Effect of Recycling Number on the Fluorescence Reduction of Fluorescent Whitening Agents in White Wastepapers
50% RH; and then, their CIE whiteness, ISO brightness, and fluorescence indices were mea- sured. Here, the fluorescence index was deter- mined from the CIE whiteness measurements un- der a D65 illuminant. The fluorescence reduction from the paper dyed with FWAs was calculated as an indicator, which represents the FWA detach- ment from paper, using the fluorescence indices before recycling and after each round of recycling. 7) The distribution of FWAs in the cross section of the paper was observed using a CLSM (JP/FW 1000, Olympus, Japan). 9)
D-FWA was added into the stock mix itself, whereas T-FWA and H-FWA were used on a lab- oratory coater for surface-sizing with oxidized starch. Fig. 2 shows the CIE whiteness and the ISO brightness values of the paper containing D-FWA as a function of the number of recycling rounds. The initial CIE whiteness and ISO brightness val- ues of the paper were proportional to the addition level of D-FWA. 10) When the addition of D-FWA was more than 0.8%, the CIE whiteness of the pa- per was more than 120% and the ISO brightness of the paper was more than 95%. As the recycling was carried out, the optical properties of the hand- sheets exponentially decreased. Figs. 3 and 4 show the CIE whiteness and the ISO brightness values of the paper that was sur- face-sized with T-FWA or H-FWA. Before recy- cling, the paper surface-sized with H-FWA showed higher optical properties than the paper that was surface-sized with T-FWA. 9) As the re- cycling was performed, the CIE whiteness and ISO brightness of the handsheet exponentially de- creased. Compared to D-FWA, T-FWA, and H-FWA showed a higher reduction in the optical properties irrespective of the lower number of re- cycling rounds. In addition, H-FWA showed the highest reduction in the optical properties among the FWAs used in this study.
FI
FI
−
FI before
after
Fluorescence reduction
× 100
=
[1]
before
where FI before is the initial fluorescence index in- duced by CIE whiteness under D65 illumination before recycling, and FI after is the fluorescence in- dex induced by CIE whiteness under D65 illumina- tion after each round of recycling.
3FTVMUTBOE%JTDVTTJPO
&GGFDUPGSFDZDMJOHPOPQUJDBMQSPQFSUJFT PGQBQFSUSFBUFEXJUI'8"T Three types of papers were prepared using D-FWA, T-FWA, and H-FWA solutions. The
Fig. 2. CIE whiteness (left) and ISO brightness (right) of the paper containing D-FWA as a func- tion of the number of recycling rounds.
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펄프·종이기술 51(2) 2019
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