JOURNAL OF NATURAL FIBERS
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bonding ability of filler matrices, which can interfere with fiber-to-fiber bonding (Yoon and Deng 2007). The tensile indexes were not negatively affected, as would be expected. A little increment was observed with the percentage increase ranged from 1.52% to 6.53%. The adsorption of Nano PCC could compensate for the reduction in fiber-to-fiber bonds caused by increasing filler retention (Yoon and Deng 2007). In terms of tear index, the findings showed that paper sheets that contain Nano PCC fillers exhibited a higher tear index compared to commercial GCC, PCC fillers, and the control sample. The increment reached 7.2%. The possible explanation for this trend could be attributed to the fact that paper resistance to tear increases with a rise in the number of particles and a decrease in filler particle size (Yoon and Deng 2007). Application. Nano PCC offers several benefits, including high brightness, fine particle size, and a significant improvement in paper opacity. Moreover, the fast ink absorption capability of calcium carbonate promotes efficient drying of printing ink, resulting in paper with a relatively soft, dense, and shiny appearance (Wu et al. 2016). The use of Nano PCC in printing paper provides numerous advantages, such as high brightness, fine particle size, improved opacity, and efficient ink absorption. The controlled combustion properties of calcium carbonate further enhance the air permeability of the paper. With its desirable characteristics, Nano PCC emerges as an ideal filler for printing paper, offering enhanced print quality and overall paper performance. Nano calcium silicate Nano calcium silicate is the main compound of silica and calcium silicate (Ca 2 O 4 Si) also known as calcium orthosilicate. The addition of nano calcium silicate as a nanofiller in pulp and paper results in a reduction in paper quality and relative density but, at the same time, increases strength, density, smoothness, filler retention, opacity, and brightness of the paper produced (Bhat et al. 2022). Using the conventional method, calcium silicate is prepared by the solid-state reaction of CaO or CaCO 3 with quartz (SiO 2 ) at a higher temperature (1150–1200 °C) for several hours (Pei et al. 2022; Shionoya, Yen, and Yamamoto 2018). Other methods are used, such as chemical methods through combustion, sol-gel, and co-precipitation, followed by heat treatment at different temperatures (Abdalla et al. 2020; Su et al. 2021). The recent method for synthesizing nano calcium silicate is through the mechano-chemical route, with the advantages of low cost, low processing energy (reaction carried out at room temperature), and mass production with homo- genous and uniform nano-sized components (Fadia et al. 2021). It is also environmentally friendly and waste-free. This method employs a high-energy milling process that involves repeated mixing, deformation, commuting, welding, and re-welding of the reactant particle powder in a closed vial during ball milling (Fadia et al. 2021). Nano kaolin Kaolin is one of the most common types of fillers used in many applications, including the pulp and paper industries (Naijian et al. 2019). It has a fine white color and contains the mineral kaolinite (Al 2 O 3 ∙2SiO 2 ∙2 H 2 O) as its main compound and ingredient (Olaremu 2015). This kaolinite is a hydrous aluminum silicate with a single silica tetrahedral layer that is linked through oxygen atoms to a single alumina octahedral layer (Olaremu 2015). Kaolin with a higher level of concentrations or loadings in papermaking affected the paper’s strength, stiffness, and bulking. On top of that, kaolin also has poor retention (Hubbe and Gill 2016). Thus, the fibers on paper are difficult to hydrophobize. The fibers require modification to enhance filler retention and mitigate the negative impact of this filler (Naijian et al. 2019). Filler modifica- tion with added bio-based modifiers and polysaccharide-based polymers is considered a promising approach (Q. Li et al. 2020). A study by Naijian et al. (2019) on the application of three types of bio-based modified kaolin clay that are from cationic starches, maize, and tapioca in papermaking as additives reported the improvement and good distribution of kaolin-starch fillers and how they bonded together to paper fibers. The kaolin-starch filler had a higher tendency to form clusters between 3.5 and 7.5 times larger compared with unmodified kaolin filler. Furthermore, the brightness and mechanical properties were better than unfilled papers as well as papers filled with unmodified kaolin. In that study, stable hydrophobic properties were also observed in kaolin-starch filled papers.
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