The use of holocellulose to study cellulose supermolecular structure

Abstract

AbstractHolocelluloses were prepared from slash pine wood at the 17–19, 4‐6, and 0‐2% lignin levels by the chlorite and chlorine–monoethanolamine methods. The products were compared with respect to carbohydrate composition, nitrate degree of polymerization, x‐ray diffraction peak width, x‐ray crystdlinitg index, mercerization resistance, and alkali solubility. Structural differences among holocelluloses at each lignin level were noted. Thest. wvre attributrd to a deperidencc of x‐ray diffraction peak width on delignification conditioris and to small differences in amount of residual lignin. It was determined that alkali‐resistant, heimictrlluloses interfere with mercerization analyses inasmuch as they diminish diffraction pattern resolution. Taking account of such interference, the swelling behavior of the cellulose in whole wood can be estimated from either type of holocellulose. It is necessary, however, to ensure that all of the lignin is removed and that cellulose degradation is not excessive. The effect of stepwise alkaline extraction of hemicelluloses from the holocelluloses containing 0–2% lignin was followed by x‐ray analyses of the extracted residues after each extraction stage. Narrowing of the 002 diffraction peak width was observed and was found to depend on an alkalicellulose interaction and on hemicellulose reinoval. Reinoval of “polyuronides” has less of an effect on peak width than removal of the “cellulosans.” The hemiceliulosic polysaccharides, araboglucuronoxylan, and glucomannan are discussed in regard to molecular structure, probable relationship to the crystalline cellulose, ease of alkaline extraction, and effect of removal on the cellulose supermolecular structure. Narrowing of the 002 peak width, independent of cause, is considered to represent an increase in crystallite width, in development of the crystal lattice, and in packing perfection of the cellulose chains within and on the surfaces of the crystallites. Structure parameters were estimated for native slash pine cellulose, and these were compared with values found for celluloses isolated from the same species by the conventional acid sulfite and prehydrolysis sulfate processes. This comparison enabled approximation of the direction and magnitude of change effected in the native cellulose structure during pulping.