Crystals shish kebabs

Study of the Crystalline Regions. According to our morphological studies, the crystalline structure of UHMWPE pseudo-gel was different under different sample preparations. For example, spherulites and lamellar single crystal stacks were observed when the pseudo-gel was prepared under quiescent conditions, shish-kebab crystals under stirring conditions, and a mixture of single and shish-kebab crystals under uncontrolled conditions (10). 

Shish-kebab. In addition to spherulitic crystals, which are formed by plate- and ribbonlike structures, there are also shish-kebab crystals which are formed by circular plates and whiskers. Shish-kebab structures are generated when the melt undergoes a shear deformation during solidification. A typical example of a shish-kebab crystal is shown in Fig. 1.17. 

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. 

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

Fig. 10.19 Illustration of crystal morphologies of polymers influenced by the different degree of preload strain rates (percentage in the figure). The arrow indicates the direction of stresses. The right-hand schematic picture for shish-kebab crystals is adopted from Pennings et al. (1970)...

Structural constitution on a submicron scale as related to crystallinity, viz., crystalline unit cells, lamellae shape and size, and stress-induced shish kebab crystals. Computer system that stores, analyzes, and adjusts the controls of a machine based on the parameters established during the operation of the machine it is controlling. It continuously analyzes output data to adjust and maintain the machine s cycle within programmed limits. Can also store data and output it as directed by programming. 

The alignment of hybrid p-form shish-kebab crystals off the axial direction was achieved via the rotation extrasion system. As a resulL the PP pipes with enhanced toughness and hoop strength were made. The hoop strength and toughness of the PP pipe were 75% and 78% higher than in the case of conventional extrusion. ... 

Fig. 11. An AFM micrograph (phase image) showing a shish-kebab crystal of polyethylene in a matrix of molten poljmier. Image collected at 135°C. The bright area in the top right of the image is the glass substrate. The extended chain backbone and lamellar overgrowths can be clearly seen. The scale bar represents 100 nm. Reprinted from Ref 92. Copyright (2001), with permission from the American Chemical Society.

In drawn thin films of PE, shish-kebab crystals have been investigated by Miles and co-workers (191). Using contact mode SFM at minimized forces in liquid, the arrangement of the lamellae and the polymer molecules comprising the lamellae were resolved in molecular detail. Similar morphologies were also observed for poly(l-butene) (192), as well as many processed polymers, because of orientation effects during the production process (193,194). 

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. 

There are a number of other possible interpretations of the data. The Si S peak could be due to the formation of oriented nuclei, foe precursor to the shish in shish-kebab crystals and row nucleation [28], but this should also lead to orientation in the WAXS which is not observed. Furthermore, foe elongation is less than a foctor of 2 which is very low for formation of such structures [7,2]. 

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

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