Fourier‐transform infrared studies of polypropylene during mechanical deformation

Abstract

AbstractQuantitative Fourier‐transform infrared (FTIR) measurements of frequency shifts Δν and absorbance profile asymmetry are reported for various polypropylene samples as a function of uniaxial stress σ. Generally, it was found that the frequency shift coefficient αχ, defined by Δν = αχσ, depended on stress rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, draw ratio, λ, molecular orientation f, tensile modulus E, and annealing conditions. With annealing, αχ decreased with increasing shrinkage in the case of highly oriented isotactic PP. The αχ values for the “helix bands” were less affected than those for the “liquid bands.” With increasing \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, generally αχ increased to an apparent asymptotic limit. With increasing λ, f, or E, αχ also increased from αχ ≃ 0 for λ = 1 (spherulitic) to maximum values for highly oriented isotactic PP. The observed variations in αχ can be interpreted in terms of the changes in the peak position and shape of the nonuniform molecular stress distribution. Analogous behavior with x‐ray diffraction peaks obtained for polymers under stress is discussed.