Intrafibrillar bridging structures in strained isotactic polypropylene

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

“…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.…”

“…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 mechanical properties were examined with an Instron-1122 instrument. We varied widely the stretching time (over a range of four logarithmic orders) and the stretching level.Here we consider the correlation of relaxation with elastic recovery; a detailed description has been given of relaxation in PP film filaments in [5], so here we merely briefly describe the main regularities in the direct relaxation: changes in internal stress in the filaments at constant strain. Families of relaxation curves σ(lg t r ) have been obtained over a wide range in given relative extension ε s (1 <ε s < 15%) with duration over 65 h. The relaxation occurs quite rapidly.…”

“…More detailed methods have been given [5] for determining the parameters in (2)-(5); the proposed method allows one to forecast the relaxation from short-time experiments to longer times and for a wide range of set strains. In the case of linear viscoelasticity, such forecasting requires only one relaxation curve, which is derived at relatively short times and with some one value of ε.…”