Characterization and Application of Nanomaterials (2023) Volume 6 Issue 1 doi:10.24294/can.v6i1.2068 1 Original Research Article Water vapor permeability of smooth cellulose nanofiber film prepared via spraying Kirubanandan Shanmugam1*, Narendhar Chandrasekar2, Ramachandran Balaji3 1 Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences, Chennai 602107, India. E- mail: Kirubanandan.shanmugam@gmail.com 2 Department of BioNano Technology, Gachon University, Seongnam 13120, Republic of Korea. 3 Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 10608, China. ABSTRACT Eco-friendly and greener barrier materials are required to replace the synthetic packaging materials as they produce a threat to environment. These can be fabricated by natural polymers such as cellulose nanofiber (CNF). The sustainability of CNF was so amazing due to its potential for circular economy and provides alternative platform for synthetic plastics. The challenging task to fabricate CNF films still existed and also current methods have various limitations. CNF films have good oxygen permeability and the value was lower than synthetic plastics. However, CNF films have poor water vapour permeability and higher than that of synthetic plastics. The fabrication method is one of strong parameters to impact on the water permeability of CNF films. The deposition of CNF suspension on the stainless-steel plate via spraying, is a potential process for fabrication for CNF films acting as barrier material against water vapour. In spraying process, the time required to form CNF films in diameter of 15.9 cm was less than 1 min and it is independent of CNF content in the suspension. The uniqueness of CNF films via the spraying process was their surfaces, such as rough surface exposed to air and smooth surface exposed to stainless steel. Their surfaces were investigated by SEM, AFM and optical profilom- etry micrographs, confirming that the smooth surface was evaluated notable lower surface roughness. The spray coated surface was smooth and glossy and its impact on the water vapor permeability remains obscure. The spraying process is a flexible process to tailor the basis weight and thickness of CNF films can be adjusted by the spraying of CNF suspension with varying fibre content. The water vapour permeability of CNF films can be tailored via varying density of CNF films. The plot between water vapour transfer rate (WVTR)/water vapour and density of CNF films has been investigated. The WVP of spray coated CNF films varied from 6.99 ± 1.17 × 10−11 to 4.19 ± 1.45 × 10−11 g/m.s.Pa. with the density from 664 Kg/m3 to 1,412.08 Kg/m3. The WVP of CNF films achieved with 2 wt% CNF films (1,120 Kg/m3) was 3.91 × 10−11 g/m.s.Pa. These values were comparable with the WVP of synthetic plastics. Given this correspondence, CNF films via spraying have a good barrier against water vapour. This process is a potential for scale up and commercialization of CNF films as barrier materials. Keywords: Cellulose Nanofiber (CNF); Spray Coating; Water Vapour Permeability; Water Vapour Transfer Rate (WVTR); Synthetic Plastics 1. Introduction Cellulose nanofiber (CNF) is a type of nanomaterial derived from natural cellulose fibres, which is the main component of plant cell walls. The notable properties of CNF are high mechanical strength, high surface area, biodegradability, and biocompatibility[1]. There are several types of nanocellulose, including cellulose nanocrystals ARTICLE INFO Received: 27 April 2023 Accepted: 13 June 2023 Available online: 21 June 2023 2 (CNCs), cellulose nanofibrils (CNFs), and bacterial cellulose (BC)[2]. CNCs were produced from acid hydrolysis of cellulose fibres and are typically rod-shaped with dimensions on the order of 5–20 nm in diam- eter and several hundred nanometres in length[2]. CNFs were also pro- duced by mechanical processing of cellulose fibres from the wood pulp and non woody pulp and the size of CNF typically has widths ranging from 5 to 50 nm and lengths ranging from several microns to several millimeters. Bacterial cellulose is produced by bacteria and has similar properties to plant-derived cellulose, but with higher purity and con- sistency[3]. Cellulose nanofiber (CNF) is a sustainable fibrous nanomaterial used as feed stock for the fabrication of free-standing films and com- posite with various nano-inorganic materials. Past decade, CNF was getting improved attention to play as alternative for synthetic plastics in packaging application. CNF has a good potential for recyclability and biodegradability. CNF was produced by the fibrillation of cellulose pulps from lignocellulosic biomass through mechanical process such as homogenization, chemical process such as Acid Hydrolysis and TEMPO and enzymatic process. CNF has low density and toxicity and provides a platform for sustainability and circular economy. The film prepared from cellulose nanofibrils has translucency and good strength[3]. CNF films were reported as a good barrier against oxygen, however poor barrier against water vapour. The challenge in this area is to bring the value of water vapour permeability (WVP) of free-stand- ing CNF films near to synthetic plastics. The fabrication of CNF films is one of the strong parameters controlling the water vapour barrier per- formance of the film[2]. The reported fabrication methods for CNF films were solvent cast- ing, hot pressing, Roll to Roll (R2R) coating, vacuum filtration and spray coating[3]. Vacuum filtration is the most common process for fab- ricating CNF films. In this method, the filtration time to form CNF films exponentially increased with CNF suspension consistency. The time for forming CNF films on the filter mesh consumes 10 min[4] to 4 h[3]. The filter marks were appeared on CNF films when the film was peeled from the filter mesh. These marks affect the uniformity of the film indirectly effects on the barrier properties and mechanical proper- ties of CNF films. Solvent casting is a laboratory scale method to fab- ricate CNF films for various applications. However, the evaporation of water from CNF suspension consumes time more than a day to form the film on the Petri dish. The limitation of cast CNF films consists of shrinkages which affects the uniformity and various properties of CNF films. This method has time constraint and not fit for scale up for com- mercialization via large scale production[3]. Recently, spraying CNF suspension on the polished metal surface is a novel process for fabrication of free-standing CNF films[5,6]. In the spraying process, CNF suspension was deposited on the stainless-steel plate via spray coating and then allowed to dry in standard laboratory COPYRIGHT Copyright © 2023 by author(s). Characterization and Application of Na- nomaterials is published by EnPress Publisher LLC. This work is licensed un- der the Creative Commons Attribution- NonCommercial 4.0 International Li- cense (CC BY-NC 4.0). https://creativecommons.org/licenses/by- nc/4.0/ 3 conditions. Dried CNF films were smoothly and easily peeled from the stainless-steel plate. In the case of fabricating CNF films via spraying, the thickness and basis weight of CNF films can be tai- lored via spraying CNF suspension with various fi- bre content. The operation time for spraying CNF suspension was independent of their solid content. The spraying process was rapid in the formation of wet CNF films[6]. The mechanical and barrier prop- erties of the film can be tailored via spraying vari- ous concentration of CNF on the stainless-steel plate[2]. Even though the film made from CNF has a good barrier against oxygen and also incomparable with synthetic plastics[7]. CNF films have poor bar- rier properties against water vapour due to high af- finity between cellulose nanofibrils and water mol- ecules. CNF is a highly hydrophilic polymer and capable for susceptible to water molecules. But CNF is much better than nominal cellulose fibres such as paper and paper board substrates in terms of water vapour permeability[3]. This is why cellu- lose nanofiber was used as high-performance bar- rier material as it forms a compact network/mesh of cellulose nanofibrils to free standing CNF films[6]. Apart from this, CNF films have very mi- nute pores and complex tortuous pathway for water vapour and air than that of normal cellulose sub- strates[1,8]. It was noticed that the fabrication methods also control the WVP of CNF films and other bar- rier properties of CNF films, such as air permeance and oxygen permeability[3]. Having spraying pro- cess for scale up potential, the WVP of spray coated CNF films should be investigated and their water vapour transfer mechanism across CNF films should be investigated. This paper deals the effect of CNF films density on the water vapour transfer rate and the water vapour permeability of CNF films and the WVP of CNF films was compared with CNF films from synthetic plastics. 2. Materials and methods The number of terminologies for cellulose nanofiber (CNF) has been mentioned in various scientific literatures. Generally, cellulose nano- fibers are also called as nano-fibrillated cellulose, cellulose nano-fibrils, micro fibrillated cellulose and nanocellulose, etc. But in this scientific study, cellulose nanofiber/nanocellulose has been re- ported throughout in this paper[2]. The CNF was used as a feed stock for fabrication of CNF films. The used raw CNF is KY 100S received from DI- ACEL Chemical Industries, Japan. The CNF con- tent in KY100S was 25 wt.% and the mean diame- ter of cellulose nanofibrils in CNF was 73 nm. The aspect ratio of Raw CNF (KY100S) was investi- gated to be 142 ± 28 and the crystallinity index of the KY 100S was evaluated to be 78%. The SEM micrographs of the Raw CNF have been shown in Figure 1[6]. Figure 1. SEM micrograph of cellulose nanofiber (KY 100S)—Diacel Chemical Industries, Japen. 2.1 Preparation of CNF suspension for spraying The CNF suspension was prepared with con- centration varying from 1 wt.% to 2 wt.% of CNF content in the water. The raw CNF quantity of in- terest was added into the double distilled water and disintegrated at 15,000 RPM for 15 min to make CNF suspension of Interest. In this way, the CNF suspension from 1 wt.% to 2 wt.% was produced for spraying process. 2.2 Fabrication of CNF films via spraying The experimental set up for spray system was shown in Figure 2. The CNF suspension was sprayed on the polished stainless-steel plate via the professional Wagner spray system. The process conditions for spraying process have been followed 4 as per the reported in our previous scientific litera- ture. There are two important parameters in the spray coating experimental system to control/tailor the thickness and basis weight of CNF films were velocity of the conveyor and CNF suspension con- sistency. In this study, the velocity of the conveyor was maintained a constant parameter at a velocity of 0.32 cm/sec and then CNF suspension was var- ied from 1 wt.% to 2 wt.% for spraying on the stainless-steel plate. The spray distance between spray tip to the circular stainless-steel plate was 30 ± 1 cm. The diameter of the orifice in spray nozzle was 0.38 mm and produces elliptical pattern and spray width of 50 cm[6]. Figure 2. Experimental system for spray coating setup. 2.3 Drying of CNF films and its characteri- zation The wet film on the stainless-steel plate was formed and dried under standard laboratory condi- tions. In drying spray coated wet CNF films, the film was kept in Laminar flow chamber with con- stant flowrate for faster removal of water from the wet film. The dried film was easily peeled from the stainless-steel plate and subjected to the measure- ment of thickness and basis weight of the film. The apparent density of CNF films was evaluated from its thickness and basis weight of the film. The sur- face topography and morphology of spray coated CNF films was evaluated by scanning electron mi- croscopy as per the reported procedure previ- ously[2]. The surface roughness of CNF films was evaluated by atomic force microscopy and optical profilometry[6]. 2.4 Evaluation of water vapour barrier of spray coated CNF films The water vapour barrier of CNF films was performed as the per standard of ASTM E96/E96M-05[9]. The films/specimen size having diameter of 76 mm was used as specimen and dried in an air oven at a temperature of 105 ℃ for 4 h. This would help the complete removal of moisture from the specimen to evaluate water vapour perme- ability of the film perfectly. As per the ASTM standard, the brass cups were filled with dried an- hydrous calcium chloride and then covered with CNF films as experimental cups and cups covered without CaCl2 as control in the experimental study. This test was carried out at 23 ℃ and 50% RH and the weight of the cup was increased/measured due to the absorption of water vapour across CNF films. From the data, the water vapour transmission rate (WVTR) is the slope derived from the plot between weight of the cup and time[2,9,10]. 푊푉푇푅 = 퐺 푡 × 퐴 where G/t refers to the slope of a straight line (g h−1) and A is the surface area of the films (m2). The water vapour permeability of CNF films was evaluated from the WVTR normalized with thickness of CNF films. The permeance of CNF films was found to be: 푃푒푟푚푒푎푛푐푒 = 푊푉푇푅 푆(푅1 − 푅2) where S is the saturation vapor pressure per mmHg (1.333 × 102 Pa) at the tested temperature, R1 is the relative humidity of the source and R2 is the rela- tive humidity of the vapor sink, expressed as a frac- tion. Finally, the WVP of the films can be evalu- ated as 푊푉푃 = 푃푒푟푚푒푎푛푐푒 × 푇ℎ푖푐푘푛푒푠푠 표푓 퐶푁퐹 푓푖푙푚 The mean of WVP from three replicates in the experiment was reported in this work. The value of WVP of CNF films was compared with the syn- thetic plastics to show the potential of CNF films as a good barrier against water vapour. 3. Results and discussion Spraying nanofibers is a new concept for fab- rication of film for various applications[11–13]. Nan- ofiber spraying has several advantages over tradi- tional fibre production methods, including a higher surface area to volume ratio, enhanced mechanical 5 properties, increased porosity, and improved bio- compatibility[3]. Applications of nanofiber spraying include drug delivery, tissue engineering, air filtra- tion[1,8], and energy storage such as fabrication of sustainable electrodes[13,14]. However, there are still challenges in scaling up nanofiber spraying for commercial production and optimizing the process parameters[6] for specific applications such as food packaging and barrier materials[7,10]. Spraying CNF suspension on the polished stainless-steel plate is a flexible method to fabricate CNF films with unique surfaces[6]. The spray coated CNF has two unique surfaces namely rough surface exposed to air and smooth surface exposed to the stainless-steel plate. Spraying CNF suspen- sion on the metal surface produce the film with glossy and shiny and the smoothness of the film was replicated from the stainless-steel plate[6]. Fig- ure 3 shows the spray coated CNF films and shows the two surfaces of the film. Spray coated CNF films have very compact and cellulose nanofibrous network[6]. The basis weight and the thickness of CNF films were tai- lored by varying CNF suspension for spraying[10]. The compactness of CNF films was achieved via the coalescence of the atomized CNF suspension from the spray jet in the spraying process. The at- omized CNF suspension formed together via form- ing hydrogen bonds between the hydroxyl group of the cellulose nanofibrils, results in forming the compact film[3,11]. 3.1 Scanning electron microscopy micro- graph Figure 4 reveals the rough and smooth sur- face of spray coated CNF films. The rough side of CNF films was porous and high surface roughness. The roughness of the film was high due to the dis- tribution of various fibres. The smooth side of CNF films was glossy and shiny. The surface roughness of the film on the smooth side was very low and fibres compressed and mimics the surface smooth- ness of the film from stainless steel plate. However, the effect of surface roughness on the barrier per- formance of CNF films remains obscure[10]. Figure 3. Spray coated CNF films. (a) (b) Figure 4. (a) Rough surface of spray coated CNF films’ SEM micrographs. (b) Smooth surface of spray coated CNF films’ SEM micrographs. 3.2 Optical profilometry images Figure 5a–b reveals the optical profilometry of CNF films confirming the rough surface and smooth surface of CNF films. In this investigation, the RMS of both surfaces were evaluated. The 6 RMS of rough and smooth side was reported to be 2000 nm and 400 nm, respectively[6,10]. The effect of surface roughness on the rough side and surface smoothness on the smooth side of CNF films were obscure on the barrier performance against water vapour. (a) Figure 5. (a) Optical profilometry image of rough side of CNF films. (b) Optical profilometry image of smooth side of CNF films. 3.3 Atomic force microscopy images AFM micrographs of CNF films confirms the surface roughness of the both surfaces at nanoscale dimension. It confirmed that the rough side of the film was very porous and high surface roughness due to various size distribution of cellulose nano- fibrils. The smooth side of the film was very glossy and shiny and their surface roughness was too low. The RMS for rough surface and smooth surface was reported to be 51.4 nm and 16.7 nm[6]. See Fig- ure 6a–b. (a) Figure 6. (a) AFM micrograph of rough side of spray coated CNF film. (b) AFM micrograph of smooth surface of CNF films. 3.4 Water vapour barrier performance of CNF films Water vapour permeability (WVP) refers to the ability of a material to allow the passage of wa- ter vapour through it. This property is important in packaging, as it affects the moisture resistance of the material. The WVP of a material depends on their structure, thickness, and other factors. The performance of CNF films as water vapour barriers has been attributed to their ability to form dense, nano porous networks that impede the movement of water molecules. It has been noticed that the fab- rication method for CNF films is one of the main 7 criteria for controlling water vapour barrier perfor- mance of the films. Figure 7 reveals the effect of film’s density on the water vapour transmission rate of CNF films. The apparent density of CNF films is defined as the ratio between basis weight and thickness of CNF films[6]. The basis weight and thickness of the CNF can be tailored by varying CNF suspension concen- tration for spraying process to fabricate the CNF[6]. The relationship between thickness and basis weight of CNF films was linear[6]. As a result, the water transmission rate of CNF films was tailored via thickness and basis weight of the film[10]. The WVTR of CNF films was comparable with syn- thetic plastics. The WVTR was normalized with thickness of CNF films to give the value of WVP[2]. 800 900 1000 1100 1200 1300 1400 1500 0 20 40 60 80 100 120 140 160 180 200 W at er v ap ou r t ra ns fe r r at e ( g /m 2. da y) Density of CNF Film (Kg/m3) Figure 7. Effect of film’s density on water vapour transfer rate. Figure 8 shows the effect of apparent density on the WVTR of CNF films. The spraying process was carried out in two different conditions. One of the conditions from fixed CNF concentration and varied velocity of the conveyor in the experimental set up was performed[2]. The other was from the fixed velocity of the conveyor and varied CNF sus- pension concentration from 1 wt.% to 2 wt.% was carried out to fabricate the CNF films. This plot confirms that the lower density of CNF films gives good barrier against water vapour. Figure 9 shows the effect of density on the water vapour permeability of CNF films. It is noted that the WVP of CNF films was comparable with synthetic plastics. The lower density of the film gives good barrier against water vapour. However, 700 800 900 1000 1100 1200 1300 1400 1500 0 20 40 60 80 100 120 140 160 180 200 Spraying Process 1 Spraying Process 2 W at er v ap ou r t ra ns fe r r at e ( g /m 2. da y) Density of CNF Film (Kg/m3) Figure 8. Effect of density on water vapour transmission rate. 660 680 700 720 740 760 780 800 820 0 1 2 3 4 5 6 7 Water vapour permeability (g/m.s.Pa* 10-11) D en si ty o f C N F Fi lm (K g/ m 3) Water vapour permeability Figure 9. Effect of density on the water vapour permeability of the CNF films. the higher density of CNF films has poor barrier performance against water vapour[2]. Figure 10 shows the effect of cellulose nano- fibrils on the water vapour permeability. This is due to the reducing effect of cellulose nanofiber. It means that cellulose nanofibrils is a hydrophilic polymer, reduced the water vapour permeability of the film when fibre diameter reduced. When the fi- bre diameter of CNF is reduced, the water vapour diffusion rate was increased across the tortuous pathway in the film. CNF films with lowest fibre diameter forms rigid fibrous network which acts as a good resistance against gaseous substances in- cluding water vapour[15]. The diameter of CNF re- duction was performed by the mechanical process such as high-pressure homogenization, chemical 8 methods such as acid hydrolysis and enzymatic process[16]. The data in Figure 10 was derived from the spraying of high pressure homogenized CNF suspension on the stainless-steel plate to fabricate CNF films which acts as high-performance barrier against water vapour[10]. 10 20 30 40 50 60 70 80 0 1 2 3 4 W ater V apo ur P erm eab ility (g /m .s .P a * 10 -11) Fi br e D ia m et er (n m ) Figure 10. Effect of fibre diameter on the WVP of CNF films. 3.5 Comparison with synthetic plastics Figure 11 reveals the potential of spray coated CNF films as a good water vapour barrier and comparable with synthetic politics. However, the thickness of packaging film also decides the barrier performance of the film against water va- pour. This is why water vapour permeability was used to describe the water vapour barrier perfor- mance of the film and this value was calculated via the normalizing thickness of the film with their WVTR values. Figure 12 shows the comparison of spray coated CNF films with synthetic plastics in terms of WVP. This plot confirms that the WVP of spray coated CNF films has comparable with syn- thetic plastics[17]. Apart from this advantage, CNF is an eco-friendly friendly nanomaterial that has ca- pacity to degrade in environment[18,19]. 3.6 Barrier mechanism of CNF films Figure 13 reveals the mechanism of water va- pour passage across the spray coated CNF films. The nanocellulose/CNF suspension was well mixed during the spraying process and sprayed on the stainless-steel plate[6,12]. It results in the for- mation of smooth CNF films[6]. It has been con- cluded that CNF films are an effective barrier against water vapour due to its physical and me- chanical properties[17]. The barrier mechanism of CNF films can be commented as the following fac- tors. The nanostructure of CNF films is a predomi- nant reason for good barrier mechanism even though CNF is a hydrophilic polymer[20,21]. Gener- ally, CNF has high aspect ratio and high surface area to volume ratio[24]. This unique nanostructure The CNF Film Spray coated (96.5 g/m2) The CNF Film Vacuum Filtration (100 g/m2) Recycled Cellulose film from Spray coated NC Cellulose Nano fibrils Acetylated CNF (Acetylation Time-30 mins) Polyvinylidene Chloride Polyethylene (PE) Plasticized (PVC) Aluminium Foil LDPE HDPE Oriented Nylon 6 Oriented Polystyrene EVA EVOH PA PET PC PS PP 0 50 100 150 200 250 WVTR in g/m2 day WVTR Figure 11. Comparison of WVTR of CNF films with conventional synthetic plastics. 9 The CNF Film Spray coated (96.5 g/m2) The CNF Film Vacuum Filtration (100 g/m2) Recycled Cellulose film from Spray coated NC Cellulose Nano fibrils Acetylated CNF (Acetylation Time-30 mins) Polyvinylidene Chloride Polyethylene (PE) Plasticized (PVC) Aluminium Foil LDPE HDPE Oriented Nylon 6 Oriented Polystyrene EVA EVOH PA PET PC PS PP 0 2 4 6 8 10 Watervapour Permeability (g/m.s.Pa) x 10-11 Watervapour Permeability Figure 12. Comparison of WVP of CNF films with synthetic plastics. Figure 13. Water vapour barrier mechanism of spray coated cellulose nanofiber film. of CNF forms a compact network of cellulose nan- ofibrils during the fabrication of CNF films via spraying[6]. It results a compact and dense film which acts as barrier against gaseous molecules. The dense packing of CNF produces a tortuous pathway for diffusion of water vapours, which re- duces the permeability of the film to water va- pour[21,22]. CNF has high source of hydroxyl groups (–OH) present in their surface of cellulose nanofibrils and offers for strong intermolecular hydrogen bonding between adjacent fibres[18]. In addition to that, CNF films were densified via crosslinking of the fibres via hydrogen bonding and it strengthens the inter- molecular and intramolecular hydrogen bonds in the film[23]. As water vapour is polar in nature and forms hydrogen bonds, the strong intermolecular hydrogen bonding between the cellulose nano- fibers creates a strong barrier to water vapour dif- fusion. Overall, the combination of the unique nanostructure and the strong intermolecular hydro- gen bonding in cellulose nanofiber films results in a highly effective water vapour barrier, making it an ideal material for a wide range of applications where water vapour barrier properties are re- quired[17,21,22]. 3.7 Recommendations for improving the WVP of CNF films The following recommendations have been mentioned to improve the water vapour barrier per- formance of CNF films. 10 1) Use a higher concentration of cellulose nanofibers: Increasing the concentration of cellu- lose nanofibers in the film can lead to smaller pores and increased density, improving the film’s ability to block water vapour[6,10]. 2) Incorporate hydrophobic materials: Adding materials that repel water, such as hydrophobic na- noparticles like silica or graphene or montmorillo- nite[24], can improve the water vapour barrier prop- erties of the film[25,26]. 3) Modify the surface of the cellulose nano- fibers: The surface of cellulose nanofibers can be modified with various chemicals to increase the surface charge or to introduce hydrophobic/hydro- philic functionalities. This can help to alter the wa- ter interactions of the film[24]. 4) Increase the number of layers: Building up multiple layers of cellulose nanofiber films can re- duce the size of the film’s pores, improving its wa- ter barrier properties[21,22]. 5) Increase the degree of orientation: By sub- jecting the cellulose nanofiber films to mechanical or thermal treatments, it is possible to achieve higher degrees of alignment in the fibres, which can improve water vapour barrier properties[27]. 6) Add plasticizers: Incorporating plasticizers, such as glycerol or sorbitol, can improve the flexi- bility of the cellulose nanofiber film, reducing the possibility of cracks or gaps that can allow water vapour to pass through[28]. 3.8 CNF for packaging applications Cellulose nanofibers (CNFs) are a promising natural and renewable material for use in packag- ing. The unique properties of CNFs, including their high strength, low weight, and excellent barrier properties, make them an attractive alternative to other packaging materials such as plastics[7]. Sev- eral packaging applications of CNFs have been ex- plored, including: 1) food packaging: CNFs have been used to produce films and coatings for food packaging, providing excellent barrier properties against oxygen and water vapor. CNF-based pack- aging can also prolong the shelf life of food prod- ucts, preventing spoilage. 2) Biodegradable pack- aging: CNFs can be used to produce biodegradable packaging materials that are environmentally friendly and fully compostable. This makes them an excellent alternative to traditional plastic pack- aging, which can take hundreds of years to decom- pose. 3) Medical packaging: CNFs have been used for the packaging of medical devices and other healthcare products due to their excellent biocom- patibility and low toxicity. 4) Electronics packag- ing: CNFs can also be utilized in electronic pack- aging due to their excellent electrical insulation properties. CNF-based packaging can help protect electronic devices from moisture, dust, and other environmental contaminants. Overall, the use of CNFs in packaging can reduce the environmental impact of packaging while providing excellent pro- tection to the packaged product. As the demand for sustainable packaging continues to grow, CNFs are likely to play a significant role in the future of packaging materials[7,22]. 4. Conclusion The spray coated cellulose nanofiber (CNF) film is a renewable, biodegradable and sustainable material that has attracted attention for its unique mechanical properties, high surface area, and good barrier properties. The film is produced by a pro- cess called spray coating, which involves spraying cellulose nanofibers onto a stainless-steel surface to form a compact film which has a notable smoothness on the spray coated side. The resulting film has two unique surfaces, potential barrier against water vapour. It is a sustainable material that can be produced in large quantities via spray- ing, a scalable process, making it an attractive al- ternative to petroleum-based materials in conven- tional packaging. The water vapour permeability of CNF films can be tailored by varying the density of the film through tailoring the thickness and basis weight of the film. It can be done by spraying var- ious CNF concentration on the stainless stee plate to fabricate the film. 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