Carbomer, also known as carbomer, is a polymer formed by chemical cross-linking of acrylic acid or acrylate and allyl ether, including polyacrylic acid (homopolymer) and long-chain alkanol acrylates Polymer (copolymer). Its molecular structure contains 52-68% acid groups, so it has a certain acidity, has hydrophilic properties, and can be dissolved in water, ethanol and glycerin.
Carbomer has the functions of thickening, suspending, stabilizing the system, regulating the release of water and active substances, and has simple process and good stability. Therefore, it is a rheological modification widely used in personal care products, pharmaceuticals and other fields. Thickener.
There are two main thickening mechanisms of carbomer, including neutralization thickening and hydrogen bond thickening.
1. Neutralization and thickening
Because it contains a certain acid group, it needs to be alkaline neutralized during the application process. After being neutralized by alkali, the carboxyl group of the carbomer is ionized. Due to the mutual repulsion of negative charges, the curled molecular chain stretches into a greatly expanded state, which increases the original volume to about 1000 times. To the effect of thickening. Commonly used neutralizers are sodium hydroxide, potassium hydroxide, potassium bicarbonate, and triethanolamine (the pH is adjusted to about 7 to get a crystal clear gel), which is why carbomer is sensitive to ions.
2. Hydrogen bond thickening
Carbomer molecules, as carboxyl donors, can combine with one or more hydroxyl groups to form hydrogen bonds and thicken. This reaction mechanism takes time. Commonly used hydroxyl donors are non-ionic surfactants, polyols and so on.
In addition, the following points need to be paid attention to when using carbomer.
1. All carbomer polymers have the ability of shear thinning, and the longer the shear time, the slower the viscosity recovery, and even the permanent loss of viscosity;
2. Carbopol polymer has poor tolerance to ions, and Carbopol 1342, which is in the transitional stage, is relatively high;
3. Ultraviolet radiation will cause loss of the viscosity of carbomer, and this loss is irreversible.
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