There are many substances that can act as thickeners, with about 40 commonly used thickeners. The current national standard "GB 2760-2014 National Food Standard Food Additive Use Standards" includes a total of 55 thickeners, which can be classified in various ways.

There are many substances that can act as thickeners, with about 40 commonly used thickeners. The current national standard "GB 2760-2014 National Food Safety Standard for Food Additives" includes 55 types of thickeners, which can be classified in various ways.

According to the chemical structure and composition of thickeners, they can be divided into two main categories: polysaccharides and polypeptides. Among them, polysaccharide thickeners include starches, celluloses, pectins, alginates, etc., which are widely distributed in nature. Polypeptide thickeners mainly include gelatin, sodium caseinate, and casein, which have limited sources, higher prices, and less application.

Thickeners can also be classified into two main categories based on their ionic properties: ionic thickeners, such as alginates, sodium carboxymethyl cellulose, and starch; and non-ionic thickeners, such as sodium propylene glycol alginate and hydroxypropyl starch.

Based on the source of thickeners, they can be divided into natural thickeners and synthetic thickeners. Among them, natural thickeners can be further divided into four categories: animal-based thickeners (gelatin, sodium caseinate, etc.), plant-based thickeners (guar gum, gum arabic, pectin, agar, carrageenan, etc.), microbial thickeners (xanthan gum, gellan gum, etc.), and enzyme-treated thickeners (enzyme-hydrolyzed guar gum, enzyme-treated starch, etc.). Synthetic thickeners mainly include modified starch, modified cellulose, propylene glycol alginate, and xanthan gum.

According to the relative molecular weight of thickeners, there are low molecular weight thickeners and high molecular weight thickeners: among them, low molecular weight thickeners and high molecular weight thickeners can also be further classified based on the functional groups contained in their molecules, mainly including inorganic thickeners, cellulose types, fatty alcohols, fatty acids, ethers, polyacrylate, and associative polyurethane thickeners, etc. Below, thickeners will be introduced one by one according to their relative molecular weight.

Low molecular weight thickeners
(1) Inorganic salt thickeners
Thickening systems using inorganic salts (such as sodium chloride, potassium chloride, ammonium chloride, monoethanolamine chloride, diethanolamine chloride, sodium sulfate, sodium phosphate, disodium phosphate, and sodium tripolyphosphate, etc.) are generally surfactant aqueous solution systems, with sodium chloride being a commonly used inorganic salt thickener that has a significant thickening effect.
(2) Fatty alcohol and fatty acid thickeners
Fatty alcohols and fatty acids (such as lauryl alcohol, myristyl alcohol, decanol, hexanol, octanol, cetyl alcohol, stearyl alcohol, behenyl alcohol, lauric acid, linoleic acid, linolenic acid, myristic acid, stearic acid, etc.) are polar organic compounds that can be regarded as non-ionic surfactants, having both lipophilic and hydrophilic groups. The presence of a small amount of these organic compounds significantly affects the surface tension and other properties of surfactants, with the effect increasing as the carbon chain lengthens, generally showing a linear relationship.
(3) Alkanolamide thickeners
Alkanolamides can thicken in the presence of electrolytes and achieve good results. Different alkanolamides have significant differences in performance, with coconut diethanolamide being commonly used. The effects differ when used alone and in combination. A drawback of these thickeners is that impurities in alkanolamides contain free amines, which are potential sources of nitrosamines.
(4) Ether thickeners
This type of thickener belongs to non-ionic thickeners, generally based on fatty alcohol polyoxyethylene ether sulfates (AES). Usually, only inorganic salts can adjust to a suitable viscosity. Additionally, the thickening effect is greatly related to the distribution of unreacted alcohols and homologs in the product. The narrower the distribution of homologs, the greater the thickening effect.
(5) Ester thickeners
This type of thickener also belongs to non-ionic thickeners, mainly used in surfactant aqueous solution systems. Its advantage is that it is not easily hydrolyzed and maintains stable viscosity over a wide pH and temperature range. Currently, PEG-150 distearate is commonly used.
(6) Oxidized amine thickeners
Oxidized amines are polar non-ionic surfactants that have thickening effects. Their characteristics are: under neutral or alkaline conditions, oxidized amines exist in aqueous solutions as non-dissociated hydrates, showing non-ionic properties; in acidic solutions, they exhibit weak cationic properties. When the solution pH < 3, the cationic nature of oxidized amines is particularly evident. Therefore, they can be well compatible with cationic, anionic, non-ionic, and amphoteric surfactants under different conditions, showing synergistic effects. Oxidized amines are commonly used as thickeners in cosmetics.
(7) Other thickeners
A few betaines and saponins can also act as thickeners, with saponins used for thickening in stick cosmetics, and betaines mainly used in surfactant aqueous systems.
High molecular weight thickeners
(1) Inorganic thickeners
Inorganic thickeners are a class of water-absorbing, swelling, and thixotropic gel minerals. The main types include bentonite, attapulgite, and aluminum silicate, among which bentonite is commonly used. Currently, research is being conducted on synthesizing thickeners by compounding inorganic materials with other substances, such as M Chtourou and others studying the synthesis of thickeners using organic derivatives of ammonium salts and montmorillonite-like Tunisian clay, with significant progress.
(2) Cellulose thickeners
The use of cellulose-based thickeners has a long history and there are many varieties, including methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose, which are widely used in various fields. Cellulose-based thickeners thicken through the hydration and expansion of long chains, exhibiting significant pseudoplastic rheological behavior.
(3) Polyacrylic Acid Thickeners
Polyacrylic acid thickeners are anionic thickeners and are currently widely used synthetic thickeners, especially in dyeing and printing. They are generally formed by the polymerization of three or more monomers, with the main monomer typically being a carboxylic acid monomer, such as acrylic acid, maleic acid or maleic anhydride, and methacrylic acid; the second monomer is usually an acrylate or styrene; the third monomer is a crosslinking monomer, such as N,N-methylene bisacrylamide, butyl diacrylate, or diacrylate of phthalic acid.
(4) Polyurethane Thickeners
Polyurethane, fully known as polyurethanes, are high molecular compounds containing the —NHCOO— unit in their molecular structure. They can be synthesized from diisocyanates and polyethylene glycol in the presence of end-capping agents. Polyurethane thickeners are newly developed associative thickeners in recent years, characterized by relatively low molecular weight and water-soluble properties. Their molecular structure contains both hydrophilic and lipophilic parts, exhibiting certain surface activity.
(5) Natural Gum Thickeners
Natural gums mainly include collagen and polysaccharides, but the natural gums used as thickeners are mainly polysaccharides.
(6) Polyethylene Oxide Thickeners
Products with a relative molecular mass >2.5×10^4 are referred to as polyethylene oxide, while those <2.5×10^4 are called polyethylene glycol. The thickening mechanism is mainly related to the polymer chain of the high molecular weight polymer. The aqueous solution of polyethylene oxide will automatically oxidize and degrade under the action of ultraviolet light, strong acids, and transition metal ions (especially Fe3+, Cr3+, and Ni2+), losing its viscosity.
(7) Other thickeners
PVM/MA deca-2-ene crosslinked polymer (crosslinked polymer of polyethylene methyl ether/methyl acrylate and deca-2-ene) is a new family of thickeners that can be formulated into transparent gel, spray gel, and latex, and can be used to thicken alcohol solutions, glycerin, and other non-aqueous systems.