Polyurethane adhesive for antibacterial plywood and preparation method

Abstract

The invention provides a polyurethane adhesive for antibacterial plywood and a preparation method, and belongs to the field of polymer preparation. Comprising the following steps: synthesizing a polysulfide polymer (S-r-CO) based on an anti-vulcanization mechanism by taking sulfur (S8), bio-based castor oil (CO), eugenol (EU) and lipoic acid (TA) as raw materials, and terminating by taking the polysulfide polymer as polyol and adopting isophorone diisocyanate (IPDI), thereby obtaining the highly crosslinked polyurethane adhesive (S-PU). The preparation method of the polyurethane adhesive for the antibacterial plywood is novel, and the polyurethane adhesive with a high cross-linked network is prepared by utilizing an anti-vulcanization mechanism and a cross-linking reaction. And the polyurethane adhesive network which has good shear strength and antibacterial property and can be used for processing and preparing plywood is prepared. And the selected raw materials are relatively low in cost, so that the preparation method has a wide market prospect. Steps are simple, operation is convenient, and practicability is high.

Description

Technical Field

[0001] The invention belongs to the field of polymer preparation, and in particular relates to an antibacterial polyurethane adhesive for plywood and a preparation method thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Currently, developing polyurethane adhesives with antimicrobial properties has become a key research area. Antimicrobial polyurethane adhesives are typically prepared by directly adding antimicrobial agents or functional materials to the polyurethane matrix. These antimicrobial ingredients can be natural substances, such as metal ions like silver, zinc, and copper, or organic antimicrobial agents like quaternary ammonium salts and cyclodextrin derivatives. However, the antimicrobial properties of polyurethane adhesives prepared using this direct antimicrobial addition method still need to be improved. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides an antibacterial polyurethane adhesive for plywood and a preparation method thereof. Sulfur (S8), castor oil (CO), eugenol (EU) and thioctic acid (TA) are used as raw materials to synthesize a polysulfide polymer (Sr-CO) based on the reverse vulcanization mechanism. The polysulfide polymer is used as a polyol and is end-capped with isophorone diisocyanate (IPDI) to obtain a highly cross-linked polyurethane adhesive (SCET-PU). The adhesion and antibacterial effect are controlled by adjusting the amount of eugenol, thioctic acid and isophorone diisocyanate added. At the same time, the application of the polyurethane adhesive in the field of plywood processing is explored. At present, a simple and convenient method can be used to realize the solvent-free synthesis of polyurethane adhesive. The polyurethane adhesive prepared by the present invention not only maintains excellent adhesion, but also has an antibacterial rate of 95% for Escherichia coli and 99% for Staphylococcus aureus, and can be processed into plywood with excellent performance.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a method for preparing an antibacterial polyurethane adhesive for plywood, comprising: Sulfur, castor oil and eugenol are mixed evenly and reacted under an inert atmosphere. After the reaction is completed, lipoic acid is added and the reaction is continued to obtain a polysulfide polymer. The polysulfide polymer is used as a polyol and is end-capped with isophorone diisocyanate to obtain a polyurethane adhesive (SCET-PU).

[0006] The raw materials of the present invention are sulfur (S8), castor oil (CO), eugenol (EU), and thioctic acid (TA). Sulfur is introduced into the polyurethane adhesive system through a desulfurization mechanism. The dual antibacterial effects of the desulfurization mechanism and oxidative stress are utilized to achieve a highly effective antibacterial effect of the polyurethane adhesive. The raw materials are derived from biomass, avoiding the use of fossil raw materials and promoting the green development of polyurethane adhesives. The entire synthesis process does not use any solvents, and the desulfurization process generates almost no waste, reducing environmental pollution and achieving high atom economy. The present invention uses sulfur, castor oil, eugenol, and thioctic acid as raw materials and introduces the desulfurization mechanism into the polyurethane adhesive.

[0007] The second aspect of the present invention provides a polyurethane adhesive prepared by the above method.

[0008] The present invention introduces eugenol and lipoic acid into the polyurethane adhesive through a reverse vulcanization process to achieve a synergistic antibacterial effect.

[0009] The third aspect of the present invention provides the use of the above-mentioned polyurethane adhesive in the fields of automobile manufacturing, furniture products, building materials and building decoration.

[0010] Beneficial effects of the present invention (1) The preparation method of the antibacterial polyurethane adhesive for plywood of the present invention is novel, has good adhesion performance and antibacterial performance, and has profound research value.

[0011] (2) Based on the reverse vulcanization mechanism, this paper designs an antibacterial polyurethane adhesive. Using sulfur (S8), bio-based castor oil (CO), eugenol (EU), and lipoic acid (TA) as raw materials, a polysulfide polymer (Sr-CO) based on the reverse vulcanization mechanism was synthesized. This polysulfide polymer was used as a polyol and capped with isophorone diisocyanate (IPDI) to obtain a highly cross-linked polyurethane adhesive (SCET-PU).

[0012] The antibacterial properties of the polyurethane adhesive were controlled by adjusting the amount of sulfur, eugenol, and lipoic acid added, while exploring its application in the field of artificial plywood processing. The invention does not require solvents and is directly synthesized in a one-pot process. The raw materials are low in cost and readily available from abundant sources.

[0013] (3) Unlike the traditional method of directly adding antibacterial substances to polyurethane, the present invention introduces antibacterial substances into polyurethane adhesive by synthesizing a polysulfide polymer. The polyurethane adhesive prepared by reaction polymerization has more stable antibacterial properties, enhances the bonding performance, and greatly improves the antibacterial effect. It also avoids the use of solvents, and the preparation process is simple, convenient, time-saving, and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0015] Figure 1 The antibacterial rate of the polyurethane adhesive (SCET-PU) in Example 1 of the present invention against Escherichia coli and Staphylococcus aureus.

[0016] Figure 2 The flexural modulus and flexural strength of the artificial plywood processed with the polyurethane adhesive (SCET-PU) in Examples 1-4 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0017] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0018] The present invention provides a method for preparing an antibacterial polyurethane adhesive for plywood, comprising: Sulfur, castor oil and eugenol are mixed evenly and reacted under an inert atmosphere. After the reaction is completed, lipoic acid is added and the reaction is continued to obtain a polysulfide polymer. The polysulfide polymer is used as a polyol and is end-capped with isophorone diisocyanate to obtain a polyurethane adhesive SCET-PU.

[0019] In some embodiments, the polysulfide polymer has a number average molecular weight of Mn=4000-5500 and a molecular weight distribution of 1.10-1.30.

[0020] The antibacterial property after cross-linking and curing is related to the content of sulfur, eugenol and lipoic acid, and the antibacterial property after cross-linking and film formation is related to the addition amount of the above three raw materials. Therefore, in some embodiments, the mass ratio of the sulfur, eugenol and lipoic acid content to the total mass of the polyurethane adhesive is: 10%-40%; In some embodiments, the mass ratio of sulfur to castor oil is 1:2-1:6; In some embodiments, the mass ratio of sulfur to eugenol is 1:0-1:3; In nature, lipoic acid and eugenol are natural small molecules with antibacterial properties. They are widely available and environmentally friendly, making them the subject of research for the next generation of antibacterial substances. Sulfur has long been used not only as an adhesive but also in medicine for its antibacterial and anti-inflammatory properties. Therefore, in some embodiments, the mass ratio of sulfur, eugenol, and lipoic acid is 1:0:0 to 1:3:3. These abundant natural antibacterial substances not only chemically react with the polyurethane matrix, thereby imparting a long-lasting antibacterial effect to the adhesive, but also ensure that other properties of the adhesive are not affected, achieving an excellent balance between adhesion and antibacterial properties.

[0021] In some embodiments, the reaction conditions of the sulfur, castor oil and eugenol are 150-180° C. for 1-1.5 hours; In some embodiments, the reaction conditions of sulfur and lipoic acid are 150-160° C. for 0.5-1 hour.

[0022] The tensile shear strength after cross-linking and film formation is related to the content of isophorone diisocyanate. Therefore, in some embodiments, the molar ratio of isophorone diisocyanate to polysulfide polymer is 1:1-2:1.

[0023] In some embodiments, isophorone diisocyanate and polysulfide polymer are uniformly mixed, reacted at 60-80° C. for 3-4 minutes under an inert atmosphere, and then placed in a mold for curing and cross-linking to obtain a polyurethane adhesive (SCET-PU).

[0024] More specifically, they include: Place sulfur, castor oil and eugenol in a mass ratio of 1:5:0-1:5:3 in a 100 ml four-necked flask, connect it to a condenser, a thermometer and a stirring paddle, heat it to 180°C under nitrogen protection and stir vigorously for 1 hour. After the reaction is completed, cool it to 150°C.

[0025] Then, thioctic acid is added according to the mass ratio of sulfur, eugenol and thioctic acid of 1:0:0-1:3:3, and the mixture is placed in an oil pan at 150° C. for reaction for 0.5 hours under nitrogen protection to obtain a polysulfide polymer (Sr-CO).

[0026] Isophorone diisocyanate (IPDI) and polysulfide polymer (Sr-CO) are placed in a four-necked flask at a molar ratio of 1:1-2:1, reacted in an oil pan at 75°C under a nitrogen atmosphere for 5 minutes, then placed in a mold and cured in an oven at 50°C.

[0027] Because the polyurethane adhesive prepared by the present invention has both good bonding strength and good antibacterial properties, the present invention also provides the aforementioned antibacterial polyurethane adhesive, or the use of the polyurethane adhesive prepared by the aforementioned method in achieving antibacterial properties of polyurethane adhesives and preparing artificial plywood.

[0028] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0029] In the following examples, the following test methods were used: Escherichia coli and Staphylococcus aureus were selected as typical bacteria to evaluate the antibacterial properties of the adhesive. The samples were immersed in PBS buffer solution for 24 h and sterilized with UV for 30 min. The samples were then placed in a culture dish and the optical density was 0.72 (equivalent to 1×108 CFU·mL -1 ) of Escherichia coli or Staphylococcus aureus were cultured with the samples at 37°C for 24 h, and the number of adherent colonies of the adhesive was determined by plate counting method. The same operation was performed on the samples as blank control group, and the antibacterial rate was calculated.

[0030] Beech veneer was selected as the processing raw material, and the polyurethane adhesive (SCET-PU) synthesized by the present invention was used to produce artificial plywood through a flat vulcanizer under the conditions of temperature of 80°C, pressure of 2 MPa, and hot pressing time of 2 h.

[0031] According to the test standards and methods specified in GB / T 17657-2022, the processed plywood was subjected to a three-point bending test to test the mechanical properties of the plywood.

[0032] Example 1 Place 0.5 g of sulfur, 2.5 g of castor oil, and 0.4 g of eugenol in a 100 ml four-necked flask, connect it to a condenser, a thermometer, and a stirring paddle, heat it to 180°C under nitrogen protection, and stir vigorously for 1 hour. After the reaction is complete, cool it to 150°C.

[0033] Then, 0.4 g of thioctic acid was added according to the mass ratio of sulfur to thioctic acid of 1:0.4, and the mixture was placed in an oil pan at 150° C. under nitrogen protection for 0.5 hour to obtain a polysulfide polymer (Sr-CO).

[0034] 3 g of isophorone diisocyanate (IPDI) was added to the polysulfide polymer (Sr-CO), and the mixture was reacted in an oil pan at 75°C under a nitrogen atmosphere for 5 minutes. The mixture was then poured into a mold and cured in an oven at 50°C to obtain a polyurethane adhesive.

[0035] Example 2 Place 0.5 g of sulfur, 2.5 g of castor oil, and 0.8 g of eugenol in a 100 ml four-necked flask, connect it to a condenser, a thermometer, and a stirring paddle, heat it to 180°C under nitrogen protection, and stir vigorously for 1 hour. After the reaction is complete, cool it to 150°C.

[0036] Then, 0.8 g of thioctic acid was added according to the mass ratio of sulfur to thioctic acid of 1:0.8, and the mixture was placed in an oil pan at 150° C. for reaction for 0.5 h under nitrogen protection to obtain a polysulfide polymer (Sr-CO).

[0037] 3 g of isophorone diisocyanate (IPDI) was added to the polysulfide polymer (Sr-CO), and the mixture was reacted in an oil pan at 75°C under a nitrogen atmosphere for 5 minutes. The mixture was then poured into a mold and cured in an oven at 50°C to obtain a polyurethane adhesive.

[0038] Example 3 Place 0.5 g of sulfur, 2.5 g of castor oil, and 1.2 g of eugenol in a 100 ml four-necked flask, connect it to a condenser, a thermometer, and a stirring paddle, heat it to 180°C under nitrogen protection, and stir vigorously for 1 hour. After the reaction is complete, cool it to 150°C.

[0039] Then, 1.2 g of thioctic acid was added according to the mass ratio of sulfur to thioctic acid of 1:1.2, and the mixture was placed in an oil pan at 150° C. under nitrogen protection for 0.5 hour to obtain a polysulfide polymer (Sr-CO).

[0040] 3 g of isophorone diisocyanate (IPDI) was added to the polysulfide polymer (Sr-CO), and the mixture was reacted in an oil pan at 75°C under a nitrogen atmosphere for 5 minutes. The mixture was then poured into a mold and cured in an oven at 50°C to obtain a polyurethane adhesive.

[0041] Example 4 0.5 g of sulfur and 2.5 g of castor oil were placed in a 100 ml four-necked flask, connected to a condenser, thermometer, and stirring paddle. The temperature was raised to 180°C under nitrogen protection and stirred vigorously for 1 hour. After the reaction was completed, 3 g of isophorone diisocyanate (IPDI) was added and reacted in an oil pan at 75°C under a nitrogen atmosphere for 5 minutes. The mixture was then poured into a mold and cured in an oven at 50°C to obtain a polyurethane adhesive.

[0042] Comparative Example 1 2.5 g of castor oil was placed in a 100 ml four-necked flask, connected to a condenser, thermometer, and stirring paddle, and heated to 75°C under nitrogen protection. Subsequently, 3 g of isophorone diisocyanate (IPDI) was added and reacted for 5 minutes. The flask was then poured into a mold and cured in an oven at 50°C to obtain a polyurethane adhesive.

[0043] Comparative Example 2 2.5 g of castor oil, 0.5 g of sulfur (molten state), 0.4 g of eugenol, and 0.4 g of lipoic acid were placed in a 100 ml four-necked flask, connected to a condenser, thermometer, and stirring paddle. Under nitrogen protection, the mixture was stirred uniformly at 75°C. Subsequently, 3 g of isophorone diisocyanate (IPDI) was added and reacted for 5 minutes. The mixture was then poured into a mold and cured in an oven at 50°C to obtain a polyurethane adhesive.

[0044] Experimental Example 1 The antibacterial test of the polyurethane adhesive prepared in Example 1 was carried out, and the test results are as follows: Figure 1 As shown, the bending modulus and bending strength tests were conducted on the artificial plywood prepared by Examples 1-4 and Comparative Examples 1-2. The test results are shown in FIG. Figure 2 shown.

[0045] Depend on Figure 1 It can be seen that the polyurethane adhesive prepared in Example 1 has excellent antibacterial effects on Escherichia coli and Staphylococcus aureus, and the antibacterial rates against Escherichia coli and Staphylococcus aureus can reach 95% and 99%, respectively.

[0046] Depend on Figure 2 It can be seen that the artificial plywood processed by the polyurethane adhesive prepared in Example 1 has a flexural modulus and a flexural strength of 15500 MPa and 195 MPa, respectively, and has a strong ability to resist deformation and good toughness.

[0047] Experimental Example 2 The tensile shear strength (MPa) and debonding work of the polyurethane adhesives prepared in Examples 1-4 and Comparative Examples 1 and 2 were tested on steel plates and pine wood boards, respectively. The results are shown in Table 1: Table 1 Performance test results

[0048] Among them, tensile shear strength refers to the stress borne by the unit bonding surface when the lap joint is destroyed under the action of tensile load.

[0049] Debonding work: refers to the work required to completely separate the interface between the adhesive and the adherend per unit area. It is used to measure the strength of the interface bond between the adhesive and the substrate and is an important physical quantity that characterizes the interfacial adhesion performance.

[0050] By comparing Examples 1-4 and Comparative Examples 1-2, it can be seen that the polyurethane adhesives prepared in Examples 1-4 have excellent antibacterial effects on Escherichia coli and Staphylococcus aureus. The antibacterial rates of the polyurethane adhesive of Example 1 against Escherichia coli and Staphylococcus aureus can reach 95% and 99%, respectively, and the polyurethane adhesive prepared this time can be further processed into plywood. The antibacterial rates of the polyurethane adhesive prepared in Comparative Example 2 against Escherichia coli and Staphylococcus aureus can reach 65% and 74%, respectively, which are lower than those in Example 1. It can be seen that the antibacterial properties of the polyurethane adhesive can be better improved by introducing antibacterial substances through polysulfide polymers. The antibacterial rate of the polyurethane adhesive prepared in Example 4 against Escherichia coli and Staphylococcus aureus was only 59% and 68%, respectively, which was significantly lower than that in Example 1. This was attributed to the use of a reverse vulcanization mechanism to introduce eugenol and lipoic acid into the polyurethane adhesive by polymerization to form a synergistic antibacterial mechanism. Sulfur has a wide range of antibacterial effects. Adding sulfur to the polyurethane adhesive can interfere with the metabolic process of bacteria and inhibit the synthesis of cell walls, resulting in damage to the bacterial structure, thereby inhibiting bacterial growth and reproduction. Secondly, lipoic acid in the adhesive is a natural antioxidant that can help bacteria produce reactive oxygen species (ROS) by increasing oxidative stress. These ROS can damage bacterial cell membranes, DNA, and other important cell structures, thereby inhibiting bacterial growth or directly causing bacterial death. In addition, eugenol can react with lipid substances in the bacterial cell membrane, destroying the integrity of the cell membrane, changing the permeability of the cell membrane, leading to leakage of intracellular substances, and thus killing the bacteria. Comprehensive analysis shows that the polyurethane adhesive prepared by the present invention has a triple antibacterial mechanism, which makes the polyurethane adhesive have excellent antibacterial properties against common Escherichia coli and Staphylococcus aureus.

[0051] The polyurethane adhesive prepared by the present invention has a large number of SS bonds and hydrogen bonds, has moderate viscosity, can be cured in a short time, and has good processability. Beech veneer is selected as a processing raw material. The polyurethane adhesive prepared by the present invention can be processed and manufactured into artificial plywood under the conditions of a temperature of 70-80°C, a pressure of 2-3 MPa, and a hot pressing time of 2-3 hours.

[0052] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing an antibacterial polyurethane adhesive for plywood, characterized in that: include: Sulfur, castor oil and eugenol are mixed evenly and reacted under an inert atmosphere. After the reaction is completed, lipoic acid is added and the reaction is continued to obtain a polysulfide polymer. The polysulfide polymer is used as a polyol and is end-capped with isophorone diisocyanate to obtain a polyurethane adhesive SCET-PU.

2. The method for preparing the antibacterial polyurethane adhesive for plywood according to claim 1, wherein: The number average molecular weight of the polysulfide polymer is: Mn=4000-5500, and the molecular weight distribution is 1.10-1.

30.

3. The method for preparing the antibacterial polyurethane adhesive for plywood according to claim 1, wherein: The mass ratio of the sulfur to the castor oil is 1:2-1:

6.

4. The method for preparing the antibacterial polyurethane adhesive for plywood according to claim 1, wherein: The mass ratio of sulfur, eugenol and lipoic acid is 1:0:0-1:3:3; Alternatively, the mass ratio of the sulfur, eugenol and lipoic acid to the total mass of the polyurethane adhesive is 10%-40%.

5. The method for preparing the antibacterial polyurethane adhesive for plywood according to claim 1, wherein: The reaction conditions of the sulfur, castor oil and eugenol are 150-180° C. and 1-1.5 hours.

6. The method for preparing the antibacterial polyurethane adhesive for plywood according to claim 1, wherein: After adding lipoic acid, the reaction is continued at 150-160° C. for 0.5-1 hour.

7. The method for preparing the antibacterial polyurethane adhesive for plywood according to claim 1, wherein: The molar ratio of the isophorone diisocyanate to the polysulfide polymer is 1:1-2:

1.

8. The method for preparing the antibacterial polyurethane adhesive for plywood according to claim 1, wherein: Isophorone diisocyanate and polysulfide polymer are mixed evenly, reacted at 60-80° C. for 3-4 minutes under an inert atmosphere, and then placed in a mold for curing and cross-linking to obtain a polyurethane adhesive SCET-PU.

9. The polyurethane adhesive prepared by the method according to any one of claims 1 to 8.

10. Use of the polyurethane adhesive according to claim 9 in the fields of automobile manufacturing, furniture products, building materials and building decoration.

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