Structural changes in polycaproamide during thermal drawing of industrial fibres

Abstract

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...

Insights into the crystal structure, polymorphism and thermal behavior of menthol optical isomers and racemates

“…Polymorphism examples are diverse and the fields in which they manifest themselves are many. One can quote, for instance, cellulose or polycaproamide treatments in textile manufacturing, 4,5 L-glutamic acid in the food industry, 6 triglycerides for cosmetic applications [7][8][9] and the carbamazepine-nicotinamide cocrystal in the pharmaceutical field. 10 The latter field is particularly connected to polymorphism issues since bioavailability and toxicology are directly impacted by the nature of the crystalline active pharmaceutical ingredients.…”

Analysis of the orientation of supramolecular structures in fibers by the method of X-ray diffractometry

“…2a showing the intensity of equatorial scattering by PCA fibers is characterized by the presence of diffraction maxima with the angles 2θ = 20.1 and 23.8°, which is typical of the α-modification PA-6 [5]. An analysis of such diffraction patterns makes it possible to reliably monitor polymorphic transformations in PCA fibers during drawing and heat treatment [6,7]. The 020 and 040 reflections, with 2θ = 10.5 and 20.8° [1], are clearly visible on the meridional scattering curve (Fig.…”