Fundamentals of Nanocellulose

#### **Chapter 1**

## Nanocellulose: Fundamentals and Applications

*Kaleemullah Shaikh, Wajahat Ahmed Khan, Md. Salim Newaz Kazi and Mohd Nashrul Mohd Zubir*

#### **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.

**Keywords:** nanocellulose, cellulose-nanocrystals (CNCs), automobiles, smart responsive device, corrosion protector

#### **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

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

molecules which demonstrate greater strength and stiffness of cellulose, and the amorphous regions provide the flexibility of bulk material [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 − 11 12 10 10 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,

#### **Figure 2.**

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

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.

#### **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].


#### **Table 1.**

*Primary characteristics of Nanocellulose types [13].*

#### **Figure 4.**

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

*Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

#### *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].

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 5.** *Various preparation methods for Nanocellulose.*

**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].

#### *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,

*Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*


#### **Table 2.**

*Cellulose nanocrystals – Their sources and dimensions [7].*

#### **Figure 7.**

*Classification of cellulose according to sources [2].*

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].

#### **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].

#### *Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

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.

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.

#### **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


*TEOS: Tetraethyl orthosilicate.*

#### **Table 3.**

*Hydrophobic treatment of cellulose-based materials.*

**Figure 8.**

*CNC altered through y quaternary ammonium salts [28].*

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

#### *Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

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 grampositive 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

**Figure 9.** *Nisin chemical structure. Replicated with approval from Salmieri et al. [49].*

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.

#### **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

*Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

**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].*

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.

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<sup>+</sup> 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

#### *Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

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.

#### *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


### **Table 4.**

#### *Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

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, selfassembly 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

#### *Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

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 thermogroundwood, 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.

#### **Acknowledgements**

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.

*Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

### **Author details**

Kaleemullah Shaikh1,2, Wajahat Ahmed Khan3 , Md. Salim Newaz Kazi1 \* and Mohd Nashrul Mohd Zubir1

1 Faculty of Engineering, Department of Mechanical Engineering, Universiti Malaya, Malaysia

2 Faculty of Engineering, Balochistan University of Information Technology, Engineering, and Management Sciences (BUITEMS), Quetta, Balochistan, Pakistan

3 Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies, Universiti Malaya, Malaysia

\*Address all correspondence to: salimnewaz@um.edu.my

© 2024 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Phanthong P, Reubroycharoen P, Hao X, Xu G, Abudula A, Guan G. Nanocellulose: Extraction and application. Carbon Resources Conversion. 2018;**1**(1):32-43. DOI: 10.1016/j.crcon.2018.05.004

[2] Seddiqi H et al. Cellulose and its Derivatives: Towards Biomedical Applications. Vol. 28, 4. Netherlands: Springer; 2021. DOI: 10.1007/ s10570-020-03674-w

[3] Dufresne A. Nanocellulose: From Nature to High Performance Tailored Materials. Berlin, Germany: Walter de Gruyter GmbH & Co KG; 2017

[4] Huang J, Dufresne A, Lin N. Nanocellulose: From Fundamentals to Advanced Materials. Lausanne, Switzerland: John Wiley & Sons; 2019

[5] Missoum K, Belgacem MN, Bras J. Nanofibrillated cellulose surface modification: A review. Materials. 2013;**6**(5):1745-1766. DOI: 10.3390/ ma6051745

[6] Lee K-Y. Nanocellulose and Sustainability: Production, Properties, Applications, and Case Studies. Lausanne, Switzerland: CRC Press; 2018

[7] Zinge C, Kandasubramanian B. Nanocellulose based biodegradable polymers. European Polymer Journal. 2020;**133**(May):109758. DOI: 10.1016/j. eurpolymj.2020.109758

[8] Klemm D et al. Nanocellulose as a natural source for groundbreaking applications in materials science: Today's state. Materials Today. 2018;**21**(7):720- 748. DOI: 10.1016/j.mattod.2018.02.001

[9] Heise K et al. Nanocellulose: Recent fundamental advances and emerging biological and biomimicking applications. Advanced Materials. 2021;**33**(3):e2004349. DOI: 10.1002/ adma.202004349

[10] Randhawa A, Dutta SD, Ganguly K, Patil TV, Patel DK, Lim KT. A review of properties of nanocellulose, its synthesis, and potential in biomedical applications. Applied Sciences (Switzerland). 2022;**12**(14):7090. DOI: 10.3390/ app12147090

[11] Thomas B et al. Nanocellulose, a versatile green platform: From biosources to materials and their applications. Chemical Reviews. 2018;**118**(24):11575- 11625. DOI: 10.1021/acs.chemrev.7b00627

[12] Isogai A. Emerging nanocellulose technologies: Recent developments. Advanced Materials. 2021;**33**(28):1-10. DOI: 10.1002/adma.202000630

[13] Sapuan RAISM, Norrrahim MNF. Industrial Applications of Nanocellulose and its Nanocomposites. Cambridge, USA: Elsevier Science; 2022

[14] Hanieh Kargarzadeh AD, Ahmad I, Thomas S. Handbook of Nanocellulose and Cellulose Nanocomposites. Weinheim, Germany: John Wiley & Sons; 2017

[15] Mateo S, Peinado S, Morillas-Gutiérrez F, La Rubia MD, Moya AJ. Nanocellulose from agricultural wastes: Products and applications—A review. PRO. 2021;**9**(9):1594. DOI: 10.3390/pr9091594

[16] Pradhan D, Jaiswal AK, Jaiswal S. Emerging technologies for the production of nanocellulose from lignocellulosic biomass. Carbohydrate Polymers. 2021, 2022;**285**:119258. DOI: 10.1016/j.carbpol.2022.119258

*Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

[17] Ramesh Oraon CMH, Rawtani D, Singh P. Nanocellulose Materials Applications, Fabrication and Industrial. 1st ed. Cambridge, USA: Elsevier; 2022

[18] Shaikh K et al. Mitigation of CaCO3 fouling on heat exchanger surface using green functionalized carbon nanotubes (GFCNT) coating. Thermal Science and Engineering Progress. 2023;**42**:101878. DOI: 10.1016/J.TSEP.2023.101878

[19] Shaikh K et al. Investigation of zirconium (Zr) coated heat exchanger surface for the enhancement of heat transfer and retardation of mineral fouling. Journal of the Taiwan Institute of Chemical Engineers. 2023;**153**:105246. DOI: 10.1016/j.jtice.2023.105246

[20] Panchal P, Ogunsona E, Mekonnen T. Trends in advanced functional material applications of nanocellulose. PRO. 2019;**7**(1):10. DOI: 10.3390/pr7010010

[21] Bravo J, Zhai L, Wu Z, Cohen RE, Rubner MF. Transparent superhydrophobic films based on silica nanoparticles. Langmuir. 2007;**23**(13):7293-7298. DOI: 10.1021/ la070159q

[22] Li S, Xie H, Zhang S, Wang X. Facile transformation of hydrophilic cellulose into superhydrophobic cellulose. Chemical Communications. 2007;**1**(46):4857-4859. DOI: 10.1039/ b712056g

[23] Song J, Rojas OJ. PAPER CHEMISTRY: Approaching superhydrophobicity from cellulosic materials: A review. Nordic Pulp & Paper Research Journal. 2018;**28**(2):216-238

[24] Teisala H, Tuominen M, Kuusipalo J. Superhydrophobic coatings on cellulosebased materials: Fabrication, properties, and applications. Advanced Materials

Interfaces. 2014;**1**(1):1-20. DOI: 10.1002/ admi.201300026

[25] Manca M, Cannavale A, De Marco L, Aricò AS, Cingolani R, Gigli G. Durable superhydrophobic and antireflective surfaces by trimethylsilanized silica nanoparticles-based sol-gel processing. Langmuir. 2009;**25**(11):6357-6362. DOI: 10.1021/la804166t

[26] Salam A, Lucia LA, Jameel H. Fluorine-based surface decorated cellulose nanocrystals as potential hydrophobic and oleophobic materials. Cellulose. 2015;**22**(1):397-406. DOI: 10.1007/s10570-014-0507-9

[27] Shang W, Huang J, Luo H, Chang PR, Feng J, Xie G. Hydrophobic modification of cellulose nanocrystal via covalently grafting of castor oil. Cellulose. 2013;**20**(1):179-190. DOI: 10.1007/ s10570-012-9795-0

[28] Salajková M, Berglund LA, Zhou Q. Hydrophobic cellulose nanocrystals modified with quaternary ammonium salts. Journal of Materials Chemistry. 2012;**22**(37):19798-19805. DOI: 10.1039/ c2jm34355j

[29] Yu M, Gu G, Meng WD, Qing FL. Superhydrophobic cotton fabric coating based on a complex layer of silica nanoparticles and perfluorooctylated quaternary ammonium silane coupling agent. Applied Surface Science. 2007;**253**(7):3669-3673. DOI: 10.1016/j. apsusc.2006.07.086

[30] Ogihara H, Xie J, Okagaki J, Saji T. Simple method for preparing Superhydrophobic paper: Spraydeposited hydrophobic silica nanoparticle coatings exhibit high waterrepellency and transparency. Langmuir. 2012;**28**(10):4605-4608

[31] Mauriello G, De Luca E, La Storia A, Villani F, Ercolini D. Antimicrobial

activity of a nisin-activated plastic film for food packaging. Letters in Applied Microbiology. 2005;**41**(6):464-469. DOI: 10.1111/j.1472-765X.2005.01796.x

[32] Kodjak A. FDA Bans 19 Chemicals Used in Antibacterial Soaps. New York, USA: Food and Drug Administration; 2016

[33] Laxminarayan R et al. Antibiotic resistance-the need for global solutions. The Lancet Infectious Diseases. 2013;**13**(12):1057-1098. DOI: 10.1016/ S1473-3099(13)70318-9

[34] Wang L, Hu C, Shao L. The antimicrobial activity of nanoparticles: Present situation and prospects for the future. International Journal of Nanomedicine. 2017;**12**:1227-1249

[35] Lü F, Ye X, Liu D. Review of antimicrobial food packaging. Nongye Jixie Xuebao/Transactions of the Chinese Society of Agricultural Machinery. 2009;**40**(6):138-142

[36] Huang KS, Yang CH, Huang SL, Chen CY, Lu YY, Lin YS. Recent advances in antimicrobial polymers: A minireview. International Journal of Molecular Sciences. 2016;**17**(9):578. DOI: 10.3390/ijms17091578

[37] Fortunati E et al. Nano-biocomposite films with modified cellulose nanocrystals and synthesized silver nanoparticles. Carbohydrate Polymers. 2014;**101**(1):1122-1133. DOI: 10.1016/j. carbpol.2013.10.055

[38] Kreuter J. Nanoparticles and microparticles for drug and vaccine delivery. Journal of Anatomy. 1996;**189**(Pt 3):503-505. DOI: 10.1002/ bit

[39] Lam E, Male KB, Chong JH, Leung ACW, Luong JHT. Applications of functionalized and nanoparticlemodified nanocrystalline cellulose. Trends in Biotechnology. 2012;**30**(5):283- 290. DOI: 10.1016/j.tibtech.2012.02.001

[40] Ramos AI et al. Analysis of the microcrystalline inclusion compounds of triclosan with β-cyclodextrin and its tris-O-methylated derivative. Journal of Pharmaceutical and Biomedical Analysis. 2013;**80**:34-43. DOI: 10.1016/j. jpba.2013.02.033

[41] Suller MTE, Russell AD. Triclosan and antibiotic resistance in *Staphylococcus aureus*. Journal of Antimicrobial Chemotherapy. 2000;**46**(1):11-18. DOI: 10.1093/jac/46.1.11

[42] Helander IM, Nurmiaho-Lassila EL, Ahvenainen R, Rhoades J, Roller S. Chitosan disrupts the barrier properties of the outer membrane of gram-negative bacteria. International Journal of Food Microbiology. 2001;**71**(2-3):235-244. DOI: 10.1016/S0168-1605(01)00609-2

[43] Rabea EI, Badawy MET, Stevens CV, Smagghe G, Steurbaut W. Chitosan as antimicrobial agent: Applications and mode of action. Biomacromolecules. 2003;**4**(6):1457-1465. DOI: 10.1021/ bm034130m

[44] Cha DS, Chinnan MS. Biopolymerbased antimicrobial packaging: A review. Critical Reviews in Food Science and Nutrition. 2004;**44**(4):223-237. DOI: 10.1080/10408690490464276

[45] Panchal P et al. Graft modification of cellulose nanocrystals: Via nitroxide-mediated polymerisation. Biomacromolecules. 2014;**1**(1):235-244. DOI: 10.1021/la070159q

[46] Lee CH, Park HJ, Lee DS. Influence of antimicrobial packaging on kinetics of spoilage microbial growth in milk and orange juice. Journal of Food

*Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

Engineering. 2004;**65**(4):527-531. DOI: 10.1016/j.jfoodeng.2004.02.016

[47] El-Tahlawy KF, El-Bendary MA, Elhendawy AG, Hudson SM. The antimicrobial activity of cotton fabrics treated with different crosslinking agents and chitosan. Carbohydrate Polymers. 2005;**60**(4):421-430. DOI: 10.1016/j. carbpol.2005.02.019

[48] Weishaupt R et al. Enhanced antimicrobial activity and structural transitions of a nanofibrillated cellulosenisin biocomposite suspension. ACS Applied Materials and Interfaces. 2018;**10**(23):20170-20181. DOI: 10.1021/ acsami.8b04470

[49] Salmieri S et al. Antimicrobial nanocomposite films made of poly(lactic acid)–cellulose nanocrystals (PLA–CNC) in food applications—Part B: Effect of oregano essential oil release on the inactivation of listeria monocytogenes in mixed vegetables. Cellulose. 2014;**21**(6):4271-4285. DOI: 10.1007/ s10570-014-0406-0

[50] Zhang H, Chen H, She Y, Zheng X, Pu J. Anti-yellowing property of polyurethane improved by the use of surface-modified nanocrystalline cellulose. BioResources. 2014;**9**(1):673- 684. DOI: 10.15376/biores.9.1.673-684

[51] Ma IAW, Sh A, Ramesh K, Vengadaesvaran B, Ramesh S, Arof AK. Anticorrosion properties of epoxynanochitosan nanocomposite coating. Progress in Organic Coatings. 2017;**113**(2008):74-81. DOI: 10.1016/j. porgcoat.2017.08.014

[52] Panda SS, Katz HE, Tovar JD. Solidstate electrical applications of protein and peptide based nanomaterials. Chemical Society Reviews. 2018;**47**(10):3640-3658. DOI: 10.1039/ c7cs00817a

[53] Csoka L, Hoeger IC, Rojas OJ, Peszlen I, Pawlak JJ, Peralta PN. Piezoelectric effect of cellulose nanocrystals thin films. ACS Macro Letters. 2012;**1**(7):867-870. DOI: 10.1021/ mz300234a

[54] Csoka L, Hoeger IC, Peralta P, Peszlen I, Rojas OJ. Dielectrophoresis of cellulose nanocrystals and alignment in ultrathin films by electric field-assisted shear assembly. Journal of Colloid and Interface Science. 2011;**363**(1):206-212. DOI: 10.1016/j.jcis.2011.07.045

[55] Le Bras D, Strømme M, Mihranyan A. Characterization of dielectric properties of nanocellulose from wood and algae for electrical insulator applications. Journal of Physical Chemistry B. 2015;**119**(18):5911-5917. DOI: 10.1021/acs. jpcb.5b00715

[56] Mihranyan A, Llagostera AP, Karmhag R, Strømme M, Ek R. Moisture sorption by cellulose powders of varying crystallinity. International Journal of Pharmaceutics. 2004;**269**(2):433-442. DOI: 10.1016/j.ijpharm.2003.09.030

[57] Gaspar D et al. Nanocrystalline cellulose applied simultaneously as the gate dielectric and the substrate in flexible field effect transistors. Nanotechnology. 2014;**25**(9):094008. DOI: 10.1088/0957-4484/25/9/094008

[58] Pereira L, Gaspar D, Guerin D, Delattre A, Fortunato E, Martins R. The influence of fibril composition and dimension on the performance of paper gated oxide transistors. Nanotechnology. 2014;**25**(9):094007. DOI: 10.1088/0957-4484/25/9/094007

[59] Liu W, Ullah B, Kuo C-C, Cai X. Two-dimensional nanomaterials-based polymer composites: Fabrication and energy storage applications. Advances in Polymer Technology. 2019;**2019**:1-15. DOI: 10.1155/2019/4294306

[60] Tang L, Zhao L, Guan L. 7 graphene/polymer composite materials: Processing, properties and applications. In: Advanced Composite Materials: Properties and Applications. Berlin, Germany: De Gruyter Open; 2017

[61] Kiziltas A, Erbas Kiziltas E, Boran S, Gardner DJ. Micro-and nanocellulose composites for automotive applications. In: Society of Plastics Engineers -13th Annual Automotive Composites Conference and Exhibition, ACCE 2013, no. February 2016. Vol. 1. Novi, MI, USA: Proceedings of the SPE Automotive Composites Conference and Exhibition (ACCE); 2013. pp. 402-414

[62] Sanoj P, Balasubramanian K. High performance structural nano cellulose composites for motor vehicle spring suspension system. International Journal of Plastics Technology. 2014;**18**:383-389. DOI: 10.1007/s12588-014-9098-4

[63] Reshmy R et al. Nanocellulose-based products for sustainable applicationsrecent trends and possibilities. Reviews in Environmental Science and Biotechnology. 2020;**19**(4):779-806. DOI: 10.1007/s11157-020-09551-z

[64] Bordes P, Pollet E, Avérous L. Nanobiocomposites: Biodegradable polyester/ nanoclay systems. Progress in Polymer Science (Oxford). 2009;**34**(2):125-155. DOI: 10.1016/j.progpolymsci.2008.10.002

[65] Xu S, Girouard N, Schueneman G, Shofner ML, Meredith JC. Mechanical and thermal properties of waterborne epoxy composites containing cellulose nanocrystals. Polymer. 2013;**54**(24):6589- 6598. DOI: 10.1016/j.polymer.2013.10.011

[66] Bras J, Hassan ML, Bruzesse C, Hassan EA, El-Wakil NA, Dufresne A. Mechanical, barrier, and biodegradability properties of bagasse cellulose

whiskers reinforced natural rubber nanocomposites. Industrial Crops and Products. 2010;**32**(3):627-633. DOI: 10.1016/j.indcrop.2010.07.018

[67] Cao Y, Zavaterri P,

Youngblood J, Moon R, Weiss J. The influence of cellulose nanocrystal additions on the performance of cement paste. Cement and Concrete Composites. 2015;**56**:73-83. DOI: 10.1016/j. cemconcomp.2014.11.008

[68] Jorfi M, Foster EJ. Recent advances in nanocellulose for biomedical applications. Journal of Applied Polymer Science. 2015;**132**(14):1-19. DOI: 10.1002/ app.41719

[69] Dong S, Roman M. Fluorescently labeled cellulose nanocrystals for bioimaging applications. Journal of the American Chemical Society. 2007;**129**(45):13810-13811. DOI: 10.1021/ ja076196l

[70] Kilgore MB et al. Cell-based analysis of the immune and antioxidant response of the nanocarrier β -cyclodextrin conjugated with cellulose nanocrystals mechanistic insights on the immune and antioxidant response of functionalized cellulose nanocrystals: Does surface charge. Free Radical Biology and Medicine. 2018;**128**:S102

[71] Domingues RMA, Gomes ME, Reis RL. The potential of cellulose nanocrystals in tissue engineering strategies. Biomacromolecules. 2014;**15**(7):2327-2346. DOI: 10.1021/ bm500524s

[72] Yang X, Cranston ED. Chemically cross-linked cellulose nanocrystal aerogels with shape recovery and superabsorbent properties. Chemistry of Materials. 2014;**26**(20):6016-6025. DOI: 10.1021/cm502873c

*Nanocellulose: Fundamentals and Applications DOI: http://dx.doi.org/10.5772/intechopen.114221*

[73] Zhou Y et al. Recyclable organic solar cells on cellulose nanocrystal substrates. Scientific Reports. 2013;**3**:24-26. DOI: 10.1038/srep01536

[74] Kim JH et al. Review of nanocellulose for sustainable future materials. International Journal of Precision Engineering and Manufacturing-Green Technology. 2015;**2**(2):197-213. DOI: 10.1007/s40684-015-0024-9

[75] Qiu X, Hu S. 'Smart' materials based on cellulose: A review of the preparations, properties, and applications. Materials. 2013;**6**(3):738- 781. DOI: 10.3390/ma6030738

[76] Way AE, Hsu L, Shanmuganathan K, Weder C, Rowan SJ. PH-responsive cellulose nanocrystal gels and nanocomposites. ACS Macro Letters. 2012;**1**(8):1001-1006. DOI: 10.1021/ mz3003006

[77] Kafy A, Akther A, Shishir MIR, Kim HC, Yun Y, Kim J. Cellulose nanocrystal/graphene oxide composite film as humidity sensor. Sensors and Actuators, A: Physical. 2016;**247**:221-226. DOI: 10.1016/j.sna.2016.05.045

[78] Zhang L, Li Q, Zhou J, Zhang L. Synthesis and photophysical behavior of pyrene-bearing cellulose nanocrystals for Fe 3+ sensing. Macromolecular Chemistry and Physics. 2012;**213**(15):1612-1617. DOI: 10.1002/ macp.201200233

[79] Sadasivuni KK, Kafy A, Zhai L, Ko HU, Mun S, Kim J. Transparent and flexible cellulose nanocrystal/reduced graphene oxide film for proximity sensing. Small. 2015;**11**(8):994-1002. DOI: 10.1002/smll.201402109

[80] Wang S, Zhang X, Wu X, Lu C. Tailoring percolating conductive networks of natural rubber composites for flexible strain sensors via a cellulose nanocrystal templated assembly. Soft Matter. 2016;**12**(3):845-852. DOI: 10.1039/c5sm01958c

[81] C. A. de Assis et al., "Conversion economics of Forest biomaterials: Risk and financial analysis of CNC manufacturing," Biofuels, Bioproducts and Biorefining, vol. 11, no. 4, pp. 682- 700, Jul. 2017, doi: doi:10.1002/bbb.1782.

[82] Jiang G et al. Bacterial nanocellulose/ Nafion composite membranes for low temperature polymer electrolyte fuel cells. Journal of Power Sources. 2015;**273**:697-706. DOI: 10.1016/j. jpowsour.2014.09.145

[83] M. J. Blair and W. E. Mabee, "Techno-economic and market analysis of two emerging forest biorefining technologies," Biofuels, Bioproducts and Biorefining, vol. 15, no. 5, pp. 1301-1317, Sep. 2021, doi: doi:10.1002/bbb.2218.

[84] Bondancia TJ et al. Production of nanocellulose using citric acid in a biorefinery concept: Effect of the hydrolysis reaction time and technoeconomic analysis. Industrial and Engineering Chemistry Research. 2020;**59**(25):11505-11516. DOI: 10.1021/ acs.iecr.0c01359

[85] Shen R et al. Research Progress and development demand of nanocellulose reinforced polymer composites. Polymers (Basel). 2020;**12**(9):2113. DOI: 10.3390/ polym12092113

[86] Arantes V, Dias IKR, Berto GL, Pereira B, Marotti BS, Nogueira CFO. The current status of the enzyme-mediated isolation and functionalization of nanocelluloses: Production, properties, techno-economics, and opportunities. Cellulose. 2020;**27**(18):10571-10630. DOI: 10.1007/s10570-020-03332-1

[87] Squinca P, Bilatto S, Badino AC, Farinas CS. Nanocellulose production in future biorefineries: An integrated approach using tailor-made enzymes. ACS Sustainable Chemistry & Engineering. 2020;**8**(5):2277-2286. DOI: 10.1021/acssuschemeng.9b06790

[88] Jiang J, Zhu Y, Jiang F. Sustainable isolation of nanocellulose from cellulose and lignocellulosic feedstocks: Recent progress and perspectives. Carbohydrate Polymers. 2021;**267**:118188. DOI: 10.1016/j.carbpol.2021.118188

[89] Kaur P et al. Nanocellulose: Resources, physio-chemical properties, current uses and future applications. Frontiers in Nanotechnology. 2021;**3**:747329. DOI: 10.3389/ fnano.2021.747329

[90] Stoudmann N, Nowack B, Som C. Prospective environmental risk assessment of nanocellulose for Europe. Environmental Science: Nano. 2019;**6**(8):2520-2531. DOI: 10.1039/ C9EN00472F

[91] Piccinno F, Hischier R, Seeger S, Som C. Predicting the environmental impact of a future nanocellulose production at industrial scale: Application of the life cycle assessment scale-up framework. Journal of Cleaner Production. 2018;**174**:283-295. DOI: 10.1016/j.jclepro.2017.10.226

[92] Turk J, Oven P, Poljanšek I, Lešek A, Knez F, Malovrh Rebec K. Evaluation of an environmental profile comparison for nanocellulose production and supply chain by applying different life cycle assessment methods. Journal of Cleaner Production. 2020;**247**:119107. DOI: 10.1016/j.jclepro.2019.119107

#### **Chapter 2**

## Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application

*Kirubanandan Shanmugam*

#### **Abstract**

Spraying cellulose nanofibers on the polished stainless-steel plate is a novel approach for the fabrication of free-standing cellulose nanofiber film (CNF). Recently, free-standing cellulose nanofiber film has gained attention as an alternative to synthetic plastic film. Free-standing/self-standing CNF film can be used as a potential barrier, in packaging application, as membranes for waste water application, in fabrication of biomedical film for wound repair and many more such applications in the fabrication of functional materials. To hasten the production of free-standing CNF film, spraying process is a considerable process-intensified method for large-scale production of film in a rapid manner. Spraying CNF on the stainless-steel plate produces the film with unique surfaces, namely a rough surface exposed to air and a smooth surface from the steel surface. The smooth surface of the film is very shiny and glossy and provides a platform for utilizing this smoothness for fabricating the functional materials such as a base substrate for flexible electronics and solar cells, etc. This chapter summarizes the production of free-standing CNF film via spraying and its characterization linked to its application.

**Keywords:** spraying, cellulose nanofibers, free-standing films, air permanence, uniformity, thickness mapping, water vapor permeability

#### **1. Introduction**

Plastic pollution is one of the serious threats to the environment in the current scenario. Packaging is the main source for these plastics' pollution and it is an alarming status to replace the synthetic plastics with biopolymers. Biopolymers are good alternatives for synthetic plastics, as they have biodegradability, serve as ecofriendly material, and possess good mechanical and barrier properties for the development of various functional materials [1]. Recently, cellulose nanofiber (CNF) has been getting a predominant place in the list of biopolymers [2].

Cellulose is the most important biorenewable, biodegradable and biopolymer that is available in plenty in nature and plays an excellent feed stock for the development of various sustainable materials on an industrial-scale production [3]. From the past decade, cellulose nanofiber is used as one of the pioneering feed stocks for the development of various functional materials. It is produced by the disintegration and

delamination of cellulose fibrils from pulp that is, in turn, produced from a variety of green sources like wood, potato tuber, hemp and flax. It has a dimension diameter ranging from 5 to 60 nanometers (nm) and length of several micrometers [4]. Moreover, having a smaller dimension in cellulose nanofibrils in CNF gives the larger surface of CNF, which is why, there is a great opportunity for developing more functional materials for various applications [4, 5].

The films made from cellulose nanofiber (CNF) have various outstanding mechanical, optical and structural properties and these properties are played to fabricate various functional materials, such as cellulose nanocomposite [4], microfibrillated film [6], inorganic nanocomposite [7], organic transistors and conducting materials [8] and immunoassays and diagnostic materials [9]. Moreover, another advantage of the nanofibrillated cellulose is that it is easy to tailor its surface properties and mechanical properties. As a result, it is used in the field of photonics, surface modifications, nanocomposites, biomedical scaffold and optoelectronics [10]. Due to barrier and colloidal properties of CNF, it is widely used in paper-making, packaging and coatings to enhance its barrier surface and then in automotive industries [11]. Recently, CNF sheets turned out to be one of the most promising highperformance functional materials potentially used as filters [12], adsorbents, catalysts [13], cell culture substrates, thermal insulators and drug carriers [14].

On top of abovementioned excellent properties, these materials are biodegradable and recyclable. Hence, they have the potential to replace some of the synthetic polymeric materials that cause serious environmental problems [1]. However, persisting problems faced during CNF film preparation include low-energy consumption and rapidity in fabrication [15]. CNF films were prepared by vacuum filtration, casting and spray coating. However, these methods are time-consuming processes, and the films are low in weight and thickness [15, 16]. Even though these processes could be efficient in the way of producing better quality of films, they have constraints in the scaling-up process in large-scale production for technology transfer and commercialization of the free-standing films [15].

In the vacuum filtration method, the CNF film formation required a high dewatering time, which shows up as a major constraint for an industrial-scale process. Furthermore, Varanasi and Batchelor [17] reported on the rapid preparation of nanofibrillated sheet using a British hand sheet maker in 10 min. However, they achieved only the mass per unit area of 57.4 g/m<sup>2</sup> and thickness of 68.9 8.90 <sup>μ</sup>m. This is why the current investigation was motivated to develop a rapid and scalable spray coating technique to produce the nanocellulose film to replace the timeconsuming conventional techniques for cellulose film [18]. Beneventi et al. [19] reported on the spray coating of the microfibrillated cellulose on the nylon fabric to prepare the nanopaper with maximum mass of the film of 124 g/m<sup>2</sup> . In this approach, the experimental setup has a conveyor system with a speed of 0.5 m/min to achieve 124 g/m<sup>2</sup> of film's basis weight. However, it failed to explain the uniformity of the film through the thickness distribution and surface morphology. This chapter reveals the rapid preparation of a CNF film using a developed laboratory-scale spray coating system to produce high basis weight film in a short span of time.

#### **2. Free-standing CNF film fabrication via spray coating process**

Spraying cellulose nanofibers on the polished stainless-steel plate is a rapid and novel process for the fabrication of a CNF wet film [20]. Previously, spraying

#### *Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

microfibrillated cellulose on three-dimensional (3D) brass metal was attempted to develop a film. However, the cracks and shrinkage on the film were formed. But this was the basic idea to develop a spray coating process to fabricate CNF film [21]. In the improved process, the microfibrillated cellulose suspension was sprayed on the fabric surface and then it was followed by vacuum filtration to remove the excess water present in the wet film [19]. The concept of spraying nanofibers has been generated from these concrete works. In addition to that, spraying provides contour coating and contactless coating with the solid surface. So that, the surface topography and morphology of the solid surface did not influence the coating process [15]. It has been reported that spraying process produces a CNF film with high basis weight without any change in the operation time [20]. The spraying CNF on the fabric surface and paper substrates was already developed for free-standing films and barrier coating on the papers'surface [19, 22]. This chapter reveals the spraying CNF on the stainlesssteel plates for the fabrication of free-standing films.

The following experimental system on spray coating to fabricate CNF film was developed.

**Figure 1** shows the experimental system for spraying CNF on the stainless-steel plate. It reveals the spraying CNF suspension on the metal plate that is kept on the conveyor. In this experimental system, there are two important parameters for tailoring the properties of a CNF film. CNF suspension consistency and velocity of the conveyor are the parameters used for tailoring the thickness and basis weight of the films. At constant velocity of the conveyor, the CNF suspension can be varied for spraying operation to get the CNF film. Normally, spraying low CNF% suspension produces the least thickness and basis weight of the film, whereas high basis weight and thickness of the film can be fabricated by spraying high CNF% suspension on the polished metal surface. Similarly, the CNF suspension concentration has been fixed and varying the velocity of the conveyor helps to tailor the thickness and basis weight of the film. It means that high basis weight and thickness of the film were fabricated at the lowest velocity of the conveyor. At that moment, a high amount of suspension gets

#### **Figure 1.**

*Experimental setup for lab-scale spray coating system for the preparation of a nanocellulose (NC) film. (A) Rough surface of the NC film. (B) Smooth surface of the NC film.*

deposited and fibers concentrated to form a high basis weight CNF film. Similarly, thin CNF films were fabricated spraying CNF suspension on the metal plate at high velocity of the conveyor. In this case, less amount of fibers were deposited on the steel plate to form a thin CNF film due to fast movement of the conveyor. Apart from these important parameters in a spray system to show their effect on CNF film's properties, the spray distance between the spray gun to the base surface, spray nozzle and spray gun position is indirectly controlling the film's properties, such as uniformity, thickness and basis weight [18, 20].

In this spray system, the CNF wet film can be fabricated and should be subjected to a drying process to remove the excess water in the wet film. The drying process can be carried out by different methods such as drying the wet film in an air oven at a temperature of 105°C and drying the wet sheets in a laminar flow chamber or fume hood with a constant flow of air under standard laboratory practice. The dried CNF film can be subjected to various characterizations and applications. The dried spraycoated CNF film has two unique but compact surfaces, namely rough surface and smooth surface. The rough surface is exposed to the air side when spraying CNF suspension on the metal plates. The smooth side of the CNF film is from the stainless-steel side and it has a shiny and glossy surface as one of the finishing qualities in this process. The surface smoothness of the CNF film is replicated from the stainless-steel plate. This smooth side of the film is used for the fabrication of numerous functional materials such as substrates for flexible electronics and printed electronics [16].

#### **3. Analysis of spray-coated CNF films and their characterization**

Spraying cellulose nanofiber suspension on the polished stainless-steel plates is a rapid process for the fabrication of a wet film of CNF. This method produces a compact film of cellulose nanofibrils having two unique surfaces, namely rough surface on the free side and smooth surface on the metal side. The operation time to form a 15.9-cm diameter CNF film consumes less than a minute and is independent of CNF suspension concentration. However, this method produces a wet CNF film and is subjected to a drying process to evaporate the water in a spray-coated CNF suspension. The drying of spray-coated wet film can be performed by keeping the wet film in an air oven at 105°C or air-drying in a laminar flow chamber under the standard laboratory conditions. The dried film on the stainless-steel plate can be easily peeled off from the plate and the CNF becomes free standing/self-standing films for various applications [20].

**Figures 2** and **3** show the spray-coated CNF film. The spraying CNF on circular stainless-steel plate and square stainless-steel plate was achieved to fabricate the circular and square sheets. The operation time in spraying CNF suspension to form a 15.9-cm diameter film was less than a minute. Unlike vacuum filtration, the CNF concentration to fabricate film was independent of their operation time in a spraying process. The spraying CNF on the metal surface produces an ultrasmooth film for various applications [18].

**Figure 4** reveals the cross-section of the scanning electron microscopy (SEM) micrographs of a CNF film prepared via spray coating. The SEM micrograph confirms the complex cellulose nanofibril layers intertwined through the hydrogen bonding between the hydroxyl groups of the CNF. This also increases tortuosity of the film and shows this effect on the barrier performance of the CNF film [16].

*Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

**Figure 2.** *Circular sheets of a CNF film via spray coating process.*

**Figure 3.** *Square sheets of a CNF film via spray coating process.*

**Figures 5** and **6** show the SEM micrographs of the spray-coated CNF film and comparison with the CNF film prepared via vacuum filtration. The CNF film via spraying has compactness and roughness on the free side and smoothness on the other side. The rough surface of the film is very porous due to various sizes of the fibre distribution. The smooth side of the film has a shiny and glossy surface and its smoothness is replicated from the surface of the stainless-steel plate [18, 20]. The mechanism of replication of the smoothness from the stainless-steel plate remains obscure [16]. The rough and smooth surface of the spray-coated CNF film has an importance in the fabrication of various functional materials [16]. For example, in the construction of flexible electronics and printed electronics, the conductive ink on the cellulose substrates should be penetrated well on the surface of the substrates. To achieve this, the sufficient roughness/smoothness of the substrates are required for

#### **Figure 4.**

*Cross-sectional view of spray-coated CNF films.*

*Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

**Figure 6.** *Smooth side of a spray-coated CNF film and the free side of the vacuum-filtered film.*

spreading the conductive ink. Similarly, the roughness and smoothness of the film can be used in the fabrication of solar cells [16].

The rough side of the spray-coated CNF film and the filter side of the vacuumfiltered CNF film are shown in **Figure 5**. The surfaces of both sides of the films are very porous and have a good surface roughness. **Figure 6** reveals the smooth side of the CNF film and the free side of the vacuum-filtered CNF film.

#### **4. Surface roughness of a free-standing CNF film**

As discussed earlier, the surface roughness of the film is one of the important criteria for the construction of functional materials. The surface roughness of the CNF film is evaluated by optical profilometry.

**Figure 7** shows the optical profilometry image of the rough side of the CNF film prepared via spray coating. The rough side of the film was very porous and it showed high surface roughness on the film. This was due to various fiber size distributions in cellulose nanofibrils. The mean surface roughness on the rough side of the CNF film was found to be 1654 nm and the root mean square (RMS) value of the surface roughness on this side was reported to be 2087 nm. **Figure 8** reveals the optical profilometry image of the smooth side of a CNF film. The Ra and Rq values from the image confirm that the surface was very smooth and shiny and glossy. The Ra and Rq values from the image were evaluated to be 278 nm and 389 nm, respectively. **Figures 9** and **10** show the optical profilometry images of free and filter sides of the CNF film prepared via vacuum filtration. The Ra and Rq values on the free side of the filtered CNF film were evaluated

**Figure 7.** *Optical profilometry image of the rough side of a CNF film via spraying.*

**Figure 8.** *Optical profilometry image of the smooth side of the CNF film via spraying.*

*Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

**Figure 9.** *Optical profilometry image of the free side of the CNF film via filtration.*

**Figure 10.** *Optical profilometry image of the filter side of the CNF film via filtration.*

to be 2150 nm and 2673 nm, respectively. Similarly, the Ra and Rq values on the filter side of the vacuum-filtered CNF film were evaluated to be 3015 nm and 3751 nm, respectively. When comparing the surface roughness of the CNF film with that from filtration, the spray-coated CNF film has smooth and less porous surface [18, 20].

Spraying CNF suspension on the polished metal surface like stainless steel produces a more smooth film than that of standard procedure such as vacuum filtration. In the filtration process, the film has rough surface on the filter side and free side and is also porous, depending on the type of cellulose nanofiber used. In spraying, the film has unique surfaces, such as smooth side from the metal side and rough side from the air side.

#### **5. Atomic force microscopy (AFM) studies**

The AFM studies on the spray-coated CNF film were investigated to analyze the nanoscale surface, roughness of the rough and smooth surfaces of the film. The visual examination of the CNF film via spraying was rough on the free side of the film and smooth on the metal side. In addition to that, the smooth side was very shiny and glossy as one of the finishing qualities of the film. The RMS surface roughness of the CNF film from the AFM micrographs was evaluated to be 51.4 nm on the rough side and 16.7 nm on the smooth side in an inspection area of 2 μm 2 μm. In the case of a vacuum-filtered CNF film, the RMS surface roughness of the CNF film was found to be 102.3 nm on the free side and 70.64 nm on the filter side on the same area of inspection. By this way, the nanoscale roughness of the CNF film was evaluated and it is implemented on these surfaces for the construction of printed and flexible electronics substrates. **Figures 11** and **12** show the surface roughness of the CNF film and RMS value evaluated from these AFM micrographs [16].

**Figure 11.** *Rough surface of the spray-coated CNF film.*

*Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

**Figure 12.** *Smooth surface of the CNF film via spraying.*

#### **6. Thickness mapping of CNF film via spraying**

Thickness of the film is one of the main parameters for controlling the barrier performance of the film. **Figure 13** shows the thickness mapping of spray-coated CNF film and its comparison with that of a vacuum-filtered CNF film (**Figure 14**). The thickness mapping of the CNF film was evaluated from 1.5 wt.% CNF film via

**Figure 13.** *Thickness mapping of the spray-coated CNF film.*

**Figure 14.** *Thickness mapping of the vacuum-filtered CNF film.*

spraying to 1.5 wt.% CNF on the stainless-steel plate. The basis weights of the film produced by vacuum filtering and spray coating, respectively, are 100.5 � 3.4 g/m<sup>2</sup> and 95.2 � 5.2 g/m2 , respectively. Vacuum filtering consumes a substantially longer dewatering time of 15 minutes to form the film. In the spraying operation, the operation time to form a film is independent of CNF suspension concentration. Even after accounting for the little variation in basis weight, the spray-coated CNF film is somewhat thicker when compared to the vacuum-filtered film. The apparent densities of the vacuum-filtered and spray-coated films were 793 and 834 kg/m<sup>3</sup> , respectively. Additionally, the thickness of the spray-coated film is distributed across a somewhat larger range. **Figures 13** and **14** reveal the uniform thickness of the CNF film fabricated via spraying and filtration processes. It seems that the spray-coated CNF film has better uniformity and is comparable with a filtered CNF film [20].

#### **7. Thickness and basis weight of the film**

**Figure 15** reveals the linear relationship between thickness and basis weight of the CNF film via spraying. It demonstrates that the central composite design (CCD) model may be used to scale up the spraying process since it matches the actual experimental data well. The thickness and basis weight of the CNF film were tailored by increasing spraying CNF suspension from 1 wt.% to 2 wt.%. The operation time for spraying CNF suspension was independent of fiber content in the CNF suspension. The following models have been developed to scale up the process. These models reveal that the basis weight and thickness of the CNF film were found to be highly influenced by the CNF suspension concentration, as opposed to conveyor speed and spray distance based on the testing's findings.

$$\begin{aligned} \text{Basis weight} &= -64.45 + 122.43 \ast \text{CNF suspension concentration} - 17.28\\ &\ast \text{Velocity of the conveyor} + 0.34 \ast \text{Splay distance} \end{aligned} \tag{1}$$

*Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

**Figure 15.** *Linear relationship between thickness and basis weight of the spray-coated CNF film.*

Thickness ¼ �0*:*106 þ 0*:*111 ∗CNF suspension concentration � 0*:*000017 <sup>∗</sup> Velocity of the conveyor <sup>þ</sup> <sup>0</sup>*:*<sup>002</sup> <sup>∗</sup> Spray distance (2)

These are linear models confirming the direct relationship between thickness and basis weight of the CNF film.

From the linear models, there were two important parameters controlling the thickness and basis weight of the CNF film. Mainly, CNF suspension concentration and velocity of the conveyor in the experimental setup were deciding parameters for tailoring the CNF film's properties [23].

#### **8. Mechanical performance of spray-coated CNF film**

**Figure 16** reveals the tensile index of the spray coated cellulose nanofiber film and its comparison with that of a vacuum filtration film. The modified configuration of an experimental spray system produces the CNF film that has tensile indices higher than that of the CNF film via vacuum filtration. This is because of the high uniformity of the CNF film that was fabricated in the modified configuration of the spray system. Generally, spraying CNF suspension on the polished metal plate is controlled by numerous parameters, mainly CNF suspension's consistency, process variables in the spray system, such as the spray distance, nozzle diameter, type of spray system and sprayability of the CNF suspension. These parameters indirectly control the uniformity of the film, which is linked with barrier and mechanical properties of the film [18].

**Figure 16.** *Tensile index of the spray-coated cellulose nanofiber film and its comparison with that of a vacuum-filtered film.*

#### **9. Cost and environmental analysis**

The free-standing CNF film has not been commercialized so far and it is in the researching and development (R&D) stage. The patents on free-standing CNF films and their composites produced via various methods have been increased. The cost of Diacel KY 100S from Diacel Chemical Pvt. Ltd. was 2500 Australian dollars (AUD) per 50 kg of nanocellulose. The cost of a spraying system was around 4000 AUD for the construction of an experimental system to spray CNF on the polished metal surface. The sizes of the film are 220 mm x 220 mm for square sheet and 159 mm for circular sheet. The basis weight of the film was assumed to be 100 g/m2 . For 1 kg of KY100S, 10 sheets can be fabricated and each sheet consumes 5 AUD for the fabrication. The operation and maintenance costs were not considered in this study. The operation time for the fabrication of a 220 mm 220 mm square sheet and 159 mm circular sheet was less than a minute. When compared with vacuum filtration (VF), a laboratory version of the paper-making machine, spraying is a process intensified for the fabrication of free-standing cellulose nanofiber films and their composites. In the case of the spraying method, there are few steps, such as spraying CNF suspension on the metal plates, followed by drying under standard approach. It has required less fixed capital and operating cost and labour cost. In the case of vacuum filtration, there are many steps, such as the agitation of CNF suspension, mixing of CNF suspension, dewatering, couching, sheet removal, drying and then pressing. It confirms that filtration requires good fixed capital and high operating cost and labour cost. Spraying operation can be integrated with other coating methods such as roll to roll (R2R) for giving a high performance in the rate of production of a CNF film. So that, the cost of CNF film will be reduced for commercializing in the market.

#### *Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

Under controlled composting circumstances, the biodegradability and compostability of nanofibrillar cellulose-based (NFC) products, such as films, concentrated NFC, and paper products incorporating NFC, were assessed. All of the NFC products that were evaluated met the criteria for biodegradability outlined in European Standard EN 13432. NFC even increased the biodegradability of paper that had 1.5% NFC added to it. The modified pilot-scale composting test EN 14045 was used to assess disintegration during composting. In 3 weeks of composting, NFC films entirely decomposed, and NFC had no effect on how easily paper products containing NFC degraded. Using a bioluminescence test using *Vibrio fischeri*, ecotoxicity during the biodegradation of NFC products in a compost environment was assessed. For any of the samples, there was no evidence of acute toxicity [24].

#### **10. Comparison with other coating process and validation**

Spraying cellulose nanofibers on the polished stainless-steel plate is a rapid process to form a compact CNF film. It is a new process and should be compared with other conventional methods to confirm the efficacy of spray coating method [25]. The current spraying method has the capacity to handle the CNF suspension from 1.0 wt. % to 2.0 wt.% to produce the thickness and basis weight of CNF film from ~60 μm to ~200 μm and ~55 g/m<sup>2</sup> to ~199 g/m<sup>2</sup> [20]. The performance of the spray coating process can be improved by the high-performance spray system that can handle the CNF suspension of more than 2.00 wt.% [16, 18]. In addition to that, the rheology modifier, such as montmorillonite (MMT) clay, can be added into the CNF suspension for spraying to avoid any interruption in forming spray jet for fabrication of the films [16]. When comparing spraying microfribillated cellulose on the 3D structures [21], this method is quite reproducible and produces the CNF film without any cracks and homogeneous film with a high degree of uniformity [18]. The earlier method of spraying microfibrillar cellulose (MFC) on a 3D brass structure produces the MFC film having the basis weight and thickness from 59 to 118 g/m2 and 46 to 68 μm, respectively. The spray-coated 3D structure consists of cracks and wrinkles formed on the surface. However, the reported method handled high solid MFC suspension, such as 4.5 wt.% and 9 wt.% MFC suspensions, resulting in the formation of a disturbed spray jet and also resulting in the formation of cracks and wrinkles on the film. A high MFC suspension behaves as a gel-like fluid and makes the spray systems lose the spraying ability [21].

Similar to the current spray coating method, the earlier spraying MFC on the nylon fabric was attempted to fabricate the free-standing CNF film. In this method, spraying MFC on the nylon fabric consumed time from 10 min to 20 min and then the wet sprayed film was subjected to water removal from the CNF suspension via applying vacuum, which is similar to vacuum filtration. The time consumed for filtration was from 15 sec to 90 sec and after that vacuum dried under standard temperature. The spray-coated MFC film from this spraying process has the basis weight that varied from 13.7 g/m<sup>2</sup> to 124 g/m2 , with the thickness of the film varying from 10 μm to 72 μm. It was also reported that the imprints of nylon fabric were marked on the spray-coated MFC film [19]. Spraying was more efficient in the fabrication of freestanding CNF film while compared with solvent casting, vacuum filtration and hot pressing. These processes were problematic in the evaporation or removal of solvent from CNF film and a time-consuming process and also limitation in the basis weight of the film. Spin coating is a laboratory approach for the fabrication of free-standing

thin CNF film for the study of biomolecules' interaction. It is not a scalable method due to the removal of water from the suspension via spinning to form ultrathin films. This method can be used to coat the substrates for laboratory-scale studies. Roll-to-roll (R2R) coating is another approach for the fabrication of CNF films and capacity for large-scale production of the film. In this method, CNF was coated on the pre-treated substrates such as plastic films. The spreading of CNF on the substrates was a challenging task and then coated and dried under pressing after peeled from the substrates. The basis weight of the CNF film can be achieved from 0.1 to 400 g/m2 [15].

Given this analysis, the spraying CNF on the base substrates is more advantageous in the fabrication of free-standing CNF film. Spraying on the stainless-steel plates produces the film with unique surfaces, mainly smooth on the steel side and it can be used for the fabrication of functional materials. When comparing with the other coating process, the operation time for spray coating in the current practice was less than a minute to fabricate a 15.9-cm diameter film and was independent of CNF suspension concentration. The integration of roll-to-roll coating with spray system is another approach for large-scale production of free-standing CNF films.

#### **11. Application of spray-coated CNF films**

Spray-coated CNF films have been utilized in various fields and applications as a substrate for developing functional materials. **Figure 17** shows various applications for CNF films in various fields. Due to the rapid process of spraying, it can be used as a barrier material to replace the synthetic plastics in the packaging sector. Generally, cellulose nanofibers are good as oxygen barrier and show a performance greater than that of synthetic plastics. However, the water vapor permeability (WVP) of CNF was not equalizing the water vapor barrier performance of synthetic plastics. Spraying CNF on the metal plates produces a film with compactness acting as a good barrier against water vapor and its performance was better than that of the vacuum filtered film and comparable with that of synthetic plastics. Furthermore, the water vapor

**Figure 17.** *Application of cellulose nanofiber films via spraying and filtration.*

#### *Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

barrier of the CNF film was improved by incorporating nano-inorganics/antimicrobial inorganics into cellulose nanofibril matrix in the CNF suspension [15].

In the case of fabrication of nanocellulose-montmorillonite composite, the time taken for dewatering in vacuum filtration process was exponentially increased with MMT concentration and time was consumed from 3 hours to 24 hours, depending on the MMT content in cellulose nanofiber suspension. To mitigate this problem, spray coating has been implemented to fabricate CNF-MMT composite and here the operation time for spraying CNF-MMT suspension was independent of MMT concentration in CNF suspension. The spray-coated CNF MMT composite was a good barrier material for replacing synthetic plastics in the packaging materials. The antimicrobial inorganics incorporated into cellulose nanofiber suspension were fabricated as composite via spray coating process. This free-standing composite can be used in antimicrobial packaging and bioactive packaging. Similarly, the free-standing CNF film prepared via spraying can be used as the membrane for waste water treatment. In this composite, titanium dioxide was also impregnated into the film and its becomes a photocatalyst for waste water treatment application [15].

The membranes were also developed from spray-coated CNF film to separate oil and water mixture. In addition to that, various composites from CNF—inorganics can be fabricated via spray coating process for various applications. The spray-coated CNF films have unique surfaces, namely rough surface and smooth surface. The smooth surface of the CNF film can be used for the development of printed and flexible electronics. **Figure 18** shows the CNF film as substrates for printed electronics and flexible electronics [16].

The spray-coated CNF film can be used as a base biomaterial for the development of tissue engineering material and drug-delivery vehicle. The silver nanoparticle

**Figure 18.** *The printed circuits on the spray-coated nanocellulose films.*

(AgNP) and MMT were coated on the spray-coated CNF film via a laboratory spraying method to develop a drug-delivery vehicle composite for the treatment of wound. The silver nanoparticle present on the surface of CNF film can eradicate the wound pathogens at the wound site and the CNF film can act as a template for skin regeneration. In addition to spray coating to prepare free-standing CNF films and composites, this methodology can be used for developing CNF barrier layers on the paper and paper board substrates for enhancing their barrier potential against air and water vapor. Furthermore, the spraying CNF suspension was implemented to coat the CNF layers for membrane development for water treatment applications [15].

#### **12. Spray-coated CNF film in packaging**

The most important application of spraying CNF on the base surface was for the fabrication of CNF film, which can be used as a barrier material and as a good alternative for synthetic plastics. **Figure 19** demonstrates the spray-coated CNF film's capability as a reliable water vapor barrier and comparison to synthetic plastics. However, the barrier efficacy of the packing film against water vapor is also determined by its thickness. Because of this, the film's water vapor permeability—a number that was determined by normalizing the thickness of the film with its water vapor transmission rate (WVTR) values—was used to characterize the performance of the water vapor barrier. **Figure 12** compares synthetic plastics with spray-coated CNF film in terms of WVP. This graphic demonstrates how comparable the WVP of spray-coated CNF film is to that of synthetic polymers. Beyond this benefit, CNF is an environmentally benign nanomaterial with the ability to break down in the environment [25].

*Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

#### **13. Conclusion**

In order to meet the speed of production of film, a rapid process is required to fabricate the free-standing film of cellulose nanofibers/nanocellulose material. To answer this need, spraying/spray coating is a rapid process to fabricate the CNF film in a free-standing manner/self-standing sheets for various applications. The current spraying process produces the free-standing film in a rapid manner, taking up operation time less than a minute in forming the spray-coated wet film. However, the drying of a spray-coated wet film consumes a time of more than 24 hours in an air-drying process under standard laboratory conditions and a couple of hours in an oven drying at 105°C under standard practice. Unlike the vacuum filtration process, the operation time/film formation time of spraying process was independent of CNF suspension concentration and a potential for scaling up. The spray-coated film has unique surfaces, such as rough and smooth, and these surfaces lead to the development of various functional materials, such as packaging, membrane and drug-delivery devices.

### **Author details**

Kirubanandan Shanmugam Saveetha School of Engineering, SIMATS, Chennai, Tamilnadu, India

\*Address all correspondence to: kirubanandan.shanmugam@gmail.com

© 2024 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Ncube LK, Ude AU, Ogunmuyiwa EN, Zulkifli R, Beas IN. Environmental impact of food packaging materials: A review of contemporary development from conventional plastics to polylactic acid based materials. Materials. 2020;**13**(21):4994

[2] Dufresne A. Nanocellulose: A new ageless bionanomaterial. Materials Today. 2013;**16**(6):220-227

[3] Klemm D, Kramer F, Moritz S, Lindström T, Ankerfors M, Gray D, et al. Nanocelluloses: A new family of naturebased materials. Angewandte Chemie International Edition. 2011;**50**(24): 5438-5466

[4] Henriksson M, Berglund LA, Isaksson P, Lindström T, Nishino T. Cellulose nanopaper structures of high toughness. Biomacromolecules. 2008; **9**(6):1579-1585

[5] Abe K, Iwamoto S, Yano H. Obtaining cellulose nanofibers with a uniform width of 15 nm from wood. Biomacromolecules. 2007;**8**:3276-3278

[6] Syverud K, Stenius P. Strength and barrier properties of MFC films. Cellulose. 2009;**16**:75-85

[7] Mörseburg K, Chinga-Carrasco G. Assessing the combined benefits of clay and nanofibrillated cellulose in layered TMP-based sheets. Cellulose. 2009;**16**: 795-806

[8] Chinga-Carrasco G, Tobjörk D, Österbacka R. Inkjet-printed silver nanoparticles on nano-engineered cellulose films for electrically conducting structures and organic transistors: Concept and challenges. Journal of Nanoparticle Research. 2012; **14**:1-10

[9] Orelma H, Filpponen I, Johansson LS, Österberg M, Rojas OJ, Laine J. Surface functionalized nanofibrillar cellulose (NFC) film as a platform for immunoassays and diagnostics. Biointerphases. 2012;**7**(1)

[10] Abitbol T, Rivkin A, Cao Y, Nevo Y, Abraham E, Ben-Shalom T, et al. Nanocellulose, a tiny fiber with huge applications. Current Opinion in Biotechnology. 2016;**39**:76-88

[11] Nechyporchuk O, Belgacem MN, Bras J. Production of cellulose nanofibrils: A review of recent advances. Industrial Crops and Products. 2016;**93**: 2-25

[12] Metreveli G, Wågberg L, Emmoth E, Belák S, Strømme M, Mihranyan A. A size-exclusion nanocellulose filter paper for virus removal. Advanced Healthcare Materials. 2014;**3**(10): 1546-1550

[13] Koga H, Tokunaga E, Hidaka M, Umemura Y, Saito T, Isogai A, et al. Topochemical synthesis and catalysis of metal nanoparticles exposed on crystalline cellulose nanofibers. Chemical Communications. 2010; **46**(45):8567-8569

[14] Bacakova L, Pajorova J, Bacakova M, Skogberg A, Kallio P, Kolarova K, et al. Versatile application of nanocellulose: From industry to skin tissue engineering and wound healing. Nanomaterials. 2019;**9**(2):164

[15] Shanmugam K, Browne C. Nanocellulose and its composite films: Applications, properties, fabrication methods, and their limitations. In: Nanoscale Processing. Elsevier; 2021. pp. 247-297

*Spray-Coated Cellulose Nanofiber Films: Preparation, Characterization and Application DOI: http://dx.doi.org/10.5772/intechopen.114328*

[16] Shanmugam K. Spray Coated Nanocellulose Films-Production, Characterisation and Applications [PhD thesis]. Monash University; 2019

[17] Varanasi S, Batchelor WJ. Rapid preparation of cellulose nanofibre sheet. Cellulose. 2013;**20**:211-215

[18] Shanmugam K, Doosthosseini H, Varanasi S, Garnier G, Batchelor W. Flexible spray coating process for smooth nanocellulose film production. Cellulose. 2018;**25**:1725-1741

[19] Beneventi D, Zeno E, Chaussy D. Rapid nanopaper production by spray deposition of concentrated microfibrillated cellulose slurries. Industrial Crops and Products. 2015;**72**: 200-205

[20] Shanmugam K, Varanasi S, Garnier G, Batchelor W. Rapid preparation of smooth nanocellulose films using spray coating. Cellulose. 2017;**24**:2669-2676

[21] Magnusson J. Method for Spraying of Free Standing 3D Structures with MFC: Creation and Development of a Method [Master thesis]. Faculty of Health Science and Technology, Department of Engineering and Chemical Science, Chemical Engineering, Karlstad University; June 14, 2016

[22] Beneventi D, Chaussy D, Curtil D, Zolin L, Gerbaldi C, Penazzi N. Highly porous paper loading with microfibrillated cellulose by spray coating on wet substrates. Industrial & Engineering Chemistry Research. 2014; **53**(27):10982-10989

[23] Alsaiari NS, Shanmugam K, Mothilal H, Ali D, Prabhu SV. Optimization of spraying process via response surface method for fabrication of cellulose nanofiber (CNF) film.

Journal of Nanomaterials. 2022; **2022**:1-10

[24] Vikman M, Vartiainen J, Tsitko I, Korhonen P. Biodegradability and compostability of nanofibrillar cellulosebased products. Journal of Polymers and the Environment. 2015;**23**:206-215

[25] Shanmugam K, Chandrasekar N, Balaji R. Barrier performance of spray coated cellulose nanofibre film. In: Micro. MDPI; 2023. pp. 192-207

### Section 2
