Rheological properties of cellulose fiber wet webs

The rheological properties of cellulose fiber suspensions were examined using a parallel-plate type rheometer. The suspensions consisted of various concentrations and types of cellulose such as: bacterial cellulose, microcrystalline cellulose made from cotton, fibrillated cellulose fiber and softwood pulp fiber. The dynamic moduli of the suspensions were almost independent of angular frequency. The concentration dependence of the moduli was discussed from the viewpoint of scalar transport of momentum. It can be said that these suspensions are in solid like under the measured condition. The dynamic storage moduli(G′) of the fiber suspensions show a strong dependence upon fiber concentration(c). The exponent is 9/4 for all the suspensions with three-dimensional isotropic networks. The value is consistent with that theoretically required for polymer gels. In contrast, the exponent is 3 for wet pulp fiber webs, which have laminated network structures, and 5 for a bacterial cellulose membrane with another laminated structure. This indicates that the exponent itself reflects the intrinsic properties of the fiber network structures. On the other hand, the front factor(k) of the power relation varies with the fiber axial ratio and fiber flexibility. Therefore, the factor reflects individual fiber characteristics. A simple two-dimensional lattice model is proposed to explain the power law.