ABSTRACT
This chapter reviews the fundamental principles involved in determining the brightness properties of lignocellulosic materials and discusses their relevance in modern papermaking processes. The production of high-brightness pulps is a sophisticated, technically demanding process, requiring a variety of chemical and/or biochemical procedures. Brightness testing instruments employing this type of directional geometry for measuring brightness are sensitive to the directionality of the fibers in the handsheets. These directionality effects have been employed for determining machine-direction and cross-direction of paper. Directional brightness measurements are dependent upon a common standard. For the TAPPI procedure, the standard brightness test is calibrated to 100% reflectance for a magnesium oxide test pellet. The brightness values of pulp and paper related materials vary greatly dependent upon the final target products. Unlike chemical pulps, bleaching operations for mechanical pulp are targeted at removing lignin chromophores without degrading lignin.
