Elastic constants of lamellar and interlamellar regions in α and mesomorphic isotactic polypropylene by AFM indentation

Abstract

A study of the nanoscale mechanical properties of isotactic mesomorphic and semi‐crystalline polypropylene (iPP) is presented. Two iPPs produced with metallocene and Ziegler‐Natta catalyst polymerization are used. The resulting fibers are characterized by wide angle X‐ray scattering, small‐angle X‐ray scattering (SAXS), and Raman spectroscopy. The spatial variability of the percentage crystallinity is evaluated based on the SAXS data. AFM indentation is performed to measure the elastic modulus of the fibers in the direction perpendicular and parallel to the fiber axis. Since the AFM probing is performed on a scale larger than the lamellar thickness, a statistical analysis of the AFM and SAXS data is necessary to infer the elastic moduli of the α crystals and of the inter‐lamellar regions. The elastic modulus of the crystalline lamellae in the direction perpendicular to the c‐axis of the α crystal probed in compression is estimated at approximately 3.3 GPa, while the effective modulus of the interlamellar regions ranges from 1.5 to 2.2 GPa. The method proposed can be applied to other material systems with similar layered structure to measure elastic moduli or hardness on length scales smaller than the resolution of the indentation test. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43649.

Fundamental influences of propylene‐based elastomer on the foaming properties of high melt strength polypropylene based on extrusion foaming

“…[ 45–48 ] The actual intensities of each band, I 808 , I 830 , and I 840 , were obtained by curve fitting frequencies in the 800–850 cm −1 range using the Lorentzian/Gaussian procedure. So, the fractions of helical crystalline ( X c ), nonhelical ( X a ), and helical defect ( X m ) phases were computed using the following equations [ 47–50 ] : The crystallization process of pure HMS‐PP and HMS‐PP/PBE 6102 blends was further investigated by a JEM‐3010 transmission electron microscope (TEM, JEOL, Japan) at 15 kV in TEM mode. The samples were first annealed at 190°C for 10 min and then compression molded into a standard sentmanat extensional rheometer (SER) bar.…”

“…A temperature ramp was performed on the polypropylene samples to melt and recrystallize, and the whole process was followed by confocal Raman spectroscopy. [45][46][47][48] The crystallization, crystallinity, and crystallization kinetics of HMS-PP, 15% 6102 and 15% 3020, were further analyzed. [47] All three samples were firstly annealed at 200 C, then fast cooling to 145 C to study the isothermal crystallization.…”

“…The 808 cm À1 band was assigned to the helical crystalline phase, the 840 cm À1 band was assigned to the helical isomeric defect phase, and a broader band at 830 cm À1 was assigned to the non-helical phase. [45][46][47][48] The actual intensities of each band, I 808 , I 830 , and I 840 , were obtained by curve fitting frequencies in the 800-850 cm À1 range using the Lorentzian/Gaussian procedure. So, the fractions of helical crystalline (X c ), nonhelical (X a ), and helical defect (X m ) phases were computed using the following equations [47][48][49][50] :…”

Injection Molding of Low-Density Polyethylene (LDPE) as a Model Polymer: Effect of Molding Parameters on the Microstructure and Crystallinity

“…The ratio of the crystalline to amorphous regions influences the different physical properties, such as mechanical, thermal, surface, and hardness [ 13 , 14 ]. Consequently, several works have qualitatively related this ratio with the final measured properties [ 10 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Zheng et al [ 6 ] employed X-ray diffraction (XRD) to calculate the intensities ratio of the amorphous halo to the most intense diffraction peak of LDPE hot-pressed at different conditions.…”

“…Wang et al [ 21 ] demonstrated by XRD and DSC that, even though polyethylene terephthalate (PET) may act as a nucleating site for the crystallization of LDPE, the addition of recycled PET did not affect the crystal form of LDPE. Picu and Osta [ 20 ] determined the elastic modulus by AFM indentation of isotactic polypropylene (iPP) spun fibers cooled at a high cooling rate (>100 °C/min). They found that the modulus was 52% lower when measured in the axial direction of the fiber than that measured in the transversal direction.…”