## Abstract

The fraction of the available fibre surface in a sheet that is bonded to other fibres is the relative bonded area (RBA), which is an important determinant of sheet mechanical properties. The main method for estimating RBA has been to extrapolate data for the light scattering coefficient as a function of tensile strength to zero tensile strength. This method can produce significant errors. In this paper, the light scattering coefficient, corrected for the total surface area of the fibres available for scattering, was plotted against sheet density, corrected for fibre shape. This was carried out for sheets made from several series of pulps, including single furnishes of long- and short-fibre bleached and unbleached pulps, as well as sheets made of blends of bleached long- and short-fibre pulps. The corrected scattering coefficient was inversely linearly correlated to the corrected density for each data set. A theory was developed to allow RBA calculation from the intercept and slope of the fitted line.

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