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M. N. A. MOHAMMAD TAIB ET AL.
The paper’s ability to withstand tensile stress can be determined by its tensile strength, which is primarily influenced by the number and quality of fiber-to-fiber bonds. Enhancing these bonds through wet pressing or refining can improve the paper’s tensile strength, but it will always be lower than that of the fibers. The introduction of nanoclay up to 2% can marginally increase the tensile strength, but further addition can lead to the formation of coarser flocs and reduced fiber-to-fiber bonding, as typical fillers are incapable of creating strong bonds with cellulose fibers (J. E. Kasmani and Samariha 2021). This phenomenon is thought to be caused by the location of fillers in relation to fibers. The fiber length was found to be a factor influencing tear strength, with tear strength being directly proportional to the average fiber length raised to the power of three halves. Although the nanoclay particles were small, adding more of them resulted in the formation of coarser flocs, distribution of flocs, and a decrease in tear strength. However, this decrease was not significant as tear strength is determined by both inter- and intra-fiber strengths. Since the nanoparticles are situated between the fibers, they weaken the fiber bond, leading to a reduction in the strength between the fibers but not affecting the strength of individual fibers (Atmakuri et al. 2020). Therefore, the decline in the tear index is minimal. Table 2 shows the mechanical properties of control paper and paper containing nanoclay Application. Nanoclay possesses remarkable barrier properties, encompassing both gas and liquid barriers. When integrated into the paper matrix or coating, nanoclay enhances the paper’s ability to withstand moisture, oil, and various liquids. This feature is particularly advantageous in packaging applications where there is a need for enhanced barrier properties. The Packaging Development Center at International Paper recently unveiled a novel technology for gas and moisture barriers in beverage packaging. This technology uses a special coating made from nanoclay, which is similar with the nanocomposite coatings previously utilized by International Paper in their jet print photo paper, marketed for inkjet and digital printing applications (Agrawal and Singha 2024). Nanocellulose There are three types of nanocellulose that can be classified according to the method of production, such as nanofibrillated cellulose (NFC) and nanocrystalline cellulose (NCC), and the source of the material, such as bacterial nanocellulose (BNC) (Hashemzehi et al. 2022). NFC is produced using mechanical shear with pretreatment using chemicals from wood and other bio-resources (kenaf, jute, pineapple leaves, and others), while NCC is typically produced using acid hydrolysis methods (Taib, Yehye, and Muhd Julkapli 2020) and BNC is produced from bacterial growth or culture such as Gluconacetobater xylus (Mohammad Taib et al. 2022). The major difference between NFC and NCC is their crystallinity structure and properties. In this sub-chapter, we will discuss NFC and NCC due to their wide usage and potential as nanofillers in the pulp and paper industry. For BNC, it is still in the early stages of development due to the high cost of production (Skočaj 2019). The nanocellulose is used because it offers several advantages, such as being made from abundantly available resources, having a low cost of production, ease of surface functionalization, having outstanding mechanical and biodegradability properties. It can be utilized in pulp and papermaking as a nanofiller to improve strength properties, and it is usually added to wet-end papermaking, laminating, and coating (Spagnuolo, D’Orsi, and Operamolla 2022). The main drawback for nanocellulose is that it forms agglomeration or flocculation when added directly to the pulp and paper process, and there is a need for further surface functionalization to improve the distribution in the pulp and paper process (Pego, Lúcia Bianchi, and Kaji Yasumura 2020a). Furthermore, the addition of nanocellulose in pulp and paper acts as a filler to cover the cellulose fibers and fill up the spaces in the paper (Morais et al. 2021). The nanocellulose has great capacity for forming interconnected networks due to the available OH bonds and provides a satisfactory coating performance. The nanocellulose can be easily surface modified to add additional Table 2. Mechanical properties of control paper and paper containing with nanoclay (J. E. Kasmani and Samariha 2021). Types of sample Burst Index (kPa.m 2 /g) Tensile Index (N.m/g) Tearing Index (mN.m 2 /g) Control paper 1.43 34.22 4.92 Paper with nanoclay 1.35 34.93 4.89
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