Cellulose molecule is one type of complex organic bio-compound that is very much found in nature. It is an important polysaccharide containing hundreds to thousands of glucose molecules which are linked together to form a chain. This biopolymer is abundantly present in living species that use cellulose as a reinforcement material.
Cellulose molecule Definition
Cellulose is a linear chain of glucose molecules ((C6H10O5)n where n=10,000 to 15,000. These are linked together through an acetal oxygen-covalently bonding C1 of one glucose ring and C4 of the adjoining ring. The hydrogen bonds in multiple cellulose chains are bonded to each other forming elementary fibrils, which collect into microfibrils that are 5-50 nm in diameter. Cellulose contains fibril regions that are disordered (amorphous-like) and highly ordered (crystalline).
Cellulose Sources
Cellulose molecules can be found mostly in cotton, jute, wood, grass, flax, hemp, sisal, jute, kenaf, ramie, straw, and bamboo.
Cellulose Types
Cellulose molecule is generally four types namely cellulose I, II, III, and IV. Cellulose I is found in nature which is also known as natural cellulose. Cellulose II is very much thermodynamically stable which is found in antiparallel strains connected by hydrogen bonding.
Cellulose structure
The cellulose molecule has β-(1 → 4)-glycosidically linked among AGU (anhydroglucose units). These AGU units are shown as d-glucopyranose ring in 4C1 chair configuration. The β-glycosidic linkage creates in a turning around of the cellulose molecule chain axis of each second anhydroglucose unit by 180°. It is measured that the length of the repeating unit of cellulose is 1.3 nm.
The anhydroglucose unit consists of three reactive hydroxyl groups. Among these groups, one is located at primary (position 6), and two secondary ones (positions 2 and 3). The reactive hydroxyl groups are positioned in the plane of the ring consisting of the anomeric carbon atom involved in the glycosidic linkage, whereas the other one consists of the d-glucopyranose unit in the semiacetal form. This form is in equilibrium with the aldehyde group.
Cellulose derivatives
There are various cellulose derivatives namely cellulose acetate, methylcellulose, hydroxypropyl cellulose, and carboxymethyl cellulose (CMC).
Cellulose acetate
It was first discovered by Paul Schützenberger in 1865. Cellulose acetate can be obtained from different natural sources, like wood and cotton. Cellulose acetate has been considered a completely environmentally friendly resin in recent years. It is highly safe for living organisms. It contains flame retardant properties and also has a high melting point so that it melts and is carbonized at 230 to 300℃.
This important cellulose derivative is stable against organic and inorganic weak acids, animal and vegetable oils, gasoline, etc. This versatile compound has low electrical conductivity and large internal and external resistance. Cellulose acetate is very much used to make fabrics molded products, coating film, paints, etc. Cellulose acetate has high resistance to sunlight and do not easily undergo degradation.
Nitrocellulose
Nitrocellulose is a very common cellulose derivative which is a mixture of nitric esters of cellulose. It is produced by the mixture of nitric esters of cellulose. It contains nitro-nitro-functional groups and shows various important characteristics. It has higher flammable characteristics and is used as the main ingredient of modern gunpowder. This cellulose derivative is used in certain lacquers and paints.
Nitrocellulose was first synthesized in 1845 by Schonbein. It is synthesized by mixing of nitric acid and sulfuric acid with cellulose molecules. This important cellulose derivative is a nitrate ester, not a nitro compound. The three OH groups of cellulose molecules can be converted into mono-nitrocellulose, di-nitrocellulose, and nitrocellulose after treating the cellulose molecule with nitric acid.
Cellulose nitrate or nitrocellulose does not aggregate by hydrogen bonding because they have fewer OH groups than cellulose molecules. Cellulose nitrate can be dissolved into many organic solvents. Di-nitrocellulose is commonly used to make most lacquers, but trinitrate is used to make explosives.
Carboxymethyl cellulose (CMC)
Carboxymethyl cellulose or CMC is a common cellulosic derivative consisting of some of the hydroxyl groups of the glucopyranose monomers that make up the cellulose backbone. It contains the carboxymethyl groups (–CH2–COOH). CMC is considered a water-soluble cellulose derivative which is an anionic.
The solubility of this compound depends on the degree of polymerization as well as the degree of substitution and the uniformity of the substitution distribution. The water solubility of this compound increases with a decreased degree of polymerization and increased carboxymethyl substitution and substitution uniformity. The viscosity properties of CMC increase with increasing degree of polymerization and increasing concentration.
It is soluble in water molecules at any temperature for has a highly hygroscopic nature. CMC hydrates rapidly and may create agglomeration and lump formation. This lump formation can be removed by adding other dry ingredients such as sugar before adding into the water and by applying high agitation while the powder is added to the water.
Carboxymethyl cellulose has higher solubility and clarity. So, it can be used in beverages and beverage dry mixes to provide a rich mouthfeel. CMC is also used in acidified protein drinks to stabilize the protein. It can be added into syrup and sauce formulations to increase viscosity. CMC is used in Bakery to improve the quality and the consistency of the end product. CMC is also used to improve the processability of the dough and to increase foldability, rollability, and textural properties at the time of making tortilla bread.
Methylcellulose
Methyl cellulose is an important cellulose derivative that is used as a thickener and emulsifier in various food and cosmetic products. It is not digestible, non-toxic, and not an allergen as like cellulose molecules. Methyl cellulose is used in arts and crafts such as in paper machines.
Methyl cellulose can be synthesized by heating cellulose with a caustic solution and treating it with methyl chloride. The hydroxyl residues (-OH functional groups) are replaced by methoxide (-OCH3 groups) during the substitution reaction and produce methylcellulose.
Methyl cellulose consists of numerous linked glucose molecules, each of which exposes three hydroxyl groups. It contains a lower critical solution temperature lies between 40 °C and 50 °C. Methyl cellulose can be dissolved in water above the lower critical solution temperature. The higher degree of substitution value of this compound gives lower solubility and lower precipitation temperatures for having the polar hydroxyl groups masked.
Methylcellulose molecule is a hydrophilic compound that contains white powder in pure form and dissolves easily in cold (but not in hot) water. It forms a clear viscous type solution or gel.
Methylcellulose compound is used in the medical field for treating constipation matter. This compound can be taken by mouth and is recommended with sufficient water for removing constipation.
Methylcellulose contains lubricating properties and has various benefits in the treatment of dry eyes. The solution containing methylcellulose or similar cellulose derivatives is used as a substitute for tears or saliva. It is very much used to make drug capsules that are edible and contain nontoxic properties. It is added to make hair shampoos, toothpaste, and liquid soaps to get a thick consistency. It can also be used to make ice cream or croquettes to give the properties of a thick consistency.
It can be used as a personal lubricant. Methyl cellulose is also used to make various construction materials for having the properties of workability, open and adjustment time, water retention, viscosity, adhesion to surfaces, etc. It is used to make mild glue which can be washed away with water. This compound can be added to paint to prevent ‘sagging’. Methyl cellulose is used to manufacture papers and textiles as it protects the fibers from absorbing water or oil.
Cellulose solubility
Cellulose molecule is insoluble in water. It can be dissolved in various ionic liquids which are considered environmentally friendly solvents, and some of them dissolve cellulose because they have lower toxic characteristics, good thermal stability, are recyclable, and promote dissolvability for cellulosic particles. There are various ionic liquids like NaOH/thiourea, LiOH/urea, 1-butyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium chloride, NaOH-urea are able to properly dissolve cellulose.
An organic solvent N-methylmorpholine-N-oxide monohydratehas also been used to dissolve cellulose. Another organic solvent NMMO is a nontoxic solventcan be recycled after dissolution.
Mechanical properties of cellulose
The various composites and cellulose molecule-based materials show impressive high-performance mechanical and functional properties. They show higher intrinsic stiffness and strength that exhibit extraordinary mechanical properties. Cellulose-based materials and composites have higher specific modulus and strength. The crystalline cellulose I along the cellulose chain contains 124–155 GPaelastic modulus.
Hygroscopic properties of cellulose molecule
Cellulose molecules and their derivatives have intrinsic hygroscopic properties due to the tendency to form hydrogen bonds with water. The water molecule easily attracts the internal structure of cellulose for having hygroscopic characteristics. The molecules of cellulose swell and lead to make cellulose-based hybrid and composite materials.
Cellulose Toxicity
Cellulose molecule has no or low toxicity. The surface modification of this compound, hydrophilization, hydrophobization, and aggregation might influence cellulose-based materials’ cytotoxicity and biocompatibility.
Applications of cellulose
Cellulose molecule is used in food industries, paper industries, textile industries, medical industries, cosmetics industries, defense industries, etc.
Cellulose in the food industries
Cellulose molecule has been used very much in food industries in production processes. It is used as a thickener and stabilizer, also known as E460. It can be used as an additive and can be found in instant dishes, wheat rolls, jams, creams, sauces, etc. It can be used in dietetic foods and specialist food supplements like yogurt, smoothies, and soups. This compound can also be used for the production of sausages and cooked or smoked cold cuts.
Cellulose in pharmaceutical industries
Cellulose molecule is used in pharmaceutical industries for making the media of drug delivery system, antibacterial packaging, various wound dressing, etc.
Cellulose in textile industries
Cellulose molecule is used in textile industries to make high-quality fiber, and cellulose derivatives like cellulose acetate, nitrocellulose, methyl cellulose, etc.
Cellulose in paper industries
Cellulose molecule is widely used in paper industries to make paper, paperboard, and various types paper paper-making materials.
The importance of cellulose
Cellulose molecule is very stable and flexible. So it can be used as the raw material in the paper industry. It is very much used to make paper, cardboard, packaging, and hygiene products (toilet paper, cleaning cloths, kitchen towels.
Cellulose molecule is used in pharmaceutical industries to make coatings/shells of tablets, capsules, powders, etc. This biopolymer molecule is also used to make medical dressings.
Cellulose molecule is used in textile industries to make various types of artificial silk and cotton-like and wool-like fibers.
Cellulose molecule is the raw material for the production of explosives and projectile propellants in the arms industry.
Cellulose molecule is used to make various biofuel derived from plant waste, wood residues, and straw.
