ACS Omega
http://pubs.acs.org/journal/acsodf
Article
Figure 4. UV/vis spectrum of AKD-I/DMAP reaction product (left) and calibration line for AKD-II (right).
in fl uence on the AKD extraction by chloroform, indicating that AKD was completely extracted from the white water. The R 2 values of the calibration lines (Figure 4) were >0.999, validating the suitability of this method for the AKD retention analysis. The absorbance at 338 nm was higher than that at 450 nm; however, the former absorbance was in fl uenced by the presence of minor contaminants. 23 Thus, the calibration line from the absorbance at 450 nm was used for analysis. 2.2. E ff ect of Papermaking Stocks on AKD Retention. The AKD retention e ff ects of stocks prepared using hardwood bleached kraft pulp (BKP) 100%, hardwood BKP 50% + bleached chemithermomechanical pulp (BCTMP) 50% (L5B5), and BCTMP 100% were tested, and the results are shown in Table 2. Pulp type had a substantial e ff ect on AKD
Table 3. E ff ect of GCC and PCC Fillers on AKD Retention for Hw-BKP Stock
Hw-BKP only Hw-BKP + GCC Hw-BKP + PCC
AKD-I AKD-II
51.5 50.4
42.5 55.0
55.8 59.8
GCC fi llers was lower than that of PCC when no retention aid was used, and this resulted in a reduction of AKD retention for the GCC stock. Many fi ne materials, such as fi llers, sizing agents, and polymeric emulsions, are contained in a papermaking stock. As the particles of these fi nes are smaller than the opening of the papermaking fabric, their retention is quite low, especially on a high-speed paper machine. Consequently, these fi nes will drain out with white water and circulate through the white water circuit, unless they can be adsorbed onto long fi ber surfaces or extensively fl occulated to be retained on the wet web. To increase the retention of fi nes, a wide variety of retention systems are used. In this study, we used the Hydrocol retention system, which comprises a cationic poly(acrylamide) (PAM) and bentonite, and evaluated its e ff ect on the retention of fi nes, including AKD. The relationship between the fi rst-pass retention (FPR) and AKD retention is depicted in Figure 5.
Table 2. E ff ect of Pulp Type on AKD Retention retention (%) with Hw-BKP 100% retention (%) with Hw- BKP 50% + BCTMP 50%
retention (%) with BCTMP 100%
AKD-I AKD-II
51.5 50.4
38.5 28.6
33.1 17.1
retention, with retention in the BKP stock being much higher than that in the BCTMP stock, while the L5B5 stock gave AKD retentions between those of the BKP and BCTMP stocks. When anionic AKD-II was used, the hardwood BKP and BCTMP stocks gave retentions of 50.4 and 17.1%, respectively, showing that anionic AKD was retained signi fi cantly less in the BCTMP stock. This was attributable to the fact that BCTMP is shorter in fi ber length, contains more fi nes, and possesses more anionic charges. Fillers are widely used in papermaking, as they provide economic bene fi ts and improve the printing and optical properties of paper. 25 Fillers, however, also cause problems in the papermaking process and in paper properties. Fillers cause strength loss and linting on the printing press. Furthermore, fi llers often cause a substantial reduction in sizing. 26,27 A number of researchers have investigated the desizing e ff ect of precipitated calcium carbonate (PCC) on AKD sizing. 11,28 Table 3 shows the e ff ects of di ff erent types of fi ller on the retention of AKD-I and AKD-II. A retention of 51.5% AKD-I was achieved when no fi ller was used, while the addition of ground calcium carbonate (GCC) and PCC led to 42.5 and 55.8% AKD-I retention, respectively. As AKD-I is positively charged, it was expected to be more adsorbed onto negatively charged GCC. Retention of anionically charged and small
Figure 5. Correlation of fi rst-pass retention in wet end and AKD retention in dynamic drainage analyzer (DDA) vacuum drainage.
The regression coe ffi cient is 0.762, indicating a strong positive correlation between these two variables and thus suggesting that controlling FPR will enable the e ff ective retention of AKD. 2.3. Factors for Improving FPR of AKD. Table 4 shows the experimental layout of the random-sequence seven-run fractional factorial design used to explore the optimization of AKD retention with di ff erent additives.
11229
https://dx.doi.org/10.1021/acsomega.0c01374 ACS Omega 2020, 5, 11227 − 11234
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