Xanthan gum is found in many products, including food items, cosmetics and personal care products. It also appears in many shampoos, conditioners and styling agents. Its current popularity can in part be attributed to its plant-based origins and biodegradability. Home-based kitchen chemists who formulate their own products have found it to be a useful and easy-to-use additive for hair gels and conditioners.
What exactly is this material, though? Its name does not reveal much information regarding its chemical nature or its purpose in a product.
Xanthan Gum's Chemical Structure
Xanthan gum is a naturally derived polymeric carbohydrate (polysaccharide) with a very high molecular weight (in the millions of grams per mole). It is obtained via a fermentation process utilizing the bacterium Xanthomonas campestris, which can be obtained from a variety of plant-based sources.
The polymer backbone is comprised of repeating units of a simple sugar molecule (beta – (1,4) D-glucose), and the side chains pendant to the backbone are trisaccharides, made up of alpha-D-mannose, beta-D-glucoronic acid, and beta-D-mannose paired with a pyruvate group. The side chains possess an anionic (negative) charge, and they make up the bulk of the weight of the polymer, and thus contribute the majority of the properties for which Xanthan gum is prized.
Xanthan Gum's Physical Properties
Xanthan gum is readily soluble in either hot or cold water. It is generally unaffected by pH, is very tolerant of electrolytes, and is stable over a wide range of temperatures. These properties make it extremely easy to work with both in formulation and production.
Xanthan gum is most often used for its unique rheological (affecting the flow of the liquid) properties. In both neutral and charged solutions, it imparts higher viscosity to the formula, making it thicker and more resistant to flow. In a neutral solution, the polymer molecules are in the random coil state, and thickening is achieved primarily via chain entanglements between the very long polymers. Imagine a mass of spaghetti noodles all piled together in a bowl and how they all become intertwined with one another.
In solutions containing electrolytes, the polymer molecules collapse and form somewhat rigid helical rods that can pack together and form gel networks via hydrogen bonding. Polymers that form gels when mixed with water like this are called hydrocolloids. These gels are stable over a wide range of temperatures. Also, since the polymers are completely soluble in the aqueous solution, the subsequent gels formed are very clear, which is a highly desirable property in the styling product market.
Hydrocolloid gels made with xanthan gum are pseudoplastic materials, meaning that the viscosity of these solutions undergoes shear thinning (decreases) when a shear force is applied. This makes it easier for the fluid to move or flow when it is shaken, stirred, or squeezed. What happens is that the forces break down the gel network so that the individual polymer molecules can slide past one another.
This is a great advantage both for processing the materials as well as for application as a finished good. Shear thinning reduces the effort required to squeeze or pump gel or lotion out of a bottle or toothpaste from a tube, which renders it easily applied to hair, skin, or a toothbrush. Once the shear force is removed, the gel network re-forms and the viscosity builds up again. This makes xanthan gum an excellent emulsion stabilizer also.