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Polymers come in many forms. Many people know about the synthetic human-made polymers seen in everyday life - commonly in the form of plastic products - but there is also an abundance of natural and biological polymeric materials. Within natural and biological polymers are a specific class known as carbohydrate polymers, and in this article, we’re going to look at some of the applications where carbohydrate polymers are used.
There are many different types of carbohydrate polymers found throughout the body and other biological materials, often in the form of polysaccharides - long chains of cyclic sugar groups connected via an oxygen bridge. Carbohydrates are often disaccharides, which are two cyclic sugar units bonded together, and these carbohydrate molecules can be extended further into polysaccharide biomolecules. These polysaccharides can have very long molecular lengths and are often termed carbohydrate polymers.
While there are many different carbohydrate polymers, they are often grouped into reserve carbohydrate polymers, structural carbohydrate polymers, and protective carbohydrate polymers; depending on the function inside the body that they perform. The most common carbohydrate polymers that are found in nature are cellulose, starch, dextrins and cyclodextrins, chitin and chitosan, hyaluronic acid, and various gums (carrageenan, xanthan, etc.).
Carbohydrate polymers are an environmentally friendly answer to synthetic polymers, have a low cost, are found in abundance, are renewable, and can be easily modified to make materials with superior properties. For these reasons, there has been a lot of interest in recent years around using carbohydrate polymers in various commercial applications.
Below, we’re going to look at some of the more widely used applications of these common carbohydrate polymers, but it is not an exhaustive list.
As carbohydrate polymers are biomolecules found in the body, they have the potential to be excellent drug delivery vessels due to their inherent biocompatibility and ability to be excreted from the body after the drugs have been delivered.
They do have to be modified first, but as a raw starting material, certain materials have great potential, with hyaluronic acid and chitosan leading the way. These materials have been used to create hydrogels, liposomes, microparticles, and granules that can carry a wide range of drugs through dermal and oral delivery routes.
As well as delivering drugs, and still in the medical field, hyaluronic acid has also been used in medical wound dressings.
Carbohydrate polymers have also been touted as a class of molecules that can prevent metals from corroding by acting as a chemical inhibitor. Chemical inhibitors can be used to protect metals against changes in pH, temperature, and moisture, as well as any changes in the device where they are used - such as changes in the electrolyte within a battery system.
Carbohydrate polymers are being trialed over other chemicals because they are less toxic, of lower cost, are less harsh to the environment once used (eco-friendlier), and are readily available. Many carbohydrate polymers have a unique inhibiting mechanism to counteract corrosion, where they have specific absorption centers that can absorb various molecules that would cause the metal to corrode.
The inhibiting center is due to the cyclic rings in the long chains being able to form bonds with the incoming molecules, thus trapping the corrosion-inducing molecules.
Carbohydrate polymers also have potential in heterogeneous catalysis - that is, catalysis where the catalyst is in a different matter state/phase to the reactants, e.g., a solid surface with liquid reactants.
The use of carbohydrate polymers has extended to using starch, cellulose, and chitosan as catalytic surfaces, where the carbohydrate polymers act as a support surface for the reaction to take place on.
There are many reasons for trialing carbohydrate polymers in catalysis applications, including the ease with which the physical and chemical properties can be tuned, the presence of desirable functional groups, low toxicity, and high thermal stability.
Another area of interest is fuel cells. In fuel cell applications, chitosan, starch, cellulose, and glycogen carbohydrate polymer have been used as the starting material in alternative synthetic pathways, to yield new low cost and eco-friendlier polymer electrolytes. In these applications, their aim has not to be more efficient but provide a less toxic and cheaper alternative to the status quo.
Chitosan has also been touted as a material that can be used in the proton-exchange membrane in fuel cells as its physical and chemical properties can be easily modified to fit the requirements required in these membranes, such as low methanol permeability and hydrophobicity.
Sources and Further Reading
- “Recent Developments on the Application of Carbohydrate Polymers”- Olatunde O. C. and Azeez M. A., IOSR Journal of Applied Chemistry, 2018, DOI: 10.9790/5736-1107016880