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PEER-REVIEWED ARTICLE
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Fig. 3. Light microscope images of composites formed at various ratios: (a) 0, (b) 0.15, (c) 0.3, and (d) 0.75 Paper Properties Paper bulk is an important property that influences printing performance. The paper basis weight will decrease if the bulk increases at a constant thickness, which reduces the amount of fibers and production cost. Figure 4 shows that when increasing the ratio of fines to FACS to 0.3, the value of paper bulk increased by 6% in comparison with the control sample (no fines). This is contrary to the popular theory that paper bulk decreases when fines content increases (Sirviö and Nurminen 2004). When the ratio was larger than 0.3, paper bulk decreased (the filler content of all paper samples was 17±0.5%). The particle size and structure of the filler are responsible for paper bulk (Brown 1998). Large particles can create greater inter-fiber spaces in the fiber-fiber bonding domain, which helps to improve bulk (Hubbe and Gill 2004). Additionally, composites with a loose structure can result in more air voids, which also creates more bulk. As shown in Fig. 3, compared with FACS flocs, composites formed at a ratio of 0.15 exhibited larger particle sizes, which improved the bulk. However, the composite formed at a ratio of 0.3 was bigger and had a looser structure than that formed at 0.15, which resulted in continued improvements to paper bulk. When the ratio was greater than 0.3, although the particle size of composite is larger than FACS, the excess amount of fines filled the voids in the bonds and placed the fibers closer to each other. This resulted in a decreased paper bulk.
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Zhang et al . (2016 ). “ Coflocculated fines & CaSiO 4 ,” B io R esources 11(3), 7406-7415.
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