Research progress of organosilicone gel for cosmetics
The structure of organosilicone gel for cosmetics and its mechanism of action with unique skin sensation are described. The research progress of organosilicone gel system is introduced from three aspects: high molecular weight polysiloxane containing Si-H bond, compounds containing unsaturated hydrocarbon groups and solvents used; The improvement of the preparation process of silicone gel was summarized from two aspects: changing the state of the nascent gel to reduce the requirement of the shearing equipment or improving the shearing method; Finally, the improvement direction of silicone gel was prospected.
Organosilicone gel for cosmetics can be regarded as discrete cross-linked siloxane elastomer gel particles dispersed in the carrier fluid, which can be used as an effective rheological thickener of low molecular weight siloxane fluid. Adding it to skin care products and cosmetics products can not only provide a mild initial feeling of low molecular weight siloxane fluid, but also provide a sense of film formation, while maintaining the high viscosity of skin care products and cosmetics products.
Some commonly used moisturizers such as glycerin, when added in large amounts to skincare and makeup products, can produce a greasy feeling that makes it difficult for the product to distribute and spread on the skin; When panthenol or niacinamide is added in large amounts to skincare and makeup products, it can cause a sticky sensation. In order to improve the spreadability and smoothness of skincare and makeup products during use, it is generally necessary to add low molecular weight silicone fluids to give the cosmetic composition a dry, smooth, and uniform touch, and increase visual luster.
However, while low relative molecular weight silicon oxygen fluids impart the desired properties to the composition, their volatile and low viscosity characteristics make them difficult to retain in the formulation, easy to separate, and may even flow uncontrollably through the skin during use, limiting their application in cosmetic compositions. If ordinary thickeners are used to increase the viscosity of the solution and slow down the evaporation loss of volatile low molecular weight silicone oil, it may reduce the spreadability of the silicone oil and leave a serious slippery feeling on the skin.
Organosilicone gel for cosmetics can be regarded as an effective thickener of low molecular weight siloxane fluid, providing unique dry, silky and other skin sensations. Therefore, it has become a daily chemical raw material with great development potential, and has good market application prospects.
1. Action mechanism of organosilicone gel – organosilicone gel for cosmetics
The organic silicon compounds react to form a polymer cross-linking network, and the pores of the cross-linking network are filled with solvent molecules. The resulting dispersion system is called organic silicon gel. Because of the interaction between the cross-linking network and the solvent, it shows a unique dry and silky skin.
The schematic diagram of organic silicon gel formation is shown in the following figure:
The mechanism of organosilicon gel can provide a good skin feeling is similar to the process of sponge water absorption. The cross-linking network of organosilicon gel swells when encountering solvent, and the solvent molecules fill the gaps between the cross-linking networks, so that when applied, it can not only provide the skin with a thin and smooth feeling of solvent, but also have a film forming feeling related to the structure of the cross-linking network itself after the solvent is absorbed or volatilized.
2. Organosilicone gel system
The skin feeling of organosilicone gel for cosmetics is determined by the interaction of cross-linking network and solvent. Through the mutual combination of different cross-linking systems and solvents, organosilicone gel for cosmetics can be prepared to provide skin care products and cosmetics with dry, silky, powdery and moist skin feeling.
The cross-linking system of common organosilicone gel for cosmetics is generally formed by hydrosilylation of high molecular weight polysiloxane containing Si-H bond and compounds containing unsaturated hydrocarbon groups, such as diene and diyne, under the action of hydrosilylation catalyst. The formation of a three-dimensional cross-linked network through hydrosilylation reaction is characterized by the absence of by-products and the ability to accurately define the cross-linking points and the resulting network structure.
Commonly used solvents of organosilicone gel for cosmetics include linear or cyclic siloxanes with low relative molecular weight, organic solvents, linear or cyclic siloxanes with low relative molecular weight and mixtures of organic solvents. The performance and skin feel of silicone gel are determined by the interaction between the cross-linked network and the solvent used, but the structure of the cross-linked network has more influence.
2.1 High Relative Molecular Weight Polysilicon Oxide with Si-H Bonds – organosilicone gel for cosmetics
2.1.1 Polysiloxane containing two or more hydrogen containing siloxane rings – organosilicone gel for cosmetics
The cross-linking network of organosilicone gel for cosmetics is prepared by using polysiloxane containing more than two hydrosiloxane rings and compounds containing at least two aliphatic unsaturated hydrocarbon groups through the action of hydrosilylation catalyst. The compatibility of the organosilicone gel for cosmetics thus prepared with the personal care ingredients is enhanced, and the aesthetic feeling of applying it on the skin is also improved.
2.1.2 Hydrogen containing Polysiloxane Resin
The linear hydride commonly used in the synthesis of silicone gel cross-linking system can make the addition polymerization more stable, but the cross-linking system formed by it does not have a tight network structure.
The linear and loose cross-linked network structure is very inefficient in improving the viscosity of low molecular weight siloxanes, which will not only increase the cost of products, but also when volatile low molecular weight siloxanes evaporate in use, the linear and loose cross-linked network structure will lead to more residues, rather than the tight cross-linked network structure that can easily form films, providing skin care products and cosmetics with the desired soft and smooth feeling. The use of MHQ resin can form a tightly cross-linked network structure, which can be prepared by the addition reaction of MHQ resin and linear alkene organopolysiloxane. The functionality of each molecule in MHQ resin is 8-20.
The MHQ resin reacts with the organic compound with at least two aliphatic unsaturated groups in the molecule to form a cross-linking network, and the organosilicone gel for cosmetics prepared thereby has improved the compatibility with personal care ingredients and the aesthetic feeling when it is applied to the skin.
2.2 Compounds containing unsaturated hydrocarbon groups
2.2.1 Unsaturated hydrocarbon compounds containing polyether groups – organosilicone gel for cosmetics
Further modify the structure of compounds with at least two aliphatic unsaturated hydrocarbon groups within the molecule to contain at least 10% polyether groups. The polysiloxane containing more than two hydrosiloxane rings, the compound with at least two aliphatic unsaturated hydrocarbon groups in the molecule or the mixture of the compound first react with the hydrosilylation catalyst to obtain the primary product, and then further react with the compound with at least two aliphatic unsaturated and hydrocarbon groups in the molecule and at least 10% polyether groups to form the cross-linked network of the organosilicon gel under the hydrosilylation catalyst.
The solvent selected for the organosilicone gel for cosmetics in the patent is decamethylcyclopentasiloxane and isododecane or isodecyl neovalerate. The patent also states that in order to ensure the stability of polydimethylsiloxane containing two or more hydrogen containing siloxane rings, inhibitors that can inhibit the hydrosilylation reaction can be added, such as triphenyl phosphate, tocopherol, and butylated hydroxytoluene.
The cross-linking network of organosilicone gel for cosmetics is prepared by reacting the copolymer formed by α-unsaturated ethylene oxide, propylene oxide and epoxy butane with linear or branched organic hydrosiloxane. When the same organic hydrosiloxane is used, increasing the number of epoxy propane units in the copolymer can improve its compatibility with many personal care ingredients.
The organic silicon polymer with hydride is reacted with olefin polyether under hydrosilylation conditions to obtain a polyether substituted hydride ternary copolymer. The ternary copolymer further reacts with alpha unsaturated epoxyethane, epoxypropane, and epoxybutane copolymers to obtain higher polymers. Subsequently, it reacted with acrylic acid to obtain a polyether substituted organosilicon polymer network crosslinked with acrylic ester. According to the relative amount of each functional group in the final cross-linked copolymer network composition, the cross-linked composition can exhibit water swelling or oil swelling properties. If the content of acrylic acid and polyether is increased, the water swelling property of the crosslinked material can be enhanced.
2.2.2 Unsaturated hydrocarbon compounds containing amide functional groups – organosilicone gel for cosmetics
By first heating a reaction mixture containing oleic acid and organic amine to generate an organic amide, and then reacting the organic amide with a polydimethylsiloxane containing at least one side hydrogen in the presence of a hydrogenation alkylation catalyst, amide functional groups can be introduced into the crosslinked structure to prepare siloxane based polyamide elastomers [9]. Suitable dienoic acids include decaenoic acid, acrylic acid, 3-butenoic acid, 4-pentenoic acid, or other dienoic acids with different lengths of carbon chains.
2.3 Types of solvents
The selection of organic silicon gel solvent generally depends on the characteristics of the cross-linking network and the requirements for skin sensation, but it is basically selected from straight chain or cyclosiloxane with low relative molecular weight, organic solvent, and the mixture of straight chain or cyclosiloxane with low relative molecular weight and organic solvent.
The use of cyclosiloxane as solvent in organosilicone gel for cosmetics can provide a mild initial feeling, and maintain the high viscosity of the product. However, cyclosiloxane itself has low viscosity and high fluidity, so it is not easy to remain in the preparation, and there are limitations in performance or compatibility distribution. When linear siloxane fluid is used as a solvent, it can provide different performance or compatibility distributions, but often requires a higher content of organosilicon polymer cross-linked network to obtain the required viscosity that can be obtained through cyclic siloxane.
This not only increases costs, but also easily produces a negative feeling of “clumping” on the skin. Reference [10] found a unique combination of organic silicon polymer network and linear silicon oxide, which can obtain a low solid content but high viscosity composition by swelling the polymer with alkyl trisiloxane as a solvent. The solid content of organosilicone gel for cosmetics formed by swelling of alkyl trisiloxane is at least about 10% lower than that of organosilicone gel for cosmetics formed by swelling of products with the same cross-linking structure and cross-linking density through other linear silicone fluids. The alkyl trisiloxanes involved include 11,1,3,5,5,5-heptymethyl-3-ethyltrisiloxane, 1,1,1,3.5.5,5-heptamethyl-3-octyltrisiloxane, 1,1,1,3,5-heptymethyl-3-hexyltrisiloxane octamethyltrisiloxane, 1,1,1,3,5,5-heptymethyl-3-hexyltrisiloxane octamethyltrisiloxane, 1,1,3,5,5-heptymethyl-3-pentyltrisiloxane and 1,1,3.5.5,5- Heptamethyl-1-hexyltrisiloxane, etc.
3. Preparation process of organosilicon gel
The preparation process of organosilicon gel is generally divided into four steps: first, reaction is used to prepare siloxane primary gel with high solid content; The primary gel is sheared or crushed at high speed to obtain small gel particle size; The treated gel is then mixed with additional solvent and diluted to the final target solid content; Further shear swelling to form a uniform silicone gel.
The improvement of the preparation process of organosilicone gel for cosmetics comes from changing the state of the nascent gel to reduce the requirements for shearing equipment or improve the shearing method.
3.1 Improve the state of nascent gel
General nascent gel need to be sheared or crushed first, and then mixed with additional solvents to prepare uniform gel through high-speed mixing or shearing. Not only is the process cumbersome and requires high grinding fineness of shearing equipment, but also the shearing equipment is prone to heat after being used for a long time, which will lead to the volatilization of the added carrier fluid, resulting in high solid content and affecting the product’s skin feel.
In the presence of low viscosity fluid, it is easy to prepare stable non adhesive gel by using vinyl MQ resin and organic hydrosiloxane with Si-H functional group in the main chain. The gel can be converted into paste gel with a wide range of consistency through simple shearing. The sheared gel can be further diluted with solvent to the required solid content, and then a translucent gel can be prepared through shearing.
When preparing a specific elastomer gel containing volatile low molecular weight siloxane, the initial gel can be synthesized by reaction first, and then mixed with the additional amount of low molecular weight siloxane to produce a uniform liquid gel through high-speed mixing or shear force.
Although the organosilicone gel for cosmetics with specific structure can react first in the preparation process to generate an initial gel that is easy for further processing, the requirement for shear equipment has been reduced in the subsequent processing, but it still needs to be mixed evenly by shear equipment.
In the reaction process, the organic silicon gel can be prepared by the process of slow stirring and rapid dispersion. Once the reactants are cross-linked, they are immediately and evenly dispersed in the solvent, which makes the reaction system directly appear as a uniform gel. After simple vacuum deaeration, transparent elastomer products can be obtained without mixing with additional solvents or special high-speed shear mixing equipment. The process is simple, the production efficiency is high, and it is easy for industrial production.
3.2 Improving Cutting Methods
In the process of shearing and crushing the primary organic silicon gel, there is a high requirement for the shearing equipment. The primary gel must be crushed to a fine enough size to make it evenly swell when mixed with additional solvents, and the product has no particle feeling when applied. Common cutting equipment includes three roll mills, two roll mills, sand mills, colloid mills, Gaulin homogenizers, and RoSSTM mixers.
In order to make the size of gel particles small enough to disperse in the solvent, the method of specially treating the siloxane elastomer composition can be adopted. The specific process is to add solvent and the composition of siloxane elastomer into the reactor, stir and mix them, transfer the composition from the reactor to the high-pressure pump, and make it pass through the small orifice plate with high
e smaller particles obtained are recycled back to the reactor for repeated cycles, and the siloxane elastomer combination with an average particle size of 0.5~30um can be obtained. The preferred device for reducing particle size is a high-pressure feed homogenizer, with the most preferred being an ultrasonic reactor.
4. Application of organosilicon gel for cosmetics
Organosilicone gel for cosmeticsis widely used in lipstick, foundation make-up, shampoo, hair conditioner, hair styling agent, bath gel, moisturizing agent, sunscreen product, antiperspirant and deodorant formula because of its unique sensory properties, reducing the viscosity of the formula and increasing the visual gloss of the product.
The polyglycerol functionalized silicone elastomer obtained by reacting hydrogen containing polysiloxane and double bond containing polyglycerol compounds in the presence of platinum catalyst can be added to cosmetic compositions to increase the stability of cosmetic compositions containing silicone oil.
Adding the silicone elastomer lotion containing MQ silicone resin to the personal care composition can improve the film performance of the personal care composition on the skin and hair, and make the composition easy to prepare.
The introduction of appropriate organosilicone gel for cosmetics into deodorant or antiperspirant can provide a smooth skin feel for the product and reduce the possibility of dehydration and shrinkage of the product.
The organosilicone gel for cosmetics containing MQ silicone resin and C18 or stearyl side chain can not only form a high-strength continuous film with good adhesion after the carrier solvent volatilizes, improve the spreading performance of pigments and other granular active substances, effectively reduce the agglomeration of inorganic sunscreen in sunscreen products, but also have good anti migration performance, which is conducive to its application in cosmetics.
5. Outlook – organosilicone gel for cosmetics
With the increasing refinement of personal care products and the continuous improvement of consumer demands, not only are nursing products required to have good efficacy, but they are also expected to provide a good skin feel and a pleasant appearance. Organosilicone gel for cosmetics is widely used in personal care products due to its unique skin feel and thickening properties. It has become a development trend of silicone gel to try more different types of crosslinking systems and different solvents to prepare silicone gel with different skin sensations, and to improve the compatibility and aesthetic properties of silicone gel with other components in the personal care product formula.
At the same time, improving the preparation process of silicone gel, simplifying the production process, and reducing production costs are also a research direction of organosilicone gel for cosmetics in the future.