## 1 Introduction
The presence of cellulose in the cell walls generally makes NF hydrophilic in nature, with moisture content (MC) of 8%-13(%) [26]. The MC influences the degree of crystallinity, crystallite orientation, tensile strength (TS), swelling behavior, porosity, and surface characteristics, which are crucial factors in NF classification [26; 27; 28; 29]. Hemicellulose is located between cellulose and lignin, and it is a mixture of sugars (e.g., glucose, galactose, xylose, mannose, and arabinose) [28]. Both the hemicellulose and cellulose chains are components of the cementing mechanism of the NF [19]. Lignin is located between individual cells and between the cellulose fibrils forming the cell walls of the NF. It is composed of nine carbon units derived from substituted cinnamyl alcohol (i.e., coumaryl, coniferyl, and syringyl alcohols) and acts as a glue. It is associated with the hemicellulose and can range from water-soluble (lignosulfonates) to insoluble (kraft lignin), even in general organic solvents (e.g., acetone). Lignin plays a vital role in the physical properties of NF and influences their structure, rate of hydrolysis, the natural decay resistance, flexibility, and morphology. The impregnation state of the lignin will predict the hardness and stiffness of NF [19; 28; 30]. Other components need to be considered, such as for example the average viscosity of the degree of polymerization of cellulose and its molecular weight. This component can be about 10 to 100 times higher than that of hemicellulose [20; 26; 28; 31; 32], and it is useful to check the influence of the cellulose on the surface treatments, and also to check the significant shortening of the NF lengths induced by the hydrolysis process [9; 33]. In general, NF are hypoallergenic and present the following properties: large surface area, high strength, and stiffness (due to the cellulose content [9; 34]), low density, abundant availability, relatively low price, renewability, ease of processing, excellent MP, higher deformity, biodegradable, richness in cellulose, no environmental health concerns (reduced pollution level during production, CO\({}_{2}\) neutral, no emission of any toxic component, environment-friendly). It can also reduce tool wear (less abrasiveness to molds and mixing equipment) and is completely degradable by a composting process (with less garbage disposal problems). NF by itself can be used in a conventional manner for the production of yams, ropes, strings, cords, cables, clothes, and matting, as well as for making handicraft products (e.g., fancy articles, baskets, mats, etc.) and furniture. NF are also used in the paper industry (e.g., tea and coffee bags, sausage casing, electrolytic papers, currency notes, cigarette filters, medical and disposal papers) and are the main materials used for marine ropes due to its strength, lightness, and water resistance [19; 26; 35]. Since the 1980s [1; 3], NF indeed received the research community attention as a potential reinforcement component in PC due to their light weight when compared to the SF-reinforced PC. The potential applications of these PC are growing rapidly in many engineering fields, particularly as non-structural building materials (e.g., wallpapers, laminated panels), construction materials (e.g., thermoacoustic insulation boards), packaging industries/products, electronics, cosmetics, biomaterials (e.g., biomedical and pharmaceutical applications such as dental and bone cements), aerospace, sports, automotive components (e.g., underfloor protection for passenger cars) and as nanomaterial [2; 3; 6; 36; 37; 38; 39; 40; 41; 42].