Rheooptical Fourier transform infrared spectroscopy of the deformation behavior in quenched and slow‐cooled isotactic polypropylene films

Abstract

Emerging technological applications for complex polymers require insight into the dynamics of these materials from a molecular and nanostructural viewpoint. To characterize the orientational response at these length scales, we developed a versatile rheooptical Fourier transform infrared (FTIR) spectrometer by combining rheometry, polarimetry, and FTIR spectroscopy. This instrument is capable of measuring linear infrared dichroism spectra during both small-strain dynamic deformation and large-strain irreversible deformation over a wide temperature range. The deformation response of quenched and slow-cooled isotactic polypropylene (iPP) is investigated. In quenched iPP, under dynamic oscillatory strain at an amplitude of ϳ0.1%, the dichroism from the orientation of the amorphous chains is appreciably less than that from the crystalline region. At large irreversible strains, we measured the dichroic response for 12 different peaks simultaneously and quantitatively. The dichroism from the crystalline peaks is strong as compared to amorphous peaks. In the quenched sample, the dichroism from the crystalline region saturates at 50% strain, followed by a significant increase in the amorphous region dichroism. This is consistent with the notion that the crystalline regions respond strongly before the yield point, whereas the majority of postyielding orientation occurs in the amorphous region. Our results also suggest that the 841 cm Ϫ1 peak may be especially sensitive to the 'smectic' region orientation in the quenched sample. The response of the slow-cooled sample at 70°C is qualitatively similar but characterized by a stronger crystalline region dichroism and a weaker amorphous region dichroism, consistent with the higher crystallinity of this sample, and faster chain relaxation at 70°C.

In situ near-infrared spectroscopic studies of the structural changes of polyethylene during melting

“…Peaks at 1728 and 1764 nm for LDPE and LLDPE are broadened in comparison to those for HDPE, which led us to conclude that the two predominant peaks include shoulder peaks associated with chain branching. According to our previous estimation of CH 3 -stretching IR absorptions, the first CH 3 stretching overtone vibration occurs in this region. 21 To assign NIR bands to PE, we measured NIR spectra of various linear alkane solvents from hexane to tetradecane, along with molten HDPE.…”

“…In situ Fourier transform infrared spectroscopic studies of the conformational changes of semicrystalline polymers such as PE and polypropylene have been conducted. [1][2][3] The mid-infrared region from 2500-25 000 nm is diagnostic for these polyolefins. However, the very high absorption in the mid-infrared region makes it difficult to assign spectra for industrial polyolefin bulk specimens; very thin films are usually required.…”

Degradation study of polypropylene (PP) and bioriented polypropylene (BOPP) in the environment

“…Fourier Transform Infrared (FTIR) Spectroscopy was utilized to identify various functional groups that emerged in the samples, as well as the disappearance of determinate groups 42,43 . Structural analysis on transparent PPv, PPa, BOPPv and BOPPa films retrieved from the landfill after 11 months burial showed new absorption regions, displayed in Figure 3.…”

“…The incidence of absorbance measured in the regions 872, 741, 695 and 614 cm -1 may possibly signal changes in crystallinity on the buried PP. spectrum bands belong to the group of regularity bands, and are related to different helix lengths of isotactic sequences 43,44 . However, the peaks at 973, 1377, and 1454 cm -1 represent segments residing predominantly in the amorphous region 44 .…”

Multi-walled carbon nanotubes effect in polypropylene nanocomposites

“…Figure 2 presents the spectra of the isotactic PP in comparison with the samples nanofilled with 2 and 4 % of mass fractions of MWCNT. All the spectra present the characteristic peaks of PP: -CH 2 and -CH 3 stretching vibrations (2800-2950 cm -1 ) 9 , -CH 3 and -CH 2 bending (1376, 1456 cm -1 ) 10,11 , and C-CH 3 stretching (841 cm -1 ) 10 .…”