Preparation method and application of stable antioxidant emulsion

Abstract

The invention relates to a preparation method and application of a stable antioxidant emulsion, and belongs to the field of antioxidants. The preparation method comprises the following steps: obtaining a molten antioxidant mixed solution; preparing an emulsifier; and preparing a stable antioxidant emulsion. The composite antioxidant is prepared into a small-particle-size stable emulsion, so that the antioxidant is uniformly distributed in a finished product, and the aging of the product is better inhibited and delayed; meanwhile, the small-particle-size stable emulsion containing the special polymer has the advantages that the antioxidant particles are not easy to aggregate and settle in the long-term storage process, so that the long-term stability is better.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a stable antioxidant emulsion, belonging to the field of antioxidants. Background Art

[0002] Adding antioxidants to rubber is a common method to inhibit or delay rubber aging, among which antioxidant emulsion is an important way to add antioxidants.

[0003] Commonly used antioxidants are mostly small molecules, which are easily volatilized by heat during processing. During use, they will migrate to the rubber surface over time and react with contact solvents to extract the rubber matrix. These physical losses lead to a significant shortening of the service life of rubber and its products; the volatilization, migration and extraction of small molecule antioxidants will also cause a certain degree of environmental pollution. Macromolecular antioxidants effectively overcome the above-mentioned shortcomings of small molecule antioxidants and show obvious advantages. CN110713622B discloses a method for emulsifying p-cresol and dicyclopentadiene butylated antioxidants with a molecular weight of about 650. However, the high melting temperature of the antioxidant in this method makes the emulsion darker, and the pressure operation puts higher requirements on the equipment. The average particle diameter of the reported antioxidant emulsion is above 360nm. The larger the particle size, the lower the dispersibility and stability of the antioxidant.

[0004] The particle size of the emulsion is one of the key factors affecting the use of macromolecular antioxidants. Smaller emulsion particle size can make the antioxidant evenly distributed in the finished product, better inhibit and delay product aging, and make the surface of the finished product smooth and delicate. Therefore, the preparation of macromolecular antioxidant small particle size emulsion has high research value and practical application significance. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a preparation method and application of a stable antioxidant emulsion, which improves the convenience of using the antioxidant, as well as the uniformity of the distribution of the antioxidant in the polymer and the convenience of adding.

[0006] The main antioxidant of the present invention is a polymeric polyphenolic substance, which has a large molecular weight and good compatibility with polymers, and has the characteristics of heat resistance and extraction resistance, and is a macromolecular antioxidant. The auxiliary antioxidant of the present invention is a low-toxic antioxidant containing phosphate and thiol groups in a chemical structure, has good thermal stability and oxidation performance, can effectively inhibit the occurrence of oxidation reactions, and can effectively delay the oxidative aging process of polymers such as synthetic resins, rubbers, and plastics under heating, light or oxygen contact when used as a polymer antioxidant, thereby extending the service life of the polymer. By combining the main antioxidant and the auxiliary antioxidant, the synergistic antioxidant effect is significantly improved. The main antioxidant has a large viscosity, and the auxiliary antioxidant helps the main antioxidant to melt and disperse. With the addition of a special emulsifier, the composite antioxidant is prepared into a small-particle stable emulsion, and the use process is more convenient, while effectively improving the dispersibility and uniformity of the antioxidant and improving the use efficiency.

[0007] The present invention designs a special emulsifier system according to the structure of the antioxidant, which specifically includes the steps of antioxidant melting, emulsifier preparation, antioxidant emulsification and the like.

[0008] The first aspect of the present invention discloses a method for preparing a stable antioxidant emulsion, comprising the following steps: 1) mixing the primary antioxidant p-methylphenol-dicyclopentadiene-isobutylated resin and the secondary antioxidant didodecanol thiodipropionate in a mass ratio of 1:0.2-2, and heating at 50-200° C. to obtain a molten antioxidant mixed solution; 2) Preparation of emulsifier: glycerol and ethylene oxide are subjected to addition reaction in a reactor at a molar ratio of 1:1-40, and glycerol polyoxyethylene ether with an average molecular weight of 1000-2000 is obtained by controlling the degree of polymerization of ethylene oxide; the obtained glycerol polyoxyethylene ether and oleic acid are reacted at a molar ratio of 1:1.5-2.5, 0.5%-1.0% by mass of p-toluenesulfonic acid is added as a catalyst, the temperature is controlled at 80-200°C, glycerol polyoxyethylene ether oleate is prepared, and the unreacted oleic acid and the catalyst are separated to obtain the desired emulsifier; 3) Dilute the emulsifier with 8 to 12 times of water, and then add it to the molten antioxidant mixture. The mass ratio of the emulsifier to the molten antioxidant mixture is 1:8-12. After shear dispersion and homogenization, a milky white emulsion is obtained, that is, a stable antioxidant emulsion.

[0009] In a preferred embodiment, glycerol polyoxyethylene ether reacts with oleic acid at 100-150°C for 2-8 hours. The addition reaction temperature of glycerol and ethylene oxide is 70-90°C (preferably 80°C) and the reaction time is 1.5-2.5 hours (preferably 2 hours).

[0010] Furthermore, by controlling the degree of polymerization of ethylene oxide, glycerol polyoxyethylene ether with an average molecular weight of 1000 to 1800 is obtained. 0.5% to 1.0% by mass of p-toluenesulfonic acid means: a mixture of glycerol polyoxyethylene ether, oleic acid, and p-toluenesulfonic acid, and the mass fraction of p-toluenesulfonic acid in the mixture is 0.5% to 1.0%.

[0011] In a preferred embodiment, glycerol and ethylene oxide are subjected to addition reaction in a reactor at a molar ratio of 1:15-30.

[0012] Furthermore, the total mass content of the primary antioxidant and the auxiliary antioxidant in the stable antioxidant emulsion is 46-50% (wt), the average particle size of the antioxidant emulsion is less than 300 nm, the viscosity is less than 400 cps at 25° C., and the pH value is 8.0-11.0.

[0013] In a preferred embodiment, the primary antioxidant and the secondary antioxidant are melted at a temperature of 50-200°C, stirred after melting, and cooled to 50-100°C to obtain a uniformly distributed molten antioxidant mixture. The purpose of cooling after melting is to prevent the components from volatilizing due to excessive temperature.

[0014] Furthermore, the stable antioxidant emulsion has an emulsifier content of 3 to 6 wt %, a solid content of 46 to 55 wt %, and is stored at room temperature for 12 months without a change in solid content of more than 1%.

[0015] In a preferred embodiment, in step 3), the shear dispersion speed is 200 to 5000 rpm, preferably 2000 to 4000 rpm; the homogenization pressure is 10 to 100 MPa, preferably 30 to 80 MPa.

[0016] The prepared emulsion is refrigerated at 3-4°C for 24 hours and then filtered with a 300-mesh polyester filter cloth to remove mechanical impurities and sediments. The emulsion is then stored at room temperature for more than 12 months, and the solid content does not change by more than 1%.

[0017] The present invention also provides an antioxidant emulsion prepared by the method for preparing the aforementioned stable antioxidant emulsion.

[0018] The invention also discloses the application of the above antioxidant emulsion in inhibiting or delaying rubber aging.

[0019] Compared with the prior art, the present invention has the following beneficial effects: the preparation process is simple and easy to control, no special equipment is required, no organic solvent is required, and industrial large-scale production can be carried out.

[0020] When preparing emulsifiers, polymer glycerol polyoxyethylene ether with an average molecular weight of 1000 to 2000 is more important for finally obtaining an average particle size of less than 300 nm. Glycerol polyoxyethylene ether is then reacted with oleic acid to form an ester to form an emulsifier. The emulsifier prepares the composite antioxidant into a small-particle stable emulsion, so that the antioxidant is evenly distributed in the finished product, and better inhibits and delays product aging; at the same time, the small-particle stable emulsion containing special polymers is not easy to aggregate and settle antioxidant particles during long-term storage, thereby having better long-term stability.

[0021] By controlling the molar ratio of glycerol to ethylene oxide to control the degree of ethylene oxide polymerization, glycerol polyoxyethylene ether is obtained, and the hydrophilicity and lipophilicity of the emulsifier are balanced, thereby emulsifying the large molecular weight composite antioxidant to make it have a better emulsion particle size. The antioxidant has a high water solubility and a high degree of ethylene oxide polymerization, and the antioxidant emulsion is difficult to demulsify during emulsion polymerization; the degree of ethylene oxide polymerization is small, and the dispersibility of the antioxidant is low. Glycerol polyoxyethylene ether is esterified with oleic acid to further enhance the water solubility and emulsification effect of the emulsifier. When the molar ratio of glycerol polyoxyethylene ether to oleic acid is 1:1.5~2.5, glycerol polyoxyethylene ether oleic acid can effectively overcome the coagulation caused by the good affinity with the antioxidant, and at the same time overcome the problem of the difficulty of demulsification of the antioxidant due to the strong water solubility. When the molar ratio of glycerol polyoxyethylene ether to oleic acid is 1:1 or higher, it is difficult to demulsify (the affinity with the antioxidant is too good); when the molar ratio of glycerol polyoxyethylene ether to oleic acid is 1:3 or lower, it causes coagulation.

[0022] The esterification reaction of glycerol polyoxyethylene ether and oleic acid needs to be carried out at high temperature in the absence of a catalyst. The degree of ether bond breakage during esterification increases and the water solubility decreases. The use of an easily separable solid catalyst reduces the esterification reaction temperature, reduces the degree of ether bond breakage during esterification, and reduces colored products. At the same time, it is easy to separate without causing additional pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the preparation method of the stable antioxidant emulsion. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with specific embodiments.

[0025] like Figure 1 As shown, the present invention discloses a method for preparing a stable antioxidant emulsion, comprising the following steps: 1) mixing the primary antioxidant p-methylphenol-dicyclopentadiene-isobutylated resin and the secondary antioxidant didodecanol thiodipropionate in a mass ratio of 1:0.2-2, and heating at 50-200° C. to obtain a molten antioxidant mixed solution; 2) Preparation of emulsifier: glycerol and ethylene oxide are subjected to addition reaction in a reactor at a molar ratio of 1:1-40, and glycerol polyoxyethylene ether with an average molecular weight of 1000-2000 is obtained by controlling the polymerization degree of ethylene oxide; the obtained glycerol polyoxyethylene ether and oleic acid are reacted at a molar ratio of 1:1.5-2.5, and the temperature is controlled at 80-200°C to obtain glycerol polyoxyethylene ether oleate. Preferably, glycerol polyoxyethylene ether and oleic acid are added to a reactor at a molar ratio of 1:1.5-2.5, 0.5%-1.0% by mass of p-toluenesulfonic acid is added as a catalyst, the temperature is raised to 100-150°C, the reaction is reacted for 2-8 hours, and the unreacted oleic acid and the catalyst are separated to obtain the desired emulsifier.

[0026] 3) The emulsifier is diluted with 8 to 12 times of water, and then added into the molten antioxidant mixture, and after shearing, dispersion and homogenization, a milky white emulsion, i.e. a stable antioxidant emulsion, is obtained; wherein the mass ratio of the emulsifier to the molten antioxidant mixture is 1:8-12.

[0027] The primary antioxidant in the examples and comparative examples is KY-616 (Jiangsu Feiya), and the secondary antioxidant is DLTP, both of which are commercially available. Example

[0028] Weigh 30 g of the primary antioxidant and 20 g of the secondary antioxidant, place them in a 500 mL beaker, adjust the temperature to 150°C, wait for the antioxidant to melt, and then cool to 50°C; Preparation of emulsifier: Addition reaction of glycerol and ethylene oxide in a reactor at a molar ratio of 1:25, the temperature of the addition reaction is 75°C, the reaction time is 2.5h, and the molecular weight of glycerol polyoxyethylene ether with a molecular weight of 1200-1500 is obtained by controlling the degree of polymerization of ethylene oxide; the obtained glycerol polyoxyethylene ether and oleic acid are in a molar ratio of 1:1.5, 0.5% mass fraction of p-toluenesulfonic acid is added as a catalyst, the temperature is controlled at 120°C, and the reaction is carried out for 8h to prepare glycerol polyoxyethylene ether oleate. Separate the unreacted oleic acid and the catalyst to obtain the desired emulsifier.

[0029] Weigh 5 g of emulsifier and 50 g of water, stir evenly and add to the beaker containing cooled molten antioxidant, start shear stirring, stirring speed 3700 rpm, stirring time 10 min; then transfer to homogenizer, homogenization pressure 70 MPa, homogenization time 10 min. Homogenized emulsion detection (dynamic light scattering laser particle size analyzer of Malvern Company, UK, the same below) particle size 270 nm, solid content (detection process: 1g emulsion is spread thinly on the surface of tin foil, at 105℃ to constant weight, the remaining mass divided by 1 multiplied by 100% is the solid content, the same below) 52.16% (wt), viscosity (25℃) 320 cps, pH value 8.5. Example

[0030] Weigh 20 g of the primary antioxidant and 30 g of the secondary antioxidant, place them in a 500 mL beaker, adjust the temperature to 150°C, wait until the antioxidant melts, and cool to 50°C; Preparation of emulsifier: Addition reaction of glycerol and ethylene oxide in a reactor at a molar ratio of 1:20, the temperature of the addition reaction is 80°C, the reaction time is 2h, and the molecular weight of glycerol polyoxyethylene ether with a molecular weight of 1100-1200 is obtained by controlling the degree of polymerization of ethylene oxide; the obtained glycerol polyoxyethylene ether and oleic acid are in a molar ratio of 1:2, 0.7% mass fraction of p-toluenesulfonic acid is added as a catalyst, the temperature is controlled at 130°C, and the reaction is carried out for 6h to prepare glycerol polyoxyethylene ether oleate. Separate the unreacted oleic acid and the catalyst to obtain the desired emulsifier.

[0031] Weigh 5 g of emulsifier and 52 g of water, stir evenly and add to the beaker containing cooled molten antioxidant, start shear stirring, stirring speed 3200 rpm, stirring time 10 min; then transfer to homogenizer, homogenization pressure 50 MPa, homogenization time 10 min. The homogenized emulsion is tested by laser particle size analyzer, the particle size is 245 nm, the solid content is 51.37% (wt), the viscosity (25℃) is 280cps, and the pH value is 9.0. Example

[0032] Weigh 25 g of the primary antioxidant and 25 g of the secondary antioxidant, place them in a 500 mL beaker, adjust the temperature to 150 °C, wait until the antioxidant melts, and cool to 50 °C; Preparation of emulsifier: Addition reaction of glycerol and ethylene oxide in a reactor at a molar ratio of 1:30, the temperature of the addition reaction is 80°C, the reaction time is 2h, and the molecular weight of glycerol polyoxyethylene ether with a molecular weight of 1500-1800 is obtained by controlling the degree of polymerization of ethylene oxide; the obtained glycerol polyoxyethylene ether and oleic acid are added in a molar ratio of 1:2.5, 1.0% mass fraction of p-toluenesulfonic acid is added as a catalyst, the temperature is controlled at 150°C, and the reaction is carried out for 6h to prepare glycerol polyoxyethylene ether oleate. Separate the unreacted oleic acid and the catalyst to obtain the desired emulsifier.

[0033] Weigh 5 g of emulsifier and 53 g of water, stir evenly and add to the beaker containing cooled molten antioxidant, start shear stirring, stirring speed 2900 rpm, stirring time 10 min; then transfer to homogenizer, homogenization pressure 40 MPa, homogenization time 10 min. The homogenized emulsion is tested by laser particle size analyzer, the particle size is 270 nm, the solid content is 50.73% (wt), the viscosity (25℃) is 320cps, and the pH value is 9.5.

[0034] Comparative Example 1 Weigh 30 g of the main antioxidant and 20 g of the auxiliary antioxidant, place them in a 500 mL beaker, adjust the temperature to 150 °C, wait for the antioxidant particles to melt, and cool to 50 °C; weigh 5 g of nonylphenol polyoxyethylene ether and 50 g of water, stir evenly and add them to the beaker containing the cooled molten antioxidant, turn on shear stirring, stirring speed 3700 rpm, stirring time 10 min; then transfer to a homogenizer, homogenization pressure 70 MPa, homogenization time 10 min. The homogenized emulsion is tested by a laser particle size analyzer, and the particle size is 380 nm, the solid content is 51% (wt), the viscosity (25 °C) is 400 cps, and the pH value is 8.0.

[0035] Comparative Example 2 The method is basically the same as Example 1, except that glycerol and ethylene oxide are added in a reaction vessel at a molar ratio of 1:100. The homogeneous emulsion has a particle size of 360 nm, a solid content of 49% (wt), a viscosity (25°C) of 380 cps, and a pH value of 8.0.

[0036] Comparative Example 3 The method is basically the same as Example 1, except that the p-toluenesulfonic acid catalyst is not added when preparing the emulsifier. The homogeneous emulsion has a particle size of 350 nm, a solid content of 52% (wt), a viscosity (25°C) of 370 cps, and a pH value of 8.5.

[0037] Comparative Example 4 The method is basically the same as Example 1, except that no auxiliary oxidant is added and the amount of the primary antioxidant added is 50 g. The homogeneous emulsion has a particle size of 480 nm, a solid content of 42% (wt), a viscosity (25°C) of 520 cps, and a pH value of 9.0.

[0038] Comparative Example 5 The method is basically the same as Example 1, except that glycerol polyoxyethylene ether and oleic acid are reacted at a molar ratio of 1:10 during the preparation of the emulsifier. The homogeneous emulsion has a particle size of 420 nm, a solid content of 46% (wt), a viscosity (25°C) of 460 cps, and a pH value of 8.5.

[0039] The emulsions of Examples 1-3 and Comparative Examples 1-2 were stored at room temperature for 16 months, and the solid content changes were 0.2%, 0.4%, 0.3%, 1.4% and 1.1%, respectively.

[0040] The above-described embodiments of the present invention do not constitute a limitation on the protection scope of the present invention. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a stable antioxidant emulsion, characterized in that: The steps include: 1) mixing a primary antioxidant p-methylphenol-dicyclopentadiene-isobutylated resin and a secondary antioxidant didodecanol thiodipropionate in a mass ratio of 1:0.2-2, and heating at 50-200° C. to obtain a molten antioxidant mixed solution; 2) Preparation of emulsifier: glycerol and ethylene oxide are subjected to addition reaction in a reactor at a molar ratio of 1:1-40, and glycerol polyoxyethylene ether with an average molecular weight of 1000-2000 is obtained by controlling the polymerization degree of ethylene oxide; the obtained glycerol polyoxyethylene ether and oleic acid are reacted at a molar ratio of 1:1.5-2.5, 0.5-1.0% by mass of p-toluenesulfonic acid is added as a catalyst, the temperature is controlled at 80-200° C., glycerol polyoxyethylene ether oleate is prepared, and unreacted oleic acid and the catalyst are separated to obtain the desired emulsifier; 3) The emulsifier is diluted with 8 to 12 times of water, and then added to the molten antioxidant mixture, the mass ratio of the emulsifier to the molten antioxidant mixture is 1:8-12, and after shear dispersion and homogenization treatment, a milky white emulsion, i.e. a stable antioxidant emulsion, is obtained.

2. The method for preparing a stable antioxidant emulsion according to claim 1, characterized in that: Glycerol polyoxyethylene ether and oleic acid are reacted at 100-150°C for 2-8h.

3. The method for preparing a stable antioxidant emulsion according to claim 1, characterized in that: Glycerol polyoxyethylene ether with an average molecular weight of 1000-1800 is obtained by controlling the polymerization degree of ethylene oxide.

4. The method for preparing a stable antioxidant emulsion according to claim 1, characterized in that: Glycerol and ethylene oxide are subjected to addition reaction in a reaction kettle at a molar ratio of 1:15-30.

5. The method for preparing a stable antioxidant emulsion according to claim 1, characterized in that: The total mass content of the main antioxidant and the auxiliary antioxidant in the stable antioxidant emulsion is 46-50% (wt), the average particle size of the antioxidant emulsion is less than 300nm, the viscosity is less than 400cps at 25°C, and the pH value is 8.0-11.

0.

6. The method for preparing a stable antioxidant emulsion according to claim 1, characterized in that: The main antioxidant and the auxiliary antioxidant are melted at a temperature of 50-200° C., stirred after melting, and cooled to 50-100° C. to obtain a uniformly distributed molten antioxidant mixed liquid.

7. The method for preparing a stable antioxidant emulsion according to claim 1, characterized in that: The emulsifier content in the stable antioxidant emulsion is 3-6wt%, the solid content is 46-55wt%, and the solid content changes by no more than 1% after storage for 12 months.

8. The method for preparing a stable antioxidant emulsion according to claim 1, characterized in that: In step 3), the shear dispersion speed is 200 to 5000 rpm, preferably 2000 to 4000 rpm; the homogenization pressure is 10 to 100 MPa, preferably 30 to 80 MPa.

9. The antioxidant emulsion obtained by the method for preparing a stable antioxidant emulsion according to any one of claims 1 to 8.

10. Use of the antioxidant emulsion according to claim 9 in inhibiting or delaying rubber aging.

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