Fibrils, fringed

The fringed micelle picture is not particularly suitable for describing synthetic polymers crystallized from solution or melt. However, the fibrils of many nat-... 

Studies of craze microstructure and the surrounding displacements of crazes have established that the only parts around a craze that undergo plastic deformation are concentrated into a process zone at the tip of the craze, and into a fringing layer all around the entire craze body. In the process zone craze matter is generated by one of the two processes discussed above, and fibrils are necked down to the final extension ratio. In the fringing layer, additions are made to craze fibrils by drawing polymer out of half space. Outside the idetifiable parts of a craze, the solid polymer remains entirely elastic while inside the craze body the fully drawn fibers carry the required craze tractions purely elastically in their orientation hardened state at the... 

Reports on the characterization and the make-up of the elementary fibrils and on their association while establishing the fiber structure - usually called fibrillar or fringed fibril structure - are present in the literamre [32]. 

No interwoven fringe micelles, no membranes, and no networks of cellulose chains seem to occur except when formed from microfibrils, laid down as units in the morphological structure. Thicker fibrils, lamellae of largely parallel microfibrils, and layers and walls of crossing fibrillar units all contain microfibrils of a certain rather well defined thickness and indefinite length. 

Figure 10.83). Some attention has also been given to lamellar [267] and folded-chain structures [268]. Examination of rayon by the electron microscope has provided ample evidence for fibrillar structure in rayon. Although the fringed fibril structure shown in Figure 10.83 appears to fit best with the tendency of some rayons to fibrillate in the wet state under certain conditions the fringed micelle structure can also account for observed properties. 

FIGURE 10.83 Cellulose structure (a) fringed micelle and (b) fringed fibril. 

Models of fringed micelles (a) and fringed fibrils (b). C, crystalline fibril A, amorphous domain. 

Hearle, J.W.S., 1963. The fine structure of fibers and crystalline polymers. 1. Fringed fibril structure. J. Appl. Polym. Sci. 7 (4), 1175—1192. 

The fringed micelle picture is not particularly suitable for describing synthetic polymers crystallized from solution or melt. However, the fibrils of many natural substances, such as cellulose and proteins (collagen, silk), consist of bundles of macromolecules in a parallel alignment, compatible with the fringed micelle model. For synthetic polymers, however, it is more often found that they crystallize such that the macromolecules fold with an essentially constant length, leading to a lamellar-type crystallite structure (switchboard-model. Fig. 1.11). 

It is generally believed that the fine fiber structure comprises fringed micelles and fringed fibrils (Figure 4.18). The presence of zinc in the bath contributes to a skin-core structure (Figure 4.19) and proportions of skin and core can be varied. Skin contains small crystallites and is stronger than the core, which contains fewer, but larger crystallites [175]. 

Figure 4.18 Cellulose structure (a) Fringed micelle (b) Fringed fibril. Source. Reprinted with permission from Dyer J, Daul GC, Rayon Fibers, Lewin M and Pearce EM eds., Handbook of Fiber Chemistry, Marcel Dekker, New York, 777, 1998. Copyright 1998, CRC Press, Boca Raton, Florida.

Concepts of two-phase structures found in fibers (a) fringed micelle, (b) fringed fibril, (c) fringed lamella and (d) pseudo fringed fibril with micelles lined up in columns. 

All native cellulose is organized into fringes and fibrils [4], which means that there are areas of crystalline order being intermixed with amorphous such as ones as shown schematically in Figure 9.1 A. Figure 9. IB shows a schematic breakdown of a cellulose fiber as it can be found in plant cells down to its polymeric unit. 

Figure 9.1. A. Fringe-fibril model of cellulose after Hearle [4] see also Zugenmaier [1], The right figure B. shows a schematic of a macro-fibril as existing in plant cells begin a composite of micro-fibrils. These consist of elementary fibrils which are made of 30-40 polymeric linear cellulose chains (picture based on the botany visual resource library [5]). The picture in figure A. is observed in crystalline cellulose, grown either artificially as for instance in textile fibers [1] or can be thought to mimic the structure of elementary fibrils.

Hearle J W S (1958) A Fringed Fibril Theory of Structure in Crystalline Polymers. J Polymer Sci 28 432—435. Botany Visual Resources Library (2001) McGraw-Hill, NY and also Uno G, Storey R, Moore R, Principles of Botany, McGraw Hill, NY. 

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