Combined neutron scattering and weight measurement studies of structural changes in microbial cellulose during drying process

酢酸菌セルロースおける水蒸発プロセスに関する研究

Zhao, Y.

Zhao, Y.

We studied how the structure of the microbial cellulose (MC) sample changes during the natural drying process, where water evaporated slowly and was replaced by air, by means of combined time-resolved measurement of small-angle neutron scattering (SANS), intermediate angle neutron scattering (IANS) and weight measurement. SANS was used to elucidate the microstructural change in the MC sample upon drying, during the process of which the coherent scattering length density of the amorphous cellulose regions swollen by water varied with the time to give a tunable scattering contrast to the crystalline cellulose regions, thus the contrast variation experiments were automatically performed by drying. In addition, IANS and weight measurement were used to determine the concentration of water and hydrogen atoms. Our results show that (1) the natural drying process does not induce crucial structural changes in the length scale of 10-125 nm, which is quite different from the observation of further crystallization and aggregation of the cellulose chains by rapid drying via vacuum; (2) The natural drying process could be divided into three time-regions: 3-dimensional shrinkage in region I, 1-demensional shrinkage along the thickness of the sample in region II, and completion in region III. (3) "bound water" along cellulose chains was estimated to be 0.35wt% by weight measurement, and verified by the quantitative analysis of the scattering data.