K. E. Perepelkin

Polylactide Fibres: Fabrication, Properties, Use, Prospects. A Review

The analysis of data on the fabrication, structure, and properties of polylactide and polylactide fibres will allow drawing a conclusion concerning the promise of using them for production of high-quality textiles and articles for domestic, medical, sanitary-hygienic, and industrial applications. The existence of a renewable raw material base (plant stock), the use of biotechnology for fabrication of the monomer (lactic acid and its dilactide), and the simple technology for fabrication and melt spinning of the polymer show that production of these fibres will be economically feasible. Manufacture of these fibres does not involve complicated environmental problems due to the nontoxicity of the initial, intermediate, and finished products, and the possibility of recycling and biodegradation in the environment. As oil, coal, and gas deposits are being exhausted, polylactide fibres could become a promising large-tonnage variety of fibre. In this respect, it is necessary to develop comprehensive research to create optimum processes for production of lactic acid, polylactide, and polylactide fibres in Russia and to create industrial plants. With a wide spectrum of applications, polylactide fibres can be considered to be at the same level as other chemical fibres. They will not directly compete with existing chemical fibres, although they can be successfully used in place of or combined with them in many cases. At the same time, they have their own niche because of their specific properties.

Thermal Characteristics of Para-Aramid Fibres

Comparative studies of the thermal characteristics of para-aramid fibres (Armos, Rusar, Terlon, Twaron, and Kevlar) were conducted using thermomechanical analysis (TMA), dynamic thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). According to the TMA data, the para-aramid fibres studied are characterized by dimensional stability up to temperatures of 400-450°C; shrinkage or spontaneous elongation does not exceed 0.5-1%. TGA and DSC revealed the temperature characteristics of the para-aramid fibres corresponding to the occurrence of thermooxidative degradation. These processes begin at 400-450°C and are accompanied by shrinkage; 4% weight loss takes place at temperatures above 490-500°C.

Oxidized (Cyclized) Polyacrylonitrile Fibres — Oxypan. A Review

Fibres made of oxidized polyacrylonitrile of the Oxypan type are an independent group of thermostable fires with a possible temperature of use of up to 300°C and slightly higher for a short time. The principles and methods of fabrication, structure, assortment, and properties of Oxypan oxidized PAN fibres are examined. Oxypan fibres, widely manufactured in different countries, are now the least expensive of all thermostable fibres. It is expedient to organize manufacture of these fibres in Russia, and the necessary equipment is available and in place.

Properties of Armos Para-Aramid Fibres in Conditions of Use. Comparison with Other Para-Aramids

The mechanical, thermal, and hygroscopic properties of Armos fibres and thread and their resistance to active media and other effects during use were analyzed. In comparing the structure and properties of Armos with other types of para-aramid fibres and thread, it was found that in the para-aramid series, Armos is distinguished by a unique combination of strength and flame resistance. Armos is a promising material for use in articles operating in conditions of exposure to high tensile loads and/or high temperatures.

Carbon Fibres with Specific Physical and Physicochemical Properties Based on Hydrated Cellulose and Polyacrylonitrile Precursors. A Review

A wide assortment of carbon fibres (CF) made from readily available hydrated cellulose (HC) and PAN staple fibres and twists, textile and other fibre materials, including heat and chemical-resistant composites, has been developed. The use of these materials is based on their unique thermal, physical, physicochemical, and biological properties. The precursor fibres have their own characteristics and the properties of the CF and CFM made from them are correspondingly different. The economic aspects of their fabrication differ slightly, and CF made from PAN perhaps now have some advantages. However, in the near future, the price ratio will vary in support of cellulose fibres since products made from crude oil, natural gas, and coal are gradually becoming more expensive. The economics of small-tonnage fibres with original specific properties should be taken into consideration based on the efficiency of their use. The uniqueness of these fibres gives those which are irreplaceable and most effective the “right to life.” In this respect, all of the CF and CFM examined are important and promising. Far from all of the possible applications of these fibres have been discovered and implemented, which makes them even more promising for the future.

Physicochemical Nature and Structural Dependence of the Unique Properties of Polyester Fibres

The structure and properties of PET and PET fibres are examined on three structural levels — molecular, supermolecular, and micromolecular. It was shown that the unique properties of the fibres are determined by the aliphatic-aromatic structure of PET and the chemically regular molecular structure. The structural dependence of the fundamental physicomechanical and physicochemical properties of PET and PET fibres was analyzed. It was shown that the high glass transition temperature of PET and PET fibres is determined more by molecular rigidity than by intermolecular interactions and varies little under the effect of moisture. This causes high stability of the structure in mechanical effects and exposure to heat and moisture, high reversibility of deformation, and insignificant creep under mechanical stresses. The structure and fundamental properties of PET and PET fibres are compared with the characteristics of other kinds of large-tonnage fibre-forming polymers and fibres and other aliphatic-aromatic polyesters and fibres. The advantages of using polyester fibres for fabrication of household and industrial articles are substantiated and summarized based on an examination of the properties of these fibres.

Determination of shrinkage of textiles made of chemical and flax fibres by different methods

Three methods of determining shrinkage were compared: standard, in boiling, and in repeated wet treatments in polyester, flax, and blended fabrics of different composition. The difference in the experimental shrinkage values obtained with these methods was demonstrated. The kinetics of shrinkage of fabrics in wet treatments are described by an exponential equation which can be used to predict shrinkage in time. The coefficients of the equation were determined for different kinds of cloth. The value of the shrinkage of these fabrics in use was determined. A fast, objective method of determining the shrinkage of fabrics in use was proposed and its practical use was substantiated. It was shown that the shrinkage for polyester—flax fabrics is an exponential function of their fibre composition.

Prediction of the change in density in systematic series of fibre-forming polymers

The density of aliphatic polyamides is determined by the concentration of amido groups and additively increases in systematic order. The packing coefficient of aliphatic polyamides determined by the ratioρa/ρc increases with an increase in the concentration of amido groups. The density of cellulose acetateis determined by the concentration of acetate groups and decreases additively in systematic order. The calculation with the group contribution method can be used to predict the density of crystallites of fibreforming polymers. but this method only gives approximate results for amorphous regions.

Changes in the Properties of Synthetic Fibres in Thermal Aging

Thermal aging of complex lavsan, nitron, and anid fibres and lavsan and nitron yarn was investigated in the temperature region above the glass transition temperature (120, 150, 180°C) in the free state and with shrinkage for up to 300 h. It was shown that thermal aging of chemical fibres in the general case includes periods of structural and thermochemical aging. The kinetic characteristics of thermal shrinkage of chemical fibres and yarn in the first period of thermal aging were investigated. An exponential curve of shrinkage in time was obtained and can be used to predict the behavior of fibres and yarn in the first period of aging in the free state. The kinetics of the change in the strength and relative elongation at break was investigated in prolonged thermal aging of chemical fibres and yarn in the free (with shrinkage) and fixed (without shrinkage) states. The exponential dependence of the change in the fibre breaking characteristics on the duration of heat treatment was demonstrated. The change in the properties in prolonged thermal aging in the free and fixed states in the first stage of aging takes place differently. With shrinkage, the strength decreases and the deformability increases as a result of relaxation phenomena in the first stage, followed by a symbatic decrease in the strength and deformability as a result of thermal degradation processes in the second stage. In heat treatment in the fixed state, the change in the mechanical properties in the first stage is slight, while the strength and deformability simultaneously decrease in time as a result of thermal aging in the second stage. The quantitative characteristics found can be used to predict the change in the mechanical properties of chemical fibres and yarn in conditions of prolonged exposure to heat.

Use of chemical fibres in drying screens for the paper industry

The basic types of chemical fibres for the development and production of drying screens for paper machines were selected and their properties were determined. Polyester fibres are the most appropriate type for fabrication of drying screens due to their elevated mechanical properties and thermohydrolytic stability. Optimum designs for drying screens based on polyester monofilaments and complex fibres with a polymer coating with defined permeability were developed. To decrease the markability of paper web, it was suggested that the outer supporting surface of the screen be coated with soft fibres or a fibrous layer of Nitron fibres.