Shish-kebab Formation Research Articles

Superior Reinforcement in Melt-Spun Polyethylene/Multiwalled Carbon Nanotube Fiber through Formation of a Shish-Kebab Structure

The formation of a shish kebab (SK) structure, where carbon nanotubes (CNTs) serve as shish and polymer lamellae serve as kebab, is particularly interesting and provides a novel way to enhance the polymer-CNT interface. A fine SK structure is achieved through melt spinning. High density polyethylene and pristine CNTs were first compounded in an extruder. The compound was then spun into fibers with different draw ratios with the aid of a capillary rheometer. The crystalline structure and mechanical behavior were characterized by scanning electron microscopy, differential scanning calorimetry, two-dimensional wide-angle X-ray scattering, polarized Raman spectroscopy, and tensile testing. An increase in tensile strength as high as 3 times has been achieved in the fiber. The formation of SKs is considered as the main mechanism responsible for the enhanced interfacial interaction and excellent tensile property.

A New Scenario of Flow-Induced Shish-Kebab Formation in Entangled Polymer Solutions

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTA New Scenario of Flow-Induced Shish-Kebab Formation in Entangled Polymer SolutionsTakeji Hashimoto*†§⊥, Hiroki Murase*†‡, and Yasuo Ohta*‡View Author Information† Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan‡ Research Center, TOYOBO Co., Ltd., 2-1-1 Katata, Ohtsu-shi, Shiga 520-0292, Japan§ Advanced Science Research Center (ASRC), Japan Atomic Energy Agency (JAEA), Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan,*Corresponding authors. E-mail: [email protected] (T.H.), [email protected] (H.M.), [email protected] (Y.O.).⊥Professor Emeritus, Kyoto University, JapanCite this: Macromolecules 2010, 43, 16, 6542–6548Publication Date (Web):July 27, 2010Publication History Received4 March 2010Revised20 July 2010Published online27 July 2010Published inissue 24 August 2010https://doi.org/10.1021/ma100496gCopyright © 2010 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1560Altmetric-Citations59LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (2 MB) Get e-AlertsSUBJECTS:Crystallization,Optical properties,Phase separation,Polymer solutions,Transmission electron microscopy Get e-Alerts

Hierarchical Orientational Relaxation Inducing Shish-Kebab Formations in Polymer Melt Crystallization

We studied athermal relaxation of bulk extended chains by means of dynamic Monte Carlo simulations, and we got intermediately relaxed melts with a memory of chain orientations but no more crystalline order. The orientational memory in the melts dominated the crystal orientation and nucleation types. The difference in crystallization behaviors induced by orientational relaxation suggested the mechanism of hierarchical crystallization. Thus, we studied the isothermal crystallization of a binary blend of different relaxed chains. We observed the prior crystallization of less relaxed chains could act as a shish to induce epitaxial crystallization of more relaxed chains to form kebabs. This mechanism had demonstrated the structure of precursors and gave insight into the formation of shish-kebab crystals in polymer melts. The results suggested that in flow-induced polymer crystallization the hierarchical orientational relaxation of chains decided the formation of shish-kebabs.

Control of Structural Morphology in Shear-Induced Crystallization of Polymers

Critical examination finds that the longest chains play a catalytic role in the formation of shish kebabs recruiting other chains into the formation of this morphology. The longest chains in an ensemble are stretched by shear flow to form the “shish” upon which the bulk of the material crystallizes as “kebabs”. A universal parameter for the formation of shish kebab structures, the specific mechanical work, and a method by which it may be measured for any given ensemble of polymers is provided. In rotating parallel-plate flow a clear boundary is observed between oriented and unoriented material which is dependent on both the shear rate and the total strain. It has been found that the necessary conditions for the formation of oriented nuclei is that the shear rate should be larger than the inverse Rouse time of the longest chain in the ensemble and that mechanical work above a critical threshold is required. The experimental procedure required to make such measurements, and the precautions necessary to avoi...

Orientation in high-density polyethylene/inorganic whisker composite fibers as studied via polarized Fourier transform infrared spectroscopy

In this article, a quantitative measurement of orientation functions for both the polymer matrix and the filler has been carried out, for the first time, in high-density polyethylene (HDPE)/inorganic whisker (SMCW) composite fibers, with aid of polarized Fourier transform infrared (FTIR) spectroscopy. A highly oriented structure was observed in the as-spun fibers, and the orientation functions of both polyethylene and the whisker decreased with the increase of whisker content. During tensile deformation of the fibers, the orientation functions were continuously enhanced as increasing of the strain for the matrix and the filler. However, a fast increase of orientation was found for pure polyethylene fiber and composite fibers with less whisker content, and a slow increase for composite fibers with higher whisker content. Very interestingly, a formation of hybrid shish-kebab structure with whisker acting as shish and polyethylene lamellae as kebab was observed in the as-spun fiber with low loading of whisker (less than 10 wt.%), resulting in a strong interfacial interaction between polyethylene and whisker. As a result, the highest tensile strength was observed in this sample even it had a lower orientation compared with that of pure HDPE. For the composite fiber with 10 and 20 wt.% whisker, no obvious formation of hybrid shish-kebab was observed, resulting in a poor interfacial interaction and subsequently, lower tensile strength. That result indicates that the tensile strength of the fibers depends not only on the orientations of the polyethylene and the whisker, more importantly, on the interfacial interaction between matrix and the filler. The change of orientations of the composite fibers by adding whisker and the formation of hybrid shish-kebab structure were discussed based on rheological measurement.

Critical Strain for Shish-Kebab Formation

A combination of extensional rheological and in situ synchrotron radiation small-angle X-ray scattering (SR-SAXS) measurements was introduced to investigate critical strain ε* for shish formation and validate whether coil−stretch transition or stretched-network is responsible for shish-kebab formation in high density polyethylene melt. With strain rates ε̇ larger than a specific value, the critical strain ε* required to induce shish formation turns out to be a constant of about 1.57, which ensure full extension of chain segments with critical entanglement molecular weight locked between two adjacent entanglement points. The results clearly demonstrate that the formation of shish-kebab in polymer melt stems from stretched network instead of coil−stretch transition.

Direct Formation of Nanohybrid Shish-Kebab in the Injection Molded Bar of Polyethylene/Multiwalled Carbon Nanotubes Composite

The formation of a nanohybrid shish-kebab (NHSK) superstructure, in which fibrillous carbon nanotubes (CNTs) act as shish while polymer lamellae act as kebab, is a novel way to bond the polymer and CNTs together and was first observed in the solution crystallization of polyethylene in the presence of CNTs. In this work, a direct formation of nanohybrid shish-kebab in the injection molded bar of high-density polyethylene (HDPE)/multiwalled carbon nanotubes (MWCNTs) composite, has been achieved, via a so-called dynamic packing injection molding technology (DPIM), in which oscillatory shear field was imposed on the gradually cooled melt during the packing solidification stage. Interestingly, whatever the long axis of CNTs is perpendicular to or parallel to the shear flow direction, the lamellae of PE is always perpendicular to long axis of CNTs. The three-step mechanism, including (1) the disentanglement and orientation of both PE and CNTs, (2) PE folded-chain lamellae directly nucleated on CNTs surface and/or first formation of PE extended-chain shish directly on CNTs surface then followed by nucleation of folded-chain lamellae, and (3) the crystallization of PE kebabs on the PE decorated CNTs fibrils, was proposed to understand the formation of NHSK under effect of shear. Importantly, the NHSK structure can bring significant mechanical reinforcement in the HDPE/MWCNTs composite. For the oriented composites containing 5% MWCNTs, its tensile strength is increased by 150% and 270%, compared to the oriented pure HDPE and the isotropic composites containing 5% CNTs, respectively; meanwhile, its Young’s modulus is enhanced by 130% and 180%, compared to the oriented pure HDPE and the isotropic composites containing 5% CNTs, respectively. This work is the first to enlarge the theoretical value and application potential of NHSK structure in the crystallizable polymer/CNTs composite.

Unusual Tuning of Mechanical Properties of Isotactic Polypropylene Using Counteraction of Shear Flow and β-Nucleating Agent on β-Form Nucleation

Isotactic polypropylene (iPP) has good comprehensive properties, viz. easy processing, high heat resistance, and good stiffness, etc., and in turn is widely used as a commodity plastic. However, under conventional processing conditions, iPP crystallizes into sizable spherulites with few tie molecules between spherulites. With such a crystalline texture, iPP exhibits very low impact toughness, especially at lower temperature, which restricts its more extensive application. Therefore, toughening of iPP has always been an open research. Up to now, four routes have been taken to improve impact strength of iPP, including copolymerizing with other olefin monomers, blending with rubber or thermoplastic elastomer, compounding with organic or inorganic fillers (e.g., nanoparticles), and adding β-nucleating agent. Without doubt, the modified iPP, more or less, increases its toughness. The enhancement of toughness is, unfortunately, at sacrifice of other properties, e.g., strength, heat resistance, etc. There are extremely few successful examples for simultaneously efficiently reinforcing and toughening iPP. It has been well established that for iPP oriented crystals (i.e., shish-kebabs) can bring out notable reinforcement on iPP, while β-form crystals of iPP can greatly increase its toughness. Flow (shear, elongational, or mixed) would induce formation of shish-kebabs whose content is governed to shear rate, shear duration, and molecular species and weight, etc. On the other hand, β-form crystals can be high production generated by addition of β-nucleating agent under quiescent conditions. This type of iPP crystals causes high toughness due to the β-R polymorphous transition and the loose structure of β-form crystals compared with R-crystals in favor of absorbing impact energy. Naturally, an idea arises that combination of flow-induced molecular orientation crystallization and β-nucleant-induced β-form crystals produces efficient reinforcement and toughening on iPP. However, as a matter of fact, there is not any example of it in the open literature. Themajor reason is that the coexistence of a β-nucleating agent and a shear flow at above a certain but low level of shear rate depresses β-form nucleation. Huo et al. performed a delicate study on iPP crystallization with β-nucleating agent and observed that as the shear rate rises, the content of β crystals constantly reduces, more greatly for higher nucleating agent content, showing counteraction between shear and β-nucleating agent for β-form formation. Apparently, it is a great practical challenge to prepare iPP parts withhighmolecular orientation and highβ-crystal proportion for the purpose of both strength and toughness enhancement. In the present work, we attempt to fabricate iPP with considerably increased strength and toughness, for the first time, utilizing the counteraction of shear-induced orientation crystallization and β-nucleating agent on β-form nucleation. The crystallization process of iPP is manipulated by two stages: one is flow-induced crystallization for high molecular orientation, and the other is β-nucleating-agent-induced nucleation for highβ-crystal content. More specifically, the oscillation shear supplied by an oscillation shear injectionmolding (OSIM) (its detailed definition is included in the Experimental Section) is imposed on β-nucleated iPP melt in the mold during injection molding. Initially, due to occurrence of shear flow and β-nucleating agent, β-form formation is restrained; thereby, the oriented R-crystals first form in the skin and intermediate layers of the sample.When the gate of the mold freezes, the shear ceases, and hereby, β-nucleating agent revives. The remainder of iPP melt in the core layer undergoes β-nucleation-induced crystallization. The results demonstrate that a large amount of shish-kebab structure appears in the surface and intermediate layers of the sample; at the same time, numerous β-form crystals form in the core layer, thus leading to prominent reinforcement and toughening for iPP.

Study on the Improvement of Crystallization in HDPE Induced by High–Molecular-Weight Polyethylene Through Dynamic Packing Injection Molding

The effect of high–molecular-weight polyethylene (HMWPE) on crystal morphology was investigated for high-density polyethylene (HDPE) through dynamic packing injection molding (DPIM). With the aid of differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), and scanning electron microscopy (SEM) measurements, a typical web-like shish kebab morphology, which markedly increases stiffness and toughness, was found in HMWPE-induced samples through DPIM. The SEM results show that the much better web-like shish kebab structure, in which most of the lamellae connect different columns, compared with conventional shish kebab, was formed in HDPE blends with 4% HMWPE content (B4) through DPIM. The WAXD studies indicate that orientation degrees of crystallographic planes (110) and (200) in the B4 samples were much higher than those of samples molded by static packing injection molding and B0 samples molded by DPIM. A combination of the higher degree of crystal orientation and the formation of web-like shish kebab led to simultaneous great increments of stiffness and toughness, which overcomes the traditional limitation that stiffness and toughness cannot be greatly enhanced simultaneously. All these results show that HWMPE favored for great improvement of crystal structures in HDPE when its content is appropriate through DPIM.

Formation and Stability of Shear-Induced Shish-Kebab Structure in Highly Entangled Melts of UHMWPE/HDPE Blends

The formation and stability of a shear-induced shish-kebab structure was investigated by in situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide-angle X-ray diffraction) measurements of highly entangled polyethylene melts based on two polymer blends, containing small fractions (2 and 5 wt %) of ultra-high molecular weight polyethylene (UHMWPE) and high-density polyethylene (HDPE). Immediately after shear, the combined SAXS and WAXD results at 142 °C confirmed the sole formation of shish without kebabs, indicating the interplay between the topological deformation of highly entangled UHMWPE chains and the extended-chain crystallization of stretched segments without the participation of coiled segments. The presence of HDPE chains influenced the entanglement of UHMWPE but they were not involved in the shish-kebab formation at the initial stage of crystallization. The final shish lengths in both blends were nearly identical at the same strain (ε = 500), even though the UHMWPE concentration was different. When the temperature was cooled to 134 °C, both sheared blends exhibited the kebab formation, following the diffusion-controlled growth process. Although the total kebab nucleation was higher in the 5/95 wt % UHMWPE/HDPE blend, the kebab density per shish was higher in the 2/98 wt % UHMWPE/HDPE blend. The thermal stability of the shish-kebab structure was also investigated by constrained melting. Both blends exhibited identical melting behavior of kebabs but different melting behavior of shish that is governed by the entanglement restraints of the stretched-chain network.

Quantum Beam Studies on Polymer Crystallization under Flow

One of the longstanding issues in polymer science is crystallization of polymers under flow, especially formation of the so-called shish-kebab. Recent progress in quantum beam technology shed light on the substantial nature in the shish-kebab formation. In this paper we review our recent experiments on polymer crystallization under flow using time-resolved depolarized light scattering, small-angle and wide-angle X-ray scattering and small-angle neutron scattering in a wide spatial scale from 0.1 nm to several tens μm. These studies revealed that the shish-kebab formation is governed by a competition between the crystallization rate and the chain relaxation rate. Small-angle neutron scattering study on an elongated blend of deuterated low molecular weight and protonated ultra-high molecular weight polyethylenes showed that a long cylindrical object 2 μm in diameter and 12 μm in length was formed from deformed network of ultra-high molecular weight chains, which included three shishs (or extended chain crystals) 9 nm in diameter.

Crystallization of Polyethylene Blends under Shear Flow. Effects of Crystallization Temperature and Ultrahigh Molecular Weight Component

We performed small-angle X-ray scattering (SAXS) measurements on crystallization processes of polyethylene blends of low molecular weight and ultrahigh molecular weight components with various blending ratios in order to clarify effects of ultrahigh molecular component on shish-kebab structure formation. Anisotropic scattering patterns due to kebab structure formation were observed above a certain concentration of ultrahigh molecular weight polyethylene. The critical concentration was about ∼0.1 wt % independent of the crystallization temperature below 125 °C, while it increased with the crystallization temperature above 125 °C. Analyzing the correlation between ultrahigh molecular weight component concentration and crystallization temperature in more detail, these results suggest that both the crystallization rate and the relaxation rate of the ultrahigh molecular weight component have significant effects on the shish-kebab formation process.

The development of organized structures in polyethylene crystallized from a sheared melt, analyzed by WAXS and TEM

The development of global orientation and morphological features in linear polyethylene crystallizing from a sheared melt are studied using in-situ time-resolving wide angle X-ray scattering (WAXS) and ex-situ transmission electron microscopy. It is found that samples subjected to a shear rate above a critical value of ∼1 s −1 result in macroscopically oriented structures in the crystallized sample. This critical shear rate appears to be independent of the differences in molecular weight distribution of the samples studied although the morphologies which develop are sensitive to quite small differences in molecular weight distributions. The presence of shish kebabs in the morphology is shown to differ markedly according to variations in the upper molecular weight fraction of the molecular weight distribution, even though the resulting global orientation does not. The WAXS also reveals that areas which evidence no row nucleated structures still realize high degrees of molecular orientation. It is proposed that the formation of shish kebab or lamellar morphologies in these samples is dependent on the critical density of contiguous elongated crystallization nuclei rather than any specific global criteria.

The influence of the extraction process and spinning conditions on morphology and ultimate properties of gel-spun polyethylene fibres

The morphology of gel-spun polyethylene fibres prior to hot-drawing, depends on the spinning conditions and the extraction process. Paraffin oil containing fibres spun at relatively low spin temperatures and high take-up speeds show a c-axis orientation parallel to the fibre axis due to shish-kebab formation in the spinline. The extraction of the paraffin oil is accompanied by stresses leading to morphological changes. For fibres spun at low take-up speeds and/or high spin temperatures this leads to a craze-like disturbance and a preferential c-axis orientation perpendicular to the fibre axis. Fibres with this type of orientation exhibit an equatorial SAXS maximum corresponding to a periodicity of 12 nm ascribed to regular packing of 12 nm thick lamella oriented with the c-axis perpendicular to the fibre axis. The formation of extended chain crystals in the case of low spin temperatures and high take-up speeds is accompanied by the introduction of flaws, which have a deteriorating effect on the ultimate properties of the fibres.

Elastic flow instabilities and shish-kebab formation during gel-spinning of ultra-high molecular weight polyethylene

The flow behaviour during gel-spinning of semi-dilute solutions of ultra-high molecular weight polyethylene in paraffin oil was investigated in relation to fibre strength and morphology. Shish-kebab morphologies observed in the as-spun filaments originate from a solidification of long flow units already developed in the polymer solution during spinning. These flow units consist of alternating bundles of elongated molecules and highly entangled clusters of unoriented molecules. Extrudate stretching leads to a demolition of these long flow units by elastic flow instabilities. As a result, the tensile properties after hot-drawing of the fibres are strongly reduced. The inclusion of 1 wt% aluminium stearate in the spinning solution preserves the long bundle-like flow units even at high take-up speeds during extrusion. This additive suppresses the adsorption of the polyethylene on the die-wall and avoids the generation of elastic turbulences. Filaments with a strength between 2.5 and 3.0 G Pa can be obtained from these doped solutions after hot-drawing, in spite of high winding speeds up to 300 m min−1 in the spinning process.

Elastic flow instabilities and shish-kebab formation during gel-spinning of ultra-high molecular weight polyethylene

Elastic flow instabilities and shish-kebab formation during gel-spinning of ultra-high molecular weight polyethylene

The interaction of fluid mechanics and crystal growth in the formation of shish kebabs from solution

AbstractSeveral observations are made regarding the role of the fluid mechanics involved in the process of flow‐induced, fibrillar crystallization from solution. Computational evaluation and discussion of various flow effects in the nucleation step, including combined shear and extensional flows, are presented in terms of the elastic dumbbell model. These results indicate the important role extensional kinematics in the growth process. A qualitative evaluation of concentration effects is also given. The evaluation of facts concerning the growth morphology is presented in terms of a model for the growth process along with data concerning rinsing and quench rate effects on the morphology and inciting behavior of shish kebab crystals.

Shish kebab formation on polyethylene monofilaments

AbstractA study has been made on skin formation of melt spun polyethylene monfilaments, which were solidified in air or in cold solvents and non‐solvents. Application of air or non‐solvents, such as water and acetone, as cooling media induced spherulitic crystallisation of the polymer, as was revealed in the scanning electron microscope. When the flowing polyethylene melt was quenched in good solvents, a 0.5 mm thick layer of lamellar or shish kebab structures developed on the polymeric fibres. It was established that shish kebabs were formed when the solvents, in which the polymer filament was quenched, were boiling during this solidification process.