EFFECT OF ORIENTATION DISTRIBUTION AND CRYSTALLINITY ON THE MEASUREMENT BY X-RAY-DIFFRACTION OF THE CRYSTAL-LATTICE MODULI OF CELLULOSE-I AND CELLULOSE-II

The crystal lattice moduli of cellulose I and II were measured by X-ray diffraction using ramie and mercerized ramie. The measured crystal lattice moduli were in the range from 120 to 135 GPa and from 106 to 112 GPa for cellulose I and II, respectively. These values were different from recent theoretical estimates of 167 and 163 GPa for cellulose I and II, respectively, reported by Tashiro and Kobayashi. To study the origin of this difference, a numerical calculation of the crystal lattice modulus, as measured by X-ray diffraction, was carried out by considering effects of the orientation factors of crystal and amorphous chains and crystallinity. In this calculation, a previously introduced model was employed, in which oriented crystalline layers are surrounded by oriented amorphous phases and the strains of the two phases at the boundary are identical. The theoretical results indicate that the crystal lattice modulus measured by X-ray diffraction is different from the intrinsic lattice modulus when a parallel coupling between amorphous and crystalline phases is predominant, while the values of both moduli are almost equal when a series coupling is predominant. Thus, the crystal lattice moduli of cellulose I and II measured by X-ray diffraction are predicted to be dependent upon the morphological properties of the bulk specimens. The numerical calculations, however, indicate that the morphological dependence is less pronounced with increasing degree of molecular orientation and crystallinity. Thus, it is concluded that fibers and films with a high degree of molecular orientation and a high crystallinity should be used as test specimens for measuring crystal lattice moduli by X-ray diffraction. © 1990, American Chemical Society. All rights reserved.