Polyacrylic acid-sodium polyacrylate aqueous dispersion and preparation method thereof

Abstract

The invention discloses a preparation method of a polyacrylic acid-sodium polyacrylate aqueous dispersion. The polyacrylic acid / sodium polyacrylate aqueous dispersion with low viscosity (1,500-2,500 cps, 25 DEG C), medium and high molecular weight (Mw = 150,000-300,000) and strong comprehensive performance is prepared by adopting a high-temperature reaction condition without using an organic solvent, the problem that high molecular weight and low viscosity are difficult to realize at the same time in a traditional process is solved, and the prepared polyacrylic acid / sodium polyacrylate has the advantages of high molecular weight, low viscosity, high molecular weight and high comprehensive performance. And the viscosity reducer has excellent film-forming property and strength, and has excellent viscosity reduction and dispersion properties in a dispersed inorganic powder test. The preparation method is green, low in cost, simple and convenient to operate and more beneficial to industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a polyacrylic acid-sodium polyacrylate aqueous dispersion and a preparation method thereof. Background Art

[0002] As an important polymer, the aqueous dispersion of polyacrylic acid-sodium polyacrylate has been widely used in many fields such as coatings, adhesives, dispersants, etc. Molecular weight is an important index of polyacrylic acid-sodium polyacrylate. High molecular weight can ensure good film-forming properties and mechanical properties of the coating, while low viscosity is beneficial to construction. However, the viscosity of its aqueous dispersion is theoretically also positively correlated with the molecular weight. The traditional preparation method of polyacrylic acid-sodium polyacrylate has a relatively low temperature (below 75°C), which cannot balance high molecular weight and low viscosity. Patent application number CN106699936A discloses a preparation method of ultra-high molecular weight sodium polyacrylate, which uses inverse emulsion polymerization (40-60°C) to obtain sodium polyacrylate solids with a molecular weight Mw = 400,000-500,000, but the viscosity of only 0.2% aqueous solution can reach 500-600 cps (25°C), the solid content is low, and increasing the solid content will result in too high viscosity, poor leveling property of the coating, difficult construction, affecting efficiency, and a large amount of organic solvents are used in the preparation process, and the recovery and other processes are cumbersome. Patent application number CN102718904A discloses a preparation method of a low molecular weight sodium polyacrylate dispersant, which uses solution polymerization (20-60°C) to obtain an aqueous dispersion of sodium polyacrylate with a weight average molecular weight of 2,000-8,000, high solid content (above 40%) and low viscosity (200-500 cps, 25°C). Therefore, there is an urgent need to develop a polyacrylic acid-sodium polyacrylate aqueous dispersion with medium to high molecular weight (Mw = 150,000-300,000) and low viscosity (1,500-2,500 cps, 25°C) and strong comprehensive performance. At the same time, new, green and efficient preparation processes are needed, which is of great significance for promoting the upgrading and sustainable development of the polyacrylic acid-related industries, and also prompts researchers to continuously explore and innovate its preparation methods to meet the dual needs of the market and the environment. Summary of the Invention

[0003] Object of the Invention: In view of the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a polyacrylic acid-sodium polyacrylate aqueous dispersion and a preparation method thereof. Using acrylic acid as the main raw material and deionized water as the dispersion solvent, the process is different from the traditional polymerization process. By increasing the polymerization temperature, acrylic acid can be quickly polymerized. Increasing the temperature also increases the reaction activity of the long chain, making the activity difference between small molecules and large molecules smaller, obtaining a macromolecular chain with a narrow molecular weight distribution. As the entanglement between small molecular chains and large molecular chains is reduced, the medium to high molecular weight polyacrylic acid / sodium polyacrylate aqueous dispersion with low viscosity characteristics is realized.

[0004] Technical solution: In the preparation method of the polyacrylic acid-sodium polyacrylate aqueous dispersion of the present invention, the reaction raw materials include the following components:

[0005] Acrylic acid 25-35 wt%;

[0006] Neutralizing agent 0.4-20 wt%;

[0007] Initiator 0.2-0.5 wt%;

[0008] Reducing agent 0-0.03 wt%;

[0009] Chain transfer agent 0-0.02 wt%;

[0010] Deionized water 65-75 wt%;

[0011] The above components are all calculated according to the mass fraction of the system;

[0012] The specific preparation method includes the following steps:

[0013] Step (1): Dissolve the initiator and part of the deionized water according to the designed ratio to form initiator solution ① and initiator solution ② for standby;

[0014] Step (2): Add the reducing agent, chain transfer agent and the remaining deionized water into the reaction kettle, stir until the solids are dissolved, and heat to 85-90 °C;

[0015] Step (3): Under the condition of 85-90 °C, simultaneously dropwise add acrylic acid and initiator solution ①;

[0016] Step (4): After the dropping is completed, carry out the first-stage reaction at a controlled temperature of 85-90 °C;

[0017] Step (5): After the first-stage reaction is completed, dropwise add initiator solution ②, and carry out the second-stage reaction at a controlled temperature of 85-90 °C;

[0018] Step (6): After the second-stage reaction is completed, cool down to below 40 °C, and dropwise add the neutralizing agent solution to the required pH value according to the formula design to obtain a polyacrylic acid-sodium polyacrylate aqueous dispersion with Mw = 150,000-300,000 and a viscosity of 1,500-2,500 mP·s at 25 °C.

[0019] Further, as a preferred embodiment, the neutralizing agent is one or more of sodium hydroxide and potassium hydroxide, the initiator is one or more of sodium persulfate, potassium persulfate, ammonium persulfate, and hydrogen peroxide, the reducing agent is one or more of sodium sulfite, potassium sulfite, sodium citrate, potassium citrate, and monovalent thiourea salts, and the chain transfer agent is one or more of sodium bisulfite, potassium bisulfite, isopropyl alcohol, n-butanol, 2-mercaptoethanol, and dodecyl mercaptan.

[0020] Further, as a preferred embodiment, the initiator solution ① in step (1) is prepared from an initiator and deionized water, and its concentration is 0.4 - 0.7 wt%; the initiator solution ② is prepared from an initiator and deionized water, and its concentration is 1 - 1.5 wt%.

[0021] Further, as a preferred embodiment, the stirring speed in step (2) is 200 - 600 rpm, and the addition amount of deionized water in the reaction kettle is 25 - 40% of its formulated amount.

[0022] Further, as a preferred embodiment, the dropping time of the initiator solution ① and acrylic acid in step (3) is 2 - 3 hours; the reaction time in the first stage in step (4) is 3 - 4 hours.

[0023] Further, as a preferred embodiment, the dropping time of the initiator solution ② in step (5) is 20 - 30 minutes, and the reaction time in the second stage in step (6) is 1 - 2 hours.

[0024] Further, as a preferred embodiment, the concentration of the neutralizing agent added in step (6) is its 30% aqueous solution, the addition method is dropping, the process temperature is controlled below 45°C, and the required pH in step (6) is 1 - 8.

[0025] The present invention also claims the polyacrylic acid - sodium polyacrylate aqueous dispersion prepared by the above method.

[0026] Beneficial effects: (1) In this technical solution, acrylic acid is used as the main raw material and deionized water is used as the dispersion solvent. The process is different from the traditional polymerization process. By increasing the polymerization temperature, acrylic acid can polymerize quickly. Increasing the temperature also increases the reaction activity of the long chain, making the activity difference between small molecules and large molecules smaller, obtaining a macromolecular chain with a narrow molecular weight distribution. As a result, the entanglement between small molecular chains and large molecular chains is reduced, thereby realizing the low-viscosity characteristic of the polyacrylic acid - sodium polyacrylate aqueous dispersion with medium to high molecular weight;

[0027] (2) The polyacrylic acid - sodium polyacrylate aqueous dispersion prepared by the present invention has a relatively high molecular weight and a low viscosity, excellent dispersion performance / film-forming performance, and can meet the application requirements in different fields;

[0028] (3) The preparation method of the present invention is simple and easy to operate, does not contain any organic solvents, is green and low-cost, and is more conducive to industrial environmental protection production. Description of the Drawings

[0029] Figure 1 It is the infrared spectrum diagram of the polyacrylic acid-sodium polyacrylate aqueous dispersion prepared in Example 1. Detailed Embodiments

[0030] In order to better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with embodiments. The purpose is to understand the content of the present invention in detail, rather than a limitation to the present invention.

[0031] Unless otherwise specified, the reagents and raw materials used in the embodiments and comparative examples of the present invention are all commercially available.

[0032] Example 1:

[0033] 0.3 g of potassium persulfate and 75 g of deionized water were mixed and stirred until completely dissolved to obtain initiator solution ①. 0.15 g of potassium persulfate and 15 g of deionized water were mixed and stirred until completely dissolved to obtain initiator solution ②. 0.01 g of sodium sulfite, 0.075 g of sodium bisulfite and 100 g of deionized water were added to the reaction kettle. When the stirrer was started and the temperature was raised to 88 °C, 75 g of acrylic acid monomer and initiator solution ① were added dropwise. The dropping time was 2-3 hours. After dropping, the first-stage reaction was carried out at a temperature in the range of 85-90 °C for 3-4 hours. After the first-stage reaction was completed, initiator solution ② was added dropwise. The dropping time was about 20-30 minutes. Subsequently, the second-stage reaction was continued at 85-90 °C for 1-2 hours. After the reaction was completed, the temperature was lowered to below 40 °C, and 30% sodium hydroxide solution was added dropwise until pH = 6-7 to obtain the polyacrylic acid-sodium polyacrylate aqueous dispersion.

[0034] As Figure 1 shown, it is the infrared spectrum diagram of the polyacrylic acid-sodium polyacrylate aqueous dispersion prepared in this example. Specifically, 3276.00 cm -1 is the stretching vibration peak of the carboxyl and hydroxyl groups in acrylic acid, 2944.74 cm -1 is the stretching vibration peak of methylene, 1734.08 cm -1 is the stretching vibration peak of the carboxyl carbonyl group in acrylic acid. The infrared spectrum diagram confirms the successful preparation of Example 1.

[0035] Example 2

[0036] This example is basically the same as Example 1, except that the feeding amount of sodium bisulfite is 0.15 g.

[0037] Example 3

[0038] This example is basically the same as Example 1, except that the chain transfer agent is 2-mercaptoethanol.

[0039] Example 4

[0040] This example is basically the same as Example 1, except that initiator solution ① consists of 0.525 g of potassium persulfate and 75 g of deionized water, and initiator solution ② consists of 0.225 g of potassium persulfate and 15 g of deionized water.

[0041] Example 5

[0042] This example is basically the same as Example 1, except that the initiator is ammonium persulfate.

[0043] Example 6

[0044] This example is basically the same as Example 1, except that pH adjustment is not performed.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that the reaction temperature is 60 - 65 °C and the addition amount of sodium bisulfite is 0.75 g.

[0047] Comparative Example 2

[0048] The difference between this comparative example and Example 1 is that the reaction temperature is 60 - 65 °C.

[0049] To verify the performance of a polyacrylic acid / sodium polyacrylate aqueous dispersion described in the present invention, the examples and comparative examples were tested. The test method was carried out in accordance with HG / T 2838. The specific test results are shown in Table 1.

[0050] Table 1 Test results of the product performance of Examples 1 - 6 and Comparative Examples 1 - 2

[0051] Performance Molecular weight Solid content / % Film-forming property Film-forming strength / MPa Viscosity / cps, 25 °C Example 1 220,000 30.22 Good 3.5 2500 Example 2 170,000 29.87 Good 2.5 1700 Example 3 200,000 30.35 Good 2.6 1900 Example 4 210,000 30.61 Good 3.0 1600 Example 5 190,000 30.72 Good 2.8 2350 Example 6 225,000 30.11 Good 3.3 2400 Comparative example 1 1000,000+ / / / Gel Comparative example 2 60,000 31.01 Poor, easy to powder 0.2 3500

[0052] As can be seen from the results in Table 1, the polyacrylic acid-sodium polyacrylate aqueous dispersions prepared in each example of the present invention all have high molecular weight, low viscosity, and excellent film-forming performance and strength. In particular, Example 1 has excellent viscosity reduction and dispersion performance in the test of dispersing inorganic powders, and has great application potential in water-based inks and architectural coatings. The comparative examples adopted traditional low-temperature polymerization. In Comparative Example 1, explosive polymerization and gelation occurred on the premise of the same formula. In Comparative Example 2, the amount of chain transfer was increased, but when the molecular weight was only 60,000, the viscosity was as high as 3500, and the film-forming performance and strength were poor.

[0053] As described above, this is only an implementation mode of the invention, and does not limit the scope of patent protection. Those skilled in the art make non-substantive changes or substitutions based on the invention, and still fall within the scope of patent protection.

Claims

1. A method for preparing a polyacrylic acid-sodium polyacrylate aqueous dispersion, characterized in that The reaction raw materials include the following components: Acrylic acid 25-35wt%; Neutralizer 0.4-20wt%; Initiator 0.2-0.5wt%; Reducing agent 0-0.03wt%; Chain transfer agent 0-0.02wt%; Deionized water 65-75wt%; The above components are calculated by system mass fraction; The specific preparation method comprises the following steps: Step (1): dissolving the initiator and part of deionized water according to the designed ratio to form initiator solution ① and initiator solution ② for standby use; Step (2): Add the reducing agent, chain transfer agent and the remaining deionized water into a reaction kettle, stir until the solid is dissolved, and heat to 85-90° C.; Step (3): at 85-90° C., simultaneously add acrylic acid and initiator solution ①; Step (4): After the dropwise addition is completed, the temperature is controlled at 85-90° C. to carry out the first stage reaction; Step (5): After the first stage reaction is completed, the initiator solution ② is added dropwise, and the temperature is controlled at 85-90° C. to carry out the second stage reaction; Step (6): After the second stage reaction is completed, the temperature is lowered to below 40° C., and a neutralizer solution is added dropwise according to the formula design to a desired pH value to obtain a polyacrylic acid-sodium polyacrylate aqueous dispersion.

2. The method for preparing the polyacrylic acid-sodium polyacrylate aqueous dispersion according to claim 1, characterized in that: The neutralizing agent is one or more of sodium hydroxide and potassium hydroxide, the initiator is one or more of sodium persulfate, potassium persulfate, ammonium persulfate, and hydrogen peroxide, the reducing agent is one or more of sodium sulfite, potassium sulfite, sodium citrate, potassium citrate, and monovalent thiourea salt, and the chain transfer agent is one or more of sodium bisulfite, potassium bisulfite, isopropanol, n-butanol, 2-mercaptoethanol, and dodecyl mercaptan.

3. The method for preparing the polyacrylic acid-sodium polyacrylate aqueous dispersion according to claim 1, characterized in that: The initiator solution ① in step (1) is prepared from an initiator and deionized water, and its concentration is 0.4-0.7 wt %; the initiator solution ② is prepared from an initiator and deionized water, and its concentration is 1-1.5 wt %.

4. The method for preparing the polyacrylic acid-sodium polyacrylate aqueous dispersion according to claim 1, characterized in that: The stirring speed in step (2) is 200-600 rpm, and the amount of deionized water added to the reactor is 25-40% of its formula amount.

5. The method for preparing the polyacrylic acid-sodium polyacrylate aqueous dispersion according to claim 1, characterized in that: The dripping time of the initiator solution ① and acrylic acid in step (3) is 2 to 3 hours; and the first stage reaction time in step (4) is 3 to 4 hours.

6. The method for preparing the polyacrylic acid-sodium polyacrylate aqueous dispersion according to claim 1, characterized in that: The dripping time of the initiator solution ② in step (5) is 20 to 30 minutes, and the second stage reaction time in step (6) is 1 to 2 hours.

7. The method for preparing the polyacrylic acid-sodium polyacrylate aqueous dispersion according to claim 1, characterized in that: The concentration of the neutralizing agent added in step (6) is a 30% aqueous solution thereof, and the adding method is dropwise addition, and the process temperature is controlled below 45° C. The required pH in step (6) is 1-8.

8. A polyacrylic acid-sodium polyacrylate aqueous dispersion prepared by the method according to any one of claims 1 to 7.

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