Cotton, fiber wall 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. 

In 1948, Hessler et al. [157] measured the DP of cotton based on the viscosity of nitrated cellulose. They found a DP of 5940 for the primary wall, while a DP of 10,650 was determined for the secondary wall. Molecular weight differences were reported for fiber taken from three different positions within the boll as well as at three different positions on the seed... 

The fiber saturation point (FSP) of cotton is the total amount of water present within the cell wall expressed as a ratio of water to solid content. It is equivalent to the water of imbibition of the fiber, also called its water retention value. The FSP has been measured using solute exclusion, centrifugation, porous plate, and hydrostatic tension techniques. It occurs at RVP greater than 0.997 and from the review of the papers, it has been concluded that the studies have yielded a value for FSP in the range of 0.43 to 0.52 g/g [303]. 

Measurements of optical birefringence and density were obtained in an attempt to determine if total polymer orientation and the amount of fiber crystallinity would correlate with aging behavior. These values are presented in Table III. Because the secondary wall of cotton comprises... 

Articles on x-ray diffraction measurements of orientation in this period were concerned with the orientation of cellulosic chains in fibers and in cell walls (29-33). A study of cotton, wood, flax, sisal, hemp, and other cellulosic structures established the occurrence of helically oriented cellulosic materials. Naturally occurring cellulose membranes were also investigated. Simon (32) proposed the use of pole figures, ie, stereographic projection of normals to crystallographic planes, to represent the orientation of the chains of crystalline cellulose (32). The development of uniaxial and uniplanar orientation was described based on the x-ray results. 

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