Rheo‐optical studies on the deformation mechanism of semicrystalline polymers. IV. On the nature of alpha mechanical dispersion of low density polyethylene in relation to the mechanism of spherulite deformation

Abstract

The dynamic mechanical and birefringence behavior of three kinds of test specimens, prepared from a low‐density polyethylene by different heat treatments, was investigated over the frequency range 0.008 to 4.3 Hz at various temperatures from 20 to 80°C. Reduction of both kinds of data to the common reference temperature of 50°C revealed rather broad frequency dispersions, corresponding to the α dispersion, with activation energies for the mechanical and optical relaxation processes of around 25 kcal/mole for all specimens. An annealed specimen was further investigated by dynamic x‐ray diffraction to determine the dispersions of crystal orientation and of lattice deformation. The mechanical and birefringence dispersions are associated with the dispersion of crystal orientation and with the relatively elastic nature of the lattice deformation. Thus, the mechanical dispersion could be assigned to an α1 mechanism arising from rotation of crystallites within the spherulites, i.e., a type of grain‐boundary phenomena, but not to an α2 mechanism resulting from a crystal disordering transition or premelting. Combining dynamic birefringence with dynamic crystal orientation, the mechanical α dispersion is further discussed in terms of dynamic orientation behavior of noncrystalline chain segments in order to elucidate the nature of the grain‐boundary phenomena in detail in relation to the dynamic deformation mechanism of the spherulitic crystalline texture, i.e., reorientation of “crystal grains” within orienting lamellae due to intralamellar shearing resulting from the paracrystalline nature of the lamellae. A mechanical model characterizing the grain‐boundary relaxation in association with the reorientation of the crystal grain is also proposed.

Rheo-Optical Studies on the Deformation Mechanism of Semicrystalline Polymers. XII. On the Nature of Alpha and Beta Mechanical Dispersions of High-Density Polyethylene in Relation to the Mechanism of Spherulite Deformation

“…In contrast to the strain-orientation coefficient function Ct, 22 to be positive or negative. Although the master curves are again the 'apparent' ones in the sense that the system has different orientation-retardation mechanisms, as suggested above, the following anomalies in the dynamic-orientation behavior must be noted: Die and Die' becoming opposite in sign as observed for Dt and Di at relatively high reduced frequencies, for Di at moderate frequencies, and for Dt at low frequencies; D~ and D; exhibiting a distinctive positive maximum and a slight negative minimum, respectively, at moderate frequencies, not of leveling off but of a change in sign with further decreasing frequency.…”

“…The dynamic crystal-orientation behavior of this bulk-crystallized high-density polyethylene is significantly different from that of a low-density polyethylene. 22 For the high-density polyethylene, the behavior at low reduced frequencies corresponding to the CJ. dispersion region is dominated in terms of the rotation of the crystal grains around the crystal b-axis in association with the lamellar detwisting mostly concentrated at the equatorial zone of spherulites.…”

Temperature dependence of the crystal lattice modulus and the Young's modulus of polyethylene

“…Sci., Polym. (44) Hashimoto, T.; Shibayama, M.;Kawai, H.;Watanabe, H.;Kotaka, T. Macromolecules 1983, 16, 361. Ed.…”

Polyethylene-polystyrene gradient polymers III. Mechanical and rheo-optical studies of relaxation processes

“…In the case of that polymer it has been shown that the spherulite size distribution and perfection of the spherulite structure strongly affect the nature of the relaxation process [1,2,4,11,12]. In the semicrystalline polymers, such a process is often characterized by the two components denoted by al and a2.…”