Ji Young Lee·Chul Hwan Kim·Hae Min Jo·Kyung Min Kim·Su Ho Kim
Fig. 3. CIE whiteness (left) and ISO brightness (right) of the paper that was surface-treated with T-FWA as a function of the number of recycling rounds.
Fig. 4. CIE whiteness (left) and ISO brightness (right) of the paper that was surface-treated with H-FWA as a function of the number of recycling rounds.
&GGFDUPGSFDZDMJOHPOUIFGMVPSFTDFODF JOEFYBOEGMVPSFTDFODFSFEVDUJPOJOUIF QBQFSUSFBUFEXJUI'8"T FWA addition improves the optical properties of paper by absorbing more UV light and emitting fluorescence. 11) The fluorescence emission can be determined by measuring the fluorescence indices of whiteness or brightness. 12) In this study, the fluorescence index of whiteness under the D65 il- luminant was measured to identify the existence of FWAs in the handsheets. The fluorescence reduc- tion was calculated using the fluorescence indices before recycling and after each round of recycling. Fig. 5 shows the fluorescence index and fluores- cence reduction for paper dyed with D-FWA. The
initial fluorescence index of the paper dyed with D-FWA was proportional to the addition level of D-FWA. After recycling, the fluorescence index of the handsheet decreased, which means that D-FWA was desorbed from the paper. The fluo- rescence reduction of D-FWA logarithmically in- creased as a function of the number of recycling rounds. However, the fluorescence reduction of D-FWA did not exceed 25% even though the recy- cling processes were performed ten times. Figs. 6 and 7 show the fluorescence indices and the fluorescence reduction in the paper surface- sized with T-FWA or H-FWA. The fluorescence indices of the paper decreased as the number of recycling rounds increased. As the number of
J. of Korea TAPPI Vol.51 No.2 Mar.-Apr. 2019 53
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