Micro fibrils structure

In micro photos of the modified fibers is the fibrillation structure of a fiber, and visible introduction hexsaazocyclanes in PETP promotes to increase order and density of the structure of the polymer. 

Extended chain crystals can be obtained by crystallization under high pressures or under uniaxial extension. So-called shish-kebob structures are frequently observed when crystallizing polymers under orientation, e.g. in stirred solutions and polymer processing from the melt. Similar to lamellae and (micro) fibrils treated in previous chapters, these structures can be routinely visualized and analyzed by AFM. 

As will be discussed later (see p. 332), these data provide strong support for the argument that the microfibrils are produced by on-the-site synthesis and orientation (apposition) of the cellulosic microfibrils under the guiding influence of the living cell, rather than by a mechanism that proposes synthesis of the micro fibrils within the cell and subsequent translocation and crystallization (deposition) of microfibrils on the cell wall by exocellular factors. Further factors relevant to these opposing theories emerge from study of the fine structure of the cellulosic microfibrils, as discussed in the following Section. 

Hydrated cellulose (viscous) fibers, unwoven materials (e.g. felt), with different fiber interweaving and chemical reagents of high purity were used. Hydrated cellulose was chosen as a polymer precursor. Its structure is a complex system composed of micro-fibrils and micro- and macropores and also of a branched network of microscopic capillaries. Cellulose has a large inner surface that plays a determining role in absorption of aqueous or organic liquids with polymer molecules. Under the impregnation of hydrated cellulose with aqueous solutions of salts, the liquid fills the space between fibers, pores on the fiber surface and interacts with cellulose macromolecules. 

An interesting structure can be found in wood, for example in the different layers of conifer tracheids, where helically arranged cellulose micro-fibril bundles are found (Fig. 9.7). The spiral-Uke lay-up and the angle of the strengthening fibers in the stem walls and of cellulose micro-fibril bundles in the cell walls is optimized according to the types and combinations of... 

Let us provide at least two examples of application of these mles. Sawyer and Jaffe (20) have defined the hierarchical fibrical structure of LC materials after processing. Macro fibrils, fibrils and micro fibrils they consider constitute the key entities at three different levels - as defined in Rule 3. 

As previously mentioned, natural fibres present a multi-level organization and consist of several cells formed out of semi-crystalline oriented cellulose micro fibrils. Each microfibril can be considered as a string of cellulose crystallites, linked along the chain axis by amorphous domains (Fig. 19.10) and having a modulus close to the theoretical limit for cellulose. They are biosynthesized by enzymes and deposited in a continuous fashion. A similar structure is reported for chitin, as discussed in Chapter 25. Nanoscale dimensions and impressive mechanical properties make polysaccharide nanocrystals, particularly when occurring as high aspect ratio rod-like nanoparticles, ideal candidates to improve the mechanical properties of the host material. These properties are profitably exploited by Mother Nature. 

Frey-Wyssling A (1954) The fine structure of cell micro-fibrils. Science 119 80... 

The structure of the porous product obtained is influenced by the polymer, the stretch ratio, and the temperature and speed used in stretching. The product obtained has a micro-composite structure composed of nodes connected together by small fibrils the spaces surrounding the nodes and the fibrils form the cavities. In general, an increase in the stretch ratio leads to an increase in the length of the fibrils, a decrease in the size of the nodes, and an increase in the porosity of the product. 

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.

Crystal structures of micro fibril reinforced polymer-polymer composites... 

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