The rheograms of wheat straw soda black liquor in a shear rate range of 10–103 s−1 were investigated by a Physica MCR 100 rheometer. The rheological properties of wheat straw soda black liquor with diﬀerent solids content were deliberated in 60–100°C temperature range. All samples exhibit shear-thinning properties with the flow behavior index (n) between 0.715 and 0.865. The Arrhenius model was used to explain the inﬂuence of temperature on apparent viscosity of soda black liquor. The Arrhenius parameters, ηo and Ea are functions of solids content and expressed by the Ostwald-de-Waele model. The empirical model obtained from the study could well depict the combined eﬀect of solid content and temperature within the range of study. It was concluded from the results that temperature along with the solids content had signiﬁcant eﬀect on the rheological properties of soda black liquor.

Rheological Properties and Statistical Analysis of Wheat Straw Soda Black Liquor

A kahu grass thick black liquor (TBL) produced in the paper manufacturing process causes serious handling problems due to its high viscosity. In the present study, the viscosity of this black liquor (having 50% solid content) has been decreased significantly in acidic medium by the addition of small concentrations (<0.1 M) of various alkali salts such as potassium bromide, potassium thiocyanate, potassium dichromate and potassium permanganate respectively. Parameters related to viscous flow, like temperature and salt concentration were evaluated and the activation energy of the viscous flow was calculated. It is believed that the protonated phenolic hydroxyl groups of the lignin macromolecule, responsible for the elevated viscosity of the black liquor, are prevented from association by the alkali salts that result in reduction of its viscosity.

Q. M. Malik

Papers

Effect of alkali salts on the viscosity of 'kahu' grass black liquor