Structure of regenerated cellulose films from cellulose/aqueous NaOH solution as a function of coagulation conditions

Abstract

The structure of regenerated cellulose films from cellulose/aqueous sodium hydroxide solution, prepared by coagulation of aqueous sulfuric acid, was investigated by X-ray diffraction and viscoelastic measurements. The X-ray crystallinity Xc and apparent crystal size decreased monotonically with increasing sulfuric acid concentration Csa and an abrupt decrease was seen at Csa ≧ 60 wt%. In the viscoelastic measurements, four kinds of dynamic absorption peaks or shoulders were observed, named α1, αsh, βa and γ, in order of decreasing temperature. The peak temperature of the α1 absorption, Tmaxα1, decreased with increasing Csa; conversely, Tmaxβa increased. This implies that there are two different kinds of amorphous regions. The activation energy of the βa absorption also increased with increasing Csa, as in the case of Tmaxβa. In other words, concentrated sulfuric acid, which can dissolve cellulose, strengthens interactions between cellulose molecules in the amorphous region expressed by the βa absorption. The tensile strength of these cellulose films showed a sudden decrease at Xc < 25%. Micro-crystals possibly acted as crosslinking points, resulting in keeping tensile strength. In addition, the amorphous also greatly affected tensile strength; desirable amorphous structures for good properties were large and homogeneous amorphous units, which was expected to reduce stress concentration in the films. © 2006 The Society of Polymer Science, Japan.