The shear and compressive yield stress of fibrillated acacia pulp fiber suspensions

The degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msub><m:mrow><m:mi mathvariant="italic">P</m:mi></m:mrow><m:mrow><m:mi mathvariant="italic">y</m:mi></m:mrow></m:msub></m:math> {Py} and shear yield stress <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msub><m:mrow><m:mi mathvariant="italic">τ</m:mi></m:mrow><m:mrow><m:mi mathvariant="italic">y</m:mi></m:mrow></m:msub></m:math> {τ y} of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msub><m:mrow><m:mi mathvariant="italic">τ</m:mi></m:mrow><m:mrow><m:mi mathvariant="italic">y</m:mi></m:mrow></m:msub><m:mo mathvariant="normal" stretchy="false">/</m:mo><m:msub><m:mrow><m:mi mathvariant="italic">P</m:mi></m:mrow><m:mrow><m:mi mathvariant="italic">y</m:mi></m:mrow></m:msub></m:math> {τ y}/{Py} were also examined and the variation of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msub><m:mrow><m:mi mathvariant="italic">τ</m:mi></m:mrow><m:mrow><m:mi mathvariant="italic">y</m:mi></m:mrow></m:msub><m:mo mathvariant="normal" stretchy="false">/</m:mo><m:msub><m:mrow><m:mi mathvariant="italic">P</m:mi></m:mrow><m:mrow><m:mi mathvariant="italic">y</m:mi></m:mrow></m:msub></m:math> {τ y}/{Py} became largely dependent on the fiber morphology and mass concentration.