What is Chitosan ?
Chitosan is a derivative of chitin, a natural polymeric material found in the exoskeletons of crustaceans and insects as well as the cell wall of fungi. Chitin is the second-most abundant natural polymer behind cellulose and is primarily obtained from crustacean shell waste produced by the seafood processing industry. Some manufacturers produce chitosan from mushroom waste.
Chitin is made up of N-acetylglucosamine monomers in a linear chain. To create chitosan, the N-acetyl group is removed, leaving an amine group. Because the process does not convert all chitin monomers, chitosan is made up of randomly distributed N-acetylglucosamine and d-glucosamine monomers.
Chitosan Characteristics and Properties
There are two primary characteristics of chitosan: degree of deacetylation (or acetylation) and molecule, weight. The degree of deacetylation is a measure of the total number of N-acetylglucosamine molecules converted into d-glucosamine molecules expressed as a percentage. The degree of acetylation is a measure of the remaining N-acetylglucosamine after the deacetylation process and is equal to one minus the degree of deacetylation. Typically, the degree of deacetylation ranges from 70% to 90%, with some chitosan products above 90%.
The molecular weight refers to the size of the polymer chain. The higher the molecular weight, the longer the polymer chain. The molecular weight of chitosan is influenced by the extraction of the chitin from its source as well as the deacetylation process.
The most popular property of chitosan is its ability to dissolve in acidic aqueous solutions. That is due to the protonation of the amine group in the d-glucosamine molecule, which creates a positive charge that attracts the negatively charged oxygen atom in water molecules. Chitosan has a pKa of 6.3, so it only requires a very dilute acid solution for it to dissolve. Dilute acetic acid solutions are the most popular solvents, and organic acid solutions in general are good solvents for chitosan.
When in solution, chitosan thickens the liquid due to the large molecular weight of the material, which impedes fluid flow because of its size and molecular interaction. Higher molecular weights increase the solution viscosity. When in solutions, chitosan can be solution-cast into fibers, films, and sheets.
Chitosan is non-toxic, non-hazardous, non-allergenic, and biodegradable. It is biocompatible with humans and is regarded as a material of low concern by the US Environmental Protection Agency. It has been shown to act as an antimicrobial and antifungal agent. Because of its environmentally friendly qualities and its properties, chitosan has been used in a wide range of applications.
Chitosan Applications
Water and Wastewater Treatment
The primary use for chitosan in water and wastewater treatment is as a coagulant or flocculant. Chitosan uses two mechanisms to attract particles in wastewater: entanglement and ionic attraction. The size of the chitosan molecular chain allows the material to entangle particles floating in wastewater. The higher the molecular weight, the greater the number of particles that can be entangled. Particles in wastewater, called colloids, are negatively charged, which allows chitosan to attract the particles to its positively charged amine groups. The greater the number of amine groups in the chitosan polymer chain, the higher the charge density, and the more effective chitosan is at attracting colloids. As chitosan collects colloids, it creates large aggregates that fall out of the solution and can be filtered. Because chitosan is biodegradable, sending the solids to a landfill does not have the same detrimental effect on the environment as using synthetic coagulants and flocculants would.
Chitosan can also be used to remove dyes from wastewater and heavy metals from water and wastewater in a process called chelation.
Agriculture
In agriculture, chitosan has been used as a crop enhancement and antifungal agent. Either sprayed on plants as they were growing or coated onto seeds, the presence of chitosan promoted a healthier and harder plant, which generally resulted in higher crop yields.
Chitosan is an effective antifungal agent. Chitosan is sprayed onto plants, destroying the fungal infection and, through continual treatments, preventing any future fungal growth.
Food preservation and packaging are two areas where chitosan is being considered. Studies have shown that foods coated with chitosan have longer shelf lives.
Cosmetics and Personal Care Products
Recent bans on the use of synthetic chemicals in cosmetics have elevated chitosan to a material of interest, particularly because it is biocompatible and non-allergenic. Chitosan’s positive charge in solution is useful in personal care products, like shampoos, for binding to negatively charged skin cells & hair. Chitosan is often used as a moisturizing agent in lotions and is a featured ingredient in anti-aging skin care products. Its antibacterial properties are useful for protecting the skin and in oral hygienics (toothpaste and mouthwash).
Textiles
Chitosan is used primarily as an antimicrobial agent, either sprayed onto fabric or woven into fibers that are then used to make cloth. Chitosan’s presence in cloth also helps with dye uptake.
Chitosan-impregnated textiles are particularly useful in maintaining cleanliness, such as bedding in hotels, and can be used in medical textile applications, such as personal protection equipment.
Nutraceuticals
Chitosan has been used for many years as a “fat-blocking” supplement. Taken before a meal, chitosan can bind to fat in the stomach, creating an aggregate that is too large to be absorbed in the intestines. Chitosan has also been reported to reduce cholesterol in the bloodstream and lower blood pressure.
Medical/Pharmaceutical
Chitosan’s positive charge allows it to bind to negatively charged blood cells, creating an artificial clot. As a result, chitosan has been used as a hemostatic agent in battlefield dressings and bandages used by emergency medical technicians. It has also been used as an effective burn treatment. Because chitosan is biocompatible and antimicrobial, it has been a material of interest in numerous medical applications worldwide.
In the pharmaceutical field, chitosan is used as a drug delivery agent as well as a material in slow-delivery capsules.
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