Sample preparation in evaluating the sorption properties of thermostable fibers

The sorption properties of thermostable fibers are essentially a function of the method of sample preparation. Drying them at a high temperature significantly decreases the sorption properties due to a decrease in the pore space volume. Preliminary drying of the samples at 20°C with evacuation over a desiccant is recommended for an accurate evaluation of the sorption properties of thermostable fibers. The preliminary effect of moisture and subsequent drying alter the structure of SVM fibers, causing a decrease in sorption with low atmospheric humidity and an increase in sorption and hysteresis with high humidity.St. Petersburg Institute of Textile and Light Industry. Translated from Khimicheskie Volokna, Vol. 25, No. 1, pp. 33–35, January–February, 1993.     

Electrical properties of different types of carbon fiber reinforced plastics (CFRPs) and hybrid CFRPs

The electrical resistance (ER)–time, current–voltage and ER–temperature behaviors of carbon fiber reinforced plastics (CFRPs) reinforced with high strength (HS), medium modulus (MM), and high modulus (HM) carbon fibers were studied. At the same time, the electrical properties of hybrid CFRPs (HCFRPs) reinforced with more than one type of carbon fibers were also studied. It was shown that the value of the current influences the electrical stability and the ER measurement accuracy. In order to obtain an accurate ER measurement, the current should be larger than 1.5 mA. All the CFRPs and HCFRPs are characterized by linear current–voltage and Ohmic behaviors. A negative temperature coefficient (NTC) behavior is exhibited for all types of specimens. The NTCs of the CFRPs reinforced with HS, MM and HM carbon fibers are 0.038, 0.033 and 0.094, respectively. For the specimens of HCFRPs containing HM carbon fibers, the NTC becomes larger with increasing the volume fraction of HM carbon fibers. The good linear and reversible relationship between the change in ER and temperature indicates that the CFRPs and HCFRPs may be used as temperature sensors.     

Effect of molecular and compositional heterogeneity on the rheological properties of cellulose acetate solutions

The properties of acetate fibers are essentially a function of the physical and chemical heterogeneity and the rheological properties of solutions of secondary cellulose acetates (SCA). For this reason, the study of the effect of the molecular and compositional heterogeneity of cellulose acetates on the rheological properties of solutions is important.Scientific-Research Institute of Cotton Cellulose Chemistry and Technology, Tashkent. Translated from Khimicheskie Volokna, Vol. 25, No. 1, pp. 15–17, January–February, 1993.     

Thermal characteristics of organic high-strength,high-modulus fibers containing finely disperse fillers

The behavior of high-strength, high-modulus filled fibers based on aromatic polyamide with heterocyclic fragments was investigated at high temperatures. It was shown that a slight shift in the critical points on the thermomechanical curves to the region of higher temperatures is characteristic of fibers filled with rare-earth element oxides. The glass transition temperature, heat resistance, and thermal stability increase in the filled fibers. These changes are characteristic of fibers containing more than 10 wt. % filler.All-Russian Scientific-Research Institute of Polymer Fibers, Mytishchi. Translated from Khimicheskie Volokna, No. 4, pp. 42–45, July–August, 1992.     

Hydraulic resistance of a deformable layer of fibrous material

Filtration of spinning solutions, spinning bath, and finishing solutions through a layer of fibrous material is widely used in different chemical fiber plants. In finishing of textile fibers on spools and cakes, the liquid is filtered through a layer of fiber attached by winding. At the same time, filtration is through a layer of unattached, freely packed fibrous material with random orientation of the individual fibers or through layers of nonwoven material in filtration on filters with a metal — gauze — asbestos gravity layer, in fiber finishing or modification processes, and in processes involving ion-exchange, chemisorption, and catalytically active fibrous materials.Moscow State Textile Academy. Translated from Khimicheskie Volokna, Vol. 25, No. 1, pp. 13–15, January–February, 1993.     

Synthetic fibres which are flammable to a limited extent

Conclusions As a result of examining the literature data, one can draw the conclusion that the new synthetic fibers which belong to the class of thermally resistant fibers are very resistant with respect to a flame.Certain forms of heat-resistant fibers do not maintain combustion even in a oxygen-enriched atmosphere, up to 40–75% by wt.Translated from Khimicheskie Volokna, No. 4, pp. 6–9, July–August, 1983.     

Dependence of the orientation strengthening of polypropylene fibers on temperature and rate of deformation

Conclusions The mean deformation rate rather fully characterizes the kinematics of polypropylene fiber stretching. It can be used as a norming parameter to obtain generalized temperature-rate characteristics of this process.The degree of orientation in stretching polypropylene fibers, like that for previously studied polymers, is determined by the magnitude of the accumulated highly elastic deformation.Translated from Khimicheskie Volokna, No. 4, pp. 24–25, July–August, 1983.     

Effect of temperature on the properties of man-made fur

The heating temperature range in which fibers used for fabrication of man-made fur lengthen and subsequently fail was established. A method was developed for determining the bending rigidity of man-made fur at low temperatures and an increase in its rigidity with a decrease in the temperature was established.L. V. Tonkoshkurova participated in the study.Translated from Khimicheskie Volokna, Vol. 25, No. 1, pp. 45–46, January–February, 1993.     

Resistance of ultrathin polyoxymethylene fibers to the action of various reagents

Conclusions Ultrathin polyoxymethylene fibers are resistant to the action of organic solvents, alkalis, and dilute acids.The effect of the highly developed surface of ultrathin polyoxymethylene fibers is displayed in the fact that concentrated mineral acids cause practically complete decomposition of the fibers, while organic solvents are sorbed by them.Translated from Khimicheskie Volokna, No. 4, pp. 44–45, July–August, 1983.     

Phase transitions and internal stresses in textured cellulose acetate fibers

The phase transitions in textured CA fibers were investigated by IH (isothermal holding), DSC, and IR spectroscopy. It was found that the degree of order of the cellulose acetate macromolecules decreases and the spatial orientation of rotamers of acetyl and hydroxymethyl groups changes during heating. It was hypothesized that the extreme curves of the internal stresses an heat capacity as a function of the temperature have a similar physical nature and are due to a change in the conformation of the macromolecules.Translated from Khimicheskie Volokna, Vol. 25, No. 1, pp. 38–40, January–February, 1993.     

Lignin-based carbon fibers for composite fiber applications

Carbon fibers have been produced for the first time from a commercially available kraft lignin, without any chemical modification, by thermal spinning followed by carbonization. A fusible lignin with excellent spinnability to form a fine filament was produced with a thermal pretreatment under vacuum. Blending the lignin with poly(ethylene oxide) (PEO) further facilitated fiber spinning, but at PEO levels greater than 5%, the blends could not be stabilized without the individual fibers fusing together. Carbon fibers produced had an over-all yield of 45%. The tensile strength and modulus increased with decreasing fiber diameter, and are comparable to those of much smaller diameter carbon fibers produced from phenolated exploded lignins. In view of the mechanical properties, tensile 400–550 MPa and modulus 30–60 GPa, kraft lignin should be further investigated as a precursor for general grade carbon fibers.     

Thermal conductivity of basalt fiber materials

The thermal conductivity of cloth from vitreous staple fibers from basalt rocks produced by the Asbotermosteklo Plant (Zheleznodorozhnyi) with different densities and fiber diameters is investigated under arbitrary regimes. Recommendations on the use of the cloth for thermal insulation of equipment with operating temperature of up to 700°C are given.Translated from Ogneupory, No. 10, pp. 25 – 26, October, 1995.     

Influence of Coagulant Temperature and On-Line Drawing on the Mechanical Properties and Permeation Performance of Cellulose Acetate Hollow Fibers

Cellulose acetate (CA) ultrafiltration hollow fibers were prepared via the dry–wet spinning technique. In the spinning process, the coagulant temperature was varied, and hence the on-line draw ratio was affected. The results revealed that the maximal draw ratio increased with the increase of coagulant temperature up to 55 ^○C and then leveled off. The inner diameters, outer diameters and thickness of the hollow fiber decreased with the increase of the draw ratio. The tensile properties of the resulting hollow fibers were measured, and the breaking tensile stress increased with the increase of draw ratio. When the coagulant temperature was increased from 25 to 70 ^○C, the porosity increased, the pore size was slightly enlarged in the outer skin, the hydraulic permeability increased, and the percentage of retention R decreased. In summary, by increasing the coagulant temperature, the maximal draw ratio can be increased, and hence the mass transfer properties and the other properties of drawn CA hollow fiber can be varied.     

Sorption studies of the structure of carbon fibers derived from pitch

Conclusions -- It has been found that the investigated pitch carbon fibers are ultra- and microporous adsorbents with a strongly developed surface.-- The studied fibers display clearly expressed molecular-sieve properties.-- With increase in activation time, the size and volume of the pores and the specific surface of the specimens increase, while the chemical activity of the surface changes only slightly.Translated from Khimicheskie Volokna, No. 2, pp. 40–41, March–April, 1993.     

Preparation and properties of looped viscose-kapron yarns

Conclusions The method of yarn texturizing with an air stream is universal: it permits one to obtain looped yarns both from natural fibers, and also from thermoplastic or nonthermoplastic man-made yarns. The main advantages of this method are the possibility of processing yarns over a broad range in linear density, a high texturizing speed, and maintenance of the physicomechanical properties of the original yarns.Using aerodynamic texturization, one can produce combined yarns which have such specific properties as incombustibility, electrical conductivity, antistatic behavior, etc.The use of yarns which have been texturized by the aerodynamic method will make it possible to enlarge the assortment of articles produced by the textile and jersey industry.Translated from Khimicheskie Volokna, No. 1, pp. 25–28, January–February, 1985.     

Fibers from a mixture of cellulose triacetate and polystyrene

Conclusions The introduction of a nonfiber-forming substance — polystyrene — into cellulose triacetate does not cause the formation of long microfibers in the polymer matrix; the polystyrene is distributed along the fiber axis in the form of stretched-out regions.The addition of polystyrene helps increase the strength figures for triacetate fibers by more than 20%.Translated from Khimicheskie Volokna, No. 4, pp. 37–38, July–August, 1983.     

Possibility of using fibrous thermal-insulation materials for lining electric furnaces containing a reducing atmosphere

Conclusions A study has been made of the possible use of fibrous thermal-insulation materials for the lining of furnaces operating with a reducing gas. The results of the study make it possible to recommend the use of ShVP-350 tiles at the maximum working temperature of 1200°C and products made from mullite-silica fiber and mineral wadding over the same interval of temperatures as in air, i.e., up to 1150 and 600°C, respectively. The use of fibers made from rocks with a high concentration of iron oxides is ruled out because of their low stability in a reducing atmosphere.The thermal conductivity of the fibrous materials in a reducing atmosphere is 25–40% higher than its value in an air atmosphere.The lowering of the thermal conductivity of fibrous linings in a reducing atmosphere makes it preferable to use them rather than normal linings of equal thickness because of their thermal-insulation properties. The use of the fibrous linings, moreover, helps to keep stable the specified composition of the furnace atmosphere. The time taken to restore this after the door has been opened is 1.5–2.0 times faster than that required for furnaces with the normal lining materials.Translated from Ogneupory, No. 2, pp. 8–11, February, 1984.     

Hollow semipermeable fibers from modified polycaproamide

Conclusions Introducing modifying compounds into polycaproamide makes it possible to vary transfer and gas separation characteristics in the hollow fibers obtained from these polymer compositions. Beneficial effects in changing permeability and selectivity of gas permeability in hollow fibers are attained as a result of changing the character of intermolecular interaction on introducing various additives into the polycaproamide before spinning.Some effective additives are technical carbon black, polyorganosiloxanes, and m-diethylbenzenesulfonylisopropylamide.Translated from Khimicheskie Volokna, No. 1, pp. 30–33, January–February, 1985.     

Selection of immersion liquids for determining the refractive indices of man-made fibers

Conclusions The immersion liquids for determining the refractive indices of polymeric materials have a number of advantages over the known ones.It is possible to determine the refractive indices of man-made fibers by the chromatic variation method using 20 immersion liquids in the range of values 1.71–1.48, with an accuracy of 0.002.A method has been proposed for determining the refractive indices, dispersions, and birefringence of man-made fibers of cylindrical form using a single immersion liquid.Translated from Khimicheskie Volokna, No. 4, pp. 57–58, July–August, 1983.     

High Temperature Resistant Environment-Friendly Silica Fibers and Materials

Methods for the preparation of silica fibers by chemical leaching of glass fibrous are described. The materials in question are composed of high-melting oxides (94 – 96 wt.% SiO₂ and 3.5 – 4.0 wt.% Al₂O₃) and display superior properties: service temperature up to 1000°C, melting point 1650 – 1700°C, heat conductivity 0.082 – 0.11 W/(m · K) at 50°C. The materials are stable on exposure to water, hydrocarbons, ammonia hydroxide, hydrochloric, nitric and sulfuric acids, high temperature, pressure, and radiation. The silica materials are commercially available as fabrics, gauzes, ribbons, filaments, fibers, and blankets.__________Translated from Novye Ogneupory, No. 12, pp. 51 – 53, December, 2004.