A high-performance thin film without surface activity and a preparation method thereof

Abstract

The present application relates to the technical field of water-resistant film preparation, and particularly relates to a method for preparing a high-performance water-resistant film through Pickering emulsion polymerization, which comprises the following steps: (1) preparing a film-forming emulsion by using semi-continuous Pickering emulsion polymerization; (2) pouring the film-forming emulsion into a mold after neutralization for film formation. The present application can obtain silica-polymer microspheres with smaller particle size and higher solid content without using surface active agents and adding auxiliary comonomers or using cationic initiators, and the silica-polymer microspheres are used for film formation. The prepared film has good transparency and better mechanical properties. By adjusting the dropping time of monomers, the particle size of the generated latex particles is adjusted, thereby the distribution of silica in the film is adjusted, and the performance of the film also changes. The high-performance film has potential applications in the field of water-based anticorrosive coatings.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thin film preparation, and in particular to a preparation method of high-performance polymer thin film. BACKGROUND

[0002] Water-based dispersion is more and more used to replace solvent-based dispersion in the field of paint, adhesive and other fields due to its low VOC emission, green environmental protection and other advantages. At present, the common water-based dispersion is mainly synthesized by secondary dispersion or emulsion polymerization method, but both methods have certain limitations. The former still needs to use part of the solvent in the polymerization process, and the latter needs to use a certain amount of surfactant to stabilize the generated emulsion, and the presence of the surfactant will affect the film forming performance of the latex particle.

[0003] In the film forming process of the latex particle, the surfactant will migrate upward in the film forming process of the latex particle, and a large amount of small molecule surfactant will be enriched on the surface. Due to the hydrophilicity of the small molecule surfactant, the film surface also has certain hydrophilicity, which is not conducive to the film used in places requiring high water resistance.

[0004] Inorganic particles have the ability to stabilize oil droplets in water, namely Pickering stabilization, and then Pickering emulsion polymerization with inorganic particles as stabilizer begins to develop. The first developed Pickering emulsion polymerization is to promote the adsorption of silica to the generated latex particle by modifying the inorganic particles such as silica, copolymerizing with the polymer monomer with opposite charge to the silica and using cationic azo initiator. Subsequent studies have shown that when using relatively hydrophilic monomer MMA, the adsorption of unmodified silica to the surface of the latex particle can be promoted by van der Waals force using KPS as initiator. However, the organic-inorganic hybrid particles prepared by this method have large particle size and it is difficult to achieve high solid content. The film forming latex particles with large particle size are not conducive to film forming.

[0005] Therefore, it is necessary to develop a high-performance film without adding surfactant, high water resistance and good mechanical strength. SUMMARY

[0006] In order to solve the above problems, the present application provides a preparation method of small particle size, high solid content Pickering emulsion, which is used for film forming, and small particle size hybrid microspheres can be obtained without adding auxiliary comonomer or cationic azo initiator, and the transparency and mechanical properties of the film can be changed by monomer dropping time.

[0007] The first aspect of the present application provides a preparation method of high-performance polymer thin film, comprising the following steps:

[0008] (1) using semi-continuous Pickering emulsion polymerization to prepare film-forming emulsion;

[0009] (2) pouring the film-forming emulsion into a mold after neutralization for film formation.

[0010] Further, the step (1) specifically comprises the following steps: S1, S2, S3;

[0011] S1, preparing a reaction solution: preparing a silica aqueous dispersion and adjusting the pH to between 3 and 6;

[0012] S2, preparing an initiator solution: dissolving an initiator in water to obtain an initiator solution;

[0013] S3, preparing a film-forming emulsion: adding a first component crosslinking monomer to the reaction solution after adjusting the pH, then slowly adding the initiator solution and the monomer into the reaction solution after heating and removing nitrogen, and continuing the reaction to obtain a film-forming emulsion;

[0014] In some preferred embodiments, step S1 further comprises the step of purging the reaction container with nitrogen to remove residual oxygen.

[0015] Further, step (2) comprises S4, S4: adding a second component crosslinking monomer to the film-forming emulsion prepared in step S3 after adjusting the pH and pouring it into a mold for film formation.

[0016] Further, in step S1, the reaction solution contains 25-88 parts by mass of solvent water and 1-10 parts by mass of silica.

[0017] In some preferred embodiments, in step S1, the amount of silica added is 1%-10% of the total mass of water and silica.

[0018] Further, the initiator includes but is not limited to any one or a combination of two or more of potassium persulfate, ammonium persulfate, azobis diisobutyl amidine hydrochloride, and azobis diisobutyl cyanide;

[0019] Further, the first component crosslinking monomer is diacetone acrylamide; and the amount of the first component crosslinking monomer is 2.2%-11% of the mass of the monomer.

[0020] Further, the second component crosslinking monomer is adipic acid dihydrazide; and the amount of the second component crosslinking monomer is 1.1%-5% of the mass of the monomer.

[0021] Further, the monomer includes but is not limited to any one or a combination of two or more of methyl methacrylate, ethyl methacrylate, n-butyl acrylate, n-ethyl acrylate, and isobutyl acrylate;

[0022] Further, in step S3, the monomer dropwise adding time is 0-180 min.

[0023] In some preferred embodiments, in step S3, the monomer dropwise adding time is 0-60 min; more preferably 30-60 min.

[0024] Further, in step S3, the initiator dropwise adding time is 0-180 min.

[0025] In some preferred embodiments, in step S3, the initiator dropwise adding time is 0-60 min.

[0026] Further, in step S3, the final emulsion particle size is 100-300 nm.

[0027] In some embodiments, in step S3, the system reaction temperature is any temperature between 50-80℃.

[0028] In one embodiment, the final emulsion solid content prepared in step S3 is 10%-50%; preferably 10%-40%.

[0029] Further, in step S4, the pH adjusting step is between 8-9.

[0030] Further, in step S4, the film forming temperature is between 60-80℃.

[0031] Further, in step S1, the silica particle size is 10-30 nm.

[0032] Further, in step S3, the monomer adding amount is 10-30% of the total emulsion mass.

[0033] In some preferred embodiments, the monomer is methyl methacrylate monomer, and the adding amount is 10-30% of the total solution mass.

[0034] Further, the initiator adding amount is 1%-3% of the total solution mass.

[0035] In some preferred embodiments, in step S3, the first component crosslinking monomer is added to the S1 system, followed by heating to 70℃, then methyl methacrylate monomer and initiator are dropwise added to the system and reacted for 12 h; the polymer emulsion is obtained.

[0036] In some preferred embodiments, step S4 specifically includes the following steps: adding ammonia to the film forming emulsion to adjust the pH, then adding the second crosslinking monomer, and then pouring the film forming emulsion into a polytetrafluoroethylene mold for film forming.

[0037] The second aspect of the present application provides a method for preparing the high-performance polymer film.

[0038] The third aspect of the present application provides a method for adjusting the transparency and mechanical properties of the high-performance film, in which the mechanical properties and transparency of the final film are adjusted by adjusting the monomer dropping time in step S3.

[0039] Advantages: Compared with the prior art, the present application has at least the following characteristics and advantages:

[0040] The present application prepares hybrid microspheres by semi-continuous Pickering emulsion polymerization, and the silica-polymer microspheres with small particle size and high solid content can be obtained without using surface active agents and adding auxiliary comonomers or using cationic initiators, and the microspheres are used for film formation; the prepared film has good transparency and good mechanical properties and water resistance.

[0041] The present application also provides a method for adjusting the film formation properties, in which the mechanical properties and transparency of the final film are adjusted by adjusting the dropping time of the monomers and initiators. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 Digital photos of the films prepared in the examples and comparative examples;

[0043] Figure 2 Cross-sectional scanning electron microscope characterization graphs of the films prepared in the examples and comparative examples;

[0044] Figure 3 Transmittance of the films prepared in the examples and comparative examples;

[0045] Figure 4 Stress-strain curves of the films prepared in the examples and comparative examples;

[0046] Figure 5 24h and 7day water absorption rate change curves of the films prepared in the examples and comparative examples. DETAILED DESCRIPTION

[0047] The present application will be further described below in conjunction with the drawings and examples. According to the following examples, the present application can be better understood. However, it is easy for those skilled in the art to understand that the specific material proportions, process conditions and their results described in the examples are only used to illustrate the present application, and should not and will not limit the present application described in detail in the claims.

[0048] Example 1: Preparation of high-performance film

[0049] This example describes in detail a method for preparing a polymer film.

[0050] Raw materials are as follows: diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), methyl methacrylate (MMA), n-butyl acrylate (BA) Ludox TM-40 (aqueous dispersion of silicon dioxide), potassium persulfate (KPS), dilute hydrochloric acid, water.

[0051] The specific preparation process is as follows:

[0052] 1, a three-necked flask is added with 20 g of ultrapure water and 25 g of Ludox TM-40, and stirred at a speed of 300 rpm to mix them uniformly. Dilute hydrochloric acid is added to adjust the pH to 5.5, then nitrogen is passed for 30 min to remove oxygen, and the temperature is raised to 70°C. Then 0.44 g of diacetone acrylamide, 10 g of methyl methacrylate and 10 g of n-butyl acrylate and 0.2 g of initiator KPS dissolved in 10 g of water are directly added, and the reaction is carried out for 12 h.

[0053] After the reaction is completed, a polymer microsphere emulsion is obtained, ammonia is added to adjust the pH to about 8-9, then 0.22 g of adipic acid dihydrazide is added and stirred, and then poured into a polytetrafluoroethylene mold to form a film at 70°C for 24 h.

[0054] Example 2: Preparation of high-performance thin film (monomer drop time 30 min)

[0055] This example describes in detail a method for preparing a polymer micro-thin film.

[0056] Raw materials are as follows: diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), methyl methacrylate (MMA), n-butyl acrylate (BA) Ludox TM-40 (aqueous dispersion of silicon dioxide), potassium persulfate (KPS), dilute hydrochloric acid, water.

[0057] The specific preparation process is as follows:

[0058] 1, a three-necked flask is added with 20 g of ultrapure water and 25 g of Ludox TM-40, and stirred at a speed of 300 rpm to mix them uniformly. Dilute hydrochloric acid is added to adjust the pH to 5.5, then nitrogen is passed for 30 min to remove oxygen, and the temperature is raised to 70°C. Then 0.44 g of diacetone acrylamide, 10 g of methyl methacrylate and 10 g of n-butyl acrylate and 0.2 g of initiator KPS dissolved in 10 g of water are directly added, and the reaction is carried out for 12 h.

[0059] After the reaction is completed, a polymer microsphere emulsion is obtained, ammonia is added to adjust the pH to about 8-9, then 0.22 g of adipic acid dihydrazide is added and stirred, and then poured into a polytetrafluoroethylene mold to form a film at 70°C for 24 h.

[0060] Example 3: Preparation of high-performance thin film (monomer drop time 60 min)

[0061] This example describes in detail a method of preparing a polymer film.

[0062] The raw materials are as follows: diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), methyl methacrylate (MMA), n-butyl acrylate (BA), Ludox TM-40 (aqueous dispersion of silicon dioxide), potassium persulfate (KPS), dilute hydrochloric acid, water.

[0063] The specific preparation process is as follows:

[0064] 1. Add 20 g of ultrapure water and 25 g of Ludox TM-40 to a three-necked flask, mix them uniformly at a stirring rate of 300 rpm, add dilute hydrochloric acid to adjust the pH to 5.5, then remove oxygen by passing nitrogen for 30 min, raise the temperature to 70°C, directly add 0.44 g of diacetone acrylamide, then slowly drop 10 g of methyl methacrylate and 10 g of n-butyl acrylate and 0.2 g of initiator KPS dissolved in 10 g of water within 60 min, and react for 12 h.

[0065] After the reaction is completed, add ammonia water to adjust the pH to about 8-9, then add 0.22 g of adipic acid dihydrazide, stir, and pour into a polytetrafluoroethylene mold to form a film at 70°C for 24 h.

[0066] Example 4: Preparation of a high-performance film (monomer drop time 90 min)

[0067] This example describes in detail a method of preparing a polymer film.

[0068] The raw materials are as follows: diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), methyl methacrylate (MMA), n-butyl acrylate (BA), Ludox TM-40 (aqueous dispersion of silicon dioxide), potassium persulfate (KPS), dilute hydrochloric acid, water.

[0069] The specific preparation process is as follows:

[0070] 1. Add 20 g of ultrapure water and 25 g of Ludox TM-40 to a three-necked flask, mix them uniformly at a stirring rate of 300 rpm, add dilute hydrochloric acid to adjust the pH to 5.5, then remove oxygen by passing nitrogen for 30 min, raise the temperature to 70°C, directly add 0.44 g of diacetone acrylamide, then slowly drop 10 g of methyl methacrylate and 10 g of n-butyl acrylate and 0.2 g of initiator KPS dissolved in 10 g of water within 60 min, and react for 12 h.

[0071] After the reaction, polymer microsphere emulsion was obtained, ammonia was added to adjust the pH to about 8-9, then 0.22 g of adipic acid dihydrazide was added, stirred and poured into a polytetrafluoroethylene mold to form a film at 70 degrees Celsius for 24 hours.

[0072] Comparative Example 1: Preparation of high-performance thin film (emulsion polymerization with surface activity)

[0073] This example describes in detail a method for preparing a polymer thin film.

[0074] The raw materials are as follows: diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), methyl methacrylate (MMA), n-butyl acrylate (BA), sodium dodecyl sulfate (SDS), potassium persulfate (KPS), dilute hydrochloric acid, and water.

[0075] The specific preparation process is as follows:

[0076] 1. A three-necked flask was added with 30 g of ultrapure water and 0.3 g of sodium dodecyl sulfate, stirred at a speed of 300 rpm to mix them evenly. Dilute hydrochloric acid was added to adjust the pH to 5.5, then nitrogen was passed for 30 min to remove oxygen, and the temperature was raised to 70°C. 0.44 g of diacetone acrylamide, 10 g of methyl methacrylate, and 10 g of n-butyl acrylate were directly added, as well as 0.2 g of initiator KPS dissolved in 10 g of water, and the reaction was carried out for 12 h.

[0077] After the reaction, polymer microsphere emulsion was obtained, ammonia was added to adjust the pH to about 8-9, then 0.22 g of adipic acid dihydrazide was added, stirred and poured into a polytetrafluoroethylene mold to form a film at 70 degrees Celsius for 24 hours.

[0078] Comparative Example 2: Preparation of polymer emulsion (emulsion polymerization with surface activity)

[0079] This example describes in detail a method for preparing a polymer thin film.

[0080] The raw materials are as follows: diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), methyl methacrylate (MMA), n-butyl acrylate (BA), Ludox TM-40 (aqueous silica dispersion), potassium persulfate (KPS), dilute hydrochloric acid, water, and sodium dodecyl sulfate (SDS).

[0081] The specific preparation process is as follows:

[0082] 1. A three-necked flask was charged with 30 g of ultrapure water, 0.3 g of sodium dodecyl sulfonate, and stirred at a rate of 300 rpm to mix them uniformly. The pH was adjusted to 5.5 by adding dilute hydrochloric acid, and then the oxygen was removed by purging nitrogen for 30 min. The temperature was raised to 70°C, and 0.44 g of diacetone acrylamide, 10 g of methyl methacrylate, and 10 g of n-butyl acrylate were directly added, and 0.2 g of initiator KPS dissolved in 10 g of water was added, and the reaction was carried out for 12 h.

[0083] After the reaction was completed, a polymer microsphere emulsion was obtained, and the pH was adjusted to about 8-9 by adding ammonia water. Then 0.22 g of adipic acid dihydrazide was added, stirred, and then 25.0 g of Ludox TM-40 silica aqueous dispersion was added and blended uniformly, and then poured into a polytetrafluoroethylene mold to form a film at 70°C for 24 h.

[0084] Table 1 Different polymerization methods for film formation

[0085]

[0086] Test Example:

[0087] Figure 1 Digital photos of films obtained by different polymerization methods; Figure 2 Cross-sectional scanning electron microscopy characterization of films obtained by different polymerization methods. As shown in Figure 1 , it can be seen that the films prepared by traditional emulsion polymerization and Pickering emulsion polymerization with monomer dropping time within 60 min (Examples 1-3, Comparative Examples 1-2) have good transparency.

[0088] The emulsion obtained by traditional emulsion polymerization was directly blended with silica sol to form a film (Comparative Example 2). The cross-section of the film was characterized by SEM, and a large number of silica agglomerates Figure 2 -B caused the white area to produce as Figure 1 -B shown.

[0089] However, when the monomer dropping time was extended to 90 min, the emulsion obtained by polymerization was used to form a film, and the film was severely cracked and could not be completely removed from the mold (Example 4). SEM characterization of the interface of the film showed that the silica was more regularly concentrated in a specific area and was more densely distributed. Therefore, the reason for the poor film forming performance may be that during the film forming process of the latex particles, the small particle size of the latex particles promotes the close packing of the silica, which hinders the movement of the polymer chains and prevents the formation of a uniform and complete film.

[0090] Examples 1-3, Comparative Examples 1 (A, C, D, and E groups) were tested by spectrophotometer in the visible light range, as shown in Figure 3 , the transmittance of the four groups of films was high, and combined with Figure 2The cross sections -A, C, D, and E also indicate that silica is relatively uniformly dispersed in the film, and the distribution of silica also affects the transmittance of the film.

[0091] Mechanical properties were tested on four groups: Examples 1-3 and Comparative Examples 1 (groups A, C, D, and E). The results are as follows: Figure 4 The monomer dropping time shown has a significant impact on the mechanical properties of the final film. Increasing the monomer dropping time from 0 min to 60 min increases the yield stress of the film from 7 MPa to approximately 13.5 MPa, but decreases the elongation at break from 380% to 44%. The changes in yield stress and elongation at break may be due to differences in the distribution of silica, such as... Figure 2 As shown in Figure CE, with the extension of monomer addition time, silica tends to form denser packing, creating individual stress concentration points that strengthen the film, but also reduce the film's elongation at break. Films prepared from conventional emulsions stabilized with 1% SDS (Comparative Example 1) without silica exhibit good toughness but low strength, with a yield stress of only about 4 MPa. Therefore, emulsion films prepared via Pickering emulsion polymerization possess excellent mechanical properties, and the relationship between film strength and toughness can be adjusted by controlling the monomer addition time.

[0092] The films prepared in this application have advantages such as low water absorption and better water resistance because no surfactant is required in the polymerization process. The water absorption rate of films formed by different polymerization methods was tested, and the changes in water absorption rate within 7 days and 24 hours were compared. Figure 5 As shown. Traditional emulsion polymerization with added surfactants (Comparative Example 1) exhibits a high water absorption rate and a high water absorption rate of approximately 39% at final equilibrium. While the group directly blending silica in the emulsion (Comparative Example 22) shows a lower water absorption rate at final equilibrium (possibly because the higher proportion of non-water-absorbing silica results in a relatively lower overall water absorption rate), the direct blending of silica, due to its hydrophilicity and the inability to achieve uniform dispersion, results in a high water absorption rate, essentially reaching equilibrium in about 5 hours. The film prepared in this application, without the addition of surfactants, exhibits uniform silica dispersion, a low equilibrium water absorption rate of approximately 10%, and a low water absorption rate.

[0093] The present application prepares high-performance water-resistant film through Pickering emulsion polymerization. The silica-polymer microspheres with small particle size and high solid content can be obtained without using surface active and adding auxiliary comonomer or using cationic initiator, and are used for film formation; the prepared film has good transparency and better mechanical properties, and has high water resistance. By adjusting the dropping time of monomers to control the particle size of the generated latex particles, the distribution of silica in the film is controlled, and the performance of the film will also change. The high-performance film has high application value in the field of water-based anticorrosive coatings.

[0094] It should be understood that the above detailed embodiments of the present disclosure are only for illustration or explanation of the principles of the present disclosure, but not to limit the present application. Therefore, any modification, equivalent replacement and improvement within the spirit and principle of the present disclosure should be included in the protection scope of the present application. At the same time, the claims of the present application are intended to cover all changes and modifications within the scope and boundary of the equivalent replacement of the claims.

Claims

1. A method for preparing a high-performance polymer film, characterized in that, comprising the following steps: S1, preparing a reaction solution: preparing a water dispersion of silica, adjusting the pH to between 3 and 6; S2, preparing an initiator solution: dissolving an initiator in water to obtain an initiator solution; S3, adding a first component crosslinking monomer to the reaction solution after adjusting the pH, then slowly adding the initiator solution and the monomer into the reaction solution after heating and removing nitrogen, and continuing to react to obtain a film-forming emulsion; S4, adjusting the pH of the film-forming emulsion prepared in step S3, adding a second component crosslinking monomer, and pouring into a mold for film formation; In step S3, the monomer drop time is 30-60 min; The drop time of the initiator is 30-60 min.

2. The method for preparing a high-performance polymer film according to claim 1, characterized in that, in step S1, the reaction solution contains 25-88 parts by mass of solvent water and 1-10 parts by mass of silica.

3. The method for preparing a high-performance polymer film according to claim 1, characterized in that, the initiator is selected from one or a combination of potassium persulfate, ammonium persulfate, azobisdimethylaminoform hydrochloride, and azobisdimethyl nitrile; And / or, the first component crosslinking monomer is diacetone acrylamide; And / or, the second component crosslinking monomer is adipic acid dihydrazide.

4. The method for preparing a high-performance polymer film according to claim 1, characterized in that, the monomer is selected from one or a combination of methyl methacrylate, ethyl methacrylate, styrene, n-butyl acrylate, n-ethyl acrylate, and isobutyl acrylate; And / or, in step S1, the amount of silica added is 1%-10% of the total mass of water and silica.

5. The method for preparing a high-performance polymer film according to claim 1, characterized in that, in step S3, the particle size of the final emulsion should be 100-300 nm.

6. The method for preparing a high-performance polymer film according to claim 1, characterized in that, in step S4, the pH adjustment step is between 8 and 9; And / or, in step S4, the film formation temperature is between 60°C and 80°C.

7. The method for preparing a high-performance polymer film according to claim 1, characterized in that, in step S1, the particle size of the silica is 10-30 nm.

8. The method for preparing a high-performance polymer film according to claim 1, characterized in that, in step S3, the amount of monomer added is 10-30% of the total mass of the emulsion; And / or, the amount of initiator added is 1%-3% of the total mass of the initiator solution; And / or, the solid content of the emulsion is between 10% and 40%.

9. A high-performance film prepared by the method of any one of claims 1-8.

10. A method for adjusting the transparency and mechanical properties of the high-performance film of any one of claims 1-9, characterized in that, the mechanical properties and transparency of the final film are adjusted by adjusting the monomer drop time in step S3. ​ ​ ​ ​ ​ ​ ​ ​ ​

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