JOURNAL OF NATURAL FIBERS
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usually make the manufacturing processes and end products more expensive (Singh and Endley 2020) The nano silica is used in pulp and paper, with improvement in whiteness, brightness, and opacity of the paper sheet as compared with an unloaded or unmodified paper sheet (Lourenço et al. 2015). Because of the smaller particle size exhibited by nano silica, it provides a large surface area for higher light scattering on a paper sheet (Morsy, El-Sheikh, and Barhoum 2019). The addition of nano silica in paper also resulted in the reduction of print-through (Chen et al. 2022). Furthermore, the nanosilica could provide paper with antibacterial properties that result in high degradation and high abatement (Julkapli and Bagheri 2016). Another extraction method involves utilizing agricultural residues. By controlled burning of these residues, ash is formed, which contains a significant amount of silica along with a minor carbon content (10%-20%) and traces of other inorganic/organic components. The composition of the ash depends on factors such as the type of furnace, burning conditions, variety of agricultural waste, geographical area, and climate. Silica nanoparticles, with a narrow size distribution ranging from 20 to 30 nm and a spherical shape, exhibit a semi-crystalline phase as indicated by the X-ray diffraction patterns showing a broad peak at 2θ = 22.5° (Morsy, El-Sheikh, and Barhoum 2019). When compared to an unloaded sample and PCC-loaded paper, paper containing nanosilica shows a lower density due to the exceptional retention and small particle size of the nanosilica, resulting in a 46.5% reduction in density. The enhanced retention of silica nanopar- ticles leads to increased inter-fiber spacing, ultimately decreasing the density of the paper sheets. Figure 1 shows the colloidal nanosilica with a spherical shape. In addition to nanosilica, colloidal silica has also been widely applied in the papermaking industry due to its excellent dispersion stability and surface reactivity. Colloidal silica consists of silica nanoparticles stably suspended in a liquid medium, typically water, where electrostatic repulsion prevents particle agglomeration (Wiśniewska et al. 2017). This stable dispersion allows colloidal silica to distribute uniformly within the fiber matrix or coating formulation. In papermak- ing, it is commonly used as a retention aid, surface modifier, and coating additive, owing to its high specific surface area and negatively charged surface, which enhance fiber – filler interactions and improve sheet formation (Taheri, Rahmaninia, and Khosravani 2022). The addition of colloidal silica has been reported to improve the surface smoothness, gloss, and printability of coated papers while simultaneously reducing surface porosity and enhancing barrier properties against liquids and oils (Samanmali et al. 2025). Furthermore, when incorporated in coating formulations, colloidal silica contributes to higher brightness and opacity through improved light scattering and better pigment distribution. Compared with conven- tional or dry nanosilica powders, colloidal silica provides better dispersion uniformity, fewer aggregates, and more consistent optical performance, making it highly suitable for high-quality coated and specialty papers (X. Li et al. 2025). Characterization. Table 1 shows the result of the burst index, tensile index, and tearing index. In terms of burst index, hand sheets containing silica nanoparticles demonstrate lower value (3.82 kPa.m 2 /g) compared to control sample (4.68 kPa.m 2 /g). This reduction was attributed to the small size of the nano-filler particles,
Figure 1. Colloidal nanosilica (Julkapli and Bagheri 2016).
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