Effect of polyvinyl alcohol on fluorescent whitening agent in surface sizing

Abstract

Fluorescent whitening agents (FWAs) have been widely used in the paper industry. These chemicals play a meaningful role in improving the CIE whiteness and the ISO brightness of a paper. It is essential for papermakers to optimize the whitening effect of external FWAs in order to decrease the production cost and improve paper quality. It is generally known that surface treatment of FWAs achieves higher retention than internal addition. This study focuses on a chemical approach to explain the whitening effect of FWA used for surface sizing. We compared the whitening effect for internal and external applications of FWA and found as expected that the surface holdout of FWA is a key factor for a high level of whitening. Chemicals with a high affinity to FWA were chosen to improve surface holdouts, and using this criterion, polyvinyl alcohol (PVOH) which has been used in practice to increase the effectiveness of FWA was selected as the best carrier chemical for FWA. Through CLSM images, it could be confirmed that PVOH contributed to the improvement of both the CIE whiteness and the ISO brightness of the surface-sized paper by increasing the surface holdout of FWA.