Bean flour-oxidized sucrose adhesive as well as preparation method and application thereof

Abstract

The invention discloses a bean flour-oxidized sucrose adhesive as well as a preparation method and application thereof, and the method comprises the following steps: mixing sucrose with water to obtain a sucrose aqueous solution; a sucrose aqueous solution and an oxidizing agent are mixed and oxidized to obtain oxidized sucrose, then the oxidized sucrose is sequentially mixed with bean flour and a polyethyleneimine solution, the bean flour-oxidized sucrose adhesive with improved bonding strength and water resistance is prepared, and the application range is expanded.

Description

Technical Field

[0001] This application relates to a soybean flour-oxidized sucrose adhesive and its preparation method and application, and more particularly to the preparation of a boiling water resistant soybean flour-oxidized sucrose adhesive based on the Schiff base reaction, belonging to the field of environmentally friendly adhesive technology. Background Technology

[0002] With the development of China's customized home furnishing industry and the continued growth in demand for formaldehyde-free engineered wood products, the demand for non-formaldehyde adhesives has increased significantly. Research on biomass adhesives has become an important research direction and hot topic in the field of wood adhesives. Sucrose, as a natural and renewable biomass resource, shows potential value in the application of adhesives.

[0003] Sucrose, as a natural polysaccharide, is rich in hydroxyl groups, which, while giving it good water solubility and reactivity, also results in extremely poor water resistance. The numerous hydrophilic hydroxyl groups in sucrose molecules readily form hydrogen bond networks with water molecules, causing the adhesive to swell in volume after absorbing water and drastically reduce interfacial adhesion. Simultaneously, due to its insufficient thermal stability, sucrose is prone to molecular chain hydrolysis and breakage under high temperature and humidity conditions, leading to microcracks within the adhesive layer and further exacerbating the degradation of bonding performance.

[0004] Existing technologies obtain oxidized sucrose through oxidative modification and utilize it to react with the amino components in soybean flour via a Schiff base reaction to improve the system's water resistance. However, the amino content in soybean flour is significantly low, resulting in an insufficient number of active sites that can participate in the Schiff base reaction. This leads to a large number of unreacted hydrophilic hydroxyl groups remaining in the adhesive system, ultimately causing the adhesive's boiling water bonding strength to fail to meet practical application requirements. Therefore, how to effectively improve the boiling water bonding strength of soybean flour-oxidized sucrose adhesives remains an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the prior art and provide a soybean flour-oxidized sucrose adhesive, its preparation method and application, to improve the bonding strength and water resistance.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a method for preparing a soybean flour-oxidized sucrose adhesive, comprising the following steps: Sucrose and water are mixed to obtain a sucrose aqueous solution; The sucrose aqueous solution is mixed with an oxidizing agent to carry out an oxidation reaction, thereby obtaining oxidized sucrose; The oxidized sucrose is mixed sequentially with soybean flour and polyethyleneimine solution to obtain soybean flour-oxidized sucrose adhesive.

[0007] In conjunction with the first aspect, further, the mass ratio of the oxidized sucrose, soybean flour and polyethyleneimine solution is 100:(5~20):(1~5).

[0008] Furthermore, the mass ratio of sucrose to water is (3-7):5; the mass ratio of the sucrose aqueous solution to the oxidant is 100:(3-8).

[0009] Furthermore, the method also includes first keeping the sucrose aqueous solution at a certain temperature, and then mixing it with an oxidizing agent to carry out an oxidation reaction.

[0010] Furthermore, the temperature range for heat preservation is 40℃~80℃; the oxidation reaction time is 20min~90min.

[0011] Furthermore, the oxidized sucrose is mixed sequentially with soybean flour and polyethylene glycol solution, and the reaction temperature is 40 ℃~80 ℃ for 20 min~150 min.

[0012] Furthermore, the oxidant is any one or more of ammonium persulfate, potassium permanganate, sodium periodate, and hydrogen peroxide; the concentration of the polyethyleneimine solution is 20% to 40%.

[0013] Furthermore, the polyethyleneimine has a hyperbranched structure, and the soybean flour is defatted soybean flour.

[0014] Secondly, this application provides a soybean flour-oxidized sucrose adhesive, prepared according to the preparation method of the soybean flour-oxidized sucrose adhesive described in any one of the first aspects.

[0015] Thirdly, this application provides an application of a soybean flour-oxidized sucrose adhesive, which is applied to solid wood boards, engineered wood panels, or particleboard. The soybean flour-oxidized sucrose adhesive is applied to the surface of the board and then hot-pressed at 100 ℃~200 ℃ for cross-linking, thereby bonding the wood.

[0016] Compared with the prior art, the beneficial effects achieved by this application are as follows: This application proposes a soybean flour-oxidized sucrose adhesive and its preparation method. The raw materials used in its preparation are widely available and belong to renewable biomass materials, which saves costs and is environmentally friendly. Furthermore, no formaldehyde is used in the reaction, and water is used as the reaction solvent, which reduces the emission of volatile organic compounds and is in line with the concept of green development.

[0017] This application describes an oxidation process for sucrose molecules, which breaks down the vicinal diol structure to generate oxidized sucrose products rich in aldehyde groups. Soybean flour, containing a large number of primary amine groups, is then added to the reaction system to undergo a Schiff base reaction with the aldehyde groups of the oxidized sucrose. The aldehyde groups and primary amine groups can rapidly undergo a Schiff base reaction (-N=CH-), significantly improving the cross-linking efficiency.

[0018] The adhesive system of this application includes oxidized sucrose, soybean flour, and polyethyleneimine. The aldehyde groups in oxidized sucrose first react with the amino groups of soybean flour protein to form crosslinks. Then, the abundant amino groups of polyethyleneimine further crosslink with the remaining aldehyde groups or the already formed Schiff base groups in the oxidized sucrose system to form a denser and more stable crosslinked network, thereby improving the stability of the soybean flour-oxidized sucrose adhesive.

[0019] The preparation method of this application optimizes the reaction path by first adding soybean flour and oxidized sucrose to react, and then adding polyethyleneimine in a specific order. This ensures that soybean flour protein and oxidized sucrose form a stable primary network, and avoids polyethyleneimine from prematurely "occupying" too many aldehyde groups, which would lead to uneven dispersion of soybean flour or insufficient reaction. This helps to form a more uniform and effective synergistic cross-linked structure.

[0020] This application provides a soybean flour-oxidized sucrose adhesive, its preparation method, and its application. Hyperbranched polyethyleneimine is introduced as a multifunctional copolymer crosslinking agent. The high-density amine groups in the polyethyleneimine molecule react with the aldehyde groups of oxidized sucrose through a Schiff base reaction, which effectively compensates for the lack of active sites in soybean flour. The resulting soybean flour-oxidized sucrose adhesive not only improves the bonding strength but also enhances the water resistance. Attached Figure Description

[0021] Figure 1 The bonding strength of soybean flour-oxidized sucrose adhesives with different polyethyleneimine addition amounts provided in the embodiments of this application; Figure 2 Residual rates of soybean flour-oxidized sucrose adhesives with different polyethyleneimine addition amounts provided in the embodiments of this application; Figure 3 The moisture absorption rate of soybean flour-oxidized sucrose adhesives with different polyethyleneimine addition amounts provided in the embodiments of this application; Figure 4 This application provides physical images of soybean flour-oxidized sucrose adhesives with different amounts of polyethyleneimine added after curing, before immersion, for the purposes of this application embodiment; Figure 5 The following are actual images of soybean flour-oxidized sucrose adhesives with different amounts of polyethyleneimine added after being soaked in the cured form, for the purposes of this application embodiment. Detailed Implementation

[0022] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and should not be used to limit the scope of protection of the present application.

[0023] This application provides a method for preparing a soybean flour-oxidized sucrose adhesive to improve the adhesive strength and water resistance of the adhesive. The preparation method includes the following steps: (1) Mix sucrose and water in a mass ratio of (3-7):5 to obtain a sucrose aqueous solution; (2) Mix the sucrose aqueous solution and the oxidant in a mass ratio of 100:(3~8) and carry out the oxidation reaction to obtain oxidized sucrose; (3) Oxidized sucrose is mixed with soybean flour and polyethyleneimine solution in sequence to obtain soybean flour-oxidized sucrose resin adhesive, wherein the mass ratio of oxidized sucrose, soybean flour and polyethyleneimine is 100: (5~20): (1~5).

[0024] Since pure polyethyleneimine has too high a viscosity, it is not conducive to its addition to soybean flour-oxidized sucrose adhesive. Therefore, in this application, a polyethyleneimine solution with a mass concentration of 20% to 40% is selected, preferably a 30% polyethyleneimine aqueous solution, wherein the polyethyleneimine has a hyperbranched structure.

[0025] Furthermore, the preferred mass ratio of sucrose to water is (80~120):100. Controlling the amount of sucrose and water within the above range is beneficial for the full dissolution of sucrose.

[0026] The preferred mass ratio of sucrose aqueous solution to oxidant is 100:(9~13), which is conducive to complete oxidation.

[0027] The preferred mass ratio of oxidized sucrose, soybean flour and polyethyleneimine is 100:(5~20):(1~5).

[0028] In this application, the specific processes of steps (1) and (2) are as follows: First, add sucrose to water and dissolve it completely. Then, keep it at a temperature of 40℃ to 80℃, preferably 55℃ to 65℃, for a period of time. Controlling the temperature and time within this range helps to ensure that the sucrose is fully oxidized in the water.

[0029] Add a peroxidant to the insulated sucrose aqueous solution to carry out an oxidation reaction, wherein the oxidation time is 20-90 min, preferably 40-50 min.

[0030] In this application, the specific process of step (3) is as follows: First, soybean flour and oxidized sucrose are mixed. Then, a polyethyleneimine solution is added to the soybean flour-oxidized sucrose adhesive for reaction. The reaction temperature is 40℃~80℃, and the reaction time is 20~150 min, resulting in the soybean flour-oxidized sucrose adhesive. Controlling the temperature and time within the above range is beneficial for the composite modification of the soybean flour-oxidized sucrose adhesive by polyethyleneimine.

[0031] Furthermore, a polyethyleneimine solution is added to the soybean flour-oxidized sucrose adhesive for reaction, with the preferred reaction temperature being 55℃~65℃ and the preferred reaction time being 55min~65min.

[0032] The specific structural formula of polyethyleneimine in this application is as follows:

[0033] The following embodiments are only used to illustrate the technical solutions of this application more clearly, and should not be used to limit the scope of protection of this application.

[0034] Example 1:

[0035] Prepare a 50% sucrose solution by mixing 50 g of sucrose and 50 g of water, and add it to a reaction vessel. Add 11 g of ammonium persulfate to the reaction system and stir at 60 °C for 45 min. Finally, add 10 g of defatted soybean flour and stir until homogeneous. Then add 3.3 g of polyethyleneimine solution and stir for 30 min to obtain soybean flour-oxidized sucrose adhesive.

[0036] Example 2:

[0037] Prepare a 50% sucrose solution by mixing 50 g of sucrose and 50 g of water, and put it into a reaction vessel. Add 11 g of ammonium persulfate to the reaction system and stir at 60 °C for 45 min. Finally, add 10 g of defatted soybean flour, stir until homogeneous, and then add 8.3 g of polyethyleneimine solution and stir for 30 min to obtain soybean flour-oxidized sucrose adhesive.

[0038] Example 3:

[0039] Prepare a 50% sucrose solution by mixing 50 g of sucrose and 50 g of water, and put it into a reaction vessel. Add 11 g of ammonium persulfate to the reaction system and stir at 60 °C for 45 min. Finally, add 5 g of defatted soybean flour, stir until homogeneous, and then add 8.3 g of polyethyleneimine solution. Stir for 30 min to obtain soybean flour-oxidized sucrose adhesive.

[0040] Example 4:

[0041] Prepare a 50% sucrose solution by mixing 50 g of sucrose and 50 g of water, and put it into a reaction vessel. Add 11 g of ammonium persulfate to the reaction system and stir at 60 °C for 45 min. Finally, add 20 g of defatted soybean flour, stir until homogeneous, and then add 8.3 g of pure polyethyleneimine solution and stir for 30 min to obtain soybean flour-oxidized sucrose adhesive.

[0042] Example 5:

[0043] Prepare a 50% sucrose solution by mixing 50 g of sucrose and 50 g of water, and add it to a reaction vessel. Add 11 g of ammonium persulfate to the reaction system and stir at 60 °C for 45 min. Finally, add 10 g of defatted soybean flour, stir until homogeneous, and then add 16.6 g of pure polyethyleneimine solution. Stir for 30 min to obtain soybean flour-oxidized sucrose adhesive.

[0044] Comparative example: Prepare a 50% sucrose solution by mixing 50 g of sucrose and 50 g of water, and add it to a reaction vessel. Add 11 g of ammonium persulfate to the reaction system and stir at 60 °C for 45 min. Finally, add 10 g of defatted soybean flour and stir for 30 min to obtain soybean flour-oxidized sucrose adhesive.

[0045] The preparation of three-layer poplar plywood was completed in the laboratory, with a double-sided glue application rate of 300g / m² for each veneer. 2 After the adhesive is applied, the veneer blanks are assembled and left to rest in a closed environment for 8 minutes before hot pressing. The specific hot pressing process is as follows: hot pressing temperature 160 ℃; hot pressing pressure 1.0 MPa; hot pressing time 6 minutes.

[0046] The dry shear strength and boiling water shear strength of the plywood prepared with soybean flour-oxidized sucrose adhesives in the comparative example and Examples 1 to 5 were tested according to the test methods in GB / T 9846-2015, as shown in Table 1.

[0047] Table 1: Example Dry shear strength (MPa) Boiling water shear strength (MPa) Comparative Example 1.03±0.09 0.55±0.15 Example 1 0.99±0.11 0.69±0.09 Example 2 1.14±0.07 0.82±0.04 Example 3 1.07±0.06 0.77±0.09 Example 4 1.27±0.09 1.03±0.04 Example 5 1.06±0.07 0.80±0.08 As shown in Table 1, the adhesive obtained using the technical solution provided in this application has a boiling water shear strength ≥0.7 MPa that is 49.1% higher than that obtained by directly using soybean flour-oxidized sucrose adhesive, and meets the Chinese national standard GB / T 9846-2015 Class II plywood standard.

[0048] Figure 1 This study compares the bonding strength of soybean flour-oxidized sucrose adhesives with different amounts of polyethyleneimine, testing both dry shear strength and boiling water shear strength at 93±3℃. Figure 1 It is evident that without the addition of polyethyleneimine, the boiling water shear strength of the soybean flour-oxidized sucrose adhesive did not meet the standard. After adding polyethyleneimine, the boiling water resistance strength was ≥0.7 MPa, meeting the Chinese national standard GB / T 9846-2015 Class II plywood standard.

[0049] This application involves oxidizing sucrose molecules to break the vicinal diol structure, generating oxidized sucrose products rich in aldehyde groups. Soybean flour, containing numerous primary amine groups, is then added to the reaction system to undergo a Schiff base reaction with the aldehyde groups of the oxidized sucrose. The aldehyde groups and the primary amine groups in the soybean flour can rapidly undergo a Schiff base reaction (-N=CH-), with a reaction rate far exceeding that of the condensation reaction between hydroxyl and amino groups, significantly improving cross-linking efficiency.

[0050] The adhesive system of this application includes oxidized sucrose, soybean flour, and polyethyleneimine. The aldehyde groups in the oxidized sucrose first react with the amino groups of the soybean flour protein to form crosslinks. Then, the amino groups in the polyethyleneimine further crosslink with the remaining aldehyde groups of the oxidized sucrose or the already formed Schiff base groups, resulting in a soybean flour-oxidized sucrose adhesive with boiling water resistance. This application utilizes the multifunctionality of the aldehyde groups to allow reaction with multiple amino groups, forming a three-dimensional network; and the crosslinked network formed by the covalent bonds of the Schiff base bonds is denser and more stable, effectively improving the bonding strength of the soybean flour-oxidized sucrose adhesive.

[0051] Figure 2 These are the results of residue tests on soybean flour-oxidized sucrose adhesives with different amounts of polyethyleneimine. After adding polyethyleneimine, the residue rates of the cured samples and those after soaking in warm water were improved.

[0052] Figure 3 This study tested the moisture absorption rate of soybean flour-oxidized sucrose adhesives with different amounts of polyethyleneimine. The cured samples were subjected to moisture absorption in a constant temperature and humidity chamber for 10 hours, repeated three times. The results showed that the water resistance of the soybean flour-oxidized sucrose adhesive was improved after the addition of polyethyleneimine.

[0053] Figure 4 and Figure 5 The images show soybean flour-oxidized sucrose adhesives with different amounts of polyethyleneimine added after being cured in a 160℃ oven, before and after soaking in warm water. Figure 4 and Figure 5 From left to right: Comparative Example, Example 2, Example 3, Example 4, and Example 5. This application uses 63°C warm water for soaking, for comparison... Figure 4 and Figure 5 It can be seen that after soaking for three hours, the sample without added polyethyleneimine precipitated out some substances and the solution turned yellow, while the sample with added polyethyleneimine remained stable after curing and the solution remained transparent.

[0054] This application also provides an application of a soybean flour-oxidized sucrose adhesive for bonding solid wood boards, engineered wood panels, or particleboard. Specifically, the soybean flour-oxidized sucrose adhesive is applied to the surface of the board and then hot-pressed at 100 ℃~200 ℃ for cross-linking, thereby bonding the board and expanding its application range.

[0055] This application compensates for the lack of active sites in soybean flour by utilizing the efficient Schiff base reaction between the high-density amino groups (-NH2 / -NH-) in polyethyleneimine molecules and the aldehyde groups in oxidized sucrose. This ultimately improves the bonding strength of the soybean flour-oxidized sucrose adhesive. Compared to adhesives crosslinked with oxidized sucrose resin using soybean flour, both bonding strength and water resistance are improved.

[0056] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a soybean flour-oxidized sucrose adhesive, characterized in that, Includes the following steps: Sucrose and water are mixed to obtain a sucrose aqueous solution; The sucrose aqueous solution is mixed with an oxidizing agent to carry out an oxidation reaction, thereby obtaining oxidized sucrose; The oxidized sucrose is mixed sequentially with soybean flour and polyethyleneimine solution to obtain soybean flour-oxidized sucrose adhesive.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the oxidized sucrose, soybean flour and polyethyleneimine solution is 100:(5~20):(1~5).

3. The preparation method according to claim 1, characterized in that, The mass ratio of sucrose to water is (3-7):5; the mass ratio of the sucrose aqueous solution to the oxidant is 100:(3-8).

4. The preparation method according to claim 1, characterized in that, The method also includes first keeping the sucrose aqueous solution at a certain temperature, and then mixing it with an oxidant to carry out an oxidation reaction.

5. The preparation method according to claim 4, characterized in that, The temperature range for heat preservation is 40℃~80℃; the oxidation reaction time is 20min~90min.

6. The preparation method according to claim 1, characterized in that, The oxidized sucrose is mixed sequentially with soybean flour and polyethylene glycol solution, and the reaction temperature is 40 ℃~80 ℃ for 20 min~150 min.

7. The preparation method according to claim 1, characterized in that, The oxidant is any one or more of ammonium persulfate, potassium permanganate, sodium periodate, and hydrogen peroxide; the concentration of the polyethyleneimine solution is 20% to 40%.

8. The preparation method according to claim 1, characterized in that, The polyethyleneimine has a hyperbranched structure, and the soybean flour is defatted soybean flour.

9. A soybean flour-oxidized sucrose adhesive, characterized in that, The soybean flour-oxidized sucrose adhesive is prepared according to any one of claims 1-8.

10. The application of the soybean flour-oxidized sucrose adhesive according to claim 9, characterized in that, It is applied to solid wood boards, engineered wood panels, or particleboard. Soybean flour-oxidized sucrose adhesive is applied to the surface of the board and cross-linked by hot pressing at 100 ℃~200 ℃, which serves to bond the wood.

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