Polymers 2022 , 14 , 3309
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the potential of cellulose-based flocculants for use in papermaking, and because, in the papermaking process, the available contact time between the flocculant and mineral filler before paper production is lower than 15 min, there is no need to extend the flocculation tests further. Typically, the available time can be even lower than 5 min, and so the most important minutes are the initial minutes of flocculation. 3.4. Mass Fractal Dimension of the PCC Flocs Thed F and SE profiles, calculated from the scattering data for the flocculation tests presented in Figure 6, are plotted in Figure 7. As previously referred to, an analysis of thed F and SE can give some insights regarding the structure (density) of the primary and secondary aggregates, respectively.
Figure7. Evolution of the scattering exponent (SE) and mass fractal dimension (d F ) as a function of flocculation time for several concentrations of the best flocculants. In this flocculation system, the primary particles can be seen as the individual smaller PCC particles. For all three samples, the d F started at ca. 2, dropping to ca. 1.7 after 2 min. Regarding the SE profile, which is more representative of the larger aggregates formed during the flocculation process, at the beginning of the test, as the secondary aggregates started to form, they presented a SE of ca. 0.5 (low density); as time elapsed and flocculation progressed, the secondary aggregates become more compact due to the inclusion of more particles, reaching steady compactness. When using CPAM, independently of the dosage used, SE increased rapidly in the initial minutes, coinciding with the fast growth of the flocs. After 6 min, the SE slowly stabilized at around 2.2. The flocs obtained with both CCs became more compact with increasing levels of addition. For sample CH0.13_F, a dosage of 1 or 2 mg/g of PCC resulted in low SE values (0.7 and 1.1, respectively). A dosage of 4 mg/g of PCC or above produced flocs with a compactness similar to that of those obtained with CPAM (SE of ca. 2.4). As for sample GT0.16_F, at the lowest dosage, flocs that were slightly denser than those obtained with CH0.13_F (SE of 1 versus 0.7) were formed. At a dosage of 2mg/g of PCC, similar densities were obtained for both CCs (SE of ca. 1.1). With a further dosage increase, the flocs became more compact, achieving a maximum SE of ca. 2 at the highest dosage of 10 mg/g of PCC (lower than the 2.2 obtained with CPAM and CH0.13_F). 3.5. Drainability and Filler Retention The drainage time and filler content/filler retention results for the pulp suspension containing pre-flocculated PCC are presented in Figure 8. A test with only pulp and PCC (no retention agent) was performed as a reference. Considering the previous flocculation results obtained by LDS, where CPAM demonstrated almost the same performance for all the dosages tested, only the lowest dosage (1 mg/g of PCC or 0.02 wt % addition) was used in the DDA tests. For both CCs (CH0.13_F and GT0.16_F), three levels of addition were tested (1, 10 and 20 mg/g of PCC, equivalent to an addition of 0.02, 0.2 and 0.4 wt %).
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