Disorder, measurement cellulose

The final colligative property, osmotic pressure,24-29 is different from the others and is illustrated in Figure 2.2. In the case of vapor-pressure lowering and boiling-point elevation, a natural boundary separates the liquid and gas phases that are in equilibrium. A similar boundary exists between the solid and liquid phases in equilibrium with each other in melting-point-depression measurements. However, to establish a similar equilibrium between a solution and the pure solvent requires their separation by a semi-permeable membrane, as illustrated in the figure. Such membranes, typically cellulosic, permit transport of solvent but not solute. Furthermore, the flow of solvent is from the solvent compartment into the solution compartment. The simplest explanation of this is the increased entropy or disorder that accompanies the mixing of the transported solvent molecules with the polymer on the solution side of the membrane. Flow of liquid up the capillary on the left causes the solution to be at a hydrostatic pressure... 

Corrections of the apparent crystallinity values of fibers materials have been carried out by taking into account a disorder parameter k, following Ruland s method. Peculiar care was taken about samples preparation (cutting and pelleting of fibers), data collection and reduction, which will be briefly described. Crystallinity and disorder parameter measurements have been performed on main textile fibers (polyester, polyamide, aramid, polypropylene, cellulosic fibers) and the results will be discussed comparatively, with those got by more conventional x-ray crystallinity determinations. The complementarities of these different approaches will be illustrated with several examples. For instance,... 

A complete definition of the fine structure of cellulose would entail a knowledge of the exact distribution of the size and shape of these ordered and disordered regions, a position which has not yet been achieved. However, a report claims that four types of material which differ in the degree of orderly arrangement of molecular chains can be distinguished in both native and regenerated celluloses, although quantitative measurements have only been made on one viscose-rayon fiber. These four types of material are ... 

Various attempts to interpret the accessibility data as related to surface area of microfibrils of measured dimensions have been made. If 10% of the microfibrils are accessible because they contain a disordered cellulose lattice, indicated by rapid hydrolysis in acid, the remaining 20-25% of the accessible OH groups should be located on microfibril surfaces. 

The distinction between fiber saturation point (the maximum water content of swollen cell walls) and the maximum possible moisture content has a diminishing value for degraded wood, which may eventually have no effective fiber saturation point at all. The ordered and disordered cellulose in sound wood are the main sites for water adsorption (ii). As they diminish over time, their relative role in determining fiber saturation also diminishes. Nevertheless, the measurement of relative water adsorption will have some value in determining the relative degradation in a wood sample. 

Periodate Oxidation. Hiis method is based on the preferential oxidation of the disordered regions of cellulose by sodium metc riodate (12,13). Conditions are selected so that the reaction is confined as far as possible to the Malaprade course resulting in the formation of 2,3 dialddiyde units. The course of the reaction is followed measuring oxidant consumption from the amount of periodate consumed. From plots of log oxidant consumption against time, a measure of the fraction of ordered material can be calculated in a manner analogous to that used with the acid hydrolysis method. 

The relative rate constants for 0(2)H, 0(3)H and 0(6)H are determined by measurements of the distribution of substituents in a sample of completely disordered cellulose (21). The resulting rate constants characterize available hydroxyl groups in ary solid crystalline cellulose for which the reaction is conducted under identical conditions. 

From F a measure of the disordered cellulose can be obtained Which does not include crystalline surfcKi es. Tbe accessibility of the saniple (A ) is givai the following equation ... 

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