The desired optical properties of a paper can be achieved through a variety of tools: pulp brightness, optical brightening agents, dyes or filler qualities. In this work, we explore the interaction between pulp brightness levels and optical brightening agents (OBA) addition on paper whiteness. Conditions were chosen that approximate an uncoated freesheet grade. Papers were prepared using eucalyptus Kraft pulps bleached to three different brightness levels. A constant filler level and optimized retention chemistry were used in the preparation. The addition of OBA was evaluated as a wet-end only application and as a wet-end/size press application. Dye addition was not a part of this evaluation. Additionally, in this work, we surveyed the optical properties of a range of commercially available uncoated freesheet paper. We found that the initial brightness of the pulp furnish sets the limit for whiteness level achievable with OBA during papermaking. It is not possible to compensate for low initial pulp brightness (<85.4 %ISO) by the addition of OBA when aiming for CIE D65 whiteness above 135. We also evaluated the economics of pulp brightness and OBA addition to show how these two variables can be balanced. Based on the conditions used in this study, it is most cost effective to use pulp having 90 %ISO brightness or higher when targeting CIE D65 whiteness above 135.
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