ACS Omega
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Article
products. Thus, we switched to using only one type of AKD and HB-PAM fi xing agent. As can be seen in Figure 7, these changes prevented any surge of spots and led to a substantial decrease in the total number of spots. These results indicated that the use of a new fi xing agent and a single AKD application were e ffi cacious in reducing the formation of waxy spots in low-grammage products and allowed cleaner operation of the A UV/vis spectrometry-based method for the analysis of AKD retention was developed, validated, and applied to investigate the role of several important factors on AKD retention. The e ff ects of extraction time, DMAP/AKD ratio, and reaction time were investigated for the quantitative analysis of AKD using UV/vis spectrometry. The AKD retention was determined by extracting the AKD using chloroform and then treating it with DMAP, followed by a UV/vis analysis at 450 nm. The results showed that an extraction time of 60 min, a DMAP/AKD ratio of 120, and a reaction time of 90 min gave consistent and accurate measurements of AKD content in white water and paper stock. This method was used to investigate the e ff ect of stock components on the quantitative measurement of AKD. A strong correlation between AKD retention and total FPR was found with the R 2 value of 0.762. This indicated the importance of retention control to AKD sizing. To fi nd e ff ective ways of improving AKD retention, the e ff ects of seven variables retention aid dosage, fi xing agent dosage, AKD type, fi xing agent type, fi ller types, fi ller dosage, and pulp type on AKD retention were tested. Retention aid dosage was found to be the most important, followed by AKD type, fi xing agent type, and dosage, and thus the e ff ects of di ff erent values of these four variables were examined in both laboratory and mill trials. The results showed that di ff erent retention aid dosages negatively a ff ected paper formation, which made this approach impractical. However, a judicious selection of fi xing agent and AKD type improved the AKD retention, drainage performance, and sizing e ffi ciency without deleterious e ff ects on paper formation and OBA quenching. Moreover, these optimal conditions led to substantial decreases in the number of waxy spots without any periodic surges in spot number over a long-term period of production. 4. EXPERIMENTAL SECTION papermaking process. 3. CONCLUSIONS 4.1. Materials. Cationic and anionic AKD emulsions, denoted AKD-I (Taekwang Chemicals, Eumseong, Korea) and
(HB-CPAM) was selected as a new fi xing agent because of its high charge density and adsorption properties. A preliminary short-term trial was conducted to investigate this agent ’ s performance, which revealed that HB-CPAM was quite e ff ective in improving retention, wire drainage, sizing, drying energy reduction, and number of waxy spots. We thus conducted a long-term trial, the results of which are shown in Table 6, which indicates that HB-CPAM leads to FPR and
Table 6. Results of Long-Term Trial Using HB-CPAM in Production of 75 g/m 2 Copy Paper
unit
control
trial
HB-CPAM dosage
%/pulp %/pulp %/starch
0
0.02 0.12
AKD dosage OBA dosage
0.15
3.3
3.0
retention
total
%
69.1 38.1
79.9 55.1
ash
wire couch roll vacuum dryer steam pressure ( # 3)
kPa
73
71
kgf/cm 2
2.07
2.02
formation index
%
62.4
63.0
g/m 2
Cobb
21 27
23 26
sizing degree
Stöckigt
s s
HST
462
403
defective waxy spots
EA/spool
12.6
8.0
ash retention increases of 10.8 and 17.0%, respectively. An increase in the sizing degree indicates that AKD retention also improves, and long-term defective spot numbers decrease substantially from 12.6 to 8.0 spots/reel. AKD sizing agents are stabilized emulsions that are usually made from cationic starch or charged polymeric stabilizers. However, cationic or anionic synthetic polyelectrolytes also have been used for AKD stabilization. To examine the e ff ect of AKD type on the defective waxy spot count, we carried out two trials using two AKDs. Alternating the use of AKD-I and AKD- II has been a usual practice in the mill. However, laboratory experiments showed that single application of an anionic AKD was better in many respects. For instance, using anionic AKD only improved the Stöckigt sizing degree from 22.6 to 20.8 g/ m 2 . Thus, we decided to stop the alternating application of AKDs and switched to single use of anionic AKD-II. It can be seen in Figure 7 that the number of spots sporadically surged, sometimes to >100 per spool. These surges of spots occurred primarily when low-grammage products were made, because this necessitated the use of 1.5 times more AKD to keep the sizing level for the low-grammage
Table 7. Properties of Anionic and Cationic AKDs
items
AKD-I
AKD-II
solids content (%)
19.9
19.6
viscosity (cPs)
6.6
7.2
average particle size ( μ m)
0.41 +9.8
0.39
− 11.9 starch
ζ -potential (mV)
stabilizer surfactant
starch
polymer
sodium lignin sulfonate
AKD-II (Laton Korea, Gongju, Korea), respectively (Table 7), were used in both laboratory experiments and mill trials. The particle size and ζ -potential of AKD emulsions were determined using a Malvern Mastersizer (Malvern Instruments Ltd, Almelo, the Netherlands) and an electrophoretic light scattering spectrophotometer (ELS Z-1000, Otsuka Elec-
Figure 7. Number of spots observed over 3 years in 60 g/m 2 wood- free papers.
11231
https://dx.doi.org/10.1021/acsomega.0c01374 ACS Omega 2020, 5, 11227 − 11234
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