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 1, sh, a and , in order of decreasing temperature. The peak
temperature of the 1 absorption, Tmax1, decreased with increasing Csa; conversely, Tmaxa increased. This implies that
there are two different kinds of amorphous regions. The activation energy of the a absorption also increased with increasing
Csa, as in the case of Tmaxa. In other words, concentrated sulfuric acid, which can dissolve cellulose, strengthens
interactions between cellulose molecules in the amorphous region expressed by the a 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.