Shish-kebab crystalline structures

A typical shish-kebab crystalline structure has been foimd by Maiti and Okamoto (2003) and Kim et al. (2001) in polyamide/organoclay nanocomposite and by Choi and Kim (2004) in PP/EPR/talc nanocomposite where a preferential orientation of polymer lamellae perpendicular to the surface of organoclay layers was inspected by TEM measurements. The unique observation of lamellar orientation (Ml the clay layers was ascribed to nucleation and epitaxial crystallization at the interface between layered silicate and polymer matrix especially the surfaces of clay platelets acted as heterogeneous nucleation sites. Orientation of iPP crystals was also enhanced in rPP/PP-MA/o-MMT injection-moulded parts, especially manufactured by dynamic packing injection moulding (Wang et al. 2005). MMT... 

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). 

FIGURE 2.17 Crystalline polymer structures formed under applied tension including flow conditions. The center shows the tertiary monofibriUar structure including platelets, the left shows these mono-fibrillar structures bundled together forming a quaternary structure fibril, and the right shows the distorted shish kebab formed with more rapid flow. 

In general, if the chains are oriented by external forces, the melting temperature is increased [28]. Further, it has been known for a long time that complex, row-nucleated structures occur if polymer solutions or melts are crystallized in the presence of flow [29,30]. These so-called shish-kebabs (sketched in Fig. 1.6), consist of a central fiber core, shish, surrounded by lamellar crystalline structures, kebabs, periodically attached along the shish. 

The fiberlike crystalline structures (shish) are highly stable to the point that they can be superheated [31]. Therefore, it is believed that the core of the shish is formed by crystallization of completely stretched polymer chains. The kebabs are believed to be folded-chain lamellar structures. The direction of growth of the kebabs is normal to the shish. The chain ahgnment in the kebabs is believed to be parallel to the shish. Similar structures are obtained by crystalhzation in polymer melt films exposed to orientational deformation [32,33]. These two-dimensional shish-kebabs also consist of a central fiber, shish, and periodically attached linear kebabs, with growth direction normal to the shish. 

As-polymerized PTFE has exceptionally high crystallinity, a melting endotherm that is prone to superheating, and, in some instances, an unusual fibrous morphology. Melillo and Wunderlich note that some as-polymerized fibers may have a shish-kebab structure. Our electron microscopy confirms that this is indeed the case (Figure 1.3). 

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). 

The epitaxial growth and the formation of a shish-kebab stmcture were also investigated in high molecular weight iPP (HMW-iPP)/low-molecular-weight LLDPE (LMW-LLDPE) blends [21]. The formation of the initial crystallization precursor structure was investigated by using synchrotron WAXS/SAXS techniques at 130 and 140 °C. Shear was applied at temperatures above the cloud points of these blends, and therefore, the HMW-iPP chains could form a flow-induced crystalline stmcture in the blends only at 6 and 9 wt% of HMW-iPP LMW-LLDPE merely served as the amorphous matrix (Fig. 5.3). When the HMW-iPP... 

The effects of the addition of two or more additives (i.e. talc, montmorillonite, Ceo, PDLA, and various polysaccharides) have been studied by Tsuji et al. [313], while those of talc and/or triphenyl phosphate as a plasticizer were investigated by Xiao et al. [330], Derivative N,N,N-tricyclohexyl-l,3,5-benzenetricarboxylamide was used as a model to tailor the crystalline superstructure of PLLA three crystal morphologies including conelike, shish-kebab, and needlelike structures were obtained by melt crystallization [331],... 

Figure 1.28 Different physical forms of crystalline polymer (a) single crystal produced by slow crystallization from unstirred solution, (b) shish-kebab structures obtained when crystallization takes place with stirring (shear conditions).

Other types of crystalline physical structures can be observed if crystallization occurs under stress (for example, under shear stress during processing). In this case, a continuous series of crystallization nucleation centers is formed by the induction of order along the lines of flow. A row structure of oriented lamellae is consequently produced. These row structures are related to the shish-kebab structures shown in Figure 5-27. 

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. 

Shish-Kebab structure shish-k3- bab n. A term borrowed from the broiling kitchen to designate a polymeric microstructure in which the random-coil chain of an amorphous polymer (shish) has been interlaced with crystalline cross-segments (kebab) produced by shearing the polymer in the molten condition or in solution. The string-of-lumps microstructure so resembles the edible dehcacy that its borrowed name seems quite apt. Ehas HG (1977) Macromolecules, vols 1—2. Plenum Press, New York. 

Figure 2 shows the crystalline structure of the skin layer schematically [6]. It is composed of shish-kebab-like main skeleton structiure, whose... 

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