Reoriented Celluloses

Crystallinity indexes calculated according to the method described by Segal et al. (32) showed that the old cotton has a crystallinity of about 38 . Aqueous treatments increased the crystallinity of the historic cotton sample to about 45 . However, the crystallinity of contemporary cotton, which is about 70 , was not reached (30). This increase suggests that water acts as an internal plasticizer and allows a segmental reorientation which leads to an increase in crystallinity. Water-induced crystallization of amorphous cellulose fibers has been reported (17). Kalyanaraman (33) investigated orientation factors of cotton fibers from historic samples and found that the orientation values of the museums samples are smaller than the values of present-day cottons. He opined that cotton may have lost its orientation over time. In view of this... 

Isotropic polymeric systems as well as particulate systems might also show time-dependent moduli after cessation of flow. As long as the shear does not induce structure growth, the moduli always increase with time after flow. An increase of the moduli upon cessation of flow has also been reported for thermotropic PLCs (18) as well as for lyotropic solutions of hydroxy propyl cellulose in water (19) and in acetic add (20). The possibility of changing in either direction seems to be characteristic for mesomorphic materials. A fundamental theory for describing complex moduli does not exist for such materials. The present results, combined with the information about optical relaxation mentioned above, could be explained on the basis of reorientation of domains or defects. The different domains orient differently, even randomly, at rest whereas flow causes an overall orientation. Depending on the molecular interaction the flow could then cause an increase or decrease in moduli as recently suggested by Larson (21). 

Mobility of water in cellulose has been studied by solid-state and high-resolution NMR as a function of moisture content within the unfreezable moisture range (0-19% dry basis).Measurements of relative mobilities were based on relative intensities, transverse and longitudinal relaxation times and line shape analysis. At 2-16% moisture content (dry basis), water molecules reoriented anisotropically, suggesting an interaction with cellulose fibers. At moisture content below the monolayer value (2.8%, dry basis), 90% of the protons were immobile and no liquid deuterium signal was detected. A sharp increase in liquid or mobile intensity (accompanied by a decreased LW) and increases in NMR Ti and T2 relaxation times were observed as moisture increased above 9% (dry basis). 

Celluloses can be converted to other useful products by reorientation of their fiber structure. Paper, parchment paper, vulcan fiber, mercerized cotton, and hydrocelluloses belong in this class. 

Wolters-Arts A.M.C. and Sassen M.M.A. 1991. Deposition and reorientation of cellulose microfibrils in elongating cells of Pelunia stylar tissue. Planta 185 179-189. 

Free arabinose and galactose, which are often associated with hydroxyproline-rich proteins, are found in the free space of cell walls (132). Levels of proteins and free hydroxyproline are increased by ethylene treatment of pea (Fisum sativa) stem segments. However, the total amount of hydroxyproline in ethanol-insoluble polymers after extraction of the free space with water and Ca was not influenced by ethylene. Terry et al. (132) propose that the response to ethylene, which is now known to be derived from methionine, can be divided into two components. One requires changes in cellulose microfibrils of the cell wall, which result in reorientation of the plane of cell expansion. The other involves a change in the hemicellulosic xyloglucan, which inhibits extension growth of these cells. 

For example, if such a column was used with a basic eluent, there is a high probability that after flushing it with an acidic eluent only a poor separation will be observed. This behavior (memory effect [25]) can be attributed to an irreversible reorientation of the helical structures of cellulose and amylose phases. Strongly basic or acidic compounds can effect such changes. A simple solution to avoid these effects is to allocate separate sets of columns for neutral, basic, and acidic conditions (in order to avoid errors in laboratory practice, labeling of columns with colored adhesive tape has proved to be quite useful, e.g. using a red tape for columns run under acidic conditions). 

The interaction between cellulose microfibrils and the hemlceUulose-xyloglucan network is believed to represent the major load-bearing structure in the primary ceU waU. In physical terms, cell shape and size are governed by the mechanics of the ceU waU. CeU expansion occurs via strictly regulated reorientation of the waU components and several enzymes play a rule in this mechanism [121]. 

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