JOURNAL OF NATURAL FIBERS
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functions as a gas barrier, change the polarity from hydrophilic to hydrophobic, and act as an antibacterial and UV protector (Spagnuolo, D’Orsi, and Operamolla 2022). Nanocellulose can be modified on its surface using different approaches to improve its dispersion ability (between nonpolar and polar materials) and further improve its properties (Taib et al. 2024). Figure 3 shows the approach for nanocellulose modifications. The abundantly available OH groups make it able to be substituted with other functional groups such as acetyl, carbonyl, carboxyl, and others through esterifica- tion, sulfonation, amidation, oxidation, and other processes. The three OH groups located at C2, C3, and C6 are considered reactive for the reaction (Mohammad Taib et al. 2022; Taib et al. 2018). NCC is composed of rod-shaped nanoparticles that are typically 10 to 20 nm in diameter and have a length of several hundred nanometers depending on the production method. It also possessed a high degree of crystallinity, ranging from 60% to 85% with rigid and highly crystalline nanoparticles (Salem et al. 2023). The morphology of the NCC is affected by various factors, including the source of the raw materials, pre-treatment methods, and the parameters of acid hydrolysis (type of acid, concentration, duration, and temperature). However, NFC typically exhibited a lower crystallinity, ranging from 50% to 70%, compared to NCC (Damásio et al. 2025; Rajinipriya et al. 2018). The morphology of NFC is also affected by several factors, including pre-treatment methods, mechanical disintegration techniques, and processes employed, as well as the degree of mechanical fibrillation, which encompasses parameters such as energy input or the number of cycles applied. Typically, the method of production (such as pre-treatment and mechanical fibrillation) has a greater impact on the dimensions of the resulting NFC compared to the source of the cellulose itself (M. C. Li et al. 2021). Figure 4 shows the morphology of NCC and NFC on a paper sheet. Characterization. The smoothness of a paper’s surface is influenced by the average length of fibers, the presence of cellulosic fines, their stability within the paper structure, and the quality of the paper’s formation. Consequently, the appropriate combination of these factors determines the effectiveness of additives in the pulp suspension (Tirronen 2024). When NFC was added at an 8% concentration, the roughness decreased by 11.1% compared to the sample without NFC. This reduction can be attributed to the
Esterification
carbamation
Silylation
Grafting onto
TEMPO oxidation
Surface functionaliztion on nanocellulose
Grafting from
Sulfonation
Phosphoryl ation
Amidation
Non- covalent crosslinking
Figure 3. Surface functionalization methods on nanocellulose.
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