Nanocellulose: Fundamentals and Applications

Abstract

Cellulose is a natural and abundant polymer which can be derived from a large variety of materials such as biomass, plants and animals etc. Nanocellulose demonstrates remarkable physicochemical, mechanical, biological and structural properties. Technological challenges such as efficient extraction of cellulose and nanocellulose from precursors are still a challenge. Several techniques such as chemical, mechanical, biological, and combined approaches are utilized for the preparation of desired nanocellulose. However, the processes available to manufacture nanocellulose are still expensive. One of the most common methods used to obtain cellulose nanocrystals is acid hydrolysis method with strong acids such as sulfuric or hydrochloric acid. Recently nanocellulose has gained great attention due to their biocompatibility, renewable nature, mechanical strength, and cost-effectiveness. Hence wide range of applications for nanocellulose are being explored such as wettable applications to make hydrophobic modification for nanocellulose, or as a carrier of antimicrobial substances, or as creating a barrier from UV rays or from chemicals, it is also being used for reinforcement, biomedical, automobiles electronic, and energy materials. However, utilization of nanocellulose is still an emerging field and faces lots of technical challenges to be utilized as a reliable, renewable, and sustainable material for modern applications.

1. Introduction

One of the most abundant biopolymers on earth is cellulose, a substance identified by Payen in 1838. It is a polysaccharide composed of repeated anhydroglucose units (AGUs) connected jointly via β-1,4-glycoside linkages. Each cellulose unit consists of three hydroxyl groups, 1 primary and 2 secondaries, as shown in Figure 1. These groups and their hydrogen bonding capability, in same chain and different chain, with adjacent groups are crucial in regulating the significant physical characteristics and directing crystallization packing. Cellulose morphology is fibrous with irregular crystalline and amorphous segments, that is, they are built up of bundles/aggregates of fibrils where every fibril consists of large order repetitive (crystalline) regions and small amorphous regions. The crystalline regions contain properly packed chain molecules which demonstrate greater strength and stiffness of cellulose, and the amorphous regions provide the flexibility of bulk material [1].

Figure 1.

Unit structure of cellulose, intramolecular and intermolecular hydrogen bonding networks in cellulose structure [1].

Cellulose, an organic polymer, has been utilized since hundreds of years as a fiber or its derived substances over a large range of materials and final product applications. Cotton is the purest form of organic cellulose, that includes ~90% cellulose, while wood contains around 40–50% cellulose. Additionally, the polymerization degree (PD) of cellulose chains contains around ~10,000 glucopyranose units in wood and ~ 15,000 in cotton cellulose [2]. The percentage variations in these celluloses relies on biomass type, soil, location, weather and yielding time. It is one of the key components in structural plants elements and living organisms supporting retain their form, also, the total amount of cellulose produced in world by all living organisms is around ${10}^{11}-{10}^{12}$ tons/year [3]. Cellulose is found in conjunction with hemicelluloses, lignin, and various other minor constituents within lignocellulosic biomass. Cellulose fibers are found in plants, stems, and forests are arranged as a support structure within a matrix of lignin [4]. The majority of animal species could not produce cellulose, while humans cannot even digest it.

The single cellulose molecules chain are assembled into primary cellulose fibrils of around 3.0–4.0 nm width and a few μm in length, through the hydrogen bonds among the hydroxyl groups of the anhydro glucose repeating units [2, 5]. The primary fibrils accumulate through hydrogen bonding interactions with adjacent primary fibrils, generate bundles of nanostructure fiber called cellulose micro fibrils as demonstrated in Figure 2. Such microfibrils are sometimes referred to as nanocellulose or cellulosic nanoparticles.

Figure 2.

Schematic of a cellulose microfibril (nanocellulose) structure showing both amorphous and crystalline regions [6].

2. Nanocellulose

Nanocellulose demonstrates remarkable physicochemical, mechanical, biological and structural properties. A wide range of applications for nanocellulose are presently being explored, including its potential usage in coatings, food sector, biomedical usage, hydrogels, treatment of wastewater, and applications in energy [7]. The utilization of nanomaterials has significantly risen during the last few years as a viable substitute for traditional artificial polymers. The polymers derived from nanocellulose have offered significant opportunities for both research and material production due to their inherent characteristics, including biodegradability, ease in processing, recycling capacity, and widespread availability [8, 9]. Furthermore, their low price, low density, reactive surface, capability to alter chemistry of surface, and remarkable mechanical characteristics, makes them suitable reinforcement material. Creating environmental sustainable and economical procedure for separating the nanocellulose from plant biomass is major achievement of real sustainability for getting full advantages from numerous applications of cellulose [10]. Nanocellulose comprises a significant quantity of hydroxyl (OH) groups, making it extremely hydrophilic and can be altered through various chemical and physical methodologies [4]. Therefore, because of the remarkable characteristics nanocellulose has gained enormous attention as an effective nanostructure to develop emerging nanomaterials (Figure 3) [11, 12].

Figure 3.

General properties of Nanocellulose [13].

2.1 Classification of nanocellulose

Cellulose is usually classified as per its source of origin, namely plant-based cellulose (PC), algae-based cellulose, wood-based cellulose (WC), animal-based cellulose (AC), and bacteria-based cellulose (BC). Moreover, nanocellulose can be classified based on its characteristics and functions or based on preparation methods and raw materials. The nanocellulose common classification consists of Nanocrystalline Cellulose (NCC)/ Cellulose-Nanocrystals (CNCs), Nano-fibrillated cellulose (NFC), Nano-whiskers (CNWs)/Cellulose-Nanofibrils (CNFs), and Microbial Cellulose/Bacterial Cellulose (BCs). While all these are chemically similar, they demonstrate variation in size of particles, structure, crystallization, and other characteristics because of the particular sources and extraction procedures utilized. The Table 1 below shows primary characteristics of nanocellulose types (Figure 4) [6, 13].

Material	Crystallinity	Surface Area (m^2g^−1)	Youngs Modulus (GPa)	Average Size
				Diameter	Length
Nanofibrillated Cellulose	50% ≈ 90%	≈ 100	50–160	10–80 nm	< 10 μm
Nanocrystalline Cellulose	≈ 90%	≈ 200	50–140	5–30 nm	≈ 100 nm
Bacterial Nanocellulose	> 80%	≈ 100	15–35	20–100 nm	1.0–5.0 μm

Table 1.

Primary characteristics of Nanocellulose types [13].

Figure 4.

Different types of nanocellulose materials categorized with respect to size and dimensions [6].

2.1.1 Nanocrystalline cellulose

As the name suggests these nanocellulose are made up of high crystallinity around 54–88%, and have shape like short rod, needle or whiskers. These are isolated crystallites having dimensions around 2–20 nm in diameter and 100–500 nm in length. These can be extracted from cellulose fibrils through various techniques, as shown in Figure 5 [13].

Figure 5.

Various preparation methods for Nanocellulose.

Hydrolysis is a process where amorphous elements are hydrolyzed and eliminated through acid. However, the crystalline items remain without any change. The procedure contains 2 steps: raw material pretreatment preliminary treatment proceeded through its hydrolysis into cellulose nanocrystals (CNCs) [6]. The raw material is comprised of various impure substances, such as wax, esters, hemicelluloses, and lignin. These impurities can be eliminated through an alkaline (NaOH) solution treatment or by employing a bleaching technique just before the process of hydrolysis. After that cleaned raw material has been heat treated in the acidic environment about 45.0 minutes to many hours to hydrolyze the amorphous parts of fibers cellulose [4]. Several acidic minerals could be utilized for this process, that is, hydrochloric, maleic, sulfuric, phosphoric, hydrobromic formic and nitric acids. The acid hydrolysis of cellulose chains within amorphous domains includes immediate protonation of glucosidic oxygen (path 1) or cyclic oxygen (path 2), leading to gradual separation of the glucosidic bonds induced through the inclusion of water. The hydrolysis procedure produces 2 smaller chain parts, while maintaining the fundamental backbone structure [14]. Generally, it is observed that greater acid concentrations, prolonged reaction durations, and greater temperatures causes a greater surface charge and reduced particle sizes of cellulose nanocrystals (CNC). But these conditions lower the yield, as well as reduced crystallization and thermal durability of CNC (Figure 6) [14].

Figure 6.

Mechanism of cellulose chain acid hydrolysis [14].

The commonly used acid in this treatment is sulfuric acid because it efficiently degrades cellulose and also introduces sulphate half-esters on the surface of CNCs. These sulphates bear a monovalent charge, resulting in colloidal stability for the CNC dispersions in water due to electrostatic repulsion. However, it is an expensive method, consuming a lot of water whereby the possibility to completely recycle the acid is prevented. By and large, it is reasonable to state that the challenges posed by the sulfuric acid method have strongly impeded the industrial development of CNCs. Moreover, the yield of acid hydrolysis method is also rather low, generally around 30%. The yield of cellulose nanocrystals in the various treatments using conventional and microwave heating ranged between 3.4–29.0% and 4.9–38.2%, respectively [3].

Source material is seen as the most decisive factor when selecting the desired dimensions for CNCs. Table 2 demonstrates the well-known effect of source materials on the width and length of the CNC. Generally, the width is thought to be determined by the microfibril width in the source, whereas the length is connected to its LODP value [15, 16].

Cellulose Source	Dimensions (D: Diameter, L: Length, T: Thickness)
Sweet Potato	D: 20–40 nm
Wood Chips	L: 225–350 nm, D: 4.5–6 nm
Corn Husk	L: 20–254 nm, D: 0.8–11.8 nm
Sugarcane Bagasse	L: 37–220 nm, D: 18–32 nm
Banana Fibers	L: 135–145 nm, D: 7–10 nm
Plum Seed Shells	L: 100–800 nm
Bacteria	L: 160–420 nm, T: 15–25 nm
Cotton	L: 100–300 nm, T: 3–5 nm
Sisal	L: 100–300 nm, T: 3–5 nm
Ramie	L: 70–200 nm, T: 5–15 nm
Tunicates	L: 195–225 nm, T: 78–90 nm
Wood Pulp	L: 200–500 nm, D: 3–35 nm
Switchgrass	L: 63–223 nm
Maize Stalk Leftover	L: 150–450 nm, D: 4–7 nm

Table 2.

Cellulose nanocrystals – Their sources and dimensions [7].

2.1.2 Nanofibrils cellulose

Cellulose nanofibrils (CNFs) are defined as fibrillar structures with diameters ranging from a few hundred nanometers or less. Fibrils higher than dimensions are generally defined as micro fibrillated or cellulose microfibrils (CMF) [14].

Nano fibrillated cellulose (NFC), also known as cellulose microfibril, cellulose nanofibrillar cellulose, cellulose nanofiber or cellulose nanofibril is a highly flexible and entanglement nanocellulose that may be mechanically distinguished from cellulose fibrils [13]. When comparing nanocrystalline cellulose to nano fibrillated cellulose, it can be observed that later has higher length to diameter aspect ratio, higher surface area, and higher number of hydroxyl groups that can be easily accessed for the alteration of surface [14].

In comparison to CNCs, the fabrication of cellulose nanofibers (CNFs) is much easier because it does not need extreme chemical splitting to alter the molecular level structure of the cellulose chain. Normally, the fabrication of carbon nanofibers (CNFs) involves a wide range of physical or chemical techniques (Figure 7) [17].

Figure 7.

Classification of cellulose according to sources [2].

3. Applications of nanocellulose

Nanocellulose has gained industrial and academia interest in the wide range of applications such as wettability, carrier of antimicrobial substances, barrier (i.e., UV protector and chemical and solvent protector), electrical, polymer reinforcement, biomedical, energy, automobiles, and smart and responsive materials are few of them.

3.1 Wettable application of nano-cellulose crystals

Wettability of substrate or surface refers to the investigation of how the liquid contacts on the solid substrate or surface, that is, it is balance between adhesion and cohesion forces. The angle of contact developed due to these forces between the liquid and substrate is called degree of wettability. The angle of contact (CA) subsequently evaluates to determine the hydrophilic, hydrophobic or hybrid nature of material or substrate [18, 19]. Because of the growing need in both the academic and industrial sectors, several scholars have been interested in fabricating hydrophobic nanomaterials in recent years. The hydrophobicity of nanocomposites is a crucial element in establishing their applicability. For industrial applications, there is a significant demand for hydrophobic materials that provide features such as self-cleaning capacity, antifouling properties, repellent to water, and lessened friction. CNCs are widely recognized for their exceptional strength and are commonly utilized as reinforcement materials. However, due to its strong hydrophilicity, CNC’s effectiveness is presently inadequate as it could not be easily mixed into several matrices of polymer which are normally hydrophobic. Hence, hydrophobic alteration of CNC can result in enhanced dispersion in hydrophobic and nonpolar matrices. Additionally, surfaces of CNC with hydrophobicity may also be utilized as coating layer substance for maritime vehicles, medicinal devices, windows, fabrics, paints, and a variety of applications. The development of hydrophobic surfaces can open several ways for commercial usages of biopolymer which exist in nature [20].

Leaves of lotus are recognized for their ability to self-clean, have a rough hierarchical structure with two different degrees of roughness [21]. Numerous synthetic hydrophobic materials have been evolved due to the inspiration of superhydrophobic qualities of the lotus. The water contact angle (WCA) is a fundamental element to examine the hydrophobicity. A substance is hydrophilic if its water contact angle is <90°, if contact angle of water >90° than substances is said to be hydrophobic, and superhydrophobic if its WCA is >150° [22, 23]. To calculate WCA, a number of relations have been devised, including Wenzel equation, Young’s equation, and Cassie equation [23]. The sliding angle is another crucial component of hydrophobicity along with the water contact angle. The sliding angle is the incline angle between a droplet and its substrate where the droplet begins to roll on the surface. The water repellent property of superhydrophobic material is frequently described as having a sliding angle smaller than 10° [23, 24].

Surface roughness or chemical modification can be utilized to control hydrophobicity. Surface energy drop through chemical alterations and higher roughness should be controlled simultaneously to achieve super hydrophobicity [25]. Materials with super hydrophobicity are produced using hazardous physical and chemical methods. Bonding of molecules with low surface energy, which includes fluorinated agents [26], silanes [25], organic hydrophobic chains [27], and phosphonates [28], and others are utilized in chemical modifications for the achievement hydrophobicity. Table 3 shows a variety of chemical modifications and bonding to cellulose-derived products like cotton, paper, and nanocrystals of cellulose.

S#	Surface	Modification	WCA	References
1	Paper	TEOS and tridecafluorooctyl triethoxysilane	170^o	[22]
2	cotton	Silica sol treated with PFSC	145^o	[27]
3	CNC	Castor Oil	97^o	[25]
4	CNC	Pentafluorobenzoyl chloride	112^o	[24]
5	CNC	Stearyltrimethylammonium chloride	71^o	[26]

Table 3.

Hydrophobic treatment of cellulose-based materials.

PFSC: perfluorooctylated quaternary ammonium silane coupling agent.

TEOS: Tetraethyl orthosilicate.

Though the chemical treatment has conventionally been employed to functionalize material surfaces for various applications, there is a recent inclination towards increasing of surface roughness, which has shown intriguing hydrophobic properties in several materials. Enhancing surface roughness is a critical factor in the improvement of water repellency [29]. Air, which is specifically hydrophobic in nature (WCA = 180°), becomes stuck in the roughness grooves [30] When a water droplet is in contact with the surface, it interacts with the trapped hydrophobic air, resulting in an increase in hydrophobicity [30]. Various surface roughness approaches, including etching, laser treatment, and electrospinning, are frequently employed [23].

Salajkova et al. [28] utilized quaternary ammonium salts alteration to produce hydrophobic alteration of CNCs. In this investigation, For the CNC alterations, four distinct quaternary ammonium salts were utilized. Figure 8 depicts the addition of stearyltrimethylammonium chloride with three structure quaternary ammonium salts (1) glycidyl trimethylammonium chloride, (2) phenyltrimethylammonium chloride, (3) and diallyldimethylammonium chloride [28]. The maximum WCA of stearyltrimethylammonium chloride altered CNC was 71.0°C, though the notable advancements in WCA of the CNC surface was noticed, a greater WCA (>90°) is generally required for utilizing the CNC hydrophobicity for advanced material applications.

Figure 8.

CNC altered through y quaternary ammonium salts [28].

3.2 CNCs as carrier of antimicrobial substances

Since the most antimicrobial substances are tiny, therefore, there is always a chance that they will leach out of the material in which they are contained (such as fabric, and plastics, etc.). When the antimicrobial elements are lost to the garments dermis, and surrounding environment, the material becomes contaminated and causes health risk to human and the environment [20]. Due to the process of leaching and the occurrence of undesirable interactions with substances of food, that is, fats and proteins, the immediate entry of antimicrobial substance leads to a reduction of its ability and efficacy [31]. A variety of antimicrobial substances including triclosan, iodine complex, phenol, and triclocarban, were detected in commercially available everyday items like soap, these antimicrobial substances were banned because they caused a human health risk [32]. Another driver for creative approaches to the development of antimicrobial carriers is the occurrence of resistance to antimicrobial drugs due to alteration of microbial and a declining efficacy of antimicrobial drugs in the treatment of usual microbial diseases [33]. There has been an increase in interest to convert antibacterial substances into chains of polysaccharides and polymers, particularly CNCs halogens, phenols, nanoparticles of silver, and salts of quaternary ammonium are frequently utilized as antibacterial substances. Antimicrobial characteristics also exist in transition oxides of metal oxides which include silver (Ag), gold (Au), magnesium (Mg), nitrogen monoxide (NO), titanium (Ti), copper oxide (CuO), iron (II, III) oxide (Fe₃O₄), and zinc oxide (ZnO) [34]. Antimicrobic peptides including magainins, cecropins, and defensins as well as antimicrobial enzymes like lactoperoxidase and lactoferrin are frequently utilized [35]. Quaternary ammonia compounds (QACs) with positive attach with a bacterium of negative charge. Once they diffused through the cell wall, they attack the surface cytoplasmic membrane, microorganisms struggle to survive and ultimately die as a result of the loss of vital cytoplasmic components [36]. So, QAC is one of the most active antimicrobial substances whereas, their poisonous effects on pathogens (fungi and protozoans), bacteria and mammals restrict their usage.

Nanoparticles of silver are recommended as antimicrobial substances because of their wide range of antimicrobial properties against a variety of pathogens, yeast, fungus, viruses, and both gram-negative and gram-positive viruses can all be killed off by silver nanoparticles [37]. The breathing function of the bacteria is disrupted and restricted via the silver particles. Nano sized silver particles are typically chosen because silver particles efficiency rises with the decreasing their size owing to an increase in surface area [38]. E. Coli (Escherichia coli) and S. aureus (Staphylococcus aureus) are both inhibited by silver particles in their growth [39]. Unwanted health effects of silver nanoparticles have restricted their usage for packaging of food in certain countries [37]. These health effects create limitations in research and application, specifically in the industries like food and medicine.

Triclosan is an artificial bio-phenol with high bactericidal activity (2,4,4′-trichloro-2′-hydroxydiphenyl ether). It kills both gram-negative and gram-positive bacteria, fungus, and mold [40], such, triclosan is used in variety of products, including mouthwash, soap, packaging, garments, and cooking kits [41]. The EPA (Environmental Protection Agency) regulates the triclosan usage because of its apparent poisonousness and ecological hazards, and due to that, its usage in everyday items is regulated [40].

Chitosan, a naturally occurring antimicrobial substance that is produced from the protein chitin, has become quite popular in industrial uses. Chitin is derived from exoskeletons of fungus, algae, and bugs [56]. It is an antibacterial and antifungal polycationic cellulose [42]. It also modifies or produces a polymers membrane on the cell surface, preventing nutrients from taking place and ultimately causing cell death [43]. Chitosan has been studied for a variety of uses including packaging, medication distribution, and number of biomedical applications [43]. But its previously mentioned activity demonstrated that it is an antimicrobial substance which works slowly, that makes it less potent than other antimicrobial substances. The most common application of antibacterial materials is in the food packaging industry. In addition to physical and moisture protection, successful packaging reduces the growth of microorganisms in the food. As a result, popularity of effective packaging is progressively raised to prevent, decrease, and eliminate microorganisms on the surface of food or in the vicinity next to the package. Recently, the demand for low preservative food from consumers has enhanced. Therefore, active packaging can be highly appealing for maintaining food quality under low preservation conditions. Active food wrapping film can extend shelf life of food product, preserve nutrient content, and offer microbiological safety while inhibiting pathogenic growth [44].

As the need of packaging with bioactive and biodegradable material rises, studies were carried out to develop effective films for packaging using Nisin as an antibacterial agent, as shown in Figure 9. Nisin, a 34-amino acid long bacteriocin, is efficient against a variety of gram-positive microorganisms found in food [45]. The utilization of nisin have been employed to stimulate chitin in order to produce an effective packaging material for pasteurized milk [46]. Furthermore, it was claimed that growth of micro bacteria on ground beef and oyster was slowed when film of activated nisin was utilized for packaging [46]. Nisin was integrated with polylactic acid-cellulose nanocrystal (PLA-CNC) compound [73]. In general, the PLA-CNC film with activated nisin exhibited all three fundamental characteristics of packaging materials, such as mechanical strength, antibacterial efficacy, and biodegradability. Weishaupt et al. [47] demonstrated the self-assembly bio composite of nanofibrillar cellulose-nisin. TEMPO-oxidized nano-fibrillated cellulose with carboxylic clusters produced a negative surface for nisin to be adsorbed onto nisin binding to nanocellulose has significant impact through electrostatic interactions. Meanwhile, the binding ability of nisin and nanocellulose was reduced at elevated concentrations of salt [48]. Nanocellulose bounded with nisin was tested against the S. aureus and decline in growth was found [48]. In contrast to traditional antimicrobial carrier agents, nanofibers can additionally offer mechanical strength, that is, essential for many applications. Which is presently an effective research field, with an emphasis on getting improved antibacterial characteristics, and optimizing cost, scale-up this research in order to commercialize.

Figure 9.

Nisin chemical structure. Replicated with approval from Salmieri et al. [49].

3.3 Applications of CNCs as barrier

Restricting the environmental impact on materials has always been a prominent priority in many sectors. Corrosion is an ongoing issue and concern in oil and gas industries, where a pipping network is the main transporting system for delivering gas and oils. The interaction of transporting system to sea water in the marine industry is continually corroding the system. Interaction of polymers with UV lights over time can affect its characteristics at micromolecular level. Except for a few academic experiments, the usage of CNCs as an application of barrier is very less [20].

3.3.1 UV protection

The visual appearance of polyurethane (PU) begins to alter gradually when exposed to UV light, causes the yellowing of the material due to photochemical degradation on the molecules surface. Zhang et al. [50] conducted a study to employ CNCs as UV stabilizer for the prevention of photochemical degradation. 3-Glycidyloxypropyl trimethoxy silane (GPTMS) was utilized to alter the CNC at numerous concentrations. After the GPTMS hydrolyzing, the CNC was added and allowed to react throughout a specific duration. Figure 10(a) depicts the suggested salinization mechanism of reaction and interaction among the altered PU and CNC. The altered CNC was subsequently mixed in the PU mixture and homogenized to disperse the altered CNC in the PU as presented in Figure 10(b) to establish the composite of CNC & PU. This mixture gradually opens to UV light. The outcomes of investigation revealed that inclusion of an altered CNC in the PU significantly decreased the UV light yellowing impacts, further reduction in UV light yellowing impacts was noticed with the raise of alter CNC concentration. With the incorporation of 1.5% of altered CNC, the yellowing impact was decreased around 58.0%, demonstrating the usefulness of CNC as an antiyellowing substance as shown in Figure 10(c). It was hypothesized that altered CNC reduced photo degradation of the CH₂ cluster while prohibiting scrubbing of urethane cluster.

Figure 10.

(a) Shows a CNC alteration reaction scheme for the utilizing 3-Glycidyloxypropyl trimethoxysilane (b) shows a graphic illustration of altered CNC dispersion inside PU. (c) Shows a bar chart indicating the impact of altered CNC amount on the PU yellowing being exposed to UV light throughout an established time period [50].

In other research, CNC was utilized as dual-purpose filler that gives polyvinyl alcohol polymer reinforcement and a UV barrier [80]. Pulp of CNC was oxidized through sodium metaperiodate and then combined in HCl solution with sodium 4-amino-benzoate to create altered CNC that had been affixed to photoactive groups. This modified CNC was then mechanically decomposed to create p-aminobenzoic acid grafted CNC (PABA-CNC). Numerous concentrations of this altered CNC were introduced to a polyvinyl alcohol (PVA) water solution. The resulting mixture solution was subsequently degassed and cast to form thin coating, that were utilized for additional testing. The UV transmission outcomes with the adding of PABA-CNC to PVA demonstrated that the existence of PVA with PABA-CNC drastically decreased UV transmittance in contrast to alone PVA. The rising concentration of demonstrate the additional decline in UV transmission with PVA coatings comprising of 0.5 and 10% PABA-CNC decline the transmission 54.0 and 12.0% respectively, as compared to clean PVA coating, which indicated 70.0% transparency. PABA-CNC inclusion also improved the mechanical characteristics of thin coating, such as tensile strength and modulus, this rise was a function of PABA-CNC concentration. Ethyl cellulose nanoparticles (ECNPs) have also been investigated as a method of confining or protecting UV light, that tends to produce species of oxygen that are reactive when subjected to UV because of photodegradation [50]. Such filters are typically employed in makeup, such as sunscreens, and can absorb cancer causing reactive species of oxygen, that could be harmful when it comes into skin contact [20].

3.3.2 Nanocellulose as protector of corrosion and chemicals

Surface coatings are commonly used in numerous industries to protect their products and equipment’s surface from surrounding environment. Some of the usage involve the application of paint to retard the rust on metallic substances, the employment of transparent epoxies on wood and plastic to avoid the scratching, and to avoid the effects of ultraviolet (UV) deterioration and decomposition. However, transparent coat epoxy resins or paints for corrosion protection do not always possess adequate strength and resistance to chemicals. Ma et al. [51], conducted a study on the characteristics of CNCs, and reported its strengthening abilities at minimal loadings because of their crystallinity and nano-size, which contributed to their utilization in the application of metals coating as a base element in epoxy. In this investigation, epoxy including 1.00, 1.50, and 2.00 wt.% CNC was properly homogenized with a rod of glass and sonicated to make sure appropriate dispersion before being painted with brush in a very thin coats on mild steel. The coated steel was permitted to dry before it was evaluated for corrosive resistance utilizing electrochemical impedance spectroscopy (EIS) during a 30-day dip in 3.5% sodium chloride. Moreover the transparency of the coating epoxy was examined through UV-vis evaluation to detect the influence of CNC. The optical transmission findings demonstrated that as CNC dosage increased, the rate of transmission reduced to 20.0% for coating comprising 2.0 wt.%. In contrast, the coating comprising 1.0 wt.% CNC was found to be exceedingly clear, with transparency of 74.0%.

Additionally, it was noticed that the light drop off transmittance for all nanocomposite was between 300 and 350 nm, indicating significant light absorbance and the absence of light reflections in the UV region between 300 and 400 nm. It demonstrates that this type of coating can be utilized to stop UV deterioration but also retains outstanding visibility when utilized for transparent coating applications, particularly at 1 wt.% of CNC. While the corrosion evaluation revealed that the application of epoxy coating significantly retards the corrosion by the addition of CNCs. This might be as a result of the CNC acting as an obstacle to the sodium hydroxide ions solution by directing them into a tortuous path. This prevented the coating’s contact entirely, therefore shielding the surface of the mild steel. After 1 day of being exposed, only the unreinforced epoxy experienced penetration. Neat clean epoxy coating exhibited two-time constants when the coatings were electrochemically analyzed using bodes plots. On the 30th day, only the unaltered epoxy kept producing two-time constants, demonstrating the CNC’s outstanding anticorrosion properties. But as the test went on over the course of the 30-day period, for the epoxy coating with a 2 wt.% CNC loaded, the presence of a two-time constant gradually emerged. It was ascribed to the CNCs potential for aggregation within the epoxy, as they did not scatter uniformly in 2 wt.% like they did in the samples loaded at 1 and 1.5 wt.%. This irregular scattering lead to corrosion of the mild steel occurred from the ions (Na⁺ and Cl) which being able to diffuse into the epoxy’s exposed areas and cause corrosion [45].

3.4 Nanocellulose in electrical and electronic applications

Study in the development of functional CNC applications in electrically active materials, such as dielectric and electric conductive materials have great future potential, whereas materials like starch [24], proteins and peptides [52] currently being investigated for the same purposes. The popularity of CNCs in electrical industries is raised due to their ease of manipulation, piezoelectric and dielectric capabilities, and sustainable characteristics similar to other bioderived materials. Csoka et al. [53] investigated extremely thin films comprising highly oriented c through a tip of diamond throughout extremely thin films ellulose nanocrystals which demonstrated piezoelectric impacts due to the cumulative production of the separate CNCs. Extremely thin films with multiple levels of CNC orientation were created using a method is reported in another paper [54]. The atomic force microscopy (AFM) in tapping mode was utilized for the displacement measurement of the film when an electric field was employed to them. Higher piezoelectric effect was noticed with a higher degree of alignment. Thus, the film’s piezoelectricity was based upon the CNCs alignment. The determined results are not merely attributed to the CNCs alignment but also owing to the CNCs crystallization in films and orientation. Figure 11(a) exhibits the AFM diagram in tapping method comprising aligned CNCs by employing an electric field across it whereas Figure 11(b) illustrates the applied voltage impact on thin films due to the CNCs displacement. The outcomes of this investigation reveal that extremely thin films by numerous levels of CNC alignment can end up to various degrees of electro-mechanical actuation, that may possibly be employed in different applications, for example, extremely sensitive weighing scales. Also the possession of a high-level CNC concentration and positioning might lead to the application of very delicate forces.

Figure 11.

(a) Dielectric characterization of ultrathin film coated with properly aligned CNC via atomic force microscopy (AFM) in tapping approach and (b) voltage impact on displacement of CNC (piezoelectric effect) [53].

CNCs can alter the polarization densities because of the greater level of crystallization. Similarly, its dielectric character enables its utilization as an effective insulating material in various purposes. The existence of moisture in the CNC plays an essential role in identifying the dielectric characteristic, because it behaves like an electrical conductor when moist exists in CNC. For the utilization of CNC in applications of dielectric, the levels of moisture should normally be around 0.50% [55], because of its hygroscopicity, it normally has a level of moisture in the range of 4.0–8.0%. These moist contents range stems from CNCs source and extremely dependent on the cellulose crystallization as studied from cellulose water sorption investigations [56]. Overall, moisture content will be lowered with the higher cellulose crystallinity. Bras et al. [55] investigated the dielectric characteristics of two different wood nanocelluloses, nano-fibrillated and algal (cladophora cellulose) nanocelluloses [55]. But they also observed the better sorption potential of NFC at both high and low moisture owing to its lesser crystalline. Even though it was thought that dielectric qualities were closely associated with crystallinity, NFC was found to have a higher dielectric characteristic than cladophora cellulose. It was because of the high porosity of cladophora cellulose, that permits air to get inside and raise its dielectric loss. It is evident that nanocellulose have good dielectric characteristics that might be used to insulate electrical wires and cables, however, the efficacy of this feature relies not just on the source but also on the nanocellulose shape [57]. It additionally demonstrated that NFCs made from CNC might be utilized for the manufacture of wood, glass and polymer dielectric substances [58].

3.5 CNC application in automobiles

Multi-functional nanocomposites not only exhibit enhanced mechanical strength, but also demonstrate electrical, optical, thermal, and magnetic characteristics. Molecular level interaction among the polymer matrix and nanomaterials, as well as the presence of interface region among the bigger polymer-nanomaterial, are assumed to play crucial part in effecting the physical and mechanical characteristics. CNC has been gaining lot of attention due to its increased mechanical characteristics, constancy in dimension and raised in modulus, flammable obstruction, outstanding thermal and process properties, and improved resistance effect, creating it more demanding substitute of metal in applications of automobiles [59, 60]. The fundamental purpose of utilization of nano-polymer in automobiles industries is to reduce weight of vehicles, enhanced efficiency of engine, CO₂ emissions reduction and enhanced performance. The polymeric composites commercial utilization starts from 1991, at that time Toyota Motor Co. introduced bio composites of nylon 6/clay in market to produce belt. During the same time, Unitika Co. of Japan launched engine cover developed from nanocomposite of nylon 6, which offered highly finished surface and weight reduction by 20%. General Motors in different phase introduced GM safari parts manufactured from polyolefin with coating of 3% nano clay. In 2002 Chevrolet Astro vans, in partnership of Basell (now LyondellBasell Industries), used nanocomposites of polymers in doors of Chevrolet Impalas [61]. During 2009 General Motor manufactured rear-floor in single piece through compression molding assembly for Solace Pontia from nano-enhanced sheet. This single piece rear floor is also utilized for GM’s Corvette ZO and Chevrolet Corvette Coupe. Automobiles industry can take advantage from nano-polymer in wide range of application for example braking systems and suspensions, body component and frames, power systems and engines, catalyst converters and systems of exhaust, paints, tires, lubricants, and electronic and electrical component etc. A scientist group of Japan Toyota Central Research Development Laboratories recognized work on nanocomposite of nylon-6/clay in late 1980s and in early 1990s developed upgraded procedures for the manufacturing of nanocomposites of nylon-6/clay using in situ polymerization alike to the Unitika procedure. The research outcomes demonstrated a key development in mechanical and physical characteristics via reinforcement of nano-polymers with clay. The same team also documented similar methods for several different polymers-based nanocomposites clay forms, that is, acrylics, epoxy resin, polystyrene, polyimides and elastomers. After that detailed research has been conducted throughout the world in the field of nanocomposites [62, 63]. The nano-polymers tiers with greater scratch resistance and catalysts for fuel-borne raises inhibitions of soot penetrability in specific filters, windshields and headlights anti-fog coatings and scratch resistance coating of vehicles body etc. The advancement in the nanocomposite R&D developments is continuously increasing due to the interest of financial agencies and organizations, as these organizations want to expand the capitalization on newly discovered products. Such as, European automobile industry spends nearly 5% of annual revenue on R & D. The primary aim is to produce effective and stronger coatings and paints. Therefore, utilization of nanocellulose composite polymer in automobiles industries is projected to raise in coming years [64].

3.6 CNCs as an applications of other advanced functional materials

CNCs are employed for wide range of applications owing to the hydroxyl clusters on their surfaces which can be functionalized to do various activities. CNCs produced by hydrolysis of sulfuric acid have negative charge on the surface, which makes electro statistical repulsion among the CNCs. Due to this, CNC is simply dispersed in polar polymer frameworks like PVA. In the past 20 years, both academic and business experts have been interested in CNC utilization. Apart from that it can be used as a reinforcing substance, CNCs have shown promising usage in biomedical science, personal care, and energy.

3.6.1 Polymeric reinforcement

Nanocrystals of cellulose are frequently utilized for filler reinforcing in matrices of polymer to raise their strength. Conventional polymers did not have their desired strength for the majority of structural applications, so they need fillers to strengthen them. Being a biodegradable material, CNC offers an outstanding polymers reinforcement. Numerous investigations have demonstrated that very low quantities of CNC enhanced the physical and thermal characteristics of polymers because of their nano-size and capability to effectively absorb matrix strength [65]. Bras et al. [66] stated the CNC impact on reinforcing the rubber material. They observed that CNCs could enhance both mechanical and thermomechanical characteristics of rubber. But, because of the hydrophilic characteristic of CNCs, rubber absorbed more water. This investigation demonstrates that CNCs could be utilized to improve the properties of polymers in certain applications where the composites will not be exposed to moisture. Moreover, Cao et al. [67] demonstrated the reinforcing abilities of CNC in cement. It was suggested that adding around 0.2 vol.% CNC raised the hydration of the paste, resulting in a 30% rise in flexural strength. These examples demonstrate that the nano-polymer could be the composite materials for future utilized in automobiles parts, furniture, construction, and several high strength materials.

CNC was effectively attached with several kinds of polymers to alter its surface and acquire the altered CNC with the desired characteristics. For example, the utilize of hydrophobic polymer attached with non-polar polymers commonly enhanced the interaction and dispersion among the CNC and polymers as well as raises the composite polymers strength. In some other situations, the attached polymer increases functionality and widens the applicability of CNC. Table 4 illustrates numerous polymers attached to CNC and accomplished the characteristic owing to the alteration.

S#	Polymer	Reaction Mechanism	Conclusion	Reference
1.	POLY(4-VINYLPYRIDINE) (PVP)	Radial polymerization with ceric ion	Thermal degradation enhanced by 60°C temperature	[66]
2.	POLYSTYRENE (PS)	Atomic Transfer Radical Polymerization (ATRP)	Enhanced the water contact angle by 50%.; 1,2,4-Trichlorobenzene (1,2,4-TCB (organic Pollutant) can absorb 50%	[67]
3.	POLYMETHYL ACRYLATE (PMA)	Polymerization with mediation of nitroxide	CNC attached PMA was around 1% weight. Was soluble in acetone and not dispersible in water.	[68]
4.	POLY TERT-BUTYL ACRYLATE (PTBA)	Grafting to	Stable suspension in acetone, chloroform, and toluene	[69]
5.	POLYLACTIC ACID (PLA)	Ring Opening Polymerization (ROP)	Well dispersed in chloroform (non-polar solvent)	[20]
6.	JEFFAMINES (POLYETHER AMINE)	Grafting to	Thermo-reversible aggregation CNC grafted Polymer has lower surface charge.	[70]
7.	POLYMETHYL METHACRYLATE (PMMA)	Radical polymerization atomic transfer	Reduced thermal stability (250-290°C).; Enhanced water contact angle by 17^o.	[71]
8.	POLY(ε-CAPROLACTONE) (PCL)	Ring Opening Polymerization (ROP)	Addition of CNC attached PLC matrix enhanced young’s modulus from 231 to 582 GPa.; For the same matrix elongation break declined significantly.	[72]
9.	POLYETHYLENE GLYCOL (PEG)	Grafting to	Thermal decay of CNC graft appears at lower temperature.	[73]

Table 4.

Nanocellulose grafted with polymer.

3.6.2 Biomedical applications

CNC application in biomedical involves its utilization in making the medical devices, wound recovering, bioimaging, tissue engineering structure, and delivery of controlled drugs [68]. Dong and Roman observed the bioimaging application with fluorescent labeled CNC [69]. In those investigations, epichlorohydrin was utilized for binding fluorescein-5′-isothiocyanate to CNC. To study the biodistribution and interactions of CNC in living organisms using fluorescence labelling, that might be meaningful for several biomedical applications. This investigation demonstrated that the enhanced CNC might be utilized to analyze the cells interaction. The researchers additionally stated that the functionalized CNC was being utilized in a different study to look at how it interacts with cells from mammals [20]. Drug transporters can occasionally trigger immunological reactions in systems associated with biology, for example the human body. An investigation [20] regarding the application of cyclodextrin carriers CNC demonstrated that it was effective in drug delivery application and had no negative side effects. Immunological responses, for example, the transmission of the pro-inflammatory cytokine interleukin 1 (IL-1), and mitochondria-derived reactive oxygen species (ROS), were found to be negligible [70]. CNC is deeply investigated for tissue engineering, in which supporting equipment was utilized for self-recovering and regrowing. In order to enhance performance, selection of proper material for scaffolding is very important. Physical, biological, and mechanical characteristics are playing crucial role in high efficiency and effective mechanical combination. Therefore, characteristics like porosity, size of pore, shape, area of surface to volume ratio, and roughness of the surface should be considered. Furthermore, the rate at which organic substances degrade plays an essential role in healthy tissue healing whereas the scaffolding material gets absorbed [20]. In most situations, unfilled polymer materials cannot be utilized to attain both biological and mechanical characteristics. Hence, nanofillers are used to create nanocomposite materials with functional characteristics including electrical conductivity, self-assembly ability, mechanical strength, and adhesiveness [71]. Domingues et al. [71] comprehensively specified the utilization of CNC-PLA composite for tissue engineering to satisfy the previous parameters for biomedical scaffold and its use in their investigation on CNC-based biological material for tissue engineering [72].

3.6.3 CNC applications in energy

CNC application in energy implies the utilization of composites materials produced from cellulose for storage of energy. With the rising of environmental and sustainability concerns in making more effective and feasible resources of renewable energy. Zhou et al. [73] designed and developed recyclable solar cell from cellulose nanocrystal by utilizing the benefits of outstanding mechanical characteristics of silver and CNC [20]. A semitransparent, recycling solar cell with electrodes was fabricated. But more improvements were required to meet the essential performance and efficiency. Kim et al. [74] stated some other energy applications of cellulose based materials like display devices, energy harvesting machines, paper transistors, and motors, where the CNC with outstanding biocompatible, mechanical characteristics and easiness in functionalization process provides its capacity to present sustainable and ecofriendly technologies.

3.6.4 CNC as a responsive and smart materials

In recent years, the responsive and smart materials utilization has risen. The responsive and smart materials modify the external environment and deliver responses. The alteration in impetus like acquaintance to heat, chemicals, light and magnetic fields might be utilized to produce mechanically adaptable materials that reply to stimuli nanocomposite and could react towards outside stimuli in several ways, for example by expanding or shrinking, and assemble and dissemble etc. [75]. These alterations can be utilized as a stimulus responsive smart material. CNC could be utilized as a material that responds to different stimuli for sensors and other products. It can adapt to respond to light, pH, heat, moisture, chemicals, and magnetic fields, which offers to respond the inputs along with the ability to reinforce. When the pH changes, the rheological characteristics of CNC composites also alter [76]. Way et al. [76] developed carboxylate and amine-functionalized CNC in order to evaluate the response of pH. Also, by modifying the CNC surface chemistry, the nanocomposites could be modified to produce numerous materials for mechanical adoption.

Smart sensors based on CNC could be designed to detect ions, moisture, biological species and organic vapors. Kafy et al. [77] developed a humidity sensor from a CNC-graphene oxide (GO) composite. CNC-GO coating demonstrated enhanced absorption of water, that is beneficial for moist sensitivity [77]. The sensing film did not compromise on its performance with the variation of temperature, illustrating the practical usage of a moist sensor [77]. CNC might additionally be customized to develop sensing material for gas, capable of detecting different organic and hazardous gases. Furthermore, sensing material based on CNC can be utilized to recognize ionic substances. For the detection of ferric (Fe³⁺) ions, CNC containing pyrene was produced [78]. This idea could be more extended to develop a material to sense the dissimilar ions, biological and chemical compounds. Some other smart sensors developed from CNC comprised of strain and proximity sensor, which was investigated by Sadasivuni et al. [79] and Wang et al. [80].

4. Economic and environmental evaluation of nanocelluloses

4.1 Economic evaluation of nanocelluloses

Manufacturing cost of nanocellulose depends on the methods of pretreatment, acid utilized in hydrolysis process, and cost of feed stock. Nanocellulose manufacturing cost stated in previous study ranges from 2000 to 2010,000 USD per ton [81, 82]. The manufacturing of CNC through sulfuric acid hydrolysis requires acid-resilient apparatus that raises the capital expenses (CAPEX). Furthermore, reclamation of acid through waste treatment and neutralization increases capital costs. Research on CNCs stated that sulfuric acid hydrolysis production costs varied from 3632 to 4420 USD per dry ton of CNCs [81]. In all the cases pulp dissolving cost was the primary contributor, which contributes around 38–45% of production cost. For zero acid reclamation, lime and acid costs contribute around 24–38% of production cost. While for acid reclamation, this contribution considerably reduced to 3–4% of production cost. The CNC minimum selling price (MSP) was mainly affected by the cost needed for pulp dissolving and CAPEX. The raise in CAPEX because of the acid reclamation, increased the MSP from 4829 to 5125 USD per CNC dry ton [81]. A study conducted by Blair et al., [83] stated that cost of equipment contributes 65% of CAPEX. Another investigation stated that CNCs acquired through citric acid hydrolysis are more environmental friendly than sulfuric acid hydrolysis, but MSP was comparatively greater and was 16,460 USD per dry ton [84]. The utilization of citric acid hydrolysis in CNC manufacturing shows a 7 million USD reduction in capital investment than sulfuric acid hydrolysis. However, the operational expenditures rose to 8.25 million USD per year, where citric acid alone accounting for 40% of OPEX at 89% acid reclamation. It means that CNC manufacture using citric acid hydrolysis will be more expensive than sulfuric acid hydrolysis. Presently, nanocelluloses are not economically viable when compared with alternate options because of their small manufacturing capacity. Shen et al. [85] evaluated the variables that impede the commercialization of nanocellulose reinforced polymer composites. The researchers stated that the pretreatment expenses and small manufacturing capabilities related to nanocelluloses lead to considerably increase the production in comparison to alternative options such nano montmorillonite and nano silica. In this regard, process optimization is crucial to attain mass production for the commercialization of nanocelluloses. Furthermore, the absence of a standardized product index, because of the variable characteristics of nanocelluloses such as synthesized from a wide range of sources and manufacturing methods, obstructs the commercialization of the nanocelluloses. Enzyme-mediated manufacturing of nanocelluloses provides a promising option to successfully tackle both environmental and economic challenges. Nevertheless, it is important to acknowledge that commercial enzymes are frequently utilized to efficiently convert cellulose and hemicellulose components into fermentable sugars. Additional investigation is required to enhance the efficiency of enzyme mixtures for the creation of nanocellulose [86]. Furthermore, the economic feasibility can be improved by producing enzymes on-site [87]. Previous investigations on nanocellulose manufacturing predominantly utilized bleached chemical pulp or pure cellulose, which had already lost biomass content by 50–60% for the manufacturing of nanocellulose [88]. This approach led to less effective employment of biomass because of the low nanocellulose yields in comparison to the original biomass. In contrast, mechanical pulping can serve as an effective substitute and requires more investigation. Additionally, research efforts must be directed towards optimizing the reaction yield to enhance the total economics of the manufacturing method [89]. Furthermore, technologies that are feedstock agnostic can play an important role in improving manufacturing scale. In such a scenario, economies of scale can be used to acquire cost-effective manufacturing. Future studies should be concentrated on approaches with moderate reactions and single-step extraction methods to enable the economical nanocellulose manufacturing.

4.2 Environmental evaluation of nanocelluloses

The growing utilization of nanocellulose in diverse industries and applications raises the probability of human contact with it throughout the different phases of the products. While nanocellulose is generally considered to be non-toxic, there are still uncertainties regarding its effects on the environment and human health. Furthermore, there are currently no established industry regulations or consumer product risk-assessment protocols in place to evaluate the health, safety, and environmental effects of nanocellulose before it is used in commercial products. This is because there is a lack of experimental data on the exposure of nanocellulose to both in vitro and in vivo systems under environmental conditions.

In order to quantify the environmental risk associated with nanocellulose, Natasha et al. [90] characterized both environmental exposure and hazard. The findings indicate a risk characterization ratio (RCR) of 6.9 × 10⁻⁵ for 2015 and 7.1 × 10⁻⁴ for 2025, indicating that based on the selected assumptions and a compound annual growth rate (CAGR) of 19% for nanocellulose production in the coming years, there is no current or anticipated environmental hazard associated with nanocellulose. Also, in accordance with the five-step procedure outlined in the framework, Piccinno et al. [91] conducted a scaled-up life cycle assessment (LCA) study for future nanocellulose production using a novel nanocellulose production pathway. They reported that the environmental impact per kilogram of manufactured nanocellulose yarn can be reduced by a factor of up to 6.5 when compared to laboratory production and suggested that the environmental impact of commercially available nanocellulose would be more comparable to that of an actual manufacturing facility.

The environmental impact of nano-fibrillated cellulose produced from thermo-groundwood, which involved the removal of extractives, lignin, and hemicelluloses, as well as TEMPO oxidation and homogenization procedures, was assessed using a Life Cycle Assessment by Turk et al. [92]. Their data indicates that the purifying procedure accounts for almost 95% of the overall impact, which is linked to a comparatively elevated usage of electrical energy and additional chemicals, specifically cyclohexane and acetone. They also reported that 1 kg of nano-fibrillated cellulose has a global warming potential similar to 800 kg of CO₂, and basic energy consumption is ~19 MJ/kg. The study also aimed to achieve a methodological objective, specifically by calculating the impact indicators using the three most significant assessment methods: ILCD/PEF, CML 2001, and ReCiPe 2016. These three strategies yield comparable outcomes in terms of their effects on global warming and acidification.

5. Conclusion

Cellulose is an organic polymer which has been utilized since hundreds of years as a fiber or its derived substances in multiple applications. Nanocellulose is an eco-friendly material and in advanced technologies its numerous applications are gradually becoming significant. The functionalization and flexibility of nanocellulose has the potential of application for the sustainable future. These materials are biodegradable and nontoxic for multiple applications, particularly considering the present environmental issues such as climate change caused by greenhouse gases released from the extraction and utilization of petroleum-derived materials. It has received special attention because of its availability throughout the world, replenish ability and the rapidly expanding technologies on its manufacturing. Thus, it is predicted that in the coming years, the nanocelluloses will become extensively and broadly utilized in automobiles, energy sector, medical, biotechnology, electrical and food industries etc. As nanocellulose continuously gains the interest of scientists all around the world, therefore enhanced understanding will expedite technology improvements.

Acknowledgments

This study is supported financially under the Fundamental Research Grant Scheme awarded by the Ministry of Higher Education Malaysia with grant number: FRGS/1/2019/TK03/UM/02/12 (FP143-2019A). The authors also gratefully acknowledge the support from grants, RMF0400-2021, ST049-2022, RK001-2022 and Department of Mechanical Engineering, Universiti Malaya to conduct this research work.