Rigidity of heat‐treated oriented isotactic polypropylene

Abstract

Uniaxially oriented commercial films of isotactic polypropylene were strained with ends keeping fixed and subjected to the heat treatment at temperatures from 50 to 2008C. The rigidity of annealed samples was characterized by the value of tangent modulus, E t , determined graphically at the initial portions of stress-strain curves. The structural changes in the samples were studied with the help of the IR and low-frequency Raman spectroscopies. The smallest E t values were obtained for the low-strained films, while the tangent moduli measured for highly strained samples exceeded the value for the original (untreated) film. The most prominent positive effect was achieved after annealing the samples at 908C.

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

“…29 The band observed at around 1735 cm 21 belongs to the oxygen-containing terminal groups. 5 In the range of 1400-1800 cm 21 , the band originating from double C@C bond 29 referred to the terminal (ACH@CH 2 ) position of the diene groups 5,30 was observed at around 1640 cm 21 which was seen as a clearly separated band in some pre-extension levels and as an overlapping band in some other pre-extension levels like the case for the bands observed at 1711 and 1735 cm 21 in the spectra.…”

“…The absorbance intensity of the methylene group bending was used as standard band, because it was supposedly unchanged and independent on the destruction process. 5,29 Here, the relative absorbance intensity of the ketone group corresponding to 1711 or 1715 cm 21 to that of standard band is known as ketone carbonyl index (IK) and calculated by the following equation.…”

“…5 When compared with other commonly used polymers, the isotactic boPP film has a range of remarkable properties such as good water barrier properties, 1 good elastic properties under short-time action, low specific density ($0.92 g/cm 3 ), high chemical resistance, almost zero hygroscopicity, and good dielectric properties. 5 From the structural point of view, isotactic polypropylene (i-PP) can be divided into a, b, and c phases. a-iPP phase is the most common crystalline form.…”

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.…”