Polyvinyl alcohol-tannic acid adhesive as well as preparation method and application thereof

Abstract

The invention discloses a polyvinyl alcohol-tannic acid adhesive which is obtained by dissolving polyvinyl alcohol powder and tannic acid powder in a binary solvent of water and ethanol, heating, dissolving and polymerizing. According to the polyvinyl alcohol-tannic acid adhesive, natural tannic acid macromolecules rich in phenolic hydroxyl groups are introduced into polyvinyl alcohol, water / ethyl alcohol serves as a solvent, and the prepared adhesive solves the problem of formaldehyde release and has the advantages of being high in bonding strength and suitable for surface bonding of different materials.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to an adhesive based on polyvinyl alcohol-tannic acid and a preparation method and application thereof. Background Art

[0002] Currently, commercially available urea-formaldehyde resins, phenol-formaldehyde resins and some polyurethane adhesives may release formaldehyde during use, causing immeasurable harm to the environment and human body.

[0003] Patent CN114806464A discloses an environmentally friendly non-toxic adhesive, including plant extract raw materials, polyamide epichlorohydrin aqueous solution, water-soluble oligomers and water; the plant extract raw material content is 0.5-1.5wt%; the polyamide epichlorohydrin aqueous solution content is 10-15wt%; the water-soluble oligomer content is 8-20wt%; the rest is water. The plant extract raw materials are selected from at least one of tannic acid, gallic acid, caffeic acid, 3,4-dihydroxybenzaldehyde or 3,4-dihydroxyphenylalanine. In the environmentally friendly non-toxic adhesive, the content of tannic acid is 0.5wt%.

[0004] The patent is based on water-soluble polymers and raw materials extracted from plants. It does not contain any formaldehyde or volatile organic pollutants and is truly environmentally friendly and non-toxic. It is produced in a one-step process without industrial waste pollution. Dopa derivatives are connected to polymers using bionic technology to obtain an environmentally friendly adhesive with strong anti-wet adhesion ability. At the same time, it is cross-linked with small molecular compounds with epoxy groups to form a network structure with strong cohesion, which improves the bonding strength. It is formaldehyde-free, free of organic volatiles, high tensile shear strength, and good water resistance.

[0005] However, the toxicity of the polyamide epichlorohydrin used in the environmentally friendly and non-toxic adhesive is still unclear, and epichlorohydrin is required in its production process. Epichlorohydrin has certain toxicity and has been included in the list of Class 2A carcinogens. In addition, the adhesive only tests the tensile shear strength of wood in dry / wet states, and has not verified its adhesive properties for other substrate materials such as glass, metal, and polymers, and does not give the change of bonding strength over time. Summary of the invention

[0006] In response to the problems that existing adhesives slowly release formaldehyde, have low bonding strength, and are difficult to bond on the surfaces of various materials, the present application proposes an adhesive based on polyvinyl alcohol-tannic acid, which introduces natural tannic acid macromolecules rich in phenolic hydroxyl groups into polyvinyl alcohol, and uses water / ethanol as solvent. The prepared adhesive improves the problem of formaldehyde release, has high bonding strength, and is suitable for bonding on the surfaces of various materials.

[0007] The present application provides a polyvinyl alcohol-tannic acid adhesive, which is obtained by dissolving polyvinyl alcohol powder and tannic acid powder in a binary solvent of water and ethanol, and heating and dissolving and polymerizing the mixture.

[0008] The molecular weight of the polyvinyl alcohol is 89000-98000, the alcoholysis degree is above 99%, and the concentration is 5wt%~20wt%.

[0009] The tannic acid, as a natural macromolecule, contains a large amount of phenolic hydroxyl groups, which can form strong hydrogen bonds with the hydroxyl groups of polyvinyl alcohol to enhance adhesion, and the concentration is 1 wt%~5wt%.

[0010] The ethanol, as a polar solvent, can improve the solubility of polyvinyl alcohol and tannic acid, and the concentration is 10% to 20wt%.

[0011] In the above, the total mass of the polyvinyl alcohol powder, tannic acid powder, water and ethanol is 100%.

[0012] The preparation method of the polyvinyl alcohol-tannic acid adhesive comprises the following steps: (1) dissolving polyvinyl alcohol powder and tannic acid powder in a water / ethanol binary solvent, heating and stirring under sealed conditions to accelerate dissolution; (2) subjecting the solution obtained in step (1) to ultrasonic vibration to remove bubbles therein; (3) The solution obtained in step (2) is cooled and allowed to stand at room temperature to obtain a polyvinyl alcohol-tannic acid adhesive.

[0013] In the above step (1), the heating temperature is 90°C and the stirring time is 30-60 min.

[0014] The purpose of the above step (2) is to remove residual bubbles in the solution, and the ultrasonic time is 10 to 30 minutes.

[0015] The bonding strength of the polyvinyl alcohol-tannic acid solution is affected by the concentration of polyvinyl alcohol and tannic acid, and increases with the increase of curing time. The introduction of ethanol solvent is to improve the solubility of polyvinyl alcohol and tannic acid powder. The polyvinyl alcohol-tannic acid adhesive can be applied to the surface of any material to be bonded. After curing for a period of time at room temperature, the bonding effect can be exerted. Generally, the highest bonding strength can be achieved after curing for 120 hours.

[0016] Compared with the prior art, this application has the following advantages: (1) The system uses polyvinyl alcohol and tannic acid as raw materials, which are abundant in sources; (2) The polyvinyl alcohol-tannic acid adhesive will not release harmful substances such as formaldehyde during its preparation and use, and is environmentally friendly and pollution-free; (3) Using water / ethanol as solvent to increase the solubility of polyvinyl alcohol and tannic acid, thereby increasing the solid content of the adhesive; (4) The bonding strength gradually increases with time; (5) It has demonstrated bonding strength to a variety of materials, including glass, copper, aluminum, and polymethyl methacrylate (PMMA). BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : The bonding strength variation trend diagram of the polyvinyl alcohol-tannic acid adhesive obtained in Example 1.

[0018] Figure 2 : The bonding strength variation trend diagram of the polyvinyl alcohol-tannic acid adhesive obtained in Example 2.

[0019] Figure 3 : The bonding strength variation trend diagram of the polyvinyl alcohol-tannic acid adhesive obtained in Example 3.

[0020] Figure 4 : The bonding strength variation trend diagram of the polyvinyl alcohol-tannic acid adhesive obtained in Example 5.

[0021] Figure 5 : The bonding strength variation trend diagram of the polyvinyl alcohol-tannic acid adhesive obtained in Comparative Example 1. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] In the following embodiments, the bonding strength is measured by a shear overlap method. Specifically, an adhesive is applied to a material to be bonded, and another material is tightly pressed against the material to be bonded and then allowed to stand at room temperature for curing.

[0024] Example 1: 1g of polyvinyl alcohol powder and 0.25g of tannic acid powder were dissolved in a mixed solution of deionized water and ethanol (16.75g of deionized water and 2g of ethanol), and magnetic stirring was performed for 60min under closed conditions at 90°C to ensure that all components were completely dissolved. Ultrasonication was performed for 10min to remove bubbles in the mixed solution. After standing and cooling, the adhesive was coated on one end of a glass sheet and tightly pressed against one end of another glass sheet. After drying for 24h, 72h and 120h, the bonding strength to the glass substrate was tested by the shear overlap method. The test results are shown in the figure. Figure 1 As shown, the bonding strength can reach 3.67 MPa after 120h.

[0025] Example 2: 2 g of polyvinyl alcohol powder and 0.5 g of tannic acid powder were dissolved in a mixed solution of deionized water and ethanol (13.5 g of deionized water and 4 g of ethanol), and magnetic stirring was performed for 60 min under closed conditions at 90°C to ensure that all components were completely dissolved. Ultrasonication was performed for 10 min to remove bubbles in the mixed solution. After standing and cooling, the adhesive was coated on one end of a glass sheet and tightly pressed against one end of another glass sheet. After drying for 24 h, 72 h and 120 h, the bonding strength to the glass substrate was tested by the shear overlap method. The test results are shown in the figure. Figure 2 As shown, the bonding strength can reach 4.54 MPa after 120h.

[0026] Example 3: 4g of polyvinyl alcohol powder and 1g of tannic acid powder were dissolved in a mixed solution of deionized water and ethanol (11g of deionized water and 4g of ethanol), and magnetic stirring was performed for 60min under closed conditions at 90°C to ensure that all components were completely dissolved. Ultrasonication was performed for 10min to remove bubbles in the mixed solution. After cooling, the adhesive was coated on one end of a glass sheet and tightly pressed against one end of another glass sheet. After drying for 24h, 72h and 120h, the bonding strength to the glass substrate was tested by the shear overlap method. The test results are shown in the figure. Figure 3 As shown, the bonding strength can reach 5.35 MPa after 120h.

[0027] Example 4: 4 g of polyvinyl alcohol powder and 1 g of tannic acid powder were dissolved in 15 g of deionized water, and magnetic stirring was performed at 90° C. under closed conditions for 60 min. The polyvinyl alcohol and tannic acid powders were not completely dissolved, and agglomeration occurred in the solution.

[0028] Example 5: 2g of polyvinyl alcohol powder and 0.5g of tannic acid powder were dissolved in a mixed solution of deionized water and ethanol (8.75g of deionized water and 8.75g of ethanol), and magnetic stirring was performed under closed conditions at 90°C for 60min to ensure that all components were completely dissolved. Ultrasonication was performed for 10min to remove bubbles in the mixed solution. After standing and cooling, the adhesive was applied to one end of PMMA, iron sheet, copper sheet, and glass sheet, and tightly squeezed with another end of PMMA, iron sheet, copper sheet, and glass sheet. After drying for 120h, the bonding strength was tested by the shear overlap method. The test results are as follows: Figure 4 As shown, the bonding strengths to PMMA, iron sheet, copper sheet and glass sheet can reach 1.36MPa, 2.55MPa, 5.68MPa and 4.54MPa.

[0029] Comparative Example 1: 1g of polyvinyl alcohol powder was dissolved in 9g of deionized water, and magnetic stirring was performed for 60min under closed conditions at 90°C to ensure that all components were completely dissolved. Ultrasonication was performed for 10min to remove bubbles in the mixed solution. After cooling, the adhesive was coated on one end of a glass sheet and tightly squeezed with one end of another glass sheet. After drying for 24h, 72h and 120h, the bonding strength to the glass substrate was tested by the shear overlap method. The test results are shown in the figure. Figure 5 As shown, the bonding strength can reach 1.40MPa after 120h.

[0030] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyvinyl alcohol-tannic acid adhesive, characterized in that: The polyvinyl alcohol powder and tannic acid powder are dissolved in water and ethanol binary solvents, and then heated to dissolve and polymerize. The molecular weight of the polyvinyl alcohol is 89000-98000, the alcoholysis degree is above 99%, and the concentration is 5wt%~20wt%; The tannic acid concentration is 1 wt%~5wt%; The ethanol concentration is 10wt%~20wt%; In the above, the total mass of the polyvinyl alcohol powder, tannic acid powder, water and ethanol is 100%.

2. The method for preparing the polyvinyl alcohol-tannic acid adhesive according to claim 1, characterized in that: The following steps are involved: (1) dissolving polyvinyl alcohol powder and tannic acid powder in a water / ethanol binary solvent, heating and stirring under sealed conditions to accelerate dissolution; (2) shaking the solution obtained in step (1) to remove bubbles therein; (3) The solution obtained in step (2) is cooled and allowed to stand at room temperature to obtain a polyvinyl alcohol-tannic acid adhesive.

3. The method according to claim 2, characterized in that: The shaking operation in step (2) is performed by ultrasonic wave.

4. The method according to claim 3, characterized in that: The purpose of step (2) is to remove residual bubbles in the solution, and the ultrasonic time is 10 to 30 minutes.

5. The method according to claim 2, characterized in that: The heating temperature in step (1) is 90°C and the stirring time is 30-60 min.

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