Nanocellulose - Progress of Natural Cellulose for Different Applications

Nanocellulose is defined as the by-products or extracts from natural cellulose, which is present in microorganisms, plants, and mammals. It is one of the most notable green materials of the modern era, which is cellulose in the form of nanostructures. NC materials have attracted increasing interest amongst the researchers recently. As of 2022, over 800 patents were published, while the total number of research papers crossed 6000 numbers. The rising interests is as a result of the alluring and exceptional qualities of nanocellulose. This include its abundance, high aspect ratio, superior mechanical capabilities, renewability, and biocompatibility. Researchers and the industry have been motivated to maximize the use of nanocellulose owing to increased demand and the use of novel applications.

Nanocellulose, which can currently be produced on an industrial scale at tonnes per day, can be used in a variety of applications in our daily lives. This includw nanocomposite materials, biomedical products, wood adhesives, batteries, super capacitors, templates for electronic components, continuous fibers and textiles, food coatings, barrier/separation membranes, antimicrobial films, paper products, cosmetics, and many other emerging uses. As of today, around 36% of the demand for NC comes from packaging, paper, and board, while about 20% is for filtration products, and over 23% for nanocomposites. Further, by 2030, the production of nanocellulose around the world is poised to cross 36,000 Tons/year, up from about 2400 Tons/year in the current day.

How is Nanocellulose Obtained?

By subjecting cellulose fibers to mechanical, oxidative, and enzymatic treatments as well as acid hydrolysis, nanocellulose can be produced. The most popular method is the chemical process of cellulose hydrolysis by acid solutions. Typically, cellulosic materials from wood and nonwood plants are acid hydrolyzed to produce nanocellulose. Wood is the primary raw material utilized to make cellulose on a global basis. In nations where wood is a limited natural resource, finding alternate sources of plant materials remains a top focus. Nonwood plants make a good alternate source for these raw elements needed to make pulp.

Main Categories of Nanocellulose:

• Cellulose Filament (CF): Without any chemical or enzymatic processing, cellulose filament (CF) is a mechanically processed cellulose fibril. The fully mechanical process can "peel" fiber longitudinally, keeping their initial length as much as possible, while lowering their diameter by about a thousand times.
• Cellulose Nanocrystal (CNC): Cellulose nanocrystals (CNC) are a kind of cellulose-based nanomaterials. These are rod-like or whisker-shaped and have a width of 3–20 nm, along with a length of 50–2000 nm. Depending on the source, it comprises 64–98% cellulose. It can often be made using a variety of techniques, the most popular of which is hydrolysis with mineral acids, particularly sulfuric acid (H2SO4), along with phosphoric acid (H3PO4) and hydrochloric acid (HCl). The acid process can yield high purity cellulose crystals by removing the majority of amorphous cellulose, giving the CNC a high crystallinity.

• Cellulose Nanofibril (CNF): Cellulose nanofibril (CNF) differs from carbon nanocrystal (CNC) in terms of size, content, and shape. It has a structure that is intricate, intertwined, and web-like. Compared to CNC, CNF's entanglement and percolation can raise the likelihood of fiber aggregation. CNF generally has a length of less than 0.2 mm and a width of 50 nm. It can be functionalized because of its high aspect ratio, low density, and high specific surface. Additionally, it is less crystalline and has more amorphous cellulose than CNC. Enzymatic hydrolysis, TEMPO-mediated oxidation, multi-pass high-pressure homogenization, and direct mechanical fibrillation are all methods for producing CNF.

• Bacterial Cellulose (BC): Numerous bacterial taxa, including Acetobacter, Achromobacter, Aerobacter, and Agrobacterium, among others, can manufacture bacterial cellulose (BC). Gluconacetobacter xylinus, formerly known as Acetobacter xylinum, is the most widely used strain of Gram-negative bacteria. The processes of fermentation and purification are crucial in the creation of cellulose made up of bacteria. The bacteria have the freedom to move about freely in the medium or connect to the cellulose fibers throughout the fermentation process, which results in a highly swollen gel structure. BC is an organic substance with the same chemical formula as plant cellulose (C6H10O5)n.