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M. N. A. MOHAMMAD TAIB ET AL.
Calcium carbonate (CaCO 3 ) is the typical filler that is used in pulp and paper processes as a pigment for brightness. It can also be extracted into nanosized particles and added together in small amounts for the same purposes in the pulp and paper process. The cost of production for this filler is considered less expensive and cheaper than titanium oxide and zinc oxide, which have the same purpose of brightening paper (Hubbe and Gill 2016). The raw material is available in the form of ground calcium carbonate that is produced from grinding limestone, marble, or chalk. Moreover, the precipitated calcium carbonate is produced from the carbonation of lime with a special precipitation process that uses special calcium carbonate pigments (Jimoh et al. 2018). This process consequently produces a wide variety of shapes and size distributions (Hubbe and Gill 2016). The CaCO 3 nanofillers that are prepared by the carbonation method are applied for wet-end papermaking applications (El-Sherbiny, El-Sheikh, and Barhoum 2015; Shen et al. 2010). The CaCO 3 nanofillers have a higher cost of production and poor retention properties. Usually, water-soluble additives are used to control the morphology, size, and surface properties. Additives such as chitosan and starch are used together to improve the CaCO 3 nanofillers strength properties in papers (El-Sherbiny, El-Sheikh, and Barhoum 2015; Zhao 2005). A surfactant, either anionic or cationic, is sometimes added to the paper processing to improve the intended properties of the paper (T. Wang et al. 2021). In a study by El-Sherbiny et al. (El-Sherbiny, El-Sheikh, and Barhoum 2015) using nano CaCO 3 in wet-end papermaking showed higher brightness and opacity compared with commercial ones. It was also reported that mechanical strength, such as burst index and tear strength, decreases, but tensile strength slightly increased from 1.52% to 6.53%. The slight increment was due to an increase in filler retention and fiber-to-fiber bonds. Another report by Fortună et al. (Fortună et al. 2020) showed that the addition of a small amount of nano CaCO 3 was not significant in reducing strength while at the same time giving better opacity and higher retention. Another study was reported by Morsy et al. (Morsy, El-Sheikh, and Barhoum 2019) on using hybrid CaCO 3 mixed with nano silica via the sol-gel method on papermaking to improve the optical properties of paper, such as brightness, whiteness, and opacity. But it reported some drawbacks on mechanical property reduction when compared with commercial CaCO 3 . Incorporating fillers caused a change in the morphology of the paper sheet, with the filler particles being deposited on the surfaces of the fibers in the fiber-based matrices. The surface of the paper sheet had a higher concentration of Nano PCC, and the distribution was more uniform compared to the commercial GCC filler. The retention of Nano PCC was higher due to its smaller particle size and more even distribution compared to the micro-sized PCC sample (Kinnunen 2025). The addition of Nano PCC in the paper results in increased bulkiness and lower density compared to unloaded paper. This was primarily attributed to the presence of filler particles, which have the tendency to create gaps between fibers that would otherwise be closely bonded in the sheet (Bown 1998). Figure 5 shows the particle morphology or TEM images of the prepared nano CaCO3 fillers: unmodified (pure CaO (PU), waste marble (MU) and limestone (LU). Marble (MU) and limestone (LU) (El-Sherbiny, El-Sheikh, and Barhoum 2015) Characterization. A decrease in the burst index was observed for paper with Nano PCC, which may be attributed to its higher retention values and the larger number of filler particles that interfere with fiber bonding. The addition of fillers to papermaking is known to decrease paper strength due to the poor
Figure 5. TEM images of the prepared nano CaCO3 fillers: unmodified (pure CaO (PU), waste.
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