Cotton Based Cellulose Nanocomposites: Synthesis and Application

Abstract

Nanocellulose is a renewable natural biomaterial which has risen to prominence due to its biodegradability and physiochemical properties making it a promising candidate to replace non-biodegradable synthetic fibers. Due to its profound qualities, nanocellulose extracted from cotton fibers have tremendous application potential and have been intensively studied particularly in the generation of nanofillers and as reinforcement components in polymer matrixes. Deposition of inorganic nanoparticles on cotton fabric result in antimicrobial textiles with multifunctional use particularly in manufacture of PPE and as filtration devices against environmental pollutants and pathogens. This chapter compiles three main sections. The first section gives an overview of the extent of work done in the creation and application potential of cotton-based nanocomposites. The second section describes the in situ and ex situ methods of nanoparticle deposition and self assembly on cotton fabrics to generate multifunctional cotton-based nanocomposites with antimicrobial potential while the final section describes the incorporation of cotton nanofibers in polymer matrices, their reinforcing properties, as well as surface modification to assist their incorporation. Finally in the conclusion, a summary of the up-to-date challenges and progresses is presented postulating the undiscovered arenas and future undertakings of this venture.

1. Introduction

With the dawn of the age of nanotechnology, there has been an intense scurrying and scavenging for nanomaterials with unique properties and specific molecular arrangements that allow it to find application in specific niches inaccessible to alternative forms. Nanostructured materials display unique physicochemical properties such as excellent electrical and thermal conductivity, solubility, porosity, surface interactions, density, band gap and surface electronic charge resulting in exceptional catalytic and optical activity and enhanced performance compared to their bulk counterparts [1]. Presently, nanoscale devices have widespread application in cell targeted therapeutic delivery, high resolution tissue imaging and in replacing damaged tissue [2]. In agriculture, nanomaterials are being used to enhance crop production as nanofertilizers [3] and for crop protection as nanopesticides and nanobiosensors [4]. These active ingredients are encapsulated in nanocapsules, micelles, gels, liposomes, mesoporous silica nanoparticles or hollow nanoparticles to ensure controlled release, better solubility and for active stablity in the long-term [5]. To compensate for hazardous emissions to the environment, nanomaterials have been functionalized to remove contaminants through adsorption [6], immobilization, photocatalytic degradation, and electro-nanoremediation [7]. It is therefore undeniable that uncovering novel multifunctional nanosized materials is an elaborate pursuit with promising outcomes, yet filled with pressing concerns which are in dire need to be addressed.

One of the primary concerns of nanotechnology is the indiscriminate release of hazardous nanowaste, generated during the manufacturing and processing of engineered of nanomaterials, which could inevitably accumulate in the environment and inevitably end up in the food chain [8]. This has roused an overdrive in the hunt for sustainable nanomaterials from renewable bioresources such as cellulose, starch, chitosan, gelatin, alginate and chitin which are biodegradable, leave minimal implications on health and the environment and could be retrieved as value added waste in the production of a new generation of green nanomaterials [9].

Cellulose is a renewable feedstock with interesting properties such as biocompatibility and biodegradability. It is found to be chemically inert, displays excellent stiffness, high strength and dimensional stability, low density and easily functionalized surface chemistry [10]. Lignocellulosic biomass such as wood and agricultural residues such as tree trunks, rice straw, sugarcane bagasse, coconut husks, oil palm empty fruit bunches energy crops and grass are excellent feedstocks for green nanomaterials derived from cellulose or nanocellulose. This natural biopolymer is abundantly available and can be used as renewable feedstock in the generation of sustainable nanomaterials [11]. Reconstruction of lignocellulosic biomass waste residues into value added products such as nanostructures is an attractive, feasible option [12].

Cotton is an abundantly available fibrous crop grown for global commercial production with over 95% cellulose in its plant structure. Cotton stalk which is an overbearing agricultural residue generated in cotton-producing countries such as India, USA, China, Brazil and Pakistan, represents a semi-wood raw material made up of cellulose, hemicellulose, and lignin which could be utilized to fabricate value-added nanocellulose, paving an excellent way to maximize the utilization of waste [13]. Nanocellulose has exceptional properties such as high tensile strength, high Young’s modulus, low weight, mechanical robustness, low coefficient of thermal expansion, biodegradability, surface functionality and hydrophilicity, biocompatibility and lack of toxicity [14]. In recent times, nanocellulose is used in energy storage, as aerogels, emulsion stabilizers, enzyme immobilization substrates, low-calorie food additives, reinforcing fillers, pharmaceutical binder, biomimetic materials and biosensors [15, 16, 17]. Nanocellulose derived from cotton feedstock can be broadly categorized as cellulose nanocrystals (CNC) and nanofibrillated cellulose (NFC). CNCs (as shown in Figure 1), also known as cellulose nanowhiskers or nanorods, are short (<500 nm) and narrow (<40 nm) rod shaped, rigid crystalline structures with diameters between 1 and 100 nm [18] with tremendous application potential in regenerative medicine [19], optoelectronics [20], automotive polymers [21] and as composite materials [22]. It is generated by eliminating the amorphous regions in cellulose fibers using acid hydrolysis [23]. CNC have been extracted from cotton fibers [24], processed cotton [25] and cotton linters [26], a byproduct of cotton processing. NFC or cellulose nanofibers (as shown in Figure 2) are longer (< 3000 nm) and wider (< 100 nm) fibers with low crystallinity obtained by the mechanical disintegration of cotton biomasses using a high-speed ball grinder [27], ultrasonicator [28] or high-pressure homogenization [29].

Figure 1.

TEM image depicting cotton-derived CNC.

Figure 2.

FESEM images of the cotton based NCFs.

Nanocomposites are materials made up of 2 or more constituent phases with at least 1 phase of nano-size particles (<100 nm) which creates a discontinuous phase over a matrix of standard material [30]. This unique multiphase structure that is reinforced by a stronger component of nanosized fillers [31] demonstrates greater mechanical and tensile strength and increased capacity for thermal expansion and conductivity [32]. CNCs are interesting materials that could function as nanofillers owing to the abundance of the -OH groups, reactivity, high surface area, mechanical, thermal and optical properties, even at low concentrations [33] which enhances tensile strength and decreases elasticity due to the strong intermolecular linkages such as covalent bonds, van der Waals forces, mechanical interlocking and molecular entanglement between the fillers and its polymeric matrix [34]. Various methods have been developed to generate cellulose nanocomposites which include melt extrusion, ball milling, injection molding, compression molding, 3D printing, layered assembly, electrospinning, among others [35, 36]. Cellulose nanocomposites find vast application as packaging material, automotive and aerospace paints and coatings, adhesives, hydrogels, nanobarriers, fire retardants, construction materials, military defense and as emerging smart hybrids which display outstanding properties such as stretch ability, high mechanical strength, optical transparency, electrical and thermal conductivity, porosity and high adsorption [37]. Cotton based cellulose nanocomposites constructed with metals, metal oxides and non-metallic elements have exhibited innovative features due to its synergetic effects which are unattainable as pure nanomaterials [38]. Nanocomposites loaded with noble metal nanostructures have antibacterial properties and are used in biomedicine, enzyme immobilization, catalysis and as biosensors [39]. Rumi et al., 2021 observed that cotton-based CNC display high crystallinity, tensile strength and stiffness making it an attractive engineering nanomaterial for composite reinforcement [40]. In a separate study, Araujo et al., 2018 found that biopolymer nanocomposites reinforced with hydrolyzed cotton NFC extracted from cotton waste textiles resulted in a composite material with greater tensile strength and thermal capacity compared to the pure biopolymer [25]. Rafaella et al., 2019 constructed a cotton NFC/chitosan nanocomposite with collagen like properties which demonstrated increased surface roughness, improved cell adhesion, spreading and proliferation when used as scaffolds in tissue engineering [41]. Thus, surface modification of polymeric materials with cotton NFC for substrates used as scaffolds in tissue engineering would result in functionalized nanocomposites with novel physicochemical properties and large surface area which allow numerous contact points between cells and the nanocomposite surfaces for cell viability and growth. In a separate study, Li et al., (2013) generated cotton CNC through electrospinning and functionalized it into composites by surface coating it with CeO2 nanoparticles using the hydrothermal reaction. The resulting cotton based cellulose nanocomposite demonstrated excellent UV-shielding and enhanced photocatalytic properties making it of great value in medicine, military operations and optoelectronics [42].

Multifunctional cotton-based nanomaterials have been inadvertently thrust into the limelight with the recent Covid-19 pandemic through the design of various nanosensor devices for viral detection, surface decontaminants, antiviral compounds and nanocomposite fabrics which serve to prevent or annihilate the SARS-CoV-2. In this aspect, cotton nanocomposites have been constructed as nanosensors in the detection of the virus and as antimicrobial textiles for medical PPE (personal protective equipment). Eissa and Zourob, (2021) fabricated a cotton CNF-tipped electrochemical immunosensor as a one-step diagnostic tool for the detection of SARS-CoV-2 viral antigen [43]. Textiles embedded with antimicrobial nanoparticles such as Ag, ZnO and CuO have been tailored as a protective measure in PPE’s for those on the frontline of defense against the SARS-CoV-2. An extensive research resulting in the design and manufacture of antibacterial cotton-based face mask embedded with CuO nanoparticles (CuONps) demonstrated that cotton could be reconstructed as an antimicrobial nanocomposite and used as a PPV fabric to secure the protection of medical personnel embodying it [37]. In this work, Perelshtein et al., 2016 functionalized cotton fabric with CuONps using ultrasound-assisted deposition by an in-situ coating process on the surface of the fabric. The resulting nanocomposite material retained excellent antibacterial properties after 65 washing cycles at 75–92°C, making it an excellent material as a reusable medical PPE [44]. In a separate study, Adhikari et al., 2021 synthesized a nanoceutical cotton ZnO composite fabric using the hydrothermal method to filter viral particles without compromising on user’s breathing mechanism [45]. The design of this nanoceutical fabric was constructed to find application as a one-way valve in a face mask that would facilitate breathing while trapping and filtering airborne viral pathogens and reducing transmission through droplets. It is therefore undisputable that cotton nanocomposite fabrics are the textiles of the future as a shield of protection in the war against the multitude of rising murderous pathogens of this millennia.

2. Synthesis of cotton based cellulose nanocomposites using in situ and ex situ methods

Cotton textiles are used widely in numerous applications and various industries particularly as sportswear and medical textiles due to its exceptional properties such as breathability, hypo allergenicity, hygroscopicity and low cost [46]. Some of the drawbacks of cotton include low tensile strength, UV-vulnerability, enhanced capacity for microbial growth and easily wrinkled [47]. Inserting nanoparticles into cotton as antimicrobial agents to form nanocomposites is a way forward to manufacture value-added fabric material [48]. These nanocomposites which are formed through the in situ or ex situ deposition of nanoparticles in the fabric material has endowed multi-functionalities to the cotton fabrics such as self-cleaning, UV protection and electric conductivity [49]. Cotton based textiles can actually be designed with self-cleaning features when hydrophobic surfaces are fabricated on these textiles to repel water in such a way that spherical droplets of water can remove stains through a mechanism known as easy roll-off. Wu et al., 2016 demonstrated that a sequential deposition of poly(ethylenimine), silver nanoparticles (AgNp) and fluorinated decylpolyhedral oligomeric silsesquioxane (F-POSS) on cotton fabrics resulted in a superhydrophobic surface entailing a 169° angle of water contact with a 3° sliding angle [50]. Cotton based nanocomposites embedded with ZnO, TiO₂ and reduced graphene oxides have also shown great promise in UV protection [51] and electromagnetic interference (EMI) shielding properties [52].

Fabrics with antimicrobial properties are sought after for the manufacture of healthcare textiles particularly as packaging material for drugs and syringes or medical tools, for the personal protective gear of medical personnel, in wound dressing, surgical aprons and hospital bedding [53]. While cotton is undoubtedly widely popular in the textile industry, its fibers are highly hydrophilic with a high tendency of water absorption and oxygen retention and with a large surface area causing it to be a breeding ground for bacteria and fungi [54]. Cotton nanocomposites have been designed to incorporate metallic nanoparticles for the demonstration of antimicrobial activity [55]. Incorporation of antimicrobial metallic nanoparticles into cotton to generate nanocomposites could be carried out via ex situ or in situ methods. An understanding of the interactions of the intramolecular forces in a cotton nanocomposite architecture is critical in the selection of methods which appropriates its functionality.

2.1 In situ synthesis of cotton based cellulose nanocomposites

The in situ synthesis of cotton based nanocomposites is a key approach to generate composites with uniform dispersity using sol–gel or hydrothermal methods. In this method, nanoparticles such as Ag, TiO₂, CuO or ZnO are synthesized in situ using a precursor, such as the aqueous salt solution of the metal and a reducing agent which could be in the form of catalysts or plant extracts as in green synthesis. This would lead to the self-assembly of nanoparticles in a one-pot synthesis [56]. The advantage of using this method is that it initiates a unique assembly of nanostructures with enhanced control of particle size, morphology and aggregation. However, synthetic processes have to be designed meticulously to optimize appropriate assembly of nanoparticles into composite structure to ensure the serving functionality of the resulting nanocomposite [57].

The cellulose structure of cotton fiber constitutes complex chain conformations based on its chirality, length and morphology which varies consistently based on the high degree of polymerization of cellulose chains in its fiber which is about 15,000 [58]. One of the major challenges in the synthesis of cotton nanocomposites is to ensure uniform dispersion of nanoparticles without particle aggregation. Nanoparticles aggregate due to high surface area, high surface energy and strong inter-particle attractions [59] leading to lower Gibb’s free energy making it detrimental to material performance [60]. The spatial distribution and nanoparticle assembly in a nanocomposite is primarily dependent on the delicate balance of intermolecular forces between nanoparticles within the matrix of its [61]. For proper particle dispersion, thermodynamic miscibility must be achieved [62]. Dispersion of the nanoparticles is highly dependent on the hydrogen bonding capacity of the cotton cellulose network. Where self-assembly of nanoparticles is strategically manipulated within a polymer matrix, it would result in a novel functionality of the forthcoming nanocomposite and expand its horizons for application due to its emerging properties such as water resistance, modulation of light, electrical conductivity and antibacterial sustenance [63]. It has to be noted that the ultimate performance of the nanocomposite is dependent on the interaction of the introduced nanoparticles and the cotton matrix which modulates the self-assembly architecture of the nanocomposite. Cotton fibers possess a backbone structure that is largely comprised of hydroxy groups which impart a strong affinity to water molecules, inducing microbial growth and raising the risk of contamination. The incorporation of the nanoparticle assembly however, renders the composite surface to be hydrophobic. Hydrogen bonding is the primary determinant in the spatial arrangement and self-assembly mechanism of molecules in cotton nanocomposites caused by the OH groups present in the glycoside backbones of the cotton cellulose fibers [57]. Hydrophobic interactions are also prevalent in cotton nanocomposites but are also responsible for the aggregation of nanoparticles in the structure [64]. Another force that participates in the self-assembly of nanoparticles in biopolymers during the in-situ synthesis of cotton nanocomposites is the van der Waals force, a short-ranged force, relatively weaker than hydrogen bonding, created by a transient dipole moment produced by an attractive force when nanoparticles move into close proximity [65].

Vajja et al., (2017) developed cotton nanocomposite material through the in situ generation of copper nanoparticles (CuNPs) using a one-step hydrothermal method which demonstrated excellent antibacterial activity [49] while El-Naggar et al., (2016) incorporated Titanium oxide nanoparticles (TiO₂NPs) on cotton fabrics through in situ synthesis. The resulting nanocomposite demonstrated a microbial reduction of more than 95% which was sustained after more than 20 washing cycles [66]. In a separate work, Marnatha et al., (2018) generated bimetallic Ag and Cu nanoparticles in situ in cotton fabric polymer matrix using Aloe vera leaf extract and observed that besides demonstrating potent antimicrobial activity against Escherichia coli, Pseudomonas, Klebsiella, Bacillus and Staphylococcus, the agglomeration of these nanoparticles were also prevented through in situ synthesis [67]. ZnO nanoparticles (ZnO Nps) are hydrophobic, inert and cost-effective and well known for its photocatalytic activity, thermal stability, absorption in a broad range UV radiation and flame-retardant properties [68]. ZnO Nps coating on cotton textiles have demonstrated improved UV protective and antimicrobial properties [69]. However, most of the cotton ZnO nanocomposites are prepared with polymeric binders using the pad-dry-cure method [70]. The nanocomposite produced using this method produces fabrics of high stiffness, poor wash durability and low air permeability [71]. As ZnO Nps are deposited on the surface of the fabric, it does not form any chemical bonds as ZnO does not have any ionic interaction with the OH groups of the cellulose, causing it to only have a lose bond to the surface of the textile. Fabrics used as hospital bedding and PPV go through frequent vigorous washing and surface deposition of ZnO is not an appropriate method to generate cotton nanocomposites for applications that require high washing frequency. In situ generation of nanoparticles in these textiles are a better option. Verbic et al., 2021 demonstrated in situ synthesis of ZnO on cotton fabric using pomegranate peel extract as a reducing agent and wood ash as alkali with excellent UV protective properties due to the uniform dispersion of ZnONps [72]. In another investigation, the in situ synthesis of ZnO cotton nanocomposites was demonstrated using the one pot hydrothermal method which showed excellent antibacterial, UV protection, and photo catalytic performance [73].

2.2 Ex situ synthesis of cotton based cellulose nanocomposites

The ex situ synthesis of cotton based cellulose nanocomposites is carried out through a 2-step process. In the first step, metal oxide or metallic nanoparticles are prepared either through homogeneous precipitation, wet chemical and hydrothermal methods [74]. In the second step, the prepared nanoparticles are dispersed directly onto the cotton fabric to form a nanocomposite. One method to disperse the prepared nanoparticles in the fabric is through blending. In this approach, pre-synthesized nanoparticles are mixed in the biopolymer such as starch or cotton through solvent mixing or melting. Compared to the in situ method, a thorough dispersion of the nanoparticles are necessary before being added to the polymer to prevent aggregation of the nanoparticles due to high surface energy. This method of nanocomposite preparation is less tedious and flexible compared to in situ synthesis and can be scaled up for commercial scale due to its to lower investment cost. The drawback using this method is to prepare uniformly dispersed nanoparticles in biopolymers such as cotton and which could remain stable in the long-term without aggregation [74].

An ex situ method used to form cotton nanocomposites of added value was by surface coating the material with metallic or metal oxide nanoparticles. Daoud et al. (2004) reported the deposition of anatase TiO2NPs on cotton and observed that the coated cotton nanocomposite had enhanced UV protection, antibacterial potential and self-cleaning properties [75]. Uddin et al. (2021) showed ex situ deposition of TiO₂NPs on cotton fabric using the sol–gel method which demonstrated similar properties [76]. A nanocomposite of AgNp loaded with SiO₂ nanoparticles was prepared using the sol–gel technique in which AgNps were generated using the Ocimum lamiifolium plant extract and the Stőber method used to obtain a SiO₂ impregnated Ag nanocomposite. When this nanocomposite was loaded onto cotton fabric, it demonstrated potent antimicrobial activity with no toxicity observed on mammalian cells [53]. In a separate method, ZnONps were applied on the surface of cotton fabric surface through layer-by-layer assembly [77]. This method otherwise known as multilayer decomposition was rarely used in textile coating. Here, cotton fabric was first cationised to generate positive charges on the surface of the fabric and then soaked alternately in anionic ZnO solution at pH 11, deionized water, cationic ZnO solution at pH 3 and deionized water repeatedly until 10–16 layers of ZnONps were deposited. Finally, the nanocomposite material was dried at 60°C and cured at 130°C for 3 min [78].

The ex situ synthesis of cotton nanocomposites using AgNP for antimicrobial activity have been carried out through the incorporation of silver salts and organic compound complexes of silver. However, this method entails a weak adhesion of this antimicrobial agent to the cotton fabric, allowing the rapid release of AgNp with increased washing resulting in lowered laundering durability. The release of Ag⁺ ions from antimicrobial cotton nanocomposites also poses unnecessary duress to health and the environment due to its potent toxicity [79]. The weak adhesion of AgNps to cotton fabrics using the sorption process is a shortcoming in the production of antibacterial cotton nanocomposite material and surface modification is required to improve loading efficiency [80]. Shahidi et al., 2010 reported plasma-treatment of the cotton fabric prior to coating with AgNps which enhanced absorption and demonstrated increased quantity of AgNps on the surface of cotton. These nanocomposite fabrics showed 95% - 100% reduction in bacterial population which remained consistent after 10 times consecutive laundering [81].

3. Cotton based nanocomposites constructed from nanocellulose extracted from cotton cellulose nanofibers

Cotton nanofibers are natural fibers which mostly constitute holocellulose (cellulose and hemicellulose) and lignin and has several advantages such as lower density, availability, biodegradability and exceptional mechanical properties which make it an ideal candidate as a polymer nanocomposite. The valorisation of agro residues of cotton would result in novel materials that could be used as fillers or reinforcement materials to form nanocomposites of potent value. Unlike other plants such as jute, flax and kenaf which are made up of only 25% cellulose and wood-based trees which contain 40–50% cellulose, cotton fibers are made up of 90% cellulose [82]. The cellulose in the cotton fibers are among the highest in molecular weight among all plant fibers and the most crystalline and fibrillated [83]. Cotton fiber comprises cellulose with 1,4-d-glucopyranose structural units [84] which accumulate as microfibrils arranged in regular pattern with excellent mechanical properties such as the Young’s Modulus and low thermal expansion [85]. Nanofibers generated from cellulose isolated from cotton fibers can be categorized as nanowires with aspect ratio beyond 1000, nanorods with aspect ratios between 3 and 5, nanoribbons and nanotubes with aspect ratios >10 [17]. Dried cotton fibers comprise large amounts of cellulose and hemi-cellulose which increase in tensile strength and durability when the impurities are removed. These cellulose based fibers are usually added as reinforcement material to generate nanocomposites needed in construction, automotive and electronics industry, as membranes for ultrafiltration, ion exchange and fuel cells and as binders in pharmaceuticals and cosmetic fillers [86]. Cellulose nanofibrils gives greater tensile strength compared to natural fibers and it has exceptionally large surface to volume ratio compared to its bulk form [87].

The extraction of cotton nanocellulose can be carried out using mechanical methods such as high-pressure homogenization, ball grinding, ultrasonication or high-speed blending [88] or chemical methods using acid hydrolysis with strong acids such as sulfuric acid or hydrochloric acid, oxidation with TEMPO (2,2,6,6-tetramethylpyperidine-l-oxyl) [89] or a combination of both mechanical and chemical methods [90]. It is found that acid hydrolysis removes the amorphous regions in the cotton fiber and generates nanocellulose with high crystallinity and uniform size distribution [89]. Sulfuric acid generates a more stable colloidal suspension of cellulose nanocrystals [24] and is preferred to hydrochloric acid which causes mass aggregation of cellulose nanocrystals because of the minimal surface charge that causes a lack of electrostatic repulsion force between the crystal particles [91]. Also, the hazards of inorganic acids and their corrosive nature are detrimental to the environment [92]. Mechanical processes generate nanofibers at a high success rate but the strong mechanical shearing forces causes disruption of the fibers, depict excessive energy consumption and homogenizer obstruction after prolonged use [88]. To elude the shortcomings presented by both the mechanical and chemical processes of nanocellulose extraction, pre-treatment with cellulase or enzymatic hydrolysis has been considered. Enzymatic hydrolysis is an appropriate pretreatment method used to disrupt interfibrillar cohesive forces and facilitate the disintegration of cotton fibers, while decreasing the size and degree of polymerization of cellulose fibers [93]. This method has been found to be highly selective and carried out at conditions with lower energy requirements [14]. Additionally, it replaces harmful solvents with biodegradable enzymes such as cellulases, which does not release hazardous emissions to the environment [94]. Cellulose is comprised of highly ordered crystalline regions interspersed with disorganized amorphous regions. The amorphous regions of cellulose are more susceptible to enzymatic degradation compared to the crystalline area. Cellulase enzyme has the potential of selective hydrolyzation of the amorphous region while maintaining the crystalline region, making it a process of choice to isolate cellulose nanocrystals. Therefore, this route has become increasingly popular as a sustainable method to prepare cellulose nanocrystals because of its high selectivity, mild conditions, and weak changes in surface chemistry [93]. Moreover, it complies with the principles of green chemistry as it leaves no carbon footprint, generates no hazardous waste and poses less water and energy consumption [95].

The addition of nanocellulose extracted from cotton as a reinforcing agent to a polymer system such as plastic, rubber or concrete improves the mechanical, thermodynamic and adsorption properties of the composite without changing the original qualities of the parent material [94]. Cotton fibers with a diameter in the range of 10–30 nm and a high aspect ratio are observed to improve the mechanical properties in a polymer composite for non-food packaging applications [96]. These nanocomposites have been postulated to hold tremendous potential in biomedicine as scaffolds in tissue engineering and for encapsulation in drug delivery [97]. The advances in mammalian cell culture technology are astounding. Here, nanocomposite biopolymers perform as biomimetic substrates for cell adhesion and proliferation. The nanotopography of substrates constructed from biomolecules such as collagen which includes surface roughness and porosity, influences interface interaction with mammalian cells or tissue that could improve cell adhesion and multiplication [98]. The incorporation of nanomaterials into these polymer matrixes can yield composites with the necessary properties for cell and tissue culture. Cotton based cellulose nanofibers (CCN) have a tremendous potential to be engineered for polymer composite reinforcement [91] as it mimics the structure of collagen in directionality and surface functionalization which is paramount to the adhesion, spreading and proliferation of cells [99].

Translating cotton based nanocellulose into polymer nanocomposites can be carried out using electrospinning, cast drying, freeze drying, vacuum assisted filtration, wet spinning, layer by layer assembly, micropatterning, melt blending, intercalated polymerization, sol-gel and solvent evaporation technique [100]. The solvent evaporation technique is the simplest method for nanocomposite synthesis which involves nanocellulose dispersion in polymer solution through energetic agitation followed by controlled evaporation of the solvent and composite film casting [101]. Li et al., (2014) prepared a nancomposite of cotton nanofiber in high density polyethylene (HDPE) using 2 different pretreatment methods. The first was blending the HDPE in a cotton CNF suspension, dehydrating and freeze drying the mixture followed by compounding and extrusion. This was a rapid, eco-friendly method as there were no chemical solvents involved in the process. In the second method, polyoxyethylene (PEO) was used as a dispersion agent to coat the cotton CNF before adding to HDPE granules and extraction. FESEM results revealed that both methods produced well dispersed CNF in HDPE and generated an excellent network structure of the cotton CNF/HDPE composites but the nanocomposite produced using the blending method was preferred as it demonstrated greater bending strength (MOR) and bending modulus (MOE) [102].

Nanocomposites have several advantages over conventional composites in their superior tensile strength, thermal capacity and barrier properties, biodegradability, recyclability and low weight [103]. Insertion of nanocellulose to biodegradable polymers to form bio-nanocomposites may improve the brittleness, poor barrier properties and low thermal stability of pure biodegradable polymers [104]. Much work has been carried out in recent times to explore the design of bionanocomposites en route to the development of higher quality bioplastics [105, 106].

A problem faced in generating cotton based cellulose nanocomposites is the limited dispersion of nanocellulose in polymers. This can be overcome by attaching a hydrophobic group to the surface of the cellulose matrix through esterification, acetylation or silanization which increases compatibility with the matrix. Solution casting is commonly used in the preparation of nanocomposite films but it its unsuitable for commercial scale production. Another method known as extrusion using melt processing has shown much promise for large scale production of cotton based cellulose nanocomposites [107]. However, for transforming research to industry and commercialization of cotton based cellulose nanocomposites, it is necessary to weigh the production costs, waste emissions, energy consumption, feasibility of the process and compliance to environmental ethics. Overall, the application prospects for nanocellulose appear to be very optimistic, but further research is needed to develop viable methods from laboratory to industrialization.

4. Conclusion

Nanocomposites are defined as multi-element materials with at least one element having a dimension of less than 100 nm [108]. In this chapter we have reviewed cotton based cellulose nanocomposites which are constructed by adding multifunctional nanoparticles to the cotton fabric using in situ or ex situ processes or by extracting nanocellulose structures from cotton fibers and incorporating it into polymer matrices. This results in novel nanocomposites with enhanced antimicrobial activity, polymer reinforcement and enhanced adhesion and adsorption in inert matrixes.

The introduction of metallic nanoparticles into cotton textiles has resulted in high performance multifunctional cotton nanocomposites which demonstrate excellent antimicrobial activity, water repellency, UV protection and antistatic finishes. These nanocomposites are gaining much interest particularly in generating antimicrobial material for protection against emerging pathogens. It is projected that further research in nanocomposite technology would decipher the details of the functional properties and performance of existing and emerging cotton nanocomposites and to determine the toxicity and safety of the generated fabrics. Additionally, there is a pressing need that the discoveries in the laboratory should be translated to commercial applications through the design of fabrication processes that favor cost effective, large scale production.

The incorporation of cotton nanocellulose into polymers as fillers to form reinforced nanocomposites also shows much promise particularly in the creation of chemical and biodegradable polymers of increased strength and tensile modulus and as scaffolds and support substrates in biomedicine. Yet there are issues that need to be addressed prior to translation into commercial viability such as the influence of the size and morphology of cotton nanocellulose fillers in the polymer matrix and the structural compatibility of the resulting polymer, biocompatibility of the nanocomposites in biomedical applications and the poor dispersion of cotton nanocellulose in the polymeric domain structure [109]. It is believed that these issues will be addressed aggressively in the near future to pave the way for the birth of a new breed of nanocomposite material using cotton nanostructures.

Conflict of interest

The author declares no conflict of interest.