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M. N. A. MOHAMMAD TAIB ET AL.
Table 1. Mechanical properties of control paper and paper loaded with nanosilica (Martin et al. 2017.). Types of sample Burst Index (kPa.m 2 /g) Tensile Index (N.m/g) Tearing Index (mN.m 2 /g) Control paper 4.68 72.74 10.02 Paper with nanosilica 3.82 50.44 10.71
allowing for better coverage of the fiber surface and reducing inter-fiber contact across a larger surface area (Martin et al. 2017). Among various filler types, silica nanoparticles have the smallest particle size and highest retention, which explains the ability to achieve the lowest hand sheet burst index. The addition of silica nanoparticles significantly decreases the tensile index, although the nanocomposite samples still exhibit acceptable values. The sample demonstrated higher retention (70.8%) compared to PCC, contribut- ing to the decrease in tensile index. When it comes to tear index, the hand sheets incorporated with silica nanoparticles exhibit higher value compared to untreated sample. This improvement was attributed to the smaller particle size and higher retention of silica nanoparticles, resulting in an enhanced tear index. In a study by Morsy, El-Sheikh, and Barhoum (2019) with the addition of nano silica in pulp and paper, the improvement of burst and tear indexes was observed because of the fine particle size and higher retention of the filler used. These tiny and fine particles would cover a larger part of the fiber surfaces and prevent inter-fiber contact over a large fraction of the surface area (Jakovljević et al. 2024). It was also reported that the tensile index decreased with the addition of this nanosilica to 40.35 N m/g as compared with 72.74 N m/g for the unmodified paper. Furthermore, the higher retention properties were also observed. In a different study by Gamelas, Lourenco, and Ferreira (2011), hydrogen bonds between cellulosic fibers of paper and silica improved the interaction between both materials. A study by Lourenço et al. (2015) also used silica but with some modification with ground calcium carbonate in the papermaking, and it increased the tensile index from 16% to 20%. The same study also reported a rise in bulk values, from 7% to 13%. The enhanced fiber-to-filler bonding may be caused by the hydroxyl groups in silica coatings and cellulosic fibers. Chemical groups known as silanol groups (-Si-OH) primarily cover the silica surface, possessing a highly polar structure and being considered chemically active (Sahakaro 2017). Application. The dispersity and flowability of the art paper coating are significantly improved when nanosilica is utilized. Additionally, the use of art paper coated with nanosilica enhances the surface strength, smoothness, and gloss of the coated paper while reducing its yellowing rate. Similarly, in the case of inkjet paper coating, incorporating nanosilica leads to better dispersity in the prepared coating. This results in coated paperboard with improved ink transfer, higher K& N value, and increased whiteness. The K& N value is referring to Kappa number test that determine how much residual lignin is present in pulp. Moreover, the ink-jet paper coating containing silica enhances the smoothness and gloss of the paperboard. The print gloss of paperboard coated with inkjet paper coating with silica is further improved through mixed with multiple types of adhesives (Liu et al. 2011). The application of nanosilica in both art paper and ink-jet paper coatings offers significant benefits. Nanosilica improves the dispersity and flowability of the coatings, resulting in enhanced surface strength, smoothness, and gloss of the coated paper. It also reduces yellowing rates in art paper coatings and promotes larger ink transfer and increased whiteness in inkjet paper coatings. Additionally, the combine application of different adhesives further enhances the print gloss of paperboard coated with ink-jet paper coating containing nanosilica. Overall, the incorporation of nanosilica proves to be a valuable approach for enhancing various properties of coated paper products. Nanoclay Natural clays are low-cost materials composed of fine-grained minerals. Currently, nanoclays are the most commonly used nanoparticles, and they exist in the form of sheets/platelets with at least one dimension in the nanoscale range. The term “clay” refers to a naturally occurring material composed of fine-grained materials that have appropriate water contents and will harden when dried or fired (Gaikwad and Ko 2015). Clays and clay minerals have been widely used and utilized in many fields and applications, such as engineering, agriculture, pulp and paper, and many more (Gaikwad and Ko 2015). Various methods, such as centrifugation, ultracentrifugation, and freeze-drying, are employed to produce nanoclays from artificial or natural bulk clay fractions (Baki et al. 2014). Nanoclay is usually added to pulp and paper
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