A method has been developed for forecasting stress relaxation in polypropylene film filaments, which is based on linear viscoelasticity. The elastic recovery has been examined for polypropylene (PP) film filaments, which is related to stress relaxation processes of various durations. The recovery curves in semilogarithmic coordinates are characterized by initial and final asymptotic levels, and also by an S-shaped elastic component of the process, an important characteristic of which is the relaxation time. The recovery parameters are complicated and are nonlinearly dependent on the given level of strain and the duration of the direct relaxation. A method is proposed for the analytic description and forecasting of elastic recovery in PP film filaments on the basis of the parameters of the preceding stress relaxation: in accordance with the duration of the direct relaxation and the given level of stretching.Polypropylene (PP) film filaments are widely used for making fabrics for container products (bags and containers), and they have replaced more expensive packing materials [1]. In response to mechanical treatments, the fibers show relaxation: creep, stress relaxation, and elastic recovery. 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. The structuring processes in deformed PP film filaments should be reflected also in the relaxation processes occurring in this material. Results have been given [5] from long researches on stress relaxation in these filaments over a wide range in strain and for various temperatures. However, in this research on relaxation, it is no less important to examine the regularities in the recovery of the filament dimensions after partial or complete removal of the external mechanical forces. The elastic recovery has not been extensively examined after the filaments have been kept for a certain time or for certain values of the strain in the deformed state, although they often occur in applications.This research has been concerned with stress relaxation and elastic recovery following stress relaxation in polypropylene film fibers, and also the development of methods of describing and forecasting those processes for long periods.We used PP film filament (made by Tver′khimvolokno Company) with drawing factor λ = 6, linear density T = 130 tex, failure load σ f = 580 MPa, and elongation at failure ε f = 22%. The mechanical properties were examined with an Instron-1122 instrument. We varied ...
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