Abstract
The apparent light-scattering coefficient of a given pigment in filled papers depends on the state of pigment dispersion and the beating level of fibers. This effect is seen on handsheets containing pigments deliberately introduced either as individual particles or as aggregates; well dispersed T102 is optically superior and its contribution to the total light scattering increases with fiber beating. In order to achieve retention of dispersed pigment particles and to avoid their flocculation caused by polymeric retention aid, the pigment, prior to its addition to the fiber suspension, can be treated with a cationic polyelectrolyte. Since pigment introduction results in tensile strength loss, which is most pronounced with dispersed particles, a plot of optical properties versus tensile strength provides a means for evaluating the pigment effectiveness and for comparing different pigments.
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