Starch-based adhesive and preparation method thereof

Abstract

The invention relates to a starch-based adhesive and a preparation method thereof, and belongs to the technical field of adhesives, cis-butadiene anhydride and a phosphate ester compound are used as raw materials, and a starch modifier is obtained by carrying out Michael addition reaction on double bonds of cis-butadiene anhydride and phosphorus-hydrogen bonds of the phosphate ester compound. The number of hydroxyl groups in molecules is reduced after the modified starch is subjected to the esterification reaction, and meanwhile, water-absorbing hydroxyl groups are introduced, so that the water absorption performance of the starch-based adhesive is effectively reduced; the problem of interface viscosity failure caused by moisture permeation is avoided; a phosphate group with a flame-retardant effect is introduced into the modified starch, so that the stability and dispersity of flame-retardant components in the starch-based adhesive are effectively improved, migration and precipitation of the flame-retardant components are reduced, and efficient flame retardance is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesives. Specifically, it relates to a starch-based adhesive and its preparation method. More specifically, it relates to a starch-based adhesive for ceramic processing and its preparation method. Background Art

[0002] Al2O3 corundum ceramics have excellent properties and are widely used. During the production process of corundum ceramics, a certain viscosity is added to the slurry to improve the strength of the green ceramic body. Currently, most manufacturers use PVA as the adhesive. PVA causes great environmental pollution. To solve the problem of environmental damage caused by PVA adhesives, it is imperative to use degradable, renewable, and pollution-free starch-based adhesives to replace PVA adhesives.

[0003] The starch-based adhesive mainly has the following technical problems. Firstly, there are a large number of hydrophilic hydroxyl groups on the surface of starch, which leads to the defect of strong hygroscopicity of the starch-based adhesive. In a humid environment, the starch-based adhesive absorbs moisture and swells, which will cause cracks in the adhesive layer and then lead to a significant decrease in the bonding strength. Secondly, the surface of the ceramic matrix is dense and has a large number of hydroxyl groups, and it cannot form effective bonding with the starch-based adhesive. Due to the poor bonding strength between the ceramic matrix and the surface of the starch-based adhesive. In addition, the starch-based adhesive is a flammable material. To make the adhesive itself have flame retardancy, a flame retardant needs to be added externally. The phosphate ester flame retardant is safe and smokeless, but the addition amount is large. Adding a large amount of phosphate ester flame retardant will cause a decrease in the bonding strength and shear strength of the adhesive to varying degrees. To solve the above technical defects, the present invention modifies starch to prepare a starch-based adhesive. Summary of the Invention

[0004] The purpose of the present invention is to provide a starch-based adhesive and its preparation method to solve the problems mentioned in the above background art.

[0005] The purpose of the present invention can be achieved by the following technical solutions: A starch-based adhesive, comprising the following raw materials in parts by mass: 10 - 12 parts of modified starch, 0.1 - 0.6 parts of oxidant, 0.01 - 0.03 parts of defoamer, and 16 - 20 parts of water; Further, the oxidant is one or a mixture of more of sodium hypochlorite, hydrogen peroxide, and ammonium persulfate.

[0006] Further, the defoamer is tributyl phosphate.

[0007] Further, the modified starch is prepared by the following steps: Step 1: Dissolve maleic anhydride, phosphate compound, and 1,5,7-triazabicyclo-[4.4.0]dec-5-ene in dichloromethane in a four-necked flask. Install a condenser and a thermometer, start mechanical stirring, and react at room temperature for 10 - 30 min. After the reaction, remove the solvent by rotary evaporation. Wash the remaining solid with deionized water and then dry it to obtain a starch modifier. Step 2: Mix starch and water in a four-necked flask and react at a temperature of 80 - 100 °C for 1 - 2 h. Then cool it to room temperature to obtain a colloidal starch. Next, mix the colloidal starch and absolute ethanol and centrifuge them in a centrifuge. The obtained precipitate, the activated starch granules, are reserved for use. Step 3: Mix the activated starch granules and an ethanol solution in a four-necked flask. Then adjust the pH to 8 - 10 with a sodium hydroxide solution. After that, add the starch modifier to the four-necked flask and react at a temperature of 40 - 60 °C for 4 - 6 h. After the reaction, adjust the pH to 5 - 7 with dilute hydrochloric acid and centrifuge the reaction solution in a centrifuge. Then wash the precipitate with deionized water and an ethanol solution respectively and dry it to obtain modified starch.

[0008] Furthermore, the phosphate compound is one or more of dimethyl phosphite, diethyl phosphite, and diphenyl phosphite.

[0009] Furthermore, the dosage ratio of maleic anhydride, phosphate compound, 1,5,7-triazabicyclo-[4.4.0]dec-5-ene, and dichloromethane used in the first step is 0.98 - 1.08:1.10 - 2.34:0.14 - 0.28:6 - 10.

[0010] Furthermore, the starch is one or more of corn starch, cassava starch, potato starch, and wheat starch.

[0011] Furthermore, the mass ratio of starch, water, and absolute ethanol used in the second step is 8 - 10:40 - 100:120 - 200.

[0012] Furthermore, the volume fraction of the ethanol solution in the third step is 80 - 90%.

[0013] Furthermore, the mass ratio of the activated starch granules, ethanol solution, and starch modifier used in the third step is 5 - 6:200 - 300:0.4 - 1.

[0014] Furthermore, the centrifugation conditions in the second and third steps are centrifugation at a speed of 3000 - 4000 rpm for 8 - 15 min.

[0015] A preparation method of a starch-based adhesive, comprising the following steps: After mixing the modified starch and water, an oxidizing agent is added and oxidation is carried out at a temperature of 30 - 60 °C for 30 - 90 min. Then, an antifoaming agent is added to the system. After stirring evenly, the starch-based adhesive is obtained and discharged.

[0016] Advantages of the present invention: In the present invention, maleic anhydride and a phosphate compound are used as raw materials. A Michael addition reaction occurs between the double bond of maleic anhydride and the P - H bond of the phosphate compound to obtain a starch modifier. Then, after the starch is gelatinized, precipitated, and separated, an esterification reaction occurs between the starch and the starch modifier to obtain the modified starch. After the esterification reaction of the modified starch of the present invention, the number of hydroxyl groups in the molecule is reduced, and at the same time, hydrophobic ester groups are introduced, effectively reducing the water absorption performance of the starch-based adhesive and avoiding the problem of interfacial adhesion failure caused by water penetration.

[0017] The carboxyl group and phosphate ester structure are introduced into the modified starch of the present invention. The carboxyl group can undergo an esterification reaction with the hydroxyl groups on the surface of the ceramic matrix to form a chemical bond, and the phosphorus atom can form a coordination bond with the metal atoms (such as aluminum and zirconium) on the surface of the ceramic group. The synergistic effect of the two can significantly improve the bonding performance between the starch-based adhesive and the surface of the ceramic matrix.

[0018] The phosphate ester group with a flame retardant effect is introduced into the modified starch of the present invention, effectively improving the stability and dispersibility of the flame retardant component in the starch-based adhesive, reducing the migration and precipitation of the flame retardant component, achieving efficient flame retardancy. The flame retardant component is introduced through chemical bonding, which can maintain the mechanical properties of the adhesive while exerting the flame retardant effect and solve the problem of the decrease in mechanical properties caused by the addition of the flame retardant. Detailed implementation manners

[0019] It should be understood that the expression "one or more of..." individually includes each of the objects recited after the expression and various different combinations of two or more of the recited objects, unless otherwise understood from the context and usage. The expression "and / or" in combination with three or more recited objects should be understood to have the same meaning, unless otherwise understood from the context.

[0020] The terms "comprising", "having", or "containing", including the use of their grammatical synonyms, should generally be understood as open and non-restrictive, for example, not excluding other unrecited elements or steps, unless specifically stated otherwise or understood from the context.

[0021] It should be understood that as long as the present invention is still operable, the order of steps or the order of performing certain actions is not important. In addition, two or more steps or actions can be carried out simultaneously.

[0022] The use of any and all examples or exemplary language in this document, such as "for example" or "including", is merely intended to better illustrate the invention and does not limit the scope of the invention unless a claim is made. No language in this specification should be construed as indicating that any unclaimed element is essential for the practice of the invention.

[0023] Example 1. A starch-based adhesive, comprising raw materials in the following parts by mass: 10 parts of modified starch, 0.1 part of oxidant, 0.01 part of defoamer, and 16 parts of water. Among them, the oxidant is sodium hypochlorite, and the defoamer is tributyl phosphate. The modified starch is prepared by the following steps: First step: By mass, dissolve 0.98 part of maleic anhydride, 1.10 parts of phosphate compound, and 0.14 part of 1,5,7-triazabicyclo-[4.4.0]dec-5-ene in 6 parts of dichloromethane in a four-necked flask. Install a condenser and a thermometer, start mechanical stirring, and react at room temperature for 10 minutes. After the reaction is completed, remove the solvent by rotary evaporation. Wash the remaining solid with deionized water and then dry to obtain a starch modifier. Second step: By mass, mix 8 parts of starch and 40 parts of water in a four-necked flask, react at 80 °C for 2 hours, then cool to room temperature to obtain a colloidal starch. Then mix the colloidal starch and 120 parts of absolute ethanol and place them in a centrifuge to centrifuge at 3000 rpm for 15 minutes. The obtained precipitate, activated starch granules, are reserved for use. Third step: By mass, mix 5 parts of activated starch granules and 200 parts of ethanol solution with a volume fraction of 90% in a four-necked flask, then adjust the pH to 8 with a sodium hydroxide solution. Then add 0.4 part of the starch modifier to the four-necked flask and react at 40 °C for 6 hours. After the reaction is completed, adjust the pH to 7 with dilute hydrochloric acid, and place the reaction solution in a centrifuge to centrifuge at 3000 rpm for 15 minutes. Then wash the precipitate with deionized water and ethanol solution respectively and dry to obtain modified starch. Among them, the phosphate compound is dimethyl phosphite, and the starch is corn starch.

[0024] A preparation method of a starch-based adhesive, comprising the following steps: After mixing the modified starch and water, add an oxidant and oxidize at 30 °C for 30 minutes. Then add a defoamer to the system, stir evenly and discharge to obtain a starch-based adhesive.

[0025] Example 2. A starch-based adhesive, comprising raw materials in the following parts by mass: 11 parts of modified starch, 0.35 part of oxidant, 0.02 part of defoamer, and 18 parts of water. Among them, the oxidant is ammonium persulfate, the defoamer is tributyl phosphate, and the modified starch is prepared by the following steps: First step: By mass fraction, dissolve 1.03 parts of maleic anhydride, 1.38 parts of phosphate compound, and 0.21 part of 1,5,7-triazabicyclo-[4.4.0]dec-5-ene in 8 parts of dichloromethane in a four-necked flask. Install a condenser and a thermometer, start mechanical stirring, and react at room temperature for 20 min. After the reaction is completed, remove the solvent by rotary evaporation. Wash the remaining solid with deionized water and then dry it to obtain a starch modifier. Second step: By mass fraction, mix 9 parts of starch and 70 parts of water in a four-necked flask, react at 90 °C for 1.5 h, then cool to room temperature to obtain a colloidal starch. Then mix the colloidal starch with 160 parts of absolute ethanol and place it in a centrifuge to centrifuge at 3500 rpm for 11.5 min. The obtained precipitate, activated starch granules, are reserved for use. Third step: By mass fraction, mix 5.5 parts of activated starch granules and 250 parts of an 85% ethanol solution by volume in a four-necked flask. Then adjust the pH to 9 with a sodium hydroxide solution. Then add 0.7 part of the starch modifier to the four-necked flask and react at 50 °C for 5 h. After the reaction is completed, adjust the pH to 6 with dilute hydrochloric acid, and place the reaction solution in a centrifuge to centrifuge at 3500 rpm for 11.5 min. Then wash the precipitate with deionized water and ethanol solution respectively and dry it to obtain the modified starch. Among them, the phosphate compound is diethyl phosphite, and the starch is cassava starch.

[0026] A preparation method of a starch-based adhesive includes the following steps: After mixing the modified starch and water, add the oxidant and oxidize at 45 °C for 60 min. Then add the defoamer to the system, stir evenly, and discharge to obtain the starch-based adhesive.

[0027] Example 3, a starch-based adhesive, contains the following raw materials by mass fraction: 12 parts of modified starch, 0.6 part of oxidant, 0.03 part of defoamer, and 20 parts of water; Among them, the oxidant is an aqueous hydrogen peroxide solution with a mass fraction of 30%, the defoamer is tributyl phosphate, and the modified starch is prepared by the following steps: First step: By mass fraction, dissolve 1.08 parts of maleic anhydride, 2.34 parts of phosphate compound, and 0.28 part of 1,5,7-triazabicyclo-[4.4.0]dec-5-ene in 10 parts of dichloromethane in a four-necked flask. Install a condenser and a thermometer, start mechanical stirring, and react at room temperature for 30 min. After the reaction is completed, remove the solvent by rotary evaporation. Wash the remaining solid with deionized water and then dry it to obtain a starch modifier. Step 2: By mass fraction, mix 10 parts of starch and 100 parts of water in a four-necked flask, react at a temperature of 100 °C for 1 h, then cool to room temperature to obtain colloidal starch. Then mix the colloidal starch with 200 parts of absolute ethanol and place it in a centrifuge to centrifuge for 8 min at a rotational speed of 4000 rpm. The obtained precipitate, activated starch granules, are reserved for use. Step 3: By mass fraction, mix 6 parts of activated starch granules and 300 parts of an ethanol solution with a volume fraction of 80% in a four-necked flask. Then adjust the pH to 10 with a sodium hydroxide solution. After that, add 1 part of a starch modifier to the four-necked flask and react at a temperature of 60 °C for 4 h. After the reaction is completed, adjust the pH to 5 with dilute hydrochloric acid, and place the reaction solution in a centrifuge to centrifuge for 8 min at a rotational speed of 4000 rpm. Then wash the precipitate with deionized water and ethanol solution respectively and dry to obtain modified starch. Among them, the phosphoric acid ester compound is diphenyl phosphite, and the starch is a mixture of potato starch and wheat starch in a mass ratio of 4:6.

[0028] A preparation method of a starch-based adhesive, comprising the following steps: Mix the modified starch and water, add an oxidant and oxidize at a temperature of 60 °C for 90 min. Then add an antifoaming agent to the system, stir evenly and discharge to obtain the starch-based adhesive.

[0029] Comparative Example 1: A starch-based adhesive, comprising the following raw materials by mass fraction: 10 parts of activated starch granules, 0.1 part of oxidant, 0.01 part of antifoaming agent, 0.8 part of flame retardant, and 16 parts of water; Among them, the starch is corn starch, the oxidant is sodium hypochlorite, the antifoaming agent is tributyl phosphate, the flame retardant is DOPO, and the activated starch granules are prepared by the following steps: By mass fraction, mix 8 parts of starch and 40 parts of water in a four-necked flask, react at a temperature of 80 °C for 2 h, then cool to room temperature to obtain colloidal starch. Then mix the colloidal starch with 120 parts of absolute ethanol and place it in a centrifuge to centrifuge for 15 min at a rotational speed of 3000 rpm. The obtained precipitate, activated starch granules, are reserved for use.

[0030] A preparation method of a starch-based adhesive, comprising the following steps: Mix the activated starch granules and water, add an oxidant and oxidize at a temperature of 30 °C for 30 min. Then add an antifoaming agent and a flame retardant to the system, stir evenly and discharge to obtain the starch-based adhesive.

[0031] Comparative Example 2: A starch-based adhesive, comprising raw materials in the following parts by mass: 10 parts of activated starch granules, 0.1 part of oxidant, 0.01 part of defoamer, and 16 parts of water; Among them, the oxidant is sodium hypochlorite, the defoamer is tributyl phosphate, and the activated starch granules are prepared by the following steps: By mass, 8 parts of corn starch and 40 parts of water are mixed in a four-necked flask, reacted at 80 °C for 2 h, then cooled to room temperature to obtain colloidal starch. Then, the colloidal starch and 120 parts of absolute ethanol are mixed and placed in a centrifuge to be centrifuged at 3000 rpm for 15 min. The obtained precipitate, the activated starch granules, are reserved for use.

[0032] A preparation method of a starch-based adhesive, comprising the following steps: After mixing the activated starch granules and water, an oxidant is added and oxidized at 30 °C for 30 min. Then, a defoamer is added to the system, and after stirring evenly, the starch-based adhesive is discharged. Experimental examples: The starch-based adhesives in Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to adhesion strength tests, tensile shear strength tests, and flame retardancy tests. The test results are shown in Table 1: Adhesion strength test: Refer to the national standard GB / T 44549-2024 to test the adhesion strength in a dry environment and a humid environment; Tensile shear strength test: Refer to the national standard GB / T 6328-2021 for testing; Flame retardancy: Refer to the national standard GB / T 2406.3-2022 to test the limiting oxygen index. The higher the limiting oxygen index, the stronger the flame retardancy;

[0033] It can be seen from Table 1 that the adhesives prepared with the modified starch of the present invention in Examples 1 to 3 have good adhesion strength and tensile shear strength while having good flame retardancy, and the adhesion strength is less affected in a humid environment. Comparative Example 2 uses conventional starch to prepare the adhesive, and it can be seen that the adhesion strength between the adhesive and the surface of the ceramic matrix is not good, and its own shear strength is also inferior to that of the adhesives in Examples 1 to 3. Comparative Example 1 is a control experiment using a conventional flame retardant. It can be seen that, compared with Comparative Example 2, the adhesion strength and tensile shear strength of Comparative Example 1 after adding the flame retardant have decreased to varying degrees.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A starch-based adhesive, characterized in that, It comprises raw materials in the following parts by mass: 10 - 12 parts of modified starch, 0.1 - 0.6 parts of oxidant, 0.01 - 0.03 parts of defoamer, and 16 - 20 parts of water; Among them, the modified starch is prepared by the following steps: Maleic anhydride, phosphoric ester compound, and 1,5,7 - triazabicyclo - [4.4.0] dec - 5 - ene are dissolved in dichloromethane and reacted at room temperature to obtain a starch modifier for standby. Then, starch and water are mixed and reacted at a temperature of 80 - 100 °C to obtain colloidal starch. The colloidal starch is mixed with absolute ethanol and centrifuged to obtain activated starch particles. The activated starch particles and absolute ethanol are mixed and the pH is adjusted to 8 - 10. Then, the starch modifier is added and reacted at a temperature of 40 - 60 °C. After the reaction, the pH is adjusted to 5 - 7, and then the reaction solution is centrifuged, and the precipitate is washed and dried to obtain modified starch.

2. The starch-based adhesive according to claim 1, wherein The oxidant is one or a mixture of sodium hypochlorite, hydrogen peroxide, and ammonium persulfate.

3. A starch-based adhesive according to claim 1, wherein The defoamer is tributyl phosphate.

4. A starch-based adhesive according to claim 1, wherein The phosphoric ester compound is one or more of dimethyl phosphite, diethyl phosphite, and diphenyl phosphite.

5. A starch-based adhesive according to claim 1, characterized in that, The starch is one or more of corn starch, tapioca starch, potato starch, and wheat starch.

6. A starch-based adhesive according to claim 1, characterized in that, The dosage ratio of maleic anhydride, phosphoric ester compound, 1,5,7 - triazabicyclo - [4.4.0] dec - 5 - ene, and dichloromethane used for preparing the modified starch is 0.98 - 1.08:1.10 - 2.34:0.14 - 0.28:6 - 10.

7. A starch-based adhesive according to claim 1, wherein The mass ratio of starch, water, and absolute ethanol used for preparing the modified starch is 8 - 10:40 - 100:120 - 200.

8. A starch-based adhesive according to claim 1, characterized in that, The volume fraction of the ethanol solution used for preparing the modified starch is 80 - 90%, and the mass ratio of the activated starch particles, ethanol solution, and starch modifier used is 5 - 6:200 - 300:0.4 - 1.

9. A starch-based adhesive according to claim 1, wherein, The centrifugation conditions are centrifugation at a speed of 3000 - 4000 rpm for 8 - 15 min.

10. A method for preparing a starch-based adhesive according to any one of claims 1 to 9, characterized in that, It includes the following steps: The modified starch and water are mixed, then the oxidant is added and oxidized at a temperature of 30 - 60 °C for 30 - 90 min. Then, the defoamer is added to the system, and after stirring evenly, the starch - based adhesive is obtained and discharged.

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