Study on the quenching of fluorescent whitening agents in white water by using polyelectrolytes

Abstract

Previous researches have shown that mechanical and chemical treatments can be used to detach fluorescent whitening agents (FWAs) from recycled fibers, and that FWAs remain soluble in the process water. Because FWAs are soluble in the process water they have a tendency to adsorb on the cellulosic fibers in the papermaking process, the detached FWAs must be removed. In this study, coagulants, including poly-DADMAC and polyethylenimine (PEI), were applied to the FWA solutions to make the FWA molecules undergo flocculation and to induce the complete sedimentation of the floes. The turbidity of the FWA solutions was measured to identify the formation of the FWA floes, and the fluorescence emissions of the supernatant of the FWA solutions were analyzed after the sedi-mentation of the FWA floes was completed. When the coagulants were added to the FWA solutions, the turbidity increased, which indicated the formation of FWA floes. The fluorescence emission decreased dramatically after the sedimentation of the floes was completed. Through these experiments, we concluded that poly-DADMAC was more effective than PEI at removing the FWAs from solution. However, the dosage of the coagulants should be determined based on the type of FWAs and coagulants being used. ? 2018 Korean Technical Assoc. of the Pulp and Paper Industry. All rights reserved.