Rheological Link Between Polymer Melts with a High Molecular Weight Tail and Enhanced Formation of Shish-Kebabs

Abstract

Presence of an ultra high molecular weight (UHMw) fraction in flowing polymer melts is known to facilitate formation of oriented crystalline structures significantly. The UHMw fraction manifests itself as a minor tail in the molar mass distribution and is hardly detectable in the canonical characterization methods. In this study, alternatively, we demonstrate how the nonlinear extensional rheology reveals to be a very sensitive characterization tool for investigating the effect of the UHMw-tail on the structural ordering mechanism. Samples containing a UHMw-tail relative to samples without, exhibit a clear increase in extensional stress that is directly correlated with the crystalline orientation of the quenched samples. Extensional rheology, particularly, in combination with linear creep measurements, thus, enables the conformational evolution of the UHMw-tail to be studied and linked to the enhanced formation of oriented structures.

Flow induced crystallization prevents melt fracture of HDPE in uniaxial extensional flow

“…The linear rheology was characterized in small angle oscillatory shear (SAOS) using an Ares G2 (TA Instruments) with 8 mm parallel plate geometry and creep using an MCR702 (Anton Paar). The creep data obtained at 150 C were inverted initially to storage and loss compliance [18] and then to storage and loss moduli as described by Wingstrand et al [19] (see also M€ unstedt and coworkers [20,21]). Inverted creep data and the frequency sweeps from SAOS obtained at 140-190 C were combined using the time temperature superposition principle (TTS) to obtain master curves of dynamic moduli over a wide range of frequencies.…”

Polymer Crystallization Studied by Hyphenated Rheology Techniques: Rheo‐NMR, Rheo‐SAXS, and Rheo‐Microscopy

“…The latter set‐up was used in the experiments presented here, and furthermore by other researchers to study block copolymers, platelet dispersions, and colloidal systems . Recently, hyphenations of extensional rheometers and X‐ray scattering techniques were used by Yan et al., Liu et al., and Wingstrand et al . to reveal the interplay of structural buildup and elongation rheology during flow‐induced polymer crystallization.…”

“…The semi-crystalline morphology of polymers depends highly on the molecular-weight distribution, chain topology, stereo-and regio-regularity, additives, and crystallization conditions. [5][6][7][8][9][10] In injection molding, film blowing, or fiber spinning, polymer melts are crystallized under strong flows which has a strong impact on the resulting micro-structure of the materials…”

Effect of carbon nanotube addition on structure and properties for extrudates of high‐density polyethylene

“…Therefore, the prompt formation of shish accelerates the whole crystallization rate. This can be achieved by adding a high‐molecular‐weight fraction with a Rouse relaxation time that is longer than the inverse of the strain rate . As well as high‐molecular‐weight components, fibrous nucleating agents also behave like “shish,” greatly affecting the processability, structure, and properties of the polymer in the solid state …”

“…This can be achieved by adding a high-molecular-weight fraction with a Rouse relaxation time that is longer than the inverse of the strain rate. [11][12][13][14][15][16][17] As well as high-molecular-weight components, fibrous nucleating agents also behave like "shish," greatly affecting the processability, structure, and properties of the polymer in the solid state. [18][19][20][21] In the present study, we focused on the strong nucleating ability of multi-walled carbon nanotubes (MWCNTs) in high-density polyethylene (HDPE).…”