S1062
V.S. Chauhan, N.K. Bhardwaj
more likely be adsorbed on the hydrophilic edges of talc (Wallqvist et al., 2009). Initially, Talc-3 filler was used to select the appropriate dos- age of wetting and dispersing agent for the proper dispersion. As shown in Fig. 2, the viscosity of talc filler dispersed in water only was 234 cP (Chauhan et al., 2012b). The lowest viscosity of separately wetted and dispersed talc slurries was around 56 and 40 cP with the addition of 7 kg/t of wetting agent and 3 kg/t of dispersant in the talc filler, respectively. Thereafter, further increasing the dosage of wetting agent and dispersant did not affect the viscosity very much. In order to analyze the combined effect of wetting and dis- persing agent, wetting agent was first added in the talc slurry at a dosage of 7 kg/t on talc and agitated for 5 min. The disper- sant was then added at three dosage levels, 3, 6 and 10 kg/t on talc. As shown in Fig. 3, it was observed that the combina- tion of 7 kg/t of wetting agent and 3 kg/t of dispersant was suf- ficient enough to decrease the viscosity to its lowest level i.e. 24 cP (Chauhan et al., 2012b). The viscosity of talc slurry in- creased slightly on increasing the dosage of dispersant. Hence- forth, the dispersion of talc filler was performed with the optimized dosage of both wetting agent and dispersant. 3.3.1. Micrographs of fillers The literature shows that the talc has platelet/lamellar struc- ture. This was further confirmed from the scanning electron micrographs of all talc fillers taken at 5000 · magnification (Fig. 4). The micrographs also corroborate the difference in particle size of talc fillers measured through a particle size ana- lyzer. The images of Talc-3 filler dispersed in water, wetting agent, dispersant, and wetting agent with dispersant taken from the Image analyzer are shown in Fig. 5. The images clearly indicated that there was no effect of dispersion method on the particle separation. The particles of Talc-3 filler were equally dispersed through using either of the dispersion techniques. 3.3.2. Particle size distribution of Talc-3 filler It is obvious that the wetting and dispersion of mineral parti- cles are always desirous to avoid the agglomeration of parti- cles. It was observed that the PSD of Talc-3 filler wetted/ dispersed in different manners was almost comparable. The median particle size of Talc-3 filler dispersed with water, wet- ting agent, dispersant, and wetting agent with dispersant was
Talc-5. The particles of Talc-1, Talc-2, Talc-3, Talc-4, and Talc-5 fillers less than 10 l m were 56.9%, 76.9%, 92.5%, 93.3% and 95.6%, respectively. Similarly, the particles of Talc-1, Talc-2, Talc-3, Talc-4, and Talc-5 fillers less than 3 l m were 0.5%, 1.3%, 2.8%, 6.4% and 7.9%, respectively. The median particle size of Talc-1, Talc-2, Talc-3, Talc-4, and Talc-5 fillers was 9.3, 7.6, 6.0, 5.7 and 5.4 l m, respectively (Table 2). The particle shape of talc fillers measured with X-ray diffractometer was lamellar (Table 1).
3.3. Wetting and dispersion of talc filler
In order to get the positive effect of the filler particles on light scattering coefficient, they were dispersed in a different manner prior to their addition to paper. In our previous study, the ef- fect of wetting and dispersion of talc filler of medium particle size (i.e. Talc-3) on papermaking was studied (Chauhan et al., 2012b). In this study too, we have used the nonionic triblock copolymer and sodium polyacrylate as wetting and dispersing agents, respectively, and have studied their effect on the disper- sion of talc fillers of different PSD. It is known that because of the amphiphilic structure of the poly(acrylic acid) based dis- persant, it can be used to increase the water solubility of hydrophobic substances such as talc. Due to the anionic charge on both dispersant and platelet talc, the dispersant was not adsorbed on the basal plane of talc, rather it would
Table 2
Particle size distribution of talc fillers.
Particulars
Abundance, % Talc-1 Talc-2 Talc-3 Talc-4 Talc-5
<20 l m <10 l m <7 l m <5 l m <4 l m <3 l m <2 l m
96.8 99.5 100
100
100
56.9 76.9 24.7 41.9 7.1 14.5
92.5 93.3 95.6 66.5 70.3 76.4 29.7 36.2 42.9 12.5 18.3 22.9
2.6 0.5 0.0
5.7 1.3 0.0 7.6 8.1
2.8 0.1 6.0 7.1
6.4 0.7 5.7 6.0
7.9 1.2 5.4 5.7
Median (D50), l m 9.3
Mean, l m
10.1
700
266
With wetting agent With dispersant
250
600
228
200
500
190
150
400
152
300
114
100
200
76
50
100
38
0
Wetting agent (7 kg/t) & dispersant (10 kg/t)
Wetting agent (7 kg/t) & dispersant (6 kg/t)
Dispersnt (3 kg/t)
Wetting agent (7 kg/t) & dispersant (3 kg/t)
Water only Wetting agent (7 kg/t)
0
0
0
2
4
6
8
10
Dosage, kg/t talc
Figure 2
Viscosity behavior of Talc-3 filler treated with varying
Figure 3
Effect of wetting and dispersing chemicals on viscosity
dosages of wetting and dispersing chemicals.
of Talc-3 filler.
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