There are many substances that can be used as thickeners, including low molecular weight thickeners and high molecular weight thickeners.

Low molecular thickener

1.1.1 Inorganic salts

1.1.2 Fatty alcohols and fatty acids

Fatty alcohols and fatty acids are polar organic substances. Some articles regard them as nonionic surfactants because they have both lipophilic and hydrophilic groups. The existence of a small amount of this kind of organic matter has a significant influence on the surface tension, omc and other properties of surfactants, and its effect increases with the lengthening of carbon chain, generally showing a linear relationship. Its action principle is that fatty alcohol and fatty acid can insert into (participate in) surfactant micelles to promote the formation of micelles. At the same time, due to the strong interaction between the polar organic matter and surfactant molecules (hydrophobic interaction between hydrocarbon chains and hydrogen bonding between polar heads), the two molecules are closely aligned on the surface, which greatly changes the micelle properties of surfactant and achieves thickening effect.

2.1.1 mineral salt

Sodium chloride, potassium chloride, ammonium chloride, monoethanolamine chloride, diethanolamine chloride, sodium sulfate, sodium phosphate, disodium phosphate and pentasodium triphosphate, etc

2.1.2 Fatty alcohols and fatty acids

Lauryl alcohol, myristyl alcohol, C12-15 alcohol, C12-16 alcohol, decanol, hexanol, octanol, cetyl alcohol, stearyl alcohol, behenyl alcohol, lauric acid, C18-36 acid, linoleic acid, linolenic acid, myristic acid, stearic acid, behenic acid, etc

2.1.3 Alkanolamides

Coconut diethanolamide, coconut monoethanolamide, coconut monoethanolamide, cocoamide, lauroyl-myricetin diethanolamide, isostearyl diethanolamide, myricetin diethanolamide, cardamom diethanolamide, cardamom monoethanolamide, oil diethanolamide, palm monoethanolamide, castor oil monoethanolamide, sesame diethanolamide, soybean diethanolamide and stearin Stearate monoethanolamide stearate, stearamide, tallow monoethanolamide, wheat germ diethanolamide, PEG (polyethylene glycol)-March cinnamamide, PEG-4 oleamide, PEG-50 tallow amide, etc

2.1.4 ether

Cetyl alcohol polyoxyethylene (3) ether, isocetyl alcohol polyoxyethylene (10) ether, lauryl alcohol polyoxyethylene (3) ether, lauryl alcohol polyoxyethylene (10) ether, Poloxamer-n (ethoxylated polyoxypropylene ether) (n=105, 124, 185, 237, 238, 238)

2.1.5 esters

2.1.6 amine oxide

Nutmeg amine oxide, isostearylaminopropyl amine oxide, coconut aminopropyl amine oxide, wheat germ aminopropyl amine oxide, soybean aminopropyl amine oxide, PEG-March laurel amine oxide, etc Sexual SAA

Cetace betaine, cocoamino hydroxysulfobetaine, etc.
Anionic SAA

2.4.1 Cellulose

2.4.2 Polyoxyethylene type

PEG-n(n=5M, 9M, 23M, 45M, 90M, 160M), etc

2.4.3 Polyacrylic acids

   
2.4.4 Natural rubber and its modified products

2.4.5 Inorganic polymer and its modifier

2.4.6 other

PVM/MA decadiene cross-linked polymer (cross-linked polymer of polyvinyl methyl ether/methyl acrylate and decadiene), PVP (polyvinyl pyrrolidone), etc
Surfactants.

2.5.1 Alkanolamides

The most commonly used is coconut diethanolamide. Alkanolamide is compatible with electrolyte to thicken and achieve the best effect. Alkanolamide

2.5.2 ether

In the formula with fatty alcohol polyoxyethylene ether sulfate (AES) as the main active substance, only inorganic salts can be used to adjust proper viscosity. The research shows that this is because AES contains unsulfurized fatty alcohol ethoxylate, which makes a significant contribution to the thickening of surfactant solution. In-depth study shows that it has the best effect when the average degree of ethoxylation is about 3EO or 10EO. In addition, the thickening effect of fatty alcohol ethoxylates is closely related to the distribution of unreacted alcohol and homologues in its products. When the distribution of homologues is wide, the thickening effect of products is poor, and the narrower the distribution of homologues, the greater the thickening effect can be obtained.

2.5.3esters

The thickeners most commonly used are esters. Recently, PEG-8PPG-3 diisostearate, PEG-90 diisostearate and PEG-8PPG-3 dilaurate were reported abroad. This kind of thickener belongs to nonionic thickener, which is mainly used in surfactant aqueous solution system. This thickener is not easy to hydrolyze, and its viscosity is stable in a wide range of pH and temperature. PEG-150 distearate is the most commonly used one at present. Esters used as thickeners generally have large relative molecular mass, so they have the properties of some polymer compounds. Thickening mechanism is due to the formation of three-dimensional hydration network in the water phase, thus including surfactant micelles. Besides being used as thickener in cosmetics, these compounds can also be used as emollients and moisturizers.

2.5.4 amine oxide

Amine oxide is a polar nonionic surfactant, which is characterized by its non-ionic and strong ionic properties in aqueous solution due to the different pH values of the solution. Under neutral or alkaline conditions, that is, when pH is greater than or equal to 7, amine oxide exists as non-ionized hydrate in aqueous solution, showing non-ion. In acidic solution, it shows weak cationic property, especially when the pH of solution is less than 3, so it can be well compatible with cationic, anionic, nonionic and zwitterionic surfactants under different conditions and show synergistic effect. Amine oxide is an effective thickener. When pH is 6.4-7.5, alkyl dimethyl amine oxide can make the viscosity of the compound reach 13.5Pa.s-18Pa.s, while alkyl amidopropyl dimethyl amine oxide can make the viscosity of the compound reach 34Pa.s-49Pa.s, and the latter can not reduce the viscosity when adding salt.

2.5.5 other

A few betaines and soaps can also be used as thickeners (see Table 1), and their thickening mechanism is similar to that of other small molecules, and the thickening effect is achieved through the interaction with surface active micelles. Soaps can be used for thickening stick cosmetics, and betaine is mainly used in surfactant water system.

Water-soluble polymer thickener

Many systems thickened by polymer thickeners are not affected by the pH value of solution or electrolyte concentration. In addition, a small amount of polymer thickener is needed to achieve the required viscosity. For example, a product needs 3.0% of surfactant thickener such as coconut diethanolamide, and only 0.5% of cellulose polymer is needed to achieve the same effect. Most water-soluble polymer compounds are used not only as thickeners, but also as suspending agents, dispersants and styling agents in cosmetic industry.

2.6.1 Cellulose

2.6.2 Polyacrylic acids

It has been 40 years since the introduction of Carbomer934 into the market by Coodrich Company in 1953, and now there are more choices for this series of thickeners (see Table 1). There are two thickening mechanisms of polyacrylic acid thickeners, namely neutralization thickening and hydrogen bonding thickening. Neutralization thickening is to neutralize the acidic polyacrylic thickener, ionize its molecules and generate negative charges along the main chain of the polymer, and the repulsion between the same charges promotes the molecules to straighten and open to form a network structure to achieve thickening effect; Hydrogen bonding thickening is that polyacrylic acid thickeners are first combined with water to form hydrated molecules, and then combined with 10%-20% of hydroxyl donors (such as nonionic surfactants with 5 or more ethoxy groups), so that their curled molecules are untied in aqueous system to form a network structure to achieve thickening effect. Different pH values, different neutralizers and the existence of soluble salts have great influence on the viscosity of the thickening system. When pH value is less than 5, the viscosity increases with the increase of pH value; The pH value is 5-10, and the viscosity is almost unchanged; However, with the increase of pH value, the thickening efficiency will decrease again. Monovalent ions only reduce the thickening efficiency of the system, while divalent or trivalent ions can not only dilute the system, but also produce insoluble precipitates when the content is sufficient.

2.6.3 Natural rubber and its modified products

Natural rubber mainly includes collagen and polysaccharide, but natural rubber as thickener is mainly polysaccharide (see Table 1). Thickening mechanism is that three hydroxyl groups in polysaccharide interact with water molecules to form a three-dimensional hydration network structure, thus achieving thickening effect. Most of their aqueous solutions are non-Newtonian fluids, but some dilute solutions have rheological properties close to Newtonian fluids. Their thickening effect is generally related to the pH value, temperature, concentration of the system and the existence of other solutes. They are very effective thickeners, with a general dosage of 0.1%-1.0%.

2.6.4 Inorganic polymer and its modifier

Inorganic polymer thickeners generally have a three-layer structure or an expanded lattice structure, and the two most commercially used types are montmorillonite and hydrosulfite. The thickening mechanism is that when the inorganic polymer is dispersed in water, the metal ions in it diffuse from the wafer, and with the hydration, it swells, and finally the lamellae are completely separated, resulting in the formation of a transparent colloidal suspension of anionic lamellar lamellae and metal ions. In this case, the lamellae have negative charge on the surface, and the corners of the lamellae have a little positive charge due to the lattice fracture surface. In dilute solution, the negative charge on the surface is larger than the positive charge on the corner, and the particles repel each other, so there is no thickening effect. With the addition of electrolyte and the increase of concentration, the ion concentration in solution increases, and the surface charge of platelets decreases. At this time, the main interaction changes from the repulsive force between lamellae to the attractive force between the negative charge on the surface of lamellae and the positive charge on the corner, and the parallel lamellae cross-link together vertically to form a so-called "carton-type compartment" structure, which causes swelling and gelation to achieve the thickening effect. The further increase of ion concentration will destroy the structure and cause flocculation, resulting in the decrease of consistency. This thickener is mainly used for thickening toothpaste, shampoo, conditioner, cream, lotion and antiperspirant. Generally, the consistency increases rapidly with the increase of concentration and then tends to be flat, and the rheological morphology is thixotropy. Besides thickening property, it also has the functions of stabilizing emulsion and suspending in the system. The modified product is mainly quaternized, which has lipophilicity after modification and can be used in systems with high oil content.

2.6.5 Polyoxyethylene type

Generally, products with a relative molecular weight greater than 25 000 are called polyoxyethylene, while those with a relative molecular weight less than 25 000 are called polyethylene glycol. The aqueous solution of polyoxyethylene is pseudoplastic fluid when its mass fraction is a few percent, and its aqueous solution tends to be sticky. For example, the object immersed in it is pulled out of the solution to form long drawing and film formation. The viscosity of polyoxyethylene with low molecular weight and narrow molecular weight distribution is lower, and the viscosity of its aqueous solution depends on the relative molecular weight, concentration, temperature and shear rate when measuring viscosity. The viscosity of its solution increases with the increase of molecular weight and concentration, and decreases sharply with the increase of temperature (10℃ ~ 90℃). The pseudoplasticity of polyoxyethylene aqueous solution decreases with the decrease of relative molecular weight, and the rheological property of aqueous solution with relative molecular weight lXl05 is close to Newtonian fluid. The thickening effect comes from the dissolution of polymer chains into surfactant system, and the thickening mechanism is mainly related to polymer chains, and does not depend on surfactant system. Under the action of ultraviolet rays, strong acids and transition metal ions (especially Fe3+, Cr3+ and Ni2+), the aqueous solution of polyoxyethylene will automatically oxidize and degrade, and lose its viscosity.