Tensile strength is roughly a measure of both
single fibre strength and interfibre bonding
strength (Page 1969). Wet zero-span tensile
strength is thought to be a measure of fibre deformation
and its influence on the ability of the fibres
to take up load (Mohlin and Alfredsson 1990).
Scott Bond energy is used as an indicator of variations
in bonding strength that are dependent on the
relative bonding area (RBA) and specific bond
strength (SBS). Light scattering and swelling capacity
are indirect measures of the bonded area. Both
Scott Bond and wet zero-span tensile strength are
slightly reduced by precipitated material. However,
neither the light scattering nor the swelling capacity
of pulps (indicated by the WRV) is significantly
changed, demonstrating that the precipitated material
does not change the RBA. The precipitated
material seems to decrease slightly the zero-span
tensile strength measured from rewetted sheets. It
seems reasonable to assume that the individual
fibre strength is not significantly affected by precipitated
material. Therefore, the decrease in tensile
and Scott Bond strength is most probably due to a
reduction in the bonding ability of fibres.
Furthermore, the increase in the light adsorption
coefficient clearly indicates the precipitation of
coloured structures originating from lignin-derived
materia