Effect of Grinding on the Crystallinity of Cellulose Fibers, as Indicated by the Acid-Hydrolysis and Other Techniques

Abstract

A study was made of an effect previously noted, that grinding cotton fibers in a Wiley mill causes a reduction in degree of crystallinity as determined by the acid-hydrolysis method. It is shown on samples of purified linters and cut cotton, ground under conditions of increasing severity, that even mild grinding—for example, through a 2-mm. sieve—causes a detectable reduction in indicated degree of crystallinity, and that as the severity of grinding increases the degree of crystallinity drops correspondingly. This drop is not caused by passage of more of the finely ground particles from the more severely ground samples through the filters. When the ground samples were moistened with water and allowed to dry, a portion of the lost crystal linity was regained. The acid-hydrolysis results are supported by accessibility, heat of wetting, and moisture adsorption measurements, which, with few exceptions, indicate increasingly larger amounts of amorphous material in the samples receiving the more severe grinding. While the x-ray diffraction patterns did not reveal any effect of the most severe grinding, it is assumed that the changes were not sufficient to permit their detection by this means. Some implications of the results on the interpretation of cellulose structure are discussed.