Development of a methodology using methylene blue to quantify the amount of UV-screen applied and to determine the homogeneity of application on paper

Methylene blue was employed as a model molecule to develop a methodology to quantify the incorporation of compounds into the paper matrix. Quantification was based on absorption and fluorescence measurements of the solutions employed to transfer methylene blue into paper. This methodology is suitable to quantify amounts which correspond to less than 1% of the paper weight, and it can be applied when testing the inhibition efficiency of UV-screens against the photoyellowing of paper made from mechanical pulp. In addition, two application methodologies were compared to establish which one led to a more homogeneous distribution of methylene blue in paper. The 'dip method' led to a more even distribution than the 'drop method'. (C) 1998 Elsevier Science S.A. All rights reserved.