The Fibrillar “Bundling” of Cellulose Molecules in Cotton
1969
Many problems of the fibrillar system of cotton can be solved with little difficulty with the aid of electron-microscope images of very large bundles. The existence of these “macrofibrils” is, however, controversial, since they cannot be isolated by mechanical structural separation. Attempts are now being made to identify the spiral-shaped striation of the surface of the fiber and by analogy such macrofibrils. By means of a stepwise degradation of the cell wall, fibrillar bundles of this order of magnitude in the secondary wall were found to be the cause of the image; these developed primarily as a result of a buildup of smaller fibrils (macrofibrils) during the formation of the fiber. The decomposition of the macrofibrils in the mechanical isolation test is due to the tensile strength of the overflowing microfibrils, the moderate lateral strength of the macrofibrils and the small difference in density between its core and its boundary zones. They can be isolated without damage by increasing this difference in density or its lateral strength. Their characteristics and origins are described. Microfibrils and elementary fibrils of the three types of wall layers of cotton fiber display significant differences in structure. The origin and time of bundling of the elementary fibrils into the microfibril also vary in these layers.
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