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M. N. A. MOHAMMAD TAIB ET AL.
Nano kaolin is modified using various methods to cover the disadvantages of kaolin, such as using centrifuge or sedimentation processes, chemical bleaching, acid activation, calcination, or thermal treat- ment (Liang, Li, and Fang 2023; Masihi and Badalians Gholikandi 2021). The surface modification is applied to kaolin using the intercalation process to modify the kaolin surface with the involvement and insertion of low molecular weight organic reagents that include guest molecules (dimethyl sulfoxide, formamide, potassium acetate, and urea) (Meziane et al. 2017). The insertion is applied between layers consisting of two-dimensional arrangements of tetrahedral and octahedral sheets (Fafard 2018). Bleaching using chemicals is a common technique to enhance the brightness of nano kaolin for high-end paper products (Hubbe et al. 2023). This process involves the discoloration of nano kaolin and the removal of iron particles in solution (Hubbe et al. 2023). Studies by Hassan et al. (Hasan and Fatehi 2018) as well as El- Gendy et al. (Gendy et al. 2014) used different polymer materials together with nano kaolin after pulping. The results enhanced the mechanical properties and water absorption. Nano kaolin and nano calcium carbonate are also used as coatings on paper surfaces instead of bright pigments on paper (El-Sherbiny, El- Sheikh, and Barhoum 2015; Julkapli and Bagheri 2016; Naijian et al. 2019). Carbon nanotubes (CNTs) are cylindrical structures made of carbon atoms arranged in a hexagonal lattice. Due to their high aspect ratio, high electricity conductivity, and high strength (Imai et al. 2010), CNTs have attracted significant attention in various fields, including electronics, energy storage, and biomedicine. Recently, CNTs have also been explored as nanofillers for papermaking to improve the electrical properties of paper products. The addition of CNTs to paper can enhance its conductivity while maintaining its flexibility and lightweight nature. This has led to the development of new types of paper products with potential applications in industries such as packaging, electronics, and biomedical engineering. However, further research is needed to fully understand the potential benefits and limitations of using CNTs as nanofillers for papermaking. CNTs are cylindrically shaped hollow structures made of a sheet of carbon atoms (R. Wang et al. 2020). CNTs are independently disseminated in the cellulose network with minimal interactions at low CNT loading. However, increasing the CNT load tends to agglomerate at high concentrations and form a continuous network (Salajkova et al. 2013). The SEM image of CNTs in cellulose composite paper is shown in Figure 6. Electrical conductivity Carbon nanotubes (CNTs)
Figure 6. Cnts in cellulose composite paper (Maria and Mieno 2017).
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