Cellulose orientational measurements

Direct measurements of cellulose orientation in fibers have yielded conflicting results. Evidence from x-ray diffraction studies of wood samples suggested that the cellulose crystallites are arranged randomly in the plane perpendicular to the fiber axis (30-33). Raman spectroscopic studies of cotton fibers dried under tenTTon, however, demonstrated that the methine C-H bonds are oriented preferentially perpendicular to the surface of the cell wall (34). Since the C-H bonds are perpendicular to the 002 plane, the orientation suggested by the Raman evidence differs from the alternating orientation in algal celluloses. 

PH Hermans and D Heikens, Orientation in cellulose fibers as derived from measurements of dichroism of dyed fibers, Reel. Trav. Chim. Pays-Bas, 71 49-55, 1952. 

Thin films of the solutions between microscope slides were sheared by applying even pressure on a coverslip while sliding it approximately one cm. The anisotropy appeared to increase as measured by increases in the birefiingence. Solutions containing 10-16% (w/w) cellulose developed a threaded texture and the mesophases were stable with time and oriented in the direction of shear. These observations, while not definitive, suggested a cholesteric to nematic transition occurred on shearing. 

The orientation of cellulosic fibers has some effect on the conductivity of the paper. The conductivity in the XY plane of the sheet (surface conductivity parallel to most of the fibers) may be quite different from the conductivity along the Z direction (bulk conductivity perpendicular to the fibers). Comparison of surface and bulk conductivity for a given paper sheet can thus yield information which reflects the anisostropy in the structural morphology due to fiber orientation. Bulk conductivity measurements are also important since many paper sheets used in reprographic processes are composed of a conductive base sheet coated with a dielectric material 16. One important specification for these types of papers is the value of the bulk conductivity of the base paper. 

Fig. 19. Plot of birefringence as measured by the compensator technique against the orientation function as measured by the sonic method. Values in parenthesis represent theoretical values for Nylon 66, cellulose, and polypropylene from top to bottom respectively...

Neither of the two earlier reviews on the infrared spectroscopy of carbohydrates " dealt with the uses of plane-polarized radiation. This is, no doubt, attributable to the fact that both reviews were principally concerned with crystalline sugars, for which few such spectra are available. However, the polarized infrared spectra of such polysaccharides as cellulose, chitin, and xylans, in the form of oriented films, have been measured " and have provided information that other techniques could not give. It is, therefore, desirable that a brief discussion should be here provided of both the experimental and the interpretational aspects (see p. 28) for a detailed discussion, the reader is referred elsewhere. The commonest method of obtaining polarized infrared radiation is with a transmission polarizer (rather than a reflection polarizer). Selenium film and silver chloride sheet have both been used of these, the latter is the more popular because it is the more robust. A stack of about six sheets, each about 50-100 m thick, is... 

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