An organic polymer-modified silica sol, a method for preparing the same, and use thereof

Abstract

This invention discloses an organic polymer-modified silica sol, its preparation method, and its application. The method involves a one-step reaction of a silicon source (silica powder, silanol, and sodium methylsilicate) with sodium hydroxide, 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, and guar ether, under the action of a maleic anhydride graft compatibilizer. The preparation process of this invention is simple, requires minimal equipment, and can be completed in one step, eliminating the need for the previously required acidification, deionization, and organic modification of the silica sol. When applied in the field of investment casting, the resulting modified silica sol can significantly shorten the drying time between shell layers and improve the wet strength of the shell.

Description

Technical Field

[0001] This invention relates to an organic polymer-modified silica sol, its preparation method, and its applications. It belongs to the fields of sol technology and precision casting technology. Background Technology

[0002] Silica sol is a colloidal solution in which silica particles are uniformly dispersed in water. It is a high-performance inorganic polymer adhesive widely used in various industrial fields. In the investment casting industry, silica sol is used as an adhesive for wax model shells. However, silica sol adhesive dries slowly, the prepared shells have low wet strength, and the shells are easily damaged during handling and coating, resulting in low shell-making efficiency. Therefore, modification treatment is required in practical applications.

[0003] To meet application requirements, polymer-modified silica sols have been developed. For example, US Patent US005118727A discloses a polymer-containing silica sol stabilized mixture comprising a silica sol solution and PVA or methylcellulose, generated at a pH of 2.7-7.0. However, this patent requires highly demanding acidification, deionization, and metal ion surface modification of the silica sol, increasing the production process. Furthermore, acidic silica sols place high demands on the performance of refractory materials used in investment casting, particularly regarding purity and leachate content, increasing production costs. Additionally, in actual production, investment casting manufacturers using water-based silica sols as binders typically use alkaline silica sols; changes in the pH of the binder can cause many incompatibilities. Therefore, the acidic silica sol provided by this patent has a cumbersome and complex production process, increasing production costs and selling prices, hindering its widespread application.

[0004] Patent application CN1414054A discloses a silica sol adhesive modified with PVA, modified starch, or modified cellulose, and its manufacturing method. The adhesive comprises alkaline silica sol, PVA, modified starch, or modified cellulose. The manufacturing method involves first preparing an aqueous solution of PVA, modified starch, or modified cellulose, then preparing an alkaline silica sol solution, and finally mixing the two solutions and ensuring homogeneity to obtain the silica sol adhesive. This patent application discloses an alkaline silica sol adhesive, overcoming the shortcomings of acidic silica sols. However, in practical production applications, it cannot significantly achieve the claimed effects of shortening the drying time between shell layers in investment casting, improving the wet strength of the shell, and reducing residual strength.

[0005] Therefore, it is of great significance to provide a silica sol with a simple production process that can significantly shorten the drying time between shell layers in investment casting and improve the wet strength of the shell. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an organic polymer-modified silica sol, its preparation method, and its application, so as to solve the problems of low wet strength of the shell and long drying time of the shell when the existing silica sol is applied in the field of investment casting.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing organic polymer modified silica sol, wherein sodium hydroxide, 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, guar gum ether and deionized water are first added to a silicon source and stirred evenly, then maleic anhydride graft compatibilizer is added and stirred evenly, heated and pressurized to react, and then post-treated to obtain the product.

[0008] Preferably, the silicon source includes silicon powder, silanol, and sodium methylsilicate, and the mass ratio of silicon powder, silanol, sodium methylsilicate, sodium hydroxide, 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, guar gum ether, and maleic anhydride graft compatibilizer is 2-3:1-2:1-2:2-2.5:0.1-0.2:0.2-0.3:0.1-0.2:0.5-1; the mass ratio of the total mass of these raw materials to the mass of deionized water is 1:1.5-2.

[0009] More preferably, the silicon powder is purchased from Shandong Minglan Silicon Powder Materials Co., Ltd., and has a median particle size of 500 nanometers.

[0010] More preferably, the silanol is trimethylsilanol, purchased from Hubei Xinyuhong Biomedical Technology Co., Ltd.

[0011] Preferably, the 2-hydroxypropyl starch is obtained by modifying starch with propylene oxide under alkaline conditions.

[0012] A further preferred method is as follows: First, add sodium sulfate to water and stir to dissolve at 40°C. Then, add starch and stir until uniform to make starch milk. Next, add sodium hydroxide solution and stir until uniform. Then, add propylene oxide in a sealed environment filled with nitrogen and react. Adjust the pH to 5.5 using a 3% hydrochloric acid solution. Centrifuge to collect the precipitate, wash with water, dry, pulverize, and sieve to obtain the final product.

[0013] More preferably, the mass ratio of sodium sulfate, water, starch, sodium hydroxide solution, and propylene oxide is 5-8:100:100:40:8-10; the starch is corn starch, and the mass concentration of the sodium hydroxide solution is 20%. In this process, sodium sulfate acts as a swelling inhibitor.

[0014] More preferably, the reaction conditions are: reaction temperature 150℃, reaction time 3-5h; preferably, the 2-hydroxyethyl modified cellulose is obtained by first treating cellulose with alkali and then reacting it with ethylene oxide.

[0015] A further preferred method is as follows: First, cellulose is added to a sodium hydroxide solution with a mass concentration of 18–30% and impregnated at 20°C to obtain alkali cellulose; then, in the presence of the diluent acetone, the alkali cellulose is reacted with ethylene oxide at 20–60°C for 1–3 hours, the pH is adjusted to 4–6 using glacial acetic acid, and the product is washed, dried, and pulverized to obtain the final product. The diluent is used to prevent the product from dissolving and to facilitate separation.

[0016] More preferably, the mass ratio of cellulose, sodium hydroxide solution, acetone, and ethylene oxide is 100:40 to 100:8 to 10, and the mass concentration of sodium hydroxide solution is 20%.

[0017] A further preferred method is to soak for 2 to 3 hours.

[0018] Preferably, the guar gum ether is obtained by first treating guar gum with alkali and then reacting it with propylene oxide.

[0019] A further preferred method is as follows: first, guar gum is stirred and dispersed in an organic solvent, then sodium hydroxide solution is added for alkali treatment to activate the hydroxyl groups of guar gum; then propylene oxide is added dropwise, and the reaction is carried out at 20-60℃ for 1-3 hours, followed by filtration, washing, drying, and pulverization to obtain the final product.

[0020] More preferably, the mass ratio of guar gum, organic solvent, sodium hydroxide solution, and propylene oxide is 100:100:40:8~10; the organic solvent is diethyl ether, and the mass concentration of the sodium hydroxide solution is 20%.

[0021] More preferably, the alkali treatment conditions are: temperature 60-75℃ and time 6-8h.

[0022] Preferably, the heating and pressurizing reaction conditions are: temperature 60-80℃, pressure 1-2MPa, and time 24h.

[0023] Preferably, the post-processing includes: natural cooling to room temperature and solid-liquid separation.

[0024] An organic polymer-modified silica sol is obtained by the aforementioned preparation method.

[0025] The aforementioned application of an organic polymer-modified silica sol in a binder for investment casting.

[0026] The beneficial effects of this invention are as follows: This invention discloses an organic polymer-modified silica sol, its preparation method, and its application. It is obtained by a one-step reaction of a silicon source (silicon powder, silanol, and sodium methylsilicate) with sodium hydroxide, 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, guar gum ether, etc., under the action of a maleic anhydride graft compatibilizer. The preparation process of this invention is simple, requires minimal equipment, and can be completed in one step, eliminating the need for the previously required high-level acidification, deionization, and organic modification of the silica sol. When applied in the field of investment casting, the obtained modified silica sol can significantly shorten the drying time between shell layers and improve the wet strength of the shell.

[0027] This invention primarily improves product performance through the synergistic effect of 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, and guar gum ether. Specifically, 2-hydroxypropyl starch is obtained by hydroxypropyl ethylation of starch. Hydroxypropyl ethyl esters exhibit steric hindrance, preventing starch chain aggregation and crystallization. Furthermore, their hydrophilic properties weaken the internal hydrogen bond strength of starch granules, facilitating swelling and gelatinization. Attached Figure Description

[0028] Figure 1 shows the modified silica sol obtained in Example 1. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that the following description is only for explaining the present invention and does not limit its content. Example 1

[0030] This embodiment provides a high-efficiency modified silica sol of organic polymer, comprising, by weight: 2 parts silica powder, 1 part silanol, 1 part sodium methylsilicate, 2 parts sodium hydroxide, 0.2 parts 2-hydroxyethyl modified cellulose, 0.1 parts 2-hydroxypropyl starch, 0.1 parts guar gum ether, 0.5 parts maleic anhydride graft compatibilizer (purchased from Shandong Shoucheng Chemical Co., Ltd.), and 10.35 parts deionized water.

[0031] The preparation method of 2-hydroxypropyl starch is as follows: Sodium sulfate is first added to water and stirred at 40°C to dissolve. Starch is then added and stirred evenly to form a starch slurry. Sodium hydroxide solution is then added and stirred evenly. Propylene oxide is then added in a sealed, nitrogen-filled environment to react. The pH is adjusted to 5.5 using a 3% hydrochloric acid solution. The precipitate is collected by centrifugation, washed with water, dried, pulverized, and sieved. The mass ratio of sodium sulfate, water, starch, sodium hydroxide solution, and propylene oxide is 5:100:100:40:8. The starch is corn starch, and the mass concentration of the sodium hydroxide solution is 20%. Sodium sulfate acts as a swelling inhibitor in this process. The reaction conditions are: reaction temperature 150°C and reaction time 3 hours. The preparation method of 2-hydroxyethyl modified cellulose is as follows: Cellulose is first added to an 18% sodium hydroxide solution and impregnated at 20°C to obtain alkali cellulose. Then, in the presence of acetone as a diluent, alkali cellulose reacts with ethylene oxide at 20°C for 1 hour. The pH is adjusted to 4 using glacial acetic acid. The cellulose is washed, dried, and pulverized. The diluent is used to prevent the product from dissolving and to facilitate separation; the mass ratio of cellulose, sodium hydroxide solution, acetone, and ethylene oxide is 100:40:8, and the mass concentration of sodium hydroxide solution is 20%; the soaking time is 2 hours.

[0032] The preparation method of guar gum ether is as follows: first, guar gum is stirred and dispersed in an organic solvent, then sodium hydroxide is added for alkali treatment to activate the hydroxyl groups of guar gum; then propylene oxide is added dropwise, and the reaction is carried out at 20°C for 1 hour. After filtration, washing, drying, and pulverization, the guar gum ether is obtained. The mass ratio of guar gum, organic solvent, sodium hydroxide, and propylene oxide is 100:100:40:8. The organic solvent is diethyl ether. The alkali treatment conditions are: temperature 60°C and time 6 hours.

[0033] This embodiment provides a highly effective modified silica sol using organic polymers. The specific steps are as follows: Sodium hydroxide, 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, guar gum ether, and deionized water are added to silica powder, silanol, and sodium methylsilicate. After stirring evenly, maleic anhydride grafted compatibilizer is added and stirring continues. The reaction is carried out in a reaction vessel. Then, the temperature is increased to 60°C and the pressure is increased to 1 MPa. The reaction is continued for 24 hours, after which the pressure and heating are stopped. After cooling, solid-liquid separation is performed to obtain the highly effective modified silica sol using organic polymers. (See Figure 1) Example 2

[0034] This embodiment provides a high-efficiency modified silica sol of organic polymer, comprising, by weight: 3 parts silica powder, 2 parts silanol, 2 parts sodium methylsilicate, 2.5 parts sodium hydroxide, 0.3 parts 2-hydroxyethyl modified cellulose, 0.2 parts 2-hydroxypropyl starch, 0.2 parts guar gum ether, 1 part maleic anhydride graft compatibilizer, and 22.4 parts deionized water.

[0035] The preparation method of 2-hydroxypropyl starch is as follows: Sodium sulfate is first added to water and stirred at 40°C to dissolve. Starch is then added and stirred evenly to form a starch slurry. Sodium hydroxide solution is then added and stirred evenly. Propylene oxide is then added in a sealed, nitrogen-filled environment to react. The pH is adjusted to 5.5 using a 3% hydrochloric acid solution. The precipitate is collected by centrifugation, washed with water, dried, pulverized, and sieved. The mass ratio of sodium sulfate, water, starch, sodium hydroxide solution, and propylene oxide is 8:100:100:40:10. The starch is corn starch, and the mass concentration of the sodium hydroxide solution is 20%. Sodium sulfate acts as a swelling inhibitor in this process. The reaction conditions are: reaction temperature 150°C and reaction time 5 hours. The preparation method of 2-hydroxyethyl modified cellulose is as follows: Cellulose is first added to a 30% sodium hydroxide solution and impregnated at 20°C to obtain alkali cellulose. Then, in the presence of acetone as a diluent, alkali cellulose reacts with ethylene oxide at 60°C for 3 hours. The pH is adjusted to 6 using glacial acetic acid. The cellulose is washed, dried, and pulverized. The diluent is used to prevent the product from dissolving and to facilitate separation; the mass ratio of cellulose, sodium hydroxide solution, acetone, and ethylene oxide is 100:100:10, and the mass concentration of sodium hydroxide solution is 20%; the soaking time is 3 hours.

[0036] The preparation method of guar gum ether is as follows: first, guar gum is stirred and dispersed in an organic solvent, then sodium hydroxide is added for alkali treatment to activate the hydroxyl groups of guar gum; then propylene oxide is added dropwise, and the reaction is carried out at 60°C for 3 hours. After filtration, washing, drying, and pulverization, the guar gum ether is obtained. The mass ratio of guar gum, organic solvent, sodium hydroxide, and propylene oxide is 100:100:40:10. The organic solvent is diethyl ether. The alkali treatment conditions are: temperature 75°C and time 8 hours.

[0037] This embodiment provides a high-efficiency modified silica sol with organic polymer, and the specific steps are the same as in Embodiment 1. Example 3

[0038] This embodiment provides a high-efficiency modified silica sol of an organic polymer, comprising, by weight: 2.5 parts silica powder, 1.5 parts silanol, 1.5 parts sodium methylsilicate, 2.25 parts sodium hydroxide, 0.25 parts 2-hydroxyethyl modified cellulose, 0.15 parts 2-hydroxypropyl starch, 0.15 parts guar gum ether, 0.75 parts maleic anhydride graft compatibilizer, and 15.8375 parts deionized water.

[0039] The preparation method of 2-hydroxypropyl starch is as follows: Sodium sulfate is first added to water and stirred at 40°C to dissolve. Starch is then added and stirred evenly to form a starch slurry. Sodium hydroxide solution is then added and stirred evenly. Propylene oxide is then added in a sealed, nitrogen-filled environment to react. The pH is adjusted to 5.5 using a 3% hydrochloric acid solution. The precipitate is collected by centrifugation, washed with water, dried, pulverized, and sieved. The mass ratio of sodium sulfate, water, starch, sodium hydroxide solution, and propylene oxide is 7:100:100:40:9. The starch is corn starch, and the mass concentration of the sodium hydroxide solution is 20%. Sodium sulfate acts as a swelling inhibitor in this process. The reaction conditions are: reaction temperature 150°C and reaction time 4 hours. The preparation method of 2-hydroxyethyl modified cellulose is as follows: Cellulose is first added to a 20% sodium hydroxide solution and impregnated at 20°C to obtain alkali cellulose. Then, in the presence of acetone as a diluent, alkali cellulose reacts with ethylene oxide at 40°C for 2 hours. The pH is adjusted to 5 using glacial acetic acid. The cellulose is washed, dried, and pulverized. The diluent is used to prevent the product from dissolving and to facilitate separation; the mass ratio of cellulose, sodium hydroxide solution, acetone, and ethylene oxide is 100:50:9, and the mass concentration of sodium hydroxide solution is 20%; the soaking time is 2 hours.

[0040] The preparation method of guar gum ether is as follows: first, guar gum is stirred and dispersed in an organic solvent, then sodium hydroxide is added for alkali treatment to activate the hydroxyl groups of guar gum; then propylene oxide is added dropwise, and the reaction is carried out at 45°C for 2 hours. After filtration, washing, drying, and pulverization, the guar gum ether is obtained. The mass ratio of guar gum, organic solvent, sodium hydroxide, and propylene oxide is 100:100:40:9. The organic solvent is diethyl ether. The alkali treatment conditions are: temperature 70°C and time 7 hours.

[0041] This embodiment provides a high-efficiency modified silica sol with organic polymer, and the specific steps are the same as in Embodiment 1.

[0042] Comparative Example 1: 2-hydroxyethyl modified cellulose and guar gum ether were omitted, and only 2-hydroxypropyl starch was added; the rest was the same as in Example 1.

[0043] Comparative Example 2: 2-hydroxypropyl starch and guar gum ether were omitted, and only 2-hydroxyethyl modified cellulose was added; the rest was the same as in Example 1.

[0044] Comparative Example 3: 2-hydroxypropyl starch and 2-hydroxyethyl modified cellulose were omitted, and only guar gum ether was added; the rest was the same as in Example 1.

[0045] Comparative Example 4: Other 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, and guar gum ether were used. Specifically, the reaction conditions for 2-hydroxypropyl starch were: reaction temperature 120°C, reaction time 1 h; the reaction conditions for 2-hydroxyethyl modified cellulose were: reaction temperature 80°C, reaction time 4 h; and the reaction conditions for guar gum ether were: reaction temperature 50°C, pressure 0.5 MPa, time 12 h. The rest were the same as in Example 1.

[0046] The performance of the silica sols obtained in Examples 1-3 and Comparative Examples 1-4 was tested, and the results are shown in Table 1.

[0047] Among them, the tensile shear strength was tested in accordance with GB / T 7124-2008; the peel strength was tested in accordance with ASD3330; the wet strength of the shell was tested using the "three-point bending test method" and the testing instrument was a bending test machine; the drying time of the shell was determined by the coating drying indicator (purchased from Suzhou Dingxin Desiccant Co., Ltd.).

[0048] .

[0049] As shown in Table 1, the silica sols obtained in Examples 1-3 have excellent properties, which greatly shorten the drying time between layers in investment casting and improve the wet strength of the shell.

[0050] Comparative Example 1 omitted 2-hydroxyethyl modified cellulose and guar gum ether, and only added 2-hydroxypropyl starch; Comparative Example 2 omitted 2-hydroxypropyl starch and guar gum ether, and only added 2-hydroxyethyl modified cellulose; Comparative Example 3 omitted 2-hydroxypropyl starch and 2-hydroxyethyl modified cellulose, and only added guar gum ether; Comparative Example 4 used other different 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, and guar gum ether, and the silica sol performance deteriorated significantly, indicating that 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, and guar gum ether synergistically improve the silica sol performance.

[0051] Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Based on the technical solutions of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

Claims

1. A method for preparing an organic polymer-modified silica sol, characterized by, The silicon source is added with sodium hydroxide, 2-hydroxypropyl starch, 2-hydroxyethyl modified cellulose, guar gum ether and deionized water, stirred uniformly, then added with maleic anhydride grafting compatilizer, stirred uniformly, heated and pressurized to react, post-treated, and obtained.

2. The production method according to claim 1, characterized by, The silicon source comprises silicon powder, silanol and sodium methyl silicate, and the mass ratio of the silicon powder, the silanol, the sodium methyl silicate, the sodium hydroxide, the 2-hydroxypropyl starch, the 2-hydroxyethyl modified cellulose, the guar gum ether, the maleic anhydride grafting compatilizer is 2-3:1-2:1-2:2-2.5:0.1-0.2:0.2-0.3:0.1-0.2:0.5-1; the mass ratio of the total mass of these raw materials to the deionized water is 1:1.5-2.

3. The production method according to claim 1, characterized by, The 2-hydroxypropyl starch is obtained by modifying the starch with propylene oxide under alkaline conditions.

4. The production method according to claim 1, characterized by, The 2-hydroxyethyl modified cellulose is obtained by alkali treatment of cellulose and then reaction with ethylene oxide.

5. The production method according to claim 1, wherein The guar gum ether is obtained by alkali treatment of guar gum and then reaction with propylene oxide.

6. The production method according to claim 1, wherein The heating and pressurized reaction conditions are: temperature 60-80℃, pressure 1-2MPa, time 24h.

7. The production method according to claim 1, characterized by, The post-treatment comprises: Natural cooling to room temperature, solid-liquid separation.

8. An organic polymer-modified silica sol, characterized in that, The organic polymer modified silica sol is obtained by the preparation method in any one of claims 1-7.

9. Use of the organic polymer modified silica sol in claim 8 in a binder for investment casting.

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