Basic stages in the development of high-strength and high-modulus viscose fibres

Translated from Khimicheskie Volokna, No. 2, pp. 17–19, March–April, 1991.     

Effect of the laser radiation wavelength on the energy threshold of initiation of heavy metal azides

The behavior of silver and lead azides (laminated and filiform crystals, pressed powders) with initiation of their explosive decomposition by a laser pulse is studied. The initiation energy thresholds are measured during irradiation at wavelengths of 1064, 532, 354.7, and 266 nm corresponding to four harmonics of laser radiation. Irradiation is performed under conditions with the sample surface being open or covered with a transparent dielectric (quartz plate) with a pressing force up to 5 · 10⁸ N/m². Surface covering does not exert any significant effect on the initiation energy threshold in the domain of transparency of the heavy metal azide matrix (first and second radiation harmonics). In the domain of bandgap absorption (fourth harmonic), the initiation threshold strongly depends on the surface conditions (open/covered). The results are discussed from the viewpoint of the influence of the transparent substrate on gas-dynamic unloading of the heat spot, which is formed in the domain of bandgap absorption owing to laser radiation absorption in a thin subsurface layer.     

The nonuniqueness and instability of the combustion regimes of a gaseous mixture under the action of laser radiation

We present the results of a theoretical investigation of the dynamical behavior of a chemically active gaseous mixture during the action of nonlinear laser radiation. The regions of possible combustion regimes are delineated by Lyapunov's first method. We show that, as a consequence of the temperature dependence of the mixture absorption coefficient, the number of steady states is increased to five. Data from a linear analysis confirms the numerical experiments.Alma-Ata. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 2, pp. 32–36, March–April, 1992.     

About the surface characteristics of natural fibres

The surface characteristics of corona and silane treated jute fibres were studied using dynamic contact angle (DCA), capillary rise and resin adsorption methods as well as inverse gas chromatography (IGC). First of all it was shown that corona treatment increases the polarity of jute fibres, whereas the dispersive part was constant over the whole range of corona energy output. This was leading to an improvement in the wettability of the fibres by a polar epoxy resin. The fibre surface energy was dependent on corona energy output used with a maximum in polarity by 130 mJ/mm². Further it was shown that the contact angles on the jute fibres for the different test liquids depend on the contact time due to the absorption of test liquid. Because of this fact, an improved method to characterise cellulose based fibre surfaces was developed based on DCA and capillary rise method. For the silane treated fibres increased specific interaction terms were characteristic.     

Formation of modified areas of porous glass saturated with glycerin under the action of laser radiation

The formation of modified areas with changed optical properties in the volume of thin plates of porous glass (composition of 94.73SiO₂ · 4.97B₂O₃ · 0.30Na₂O), saturated with glycerin—a substance with a high polarization capacity, under the action of laser radiation was investigated. A continuous wave ytterbium fiber laser with radiation wavelength λ = 1.07 μm weakly absorbed by porous glass was used as the radiation source. When the radiation power was within the range of 9.6–16.5 W and the irradiation time was 270–300 s, optical-grade modified areas were obtained. During the experiment, the dependences of temperature in the spots of the impact and of the power of the radiation transmitted through a thin plate of porous glass, on irradiation time were registered.     

Fixation characteristics of carboxylated dyes on polyamide fibres

Reactions of dyes, some of which contain a carboxylic acid group, on polyamide have been investigated using nine different dyes of differing chemical structures. Fixation characteristics and dye–fibre bond stability to alkaline washing were also studied. Light fastness and ability to cover barre effects on nylon were investigated. Studies were also made on the effect of carbodiimide on fixation and dye–fibre bond stability of these dyes on nylon fibres.     

Ureidosilanes on E-glass fibres: deposition and surface characteristics

The behaviour of methoxy- and ethoxy-ureidosilanes deposited onto E-glass fibres from both organic and aqueous solutions is reviewed. γ-Ureidopropyltri(m)ethoxysilanes are used as coupling agents for paints to metal surfaces, but they have not found much use as coupling agents for E-glass fibres. On metal surfaces, the silane is deposited with the ureido-functional group outermost, available for reaction with a paint/polymer matrix. On E-glass surfaces, however, unless specific conditions are employed, ureidosilanes tend to deposit with a highly cross-linked siloxane surface. The silanol groups condense not only with silanols of adjacent silanes and the E-glass surface, but also with aluminium hydroxides leached from the E-glass surface. This forms a highly cross-linked aluminosiloxane outer layer. The aluminosiloxane forms at all pHs between 4 and 10, and also when a range of organic deposition solvents is used. ²⁹Si-NMR results are presented which illustrate the high level of condensation; silane to silicate binding via the amino group was not detected. A small proportion of Si—O—Si (silane-glass) bonds was inferred, indicating that a small number of sparsely distributed Si—O—Si links bound the silane to the surface. Electrokinetic analysis of the surfaces confirmed patchy deposition with a siloxane outer surface. Using AFM and ab initio calculations, it was estimated that the patchwise deposition of the silane was in the form of bilayers (or multiples of bilayers). The bilayer structure consisted of siloxane outer layers, with the inner ureido layers forming hydrogen bonds. A graphical fit using the mole and volume fractions of silane and organic solvents confirmed the various types of siloxane surfaces as deposited from different organic solvents. Chlorinated solvents tended to produce a ureido outer surface, which was condensed, but solventswollen; deposition from alcohol and acetone resulted in a siloxane surface. Toluene and THF both produced minimally condensed ureido surfaces, which were easily removed by washing with methylene chloride.     

Effect of molecular mobility on the deformation characteristics of polycaproamide fibres

The deformation characteristics of PCA fibres are a function of the deformation temperature to a significant degree. The character of the curves of E(ε), E_max(t), σ_b(t), and ε_b(t) indicate a pronounced change in the mechanical properties of PCA fibres not only in “thawing” of segmental mobility in amorphous regions of the polymer, but also in passage of crystallites into the mesomorphic state, which is characterized by pronounced weakening of interchain interactions in the crystallites. The first segment of σ(ε) is only observed in the curves for PCA fibres in the glassy state. In activation of segmental mobility, the σ(ε) curves only contain the second and third segments. St. Petersburg State University of Technology and Design. Translated fromKhimicheskie Volokna, No. 6, pp. 30–31, November–December, 1999.     

Combustion characteristics of cellulosic loose fibres

The aim of this paper is to study the combustion characteristics of loose fibrous cellulosic compounds through cone calorimeter measurements. The challenge in studying loose fibrous materials by cone calorimeter in a reproducible manner is met by optimizing various process parameters such as sample weight, heat flux and grid type. The method is validated using cotton fibres and fabrics with a range of flame retardant properties. Good correlations are obtained between the flame retardant content of samples and the heat release parameters for both the fibres and the fabrics. In addition, fibres from specific cotton cultivars showed statistically significant differences in heat release characteristics. This shows that valuable data concerning the combustion behaviour and the corresponding kinetics of loose fibrous compounds can be successfully gathered using a cone calorimeter. Thus, such data can be exploited to well define future fibre breeding programmes or fibre modification research. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of the conditions of laser treatment on the thermal and strength indexes of polyacrylonitrile fibres

The results of laser treatment of fibres are not only determined by the average laser energy flux density on the sample during treatment but also the irradiation regimen. In going from a continuous irradiation mode to a pulsed mode, the probability of accumulation of energy in chemical bonds increases, and this increases the probability of their breaking and is the cause of a decrease in the strength indexes of the fibres. The probability of destructive processes increases with a decrease in the duration of the pulse and correspondingly with an increase in the peak laser energy flux values and with an induced decrease in molecular mobility due to removal of heat from the processed fibres. Changing the conditions of laser treatment of fibres allows varying the thermal indexes of PAN fibres during pyrolysis.St. Petersburg State University of Design and Technology. Translated from Khimicheskie Volokna, No. 3, pp. 20–23, May–June, 1996.