Sources and Applications of Nano Cellulose Tailored Materials

Abstract

Cellulose is one of the most economical, biodegradable, and biosafe components found in nature. It is extracted from biomass found in forests or crops being treated enzymatically, chemically or mechanically. The extracted cellulose on acid hydrolysis and other mechanical treatment yields bacterial cellulose, nano-fibrillated cellulose, and cellulose nanocrystals. Nanosized cellulose can be attributed to the size reduction of the polymer chains in cellulose from micro to nanoscale. The size range was found suitable from 1–100 nm to be called nanosized cellulose. Nano cellulose hogged much limelight in the modern era due to its low toxicity, biocompatibility, and biodegradability. Due to the rapid evolution in this field, it is an obvious need to synthesize nano cellulose from different sources for its huge potential in pharmaceuticals and other industries. The tiny size made the nano cellulose mechanically strong and stable thus rendering it suitable for application, especially in pharmaceuticals, drug delivery, tissue engineering, and regenerative medicine. Recent research has been focused on the development and applications of nanocellulose products due to their eco-friendly nature and diversity of its application. However, there are challenges too, related to its scale-up, cost, and stability may be registered. This chapter will further discuss in detail the synthesis and preparations of nanosized cellulose and its theragnostic applications.

1. Introduction

Cellulose is one of the most widespread and abundantly available biopolymers in the biosphere, and can be easily obtained from algae, fungi, bacteria, and plants as well. Among all other similar polymers including chitosan, gelatin, starch, cellulose is considered one of the promising exhaustive renewable compounds mostly produced by photosynthesis [1]. The chemical structure of unmodified cellulose comprises a linear chain of D-glucopyranose units in the range of several hundred to thousands joined together by β-(1–4)-glycosidic linkages, whereas bacterial nano cellulose comprises nothing but a similar structure while the repeating unit is found to be disaccharide cellobiose [2]. Due to the natural hierarchy of the chemical structure in cellulose owing to its nano fibrillar components, this seemingly contributes to the unique mechanical strength, and elastic properties of the higher plant cells. Its unusually high strength-to-weight ratio also prohibits a dimensional change in response to water absorption in large amounts, shrinkage, and swelling as evident in common aqueous and terrestrial flora and fauna [3].

Consecutively reducing resources of non-renewable products is shifting the research paradigm towards the establishment of sustainable resources, which led to further purification, modification, and destructing of cellulose employing mechanical as well as chemical strategies. Chemical degradation and mechanical degradation lead to the formation of cellulose nanocrystals and cellulose microfibrils respectively. Such degradation of natural fibers separates the highly crystalline cellulose microfibrillar bundles from the remaining imperfect amorphous residue having pits and nodes [4].This homogeneous dispersion reportedly confers much superior elastic modulus and mechanical properties. However, the mechanical reinforcement can be slightly compromised for these nanocomposites since it also possesses self-associating properties due to the abundance of surface hydroxyl groups despite its ability to form load-bearing stiff structures interpenetrating suitable polymer matrix [5, 6]. The stiffness was found to increase with the aspect ratio of the nanostructures present within the microfibrils. Concerning optical properties, loading or mechanical compression of the nanocellulose fibers prevents light scattering rendering it optically transparent while the recovery of nanofibers subject to reversal of stress forms open spaces and interstices allowing light scattering [7]. Lastly, the high surface-to-volume ratio, and nanosize reduce the permeability of cellulose furthermore by enhancing the interaction of the particles with the surrounding polymer thereby reducing the mobility of chain segments, diffusivity, and reactivity to a great extent [8].

These aforementioned exclusive features of nano cellulose offer a great diversity in its application ranging from the fabrication of packaging materials to extend food shelf-life to the formulation of decontaminants, wood-adhesives, and adsorptive to name a few. The advanced medical technology has been utilizing this magical substance for the fabrication of biosensors and bio-imaging facilities [9]. The nanofibrous cellulose sheet not only offers all the advantages of conventional paper-based biosensors but this is also devoid of surface roughness, optical opaqueness, increased thermal expandability, and inability to fold. One of its several noteworthy applications includes the accurate and precise detection of S. aureus bacterial species for any infectious disease [10]. This article, however, gives an overview of the sources and extraction procedure of nano cellulose in its various forms along with its multi-dimensional usage.

2. Sources of nano cellulose

Nano cellulose can be prepared from several sources which contain cellulose. Nano cellulose is prepared from fibers of cellulose [11]. Generally, cellulose can be extracted from bacterial and algal sources, biomass from agriculture, tunicates, soft or hardwood, plants, etc. [12].

The concentration of cellulose is similar in the above-mentioned species, however, their structures may vary. For example, in plants cellulose possesses about 44–65% of crystals and has a diameter ranging from 13–22 microns [13]. However, the bacterial cellulose possesses about 90% crystals and is nano-structured with a diameter ranging from 10 to 100 nm [14]. Among the three classes of nano cellulose, nanofibrils have a length of a few micrometers and diameters ranging from 5 to 60 nm. Nanocellulose has both crystalline and amorphous forms and that can be generally extracted from plant woods by oxidizing technique [15, 16]. However, the nanocrystals are mostly crystalline with a needle shape, shorter in length ranging from 20 to 100 nm and 5 nm in diameter. Acid hydrolysis is used to extract the nanocrystals [17]. Again the nano cellulose obtained from bacterial sources has a ribbon-shaped structure, length of a few microns and diameter ranging from 20 to 100 nm [11].

2.1 Nano cellulose extracted from agriculture waste biomass

Cellulose has been extracted from agricultural wastes like pineapple peel, rice and wheat stalks, oat husk, straw, leaves, sisal, etc. using chemical methods like treatment with alkali, acid hydrolysis and bleaching. One of the most commonly used resources is sugarcane. After sugar is extracted from sugarcane the biomass left is used for extracting cellulose by chemical treatment or irradiation. The agro waste may also contains fiber, lignin, hemicelluloses, sugar, etc. apart from cellulose. Cellulose is also obtained from dietary fibers extracted from plants. Various parts of the plants can yield cellulose, for example, peel, pomace, stems, leaves, reeds, bast or roots, etc. Depending on the type of material, the extraction process differs and the use of acid, alkali, enzymes, mechanical methods, etc. Further, the structure of the cellulose obtained as a product depends not only on the type of raw material but also on the time for reaction [18].

2.2 Nano cellulose extracted from forest wood

Most commonly fibers from wood pulp are used to extract cellulose. The cellulose extracted from the wood pulp has highly cellulose content with high mechanical strength & good ductile properties. The wood pulp can be derived from both hard and softwoods.

Cellulose can be derived from the wood pulp of the trees like pine or eucalyptus, etc. in forest reserves by various chemical methods including acid treatment or oxidation and by biological methods by using fungi on softwoods [19].

2.3 Nano cellulose extracted from waste paper

A good amount of waste paper is found in the form of newspapers, newsprints, etc. from which nano cellulose has been extracted. Nanocrystals have been prepared through chemical treatment like acid hydrolysis. Nanofibers have been prepared by combining both chemical and mechanical methods like acid hydrolysis, ultrasonication or centrifugation.

2.4 Nano cellulose extracted from animal sources

Nano cellulose can also be prepared using crabs, prawns or tunicates. Nanofibers have been derived from prawns or crabs by mechanical methods. Further cellulose is also extracted from tunicates like Halocynthiapapillosa, Metandroxarpauedai, Halocynthiaroretzi, etc., which are marine invertebrate animals. Their outer tissue also called tunic contains crystalline cellulose in pure form [20].

2.5 Nano cellulose extracted from bacterial/algal sources

Among the algal species, cellulose is generally extracted from Cladophora, which is also known as green algae. The fermentation of bacterial species like Sarcina, Agrobacterium, Gluconacetobacterand Rhizobium, etc. yields nano cellulose as an extracellular product [21]. The production of bacterial cellulose was reported in both synthetic and non-synthetic media by Gluconacetobacter, Agrobacterium, and Sarcina through oxidative fermentation. The gram negative Gluconacetobacter is one of the most important one to produce bacterial cellulose in a large quantity. After starting the bacterial cellulose synthesis, the next process initiates to form the glucose chains in to the bacterial cell & it leaches out through the microscopic cellular pore and again accumulate to form the microfibrils, that leads to cellulose strip formations. That cellulose fibrils then form the web like structures & create a highly porous matrix. The cellulosic chains are attached together by the hydrogen bonding. The interesting fact regarding the bacterial cellulose is that it is 100 times smaller than the plant mediated cellulose. Many researchers & companies have developed bacterial cellulose in treating of wound, high quality excipients of papers, materials of fibre glasses etc (Figure 1).

Figure 1.

Extraction of nano fibril from bacteria and algae.

3. Preparation and application of nano cellulose

Natural polymers are widely applied materials for different purposes. Due to the green approaches, they are the automatic choice of application over synthetic polymers. These green composites can be registered in different applications, especially in pharma, food, packaging, building materials and the automobile industry. Cellulose is one of them. It has comparatively a broader perception which can be found in different natural fibers such as cotton, jute, sugarcane bagasse, etc. That can be found in different bacteria, fungi and sea animals also [22, 23, 24]. Cellulose can be easily extracted on different scales such as micro-scale and nano-scale. Nano cellulose can be extracted as nano-structured cellulose fiber with a definite size range of less than 100 nm [25]. A cellulose fiber can be synthesized with the accumulation of a single cellulose fiber with a definite size range 25–30 μm in diameter. The single cellulose fiber is manufactured by the accumulation of several microfibers with a definite size range 0.1–1 μm. Nanofiber is too small with a sigh range 10–70 nm in diameter [26]. Due to its uniform tiny size and tremendous mechanical stability nano-sized cellulose is getting more interest in the present era. Different extraction procedures and other techniques are responsible to vary the characteristics of nano cellulose such as crystallinities, surface area and mechanical strength [27]. For example, the synthesis process of nano cellulose with the application of sulfuric acid (H₂SO₄) requires the selective hydrolysis of the amorphous cellulose zone as a result it forms pure crystalline particles with definite dimensions. In addition, on the surface of nano-sized cellulose particles negatively charged sulphate groups are attached through the accumulation of nanoparticles in aqueous suspensions due to the electrostatic repulsion forces. Due to the synthesis process and preparation technique of nano cellulose which hold up its dimension, composition and mechanical strengths, it can be categorized into three parts

1. Cellulose nanocrystals it is also known as cellulose whiskers.

2. Cellulose nanofibers it is also known as cellulose nanofibers.

3. Bacterial cellulose (BC) and electrospun cellulose nanofibers (ECNFs).

The first two phases mentioned cellulose nanocrystals and cellulose nanofibers are formed due to the fragmentation of cellulose fibers at the nano-sized level. This nano cellulose preparation technique follows the top-to-bottom approach, in the next phase such as bacterial cellulose and ECNF sugars with low molecular weight or dissolved cellulose is formulated through the bacteria or electrospinning, respectively, this process follows the opposite of the first phase which is bottom to top approach. As a result, the scale, of the process of Bacterial cellulose (BC) and electrospun cellulose nanofibers (ECNFs) is always a difficult challenge in industry [28].

4. Nano cellulose synthesis methods

4.1 Pretreatment method

Pretreatment method of plant cellulose is a widely accepted technique that decreases the required energy of mechanical nano fibrillation to accelerate the degree of nano fibrillation process. In the nano-fibrillation technique, the major complaint is regarding the huge energy consumption to produce the nanofibril. As a result, pretreatment is an important step to overcome this drawback. The pretreatment process is also a major step to producing more nanofibers through the nano-fibrillation technique. It is very common that two major issues are specifically noticed in pretreatment method specially during the mechanical fibrillation of cellulose i. fibril aggregation in to the disintegration device when the slurry was pumped & another is high energy consumption associated with the fiber de lamination. High energy sources & input is important to overcome the barriers such as e interfibrillar hydrogen bonding. Different scientifical works also proved that the potent or actual pretreatment method actually reduces the energy at least 20–30 folds. The choice of the pretreatment method is actually depending upon the sources of the cellulosic fibers & its detailed morphology. For instance, the pretreatment method is really effective to remove the non-cellulosic materials from the plant such as (hemicellulose, lignin, etc). Pretreatment of tunicate associates the execution of the protein matrix, isolation of the mantel, and the isolation of individual cellulose fibrils. Pretreatment of algae basically involves the separation of the matrix substance from the cell wall of algae, whereas in pretreatment method of bacterial nitrocellulose expresses the procedure of separation of bacteria & other impurities from the prepared slurry. This pretreatment procedure is very vital one especially to produce the nano cellulose because it can alter the structural orientation, crystallinity & polymorphism [29].

4.2 Enzyme hydrolysis

Some enzymes are able for selective hydrolysis for example laccase can modify the lignin content or hemicellulose content without any alteration of the main cellulose content. Cellulose fibers are made with different compounds with sound structures as a result, a particular enzyme cannot alter the structure of a nanofiber. There are some of the enzymes are required to decompose the extra cellulose compounds [3].

1. Cellobiohydrolases: It strikes mostly on crystalline cellulose.

2. Endoglucanases: These strike mostly the affected structure of the cellulose.

A group of scientists Pääkkö and Ankerfors has shown the pathway to prepare nano cellulose from the bleached softwood pulp [30]. In this preparation method the enzymatic hydrolysis technique was used to prepare nano cellulose and after that for better nano structure homogenization and purification process followed. Another finding from this analytical procedure is mild hydrolysis with the application of endoglucanase has escalated the aspect ratio of nano cellulose without any conflict as compared to the acid hydrolysis technique. Another advantage of this pretreatment method is that it elevates the solid level thereby it permits a smooth path during HPH processing [31]. Other scientists also worked with this technique and found the results of TEM to be very suitable. 90% of the prepared nanofibers have given a diameter of less than 50 nm. It also gives a proper and better aspect ratio as compared to the untreated version [32].

4.3 Alkaline–acid

Before the mechanical isolation technique of nano cellulose, alkaline acid pretreatment is playing a major role to solubilize lignin, hemicellulose, and pectin. This method is following different steps which are given below.

1. It is mandatory to soak the fibers with a concentration of 12–17.5% sodium hydroxide solution at least for 2 hours. That can increase the surface morphology of the nanofibers and make the hydrolysis process easier.

2. Soaking of the fiber in 1 M hydrochloric acid solution at a temperature of 60–75°C. This technique can solubilize the hemicellulose most efficiently.

3. For breaking the linkage between carbohydrate and lignin structure sodium hydroxide 2% solution is treated at 60–80°C.

Alkaline pre-treatment is an effective technique that can increase the yield value of different nano cellulose from 42–80% [33].

4.4 Ionic liquids

Thermal stability, chemical stability & low vapor pressure are adopted as some of the special facility in the ionic liquid process. This is an exciting technique for formulation scientists to use as a solvent for dissolving cellulosic materials. Scientists reported some of the work where 1-butyl-3-methylimidazolium chloride [(Bmim)Cl] as an ionic liquid (solvent) to treat sugarcane bagasse. After that, the homogenization process was followed to prepare nano cellulose [34].

4.5 Mechanical process

Mechanical treatment is an important step for the defibrillation of cellulosic materials. The pretreatment process is the primary process either by chemical or enzyme included to make it easier. The application of chemical treatment has done for widening the surface space between the hydroxyl group, which elongates the internal surface, it also alters the crystallinity and create fragment of cellulose hydrogen bonds. Thereby, the surface area is increased which boots up the reactivity of the nanofiber [35]. Plenty of methods are available to prepare the nano cellulose from cellulose fiber, such as homogenization, grinding, microfludized technique, cyrocrushing and high-density ultrasonication technique [36].

4.6 Homogenization technique

This process was introduced in 1983, it is one of the simplesttechnique to process the nano fibers from cellulose fibers. This process does not require any organic solvent [37]. In homogenization technique the cellulose pump is required & it is designed with a very tiny nozzle withremarkable high pressure. Mostly the high impact and shear forces are applied for preparing the nano cellulose. The forces generate high shear rates as a result the nano scale fibers are formed [38]. Some good numbers of peer-reviewed journals reported that bleached sugar beet and the extraction process of prickly has been done through this process. But still there is some limitation notified in this process one of them is clogging. To bypass this clogging issue the cellulosic fiber has to be chopped into very small pieces before introducing in homogenizer [39].

4.7 Micro fluidization technique

The working procedure of microfludization technique was more or less the same as the homogenization technique. Microfluidizers have been applied in nano cellulose preparation to enhance the pressure as an intensifier pump. Both forces worked into the interaction chamber (Impact and shear forces) against colliding streams to de-fibrillate the cellulose fibers. Higher numbers of hydroxyl groups(-OH) were observed in cellulose fibrils due to the higher surface area. The size of the nano cellulose was determined by the actual number of chopped fibers through the homogenizer [40].

4.8 Grinding

This technique is another technique to prepare nano-size cellulose from normal cellulose fibres. This process works with the impact and attrition principle. In this context, the pulp of the cellulose was introduced between two stones. One stone is static and another stone is movable. The grinding mechanism is applied to create the shear forces which break the hydrogen bond & damage the cell wall completely. As a result the nano sized cellulose is formed from the normal cellulose. Wang et al. reported through their scientific work after the application of a stone grinder the normal pulp of bleached eucalyptus can be modified to nano cellulose [41]. The attrition and friction process from the stone grinder generates heat which can evaporate water and creates more solid contents. It requires a long time (11–12 h) to create actual fibrillation energy to make nano-scale products [42].

4.9 Cyrocrushing

This method is another method that can create the fragmentation into the cell wall of the normal cellulose to prepare nano-sized cellulose. The cellulose is introduced into the water to absorb the moisture into the cellulose cavity. The soaked cellulose is deeped into the liquid nitrogen carefully that makes solid content of water, and after that, it is crushed into the mortar pastle [43]. Due to the application of the high impact force (impact) on the pre-freeze cellulosic fibers that break into fragments and as a result, create nano cellulose. Scientists have found 50–100 nm nanofibers from the soya stock after using this technology along with high-pressure homogenization technology [44].

4.10 High-intensity ultrasonication technique

Ultrasonication technique is one of the most common techniques to prepare different nanoparticles along with various conditions. This process includes hydrodynamic power with the effect of ultrasound as a result it can create nanofibers. Different studies have prepared nano cellulose fibers through the high-intensity ultrasonication technique with the effect of temperature, pressure, size, time, and distance from the probe tip on the degree of fibrillation [45].

4.11 Ball milling

It is one of the oldest methods to prepare nano cellulose or nanofiber through the application of impact and attrition technique. The hollow chamber of the ball mill contains balls specially made for ceramics or stainless steel. The cylinder rotates with the help of the motor so that a high-energy collision occurs with the ball and cellulose fibers. As a result, the size reduction was taken place and the normal cellulose fiber turns up to nano cellulose (Figure 2) [46].

Figure 2.

Schematic diagram of preparation of nano cellulose.

5. Application of nano cellulose in industry

Nano cellulose is one of the materials which is supposed to be the alternative to synthetic material and is eco-friendly. It is a comparatively new biomaterial that has different roles in industries such as the paper industry, packaging industry, automotive, electronic, medical, and wastewater treatment, etc. Due to its excellent mechanical and chemical stability, it is one of the choices in the industry. Some interesting equipment such as windmills is made with nano cellulose due to its stable mechanical structures and huge strength. In the paper industry nano cellulose is used because of its soft nature, folding capacity and clarity. Due to its less toxicity and mechanical strength, it is also applied in the medical industry, especially for operation theater. Scientists have found that nano cellulose is applied in dressing and it has unique biocompatibility in skin drafting and tissue engineering rather than the others [47]. Nano cellulose dressing can be well-designed and safe and easily detachable after skin recovery. However, nano cellulose is presently a positive choice for different industries such as automotive, pharmaceuticals, paper & ink & cosmetics etc. It can also be applied as a membrane of high accuracy ultrafiltration technique, ion exchange & fuel cell etc. Nano cellulose is also one of the major choices for bio nano composites especially to prepare different film for transdermal application, absorption & preparation of medicated foam. Researchers reported that scaffolding of polymeric potato starch matrix & nano fiber as a rein forcing agent can improve the mechanical properties of nano composites remarkably. At present day it is established that nano cellulose is one of the best choices as a reinforcing agent. Another delivery of the nano cellulose is also notified by some peer-reviewed journals such as drug delivery, implantation, tissue drafting, tissue engineering, etc.

5.1 Application of nano cellulose in paper industry

Application of nano cellulose in paper industry was deputed to replace the application of the hazards petrochemicals. More than 100 million tons of commercially available cellulose fiber was introduced in the paper industry every year. There are various steps also available to produce fine paper such as arrangement of paper components, wet refining, preparation of fine sheet, drying, calendaring, Finishing and polishing. A mandatory step for paper making is to refine the cellulose fiber in a moist medium is common and best to make a quality paper. Nano cellulose can increase the tensile strength of the paper when applied. These fine paper sheets have better mechanical properties than normal paper. But one major drawback of this process is too costly [48]. Nanocellulose is blessed with different properties one of them is tiny size with nano scale & gas & water barrier properties make it stronger applicant for paper industry. Due to these properties, it can prepare a definite thin film with good mechanical strength, which is one of the requirements for paper industry. Moreover, it is extracted from the natural sources and it is nontoxic& non irritative in nature as a result it is also applied in food packing especially for export purposes. It is reported in some peer reviewed scientific literature that application of nano clay & poly lactic acid having nano cellulose one of the rein forcing agent has definite mechanical strength to produce a proper texture for food packaging as a barrier of oxygen & water specially.

5.2 Application of nano cellulose in medical industry

In biomedical industry application of nano cellulose is comparatively new & in modern era it has got a huge appreciation in medical as well as pharma industry. It is observed through different research that electrospunpolylactide-co-glycolide (PLGA) is more effective than normal PLGA for skin tissue engineering. Electro-spun polylactide-polyglycolide has better cell compatibility in skin tissue engineering this affects the adhesion, spreading and proliferation of the fibroblasts. The mechanical stability of different engineered tissues also increased due to the application of nano cellulose. In vascular tissue engineering replacement and repairing of tissues are very common. Lacking endothelial cell linings, it causes thrombosis when reconstruction of tiny diameter blood vessels. As a result, endothelialization is an essential parameter to produce artificial blood vessels. Among some natural molecules collagen, hyaluronic acid has tremendous potential and good biocompatibility but they have lacuna in mechanical strength [49]. Among some synthetic polymer like polyethylene terephthalate is mechanically stable but have an issue with the affinity towards the cell and tissue that causes severe complication in scaffolding. Nano cellulose is chosen because of its tiny size and high biocompatibility with others and also biodegradable. In neural tissue engineering also nano cellulose has tremendous potency. Its mechanical stability, porosity and sound biocompatibility make it advantageous over the others (Figure 3) [50].

Figure 3.

Application of nano cellulose in different industry.

6. Future prospects of nano cellulose

Several research studies and innovations have been continuing with nano cellulose and its modified forms for the last 20 years. Several limitations have been overcome and modifications are done as per the requirement of the industry with eco-friendly features. In this present book chapter, nano cellulose has been explored concerning its true potentiality towards the green concept as well as full its ecofriendly nature. It has some tremendous properties which make nano cellulose always better suited compared to others such as high surface area, better chemical and mechanical stability, proper anisotropic shape, etc. These properties make nano cellulose an excellent addition in biomedical and other fields with high potentiality and more durability. Due to the cost-effective and eco-friendly behavior, it can get a lodge of new applications as per the industry requirement. It is also observed that the applications of nano cellulose in different industries are in global demand. As a result, the interest in nano cellulose preparation and modification is an automatic choice in the future. Therefore, it is an obvious need to facilitate and improve the technology to prepare and modify nano cellulose from lab scale to industrial scale for future application. This technology should be improved due to the transition gap between lab scale to industry and finally to the market. The future target of nano cellulose research is to fill the gap between the transition state of technology transfer and scale-up. Optimization of the whole scale-up process and its stability should be justified in future studies. The life cycle assessment of nano cellulose-based products should be justified for future betterment and a futuristic approach. Innovation and technology should look after energy consumption and time management to produce nano cellulose-based products from cellulose and its derivatives. Despite all the limitations, cost and other amenities we hope that the formulation scientists will adopt the newer technologies to prepare nano cellulose-based materials to improve people’s quality of life in the near future [51].

7. Conclusion

In the whole chapter, we have discussed the sources, preparation methods and applications of nano cellulose. We have observed that there are several sources from which cellulose fibers can be collected and further nano cellulose may be produced by various means. The various types of nano cellulose can be developed from various sources and methods whether physical, chemical or biological. Nano cellulose has highly beneficial properties concerning durability, biodegradability, and mechanical strength and thus finds an end number of applications in pharmaceuticals, biopharmaceuticals, paper or food industry. Keeping in mind the huge number of applications and the growing interest of researchers to work with nano cellulose, proper development and scale-up methods need to be established so that nano cellulose may be applied cost-effectively and productively in products adding value to human life.