Surfactant thickener: A portion of betaine can also be used as a thickener. The thickening principle is similar to that of other small molecules. The thickening is achieved by interacting with surfactant micelles with a mass fraction of 10%-20% hydroxyl groups. Soaps can be used for thickening in stick cosmetics. Natural gums mainly include collagen and polysaccharides. Betaine is mainly used in surfactant water systems. Water-soluble polymer thickeners: Many polymer thickeners thicken systems that are not affected by the pH value of the solution. (Pyrrolidone) In addition, polymer thickeners require a smaller amount to achieve the required viscosity, and only 0.5% of cellulose polymer is required to achieve the same viscosity. Most water-soluble polymer compounds are used not only as thickeners in the cosmetics industry, but also as suspending agents, dispersants and setting agents.
Cellulose is an effective thickener in water-based systems. Cellulose is a natural product that contains repeated glucoside units. Each glucoside unit contains 3 hydroxyl groups, and various derivatives can be formed through these hydroxyl groups. Cellulose thickeners thicken by hydrating and expanding long chains, and the cellulose thickened system exhibits a pseudoplastic rheological morphology. (Pyrrolidone) The usage is generally about 1% by mass. Polyacrylic acid thickeners have a history of 40 years since Coodrich introduced Carbomer934 to the market in 1953. Now this series of thickeners has more choices (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 acid thickener, so that its molecules are ionized and negative charges are generated along the main chain of the polymer. The repulsion between like charges causes the molecules to stretch and open to form a network structure to achieve thickening; hydrogen bonding thickening is that the polyacrylic acid thickener first combines with water to form a hydrated molecule, and then combines with a donor (such as a non-ionic surfactant with 5 or more ethoxy groups) to unwind its curled molecules in the aqueous system to form a network structure to achieve thickening. (Pyrrolidone) 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 pH value; the viscosity remains almost unchanged at pH 5-10; but as the pH value continues to increase, the thickening efficiency decreases. Monovalent ions only reduce the thickening efficiency of the system, while divalent or trivalent ions can not only make the system thinner, but also produce insoluble precipitates when the content is sufficient.
