Structural dependence of the deformation characteristics of polypropylene film fibre in stress relaxation

Abstract

The deformational rigidity increases due to relaxation of stresses in oriented PP fibres. Elongation of PP fibres is accompanied by mechanical failure in all stages, which is a distinctive feature of deformation processes in these materials. Ordering of the structure of amorphous regions, manifested by an increase in the deformational rigidity of these fibres, is the result of stress relaxation in oriented PP fibres.Isotactic polypropylene is widely used for manufacturing industrial fibres, and the high strength at relatively low density should be noted above all [1][2][3]. The manufacturing process for polypropylene (PP) fibres is a multistage process, and the fibre undergoes temperature and deformation treatment in different stages [4,5]. To improve product quality and optimize industrial orientation of PP fibre, it is necessary to understand the structural processes that take place in fixing the fibre in the stitched state, i.e., as a result of stress relaxation [6].The relaxation processes that take place in stitched (loaded) fibres and yarns in many cases significantly alter their performance properties. There is currently no complete representation of the structural processes that cause such changes in the deformation properties of fibres and yarns. The change in the deformation characteristics of fibres in the stretched state must undoubtedly be taken into account for reliable prediction of the deformation properties of synthetic fibres and the articles made from them, which is not always done in practice.We established the character of the change in the rigidity of stretched film PP fibres during stress relaxation and elucidated the structural nature of these changes. We investigated PP film fibre (manufactured by Tverkhimvolokno OJSC) with a linear density of 130 tex and draw ratio of λ = 6, tensile strength of σ t = 580 MPa, and elongation at break of ε b = 22%.The deformation-strength properties in the stress relaxation and active stretching regime and the structural rearrangements that take place in stitched fibers and yarns were investigated. The studies of the mechanical properties of the fibres in active stretching (obtaining the stress-strain diagrams) and stress relaxation regimes were conducted on an Instron-1122. The tests in conditions of stopping stretching and then stretching again were performed on the same setup. IR spectroscopy was used to reveal the moleculardecomposition processes that take place in stretched oriented samples. The valence bond breaks in the macromolecules were recorded with this method based on the newly formed stable terminal groups formed as a result of decomposition. The data were obtained by frustrated total internal reflection on a Spectrum One Fourier IR spectrometer. The absorption bands at 1742 and 1650 cm -1 were considered the molecular-decomposition bands in the IR spectrum of PP [7]. Low-frequency Raman spectroscopy, which is sensitive to the regular segments of macromolecules of any type regardless of their localization both in amorphous and in crystalline ...

The correlation of stress relaxation with elastic recovery in polypropylene film filaments

“…For prolonged recovery, ε ∞ corresponds to the irreversible plastic strain with given initial levels for the strain and length of the direct relaxation t r . The plastic strains are fairly high (up to 15-20% of the initial stretching), which is confirmed by our data on the irreversibility of the structural rearrangements arising from stress relaxation in PP film filaments [2][3][4]. The experiments gave the dependence of the asymptotic levels on the given strain and on the duration of the direct process, i.e., ε ∞ (ε s , t r ) and ε 0 (ε s , t r ).…”

“…ε = 11, 13, or 15%, the value of σ decreases by a factor 1.5-2, which confirms that there are the appreciable structural changes identified previously [2][3][4]. To elucidate the relaxation, the σ(lg t r ) curves were reconstructed in E -lg(t r ) coordinates in which E = σ(t r )/ε s is the relaxation modulus (Fig.…”

“…As such processes lead to considerable changes in deformation characteristics, they must be considered in the technology of processing and using the fibers. The relationship has been established [2][3][4] between the strain characteristics and the structural changes caused by relaxation in PP film fibers. Infrared spectroscopy and Raman scattering have shown that a consequence of stress relaxation is ordering in the structure of the amorphous regions, which makes itself felt in an increase in the deformation rigidity, while molecular destruction processes occur from the initial stages of stretching and continue up to the point where the filaments break.…”

Analysis of the contribution of the microfibrils and matrix to the deformation processes in wool fibers

“…This result drew our attention because, for many polymers, extension leads to an increase in the initial rigidity due to orientation processes. [15][16][17] Another interesting result, as shown in Figure 5, was the increase of the average value of E y in the second deformation region after the application of preliminary stretching. Although e p increased up to about 16%, E y increased slightly, but beyond this value, it increased sharply.…”

Effect of strain level on stress relaxation and recovery behaviors of isotactic biaxially oriented polypropylene films

“…In the literature, the stress-relaxation behaviors of PP at different forms such as thin films, PP-based composites, fibers, and sutures at different temperatures and the effect of stress-relaxation processes on their deformation properties were discussed in some studies [6][7][8][9][10][11][12][13] and some studies were devoted to propose and discuss the mathematical description of the stress-relaxation process and viscoelasticity and viscoplasticity of isotactic PP. 4,11,14 Influence of stretching and drawing on the surface and structure of the PP films were discussed in some studies which involved generally the effect of the stretching conditions in the production stages of boPP films.…”