Effect of Carrier Chemicals on the Optical Properties of Paper Surface-Sized with Fluorescent Whitening Agents

Fluorescent whitening agents (FWAs) are important chemicals for improving the CIE whiteness and ISO brightness of papers. However, papermakers must reduce the amount of FWAs added to their products because FWAs present many disadvantages associated with the papermaking process, as well as paper quality; the public also has concerns about these chemicals in papers. Because the first step to reducing FWAs in the papermaking process is to improve their whitening effect, a new strategy for the effective use of FWA carrier chemicals must be developed. In this study, the whitening effects of tetra-sulpho FWA (T-FWA) and hexa-sulpho FWA (H-FWA) are compared in surface sizing, as well as with carrier chemicals. H-FWA showed a greater whitening effect than T-FWA in surface sizing, and carrier chemicals improved the optical properties of the paper when surface-sized with FWAs. It is concluded that carboxymethyl-celluloses (CMCs) were a more effective carrier chemical for T-FWA; polyvinyl alcohol (PVOH) is effective with H-FWA in the surface-sizing process to increase paper sheet whiteness.