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M. N. A. MOHAMMAD TAIB ET AL.
Table 6. Mechanical properties of control paper and paper loaded with nano TiO 2. Types of sample Tensile Index (N.m/g) Tearing Index (mN.m 2 /g) Control paper 45.76 4.69 Paper with nano TiO 2 -10% 51.16 5.26
Characterization. Table 6 shows the enhancement in both the tensile index and tear index when compared to control paper. This observation highlights the beneficial impact of TiO 2 nanofiller on the mechanical properties of cellulosic paper. However, as the loading of TiO 2 nanofiller increased, the surface-coated paper exhibited an initial upward trend followed by a subsequent decline in its mechanical properties. The tensile and tear index of the control paper measured 45.76 N m/g and 4.69 mN m 2 /g, respectively. However, after loading with a 10% TiO 2 nanofiller, the corresponding parameters significantly increased to 51.16 N m/g and 5.26 mN m 2 /g, respectively. This phenomenon can be explained by the TiO 2 nanofiller reinforcement capabilities, leading to significant enhancements in the physical properties of cellulosic paper and the intrinsic size effect of TiO 2 nanoparticles at the nanoscale establishes a close interconnection with the cellulosic fibers (Cazan, Enesca, and Andronic 2021). This interconnection becomes stronger as the loading of TiO 2 nanoparticles increases, as observed in previous studies (Ling et al. 2013). Study by Huang et al. (2011) conducted a study on the fabrication of paper hand sheets using modified nano TiO2 to enhance the paper’s hydrophobic and opacity qualities. According to the findings, nano TiO2 reduced the tensile strength but had superior hydrophobic qualities and a higher opacity index. The reason is due to the good distribution of modified nano TiO 2 with the coupling agent, MPS ((3-trimethoxysilyl) propyl methacrylate) that was added before final paper sheet fabrication. In another study by El-Sherbiny et al. (El-Sherbiny et al. 2014) on nano TiO 2 as a special paper coating pigment, it was shown that the addition of nano TiO 2 increased the brightness and opacity but at the same time decreased the paper roughness and air permeance until it was stable at the 50% level. Application. The papermaking industry has utilized nano TiO 2 as a superior white pigment due to its exceptional properties, including a high refractive index, excellent brightness, superior whiteness, favorable hiding power, and insolubility in alkaline and acidic solutions (Tao, He, and Zhao 2015). Furthermore, the application of nano TiO 2 coatings on cellulosic paper has demonstrated significant improvements in various properties. These coatings have proven effective in enhancing the mechanical properties of the paper and providing it with high antibacterial activity. As a result, nano TiO 2 holds great potential for application in antibacterial packaging within the papermaking industry (Tang et al. 2016). In conclusion, nano TiO 2 offers numerous advantages and has diverse applications. It exists in poly- morphic phases, with rutile and anatase being the most commonly synthesized. When used as a nanocomposite in cellulosic paper, nano TiO 2 enhances its mechanical properties, such as the tensile index and tear index. However, there is an optimal loading level, as excessive amounts can lead to a decline in performance. Overall, nano TiO 2 shows promise for improving the physical properties of materials in various applications. Table 7 shows the summary of the nano additives in terms of shape, size, loading concentration, cost and properties enhancement.
Comparative summary of paper with different nanofillers Challenges and future recommendations
The challenges in extracting and processing the nano additives in pulp and paper with desirable properties become a major concern. This is also related to the cost of manufacturing, which will be an issue for industry to produce and use in large volumes. The cost associated with inorganic additives such as nano TiO 2 , ZnO and CNTs are considered expensive, and they need to be used wisely, even though the improvement in mechanical properties is higher as compared with others. The challenge of poor retention, which affected the final products, also needs to be overcome. Furthermore, the addition of the inorganic nano additives leads to a non-green and non-environmentally friendly product. The inorganic materials, such as nano calcium silicate, also required a high temperature and long processing time to obtain a low-yield end product. The use of nano additives from natural resources will become a main subject and priority for
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