Thickeners are the skeleton structure and core foundation of various cosmetic formulations, and are crucial to the appearance, rheological properties, stability, and skin feel of products. Select commonly used and representative different types of thickeners, prepare them into aqueous solutions with different concentrations, test their physical and chemical properties such as viscosity and pH, and use quantitative descriptive analysis to check their appearance, transparency, and multiple skin sensations during and after use. Sensory tests were carried out on the indicators, and the literature was searched to summarize and summarize various types of thickeners, which can provide a certain reference for cosmetic formula design.

1. Description of thickener

There are many substances that can be used as thickeners. From the perspective of relative molecular weight, there are low-molecular thickeners and high-molecular thickeners; from the perspective of functional groups, there are electrolytes, alcohols, amides, carboxylic acids and esters, etc. Wait. Thickeners are classified according to the classification method of cosmetic raw materials.

1. Low molecular weight thickener

1.1.1 Inorganic salts

The system that uses inorganic salt as a thickener is generally a surfactant aqueous solution system. The most commonly used inorganic salt thickener is sodium chloride, which has an obvious thickening effect. Surfactants form micelles in aqueous solution, and the presence of electrolytes increases the number of associations of micelles, leading to the transformation of spherical micelles into rod-shaped micelles, increasing the resistance to movement, and thus increasing the viscosity of the system. However, when the electrolyte is excessive, it will affect the micellar structure, reduce the movement resistance, and reduce the viscosity of the system, which is the so-called “salting out”. Therefore, the amount of electrolyte added is generally 1%-2% by mass, and it works together with other types of thickeners to make the system more stable.

1.1.2 Fatty alcohols, fatty acids

Fatty alcohols and fatty acids are polar organic substances. Some articles regard them as nonionic surfactants because they have both lipophilic groups and hydrophilic groups. The existence of a small amount of such organic substances has a significant impact on the surface tension, omc and other properties of the surfactant, and the size of the effect increases with the length of the carbon chain, generally in a linear relationship. Its principle of action is that fatty alcohols and fatty acids can insert (join) surfactant micelles to promote the formation of micelles. The effect of hydrogen bonding between the polar heads) makes the two molecules arranged closely on the surface, which greatly changes the properties of the surfactant micelles and achieves the effect of thickening.

2. Classification of thickeners

2.1 Non-ionic surfactants

2.1.1 Inorganic salts

Sodium chloride, potassium chloride, ammonium chloride, monoethanolamine chloride, diethanolamine chloride, sodium sulfate, trisodium phosphate, disodium hydrogen phosphate and sodium tripolyphosphate, etc.;

2.1.2 Fatty alcohols and fatty acids

Lauryl Alcohol, Myristyl Alcohol, C12-15 Alcohol, C12-16 Alcohol, Decyl Alcohol, Hexyl Alcohol, Octyl Alcohol, 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

Coco Diethanolamide, Coco Monoethanolamide, Coco Monoisopropanolamide, Cocamide, Lauroyl-Linoleoyl Diethanolamide, Lauroyl-Myristoyl Diethanolamide, Isostearyl Diethanolamide, Linoleic Diethanolamide, Cardamom Diethanolamide, Cardamom Monoethanolamide, Oil Diethanolamide, Palm Monoethanolamide, Castor Oil Monoethanolamide, Sesame Diethanolamide, Soybean Diethanolamide, Stearyl Diethanolamide, Stearin Monoethanolamide, stearyl monoethanolamide stearate, stearamide, tallow monoethanolamide, wheat germ diethanolamide, PEG (polyethylene glycol)-3 lauramide, PEG-4 oleamide, PEG-50 tallow amide, etc.;

2.1.4 Ethers

Cetyl polyoxyethylene (3) ether, isocetyl polyoxyethylene (10) ether, lauryl polyoxyethylene (3) ether, lauryl polyoxyethylene (10) ether, Poloxamer-n (ethoxylated Polyoxypropylene ether) (n=105, 124, 185, 237, 238, 338, 407), etc.;

2.1.5 Esters

PEG-80 Glyceryl Tallow Ester, PEC-8PPG (Polypropylene Glycol)-3 Diisostearate, PEG-200 Hydrogenated Glyceryl Palmitate, PEG-n (n=6, 8, 12) Beeswax, PEG -4 isostearate, PEG-n (n=3, 4, 8, 150) distearate, PEG-18 glyceryl oleate/cocoate, PEG-8 dioleate, PEG-200 Glyceryl Stearate, PEG-n (n=28, 200) Glyceryl Shea Butter, PEG-7 Hydrogenated Castor Oil, PEG-40 Jojoba Oil, PEG-2 Laurate, PEG-120 Methyl glucose dioleate, PEG-150 pentaerythritol stearate, PEG-55 propylene glycol oleate, PEG-160 sorbitan triisostearate, PEG-n (n=8, 75, 100) Stearate, PEG-150/Decyl/SMDI Copolymer (Polyethylene Glycol-150/Decyl/Methacrylate Copolymer), PEG-150/Stearyl/SMDI Copolymer, PEG- 90. Isostearate, PEG-8PPG-3 Dilaurate, Cetyl Myristate, Cetyl Palmitate, C18-36 Ethylene Glycol Acid, Pentaerythritol Stearate, Pentaerythritol Behenate , propylene glycol stearate, behenyl ester, cetyl ester, glyceryl tribehenate, glyceryl trihydroxystearate, etc.;

2.1.6 Amine oxides

Myristyl amine oxide, isostearyl aminopropyl amine oxide, coconut oil aminopropyl amine oxide, wheat germ aminopropyl amine oxide, soybean aminopropyl amine oxide, PEG-3 lauryl amine oxide, etc.;

2.2 Amphoteric surfactants

Cetyl Betaine, Coco Aminosulfobetaine, etc.;

2.3 Anionic surfactants

Potassium oleate, potassium stearate, etc.;

2.4 Water-soluble polymers

2.4.1 Cellulose

Cellulose, cellulose gum, carboxymethyl hydroxyethyl cellulose, cetyl hydroxyethyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, formazan Base cellulose, carboxymethyl cellulose, etc.;

2.4.2 Polyoxyethylene

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

2.4.3 Polyacrylic acid

Acrylates/C10-30 Alkyl Acrylate Crosspolymer, Acrylates/Cetyl Ethoxy(20) Itaconate Copolymer, Acrylates/Cetyl Ethoxy(20) Methyl Acrylates Copolymer, Acrylates/Tetradecyl Ethoxy(25) Acrylate Copolymer, Acrylates/Octadecyl Ethoxyl(20) Itaconate Copolymer, Acrylates/Octadecane Ethoxy(20) Methacrylate Copolymer, Acrylate/Ocaryl Ethoxy(50) Acrylate Copolymer, Acrylate/VA Crosspolymer, PAA (Polyacrylic Acid), Sodium Acrylate/ Vinyl isodecanoate crosslinked polymer, Carbomer (polyacrylic acid) and its sodium salt, etc.;

2.4.4 Natural rubber and its modified products

Alginic acid and its (ammonium, calcium, potassium) salts, pectin, sodium hyaluronate, guar gum, cationic guar gum, hydroxypropyl guar gum, tragacanth gum, carrageenan and its (calcium, sodium ) salt, xanthan gum, sclerotin gum, etc.;

2.4.5 Inorganic polymers and their modified products

Magnesium aluminum silicate, silica, sodium magnesium silicate, hydrated silica, montmorillonite, sodium lithium magnesium silicate, hectorite, stearyl ammonium montmorillonite, stearyl ammonium hectorite, quaternary ammonium salt -90 montmorillonite, quaternary ammonium -18 montmorillonite, quaternary ammonium -18 hectorite, etc.;

2.4.6 Others

PVM/MA decadiene crosslinked polymer (crosslinked polymer of polyvinyl methyl ether/methyl acrylate and decadiene), PVP (polyvinylpyrrolidone), etc.;

2.5 Surfactants

2.5.1 Alkanolamides

The most commonly used is coconut diethanolamide. Alkanolamides are compatible with electrolytes for thickening and give the best results. The thickening mechanism of alkanolamides is the interaction with anionic surfactant micelles to form non-Newtonian fluids. Various alkanolamides have great differences in performance, and their effects are also different when used alone or in combination. Some articles report the thickening and foaming properties of different alkanolamides. Recently, it has been reported that alkanolamides have the potential hazard of producing carcinogenic nitrosamines when they are made into cosmetics. Among the impurities of alkanolamides are free amines, which are potential sources of nitrosamines. There is currently no official opinion from the personal care industry on whether to ban alkanolamides in cosmetics.

2.5.2 Ethers

In the formulation with fatty alcohol polyoxyethylene ether sodium sulfate (AES) as the main active substance, generally only inorganic salts can be used to adjust the appropriate viscosity. Studies have shown that this is due to the presence of unsulfated fatty alcohol ethoxylates in AES, which contribute significantly to the thickening of the surfactant solution. In-depth research found that: the average degree of ethoxylation is about 3EO or 10EO to play the best role. In addition, the thickening effect of fatty alcohol ethoxylates has a lot to do with the distribution width of unreacted alcohols and homologues contained in their products. When the distribution of homologs is wider, the thickening effect of the product is poor, and the narrower the distribution of homologues, the greater the thickening effect can be obtained.

2.5.3 Esters

The most commonly used thickeners are esters. Recently, PEG-8PPG-3 diisostearate, PEG-90 diisostearate and PEG-8PPG-3 dilaurate have been reported abroad. This kind of thickener belongs to non-ionic thickener, mainly used in surfactant aqueous solution system. These thickeners are not easily hydrolyzed and have stable viscosity over a wide range of pH and temperature. Currently the most commonly used is PEG-150 distearate. The esters used as thickeners generally have relatively large molecular weights, so they have some properties of polymer compounds. The thickening mechanism is due to the formation of a three-dimensional hydration network in the aqueous phase, thereby incorporating surfactant micelles. Such compounds act as emollients and moisturizers in addition to their use as thickeners in cosmetics.

2.5.4 Amine oxides

Amine oxide is a kind of polar non-ionic surfactant, which is characterized by: in aqueous solution, due to the difference of the pH value of the solution, it shows non-ionic properties, and can also show strong ionic properties. Under neutral or alkaline conditions, that is, when the pH is greater than or equal to 7, amine oxide exists as a non-ionized hydrate in aqueous solution, showing non-ionicity. In acidic solution, it shows weak cationicity. When the pH of the solution is less than 3, the cationicity of amine oxide is particularly obvious, so it can work well with cationic, anionic, nonionic and zwitterionic surfactants under different conditions. Good compatibility and show synergistic effect. Amine oxide is an effective thickener. When the 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 oxide Amines can make the compound viscosity up to 34Pa.s-49Pa.s, and adding salt to the latter will not reduce the viscosity.

2.5.5 Others

A few betaines and soaps can also be used as thickeners. Their thickening mechanism is similar to that of other small molecules, and they all achieve the thickening effect by interacting with surface-active micelles. Soaps can be used for thickening in stick cosmetics, and betaine is mainly used in surfactant water systems.

2.6 Water-soluble polymer thickener

Systems thickened by many polymeric thickeners are not affected by the pH of the solution or the concentration of the electrolyte. In addition, polymer thickeners need less amount to achieve the required viscosity. For example, a product requires a surfactant thickener such as coconut oil diethanolamide with a mass fraction of 3.0%. To achieve the same effect, only fiber 0.5% of plain polymer is enough. Most water-soluble polymer compounds are not only used as thickeners in the cosmetic industry, but also used as suspending agents, dispersants and styling agents.

2.6.1 Cellulose

Cellulose is a very effective thickener in water-based systems and is widely used in various fields of cosmetics. Cellulose is a natural organic matter, which contains repeated glucoside units, and each glucoside unit contains 3 hydroxyl groups, through which various derivatives can be formed. Cellulosic thickeners thicken through hydration-swelling long chains, and the cellulose-thickened system exhibits obvious pseudoplastic rheological morphology. The general mass fraction of usage is about 1%.

2.6.2 Polyacrylic acid

There are two thickening mechanisms of polyacrylic acid thickeners, namely neutralization thickening and hydrogen bond thickening. Neutralization and thickening is to neutralize the acidic polyacrylic acid thickener to ionize its molecules and generate negative charges along the main chain of the polymer. The repulsion between the same-sex charges promotes the molecules to straighten and open to form a network. The structure achieves the thickening effect; hydrogen bonding thickening is that the polyacrylic acid thickener is first combined with water to form a hydration molecule, and then combined with a hydroxyl donor with a mass fraction of 10%-20% (such as having 5 or more ethoxy groups) Non-ionic surfactants) combined to untangle the curly molecules in the aqueous system to form a network structure to achieve a thickening effect. Different pH values, different neutralizers and the presence of soluble salts have a great influence on the viscosity of the thickening system. When the pH value is less than 5, the viscosity increases with the increase of the pH value; when the pH value is 5-10, the viscosity is almost unchanged; but as the pH value continues to increase, the thickening efficiency will decrease again. Monovalent ions only reduce the thickening efficiency of the system, while divalent or trivalent ions can not only thin the system, but also produce insoluble precipitates when the content is sufficient.

2.6.3 Natural rubber and its modified products

Natural gum mainly includes collagen and polysaccharides, but natural gum used as a thickener is mainly polysaccharides. The thickening mechanism is to form a three-dimensional hydration network structure through the interaction of three hydroxyl groups in the polysaccharide unit with water molecules, so as to achieve the thickening effect. The rheological forms of their aqueous solutions are mostly non-Newtonian fluids, but the rheological properties of some dilute solutions are close to Newtonian fluids. Their thickening effect is generally related to the pH value, temperature, concentration and other solutes of the system. This is a very effective thickener, and the general dosage is 0.1%-1.0%.

2.6.4 Inorganic polymers and their modified products

Inorganic polymer thickeners generally have a three-layer layered structure or an expanded lattice structure. The two most commercially useful types are montmorillonite and hectorite. The thickening mechanism is that when the inorganic polymer is dispersed in water, the metal ions in it diffuse from the wafer, as the hydration proceeds, it swells, and finally the lamellar crystals are completely separated, resulting in the formation of anionic lamellar structure lamellar crystals. and metal ions in a transparent colloidal suspension. In this case, the lamellae have a negative surface charge and a small amount of positive charge at their corners due to lattice fractures. In a dilute solution, the negative charges on the surface are greater than the positive charges on the corners, and the particles repel each other, so there will be no thickening effect. With the addition and concentration of electrolyte, the concentration of ions in solution increases and the surface charge of lamellae decreases. At this time, the main interaction changes from the repulsive force between the lamellae to the attractive force between the negative charges on the surface of the lamellae and the positive charges at the edge corners, and the parallel lamellae are cross-linked perpendicularly to each other to form a so-called “carton-like The structure of “interspace” causes swelling and gelation to achieve the effect of thickening. Further increase in ion concentration will destroy the structure