Oil and water naturally refuse to blend, and the Emulsifier plays the role of an intermediary in this process. It stands on the oil-water interface, propping up a film, wrapping tiny oil droplets or water droplets, keeping the system uniform and stable, and finally showing the familiar lotion, cream, sunscreen and base makeup forms.The selection of emulsifiers seems to be just a small part of the formula. In fact, it determines the direction of the entire system, and it also determines whether the product can survive the storage cycle and the skin feeling experience of consumers when using it.
I. Determine the emulsifying structure: oil-in-water or water-in-oil
Before choosing an emulsifier, the first step is not to look at the raw materials, but to determine what structure the product should be made into.
Oil-in-water (o/w): The oil droplets are evenly dispersed in the aqueous phase, and the outer phase is water.This kind of system has a refreshing skin feeling, fast absorption, and low greasy feeling. It is suitable for lotions, lightweight creams, and most sunscreens. It is also more suitable for spring and summer products and oily and oily skin.When choosing an emulsifier, in addition to the basic emulsifying ability, it is necessary to take care of the fluidity and freshness of the material, so as to avoid the heavy and sticky membrane feeling of the emulsifier.
Water-in-oil (w/o): The aqueous phase is wrapped in a continuous oil phase, and the outer phase is grease.This kind of system has a stronger moisturizing ability and longer-lasting water retention. It is suitable for dry skin repair cream and high-moisturizing body care.
II. The core judgment basis for selecting emulsifiers
Look at HLB, but not just rely on HLB. The hydrophilic and oleophilic equilibrium value is the basic reference for selection. The two emulsifiers of the same HLB have different chemical structures, and the strength and electrolyte resistance of the interfacial membrane formed are very different.Some interfacial membranes are too thin, and when they encounter moisturizing ingredients or plant extracts with high ion content, they are easy to layer and analyze oil after being placed for a long time; some membranes are more resilient and resistant to ion disturbances, making them suitable for creams with high added active substances.
See if there is a charge. Charged emulsifiers are more sensitive to ions in the system, and they are prone to problems when encountering salts and electrolytes.The non-ionic type is relatively worry-free and has a wide range of compatibility.
Control the amount and do not pursue excess. The more the emulsifier is added, the more stable it is.Excessive addition, the excess components are free in the system, which not only increases the cost, but also easily makes the paste sticky, stuffy, and even induces the material to become thinner and effluent.A more reasonable idea is to find the lowest effective amount that just covers all the oil phases, and then rely on the synergistic stability of structural additives and thickening components, rather than blindly stacking emulsifiers.
III.The influence of oil and moisturizing components on the emulsifying system
The emulsifier does not work alone. In the system in which it is located, oils, moisturizers, and thickeners will indirectly affect its performance.
The composition of grease is the key to the difficulty of emulsification.High-polarity synthetic esters are more likely to be wrapped in emulsifiers, and the difficulty of emulsification is low; long-chain saturated oils and high-viscosity vegetable oils are weakly polar, and if you want to stabilize the emulsification, you often have to rely on a composite emulsifying system, relying on multiple components to form a film at the oil-water interface.Many formulas will add structural additives to the oil phase to assist in stabilization. OILREE®MY720 TRIHYDROXYSTEARIN is very commonly used. it can form a weak mesh structure inside the oil phase, limiting the flow and aggregation of oil droplets, and reducing the risk of oil analysis after long-term storage.
The choice of emollient esters will also affect emulsification.OILREE®MY916 CETYL PALMITATE and OILREE®MY914 MYRISTYL MYRISTATE are both solid or semi-solid emollient esters with a clear melting point and can support the rich texture of the cream, but special attention should be paid when testing for low temperature stability. Such esters will crystallize slowly when the temperature drops. If the interfacial membrane is not supported enough, the crystallization growth may pierce the membrane that wraps the oil droplets and cause demulsification.NSOAF™IPM Isopropyl myristate is a low-viscosity lightweight ester with fast spreading and light residue. It can weaken the stuffy feeling of grease and put less pressure on the emulsifying system. It is used frequently in lightweight emulsions.
Moisturizers in the aqueous phase will also participate.OILREE®MY EG-26 Glycereth-26 is a polyol Moisturizer with stable moisture absorption performance. Adding to the aqueous phase can continuously replenish the sense of hydration, while changing the viscosity and polarity of the aqueous phase, slowing down the collision speed of oil droplets, and assisting stability from the side.
IV.Verify the long-term stability of the formula through testing
The completion of the formula is only the first step, and whether it can withstand time is the real test.There are only a few common manifestations of stability problems: water separation, oil analysis, thinning, granulation, discoloration and odor. The reasons behind them are different.
High-temperature placement will accelerate molecular movement, and the probability of oil droplet collision and merger will increase. Many weakly stable systems will first appear slightly stratified at high temperatures.Standing at low temperature tests the crystallization control ability of oils and esters. Many formulas are intact at room temperature, and particles precipitate directly after refrigeration.The hot and cold cycle simulates temperature fluctuations during transportation, which is the most likely to expose hidden hidden dangers.Many instability will not appear in three or five days, and it needs to be continuously observed for four weeks or even longer.
V.The emulsification operation process and the main points of enlarged production
Even if the combination of emulsifiers is no problem, improper process operation will also destroy the entire formula.The oil phase and the water phase should be heated to the corresponding temperature separately to ensure that all solid raw materials are completely melted and there are no remnants of unmelted particles.When the two phases are mixed, the feeding speed, homogenization speed, and duration must be matched.Most of the oil-in-water is added to the aqueous phase by the oil phase. In turn, the water-in-water phase is slowly added to the oil phase. If the feeding is too fast and the local concentration is unbalanced, the emulsification will directly fail.
Homogenization is not that the higher the speed, the better.Excessive homogenization will destroy part of the structure of the emulsifier, the interfacial membrane will be damaged, and the stability will decrease in the later stage.The cooling stage after homogenization should be stable. Quench will induce rapid crystallization of grease and increase the risk of demulsification.
VI.Reference for the collocation of emulsified raw materials in different scenarios
In actual development, composite emulsifying systems are more common than single emulsifiers, and composite collocation can complement each other's strengths and build a tougher interfacial membrane.
OILREE®MY940 Peg-40 Hydrogenated castor oil is also a non-ionic component derived from hydrogenated castor oil. It has a wide range of compatibility and is often combined with other emulsified components to balance stability and skin feeling.Bis diglyceryl polyacyladipate 2 has both emollient and film-forming properties, which can give the cream a soft touch to the skin, while assisting the emulsification system and reducing the tendency of oil-water separation.
Makeup emulsified formulas have their own unique needs.In addition to the stable foundation of the makeup system, it must also take into account the dispersion of the powder, the formation of the film, and the smooth application of makeup. Formulas such as Makeup moisturizer, which tend to moisturize the base makeup, have more special requirements for emulsifiers. Too strong emulsification will cause excessive wetting and dullness of the powder, and insufficient emulsification will cause the powder to clump and get stuck. Mottled powder.OILREE®MY9176 Peg/ppg-17/6 copolymer is a block copolymer raw material that can adjust the smoothness of spreading and weaken the stickiness of heavy oils. It is often used in combination with base makeup and light repairing lotion.OILREE®MY3874 Glycol distearate is mainly used to create a soft pearlescent texture and is an auxiliary modification raw material.OILREE®MY928 Peg-80 sorbitan laurate has stable emulsification efficiency, mild resistance and balanced compatibility. Many general-purpose oil-in-water formulas will be given priority to simplify the complex formula scheme.
VII.Efficient proofing and debugging of the emulsifying system
The debugging of the emulsifying system is essentially a process of continuous trial and error and continuous fine-tuning. There is no single emulsifier suitable for all categories.Some emulsifiers are stable but the skin feels heavy, and some are made to be light and refreshing but have poor electrolyte resistance.Put product positioning first when selecting models: for oily skin, priority is given to low-viscosity and lightweight emulsification with lightweight esters; for dry skin repair, priority is given to solutions with strong interface film and high moisturizing oils; makeup base makeup, taking into account powder compatibility and film-forming makeup effect.
It is recommended to use the univariate debugging method for proofing. Only one raw material or one parameter is changed at a time, and the rest is consistent so that the source of the change can be clearly judged.At the same time, mark the samples, record the ratio of emulsifiers, grease types, process parameters, and stability observations over different time periods. The accumulated data will save a lot of trial and error time in subsequent development.
Hubei Mingya New Material Technology Co., Ltd.
