| The yield-stress-based rheological behavior of pulp fiber suspension affects the energy consumption and production efficiency in papermaking. The yield stresses of slurry suspensions of old corrugated containers (OCC) and old news papers (ONP) with mass concentration of 1.5%~4.0% were evaluated by two measurement methods with the SPSS statistical analysis software and, then, compared with that from the virgin wood pulp. The results showed that the relations of yield stress τy and concentration Cm of the ONP pulp and OCC pulp based on rheological curve regression method (RCRM) satisfied respectively the exponential equations τy=3.34C2.43m and τy=2.33C2.57m, and τy and Cm based on shear stress gradient method (SSGM) satisfied respectively τy=3.58C2.43m and τy=2.83C2.47m; based on the same concentration and measurement method, the τy of ONP pulp was larger than that of OCC pulp, and, comparing on the same concentration and the same kind of pulp, τy based on SSGM was higher than that based on RCRM, 5.1%~9.4% higher for ONP pulp and 1.3%~13.9% higher for OCC pulp. The deviation of yield stress values measured by the two methods increased with the concentration increasing when the deviation was in the between of 2.7～17.2 Pa, which meant that τy of the pulp increased with the increase of concentration and fiber aspect ratio for waste paper. Taking a comparison, the τy of bleached softwood pulp was significantly larger than those of recycled pulp and hardwood pulp. |
