| Popis: |
The controversy as to whether the accessibility of cellulose is a measure of crystal surfaces or of amorphous regions in the cellulose is reviewed. Recent claims that cellulose is composed of completely crystalline elementary fibrils of dimensions 40 × 50 A and that all chemical reactions of cellulose occur on the surface of the fibrils, do not explain many observations which indicate the presence of amorphous structures. Based on X-ray diffraction, chemical hydrolysis, moisture absorption, theoretical calculations of elastic constant, kinetic studies of alkaline degradation, and the lateral-order distribution curve of cellulose, evidence exists favouring the conventional micellar theory. The assumption of a gradual transition between the amorphous and crystalline regions in cellulose offers an explanation of the discrepancies among the accessibility values recorded by different methods. |
