Emulsion thickening agent with acid return stability and preparation method thereof

Abstract

The invention provides an emulsion thickener with acid return stability and a preparation method thereof, and relates to the technical field of thickeners. The emulsion thickener comprises the following raw materials: a polymeric monomer, an emulsifier, an initiator, a cross-linking agent, water and a structural additive, the polymeric monomer comprises a first monomer and a second monomer, the first monomer is an alpha, beta-unsaturated acid monomer, the second monomer is an alpha, beta-unsaturated ester monomer, and the structural additive is polypeptide comprising polar amino acid residues. When a system is changed from an alkaline condition to an acidic condition, the emulsion thickener with the acid return stability can quickly recover to the alkaline viscosity and gradually increase the viscosity, so that the response rate of network reconstruction is effectively improved, and a self-repairing function is realized. The preparation method of the emulsion thickening agent with the acid return stability is simple, convenient and easy to implement, good in stability and suitable for industrial implementation.

Description

Technical Field

[0001] The present invention relates to the technical field of thickeners, and in particular to an emulsion thickener with acid-reversion stability and a preparation method thereof. Background Art

[0002] Acid-reversible emulsion thickeners with acid-reversible stability have been widely used in various emulsion systems. These thickeners utilize a lightly cross-linked acrylic acid-acrylate copolymer network structure. Their unique molecular structure, characterized by a dense distribution of multiple carboxyl and polyester groups within the molecular chain, enables them to synergistically stabilize with a variety of ionic and nonionic surfactants. After compounding and alkali neutralization, acid-reversible emulsion thickeners can significantly enhance the suspension, stabilization, and thickening properties of emulsion systems when the pH drops to acidic conditions, imparting a transparent, bright appearance to the product.

[0003] Compared to traditional acrylic thickener powders, acid-reversible emulsion thickeners exist as low-viscosity liquids, making them easier to mix quickly with other formulation ingredients. This overcomes the technical bottleneck of limited compatibility with surfactant systems and significantly improves stability and suspension. Furthermore, after alkaline activation, acid-reversible emulsion thickener systems can still withstand the introduction of subsequent acidic substances, maintaining high viscosity and rheological properties even when the system is adjusted back to a weakly acidic state. This thickener is effective over a wide pH range (4.0-11.0), transcending the acid-base sensitivity limitations of traditional acrylic thickeners in compounding processes, thus extending its application scope.

[0004] Previous studies have confirmed that the acid recovery mechanism of acid-recovery emulsion thickeners typically relies on static crosslinking through the protonation / deprotonation equilibrium of carboxylic acid groups. As the pH of the system shifts toward the acidic direction, the carboxylic acid groups protonate, causing the molecular chains to contract and form a physical crosslinked network. However, when the pH of the system drops from alkaline to acidic, there is a certain hysteresis in the reconstruction of the crosslinked network, which is manifested in a significant slowdown in the system's recovery to high viscosity and difficulty in returning to the alkaline viscosity. Therefore, the limitations of this traditional mechanism are becoming increasingly prominent, and further optimization of acid-recovery performance is needed. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention discloses an emulsion thickener with acid return stability and a preparation method thereof. The preparation method adds a composite emulsifying system and a structural additive into a polymerization system, thereby enhancing the acid return performance of the prepared emulsion thickener.

[0006] In order to achieve the above technical objectives, on the one hand, the present invention proposes an emulsion thickener with back acid stability, the raw materials of the emulsion thickener including a polymer monomer, an emulsifier, an initiator, a cross-linking agent, water and a structural additive; the polymer monomer includes a first monomer and a second monomer, the first monomer is an α,β-unsaturated acid monomer, the second monomer is an α,β-unsaturated ester monomer, and the structural additive is a polypeptide including polar amino acid residues.

[0007] The emulsion thickener with acid-return stability of the present invention comprises a polypeptide with polar amino acid residues as a structural additive, which enhances the acid-return performance of the emulsion thickener and imparts biocompatibility. Specifically, the polypeptide exhibits a stretched conformation in the alkaline polymerization stage and folds or self-assembles into a β-sheet / α-helical structure in the acid-return stage. Therefore, the structural additive can regulate the conformational changes of the thickener molecules in an acidic environment by interacting with the thickener molecules, effectively improving the response rate of network reconstruction, promoting the system to achieve self-repair function, and imparting additional functions such as biocompatibility. In addition, the hydrophilic group of the polypeptide improves the emulsification efficiency by interacting with the emulsifier. The embodiments and comparative examples confirm that the emulsion thickener of the present invention has excellent acid-return stability and has a wide range of application value.

[0008] Based on the above technical solution, the structural additive is a polypeptide comprising charged amino acid residues, and the molecular weight of the structural additive is 500-5000 Daltons.

[0009] Based on the above technical solution, the mass of the structural additive is 0.5% to 3% of the mass of the polymerized monomer, preferably 1% to 2.5%, and more preferably 1% to 2%.

[0010] Based on the above technical solution, the emulsifier is a composite emulsifier of anionic emulsifier and nonionic emulsifier, the mass of the emulsifier is 0.1% to 3% of the mass of the polymerized monomer, preferably 0.1% to 1%, and more preferably 0.2% to 1%; the mass ratio of the nonionic emulsifier to the anionic emulsifier is (1 to 4):1, preferably (1 to 3):1, and more preferably (1 to 2):1.

[0011] Based on the above technical solution, the cross-linking agent includes one or more of pentaerythritol triacrylate, trimethylolpropane triacrylate, dipentaerythritol pentaacrylate, 1,6-hexanediol diacrylate, trimethylolpropane trimethacrylate, diallyl phthalate, and pentaerythritol tetraacrylate, preferably pentaerythritol triacrylate and / or diallyl phthalate.

[0012] Based on the above technical solution, the mass of the cross-linking agent is 0.1% to 3% of the mass of the polymerized monomer, preferably 0.5% to 2%, more preferably 0.5% to 1%, preferably 0.05% to 0.5%, more preferably 0.05% to 0.2%.

[0013] Based on the above technical solution, the initiator includes a first initiator and a second initiator, and the first initiator and the second initiator are independently selected from one or more of potassium persulfate, sodium persulfate, ammonium persulfate, sodium thiosulfate, azobisisobutylamidine hydrochloride and azobisisobutylimidazoline hydrochloride, preferably potassium persulfate and / or sodium persulfate.

[0014] Based on the above technical solution, the sum of the masses of the first initiator and the second initiator is 0.05%~1% of the mass of the polymerized monomer; the mass ratio of the first initiator to the second initiator is (0.2~5):1, preferably (0.2~2):1, and further preferably (0.2~1):1.

[0015] The present invention provides a method for preparing an emulsion thickener with acid back stability, the method comprising the following steps: S1: Under an inert atmosphere, heating a first material to a first temperature, adding a second material and mixing them uniformly to obtain a first reaction system; S2: adding a third material and a fourth material dropwise to the first reaction system to obtain a second reaction system after the addition is completed; S3: heating the second reaction system to a second temperature for reaction to obtain the emulsion thickener with back acid stability; The emulsifier used in the preparation method is added in two parts; the first material is a mixture of a portion of the emulsifier and water; the second material is a mixture of a first initiator and water; the third material is a mixture of a polymerization monomer, a cross-linking agent, another portion of the emulsifier and water; the fourth material is a mixture of a second initiator, a structural additive and water; and the structural additive is a polypeptide comprising polar amino acid residues.

[0016] In the above technical solution, a polypeptide comprising polar amino acid residues is added to the reaction system as a structural additive. The polypeptide exhibits a stretched conformation in the alkaline polymerization stage and folds or self-assembles into a β-folding / α-helical structure in the acid-return stage. By interacting with the thickener molecules, the conformational changes of the thickener molecules in an acidic environment can be adjusted, effectively improving the response rate of network reconstruction, promoting the system to achieve self-repair function, and giving it additional functions such as biocompatibility; the hydrophilic group of the polypeptide improves the emulsification efficiency by interacting with the emulsifier; and the polypeptide structural additive is a green adjuvant, so the above technical solution provides key technical support for the design of green and efficient emulsions. In addition, in the above technical solution, the stability of the emulsification can be improved by adding the emulsifier in steps, and it is helpful to control the thickener emulsion particle size and its distribution, so that the emulsion thickener of the present invention has a better thickening effect.

[0017] It should be noted that the present invention does not limit the specific preparation methods of the first, second, third, and fourth materials. In an optional embodiment of the present invention, the first material is obtained by uniformly mixing a portion of an emulsifier with water; the second material is obtained by uniformly mixing a first initiator with water; the third material is obtained by uniformly mixing the polymerizable monomer, a crosslinker, and another portion of an emulsifier in water; and the fourth material is obtained by uniformly mixing a second initiator, a structural additive, and water. It should also be noted that the order in which the first, second, third, and fourth materials are prepared is not limited.

[0018] The acid reversion stage, as described herein, refers to the process phase in which the pH of the thickener system is gradually reduced from the alkaline range to the acidic range. Acid reversion performance characterizes the ability of a thickener system to maintain and restore its viscosity after the pH is gradually reduced from the alkaline range to the acidic range. Acid reversion stability characterizes the ability of a thickener system to maintain and restore its viscosity to that of the alkaline polymerization stage during the acid reversion stage.

[0019] In a further example of the present invention, the composition and amount of the structural additions were explored and optimized.

[0020] Optionally, the structural additive is a polypeptide containing charged amino acid residues. The charged amino acid residues in the polypeptide contain one or more of a carboxyl group (-COOH) or an amino group (-NH2). These groups can form hydrogen bonds, ionic bonds, or participate in condensation reactions with amino, carboxyl, or hydroxyl groups (-OH) in the thickener molecule. Extensive experiments conducted in the present invention have demonstrated that the interaction between the charged amino acid residues and the thickener molecules helps incorporate the polypeptide into the thickener molecular structure or stabilize its presence in the system, thereby affecting the thickener's acid resorption properties.

[0021] Optionally, the molecular weight of the structural additive is 500 to 5000 Daltons. The Examples and Comparative Examples of the present invention demonstrate that polypeptide structural additives within this molecular weight range have good solubility and diffusivity in emulsion thickener systems and can effectively interact with thickener molecules. In an optional example of the present invention, the molecular weight of the structural additive is 500 to 2000 Daltons.

[0022] Optionally, the structural additive is a polypeptide chain comprising at least one charged amino acid residue of lysine, arginine, histidine, glutamic acid or aspartic acid, and the optimization of the structural form of the polypeptide chain is conducive to the effectiveness of the charged amino acid residue.

[0023] It should be noted that the present invention does not limit the source of the structural additives, and the structural additives can be extracted from nature or designed and synthesized artificially as needed.

[0024] Further optionally, the polypeptide chain includes at least one charged amino acid residue of histidine, whose imidazole group has unique acid-base properties near physiological pH. The comparative examples of the present invention demonstrate that the addition of a structural additive containing a charged amino acid residue of histidine can effectively enhance the viscosity of the thickener under conditions of reduced pH and promote the production of a cosmetic product with a better skin feel. In an optional example of the present invention, the polypeptide chain includes at least three charged amino acid residues of histidine.

[0025] Optionally, the mass of the structural additive is 0.5% to 3% of the mass of the polymerized monomer. An appropriate amount of the structural additive facilitates the interaction between the polypeptide and the emulsifier during the preparation process, thereby improving the acid stability of the prepared emulsion thickener. In an optional example of the present invention, the mass of the structural additive is 1% to 2.5% of the mass of the polymerized monomer, preferably 1% to 2%.

[0026] In a further example of the present invention, the composition and dosage of the emulsifier were explored and optimized.

[0027] Optionally, the emulsifier is a composite emulsifier comprising an anionic emulsifier and a nonionic emulsifier. In the polypeptide comprising polar amino acid residues, the hydrophilic group thereof can interact with the negative charge of the anionic emulsifier, or form hydrogen bonds with the hydrophilic segments of the nonionic emulsifier, thereby changing the arrangement of the emulsifier at the oil-water interface and improving the emulsification efficiency. In addition, anionic emulsifiers are efficiently dispersed under alkaline conditions by electrostatic repulsion, while nonionic emulsifiers can maintain stability in acidic environments by steric hindrance, avoiding the risk of demulsification caused by pH fluctuations in a single emulsifier system. The embodiments of the present invention and comparative examples confirm that the present invention adopts the step-by-step addition of composite emulsifiers, and the resulting emulsion thickener is particularly suitable for systems that need to undergo dynamic changes in acidity and alkali, and is superior to a single emulsifier system in terms of stability, thickening efficiency and applicable scenarios.

[0028] Optionally, the anionic emulsifier includes one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, sodium dodecyl phosphate, sodium stearate, sodium lauroyl sarcosinate, sodium laureth sulfate, sodium tetradecyl sulfate, and sodium dioctyl sulfosuccinate, preferably one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and sodium dodecylsulfonate, preferably one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and sodium dodecylsulfonate.

[0029] Optionally, the nonionic emulsifier includes one or more of Tween-80, Span-80, Span-60, glyceryl laurate, polyglyceryl fatty acid ester, sucrose fatty acid ester, alkyl glucoside, and methyl glucoside polyoxyethylene ether, preferably includes one or more of Tween-80, Span-80, and Span-60.

[0030] Optionally, the mass ratio of the nonionic emulsifier to the anionic emulsifier in the emulsifier is (1-4):1. Optimizing the mass ratio of the nonionic emulsifier to the anionic emulsifier helps improve the stability of the thickener when the pH value of the application system drops from alkaline to acidic. In an optional example of the present invention, the mass ratio of the nonionic emulsifier to the anionic emulsifier is (1-3):1, preferably (1-2):1.

[0031] Optionally, the mass of the emulsifier is 0.1% to 3% of the mass of the polymerized monomers. Optimizing the amount of the emulsifier can control the particle size and distribution of the monomer droplets in the emulsion, and help improve the rheological properties and stability of the thickener. In an optional embodiment of the present invention, the mass of the emulsifier is 0.1% to 1%, preferably 0.2% to 1%, of the mass of the polymerized monomers.

[0032] Optionally, the mass ratio of the emulsifier contained in the third material to the first material is (0.2-5):1. In the present invention, by adding portions of the emulsifier to the third material and the first material, the emulsifier is added stepwise, thereby improving the morphology and distribution of the resulting thickener polymer particles and enhancing operational stability. In an optional example of the present invention, the mass ratio of the emulsifier contained in the third material to the first material is (1-4):1, preferably (2-4):1.

[0033] In a further example of the present invention, the type and amount of the polymerization monomers are explored and optimized.

[0034] Optionally, the polymerizable monomer is a mixed monomer including a first monomer and a second monomer, wherein the first monomer is an α,β-unsaturated acid monomer and the second monomer is an α,β-unsaturated ester monomer.

[0035] Optionally, the first monomer comprises one or more of acrylic acid, methacrylic acid, crotonic acid, maleic acid, cinnamic acid, fumaric acid, citraconic acid and mesaconic acid, preferably acrylic acid and / or methacrylic acid.

[0036] Optionally, the second monomer includes one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, palmitic acrylate and ethylene glycol dimethacrylate, preferably one or more of butyl acrylate, ethyl methacrylate and glycidyl methacrylate.

[0037] Optionally, the mass concentration of the polymerized monomer in the second reaction system is 5% to 50%. Exploring the concentration of the polymerized monomer is beneficial for producing a thickener with a reasonable molecular weight distribution and stable structure, and improving the rheological properties of the produced thickener. In an optional example of the present invention, the mass concentration of the polymerized monomer in the second reaction system is 10% to 40%, preferably 30% to 40%.

[0038] In a further example of the present invention, the composition and dosage of the initiator were explored and optimized.

[0039] Optionally, the first initiator and the second initiator are independently selected from one or more of potassium persulfate, sodium persulfate, ammonium persulfate, sodium thiosulfate, azobisisobutylamidine hydrochloride and azobisisobutylimidazoline hydrochloride, preferably potassium persulfate and / or sodium persulfate.

[0040] In the above technical solution, the first initiator and the second initiator may be of the same or different types. In an optional example of the present invention, the first initiator and the second initiator are of the same type.

[0041] Optionally, the sum of the mass of the first initiator and the second initiator is 0.05% to 1% of the mass of the polymerized monomer. Optimizing the amount of initiator is beneficial to controlling the reaction process, improving operational stability, and contributing to obtaining a structurally stable thickener product. In an optional example of the present invention, the sum of the mass of the first initiator and the second initiator is 0.05% to 0.5%, preferably 0.05% to 0.2%, of the mass of the polymerized monomer.

[0042] Optionally, the mass ratio of the first initiator to the second initiator is (0.2-5):1, thereby combining the staged addition of the initiator with the staged cross-linking reaction, gradually controlling the initiation and rate of the polymerization reaction, and making the polymerization reaction more uniform and stable. In an optional example of the present invention, the mass ratio of the first initiator to the second initiator is (0.2-2):1, preferably (0.2-1):1.

[0043] In a further example of the present invention, the composition and dosage of the cross-linking agent were explored and optimized.

[0044] Optionally, the crosslinking agent includes one or more of pentaerythritol triacrylate, trimethylolpropane triacrylate, dipentaerythritol pentaacrylate, 1,6-hexanediol diacrylate, trimethylolpropane trimethacrylate, diallyl phthalate, and pentaerythritol tetraacrylate, preferably pentaerythritol triacrylate and / or diallyl phthalate.

[0045] Optionally, the mass of the cross-linking agent is 0.1% to 3% of the mass of the polymerized monomers. Optimizing the amount of the cross-linking agent can promote cross-linking polymerization between the polymerized monomers and improve efficiency. In an optional example of the present invention, the mass of the cross-linking agent is 0.5% to 2% of the mass of the polymerized monomers, preferably 0.5% to 1%.

[0046] In a further example of the present invention, the first temperature is 50-80°C. In a further example of the present invention, the second temperature is 70-90°C, and the reaction time at the second temperature is 1-5 hours. Temperature control at different polymerization stages facilitates the formation of a uniform and stable crosslinked network during the crosslinking reaction at each stage, thereby improving the operability of the method.

[0047] In the above technical solution, the relative dropping speeds of the third material and the fourth material are not limited and can be the same or different. In a further example of the present invention, in step S2, the dropping speeds of the third material and the fourth material are the same, and the dropping operation of the two materials is completed within a time range of 0.5 to 3 hours.

[0048] It should be noted that in the present invention, the inert atmosphere refers to a gas environment composed of gases that do not chemically interact with the reactants, such as a nitrogen atmosphere, or an atmosphere formed by a gas of the zeroth group of the periodic table (such as argon).

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: the emulsion thickener with acid return stability of the present invention includes a structural additive of polar amino acid residues, which enhances the acid return performance of the emulsion thickener and imparts biocompatibility, so that when the system changes from alkaline conditions to acidic conditions, the emulsion thickener of the present invention can quickly recover to the viscosity at alkaline conditions and gradually increase, effectively improving the response rate of network reconstruction, realizing self-repair function, and can be used in a wider range of pH conditions and formulas; in addition, the emulsion thickener with acid return stability of the present invention can also promote the acquisition of cosmetic products with better skin feel in practical applications.

[0050] The preparation method of the emulsion thickener with acid reversibility of the present invention adds a structural additive including polar amino acid residues, and forms a reversible dynamic cross-linking network in combination with the step-by-step addition of an emulsifier, thereby enhancing the acid reversibility of the emulsion thickener and imparting biocompatibility. The preparation method of the present invention is simple and easy to implement, has good stability, and can be implemented industrially. DETAILED DESCRIPTION

[0051] To facilitate understanding of the present invention, the present invention will be described in more detail below, with preferred embodiments of the present invention provided. However, it should be understood that these embodiments are merely for the purpose of further explanation and are not to be construed as limiting the present invention in any form, i.e., they are not intended to limit the scope of protection of the present invention.

[0052] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental methods described, unless otherwise specified, are conventional methods.

[0053] The viscosity test method for the emulsion thickener in the present invention is a body wash formula viscosity test. Specifically, the emulsion thickener prepared in the examples and comparative examples is formulated into a transparent body wash according to the formula shown in Table 1; stirring is maintained throughout the formulation process; water, chelating agent, thickener, and surfactant are added to a beaker in order, and then a 20% mass concentration of sodium hydroxide aqueous solution is added to the solution while stirring to adjust the pH of the formula to approximately 7.0. Finally, 50% citric acid is added to adjust the pH to 5, 4, and 3 to obtain a hydrogel. During the specific viscosity test, the hydrogel is transferred to a centrifuge tube at each pH value and defoamed by centrifugation. The viscosity of the hydrogel is measured at 25°C using a Brookfield DV2T-RV rotational viscometer at a speed of 20 rpm.

[0054] Table 1

[0055] The smoothness of the prepared bath lotion formula is tested by visual inspection and hand touch to evaluate the sample surface, and the surface is divided into two levels: rough and smooth.

[0056] Example 1 A method for preparing an emulsion thickener with acid back stability comprises the following steps: under a nitrogen atmosphere, adding 200 g of water, 0.1 g of sodium dodecyl sulfate, and 0.1 g of Span-60 (a first material) into a 1 L three-necked flask, stirring and mixing the mixture until uniform, and heating the mixture to 50° C.; and adding 20 g of water and 0.03 g of potassium persulfate (a second material) into a beaker, mixing the mixture until uniform, and then adding the mixture to the three-necked flask all at once. Take two other beakers and prepare the third material and the fourth material respectively; wherein the composition of the third material is 0.2g sodium dodecyl sulfate, 0.2g Span-60, 45g methacrylic acid, 105g glycidyl methacrylate, 0.75g pentaerythritol triacrylate and 40g water, and the composition of the fourth material is 0.12g potassium persulfate, 1.5g heptapeptide HSHGHEK (whose molecular weight is 830 Daltons, amino acid sequence is: histidine-serine-histidine-glycine-histidine-glutamic acid-lysine) and 40g water. After stirring them evenly, the third material and the fourth material are added dropwise to the three-necked flask at the same speed for about 0.5~3h. After the addition is completed, the reaction temperature is raised to 80°C and the reaction is continued for 2h. After cooling to room temperature, the target emulsion thickener is obtained by filtration. In Test Example 1, a transparent shower gel was prepared using the emulsion thickener of this embodiment according to the formula in Table 1, and viscosity tests were subsequently performed at different pH values. The test results are shown in Table 2.

[0057] Example 2 A method for preparing an acid-stable emulsion thickener comprises the following steps: Under a nitrogen atmosphere, 80g of water, 0.05g of sodium lauryl sulfate, and 0.1g of Span-80 (the first material) are added to a 1L three-necked flask, the mixture is stirred and heated to 80°C. 20g of water and 0.05g of potassium persulfate (the second material) are added to a beaker, the mixture is mixed and then added to the three-necked flask all at once. The third and fourth materials are prepared in two separate beakers. The third material consisted of 0.2g sodium lauryl sulfate, 0.3g Span-80, 28g acrylic acid, 44g ethyl methacrylate, 0.72g diallyl phthalate, and 30g water. The fourth material consisted of 0.05g potassium persulfate, 1.2g heptapeptide WLHAEQS (molecular weight 870 daltons, amino acid sequence: tryptophan-leucine-histidine-alanine-glutamic acid-glutamine-serine), and 30g water. After stirring thoroughly, the third and fourth materials were added dropwise to a three-necked flask at a constant pump rate for approximately 0.5-3 hours. After the addition was complete, the reaction temperature was raised to 90°C and the reaction continued for 4 hours. After cooling to room temperature, the target emulsion thickener was filtered to obtain the target emulsion thickener. In Test Example 2, the emulsion thickener of this example was formulated into a transparent shower gel according to the formula in Table 1. Viscosity tests were then conducted at different pH values. The test results are shown in Table 2.

[0058] Example 3 A method for preparing an acid-stable emulsion thickener comprises the following steps: Under a nitrogen atmosphere, 150g of water, 0.2g of sodium dodecylbenzenesulfonate, and 0.2g of Tween-80 (the first material) are added to a 1L three-necked flask, the mixture is stirred and heated to 60°C; 20g of water and 0.02g of potassium persulfate (the second material) are added to a beaker, the mixture is mixed and the mixture is added to the three-necked flask all at once. The third and fourth materials are prepared in two separate beakers. Among them, the composition of the third material is 0.6g sodium dodecylbenzenesulfonate, 0.6g Tween-80, 64g methacrylic acid, 96g butyl acrylate, 0.8g diallyl phthalate and 30g water, and the composition of the fourth material is 0.06g potassium persulfate, 2g decapeptide GHDFRKYWQS (whose molecular weight is 1323 Daltons, and the amino acid sequence is: glycine-histidine-aspartic acid-phenylalanine-arginine-lysine-tyrosine-tryptophan-glutamine-serine) and 40g water. After stirring evenly, the third material and the fourth material are dripped into the three-necked flask at a certain pump speed, and the dripping time is about 0.5~3h; after the dripping is completed, the reaction temperature is raised to 70°C and the reaction is continued for 5h. After cooling to room temperature, the target emulsion thickener is obtained by filtration. In Test Example 3, a transparent shower gel was prepared using the emulsion thickener of this embodiment according to the formula in Table 1, and subsequent viscosity tests were conducted at different pH values. The test results are shown in Table 2.

[0059] Comparative Example 1 A method for preparing an emulsion thickener, wherein the parameter control and operating steps of this preparation method are the same as those in Example 1, except that the fourth material described in this comparative example does not contain a structural additive. In Test Example 4, an emulsion thickener was prepared using this comparative example and formulated into a transparent shower gel according to the formulation in Table 1. Subsequently, viscosity tests were conducted at different pH values. The test results are shown in Table 2.

[0060] Comparative Example 2 A method for preparing an emulsion thickener is described. The parameter control and operating steps of this method are the same as those in Example 1, except that the emulsifier used in this comparative example is sodium dodecyl sulfate, and the fourth material does not contain a structural additive. In Test Example 5, an emulsion thickener was prepared using this comparative example and formulated into a transparent shower gel according to the formulation in Table 1. Viscosity tests were subsequently conducted at different pH values. The test results are shown in Table 2.

[0061] Comparative Example 3 A method for preparing an emulsion thickener. The parameter control and operation steps of the preparation method are the same as those of Example 1, except that the structural additive used in this comparative example is a 50-mer peptide with a molecular weight of approximately 5900 daltons and an amino acid sequence of: WHLEQKLRASGLAEHLGALESWLHQEALERSQLEWLGALESWLRQEALER (tryptophan-histidine-leucine-glutamic acid-glutamine-lysine-leucine-arginine-alanine-serine-glycine-leucine-alanine-glutamic acid-histidine-leucine-glycine-alanine-leucine-glutamic acid-serine-tryptophan-leucine-histidine-glutamine-glutamic acid-alanine-leucine-glutamic acid-arginine-serine-glutamine-leucine-glutamic acid-tryptophan-leucine-glycine-alanine-leucine-glutamic acid-serine-tryptophan-leucine-arginine-glutamine-glutamic acid-alanine-leucine-glutamic acid-arginine). In Test Example 6, the emulsion thickener prepared in this comparative example was used to prepare a transparent shower gel according to the formula in Table 1, and subsequent viscosity tests at different pH values were performed. The test results are shown in Table 2.

[0062] Comparative Example 4 A method for preparing an emulsion thickener. The parameter control and operating steps of this preparation method are the same as those in Example 1, except that the structural additive used in this comparative example is a tetrapeptide with a molecular weight of approximately 400 Daltons and an amino acid sequence of GAAS (glycine-alanine-alanine-serine). In Test Example 7, an emulsion thickener was prepared using this comparative example and formulated into a transparent body wash according to the formulation in Table 1. Viscosity tests were then conducted at different pH values. The test results are shown in Table 2.

[0063] Comparative Example 5 A method for preparing an emulsion thickener. The parameter control and operating steps of this preparation method are the same as those in Example 1, except that the emulsifier used in this comparative example is sodium lauryl sulfate. In Test Example 8, an emulsion thickener was prepared using this comparative example and formulated into a transparent shower gel according to the formulation in Table 1. Viscosity tests were subsequently conducted at different pH values. The test results are shown in Table 2.

[0064] Comparative Example 6 A method for preparing an emulsion thickener. The parameter control and operating steps of this preparation method are the same as those in Example 1, except that the emulsifier used in this comparative example is Span-60. In Test Example 9, an emulsion thickener was prepared using this comparative example and formulated into a transparent shower gel according to the formulation in Table 1. Subsequently, viscosity tests were conducted at different pH values. The test results are shown in Table 2.

[0065] Comparative Example 7 A method for preparing an emulsion thickener. The parameter control and operating steps of this preparation method are the same as those in Example 1, except that the emulsifier used in this comparative example is added all at once and is contained in the first material. In Test Example 10, an emulsion thickener was prepared using this comparative example and formulated into a transparent shower gel according to the formulation in Table 1. Viscosity tests were subsequently conducted at different pH values. The test results are shown in Table 2.

[0066] Table 2

[0067] Combined with Test Examples 1 to 3 in Table 2, it can be confirmed that when the thickener prepared by the preparation method of the emulsion thickener with acid-return stability of the present invention is used in the preparation of a cosmetic bath lotion, after neutralization with a composite alkali (pH = 7), it can exert excellent suspension, stabilization and system thickening effects, and obtain a cosmetic product with a smooth skin feel; when the pH value of the system decreases toward the acidic direction, the bath lotion containing the emulsion thickener of the embodiment of the present invention can still maintain a high viscosity and rheological properties, and the system viscosity can quickly return to the neutral level and gradually increase, reflecting the excellent network reconstruction response rate and self-repair function of the emulsion thickener of this embodiment, with excellent acid-return stability, and can be applied to a wider range of pH conditions and formulas.

[0068] By combining Test Example 1 with Test Example 4 and Test Examples 6-7 in Table 2, it is confirmed that the addition of a polypeptide containing a specific polar amino acid residue in the preparation method of the present invention improves the acid recovery performance and thickening efficiency of the entire thickener system, and has better thickening performance under acidic conditions; and the addition of a structural additive with a specific molecular weight during the preparation process enables the emulsion thickener to exert better acid recovery performance. Further combined with Test Example 5, it is confirmed that the use of a composite emulsifier and a specific polypeptide structural additive in the preparation method of the present invention synergistically improves the acid recovery performance of the system containing the emulsion thickener, not only improving the skin feel of the system, but also enhancing its interfacial stability and improving its rheological properties under acidic conditions.

[0069] By combining Test Example 1 with Test Examples 8-9, it was verified that the addition of a composite emulsifier comprising an anionic emulsifier and a nonionic emulsifier in the preparation method of the present invention can effectively promote the formation of a cross-linked network, not only improving the thickening performance of the emulsion thickener during alkali activation, resulting in a cosmetic product with high viscosity and better skin feel, but also effectively promoting the formation of a reversible dynamic cross-linked network when the pH value of the system is acidic, maintaining the viscosity and skin feel of the cosmetic. Combined with Test Example 1 and Test Example 10, it was confirmed that the step-by-step addition of emulsifiers in the preparation method of the present invention helps to control the thickener emulsion particle size and its distribution, and improve the thickening effect under acid reversion conditions.

[0070] It should be noted that the above is a further detailed description of the present invention in conjunction with specific embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, several simple improvements can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. An emulsion thickener with acid stability, characterized in that: The raw materials of the emulsion thickener include polymer monomers, emulsifiers, initiators, cross-linking agents, water and structural additives; The polymerizable monomers include a first monomer and a second monomer, the first monomer is an α,β-unsaturated acid monomer, the second monomer is an α,β-unsaturated ester monomer, and the structural additive is a polypeptide including polar amino acid residues.

2. The acid-stable emulsion thickener according to claim 1, characterized in that The structural additive is a polypeptide comprising charged amino acid residues, and the molecular weight of the structural additive is 500 to 5000 Daltons; And / or, the mass of the structural additive is 0.5% to 3% of the mass of the polymerized monomer.

3. The acid-stable emulsion thickener according to claim 1, characterized in that The emulsifier is a composite emulsifier of anionic emulsifier and nonionic emulsifier, the mass of the emulsifier is 0.1%~3% of the mass of the polymerized monomer, and the mass ratio of the nonionic emulsifier to the anionic emulsifier is (1~4):

1.

4. The acid-stable emulsion thickener according to claim 1, characterized in that The cross-linking agent includes one or more of pentaerythritol triacrylate, trimethylolpropane triacrylate, dipentaerythritol pentaacrylate, 1,6-hexanediol diacrylate, trimethylolpropane trimethacrylate, diallyl phthalate, and pentaerythritol tetraacrylate; the mass of the cross-linking agent is 0.1% to 3% of the mass of the polymerized monomer; And / or, the initiator includes a first initiator and a second initiator, the first initiator and the second initiator are independently selected from one or more of potassium persulfate, sodium persulfate, ammonium persulfate, sodium thiosulfate, azobisisobutylamidine hydrochloride and azobisisobutylimidazoline hydrochloride; the mass ratio of the first initiator to the second initiator is (0.2~5):1; the initiator accounts for 0.05%~1% of the mass of the polymerized monomer.

5. A method for preparing an emulsion thickener with acid stability, characterized in that: The raw materials of the emulsion thickener include polymerizable monomers, emulsifiers, initiators, crosslinking agents, water and structural additives, the polymerizable monomers include a first monomer and a second monomer, the first monomer is an α,β-unsaturated acid monomer, the second monomer is an α,β-unsaturated ester monomer, the structural additive is a polypeptide including polar amino acid residues, and the initiators include a first initiator and a second initiator; The preparation method comprises the following steps: S1: Under an inert atmosphere, heating a first material to a first temperature, adding a second material and mixing them uniformly to obtain a first reaction system; S2: adding a third material and a fourth material dropwise to the first reaction system to obtain a second reaction system after the addition is completed; S3: heating the second reaction system to a second temperature for reaction to obtain the emulsion thickener with back acid stability; The emulsifier used in the preparation method is added in two parts; the first material is a mixture of a portion of the emulsifier and water; the second material is a mixture of the first initiator and water; the third material is a mixture of the polymerization monomer, the cross-linking agent, another portion of the emulsifier and water; and the fourth material is a mixture of the second initiator, the structural additive and water.

6. The method for preparing an emulsion thickener having acid return stability according to claim 5, wherein: The structural additive is a polypeptide comprising charged amino acid residues; and / or, the molecular weight of the structural additive is 500 to 5000 Daltons; and / or, the structural additive is a polypeptide chain comprising at least one charged amino acid residue of lysine, arginine, histidine, glutamic acid or aspartic acid; And / or, the mass of the structural additive is 0.5% to 3% of the mass of the polymerized monomer.

7. The method for preparing an emulsion thickener having acid return stability according to claim 5, wherein: The emulsifier is a composite emulsifier of anionic emulsifier and nonionic emulsifier; The anionic emulsifier includes one or more of sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium laurylsulfonate, sodium laurylphosphate, sodium stearate, sodium lauroyl sarcosinate, sodium laureth sulfate, sodium tetradecyl sulfate, and sodium dioctyl sulfosuccinate; and / or, The nonionic emulsifier includes one or more of Tween-80, Span-80, Span-60, lauric acid glyceryl ester, polyglycerol fatty acid ester, sucrose fatty acid ester, alkyl glucoside, and methyl glucoside polyoxyethylene ether; In the emulsifier, the mass ratio of the nonionic emulsifier to the anionic emulsifier is (1-4):1; the mass of the emulsifier is 0.1%-3% of the mass of the polymerized monomer; And / or, the mass ratio of the emulsifier contained in the third material to the first material is (0.2~5):

1.

8. The method for preparing an emulsion thickener having acid return stability according to claim 5, wherein: The first monomer comprises one or more of acrylic acid, methacrylic acid, crotonic acid, maleic acid, cinnamic acid, fumaric acid, citraconic acid and mesaconic acid; and / or, the second monomer comprises one or more of methyl acrylate, ethyl acrylate, butyl acrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, palmitic acrylate and ethylene glycol dimethacrylate; And / or, the mass concentration of the polymerization monomer in the second reaction system is 5% to 50%.

9. The method for preparing an emulsion thickener having acid back stability according to claim 5, wherein: The first initiator and the second initiator are independently selected from one or more of potassium persulfate, sodium persulfate, ammonium persulfate, sodium thiosulfate, azobisisobutylamidine hydrochloride and azobisisobutylimidazoline hydrochloride; the sum of the mass of the first initiator and the second initiator is 0.05% to 1% of the mass of the polymerized monomer; the mass ratio of the first initiator to the second initiator is (0.2 to 5):1; And / or, the cross-linking agent includes one or more of pentaerythritol triacrylate, trimethylolpropane triacrylate, dipentaerythritol pentaacrylate, 1,6-hexanediol diacrylate, trimethylolpropane trimethacrylate, diallyl phthalate, and pentaerythritol tetraacrylate; and the mass of the cross-linking agent is 0.1% to 3% of the mass of the polymerized monomer.

10. The method for preparing an emulsion thickener having acid return stability according to claim 5, characterized in that: The first temperature is 50-80°C; And / or, the second temperature is 70-90° C., and the reaction time under the second temperature condition is 1-5 hours; And / or, in step S2, the third material and the fourth material are added at the same speed, and the addition of the two materials is completed within a time range of 0.5 to 3 hours.

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