S1064
V.S. Chauhan, N.K. Bhardwaj
Figure 5 Micrographs of Talc-3 filler dispersed in different mediums taken from an Image analyzer at 1000 magnification dispersed with (a) water only, (b) wetting agent, (c) dispersant, and (d) wetting agent and dispersant.
As the pH has an effect on the colloidal charge demand of fil- ler, the latter was measured at 9.0–9.2 pH. The cationic colloi- dal charge demand of Talc-3 filler dispersed in water only was 2.0 l eq/g which increased slightly to 3.3 l eq/g in the case of Talc-3 dispersed using wetting agent. The anionicity of Talc- 3 filler increased substantially in the case of its dispersion with the dispersing agent; the cationic colloidal charge demand in- creased to 24.2 l eq/g. These results indicated that the anionic- ity of the talc filler increased on the addition of dispersant. The use of talc filler of higher anionicity will ultimately increase the anionicity of the papermaking slurry and will reduce the filler retention due to more repulsion of anionic–anionic particles. This effect was confirmed from the results of first pass ash retention (FPAR) of Talc-3 filler dispersed in different man- ners. The FPAR of Talc-3 filler dispersed in water only was 41.1% which decreased to 38.8%, 25.0% and 23.4% when Talc-3 filler was dispersed with wetting agent, dispersant, and both wetting agent and dispersant, respectively (Fig. 6). 3.3.3. Effect of dispersion time on retention and light scattering coefficient of Talc-3 filler The Talc-3 filler was dispersed in deionized water and agitated in an emulsifier (2000 rpm) for different time intervals. The talc slurry was agitated for 30, 60, 90 and 120 min, and was then added to the refined pulp stock. Paper handsheets of 60 g/m 2 were prepared with the target ash content of around 15%. It was observed that the ash retention as well as scattering
Table 3
Particle size distribution of Talc-3 filler dispersed
using different methods.
Particular
Abundance, % With water only With wetting agent a
With dispersant b
With wetting
agent a and dispersant b
<20 l m <10 l m <7 l m <5 l m <4 l m <3 l m <2 l m
100 100
100
100
92.1 93.4 65.8 68.3 30.0 31.8 13.1 14.0 3.2 3.4 0.2 0.2
92.3 66.8 31.5 14.2
93.0 67.6 31.4 13.9
3.6 0.2 6.0 6.4
3.4 0.2 6.0 6.3
Median (D50), l m 6.0 6.0
Mean, l m
6.4 6.3
a Wetting agent, 7 kg/t filler. b Dispersant, 3 kg/t filler.
plane of talc. Moreover, the nonionic triblock polymer used as a wetting agent resulted in a complete removal of the bubble- induced attractive force. Moreover, there was only one component affected by the wetting/dispersion that is colloidal charge of talc filler slurry.
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