Lactosyl covalent organic framework adhesive as well as preparation method and application thereof

Abstract

The invention discloses a lactosyl covalent organic framework adhesive as well as a preparation method and application thereof, and belongs to the technical field of adhesives, the lactosyl covalent organic framework adhesive LHC (COFPN) is firstly prepared into a lactosyl adhesive LHC through a Schiff base reaction, the problem that a traditional biomass adhesive is insufficient in adhesive property in a high-temperature and humid environment is solved, and the problem that the adhesive property of the traditional biomass adhesive is poor is solved. The lactose-based covalent organic framework adhesive LHC-COFPN is prepared by introducing a covalent organic framework COFPN into a lactose-based adhesive LHC, the flame retardance is improved, the mechanical strength of the adhesive is further enhanced, the dry shear strength of plywood prepared from the lactose-based covalent organic framework adhesive LHC-COFPN can reach 1.61 MPa or above, and the plywood has the good flame retardance. The strength of the plywood prepared from the lactose-based adhesive LHC still reaches 1.49 MPa or above after the plywood is soaked in hot water at 63 DEG C and hot water at 93 DEG C for 3 h, the strength of the plywood is higher than that of the plywood prepared from the lactose-based adhesive LHC, the limit oxygen index of the plywood is 37.6, and compared with the lactose-based adhesive LHC, the flame retardance of the plywood is higher, and the plywood is suitable for high-performance application of various wood substrates.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and specifically discloses a lactose-based covalent organic skeleton adhesive and a preparation method and application thereof. Background Art

[0002] With the rapid development of the wood industry, wood plays a vital role in the construction field. Wood used for structural construction needs to have excellent mechanical properties and long service life, and these properties are closely related to the wood adhesive used. Therefore, the selected wood adhesive must have excellent adhesion, fire resistance and weathering resistance, while the existing biomass adhesives cannot meet the requirements in terms of durability, flame retardancy and mechanical properties in hot and humid environments. Summary of the invention

[0003] The technical problem to be solved by the present invention is that the durability, flame retardancy and mechanical properties of existing biomass adhesives in high temperature and humid environments cannot meet the requirements, and a lactose-based covalent organic skeleton adhesive and its preparation method and application are proposed.

[0004] In order to solve the above technical problems, the present invention provides a lactose-based covalent organic framework adhesive (LHC@COF PN ), comprising the following steps:

[0005] S1. Preparation of citric acid-based hyperbranched polyamine HC: trimethyl citrate and 1,6-hexanediamine are mixed, methanol is added to dissolve, and the mixture is stirred at room temperature until the reaction is completed, and excess methanol in the product is removed to obtain citric acid-based hyperbranched polyamine HC;

[0006] S2, preparing lactose-based adhesive LHC: mixing the citric acid-based hyperbranched polyamine HC prepared in step S1 with lactose, reacting at 70-90° C. for 2-6 hours, cooling to room temperature, adding deionized water at 30-50% of its solid content to completely dissolve it, and preparing lactose-based adhesive LHC;

[0007] S3. Preparation of covalent organic framework COF PN : Hexachlorocyclotriphosphazene (HCCP) and p-phenylenediamine (PDI) were dissolved in anhydrous tetrahydrofuran (THF) to form a suspension, sealed in a high-pressure reaction vessel at 90°C for 24 hours, cooled to room temperature, filtered, washed, and vacuum dried to obtain a covalent organic framework COF PN ;

[0008] S4. Preparation of lactose-based covalent organic framework adhesive LHC@COF PN : The lactose-based adhesive LHC prepared in step S2 and the covalent organic framework COF prepared in step S3 are PNMix at room temperature, react at 80°C for 1 hour, cool to room temperature, add deionized water at 50% of its solid content to completely dissolve it, and then obtain lactose-based covalent organic framework adhesive LHC@COF PN .

[0009] Specifically, the preparation process of p-phenylenediamine (PDI) described in step S3 is: dissolving ethylenediamine in anhydrous ethanol, slowly adding an anhydrous ethanol solution of terephthalaldehyde under stirring, reacting at 60° C. for 24 hours, pouring the reaction solution into cold water to precipitate a solid product, collecting the solid product and washing it with cold anhydrous ethanol, and vacuum drying to obtain p-phenylenediamine (PDI).

[0010] Specifically, in step S1, the molar ratio of trimethyl citrate to 1,6-hexanediamine is 1:3.

[0011] Specifically, in step S2, the mass ratio of citric acid-based hyperbranched polyamine HC to lactose is 1:(2-6), preferably 1:3.

[0012] Specifically, in step S3, the molar ratio of hexachlorocyclotriphosphazene (HCCP) to p-phenylenediimide (PDI) is 1:3.

[0013] Specifically, in step S4, the covalent organic framework COF PN The mass ratio of the lactose-based adhesive LHC is (0.01-0.1):1, preferably 0.3:1.

[0014] In order to solve the above technical problems, the present invention also provides a lactose-based covalent organic framework adhesive LHC@COF PN , prepared according to the preparation method.

[0015] In order to solve the above technical problems, the present invention also provides a lactose-based covalent organic framework adhesive LHC@COF PN Application in the preparation of laminated plywood.

[0016] Furthermore, the plywood is three-layered, and the preparation process is as follows:

[0017] SS1, Drying: Dry the veneer to be pressed until the moisture content is less than 10%;

[0018] SS2, Gluing: Apply the lactose-based covalent organic framework adhesive LHC@COF on both sides of the dried veneer. PN ,Lactose-based covalent organic framework adhesive LHC@COF PN The total coating amount is 320g / m 2 ;

[0019] SS3, assembly: arranging and assembling the veneers coated with the lactose-based covalent organic framework adhesive in a vertical texture manner to form a blank of a predetermined shape and size;

[0020] SS4, hot pressing: hot pressing the assembled green body at 180-220° C. and 1.0-1.5 MPa for 5-8 minutes to obtain a laminated plywood.

[0021] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0022] (1) The lactose-based adhesive prepared by the Schiff base reaction of the present invention overcomes the problem of insufficient bonding performance of traditional biomass adhesives in high temperature and humid environments, improves the performance of the adhesive in high temperature and humid environments, and makes it show better stability and reliability under harsh conditions;

[0023] (2) By introducing covalent organic frameworks (COFs) containing phosphorus (P) and nitrogen (N) elements PN , significantly improving the flame retardant properties of the adhesive, which is a function that is difficult to achieve with traditional biomass adhesives, making it more suitable for applications with high safety requirements;

[0024] (3) By using the covalent organic framework COF PN Combined with lactose-based adhesive LHC, it not only improves flame retardancy, but also further enhances the mechanical strength of the adhesive, broadening its application range under higher load conditions;

[0025] (4) Lactose-based adhesives were prepared by using citric acid-based hyperbranched polyamine HC and lactose as raw materials for Schiff base reaction, which provided a new idea for optimizing the performance of biomass adhesives.

[0026] In general, the lactose-based covalent organic framework adhesive LHC@COF of the present invention PN The preparation method is a new strategy based on Schiff base reaction, which not only improves the performance of adhesives in high temperature and humid environments, but also introduces covalent organic frameworks (COFs) containing phosphorus and nitrogen elements. PN , while improving the heat resistance and moisture resistance of the adhesive, it also enhances its flame retardancy and mechanical strength, and the reaction conditions are low and the requirements for reaction equipment are not high; at the same time, the main raw materials used are derived from biomass, avoiding the use of formaldehyde, while reducing production costs, improving the environmental performance of the board, reducing environmental pollution, and promoting the rational development and utilization of renewable resources. Therefore, the present invention greatly improves the applicability of biomass adhesives in high-performance applications, especially in the fields of wood substrates and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is the reaction principle diagram of citric acid-based hyperbranched polyamine HC;

[0028] Figure 2 It is a schematic diagram of the reaction principle and preparation process of lactose-based adhesive LHC;

[0029] Figure 3 It is a covalent organic framework (COF) containing phosphorus and nitrogen elements. PN Schematic diagram of reaction principle and preparation process;

[0030] Figure 4 Lactose-based covalent organic framework adhesive LHC@COF PN Schematic diagram of reaction principle and preparation process;

[0031] Figure 5 Lactose-based covalent organic framework adhesive LHC@COF PN Diagram of flame retardant mechanism. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0033] The reaction principle of the citric acid-based hyperbranched polyamine HC used in the following examples is as follows: Figure 1 As shown, the preparation method thereof is specifically as follows:

[0034] The trimethyl citrate and 1,6-hexanediamine were mixed in a molar ratio of 1:3, methanol was added to dissolve, and the mixture was stirred at room temperature for 48 hours. After the reaction was completed, the excess methanol in the product was removed by a rotary evaporator to obtain a citric acid-based hyperbranched polyamine HC.

[0035] Example 1

[0036] This embodiment provides a method for preparing a lactose-based adhesive LHC, and its reaction principle and preparation process are as follows: Figure 2 As shown, specifically:

[0037] 2g of citric acid-based hyperbranched polyamine HC and 4g of lactose were mixed and reacted at 80°C for 3h. After the reaction was completed, the product was cooled to room temperature and deionized water was added at 50% of its solid content to completely dissolve it, thereby obtaining a lactose-based adhesive LHC.

[0038] Examples 2-14 are all methods for preparing lactose-based adhesive LHC, wherein the reaction conditions are different. The specific reaction conditions are shown in Table 1 and will not be repeated here.

[0039] The covalent organic framework COF used in the following examples PN The reaction principle and preparation process of Figure 3 As shown, the preparation method thereof is specifically as follows:

[0040] 1.34 g of terephthalaldehyde was dissolved in 10 mL of anhydrous ethanol to obtain a terephthalaldehyde solution, and then a mixture of 1.20 g of ethylenediamine and 10 mL of anhydrous ethanol was added to a reaction bottle and stirred, and then the terephthalaldehyde solution was slowly added to the ethylenediamine solution, and the mixture was stirred continuously and reacted in a sand bath at 60° C. for 24 hours. The solution turned yellow, indicating the formation of the intermediate p-phenylenediamine. After the reaction was completed, the mixture was poured into 100 mL of cold water to precipitate a solid product, and the solid was collected by vacuum filtration, washed with a small amount of cold anhydrous ethanol, and finally dried in a vacuum drying oven at 70° C. for 24 hours to obtain purified p-phenylenediamine (PDI);

[0041] Hexachlorocyclotriphosphazene (HCCP) and p-phenylenediamine (PDI) were dissolved in 50 mL of anhydrous tetrahydrofuran (THF) at a molar ratio of 1:3 to form a suspension, and then the suspension was transferred to a high-pressure reaction vessel, sealed and reacted at 90 ° C for 24 hours. After the reaction, it was cooled to room temperature, and the orange powder was collected by filtration, washed with deionized water and ethanol until the filtrate was colorless, and vacuum dried at 70 ° C for 24 hours to obtain a light yellow covalent organic framework COF PN .

[0042] Table 1 Reaction conditions of the method for preparing lactose-based adhesives in Examples 3-15

[0043]

[0044] Embodiment 15

[0045] This embodiment provides a lactose-based covalent organic framework adhesive LHC@COF PN The preparation method, its reaction principle and preparation process are as follows Figure 4 Specifically, 10 g of the lactose-based adhesive LHC prepared in Example 7 and 0.1 g

[0046] Example 16 Covalent organic framework (COF) prepared PN The mixture was mixed at room temperature and stirred at 80°C for 1 hour. The product obtained after the reaction was cooled to room temperature and deionized water was added at 50% of its solid content to completely dissolve it to obtain the lactose-based covalent organic framework adhesive LHC@COF. PN .

[0047] Examples 16-18 are all lactose-based covalent organic framework adhesives LHC@COF PN The preparation method, wherein the reaction conditions are different, the specific reaction conditions are shown in Table 2, and will not be repeated here.

[0048] Table 2 Reaction conditions of the preparation method of lactose-based covalent organic skeleton adhesive in Examples 16-18

[0049]

[0050] Embodiment 19 performance test:

[0051] 1. Bonding strength test:

[0052] In order to test the lactose-based adhesive LHC and lactose-based covalent organic framework adhesive LHC@COF prepared by the present invention PN The properties of the prepared laminated plywood were respectively prepared using the lactose-based adhesive LHC prepared in Examples 1-14 and the lactose-based covalent organic framework adhesive LHC@COF prepared in Examples 15-18. PN 18 three-layer laminated plywood panels were prepared, and the specific preparation process was as follows:

[0053] Dry the veneer to be pressed until the moisture content is less than 10%; apply lactose-based adhesive LHC or lactose-based covalent organic framework adhesive LHC@COF on both sides of the dried veneer PN The total coating amount is 320g / m 2 ; Then arrange and combine them in a vertical texture manner to form a blank of a predetermined shape and size; hot press the assembled blank at 200°C and 1.5MPa for 6 minutes to obtain 18 laminated plywood panels.

[0054] Adhesion strength test: The evaluation of adhesion strength is carried out in accordance with the provisions of the national standard GB / T17657-2013. First, the samples are cut into the same size (100mm×25mm), and then slotted so that the area of ​​the bonding part is 25mm×25mm. Next, the samples are immersed in a water bath at 63±3℃ and 93±3℃ for 3h, respectively. After taking it out, place it at room temperature for 10min, and then use an electronic universal mechanical testing machine to test the bonding strength. The test results are shown in Tables 3 and 4.

[0055] Results analysis: From the data in Table 3 and Table 4, it can be seen that the dry shear strength of the laminated plywood prepared with lactose-based adhesive LHC is 0.72-1.68 MPa, while that of the laminated plywood prepared with lactose-based covalent organic framework adhesive LHC@COF is PN The dry shear strength of the prepared laminated plywood is greater than 1.61MPa, and the maximum can reach 1.88MPa, which is much higher than the dry shear strength of the laminated plywood prepared with lactose-based adhesive LHC. The wet strength of the laminated plywood prepared with lactose-based adhesive LHC after immersion in hot water at 63℃ for 3h is 0.68~1.47MPa, while that of the laminated plywood prepared with lactose-based covalent organic framework adhesive LHC@COF is 0.68~1.47MPa. PNThe wet strength of the laminated plywood prepared by the method after immersion in hot water at 63℃ for 3h was greater than 1.49MPa, and the maximum was 2.28MPa. The wet strength of the laminated plywood prepared by the lactose-based adhesive LHC after immersion in hot water at 93℃ for 3h was 0.77~1.50MPa; while the wet strength of the laminated plywood prepared by the lactose-based covalent organic framework adhesive (LHC@COF PN The wet strength of the laminated plywood prepared with ) after immersion in hot water at 93℃ for 3h is greater than 1.57MPa, and the maximum can reach 2.20MPa, which is also higher than the wet strength of the laminated plywood prepared with lactose-based adhesive LHC.

[0056] Conclusion: The above performance test data show that the introduction of covalent organic framework COF containing P and N elements into the lactose-based adhesive LHC PN , improving the heat resistance, moisture resistance and mechanical strength of the adhesive.

[0057] Table 3 Properties of laminated plywood prepared with lactose-based adhesive LHC from different examples

[0058] Group No. Dry shear strength / MPa 63℃ immersion wet strength / MPa 93℃ immersion wet strength / MPa Example 1 1.22 1.39 1.28 Example 2 1.50 1.46 1.30 Example 3 1.12 1.24 1.00 Example 4 1.42 1.17 1.00 Example 5 1.44 1.13 0.90 Example 6 1.68 1.28 1.12 Example 7 1.54 1.47 1.50 Example 8 1.53 1.28 1.20 Example 9 1.46 1.28 1.20 Example 10 1.26 1.44 1.24 Embodiment 11 1.47 1.35 1.31 Example 12 0.72 0.68 0.77 Example 13 1.64 1.16 0.96 Embodiment 14 1.42 1.46 1.40

[0059] Table 4 Lactose-based covalent organic framework adhesives LHC@COF in different embodiments PN Properties of prepared laminated plywood

[0060]

[0061] 2. Flame retardancy test:

[0062] The laminated plywood prepared with the lactose-based adhesive LHC (prepared in Example 7) was cut into three control samples of equal length (80 mm × 10 mm) and the lactose-based covalent organic framework adhesive LHC@COF PN The laminated plywood prepared (prepared by Example 16) was cut into three experimental group samples of equal length (80 mm×10 mm), and then the two groups of samples were tested for limiting oxygen index (LOI). The test results are shown in Table 5. It can be seen from Table 5 that the LOI of the experimental group samples is much higher than that of the control group samples, indicating that the experimental group samples have stronger flame retardancy.

[0063] from Figure 5 Lactose-based covalent organic framework adhesive LHC@COF PN The flame retardant mechanism of lactose-based covalent organic framework adhesive LHC@COF PN During combustion, NH3 / N2, PO * / P * and H2O, forming an isolation film on the surface, isolating oxygen, reducing the surface oxidation heat and preventing combustion.

[0064] Table 5 Limiting oxygen index (LOI) of two groups of samples

[0065] Control group samples Experimental group samples LOI(%) 25.8 37.6

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. A person skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the present invention.

Claims

1. A method for preparing a lactose-based covalent organic skeleton adhesive, characterized in that: The following steps are involved: S1. Preparation of citric acid-based hyperbranched polyamine: trimethyl citrate and 1,6-hexanediamine were mixed, methanol was added to dissolve, and the mixture was stirred at room temperature until the reaction was completed, and excess methanol in the product was removed to obtain citric acid-based hyperbranched polyamine; S2, preparing a lactose-based adhesive: mixing the citric acid-based hyperbranched polyamine prepared in step S1 with lactose, reacting at 70-90° C. for 2-6 hours, cooling to room temperature, adding deionized water at a solid content of 40-60% to completely dissolve the mixture, and preparing a lactose-based adhesive; S3, preparing a covalent organic framework: dissolving hexachlorocyclotriphosphazene and p-phenylenediamine in anhydrous tetrahydrofuran to form a suspension, sealing and reacting in a high pressure reaction vessel at 90° C. for 24 hours, cooling to room temperature, filtering, washing, and vacuum drying to obtain a covalent organic framework; S4. Preparation of lactose-based covalent organic skeleton adhesive: The lactose-based adhesive prepared in step S2 and the covalent organic skeleton prepared in step S3 are mixed at room temperature, reacted at 80° C. for 1 h, cooled to room temperature, and deionized water is added at 50% of the solid content to completely dissolve the mixture, thereby obtaining a lactose-based covalent organic skeleton adhesive.

2. The method for preparing the lactose-based covalent organic skeleton adhesive according to claim 1, characterized in that: The preparation process of p-phenylenediamine described in step S3 is: dissolving ethylenediamine in anhydrous ethanol, slowly adding an anhydrous ethanol solution of terephthalaldehyde under stirring, reacting at 60° C. for 24 hours, pouring the reaction solution into cold water to precipitate a solid product, collecting the solid product and washing it with cold anhydrous ethanol, and vacuum drying to obtain p-phenylenediamine.

3. The method for preparing the lactose-based covalent organic skeleton adhesive according to claim 1, characterized in that: In step S1, the molar ratio of trimethyl citrate to 1,6-hexanediamine is 1:

3.

4. The method for preparing the lactose-based covalent organic skeleton adhesive according to claim 1, characterized in that: In step S2, the mass ratio of the citric acid-based hyperbranched polyamine to lactose is 1:(2-6).

5. The method for preparing the lactose-based covalent organic skeleton adhesive according to claim 1, characterized in that: In step S3, the molar ratio of hexachlorocyclotriphosphazene to p-phenylenediimide is 1:

3.

6. The method for preparing the lactose-based covalent organic skeleton adhesive according to claim 1, characterized in that: In step S4, the mass ratio of the covalent organic framework to the lactose-based adhesive is (0.01-0.1):

1.

7. A lactose-based covalent organic skeleton adhesive, characterized in that: Prepared according to the method described in any one of claims 1 to 6.

8. Use of the lactose-based covalent organic skeleton adhesive according to claim 7 in the preparation of laminated plywood.

9. The use of the lactose-based covalent organic skeleton adhesive in the preparation of laminated plywood according to claim 7, characterized in that: The plywood is three-layered and the preparation process is as follows: SS1, Drying: Dry the veneer to be pressed until the moisture content is less than 10%; SS2, Gluing: Apply the lactose-based covalent organic skeleton adhesive described in claim 7 on both sides of the dried veneer, and the total amount of the lactose-based covalent organic skeleton adhesive applied is 320g / m 2 ; SS3, assembly: arranging and assembling the veneers coated with the lactose-based covalent organic skeleton adhesive in a vertical texture manner to form a blank of a predetermined shape and size; SS4, hot pressing: hot pressing the assembled green body at 180-220° C. and 1.0-1.5 MPa for 5-8 minutes to obtain a laminated plywood.

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