To couple generalized delignification and brightening models to simulate an entire Elemental Chlorine-Free (ECF) bleach sequence, one needs a mathematical relationship that correlates the post-extraction kappa number from bleaching delignification to the brightness entering into the chlorine dioxide brightening stage (D,). This was the focus of the current study. A linear relationship was observed for a given pulp when its extracted kappa number (~2 to 8) was plotted against its k/s value (i.e., ratio of adsorption (k) to scattering (s) coefficient). The k/s ratio was related to the pulp's brightness by the Kubelka-Monk remission function. A common y-axis intercept value of 0.025 was found for a variety of softwood brownstocks and oxygen-delignified pulps treated by chlorine dioxide delignification (e.g., D0(EO), D0(EOP)., ect.). The slope of this line for D0(EO)-treated pulps varied considerably, from 0.010 to 0.070. This variation was influenced by kraft pulping conditions, such as effective alkali and H-factor, although no specific function was found. Oxygen delignification was found to decrease the pulp's slope value by approximately one-third when compared to its corresponding brownstock. The slope of the D0(EO) kappa-k/s expressions decreased proportionally to the amount of peroxide used in the extraction stage (e.g., (EOP)). On the other hand, the slope from D0E1-treated pulps was typically 10% to 20% higher than for D0(EO)-treated pulps. Applications of the proposed kappa-to-brightness model to link bleaching delignification and brightening models are illustrated.
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