A preparation method of modified polyvinyl alcohol adhesive

Abstract

The present invention relates to the technical field of adhesives, and discloses a preparation method of a modified polyvinyl alcohol adhesive. The present invention adds 100 parts by weight of sulfonated polyvinyl alcohol and 0.3-1.5 parts by weight of modified carbon nanotubes to water, stirs and mixes, and then adds 4-9 parts by weight of isocyanate cross-linking curing agent to obtain the modified polyvinyl alcohol adhesive. Cross-linking curing agents such as toluene diisocyanate react with hydroxyl groups of polyvinyl alcohol and hydroxyl groups of modified carbon nanotubes respectively, and at the same time, sulfonate anions of polyvinyl alcohol react with quaternary ammonium salt cations of modified carbon nanotubes by electrostatic cross-linking, thereby forming a double network curing cross-linking system in the polyvinyl alcohol adhesive, improving the cohesion and bonding strength of the adhesive, and at the same time, enhancing the interfacial bonding force between carbon nanotubes and polyvinyl alcohol, improving the compatibility between the two, and improving the tensile properties of the adhesive.

Description

Technical Field

[0001] The invention relates to the technical field of adhesives, in particular to a method for preparing a modified polyvinyl alcohol adhesive. Background Art

[0002] Polyvinyl alcohol is cheap and easy to obtain, biodegradable, and has excellent bonding properties. It can be used as an adhesive and is widely used in wood, paper, ceramics, etc. Polyvinyl alcohol contains active hydroxyl groups and can react with benzaldehyde, formaldehyde, etc. to form high-performance polyvinyl alcohol materials. Adding nanofillers such as nanosilicon dioxide, carbon nanotubes, montmorillonite, etc. to polyvinyl alcohol can improve its mechanical and heat-resistant properties. Among them, carbon nanotubes have good mechanical strength, modulus and high temperature resistance, and have a large specific surface area and are easy to surface modify. Through chemical modification, amino, carboxyl, quaternary ammonium salt and other groups can be introduced on the surface, which can improve its compatibility with polymer materials and play a better reinforcing role. Chinese patent CN116120685B discloses a polyvinyl alcohol composite material and a preparation method thereof. With polyvinyl alcohol, acid-modified carbon nanotubes, and quaternary ammonium salt-modified montmorillonite as raw materials, the obtained polyvinyl alcohol composite material has excellent electromagnetic shielding performance and flame retardancy. However, the patent does not improve the tensile properties and bonding strength of polyvinyl alcohol, which is not conducive to the practical application of polyvinyl alcohol in the field of adhesives. Summary of the invention

[0003] The invention solves the problem that the mechanical strength and bonding performance of the polyvinyl alcohol adhesive are poor.

[0004] The technical solution of the present invention: a method for preparing a modified polyvinyl alcohol adhesive:

[0005] (1) Add 100 parts by weight of polyvinyl alcohol to dimethyl sulfoxide, heat to 75-90°C, stir, add 2-6 parts by weight of benzaldehyde and 0.15-0.5 parts by weight of p-toluenesulfonic acid, react for 1-4 hours, pour the solution into water, filter, wash the precipitate with water, and dry to obtain polyvinyl alcohol benzaldehyde.

[0006] (2) Add polyvinyl alcohol benzaldehyde to fuming sulfuric acid, filter after reaction, add the product to sodium hydroxide solution, heat up to volatilize and precipitate a large amount of precipitate, filter, wash with ethanol, and dry to obtain sulfonated polyvinyl alcohol. The preparation reaction formula is:

[0007]

[0008] (3) Adding amino carbon nanotubes and 2,3-epoxypropyltrimethylammonium chloride to the solvent, filtering after the reaction, and washing with water and ethanol in sequence to obtain modified carbon nanotubes. The preparation reaction formula is:

[0009]

[0010] (4) Add 100 parts by weight of sulfonated polyvinyl alcohol and 0.3-1.5 parts by weight of modified carbon nanotubes into water, stir and mix, and then add 4-9 parts by weight of isocyanate cross-linking curing agent to obtain a modified polyvinyl alcohol adhesive.

[0011] Preferably, the ratio of fuming sulfuric acid to polyvinyl benzaldehyde in (2) is 1L: (200-600)g.

[0012] Preferably, the reaction temperature in (2) is 80-100°C and the reaction time is 40-60 min.

[0013] Preferably, the solvent in (3) is water, ethanol or isopropanol.

[0014] Preferably, in (3), the ratio of the amino carbon nanotubes to 2,3-epoxypropyltrimethylammonium chloride is 1 g:(5-8) g.

[0015] Preferably, the reaction temperature in (3) is 50-75°C and the reaction time is 12-18h.

[0016] Preferably, the isocyanate cross-linking curing agent in (4) is toluene diisocyanate or hexamethylene diisocyanate.

[0017] The technical effect of the present invention is as follows: 2,3-epoxypropyltrimethylammonium chloride is used to react with the amino groups of the aminated carbon nanotubes, thereby generating hydroxyl groups and quaternary ammonium salt groups on the surface of the carbon nanotubes, and then sulfonated polyvinyl alcohol is used as the main agent of the adhesive, toluene diisocyanate and the like are used as crosslinking curing agents, and modified carbon nanotubes are used as fillers to obtain modified polyvinyl alcohol adhesives. Crosslinking curing agents such as toluene diisocyanate respectively react with the hydroxyl groups of polyvinyl alcohol and the hydroxyl groups of the modified carbon nanotubes to form a first chemical crosslink, and at the same time, the sulfonate anions of the polyvinyl alcohol and the quaternary ammonium salt cations of the modified carbon nanotubes undergo electrostatic crosslinking to form a second crosslink, thereby forming a double network curing crosslinking system in the polyvinyl alcohol adhesive, improving the cohesive force of the adhesive, which is beneficial to improving the bonding strength and bonding performance, and at the same time, enhancing the interfacial bonding force between the carbon nanotubes and the polyvinyl alcohol, improving the compatibility between the two, and the carbon nanotubes are uniformly dispersed in the adhesive matrix, having a better reinforcement effect, and improving the tensile properties of the adhesive. DETAILED DESCRIPTION

[0018] The following polyvinyl alcohol, model 1788, Shandong Zhongtian Chemical Co., Ltd. Carbon nanotubes, model XFM34, Suzhou Beike Nanotechnology Co., Ltd. Aminated carbon nanotubes, model XFM62-1, Jiangsu Xianfeng Nanomaterials Technology.

[0019] Example 1: Preparation of modified polyvinyl alcohol adhesive.

[0020] (1) Add 200 g of polyvinyl alcohol to 1.2 L of dimethyl sulfoxide, heat to 85 °C, stir, add 4 g of benzaldehyde and 0.3 g of p-toluenesulfonic acid, react for 1 h, pour the solution into water, filter, wash the precipitate with water, and dry to obtain polyvinyl alcohol benzaldehyde.

[0021] (2) Add 100 g of polyvinyl alcohol benzaldehyde to 500 mL of 65% fuming sulfuric acid, heat to 100 °C, react for 40 min, cool, filter, add the product to sodium hydroxide solution, stir for 1 h, heat to evaporate and precipitate a large amount of precipitate, filter, wash with ethanol, and dry to obtain sulfonated polyvinyl alcohol.

[0022] (3) Add 0.5 g of amino-modified carbon nanotubes and 2.5 g of 2,3-epoxypropyltrimethylammonium chloride to 30 mL of water, raise the temperature to 50 °C, react for 18 h, filter, and wash with water and ethanol in turn to obtain modified carbon nanotubes.

[0023] (4) Add 100 g of sulfonated polyvinyl alcohol and 0.3 g of modified carbon nanotubes to 900 mL of water, heat to 90 °C, stir to mix, cool to 70 °C, and then add 4 g of cross-linking curing agent toluene diisocyanate to obtain a modified polyvinyl alcohol adhesive.

[0024] Example 2: Preparation of modified polyvinyl alcohol adhesive.

[0025] (1) Add 200 g of polyvinyl alcohol to 1.2 L of dimethyl sulfoxide, heat to 75 °C, stir, add 8 g of benzaldehyde and 0.6 g of p-toluenesulfonic acid, react for 4 h, pour the solution into water, filter, wash the precipitate with water, and dry to obtain polyvinyl alcohol benzaldehyde.

[0026] (2) Add 200 g of polyvinyl alcohol benzaldehyde to 600 mL of 65% fuming sulfuric acid, heat to 80 °C, react for 60 min, cool, filter, add the product to sodium hydroxide solution, stir for 1 h, heat to evaporate and precipitate a large amount of precipitate, filter, wash with ethanol, and dry to obtain sulfonated polyvinyl alcohol.

[0027] (3) Add 0.5 g of amino-modified carbon nanotubes and 3.2 g of 2,3-epoxypropyltrimethylammonium chloride to 40 mL of isopropanol, heat to 75 °C, react for 12 h, filter, and wash with water and ethanol in turn to obtain modified carbon nanotubes.

[0028] (4) Add 100 g of sulfonated polyvinyl alcohol and 1 g of modified carbon nanotubes to 1200 mL of water, heat to 90 °C, stir to mix, cool to 70 °C, and then add 9 g of cross-linking curing agent hexamethylene diisocyanate to obtain a modified polyvinyl alcohol adhesive.

[0029] Example 3: Preparation of modified polyvinyl alcohol adhesive.

[0030] (1) Add 200 g of polyvinyl alcohol to 1.4 L of dimethyl sulfoxide, heat to 90 °C, stir, add 12 g of benzaldehyde and 1 g of p-toluenesulfonic acid, react for 2 h, pour the solution into water, filter, wash the precipitate with water, and dry to obtain polyvinyl alcohol benzaldehyde.

[0031] (2) Add 300 g of polyvinyl alcohol benzaldehyde to 600 mL of 65% fuming sulfuric acid, heat to 90 °C, react for 60 min, cool, filter, add the product to sodium hydroxide solution, stir for 1 h, heat to evaporate and precipitate a large amount of precipitate, filter, wash with ethanol, and dry to obtain sulfonated polyvinyl alcohol.

[0032] (3) Add 0.5 g of amino-modified carbon nanotubes and 4 g of 2,3-epoxypropyltrimethylammonium chloride to 50 mL of ethanol, heat to 65 °C, react for 18 h, filter, and wash with water and ethanol in turn to obtain modified carbon nanotubes.

[0033] (4) Add 100 g of sulfonated polyvinyl alcohol and 1.5 g of modified carbon nanotubes to 1000 mL of water, heat to 90 °C, stir to mix, cool to 70 °C, and then add 5 g of cross-linking curing agent toluene diisocyanate to obtain a modified polyvinyl alcohol adhesive.

[0034] Comparative Example 1: Preparation of polyvinyl alcohol adhesive.

[0035] (1) Add 200 g of polyvinyl alcohol to 1.2 L of dimethyl sulfoxide, heat to 85 °C, stir, add 4 g of benzaldehyde and 0.3 g of p-toluenesulfonic acid, react for 1 h, pour the solution into water, filter, wash the precipitate with water, and dry to obtain polyvinyl alcohol benzaldehyde.

[0036] (2) Add 100 g of polyvinyl alcohol benzaldehyde to 500 mL of 65% fuming sulfuric acid, heat to 100 °C, react for 40 min, cool, filter, add the product to sodium hydroxide solution, stir for 1 h, heat to evaporate and precipitate a large amount of precipitate, filter, wash with ethanol, and dry to obtain sulfonated polyvinyl alcohol.

[0037] (3) Add 100 g of sulfonated polyvinyl alcohol to 900 mL of water, heat to 90 °C, stir to mix, cool to 70 °C, and then add 4 g of cross-linking curing agent toluene diisocyanate to obtain a polyvinyl alcohol adhesive.

[0038] Comparative Example 2, preparing a polyvinyl alcohol adhesive.

[0039] (1) Add 200 g of polyvinyl alcohol to 1.2 L of dimethyl sulfoxide, heat to 85 °C, stir, add 4 g of benzaldehyde and 0.3 g of p-toluenesulfonic acid, react for 1 h, pour the solution into water, filter, wash the precipitate with water, and dry to obtain polyvinyl alcohol benzaldehyde.

[0040] (2) Add 100 g of polyvinyl alcohol benzaldehyde to 500 mL of 65% fuming sulfuric acid, heat to 100 °C, react for 40 min, cool, filter, add the product to sodium hydroxide solution, stir for 1 h, heat to evaporate and precipitate a large amount of precipitate, filter, wash with ethanol, and dry to obtain sulfonated polyvinyl alcohol.

[0041] (3) Add 100 g of sulfonated polyvinyl alcohol and 0.3 g of carbon nanotubes to 900 mL of water, heat to 90 °C, stir to mix, cool to 70 °C, and then add 4 g of cross-linking curing agent toluene diisocyanate to obtain a polyvinyl alcohol adhesive.

[0042] Comparative Example 3, preparing polyvinyl alcohol adhesive.

[0043] (1) Add 200 g of polyvinyl alcohol to 1.2 L of dimethyl sulfoxide, heat to 85 °C, stir, add 4 g of benzaldehyde and 0.3 g of p-toluenesulfonic acid, react for 1 h, pour the solution into water, filter, wash the precipitate with water, and dry to obtain polyvinyl alcohol benzaldehyde.

[0044] (2) Add 100 g of polyvinyl alcohol benzaldehyde to 500 mL of 65% fuming sulfuric acid, heat to 100 °C, react for 40 min, cool, filter, add the product to sodium hydroxide solution, stir for 1 h, heat to evaporate and precipitate a large amount of precipitate, filter, wash with ethanol, and dry to obtain sulfonated polyvinyl alcohol.

[0045] (3) Add 100 g of sulfonated polyvinyl alcohol and 0.3 g of amino carbon nanotubes to 900 mL of water, heat to 90 °C, stir to mix, cool to 70 °C, and then add 4 g of cross-linking curing agent toluene diisocyanate to obtain a polyvinyl alcohol adhesive.

[0046] Comparative Example 4, preparing polyvinyl alcohol adhesive.

[0047] (1) Add 0.5 g of amino-modified carbon nanotubes and 2.5 g of 2,3-epoxypropyltrimethylammonium chloride to 30 mL of water, heat to 50 °C, react for 18 h, filter, and wash with water and ethanol in turn to obtain modified carbon nanotubes.

[0048] (2) Add 100 g of polyvinyl alcohol and 0.3 g of modified carbon nanotubes to 900 mL of water, heat to 90 °C, stir to mix, cool to 70 °C, and then add 4 g of cross-linking curing agent toluene diisocyanate to obtain a polyvinyl alcohol adhesive.

[0049] Comparative Example 5, preparing a polyvinyl alcohol adhesive.

[0050] (1) Add 200 g of polyvinyl alcohol to 1.2 L of dimethyl sulfoxide, heat to 85 °C, stir, add 4 g of benzaldehyde and 0.3 g of p-toluenesulfonic acid, react for 1 h, pour the solution into water, filter, wash the precipitate with water, and dry to obtain polyvinyl alcohol benzaldehyde.

[0051] (2) Add 0.5 g of amino-modified carbon nanotubes and 2.5 g of 2,3-epoxypropyltrimethylammonium chloride to 30 mL of water, heat to 50 °C, react for 18 h, filter, and wash with water and ethanol in turn to obtain modified carbon nanotubes.

[0052] (3) Add 100 g of polyvinyl alcohol benzaldehyde and 0.3 g of modified carbon nanotubes to 900 mL of water, heat to 90 °C, stir to mix, cool to 70 °C, and then add 4 g of cross-linking curing agent toluene diisocyanate to obtain a polyvinyl alcohol adhesive.

[0053] Poplar veneer with a thickness of 1.5 mm and polyvinyl alcohol adhesive were made into plywood specimens according to GB / T 9846-2015 standard. The total amount of glue applied was 800 g / m 2 The hot pressing temperature is 120℃, the hot pressing time is 15min, and it is placed at room temperature for 24h after gluing. The bonding strength is tested according to GB / T17657-2022 standard.

[0054] The adhesive was poured into the mold, vacuum degassed, cured at 70°C for 4 hours, and then placed at room temperature for 24 hours to form a dumbbell-shaped specimen with a 50mm×10mm rectangular shape in the middle of the specimen. The tensile properties were tested according to the method of GB / T 1040.1-2018, and the tensile rate was 50mm / min.

[0055] Table 1 Performance test of adhesive

[0056]

[0057] After testing, the polyvinyl alcohol adhesives of Examples 1-3 have higher bonding strength and tensile properties. This is because the cross-linking curing agents such as toluene diisocyanate react with the hydroxyl groups of polyvinyl alcohol and the hydroxyl groups of the modified carbon nanotubes to form a first chemical crosslink, and at the same time, the sulfonate anions of the polyvinyl alcohol and the quaternary ammonium salt cations of the modified carbon nanotubes undergo electrostatic crosslinking to form a second crosslink, thereby forming a double network curing crosslinking system in the polyvinyl alcohol adhesive, which improves the cohesive force of the adhesive and is beneficial to improving the bonding strength. At the same time, the interfacial bonding force between the carbon nanotubes and the polyvinyl alcohol is enhanced, and the compatibility between the two is improved. The carbon nanotubes are evenly dispersed in the adhesive matrix, have a better reinforcement effect, and improve the tensile and other mechanical properties of the adhesive.

[0058] Compared with Example 1, the polyvinyl alcohol adhesive of Comparative Example 1 does not add modified carbon nanotubes, and the bonding strength and tensile properties of the adhesive are poor. Comparative Example 2 adds unmodified carbon nanotubes, and the surface does not contain hydroxyl groups and quaternary ammonium salt groups, and it is impossible to form a dual network curing crosslinking system with sulfonated polyvinyl alcohol, and the compatibility and dispersibility of unmodified carbon nanotubes in polyvinyl alcohol adhesives are poor, resulting in lower bonding strength and tensile properties of the adhesive. Comparative Example 3 adds amination carbon nanotubes, and its amino group can also react with the hydroxyl group of polyvinyl alcohol through toluene diisocyanate, which is conducive to improving the bonding strength and tensile properties of the adhesive, but the amination carbon nanotubes do not contain quaternary ammonium salt groups, and it is impossible to form an electrostatic crosslinking effect and a dual network curing crosslinking system with sulfonated polyvinyl alcohol, resulting in lower bonding strength and tensile properties of the adhesive than Example 1. The polyvinyl alcohol of Comparative Example 4 and the polyvinyl alcohol benzaldehyde of Comparative Example 5 do not contain sulfonate anions, and cannot form electrostatic crosslinking and dual network curing crosslinking systems with the quaternary ammonium salt cations of the modified carbon nanotubes, resulting in the bonding strength and tensile properties of the adhesive being lower than those in Example 1.

Claims

1. A method for preparing a modified polyvinyl alcohol adhesive, characterized in that: The preparation method is: (1) Add polyvinyl alcohol benzaldehyde to fuming sulfuric acid, filter after reaction, add the product to sodium hydroxide solution, heat up to volatilize and precipitate, filter, wash with ethanol, and dry to obtain sulfonated polyvinyl alcohol; (2) adding aminated carbon nanotubes and 2,3-epoxypropyltrimethylammonium chloride to a solvent, filtering after the reaction, and washing with water and ethanol in sequence to obtain modified carbon nanotubes; (3) adding 100 parts by weight of sulfonated polyvinyl alcohol and 0.3-1.5 parts by weight of modified carbon nanotubes to water, stirring and mixing, and then adding 4-9 parts by weight of isocyanate cross-linking curing agent to obtain a modified polyvinyl alcohol adhesive; The preparation method of the polyvinyl alcohol benzaldehyde acetal is as follows: add 100 parts by weight of polyvinyl alcohol to dimethyl sulfoxide, heat to 75-90° C., add 2-6 parts by weight of benzaldehyde and 0.15-0.5 parts by weight of p-toluenesulfonic acid after stirring, react for 1-4 hours, pour the solution into water, filter, wash the precipitate with water, and dry to obtain the polyvinyl alcohol benzaldehyde acetal.

2. The method for preparing the modified polyvinyl alcohol adhesive according to claim 1, characterized in that: The ratio of fuming sulfuric acid to polyvinyl alcohol benzaldehyde in (1) is 1L: (200-600)g.

3. The method for preparing the modified polyvinyl alcohol adhesive according to claim 1, characterized in that: The reaction temperature in (1) is 80-100°C and the reaction time is 40-60min.

4. The method for preparing the modified polyvinyl alcohol adhesive according to claim 1, characterized in that: The solvent in (2) is water, ethanol or isopropanol.

5. The method for preparing the modified polyvinyl alcohol adhesive according to claim 1, characterized in that: The ratio of the amino carbon nanotubes to 2,3-epoxypropyltrimethylammonium chloride in (2) is 1 g:(5-8) g.

6. The method for preparing the modified polyvinyl alcohol adhesive according to claim 1, characterized in that: The reaction temperature in (2) is 50-75°C and the reaction time is 12-18h.

7. The method for preparing the modified polyvinyl alcohol adhesive according to claim 1, characterized in that: The isocyanate cross-linking curing agent in (3) is toluene diisocyanate or hexamethylene diisocyanate.

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