JOURNAL OF NATURAL FIBERS
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would be fully covered, reducing the pulp retention process. Many studies have shown that the addition of nanofillers can improve paper products’ tensile strength, tear resistance, air and water vapor permeability, hydrophobicity, and thermal stability. Nanocellulose, in particular, has gained attention for its biocompatibility, renewability, and reinforcing potential when blended with pulp fibers or used as coating layers. Meanwhile, mineral and synthetic nanofillers such as carbon nanotubes have shown promise in imparting antibacterial, UV-blocking, or electrical conductivity to paper substrates. However, despite these promising laboratory-scale advancements, the industrial deployment of nano- filler-enhanced paper products remains limited. Existing reviews often focus either on the properties of individual nanofillers or on isolated applications, without systematically addressing the integration challenges and processing, property, and application relationships across the papermaking value chain. This review paper discusses the recent study of the nanofillers used in pulp and paper processing and the characterization of the nanofillers after addition in papermaking. Lack of study on nanofiller processing and properties thus comes to our attention for this review paper. Furthermore, the process involved with the addition of nanofillers in pulp and paper production was also discussed to provide a deeper understanding of which type of nanofillers should be used in different applications. This review paper also elaborated in detail on the functioning of different nanofillers in pulp and paper processes. Overview of nano additives in papermaking Nano additives can be added in several ways to pulps and papers that provide several functionalities, depending on the final applications and use of the end products. Nano additives can be added as bleaching or pigment agents to enhance brightness, and can also be used as nanosizing agents to improve wear properties and adsorption characteristics. Another use of nano additives is to enhance the strength and mechanical performance of materials. The different nano additives are used based on their functions and properties. The typical use of nano additives is as pigment agents. The pigment agents are important components in papermaking because they affect the final properties of the paper produced (El-Sherbiny et al. 2014; Shen et al. 2010). The examples used of nano additives are inorganic compounds such as calcium carbonate and kaolin. Titanium dioxide is also responsible as a pigment agent (El-Sherbiny, El-Sheikh, and Barhoum 2015; Gendy et al. 2014). The use of these additives as pigment agents will also fill up the voids and empty gaps in pulp and paper. It also provides strong retention properties and a barrier (Shen et al. 2010). The uses of other nanofillers are for retention agents, bleaching agents, nanosizing agents, nano-minerals, and improvements in mechanical perfor- mance such as tensile, tear, and burst strength, as well as superconductor agents (Chauhan and Chakrabarti 2012; Julkapli and Bagheri 2016; Lourenço et al. 2019). Nano additives are often added during the wet-end processing in papermaking to create a good uniform distribution with excellent properties in the pulp and paper process. This process involves the dewatering the pulp from its slurry form. This pulp slurry is a mixture of the fibers and water. The process consists of different stages: singeing, desizing, kiering, bleaching, mercerizing, and dyeing. The nanofillers can be added or mixed together during the wet-end processing. Thus, it was considered a convenient way to add the filler during processing. For example, in a study by Xie et al. (Xie et al. 2016), 0.05 wt% cationic polyacrylamide (CPAM) was added as a retention agent to a 0.4 wt% water suspension of pulp slurry and fillers. The fillers were prepared from precipitated calcium carbonate (MPCC) which was modified by using an organic titanium ionic crosslinking agent. The handsheet paper with a target density of 70 g/m 2 was formed using a handsheet former. The handsheet was pressed at 4 MPa for 1 min and dried using an electric heating plate at 80°C for 10 min. The formed papers were further conditioned for 24 hours at 23°C and 50% relative humidity before testing. El-Sherbiny et al. (El-Sherbiny, El-Sheikh, and Barhoum 2015) prepared low-cost CaCO 3 nano additives for wet-end papermaking applications.The nano CaCO 3 was prepared from commercial limestone and white waste marble dust using the wet carbonation technique. The paper handsheet was prepared from hardwood and softwood chemical pulp at 85:15 based on dry weight percentage. Moreover, the cationic polyacrylamide was added (0.1%) to the dry pulp. The prepared nano CaCO 3 was added directly to pulp stock before handsheet forming. The addition of modified nano CaCO 3 increased retention and made it bulkier (having a lower density).
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