Analysis on the development of BB cream and CC cream④

Stability Influencing Factors

Emulsifier

In the emulsified system, the emulsifier is very critical to the stability of the emulsion system. The emulsifier molecules gather on the oil-water phase interface, and its hydrophilic group extends into the water phase, and its lipophilic group extends into the oil phase, which reduces the interfacial tension of the water-oil interface and stabilizes the emulsification system. The influence of emulsifiers on stability can be evaluated from the following three aspects.

1. The selection of emulsifier should comprehensively consider the following points:

First, try to choose emulsifiers with larger lipophilic ends as the main emulsifiers. This is because the emulsifier molecules form a tight adsorption layer on the surface of the droplet, and form a directional wedge interface at the interface layer, so the structure and spatial arrangement of the emulsifier molecules have a more critical impact on the stability. If an emulsifier with a larger lipophilic end is selected as the main emulsifier, the strength and stiffness of the interfacial film formed by the emulsifier on the interface will be greater, making it relatively difficult for the emulsified system to undergo phase inversion.

Secondly, choose emulsifiers with similar molecular structures and different molecular weights. The toughness of the interfacial film plays a pivotal role in the stability of the emulsified system. Considering the steric hindrance, emulsifiers with different molecular weights are selected as composite emulsifiers, which can fill the gaps between emulsifiers. The composite film formed by mixing emulsifiers not only has strong strength, but also has strong toughness. Such an interface film is not easy to break, and the emulsified system tends to be more stable. When choosing an emulsifier to form a mixed emulsifier, it should be noted that the interaction force between the molecules of each component should be strong, and at the same time be closely arranged in the interface phase. If emulsifiers with similar molecular structures and different molecular weights can be selected for compounding, their emulsifying performance and stability will be greatly improved.

Selection of the HLB value of the re-emulsifier: the main emulsifier is between 5-6, and the co-emulsifier is between 2-8. Contribute to the stability and improvement of the system. HLB changes with the change of temperature and the amount of reactive groups in the system. Usually the temperature increases, the HLB value decreases, and the temperature decreases, the HLB value increases. Often through the temperature change between low temperature and normal temperature, the oil-water separation and phase inversion of the water-in-oil system to oil-in-water system are caused by such reasons. Therefore, without affecting the emulsification performance of the system, appropriately increasing the emulsifier with low HLB value will help to improve the cold resistance stability of the formula.

2. Choice of emulsifier: The composition of the oil phase in the formula can be divided into two categories: silicone oil and grease. Emulsifiers can be divided into three categories, water-in-silicone emulsifier W/Si, water-in-oil emulsifier W/O, silicon emulsifier with alkyl linear chain (that is, emulsifier in silicone oil that can emulsify oil) W/ (Si+O). The oil phase in the formula is mainly composed of silicone oil + a small amount of oil. You can use W/Si emulsifier as the main part with W/O emulsifier; or use W/(Si+O) as the main part with W/Si emulsifier. The medium oil phase in the formula is based on oil + a small amount of silicone oil. You can choose W/O emulsifier as the main part, with some W/(Si+O) emulsifier or W/Si emulsifier. See the table below for details. Take the (W/(Si+O) emulsification system with a total oil phase content of 30% in the formula as an example, and the emulsifier used is W/Si emulsifier PEG-10 polydimethylsiloxane, W/(Si +O) emulsifier cetyl PEG/PPG-10/1 polydimethylsiloxane, the total amount of emulsifier in the formula is about 3-4%. The vertical axis indicates the addition of grease/silicone oil and emulsifier in the formula amount (wt%).

3. Amount of emulsifier: Usually, the amount of emulsifier added in the formula is about 2%-4%. In the emulsification system containing polar oil and high powder content, it needs to be increased appropriately, generally about 3%-5%. In the emulsified system, the higher the amount of emulsifier, the more stable it is. When the dosage is higher than a certain range, the stability of the system will decrease instead. This is because the steric hindrance effect of the interface formed by the emulsifier => the emulsifier exceeds a certain amount. Due to the interaction between emulsification, the compactness of the interface is reduced; the HLB value of the emulsifier in the system is generally between 2 and 8, which is not strongly hydrophilic and has a low ability to form oily micelles. Excessive water-in-oil emulsifiers are active in the interface layer. Due to their amphiphilic characteristics, the more polar oils have more impact on the attack and penetration of the interface layer. As a result, the strength of the interface layer decreases and the looseness increases, and the system is prone to demulsification, or the emulsifier precipitates from the oil phase, resulting in "oil out".

This issue will stop here for everyone, and the next issue will continue to explain the factors affecting stability. Welcome more people to pay attention to our Zhuhai Baoli Foam Spray Pump Co., Ltd.

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