Fiber shish-kebab morphology

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. 

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). 

Studies using gold decoration have been performed in several laboratories [282-286]. Thin solution cast films of nylon were studied by Spit [283], while Krueger and Yeh [284] studied stirred PE solutions which formed shish kebabs. Kojima and Magill [287] studied the morphology of spherulites of block copolymers by gold decorating sections. Shimamura [288] applied this method to the study of the internal structure of PE fibers. 

The crystallization induced by orientation consists of stretching polymer chains to form fibrous crystals or fibers [25], The formation of such fiber-like morphology is accompanied by the formation of a typical shish-kebab or bottiebrush morphology [2,4-12,25-27]. A relevant reference for crystallization under orientation during different polymer processing operations has been recently published [28]. 

We obtain a bundle of thin libers by stirring the solution in a circular fashion. Transmission electron microscopy (TEM) observation reveals the morphology to be similar to a necklace, which we call the shish-kebab structure (Fig. 5.1d). The core consists of a bundle of extended-chain crystals (ECC), around which the FCC form at generally regular and repetitive periods along the fiber axis. 

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