Rupture Behavior of Paper Sheets Immersed in Carboxymethyl Cellulose Aqueous Solutions

The mechanical characteristics and the rupture behavior of dry paper and papers immersed in pure water or a carboxymethyl cellulose (CMC) aqueous solution were investigated by measuring the shape changes due to the immersion and by uniaxial tensile tests. The weight changes and dimensional changes for these samples due to the immersion were evaluated by the gravimetric method and image analysis, respectively. The absorption ratio of the paper was 2.3 for pure water, and it increased up to 2.7 with the CMC concentration. A deformation of 5% at maximum was observed in the direction perpendicular to the fiber orientation due to the absorption. All the samples demonstrated similar stress-strain curves in the regions of linear viscoelasticity and plastic deformation. The peak stress, Young's modulus, and strain energy density of CMC wet paper showed lower values than those of water wet paper, while the peak strain was the same for both samples. Similar behavior was found in the cross direction, although the difference was not significant. These results strongly indicate that the penetration and adsorption of CMC molecules lead to a large expansion, resulting in the disentanglement of paper fibers and a significant reduction in the mechanical properties due to the strong fluid lubrication effect.