Cellulose fringed micelles, model

Fig. 26. Fringed micelle model of cellulose derivatives in solution, according to Schulz and Burchard. Reprinted from Ref. 82 with permission from Wiley-VCH Verlag GmbH Co, Copyright 2000.

Some cotton cellulose is noncrystalline or amorphous in the sense of lacking definite crystalline form. One reason is that cotton cellulose has a broad molecular weight distribution, making high-crystalline perfection impossible. The small crystallites constitute deviations from ideal crystals that are infinite arrays. The remaining amorphous character of most polymers is often thought to arise from the fringed micelle model of the solid structure. In... 

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). 

The proposal that transverse sectioning of natural cellulose fibres can be used to test theories on the structure of microfibrils has been examined theoretically. It was concluded that fibre-sectioning experiments described in the literature do not disprove the folded-chain model, and it was suggested that clearly divided sections exist along the axis of the microfibril at intervals of 200 A. This cannot be explained in terms of a fringed micelle model. However, it is possible that cellulose II has a folded-chain conformation, since a single molecule of cellulose can be folded back and forth in the (101) plane to form a sheet-like structure that fits into the unit cell. A cellulose molecule can achieve a sharp U-tum in the... 

Various models of elementary fibril were proposed to visualize the supermolecular structure of cellulose. Back in the 19th century, Nageli put forward the idea that natural cellulose consists of micelles—small crystallites embedded in an amorphous matrix (Zugenmaier, 2009). Further development of this idea led to the model of "fringed micelles" (Fig. 7.24). This model can represent the structure of precipitates and cast films but is not suitable for the characterization of the supermolecular structure of natural and artifrcial cellulose fibers. 

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