The fine structure of the aramid fibres Amos, SVM, and VMN was investigated by x-ray diffraction. It was found that the fine structure of Armos, SVM, and VMN The indifference of the structure of a fibre filler to the components of the solution of binder is a distinctive feature of polymeric composite materials reinforced with fibres based on aromatic polyamides with heterocycles in the main chain [1]. Alteration of the structure of the fibre, usually evaluated by x-ray structural analysis, is the consequence of this reaction. In view of this situation, a detailed x-ray diffraction analysis of Kevlar, Armos, VMN, and SVM fibres was conducted to develop methodical methods for the quantitative evaluation of the change in their fine structure.X-ray scattering by the objects investigated was analyzed on a standard DRON-3 diffractometer using CuKct radiation separated by a nickel ftlter and differential discriminator. Exposure was by the "transillumination" scheme in the "diagram recording" or "point recording" mode in the 20 diffraction angle range of 8 to 47* with simultaneous rotation of the radiation detector and sample.Oriented fibres parallelly positioned in a special holder attached to a goniometric attachment which made it possible to rotate the samples in the vertical plane were investigated in the first stage. An x-ray collimator with a cap 1 mm in diameter was used to obtain a parallel x-ray beam and decrease the size of the irradiated surface of the sample.The experimental intensity curves of equatorial and meridioual x-ray scattering by Kevlar, Armos, SVM, and VMN fibres are shown in Figs. 1 and 2. The significant difference in the equatorial and meridional diffraction pictures indicates the pronounced anisotropy of these fibres. The results of the analysis of the angular position of the basic reflections are reported in Table 1. Kevlar fibre, whose f'me structure has been studied in the most detail, was used as the comparison sample [2]. The data in Figs. 1 and 2 and in Table 1 show that a set of sharp diffraction reflexes both on the equatorial and on the meridional scattering curves is characteristic of Kevlar fibre. In addition, the monotonic increase in the diffraction intensity on the equator in the 12-17 ~ region of 20 angles and the smooth decrease in the x-ray scattering in the 20 region of 32-35 ~ indicates the presence of a diffuse halo for this polymer. Judging by the experimental results, Kevlar fibre contains both amorphous regions and segments having three-dimensional long-range order in the position of the molecular chains (crystallites), which is in agreement with the published data [2].We separated Armos, VMN, and SVM fibres, which have a similar chemical nature, into a separate group. Only the features of the fine structure of SVM fibre have been partially clarified in the literature [3, 4]. We attempted to study the structure of all of these fibres in detail.The x-ray diffraction analysis showed that only a diffuse maximum at 20 of 20.2, 21.0, and 21.5 ~ appears on the equatorial scat...
It was shown that in going from the mesomorphic γ-modification of PA-6 to the stable α-form, formation of intermediate structures can play an important role. It was found that the formation of the polymorphous α-modification in conditions of heat treatment at 180°C takes place due to the amorphous regions of the polymer.The supramolecular structure of polycaproamide (PCA) is formed to a significant degree during thermal drawing of the fibres. For this reason, assessing the effect of deformation and temperature factors on the polymorphous composition, amorphous phase content, and the orientation and size of crystallite formations in the polymer is important.For this reason, we conducted a detailed x-ray diffraction study of PA-6 treated in different conditions. The analysis was performed on a DRON-3 diffractometer using CuKα radiation separated with Ni and Co filters. The photographs were taken with the by transillumination scheme with simultaneous rotation of the sample and the detector. To obtain comparative data, the scattering parameters were normalized with an algorithm that makes it possible to calculate the differences in the radiating power, geometric parameters of the shot, and the mass of the preparations in the primary beam [1].Evaluating the change in the crystallinity of PCA fibres which determines their physicochemical and mechanical indexes is of great interest. Solving this problem by x-ray diffraction requires eliminating the anisotropy of the preparations. The samples were prepared from ground fibres and placed in a flat cell attached in a holder that rotated the objects. The lack of an amorphous standard makes it difficult to estimate the absolute degree of crystallinity of PCA. In view of this situation, we used the relative degree of amorphicity of a polymer (Am rel ), determined with the method of comparison in [2], in the study. Am rel was calculated with the normalized intensities of the diffuse halo at 2θ = 14° for the investigated and initial samples. Selection of this point ensured exclusion of the effect of diffraction by PCA crystallites on the scattering intensity. In this approach, the initial fibres play the role of standard.The equatorial and meridional x-ray scattering by the oriented fibres were analyzed for a more detailed analysis of the supramolecular structure of PCA. A cell that provides for formation of a flat sample of parallelly positioned fibres and an attachment that provides for their controlled rotation in their own plane was used for this purpose.Samples of PCA industrial fibre from Shchekino Khimvolokno Co. were investigated: as-spun (410 tex); treated with heat at 180°C for 2 h; drawn to 408% at 25 or 180°C.The study of the initial material ( Fig. 1) showed the presence of the hexagonal mesomorphic γ-modification of PA-6 [3]. The analysis of equatorial and meridional x-ray scattering revealed the anisotropy of the initial fibres due to spinneret drawing. Based on meridional reflection 002, it was found that the angle of disorientation (ϕ) and longitudinal crystalli...
The effect of heat treatment of Armos fibre in different conditions on the supramolecular structure of the polymer was investigated by x-ray structural analysis. The analysis of the physicomechanical indexes of fibres treated with heat in different conditions showed that it was more effective in the presence of superheated steam. It was found that heating the fibres in the presence of superheated steam causes deeper structural modification of the polymer, which increases the physicomechanical indexes.The creation of ultrastrong Armos aramid fibres allowed manufacturing universal composite materials capable of being used for a long time in any extreme conditions. Preservation of the strength on loading, the reliability and lifetime of the composite are determined by the physicomechanical indexes of the reinforcing fibre.Heat treatment is the most important process stage in fabrication of organic high-strength, high-modulus fibres from aromatic polyamides. As a result of treating these fibres at a temperatures almost 100° higher than their glass transition temperature, the breaking stress and initial modulus increase by one order of magnitude, and the relative elongation decreases. This effect is primarily due to the changes in the structure of the fibres that take place during heat treatment: healing of defects, decrease in internal stresses, ordering of structural elements, and increase in molecular mass as a result of solidphase polycondensation [1].We tested the hypothesis that the evolution of all of these processes should increase the mobility of the structural elements of fibres on incorporation of a temporary plasticizer. In the given case, superheated steam was used as the plasticizer.The experimental method consisted of the following: a weighed sample of Armos aramid fibres not treated with heat was attached with low tension to a frame and placed in an autoclave. The autoclave was hermetically sealed and evacuated to a residual pressure of 6 kPa while parallelly heating. When the necessary temperature was attained, a fixed amount of water was fed through a valve with a syringe and the pressure in the autoclave increased. After 5 min, the autoclave was again connected to the pump and a residual pressure of 6 kPa was created until heat treatment ended.The efficacy of the heat treatment was assessed with the physicomechanical indexes of three samples of fibres: untreated; treated in a laboratory unit with parameters close to an industrial unit; heat-treated in the presence of superheated steam.The experimental data in Table 1 graphically demonstrate the important increase in the physicomechanical indexes of Armos fibres treated with heat in the presence of superheated steam, which could be due to the more complete structure of the polymer.It was interesting to assess the structural changes in the samples obtained in the different conditions to explain the experimental data. In this respect, the supramolecular structure of the different preparations was investigated by the x-ray method. X-ray scattering was a...
It was shown that acetone and ethanol dissolved in aramid fibres at the level of 2-8 vol. % cause alterationsin the fine structure of these fibres. The direction and degree of the changes in the structure of the fibres are a function of the features of the molecular structure of the polymer.The physicomechanical properties of polymeric composite materials based on organic, particularly aramid, fibre fillers are greatly determined by the character of the processes that take place on the surface and in the bulk of the fillers in the stage of their impregnation with solutions of binders [1]. When bulk reactions are involved, not only the possibility of diffusion of the components of the binder into the matrix of the fibre substrate and their subsequent hardening there with the formation of strong chemical bounds on the fibre-binder interface, but also the possibility of relatively rapid structural transformations in the matrix of the fibre as a result of its reaction with the liquids used for preparing the solution of the binder must be taken into consideration.We mean here not only "catastrophic" structural transformations similar, for example, to the repeatedly described [2, 3] spontaneous crystallization of polyethylene terephthalate, but also free changes causing differences in the density of the fibres determined by pycnometry or hydrostatic weighing in liquids having a different affinity for the polymer [4].The characteristics of the reaction of four aramid fibres: Kevlar, VMN, Armos, and SVM, with ethanol and acetone, widely used as solvents of cured composites, are examined from these aspects in the present article.The solubility of liquids in the polymer matrix was determined by osmotic dilatometry [5] on samples in the form of pellets molded at a pressure of 500 MPa from finely cut fibres. The density of the fibre was found by hydrostatic weighing in a cell that can be evacuated before filling with the liquid, thus eliminating formation of air bubbles in the spaces between fibres, using samples in the form of small (0.2 g) skeins of fibres.The x-ray diffraction patterns were made on a DRON-3 diffractometer with the method in [6], but using a special flat hermetically sealed cuvette with polyethylene terephthalate film windows 5 lain thick. The film prevented evaporation of the liquid from the polymer sample investigated (pellets similar to those used in the sorption experimen0 and allowed obtaining the diffractograms of the liquids themselves. The background (scattering by air and holders) was taken into consideration in each case by parallel plotting of an empty cell using differential filters and placing the sample in front of the receiving slit of the radiation detector.As Table 1 shows, acetone and ethanol are soluble in all fibres investigated to the degree that the change in the volume of the fibres as a result of swelling attains (1.6-5.3)-10 -2 cm 3 per 1 g of aramid or, with consideration of the density of the untreated fibres, determined by hydrostatic weighing in toluene and o-xylene (Table 2), ...
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