosphate

Thermal transformations of PAN fibres modified with polyphosphate (PP) were investigated. It was found that PP affects cyclization and persists in the structure of the carbon fibre. The decrease in ordering of the structure of the carbon fibre with an increase in the concentration of PP in the fibre decreases the strength and modulus of elasticity with a simultaneous increase in the electric conductivity of the modified fibre. Translated from Khimicheskie Volokna, No. 4, pp. 40–41, July–August, 1998.     

World production and consumption of carbon fibres

The total world production volume of carbon fibres (CF) is 70–80,000 tons/year. In the last two to three years, there has been a trend toward significant growth in their production and use. Polyacrylonitrile fibre is the basic type of raw material for production of CF. New areas of application of CF have appeared. The quality level attained for carbon fibres is examined on the example of several leading manufacturers.     

The shear strength of Calabrian pine (Pinus brutia Ten.) bonded with polyurethane and polyvinyl acetate adhesives

In this study, the change in shear strength on radial and tangential surfaces of Calabrian Pine (Pinus brutia Ten.) wood having different roughness values as the result of sawing with a circular ripsaw, planing and sanding, and bonded with polyurethane (PU) and polyvinyl acetate (PVAc) adhesives at the pressure levels of 3, 6, and 9 kgf/cm², was studied. Each of the 360 specimens prepared to determine the effect of the variables on bond performance were subjected to shear test in an universal test machine in accordance with the ASTM D 905–98 standards. The values obtained were analyzed statistically and the results were interpreted. The highest shear strength (11.83 N/mm²) for plane of cut was obtained on the tangential surface after sanding and applying PVAc adhesive with a pressing pressure of 9 kgf/cm². The lowest shear strength (6.01 N/mm²) was obtained in the joinings made on the planed surfaces by using PU adhesive and a pressing pressure of 3 kgf/cm². The highest shear strength (9.10 N/mm²) on the radial surface was obtained after sanding and applying PVAc adhesive and pressing with a pressure of 6 kgf/cm². The lowest shear strength (3.76 N/mm²) was obtained in the specimens whose surfaces were sanded and glued with PU adhesive with a pressing pressure of 3 kgf/cm². In general, in the radial surfaces, just like in the tangential surfaces, the specimens bonded with PVAc exhibited a higher shear strength compared with those glued with PU. According to these results, it is definitely necessary to sand the surfaces prior to the bonding process to have a higher shear strength. The bonding process should be made on the tangential surfaces with higher pressures. The PVAc adhesive should be preferred instead of the PU adhesive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3050–3061, 2006     

Effect of ammonium orthophosphate on thermochemical transformations of hydroxyl-containing polymers

Ammonium orthophosphate is an active pyrolytic additive for PVA fibre which can increase the yield of CF to 72% of the theoretical carbon content in the polymer. The conditions that ensure obtaining inactivated CFM with 60–85% sorption capacity, at the same level as BAU-grade industrially manufactured activated carbons were found. __________ Translated from Khimicheskie Volokna, No. 2, pp. 5–8, March–April, 2006.     

Modification of synthetic materials to reduce combustibility

The studies conducted demonstrated the effectiveness of using Phosdiol for reducing the combustibility of PE fibres and the small effect of PAN and PA fibre fire barriers. The oxygen index of flameproof fibrous polyester material was 27.5%, which allows assigning it to difficultly combustible polymers, and the strength of the fibre increases by 12–15%. __________ Translated from Khimicheskie Volokna, No. 1, pp. 35–38, January–February, 2006.     

An application of polyalcohols prepared from diols. I. Elastic polymers with functional groups prepared by chemical modifications

An elastic polymer with hydroxymethyl side chains, which contains some crosslinked structure, has been prepared by treating its prepolymer with maleic anhydride and styrene in the presence of an initiator. Its mechanical properties were varied largely by the molar ratio of the hydroxyl group:maleic anhydride:styrene. A typical example of the polymer showed elongation 69%, tensile strength 0.85 kgf/mm², and Young's modulus 9.4 kgf/mm². Some other modifications are also examined.     

Performance characteristics of heater elements made of carbon fibres

The optimum concentration of a solution of adhesive required for impregnating CF is 35±5%, which corresponds to a 45±5% content in the fibre. An electric current is transmitted in CF due to the relatively low resistance of the fibre filaments and according to a “chain” scheme. The change in the strength of CF under the effect of cyclic double bending and preliminary loading was determined. The characteristics of the increase in the electrical resistance as a function of the number of double bending cycles, correlated with breaking of the CF filaments and a decrease in the contacts between them, were established. __________ Translated from Khimicheskie Volokna, No. 3, pp. 33–35, May–June, 2006.     

Thermoreactive compaction of an alumina — Polymethylsiloxane composition

Conclusions An investigation was carried out of the thermoreactive compaction of a composition of alumina with polymethylsiloxane, the technological parameters being varied. Before a heat treatment the open porosity of specimens containing 20% PMS is 0.8%, the bending strength 260 kgf/cm², and the cold-crushing strength 1070 kgf/cm².Firing at 1700°C gave a high-alumina composition ceramic with an open porosity of 2%, a bending strength of 1000 kgf/cm², a cold-crushing strength up to 5000 kgf/cm², and a thermal-shock resistance of 14–20 reversals from 1300°C into water (in tests with specimens).Translated from Ogneupory, No. 5, pp. 47–50, May, 1978.     

Oxidation of polyvinyl alcohol fibres in the presence of phosphorus-containing compounds

The oxidation temperature-time regime that results in carbon fibre materials (CFM) with a yield of approximately 30% and a 94–95% concentration of carbon was established based on a study of the fundamental characteristics of thermal transformations of polyvinyl alcohol (PVA) fibres in the presence of phosphorus-containing compounds. It was shown that the effective active energy of decomposition of oxidized PVA fibres and their capacity for coke formation increase in the presence of [NH ₄]₂HPO₄. The effect of the increase in the elasticity of CF caused by the action of the phosphorus-containing compound on cross-linking of the carbon during high-temperature treatment was determined. Translated from Khimicheskie Volokna, No. 2, pp. 14–18, March–April, 1997.     

Highly efficient preparation of multi-angle continuous carbon fibre reinforced hydroxyapatite composites by electrostatic splitting method

An electrostatic splitting device was self-designed and manufactured for highly efficient preparation of multi-angle continuous carbon fibre (CF)-reinforced ceramic-based composites and was used to prepare multi-angle continuous CF and nano-hydroxyapatite (nHA)-coated CF reinforced HA composites with improved CF dispersion and content. The compressive strength of sintered [0°/90°] CF reinforced hydroxyapatite (CF/HA) composites is more than two and a half times that of hydroxyapatite and is superior to that of cortical bone (26.42–110.7%). Compared with hydroxyapatite, fracture toughness of [0°/0°], [0°/90°] and [? 45°/+ 45°] CF/HA composites increase by 28.83%, 66.32% and 115.95%, respectively. The strength and fracture toughness (30.2 MPa·m^1/2) of [? 45°/+ 45°] CF/HA bioceramics display synchronously improving. Micromechanical property and crack propagation process of the composites were simulated in depth. Based on optimised dispersion and arrangement of CF, the introduction of nHA coating enhances the mechanical properties of nHA-coated CF reinforced HA composites because nHA coating can block the generation and propagation of cracks.     

World development of chemical fibres in 1996

The Near and Far East (except for Japan) will be the primary promising markets for chemical fibres to the end of the 1990s. In particular, Taiwan is now in second place in the world (after the US) in production of chemical fibres. The fibre production capacities of China, the Republic of Korea, and recently India are continuously expanding. In China, according to plan specifications, the capacities of the chemical fibre industry will significantly increase from 3.5 million tons in 1995 to 4.5 million tons in 2000, while production will increase from 2.9 to 4.0 million tons, respectively. It is believed that this will allow increasing the degree of supplying the textile industry with domestically produced chemical fibres to 85–90% by 2000. The total production volume of chemical fibres in “third world≓ countries is now almost four times higher than the production volume for all of Western Europe. The structural changes in the world chemical fibre industry can thus hardly be considered complete; global, radical changes in the market for these fibres are most probably coming, and Russia will carefully monitor them, exhibiting patience and interest in the development of her own potential. Translated from Khimicheskie Volokna, No. 3, pp. 3–7, May–June, 1998.     

Fabrication of carbon fibres from wet-spun commercial polyacrylonitrile fibres

The possibility of fabricating carbon fibre from commercial PAN fibres for textile applications was demonstrated. It is necessary to make some changes in the temperature—time conditions for total completion of the thermal stabilization process. Better strength of the carbon fibres, equal to 1401 MPa, was attained in conducting thermal stabilization cycle B. __________ Translated from Khimicheskie Volokna, No. 5, pp. 31–33, September–October, 2006.     

Method of measuring the modulus of elasticity of carbon tow

In comparison to static and ultrasound methods, the examined method of measuring the modulus of elasticity of carbon fibres (tow) has the following advantages: the method of measurement is contactless and nondestructive; the minimum necessary linear size of the tow required for the measurement (5 cm) is much less than for other existing methods; the results of the measurement are not a function of the method of fastening and tension of the tow; continuous monitoring of the elastic properties during movement of the tow is possible; the E of the tow in both elastic and in the initial fibre material can be measured; this allows measuring the modulus of elasticity of fragments of structures manufactured with fibre materials. __________ Translated from Khimicheskie Volokna, No. 1, pp. 57–59, January–February, 2007.     

Production and use of polypropylene fibres and yarn

World production of PP fibres in 2004 was approximately 6.3 million tons, including 2.1 million tons of film fibres. The total consumption of PP fibres, including spunbond/meltblown, on the European continent increased by 2.5% in 2004, reaching 2.4 million tons. In the near future, expansion of use of PP fibres for production of nonwovens is projected. The world market capacity will increase by 2008 to 3.55 million tons, including up to 1.0 million tons in North American countries. A wide assortment of PP products in the form of films, ribbons, fibrillized materials, staple fibre, complex yarns, spunbond, meltblown, etc., for manufacturing bags, soft containers, agrotextiles, packaging, cables, carpets, hygienic and medical goods, etc., has been developed. __________ Translated from Khimicheskie Volokna, No. 5, pp. 3–7, September–October, 2006.