Structural Evolution of Tensile-Deformed High-Density Polyethylene during Annealing:  Scanning Synchrotron Small-Angle X-ray Scattering Study

Abstract

The structural evolution of high-density polyethylene subjected to uniaxial tensile deformation was investigated as a function of strain and after annealing at different temperatures using a scanning synchrotron small-angle X-ray scattering (SAXS) technique. The results confirm that in the course of tensile deformation intralamellar block slips were activated at small deformations followed by a stress-induced fragmentation and recrystallization process yielding thinner lamellae with their normal parallel to the stretching direction. The original sheared lamellae underwent severe internal deformation so that they were even less stable than the newly developed thinner lamellae. Accordingly, annealing results in a melting of the original crystallites even at moderate strains where the stress-induced fragmentation and recrystallization just sets in and generates a distinctly different form of lamellar stacks aligned along the drawing direction. It was found that the lamellae newly formed during stretching at moderate strains remain stable at lower temperature. Only at a very high annealing temperature of 120 °C can they be melted, leading to an isotropic distribution of the lamellar structure.

Tensile Deformation of Oriented Poly(ε-caprolactone) and Its Miscible Blends with Poly(vinyl methyl ether)

“…As discussed in our previous investigations, for a semiquantitative discussion of the dependence of the long spacing on the strain, the type of data treatment (Lorentz correction versus no correction) plays only a subordinate role. [26][27][28] Consequently, Lorentz-corrected scattering curves were applied in the present work to evaluate the microstructural parameters. The average thicknesses of the crystalline lamellae and amorphous layers measured along the stretching direction can be derived from the one-dimensional electron density correlation function K(z) as follows: [41][42][43][44][45] …”

“…The characteristics of the evolution of the microstructure in the systems during stretching follow a common scheme as discussed before for isotropic semicrystalline polymers. 27,28,40 Figure 13 presents the variation of SAXS diagrams with strain for the skin layers of micro-molded mixtures. As can be seen, the SAXS pattern shows a highly anisotropic scattering distribution prior to deformation indicating an oriented lamellar structure along the flow direction.…”

“…1,[19][20][21][22][23] The behavior of the polymers during stretching is generally influenced by both the crystalline and the amorphous phases. 12,[24][25][26][27][28] The small-deformation properties are found to depend only on the nature of crystalline lamellae; whereas the ultimate properties are dominated by the entangled amorphous network. 11,13,25 Poly(ε-caprolactone) (PCL) is a biodegradable polymer, which can form homogeneous mixtures in the melt and solution with a wealth of other noncrystallizable compounds, including poly(vinyl methyl ether) (PVME), 24,29 poly(styrene-co-acrylonitrile), 30,31 and poly(vinyl chloride).…”

Application of catastrophe theory to neck initiation of metallocene-catalyzed high-density polyethylene

“…29 As the cubic cluster units are assumed to be rigid, the current model has no ability to describe the changes in long spacing and lamellar thickness. The compression of cubic cluster units and deformation within the cubic units may need to be taken into account under close packing and rearrangement of cubic units during necking.…”

Influence of deformation temperature on structural variation and shape-memory effect of a thermoplastic semi-crystalline multiblock copolymer

“…Influence of deformation temperature on structural variation and shape-memory effect of a thermoplastic semi-crystalline multiblock copolymer The deformation temperature (T deform ) has significant effects on deformation behaviors of semi-crystalline polymers on the microscopic and macroscopic scale [9,10], with structural variations during the deformation playing a dominant role in determining their mechanical properties [11,12]. It also has been reported that T deform can affect the SME of semicrystalline MBCs, i.e., if the samples are deformed at a temperature lower than the thermal transition temperature (T trans ) of switching domains, reduction in fixity ratio (R f ) and switching temperature (T sw ) can be observed as well as a higher maximum stress (!…”