ACS Omega
http://pubs.acs.org/journal/acsodf
Article
Table 4. Experimental Layout of Seven-Run Fractional Factorial Designs and AKD Retention
no.
BCTMP (%)
fi xing agent (%/pulp) PAM 0.025 PAM 0.050
AKD
fi ller (%/pulp)
PAM/bentonite (%/pulp)
AKD retention (%)
1 2 3 4 5 6 7 8
20 20 20 20 40 40 40 40
AKD-I AKD-II AKD-I AKD-II AKD-I AKD-II AKD-I AKD-II
GCC GCC PCC PCC PCC PCC GCC GCC
15 30 15 30 30 15 30 15
0.025/0.125 0.050/0.250 0.050/0.250 0.025/0.125 0.025/0.125 0.050/0.250 0.050/0.250 0.025/0.125
88.6 95.3 95.0 93.0 91.3 94.3 94.0 93.0
PAE PAE
0.050 0.025
PAM 0.050 PAM 0.025
PAE PAE
0.025 0.050
in mill trials, i.e., PAE resin and highly branched cationic PAM (HB-CPAM). PAE resin has been widely used as a fi xing agent, and it often increases AKD retention. 31,32 Thus, a mill trial was carried out on a paper machine that produced wood-free paper with a basis weight of 80 g/m 2 . The stock was prepared with 15% softwood BKP, 65% hardwood BKP, and 20% BCTMP, with GCC and PCC used as fi llers. The proportions of PCC and GCC were 70 and 30%, respectively, and the total ash content in the paper was approximately 26%. In the fi rst trial, 0.05% PAE increased the ζ -potential of the machine chest and headbox stocks, which resulted in a 3 − 4% total retention improvement compared to the control run. This increased retention also increased the sizing degree, did not negatively a ff ect paper formation, and decreased the number of waxy spots per spool by 0.9 spots per reel, which was measured using a web imaging system (ULMA, ABB Ltd., Louth, Ireland) installed at the end of the paper machine. Nevertheless, we required a greater reduction in the number of waxy spots per spool to produce a better-quality paper. To achieve this, in the second trial, we increased the PAE resin dosage to 0.1 − 0.2% and decreased the addition of sizing agent from 0.48 to 0.35% (Table 5). Despite this decreased addition
Figure 6 shows a Pareto chart summarizing the e ff ect of di ff erent variables on AKD retention. Brie fl y, a Pareto chart is
Figure 6. Pareto chart of e ff ects for AKD retention, based on pooled data.
invaluable for determining the factors that need the most attention to improve a process. A bar graph with values plotted in decreasing order of the e ff ect on a given system is the usual way to present the data on a Pareto chart. 29 Thus, a Pareto chart is a basic tool of quality control, in which independent variables (in this case, retention aid dosage, AKD type, fi xing agent type and dosage, etc.) are shown on the axis and dependent variables (in this case, AKD retention) are represented in bars of di ff erent lengths. The Pareto analysis showed that retention aid dosage, AKD type, and fi xing agent type and dosage were the four main factors a ff ecting AKD retention greater than a threshold (standardized) value. AKD retention increased in proportion to the retention aid dosage, which showed the importance of FPR for AKD sizing. Themain e ff ect plot (not shown) for AKD retention from the fractional factorial experiment data showed that AKD-II performed better than AKD-I when various stock components such as cationic starch and fi xing agents were used before AKD addition. The use of fi xing agent was found to be an important factor a ff ecting the AKD retention. For example, the addition of polyamidoamine-epichlorohydrine (PAE) resin led to better AKD retention than the addition of a PAM-type fi xing agent. The strong cationic charge density of the PAE resin made it e ff ective as a fi xing agent for AKD. 30 2.4. Short-Term Mill Trials with PAE Fixing Agent. Among the seven factors tested, a 0.025% increase in the retention aid dosage was found to be the most e ff ective way to increase AKD retention. This approach, however, deleteriously a ff ected the formation and other properties of paper. As a second option, we compared the e ffi cacies of two fi xing agents
Table 5. Results of the First Mill Trial Using PAE Resin
trial
item
unit
control
after 4 h after 8 h
PAE dosage AKD dosage OBA dosage
%/pulp %/pulp %/starch
0
0.1
0.2
0.48 1.60
0.40 1.73
0.35 1.90
retention total
%
75.5 31.3
81.4 39.5
84.6 44.1
ash
2
dryer steam pressure ( # 3)
kg f /cm
1.18
1.08
1.08
formation index
%
49.6
51.0
49.6
Stöckigt sizing degree s
11 19
13 14
15 15
defective waxy spots
EA/spool
of sizing agent, the Stöckigt sizing degree increased from 11 to 15 s. In addition, the FPR increased from 75.5 to 84.6%, and the FPR of ash increased substantially, from 31.3 to 44.1%. We also observed a concomitant improvement in the wire drainage and decreased steam consumption for drying, and the number of defective waxy spots per spool decreased from 19 to 14 − 15. However, 0.1% or more PAE also led to quenching of the fl uorescent whitening agent, which necessitated an increase of the optical brightening agent (OBA) dosage from 1.60 to 1.90%. To solve this UV quenching e ff ect by PAE, other fi xing agents were explored. 2.5. Long-Term Mill Trial Using Highly Branched C- PAM and Anionic AKD. Highly branched cationic PAM
11230
https://dx.doi.org/10.1021/acsomega.0c01374 ACS Omega 2020, 5, 11227 − 11234
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