Cellulose helical parameters

So far, we have been describing the cellulose shapes in terms of the polymeric descriptors, n and h. These parameters do not apply to small molecules that are not helices. Instead, the most important shape variables for the small molecules are 9 and /, the linkage torsion angles indicated in Figures 15-1 and Figure 15-5. To proceed, we need to present a conversion of

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From this point of view, it is clear that rigid-chain macromolecules, i.e., macromolecules in which the length of the Kuhn segment of the chain / is much greats than the charactmstic thickness of the chain d, should easily form a liquid-crystalline phase. This is actually so coiled molecules (a-helical polypeptides, macromolecules of DNA, etc.), aromatic polyamides, a number of cellulose ethers, and some polyisocyanates are examples of macromolecules capable of forming liquid-crystalline phases of different types [3-5]. The asymmetric shape parameter of such macromolecules (i.e., ratio l/d) can be very large (it can attain several hundred for the first two polymers mentioned above). 

Each fibril has a complex, layered structure consisting of a thin primary wall that is the first layer, deposited during cell growth and encircling a secondary wall. The secondary wall is made up of three layers and the thick middle layer determines the mechanical properties of the fibers. The middle layer consists of a series of helically wound cellular microfibrils formed from long chain cellulose molecules the angle between the fiber axis and the microfibrils is called the microfibrillar angle. The characteristic value for this parameter varies from one fiber to another [10]. 

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