Silicon dioxide / organic silicon defoaming agent and preparation method thereof

Abstract

According to the preparation method of the defoaming agent, the organic silicon defoaming agent is prepared from hydrophilic silicon dioxide. Comprising the following steps: (1) mixing an organosilicon polymeric monomer with an end-capping reagent, heating, and adding a catalyst for ring opening polymerization to form a polysiloxane prepolymer; and (2) adding hydrophilic silicon dioxide powder or silicon dioxide slurry into the prepolymer, wherein silicon dioxide participates in organic silicon polymerization reaction. And (3) removing the catalyst and small molecules, and cooling to room temperature to obtain the defoaming agent. The silicon dioxide is added in the organosilicon polymerization process through an in-situ synthesis method, so that part of organopolysiloxane is grafted and grown on the surface of the silicon dioxide and forms the organosilicon defoaming agent together with polysiloxane, and the organosilicon defoaming agent has a good defoaming effect. The method is different from a conventional technical path for preparing the organic silicon defoaming agent by adopting hydrophobic nano silicon dioxide, the product cost is low, and large-scale production and application are easy.

Description

Technical Field

[0001] The invention belongs to the technical field of nano hybrid materials, and particularly relates to an organosilicon defoamer prepared by adopting hydrophilic silicon dioxide and a preparation method thereof. Background Art

[0002] In industrial production, stirring and other processes will generate a large amount of unnecessary foam, which will cause problems such as reduced production capacity and reduced product quality. Therefore, defoaming agents can generally be added to quickly eliminate foam and reduce the harm caused by foam. At present, the commonly used defoaming agents in industry include mineral oils, polyethers, silicones, polyether-modified silicones, etc. Silicone oil defoamers are widely used due to their low surface tension, good thermal stability, chemical inertness, and non-physiological toxicity. However, the dispersion stability and defoaming effect of pure silicone oil in the solution are poor, so hydrophobic nano-silica is usually added to improve the dispersibility of the silicone defoamer, thereby enhancing the defoaming effect.

[0003] At present, nano-silica used in combination with silicone has good hydrophobicity. For example, patents CN102407032A, CN103641195B and CN109796601A all combine silicone with hydrophobic nano-silica, and then make silicone defoamers through different processes. Hydrophobic silica can promote oil droplets to enter the bubble film, forming a needle effect and improving the defoaming efficiency. However, hydrophobic silica is usually hydrophobically modified by silane coupling agent or other modifiers on hydrophilic silica powder; or the hydrophilic silica slurry is liquid-phase in-situ modified, then dried and crushed. Directly adding hydrophilic silica in the process of in-situ polymerization of silicone oil can reduce the modification, drying, crushing and other processes, which is green and energy-saving.

[0004] The invention provides a method for preparing an organosilicon defoamer from hydrophilic silica. The method adopts an in-situ synthesis method, unmodified nano-silica is added into a polymerization reaction system, and part of the organopolysiloxane is chemically bonded with the nano-silica to obtain an organosilicon defoamer with a partial network structure. The defoamer has excellent defoaming and anti-foaming effects and high stability. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide an organosilicon defoamer prepared by hydrophilic silica. The organosilicon defoamer adopts an in-situ synthesis method, adds unmodified nano-silica to a polymerization reaction system, and chemically bonds part of the organopolysiloxane with the nano-silica to obtain an organosilicon defoamer with a partial network structure. The defoamer has excellent defoaming and anti-foaming effects and high stability.

[0006] The present invention also provides a method for preparing the organosilicon defoaming agent by using the hydrophilic silicon dioxide.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing a silicon dioxide / organic silicon defoamer comprises the following steps: (1) The organosilicon monomer is mixed with the end-capping agent, and after heating, a catalyst is added to perform ring-opening polymerization to form a polysiloxane prepolymer with a certain molecular weight; (2) Adding hydrophilic silica powder or silica slurry to the polysiloxane prepolymer, the silica participates in the polymerization reaction of the organosilicon; wherein, after the silica slurry is added, the solvent needs to be removed by vacuum as soon as possible; (3) Remove the catalyst and small molecule compounds and cool to room temperature to obtain the product.

[0008] Specifically, the organosilicon monomer used in step (1) can be methylcyclosiloxane or a mixture of methylcyclosiloxanes, including a mixture of dimethylcyclosiloxanes (DMC), a hydrolyzate of dichlorodimethylsilane (Me2SiCl2), octamethylcyclotetrasiloxane (D4), etc. The end-capping agent used in step (1) is one or more of hexamethyldisilazane (HMDS), hexamethyldisiloxane, decamethylsiloxane, etc., and the amount of the end-capping agent can be 0-5% of the mass of the organosilicon monomer. When the end-capping agent is not added, the silica slurry will be grafted onto the open-ring polysiloxane chain after addition, which can prevent the growth of the polymer to a certain extent.

[0009] Furthermore, the catalyst used in step (1) can be an acidic catalyst or a basic catalyst. The acidic catalyst can be one or more of concentrated sulfuric acid, trifluorosulfonic acid or solid acid, and the basic catalyst can be tetramethylammonium hydroxide (TMAH), potassium hydroxide, etc. The amount of the catalyst can be 0.01-0.1% of the mass of the organosilicon monomer. The ring-opening polymerization reaction temperature in step (1) is 80-130°C. If the temperature exceeds 130°C, the catalyst decomposes. If the temperature is too high, the viscosity increases rapidly. The reaction time is 0.5-4h.

[0010] Specifically, the particle size of the hydrophilic silica powder used in step (2) is 3-10 μm, and the amount of the hydrophilic silica powder added is 0.5-10% of the mass of the organosilicon monomer. The hydrophilic silica powder is silica prepared by a gas phase method or a precipitation method, has not been hydrophobically modified, and exhibits hydrophilicity.

[0011] Furthermore, the silica slurry in step (2) can be a silica product prepared by a gas phase method or a precipitation method and dispersed in a low boiling point solvent (ethanol, acetone, etc.); or the silica slurry can also be a reaction slurry of nano-silica obtained by a liquid phase method before drying. Preferably, the silica slurry in step (2) is synthesized by a precipitation method, and the nano-silica synthesized by adding acid to a sodium carbonate solution. When added in the form of silica slurry, the added amount is calculated as silica, and the amount of silica added is 0.5-10% of the mass of the organosilicon monomer.

[0012] Furthermore, the polymerization reaction time of step (2) is 0.5~4h.

[0013] Specifically, in step (3), the temperature is raised to 130-170° C. and maintained for more than 30 min to decompose the catalyst, and un-ring-opened raw materials and small molecular compounds are removed by reduced pressure distillation.

[0014] The present invention provides a silicon dioxide / organosilicon defoamer prepared by the above preparation method. The prepared defoamer is a silicon dioxide / organosilicon composite defoamer, and part of the polysiloxane is chemically bonded with nano silicon dioxide to obtain an organosilicon defoamer with a partial network structure.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention introduces hydrophilic nano-silica that has not been hydrophobically modified into the polymerization process of organic silicon, so that the silicon dioxide and part of the polysiloxane are chemically bonded, thereby achieving the effect of simultaneous polymerization and hydrophobic modification.

[0016] 2) The present invention adopts an in-situ synthesis method, the production process is simple, and the obtained organosilicon defoamer product has lower raw material and production costs. The present invention obtains an organosilicon defoamer with a partial network structure, which has excellent defoaming and anti-foaming effects. The defoaming time does not exceed 2.7s after 10 shakes, and the defoaming time does not exceed 3.2s after 100 shakes, which is much better than 208.2s and 14.0s of Comparative Example 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The silica (Si-J) and nano-silica powder (Si-0) obtained by eluting the silica / organic silicon defoamer prepared in Example 2 with toluene were subjected to thermogravimetric testing, and the microstructural changes of silica in the defoamer were analyzed by weight loss curves; Figure 2 is the contact angle (a) of nano-silica powder (Si-0) and the contact angle (b) of silica (Si-J) obtained after the defoamer in Example 2 was eluted with toluene; Figure 3TEM image (a) of nano-silica powder (Si-0) and TEM image (b) of silica (Si-J) obtained after the defoaming agent in Example 2 was eluted with toluene. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0019] In the following examples, the raw materials used are all common commercial products that can be directly purchased or prepared using conventional techniques in the art. The particle size of the hydrophilic silica powder used is 3-10 μm.

[0020] Room temperature refers to 25±5°C.

[0021] Example 1 and Example 2: Hydrophilic silica powder is added during the synthesis of polysiloxane, the reaction is continued for a period of time, and the temperature is increased to decompose the catalyst and remove small molecular compounds to obtain a silica / organic silicon defoaming agent.

[0022] Example 3 and Example 4: First, a silica slurry is prepared, the prepared slurry is washed with water, and replaced with an organic solvent. Then, the organic slurry is added during the synthesis of polysiloxane, the organic solvent is removed by vacuuming, the reaction is continued for a period of time, and the temperature is increased to decompose the catalyst and remove small molecular compounds, thereby obtaining a silica / organic silicon defoamer.

[0023] Example 1 100g of dimethylcyclosiloxane mixture (DMC, Shenzhen Jipeng Silicon Fluoride Material Co., Ltd., JP-201) and 0.32g of hexamethyldisilazane (HMDS) were added to a three-necked flask, heated to 90°C (reaction constant temperature at 90°C) under stirring conditions, 0.05g of catalyst tetramethylammonium hydroxide (TMAH) was added, and the ring-opening polymerization reaction was carried out for 2h to form a polysiloxane prepolymer; 5g of hydrophilic nano-silica powder (Henan Heda Nanomaterial Engineering Research Center Co., Ltd., DNS-400) was added, and the reaction continued for 1h. After that, the temperature was raised to 130°C and maintained for 30min to decompose the catalyst, and the reduced pressure distillation was carried out until no fraction was removed. After cooling to room temperature, the organosilicon defoamer was obtained.

[0024] Example 2 100g DMC and 0.65g HMDS were added to a three-necked flask, and the temperature was raised to 95°C (the reaction temperature was kept at 95°C) under stirring conditions. 0.05g of catalyst TMAH was added, and the ring-opening polymerization reaction was carried out for 0.5h to form a polysiloxane prepolymer. Then 7g of hydrophilic nano-silica powder (Henan Heda Nanomaterial Engineering Research Center Co., Ltd., DNS-400) was added, and the reaction continued for 4h. After that, the temperature was raised to 140°C and maintained for 30min to decompose the catalyst. The reduced pressure distillation was carried out until no fraction was removed. After cooling to room temperature, the organosilicon defoamer was obtained.

[0025] Figure 1 The silica (Si-J) obtained by eluting the silica / organosilicon defoamer prepared in Example 2 with toluene is given, and the silica (Si-J) is subjected to thermogravimetric testing with nano-silica powder (Si-0), and the microstructural changes of silica in the defoamer are analyzed by the weight loss curve. Silicone is dissolved in toluene, and the polysiloxane molecular chains free or adsorbed on the surface of silica can be removed after multiple ultrasonic and centrifugal washings. It can be seen from the thermogravimetric graph that the weight loss of Si-J increases significantly between 400 and 550°C, indicating that after the reaction of silica and organosilicon, some polysiloxane molecular chains are grafted on the hydroxyl groups on the surface of silica through chemical bonds.

[0026] Figure 2 The contact angle of the silica Si-J obtained after toluene elution in Example 2 is given. As can be seen from the figure, the hydrophobicity is very good, proving that the polysiloxane molecular chain is grafted on the silica surface.

[0027] Figure 3 The TEM image of silica Si-J obtained after toluene elution in Example 2 is given. As can be seen from the figure, the primary particle size of the eluted silica Si-J is larger than that of silica Si-0, the dispersibility is better, the agglomeration phenomenon is improved, and the spatial network structure still exists.

[0028] Figure 1-3 The main purpose is to compare the silica obtained after the prepared silica / silicone defoamer is eluted with toluene with the silica before being added to the reaction, in order to prove that in the process of adding silica by in-situ synthesis, the silica is combined with the polysiloxane in the form of chemical bonds, thereby playing a defoaming role.

[0029] Example 3 Add 83.0g of sodium carbonate solution with a modulus of 3.36 and a silica content of 25.31% to a flask, add 217.0g of pure water, add sulfuric acid to adjust the pH to 8-9, heat to 60°C and react at a constant temperature for 1h, then heat to 80°C and react at a constant temperature for 1h. Wash the obtained slurry with water to remove the generated inorganic salts, wash with water until the conductivity is below 150μs / m, add a small amount of ethanol to filter and wash, repeat 3 times, the water in the slurry is replaced by ethanol, and ethanol is added to prepare an ethanol slurry with a silica content of 8% for standby use.

[0030] Weigh 100g of octamethylcyclotetrasiloxane (D4) and add it to a three-necked flask. Heat it to 100°C under stirring, add 0.03g of catalyst TMAH, and perform ring-opening polymerization for 0.5h to form a polysiloxane prepolymer. Add 62.5g of ethanol slurry with a silica content of 8% prepared above, and quickly remove the ethanol by vacuum distillation. The remaining silica and silicone continue to react at 100°C for 3h. Then heat it to 135°C and keep it for 30min to decompose the catalyst. Vacuum distill until no fraction is removed. After cooling to room temperature, a silica / silicone defoamer is obtained.

[0031] Example 4 Add 54.9g of sodium carbonate solution with a modulus of 3.06 and a silica content of 24.6% to a flask, add 245.1g of pure water, add ammonium bicarbonate to adjust the pH to about 7, heat to 60°C and react at a constant temperature for 1h, then heat to 80°C and react at a constant temperature for 2h. Wash the obtained slurry with water to remove the generated inorganic salts, wash with water until the conductivity is below 300μs / m, add a small amount of acetone to filter and wash, repeat 3 times, the water in the slurry is replaced by acetone, and acetone is added to prepare an acetone slurry with a silica content of 6% for standby use.

[0032] Weigh 100g of DMC and add it to a three-necked flask. Heat it to 90°C under stirring, add 0.05g of catalyst TMAH, and perform ring-opening polymerization for 45min to form a polysiloxane prepolymer. Add 50.0g of acetone slurry with a silica content of 6% prepared above, and quickly remove the acetone by vacuum distillation. The remaining silica and silicone continue to react at 90°C for 4h. Then heat it to 140°C and keep it for 30min to decompose the catalyst. Vacuum distill until no fraction is removed. After cooling to room temperature, a silica / silicone defoamer is obtained.

[0033] Comparative Example 1 100 g (viscosity 500 mPa·s) of dimethyl silicone oil was weighed, and 5 g of hydrophobic silica (Henan Heda Nanomaterial Engineering Research Center Co., Ltd., DNS-418) was added thereto. The temperature was raised to 150 ºC and kept constant for 4 h under stirring, and then cooled to room temperature to obtain a hydrophobic silica / silicone defoaming agent.

[0034] Table 1 is a comparison chart of the defoaming time of the silica / silicone defoamers prepared in each embodiment and comparative example. The defoaming effect test was carried out with reference to GB / T 26527-2011. It can be seen from Table 1 that the defoamers prepared in each embodiment showed good defoaming effect under 10 times of shaking and 100 times of shaking. The defoaming time did not exceed 2.7s after 10 times of shaking, and did not exceed 3.2s after 100 times of shaking, which was much better than 208.2s and 14.0s of comparative example 1.

[0035] Table 1 Comparison of defoaming time of silicon dioxide / organic silicon defoaming agent in various embodiments and comparative examples In summary, the present invention uses an in-situ synthesis method to add silicon dioxide during the polymerization of organosilicon, so that part of the organopolysiloxane is grafted and grown on the surface of silicon dioxide, and together with the polysiloxane, it forms an organosilicon defoamer with good defoaming effect. This method is different from the conventional technical route of using hydrophobic nano-silica to prepare organosilicon defoamers, and the product cost is low and easy to mass produce and apply.

Claims

1. A method for preparing a silicon dioxide / organic silicon defoamer, characterized in that: The following steps are involved: (1) The organosilicon monomer is mixed with the end-capping agent, and after heating, a catalyst is added to carry out ring-opening polymerization to form a polysiloxane prepolymer; (2) Adding hydrophilic silica powder or silica slurry to the polysiloxane prepolymer, the silica participates in the polymerization reaction of the organosilicon; wherein, after the silica slurry is added, vacuum is applied to remove the solvent; (3) Remove the catalyst and small molecule compounds and cool to room temperature to obtain the product.

2. The method for preparing the silicon dioxide / organic silicon defoamer according to claim 1, characterized in that: The organic silicon monomer used in step (1) is methylcyclosiloxane or a mixture of methylcyclosiloxanes.

3. The method for preparing the silicon dioxide / organic silicon defoamer according to claim 1, characterized in that: The end-capping agent used in step (1) is one or more of hexamethyldisilazane, hexamethyldisiloxane, and decamethylsiloxane, and the amount of the end-capping agent is 0-5% of the mass of the organosilicon monomer.

4. The method for preparing the silicon dioxide / organic silicon defoamer according to claim 1, characterized in that: The catalyst used in step (1) is one or more of tetramethylammonium hydroxide, potassium hydroxide, concentrated sulfuric acid, trifluorosulfonic acid or solid acid, and the amount of the catalyst used is 0.01-0.1% of the mass of the organosilicon monomer.

5. The method for preparing the silicon dioxide / organic silicon defoamer according to claim 1, characterized in that: In step (1), the ring-opening polymerization reaction temperature is 80-130° C., and the reaction time is 0.5-4 h.

6. The method for preparing the silicon dioxide / organic silicon defoamer according to claim 1, characterized in that: The particle size of the hydrophilic silica powder used in step (2) is 3-10 μm, and the amount of the hydrophilic silica powder added is 0.5-10% of the mass of the organosilicon monomer.

7. The method for preparing the silicon dioxide / organic silicon defoamer according to claim 1, characterized in that: The silicon dioxide slurry in step (2) is obtained by dispersing the silicon dioxide product prepared by gas phase method or precipitation method in low boiling point solvent ethanol or acetone; or the silicon dioxide slurry is the reaction slurry of nano silicon dioxide obtained by liquid phase method before drying.

8. The method for preparing the silicon dioxide / organic silicon defoamer according to claim 1, characterized in that: The polymerization reaction time of step (2) is 0.5~4h.

9. The method for preparing the silicon dioxide / organic silicon defoamer according to claim 1, characterized in that: Step (3) The temperature is raised to 130-170° C. to decompose the catalyst, and unopened raw materials and small molecular compounds are removed by vacuum distillation.

10. The silicon dioxide / organic silicon defoamer prepared by the preparation method according to any one of claims 1 to 9.

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