Determination of specific surface area of mechanical pulp fines from turbidity measurements

Turbidity measurements on suspensions of known consistency can be used to determine the specific surface of mechanical pulp fines. The relationship between turbidity and specific surface is developed from the assumption that the scattering of light by these suspensions can be adequately described as ''large particle scattering''. The validity of this assumption is supported by the absence of dependence of the measured turbidities on the wavelength of the light used. Experimental values for the needed constants are derived from turbidity measurements on polystyrene spheres of known dimensions, combined with a knowledge of the water content of the fines. Optical specific surfaces of wet fines thus obtained are in reasonable agreement with specific surfaces obtained by liquid permeability and nitrogen adsorption measurements. Preliminary considerations suggest that there is about a 90% decrease in the specific surface of mechanical pulp fines during drying.