The plant Ensete ventricosum, often known as the false banana, is a member of the genus Ensete, family Musaceae Ensete, and order Scitamineae [1]–[5]. This plant is commonly grown in sub-Saharan, central, and eastern Africa. And in the southern, south-western, and central regions of Ethiopia, it is one of the staple food crops eaten by about 20% of the population [1], [5]–[8]. Ensete ventricosum is a plant that is commonly farmed for food, and the procedures involved in its cultivation and food preparation generate enormous amounts of lignocellulose biomass waste [1], [3]. The pseudo-stem (a bundle of fibers) and leaves of the plant are the main sources of these residual wastes [3], [9]–[11]. The leaf lamina, leaf midribs, pseudo stem, and corm are the four fractional portions that make up the majority of Ensete ventricosum's dry matter [3]. According to studies, these dry substances are composed of the following percentages: leaf lamina 15–17 percent, pseudo stem 45–51 percent, stalk 9–11 percent, and corm 26–29 percent [3], [10], [12], [13]. One of the plant's parts, the Ensete ventricosum pseudo stem, has a great deal of potential for producing natural fibers for various applications by removing the undesirable components (hemicellulose 22.13–27.9, lignin as 6.88 ± 0.55–10.53 percent, and other trace amounts of impurities) for particular uses [9], [14]. Lignin, hemicellulose, wax, extractive, and other undesirable components of the pseudo-stem fiber must therefore be removed in order to produce cellulose nanocrystals.
Cellulose nanocrystals (CNCs) are cellulose derivatives that are extremely crystalline nanoparticles with dimensions in the nanometer range, widths ranging from 2–30 nm, and lengths ranging from 100–300 nm [15]–[18]. Due to its intriguing features, CNCs stand out among cellulose nanoparticles as a material that is suitable for various nanotechnology applications [19], [20]. Due to their origin and nature, CNCs offer distinct and promising physical, chemical, and mechanical properties, including high surface area, high aspect ratio, high tensile strength, high stiffness, and high fracture toughness. They are also very biodegradable and have a lot of hydroxyl groups [21], [22]. As a result, CCNs have grown in popularity in a wide range of applications, including packaging, paper, paperboard, catalysis, food industries, and medical products [15], hygiene products, paints, cosmetics, optical, biosensors [23], and nanocomposite [24]–[26]. Also, in different domains of application, such as concrete, ceramics, plastics, etc., they are used as reinforcing elements to improve the mechanical properties of composite materials [27].
It is possible to isolate CNCs using lignocellulose biomasses, which are made up of cellulose, lignin, and hemicellulose. However, the direct use of these lignocellulose biomasses by bacteria and acid for CNC synthesis is exceedingly sluggish and ineffective because of their crystallinity and heterogeneity [19], [28]. Therefore, there should be a pretreatment process to eliminate undesirable components from particular lignocellulose biomasses before the isolation of CNCs. The extraction of CNCs can be facilitated by a number of preprocessing techniques [29]. Acid hydrolysis procedures are frequently utilized in the extraction of CNCs because they are suitable for cellulose hydrolysis and are simple to use [16]. To eliminate the amorphous cellulose areas, the pretreated cellulose materials are subjected to hydrolysis with a strong acid under tightly regulated conditions [30]. Because they are more sensitive to acid than the crystalline areas of cellulose, the low-density amorphous regions of cellulose effectively hydrolyze [31]. Therefore, by breaking up the amorphous regions, which are glyosidic bond, crystallites are freed from cellulose chain that has been subjected to acid treatment [21]. A variety of acids have been used to extract CNCs, with hydrochloric acid, phosphoric acid, and sulfuric acid being the principal ones [27]. For isolating CNCs, mineral acid hydrolysis is more efficient and uses less energy [32], [33]. Sulfuric acid is the most preferred and often used acid for the acid hydrolysis extraction of CNCs because to its strong isolation capabilities, ability to create a stable colloidal structure, and esterification of hydroxyl groups by sulfate ions [34][35]. In general, cellulose sources, sulfuric acid concentration, hydrolysis time and temperature, acid to cellulose ratio, and mixing speed have a significant impact on the yield and characteristics of CNCs recovered from lignocellulose biomass cellulose by sulfuric acid hydrolysis [36]. The most researched conditions for sulfuric acid extractions include hydrolysis periods of 10 to 120 minutes, temperatures of 25 to 85°C, and acid concentrations of 30 to 65 weight percent [27], [30], [37]–[39].
Since there is presently almost no study using the cellulose of Ensete ventricosum pseudo stem fibers for the isolation of CNC for subsequently using in a wide range of application fields, this study focuses on transforming it into nano-scaled material, cellulose nanocrystals. The cellulose in Ensete ventricosum pseudo stem fiber was hydrolyzed with sulfuric acid to isolate CNC using the acid hydrolysis technique. The optimum conditions for CNC isolation from the cellulose of Ensete ventricosum pseudo stem fibers were determined through an analysis of the RSM optimization of the sulfuric acid hydrolysis process.