X-ray Diffraction Study of Cellulose Powders and Their Hydrogels. Computer modeling of the Atomic Structure

Resumo

Cellulose powders from flax fiber and deciduous wood and hydrogels regenerated from DMA/LiCl solutions of them were studied using x-ray diffraction. Structural characteristics were calculated. Three-dimensional models of atomic positions in the short-range order of amorphous hydrogels were constructed. It was found that flax cellulose was characterized by a higher degree of crystallinity and larger transverse cross section and monofilament length than deciduous cellulose. Super-swelled and lyophilized hydrogels from the cellulose solutions gave diffuse diffraction patterns characteristic of amorphous materials. The calculated coordination-sphere radii for lyophilized hydrogels corresponded to analogous data for cellulose II. Differences in the coordination numbers were due to structural differences in the short-range order. The distribution of atoms in the short-range ordered region was modeled using molecular dynamics and corresponded to a disordered cellulose II cluster with dimensions along the crystallographic axes of 2a, 2b, and 5c (15, 16, and 52 Å). A cluster consisted of 16 cellulose chains ~52 Å in length.