Polyethylene shish-kebabs

FIG. 19.16 Electron micrograph of polyethylene shish kebabs . From Pennings et al. (1970). 

Figure 6 (a) Sketch of the chain arrangement in shish-kebab structures. Reproduced from [67] with permission, (b) Polyethylene shish-kebabs crystalled from solution [68]. Reproduced with permission from H. D. Keith, 1996 American Institute of Physics, (c) Mannan-lamellae, epitaxially grown on cellulose fibres [69]. Reproduced from H. Chanzy, reprinted with permission from John Wiley Sons, Inc. 

Fig. 4 Electron diffraction micrograph of polyethylene shish-kebab structure. (From Ref.Pf)...

Hobbs J K and Miles M J (2001) Direct observation of polyethylene shish-kebab crystallization using in situ atomic force microscopy. Macromolecules 34 353-355. 

Hobbs JK, Miles MJ. Direct observation of polyethylene Shish-Kebab crystallization using in-sim atomic force microscopy. Macromolecules 2001 34(3) 353-5. 

Figure 8.7. (a) Idealised view of a shish-kebab structure (after Pennings ei cil. 1970, Macklcy and Keller 1975). (b) Shish kebabs generated in a llowing solution of polyethylene in xylene (after... 

T. Tao, L. Zhang, J. Ma, C. Li, Production of flexible and electrically conductive polyethylene-carbon nanotube shish-kebab structures and their assembly into thin films, Ind. Eng. Chem. Res, vol. 51, pp. 5456-5460, 2012. 

By variation of the conditions of crystallization (see Sect. 1.3.3.3) polyethylene can be obtained either as folded lamellae, as extended chain crystals (high strength fiber), or as so-called shish kebabs (fibrils with a morphology similar to cellulose). All these variants differ in properties. 

De Gennes scaling concepts for polymer solutions and melts and the concept of reptation movement of polymer chains in melts Pennings discovery of chain extension and shish-kebab formation in stirred solutions of very high MW polyethylene this eventually led to the ultra-high modulus gel-spinning process of polyethylene... 

FIG. 19.1 Morphological models of some polymeric crystalline structures. (A) Model of a single crystal structure with macromolecules within the crystal (Keller, 1957). (B) Model of part of a spherulite (Van Antwerpen, 1971) A, Amorphous regions C, Crystalline regions lamellae of folded chains. (C). Model of high pressure crystallised polyethylene (Ward, 1985). (E) Model of a shish kebab structure (Pennings et al., 1970). (E) Model of paracrystalline structure of extended chains (aramid fibre). (El) lengthwise section (Northolt, 1984). (E2) cross section (Dobb, 1985). 

This development started with an observation of Pennings and Kiel (1965) that, when dilute solutions of polyethylene were cooled under conditions of continuous stirring, very fine fibres were precipitated on the stirrer. These fibres had a remarkable morphology a fine central core of extended CH2-chains, with an outer sheath of folded chain material. Electron microscopy revealed a beautiful "shish kebab" structure (see Fig. 19.16). Shish kebabs have also been observed in experiments without any stirring. For example, by washing polyethylene powder with xylene (Jamet and Perret, 1973) and by crystallising nylon 4 from a glycerol/water mixture (Sakaoku et al., 1968). 

Production. Recognition that the shish-kebab fibers produced by the surface-growth procedure result from the deformation of a gel-like entangled network layer at the rotor surface led to the development of gel-spun polyethylene fibers. The fiber is made by the solution spinning method. The polymer is... 

Jandt, K.D. Buhk, M. Miles, M.J. Petermann, J. Shish-kebab crystals in polyethylene investigated by scanning force microscopy. Polymer 1994, 35, 2458. 

Information on how orientation during melt crystallization affects the transport properties of polymers is sparse however, increases in the permeability have been attributed to the "shish kebab" morphology (ill). Most of the work involving barrier properties of oriented semicrystalline polymers has dealt with materials drawn at temperatures well below the melting point. The transport properties of cold-drawn polyethylene (34f 42-46), polypropylene (42,42), poly(ethylene terephthalate) (12,42-4 9), and nylon 66 (22) among others have been reported. 

If crystallisation occurs in an oriented melt, then non-spherulitic microstructures can form, with preferred orientation of the crystals (Section 3.4.10). Fibrous nuclei, believed to contain fully extended polymer chains, can form in an oriented melt. Figure 6.7a shows several fibrous nuclei, in a polyethylene injection moulding, aligned with the flow direction. On either side of these dark nuclei is a bright layer, where lamellar crystals have grown from the nucleus. The c axes of the lamellar crystals are parallel to the fibrous nucleus the microstructure of platelet crystals skewered by a rod-like nucleus has been described as a shish kebab. The rest of the microstructure consists of small spherulites. 

Mullin N, Hobbs J (2011) Direct imaging of polyethylene films at single-chain resolution with torsional tapping atomic force microscopy. Phys Rev Lett 107 197801 Murase H, Ohta Y, Hashimoto T (2011) A new scenario of Shish-Kebab formation from homogeneous solutions of entangled polymers visualization of structure evolution along the fiber spinning line. Macromolecules 44 7335-7350... 

The use of Small-Angle Neutron Scattering (SANS) has been exponentially increasing for the study of polymers, largely of elastomers and nanopolymers, for the last 40 years [198]. Matsuba et al. [199] worked on an isotropic blend of deuterated PE and hydrogenated polyethylene (HPE 3 wt%) during uniaxial drawing at 125°C to understand the formation mechanism of the shish kebab from the isotropic film. In the early... 

Because of epitaxy matching, carbon nanotubes are good nucleating agent for linear polyethylene. The presence of single-walled carbon nanotube, SWCNT, accelerates the crystallization kinetics of polyethylene not only in the qiriescent conditions but also at the relatively low shear rates. For the low shear (<50/s), the shish-kebab structure that is formed due to the chain orientation is enhanced by the presence of SWCNTs. ... 

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