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Fig. 6. Scanning electron micrograph of composites in paper sheet Proposed Mechanism Models
Some possible mechanisms of the composite formation process are shown in Fig. 7. The FACS and fines slurry is homogenously dispersed until the addition of CPAM. The chains of CPAM extend its loops and tails, which attach to the filler particles or fines randomly and interact with other particles to form open-structure composites. Without fines, FACS particles flocculate together to form filler flocs. At ratios of 0.15 and 0.3, all the filler and fines form composites, and no fines or FACS particles exist alone. Moreover, the composite formed at a ratio of 0.3 has larger size and looser structure than that formed at 0.15. However, with an increased ratio, excess fines exist or flocculate to flocs, which fill the voids in fiber networks and cause fibers to be closer to each other, resulting in a decreased paper bulk.
Fig. 7. Scheme of fines and FACS co-flocculation by CPAM at various fines to FACS ratios: (a) 0, (b) 0.15, (c) 0.3, (d) 0.45, (e) 0.6, and (f) 0.75 The mechanism model demonstrates the interaction between fibers and composites (Fig. 8). In the traditional filling method, some fillers exist on the surface of fibers and disturb the fiber-fiber hydrogen bonding. In contrast, in the co-flocculation filling method, FACS are enfolded and entwined by fines, which decrease the direct contact between fillers and fibers. Fines bridge the interaction between fibers and fillers and bring fibers closer together, which increases paper strength and decreases bulk. However, the formed composites have a larger particle size than FACS flocs, which compensates for the decrease
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Zhang et al . (2016 ). “ Coflocculated fines & CaSiO 4 ,” B io R esources 11(3), 7406-7415.
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