Share this article: All natural, aqueous-based polymeric thickeners are derived from polys
All natural, aqueous-based polymeric thickeners are derived from polysaccharides with the most common being sourced from cellulose (wood, cotton) and starch (corn, potato). Other important polysaccharide sources include seaweed, plant seeds/roots, and those derived from fermentation. Most natural-based thickeners are either soluble or swellable polymers that bind or immobilize water to create structure or viscosity.
Cellulosics are the most commercially important and diverse class of natural-based thickeners with numerous anionic, cationic, and nonionic versions available. All derivatives are produced by first solubilizing cellulose with sodium hydroxide and then reacting with the functionalizing chemical.
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Carboxymethylcellulose (CMC) is one of the most important and cost effective natural-based thickeners on the market. It is an anionic polymer produced by reacting alkali cellulose with chloroacetic acid. Key properties are determined by the MW of the cellulose (high-700K, medium 250K, low-90K) and the degree of carboxylation per glucose molecule (DS-theoretical is 3). CMC can be either a soluble or swollen polymer or a combination depending on the MW and DS. Salt sensitivity is reduced using a low MW and high DS grade. The most thixotropic, viscous grades have a high MW and low DS.
Nonionic grades are produced by reacting alkali cellulose with ethylene oxide (hydroxyethylcellulose) or propylene oxide (hydroxypropylcellulose). Hydroxypropylmethylcellulose is made by first reacting the alkali cellulose with methyl chloride and then propylene oxide. Nonionic cellulosics are useful in formulations because they have excellent cationic, salt, PH tolerance and solvent tolerance. Some, like hydroxypropylcellulose, are also good thickeners for solvents like ethanol.
Starch derivatives are not commonly used in personal care. Many have poor viscosity stability over time. Hydroxypropyl starch phosphate is the only significant starch derivative used.
Xanthan is an anionic, fermentation-derived, polysaccharide that is widely used in cosmetics. Xanthan has an MW of 2-3 million Daltons and forms a double helical structure in most ionic solutions. Xanthan was discovered by the United States Department of Agriculture and commercialized in 1964 by CP Kelco. The key benefits of Xanthan include good salt/PH tolerance, high viscosity at low concentration, and the ability to maintain its viscosity profile at elevated temperatures.
Carrageenan is the most important seaweed-derived thickener used in personal care products. It is a sulfated, anionic polysaccharide that exists in three forms; Kappa, which has 1 sulfate group per galactose molecule, Iota- 2 sulfate groups, and Lamba-3 sulfate groups. Only the Iota form is widely used as a thickener.
Plant seed/root-based thickeners are widely used in foods but not in personal care formulations. The most significant materials are konjac mannan, locust bean, guar, and tara gum. These are galactomannans that react synergistically to build viscosity when combined with xanthan.
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