High-water-resistance glyoxal-group copolymer resin for wood bonding and preparation method of high-water-resistance glyoxal-group copolymer resin

Abstract

The invention provides high-water-resistance glyoxal copolymer resin for wood bonding and a preparation method of the high-water-resistance glyoxal copolymer resin, and belongs to the technical field of chemical synthetic resin. The high-water-resistance glyoxal group copolymer resin for wood bonding is prepared through copolycondensation reaction of chitosan, urea, glyoxal and glycerol, the water resistance of the prepared resin is remarkably improved and far exceeds the use requirement of class II plywood in the national standard, the preparation process is simple, the high-water-resistance glyoxal group copolymer resin can be smoothly butted with existing industrial glue preparation equipment, and the production cost is reduced. And a good foundation is laid for industrial popularization. In addition, harmful substances such as organic solvents, phenols and formaldehyde are not used in the preparation process, and the method has the prominent characteristics of greenness, environmental protection and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthetic resins, and in particular relates to a highly water-resistant glyoxal-based copolymer resin for wood gluing and a preparation method thereof. Background Art

[0002] Chemically synthesized resins are the primary source of adhesives for wood bonding and wood-based panels. Formaldehyde-based synthetic adhesives, in particular, include urea-formaldehyde (UF), melamine-formaldehyde (MF), phenol-formaldehyde (PF), and their various modified resins. With their excellent performance and mature, stable production processes, they have played a significant role in driving the development of the wood industry. Despite this, persistent formaldehyde emissions have significantly hindered the application of these adhesives. This has been particularly evident over the past decade, as growing environmental awareness has driven increased market demand for green and environmentally friendly products. Therefore, the development of formaldehyde-free wood adhesives is urgently needed.

[0003] Numerous studies have shown that replacing formaldehyde with low-toxicity, low-volatility glyoxal in the synthesis of wood adhesives is one effective way to address these issues. While theoretically glyoxal has a dialdehyde group and is more reactive than formaldehyde, in reality, resins synthesized using glyoxal instead of formaldehyde suffer from poor bonding strength and water resistance. Numerous studies have shown that when glyoxal is used to replace formaldehyde in existing process routes, its functionality is not fully utilized, resulting in insufficient cross-linking of the synthetic resin. After curing, the resin struggles to form a dense cross-linked system, lacks moisture resistance, and easily dissolves in water, losing its bonding ability.

[0004] Based on this, it is very necessary to provide a glyoxal-based high water-resistant resin with a simple production process, excellent comprehensive performance and controllable cost. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a highly water-resistant glyoxal-based copolymer resin for wood bonding and a preparation method thereof.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A method for preparing a highly water-resistant glyoxal-based copolymer resin for wood bonding is obtained by co-polycondensation of chitosan (CS), urea (U), glyoxal (G) and glycerol (Gly), comprising the following steps:

[0009] At room temperature, urea is added to a chitosan-acetic acid-water mixture and stirred to obtain a chitosan-urea copolymer product (denoted as CSU);

[0010] The chitosan-urea copolymer product is mixed with a glyoxal aqueous solution, the pH value is adjusted to be weakly alkaline, and the mixture is heated and kept warm to react to obtain a chitosan-urea-glyoxal copolymer product (denoted as CSUG);

[0011] The chitosan-urea-glyoxal copolymer product is mixed and stirred with glycerol at room temperature to obtain the highly water-resistant glyoxal-based copolymer resin for wood bonding (denoted as CSUG-Gly).

[0012] Furthermore, the mass fraction of chitosan in the chitosan-acetic acid-water mixture is 3-4%.

[0013] Furthermore, the molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture is 1:(5-6).

[0014] Furthermore, the urea is in the form of analytically pure solid crystals, and the average molecular weight of chitosan is 10,000 to 15,000.

[0015] Furthermore, the mass concentration of the glyoxal aqueous solution is 40%.

[0016] Furthermore, the molar ratio of glyoxal to urea in the glyoxal aqueous solution is 1.25:1.

[0017] Furthermore, an alkaline solution is used to adjust the pH value to 7.5-8.5; the alkaline solution is selected from sodium hydroxide aqueous solution and / or potassium hydroxide aqueous solution.

[0018] Furthermore, the heating and insulation reaction is carried out in two stages, the first heating and insulation temperature is 80° C. and the time is 1 hour, and the second heating and insulation temperature is 90° C. and the time is 2 hours.

[0019] Furthermore, the molar ratio of the urea to the glycerol is 1:(0.1-0.2).

[0020] The second technical solution of the present invention:

[0021] A highly water-resistant glyoxal-based copolymer resin for wood gluing is prepared according to the preparation method.

[0022] The third technical solution of the present invention:

[0023] Application of the highly water-resistant glyoxal-based copolymer resin in wood bonding.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] (1) The present invention provides a highly water-resistant glyoxal-based copolymer resin, which is a water-based thermosetting resin. Through the synergistic effect of chitosan, urea, glyoxal and propylene glycol, the water resistance of the synthesized glyoxal-based resin is significantly improved, far exceeding the use requirements of Class II plywood in the national standard.

[0026] (2) The present invention also provides a method for preparing the above-mentioned resin. This method has a simple preparation process and can be smoothly integrated with existing industrial glue-making equipment, laying a good foundation for industrial promotion. In addition, the preparation process does not use harmful substances such as organic solvents, phenols, and formaldehyde, and has outstanding characteristics such as being green and environmentally friendly.

[0027] (3) The resin synthesized in the present invention is a weakly acidic system. No additional curing agent or organic additive is required in actual use. Cross-linking and curing can occur only under reasonable hot pressing process conditions to generate bonding strength. It is relatively convenient to use and is also conducive to controlling the cost of the resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 is the C1s deconvolution peak of CSU in Example 1;

[0030] Figure 2 is the O1s deconvolution peak of CSU in Example 1;

[0031] Figure 3 This is the C1s deconvolution peak diagram of CSUG in Example 1;

[0032] Figure 4 is the O1s deconvolution peak of CSUG in Example 1;

[0033] Figure 5 This is the C1s deconvolution peak diagram of CSUG-Gly in Example 1;

[0034] Figure 6 This is the O1s deconvolution peak diagram of CSUG-Gly in Example 1;

[0035] Figure 7 FT-IR test results of G, CSU and CSUG in Example 1;

[0036] Figure 8 FT-IR test results of Gly, CSUG, and CSUG-Gly in Example 1;

[0037] Figure 9is the structural formula of the final product CSUG-Gly in Example 1;

[0038] Figure 10 These are photos of products at different stages during the reaction of Example 1;

[0039] Figure 11 These are the bonding strength test results of the plywood prepared in Examples 1 to 3 and Comparative Examples 1, 2, 5, and 6. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0043] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0044] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0045] The present invention provides a method for preparing a highly water-resistant glyoxal-based copolymer resin for wood bonding, which is obtained by a co-condensation reaction of chitosan (CS), urea (U), glyoxal (G) and glycerol (Glycerol, abbreviated as Gly), comprising the following steps:

[0046] (1) At room temperature, urea is added to a chitosan-acetic acid-water mixture and stirred to obtain a chitosan-urea copolymer (denoted as CSU);

[0047] (2) mixing the chitosan-urea copolymer product with a glyoxal aqueous solution, adjusting the pH value to a weakly alkaline state, and heating and preserving the mixture to obtain a chitosan-urea-glyoxal copolymer product (denoted as CSUG);

[0048] (3) Chitosan-urea-glyoxal copolymerization products were mixed and stirred with glycerol at room temperature to obtain a highly water-resistant glyoxal-based copolymer resin for wood bonding (denoted as CSUG-Gly).

[0049] To fully leverage the advantages of glyoxal and significantly improve the water resistance of the resin, the present invention, based on extensive testing, proposes an integrated resin preparation method using chitosan (CS), glycerol (Gly), urea (U), and glyoxal (G) as the main raw materials. This preparation method can fully utilize the structural and functional group advantages of CS, greatly improving the bonding strength and water resistance of the resin. Because CS itself is relatively expensive, the present invention also achieves an effective balance between resin performance and cost. The following is the structural formula of CS:

[0050]

[0051] In the preparation method of the present invention, the reaction between CS and U begins. Since CS is protonated by acetic acid, chemical crosslinking occurs through ionic bonds. The addition of U further strengthens the bond between acetic acid and CS. In particular, the anionic acetic acid, hydrogen atoms, and nitrogen atoms of U form strong chemical bonds with oxygen atoms, amides, and hydroxyl groups in CS. Following this transformation, glyoxal (G) undergoes a Schiff base reaction with amino groups in the CSU solution, forming a crosslinked network structure, resulting in CSUG. The introduction of glycerol (Gly) further forms a dual crosslinking network system, both chemically and physically, ultimately yielding the target adhesive product, CSUG-Gly, which exhibits excellent water resistance and bonding strength.

[0052] In step (1) of the preferred embodiment of the present invention, the mass fraction of chitosan in the chitosan-acetic acid-water mixture is 3-4%, wherein the volume ratio of acetic acid to water in the chitosan-acetic acid-water mixture is 1:47.

[0053] In step (1) of the preferred embodiment of the present invention, the molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture is 1:(5-6). If the amount of chitosan added is too large, gelation will occur quickly in step (2), and a stable adhesive cannot be synthesized. If the amount of urea added is too large, the CSUG polymer product synthesized in step (1) will be unstable and subsequent reactions will be impossible.

[0054] In step (1) of the preferred embodiment of the present invention, the average molecular weight of chitosan is 10,000 to 15,000. The reason for introducing chitosan is that the cross-linking degree of urea-glyoxal resin (UG resin) is too low to form sufficient cohesion. If the mass fraction of chitosan is too low, the system cross-linking degree in the resin structure of the product is still insufficient, and it is difficult to form sufficient cohesion after curing, which does not meet the use requirements. If the mass fraction of chitosan is too high, the cost is too high and the polymerization process is difficult to control.

[0055] In step (1) of the preferred embodiment of the present invention, mixing and stirring are carried out at room temperature for 1 to 3 hours.

[0056] In step (2) of the preferred embodiment of the present invention, the mass concentration of the glyoxal aqueous solution is 40%.

[0057] In step (2) of a preferred embodiment of the present invention, the molar ratio of glyoxal to urea in the glyoxal aqueous solution is 1.25:1.

[0058] The molar ratio of G to U is 1.25:1, which is the optimal ratio based on a large number of experiments. If the molar ratio is reduced, it means that the amount of urea used increases, and there is also the problem of instability of the synthesized product, which is manifested in that precipitation is very likely to occur after cooling, and the effect of using the resin as an adhesive is even worse. If the molar ratio is increased, it means that the amount of urea used is reduced, but when mixed with glyoxal, gelation is very likely to occur, and the synthesis is difficult to continue.

[0059] In step (2) of the preferred embodiment of the present invention, an alkaline solution is used to adjust the pH value to 7.5-8.5; the alkaline solution is selected from a sodium hydroxide aqueous solution and / or a potassium hydroxide aqueous solution, and the mass concentration is 30%-40%.

[0060] In step (2) of the preferred embodiment of the present invention, the heating and insulation reaction is carried out in two stages, the first heating and insulation temperature is 80°C for 1 hour, and the second heating and insulation temperature is 90°C for 2 hours.

[0061] In step (3) of a preferred embodiment of the present invention, the molar ratio of urea to glycerol is 1:(0.1-0.2).

[0062] The embodiment of the present invention further provides a highly water-resistant glyoxal-based copolymer resin for wood bonding, which is prepared according to the above preparation method.

[0063] The highly water-resistant glyoxal-based copolymer resin for wood gluing prepared in the embodiment of the present invention can be used in wood gluing. The resin can be directly used as a wood adhesive. The prepared plywood has good dry strength and wet strength.

[0064] In the examples and comparative examples of the present invention, all the raw materials used were purchased commercially, wherein urea was in the form of analytically pure solid crystals, and chitosan was purchased from Yuanye Biotechnology Co., Ltd., with an average molecular weight of 10,000 to 15,000, a light yellow powder appearance, a deacetylation degree of 90%, a pH value of 4.5 to 6.5, and was stored at room temperature.

[0065] Unless otherwise specified, % in the embodiments of the present invention represents mass percentage.

[0066] The room temperature in the examples and comparative examples of the present invention refers to "25±3°C".

[0067] The technical solution of the present invention is further illustrated by the following examples.

[0068] Example 1

[0069] A method for preparing a highly water-resistant glyoxal-based copolymer resin for wood gluing comprises the following steps:

[0070] (1) Chitosan (CS) with a deacetylation degree of 90% was slowly added to an acetic acid aqueous solution (acetic acid to water ratio of 1:47) at room temperature to obtain a chitosan-acetic acid-water mixture with a mass fraction of 3%. The chitosan-acetic acid-water mixture was allowed to stand at room temperature for 2 hours, and then urea was added and stirred for 1 hour to adjust the molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture to 1:6, to obtain a light yellow transparent copolymer product, which was recorded as CSU.

[0071] (2) At room temperature, a 40% glyoxal solution (G) and the CSU obtained in step (1) were weighed to make the molar ratio of glyoxal to urea in the glyoxal aqueous solution be 1.25:1. The CSU and the glyoxal aqueous solution were added to a reaction vessel and mixed. The pH value was adjusted to 7.5-8.0 with a 40% sodium hydroxide aqueous solution. The reaction system was then heated to 80° C. in a water bath, stirred, and refluxed. After the reaction was kept warm for 1 hour, the pH value of the reaction system was again adjusted to 7.5-8.0, and the temperature was raised to 90° C. The reaction was continued to be kept warm for 2 hours under continuous stirring. The product was discharged and cooled to obtain a chitosan-urea-glyoxal copolymer product, which was recorded as CSUG.

[0072] (3) At room temperature, glycerol (Gly) was weighed and added to the product CSUG obtained in step (2) (the molar ratio of urea to glycerol was 1:0.1 at this time), and then added to a reaction vessel and stirred continuously for 10 minutes to obtain a highly water-resistant glyoxal-based copolymer resin for wood bonding, which was recorded as CSUG-Gly.

[0073] Example 2

[0074] A method for preparing a highly water-resistant glyoxal-based copolymer resin for wood gluing comprises the following steps:

[0075] (1) At room temperature, chitosan with a deacetylation degree of 90% was slowly added to an acetic acid aqueous solution (the ratio of acetic acid to water was 1:47) to obtain a chitosan-acetic acid-water mixture with a mass fraction of 3%. After the chitosan-acetic acid-water mixture was allowed to stand at room temperature for 2 hours, urea was added and the mixture was stirred for 1 hour to adjust the molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture to 1:6, thereby obtaining a light yellow transparent copolymer product, which was recorded as CSU.

[0076] (2) At room temperature, a 40% glyoxal solution and the CSU obtained in step (1) were weighed to make a molar ratio of glyoxal to urea in the glyoxal aqueous solution of 1.25:1. The CSU and the glyoxal aqueous solution were added to a reaction vessel and mixed. The pH value was adjusted to 7.5-8.0 with a 40% sodium hydroxide aqueous solution. The reaction system was then heated to 80° C. in a water bath, stirred, and refluxed. After the reaction was kept warm for 1 hour, the pH value of the reaction system was again adjusted to 7.5-8.0, and the temperature was raised to 90° C. The reaction was continued to be kept warm for 2 hours under continuous stirring. The product was discharged and cooled to obtain a chitosan-urea-glyoxal copolymer product, which was recorded as CSUG.

[0077] (3) At room temperature, glycerol was weighed and added to the product CSUG obtained in step (2) (the molar ratio of urea to glycerol was 1:0.15), and then added to a reaction vessel and stirred for 10 minutes to obtain a highly water-resistant glyoxal-based copolymer resin for wood bonding, which was designated as CSUG-Gly.

[0078] Example 3

[0079] A method for preparing a highly water-resistant glyoxal-based copolymer resin for wood gluing comprises the following steps:

[0080] (1) At room temperature, chitosan with a deacetylation degree of 90% was slowly added to an acetic acid aqueous solution (the ratio of acetic acid to water was 1:47) to obtain a chitosan-acetic acid-water mixture with a mass fraction of 3%. After the chitosan-acetic acid-water mixture was allowed to stand at room temperature for 2 hours, urea was added and the mixture was stirred for 1 hour to adjust the molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture to 1:5, thereby obtaining a light yellow transparent copolymer product, which was recorded as CSU.

[0081] (2) At room temperature, a 40% glyoxal solution and the CSU obtained in step (1) were weighed (the molar ratio of glyoxal to urea in the glyoxal aqueous solution was 1.25:1). The CSU and the glyoxal aqueous solution were added to a reaction vessel and mixed. The pH value was adjusted to 7.5-8.0 with a 40% sodium hydroxide aqueous solution. The reaction system was then heated to 80° C. in a water bath, stirred, and refluxed. After the reaction was kept warm for 1 hour, the pH value of the reaction system was again adjusted to 7.5-8.0, and the temperature was raised to 90° C. The reaction was continued with continuous stirring for 2 hours. The product was discharged and cooled to obtain a chitosan-urea-glyoxal copolymer product, which was recorded as CSUG.

[0082] (3) At room temperature, glycerol was weighed and added to the product CSUG obtained in step (2) (the molar ratio of urea to glycerol was 1:0.2), and then added to a reaction vessel and stirred for 10 minutes to obtain a highly water-resistant glyoxal-based copolymer resin for wood bonding, which was designated as CSUG-Gly.

[0083] Comparative Example 1

[0084] A method for preparing urea-glyoxal resin (UG resin) comprises the following steps:

[0085] A 40% mass concentration of glyoxal solution (G) and urea (U) are prepared according to a molar ratio of glyoxal to urea of ​​1.4:1 in the glyoxal aqueous solution. The entire glyoxal solution and 70% mass proportion of urea are added to a reaction vessel at room temperature. The pH value of the system is adjusted to 7.5-8.0 with a 40% sodium hydroxide aqueous solution. The temperature is raised to 90° C. in a water bath, and the remaining 30% of urea is added. The reaction is kept warm for 2 hours, discharged, and cooled to obtain the target product, i.e., UG resin.

[0086] Comparative Example 2

[0087] A method for preparing chitosan-urea-glyoxal copolymer resin (CSUG resin) comprises the following steps:

[0088] (1) At room temperature, chitosan with a deacetylation degree of 90% was slowly added to an acetic acid aqueous solution (the ratio of acetic acid to water was 1:47) to obtain a chitosan-acetic acid-water mixture with a mass fraction of 3%. After the chitosan-acetic acid-water mixture was allowed to stand at room temperature for 2 hours, urea was added and the mixture was stirred for 1 hour to adjust the molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture to 1:6, thereby obtaining a light yellow transparent copolymer product, which was recorded as CSU.

[0089] (2) At room temperature, a 40% glyoxal solution and the CSU obtained in step (1) were weighed (the molar ratio of glyoxal to urea in the glyoxal aqueous solution was 1:1). The CSU and the glyoxal aqueous solution were added to a reaction vessel and mixed. The pH value was adjusted to 7.5-8.0 with a 40% sodium hydroxide aqueous solution. The reaction system was then heated to 80° C. in a water bath, stirred, and refluxed. After the reaction was kept warm for 1 hour, the pH value of the reaction system was again adjusted to 7.5-8.0, and the temperature was raised to 90° C. The reaction was continued to be kept warm for 2 hours under continuous stirring. The product was discharged and cooled to obtain a chitosan-urea-glyoxal copolymer product, which was recorded as CSUG resin.

[0090] Comparative Example 3

[0091] The method is the same as Example 1, except that in step (2), a glyoxal solution (G) with a mass concentration of 40% and the CSU obtained in step (1) are weighed, and the molar ratio of glyoxal to urea in the glyoxal aqueous solution is 0.75:1.

[0092] In this comparative example, since the amount of glyoxal (G) added was too small, the reaction could not proceed sufficiently and a stable adhesive could not be synthesized.

[0093] Comparative Example 4

[0094] The same as Example 1, except that in step (2), a glyoxal solution (G) with a mass concentration of 40% and the CSU obtained in step (1) are weighed, and the molar ratio of glyoxal to urea in the glyoxal aqueous solution is 1.75:1.

[0095] In this comparative example, since the amount of glyoxal (G) added was too large, the CSUG polymer product synthesized in step (2) was unstable and demixed and precipitated within 1 day, making subsequent reactions impossible.

[0096] Comparative Example 5

[0097] The same as Example 1, except that, in step (3), glycerol (Gly) is weighed and added to the product CSUG obtained in step (2), and the molar ratio of urea to glycerol is 1:0.05.

[0098] Comparative Example 6

[0099] The same as Example 1, except that in step (3), glycerol (Gly) is weighed and added to the product CSUG obtained in step (2), and the molar ratio of urea to glycerol is 1:0.25.

[0100] Comparative Example 7

[0101] The same as Example 1, except that in step (1), the chitosan-acetic acid-water mixture was allowed to stand at room temperature for 2 hours, and then urea was added and stirred for 1 hour to make the molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture 1:4, to obtain a light yellow transparent copolymer product, recorded as CSU.

[0102] In this comparative example, since the amount of chitosan added was too large, the synthesized CSUG polymer product was too viscous and not conducive to coating the board.

[0103] Comparative Example 8

[0104] The same as Example 1, except that in step (1), the chitosan-acetic acid-water mixture was allowed to stand at room temperature for 2 hours, and then urea was added and stirred for 1 hour to make the molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture 1:8, to obtain a light yellow transparent copolymer product, recorded as CSU.

[0105] In this comparative example, since the amount of chitosan added was too small, the reaction could not proceed fully and a stable adhesive could not be synthesized.

[0106] Comparative Examples 3 and 4 demonstrate that the molar ratio of U to G cannot be set arbitrarily; a molar ratio that is too high or too low will not yield a stable adhesive. Comparative Examples 5 and 6 also demonstrate that if the amount of glycerol used is outside the scope of the present invention, a stable adhesive with excellent performance cannot be obtained. Comparative Examples 7 and 8 also demonstrate that if the amount of chitosan used is outside the scope of the present invention, an adhesive suitable for application cannot be obtained.

[0107] Performance Testing

[0108] The XPS characteristics of the products at different stages during the reaction of Example 1 are as follows: Figures 1 to 6 As shown. Figure 1 is the C1s deconvolution peak of CSU; Figure 2 is the O1s deconvolution peak of CSU; Figure 3 is the C1s deconvolution peak of CSUG; Figure 4 is the O1s deconvolution peak of CSUG; Figure 5 is the C1s deconvolution peak of CSUG-Gly; Figure 6 This is the O1s deconvolution peak of CSUG-Gly.

[0109] The FT-IR test results of G, CSU and CSUG in Example 1 are shown in Figure 7 , FT-IR test results of Gly, CSUG, and CSUG-Gly are shown in Figure 8 .

[0110] from Figures 1 to 6The changes in the content of functional groups in the CSU polymer, glyoxal (G) successfully produced a cross-linking reaction with the CSU polymer, and the hydroxyl and amino groups reacted with each other. After the co-condensation reaction with glycerol, the Figure 7 The mid-infrared spectrum shows that a unique product distribution characteristic has been formed. The structural formula of the final product is shown in Figure 9 .

[0111] according to Figures 7 and 8 From the changes in the spectral lines corresponding to different systems in the figure, it can be seen that an effective cross-linking reaction is formed between CSU, glyoxal (G), CSUG, and propylene glycol (Gly). In addition to retaining some functional groups of the above substances, some new characteristic absorption peaks appear in the CSUG-Gly system, indicating that polymerization products with different connection modes are formed, which means that the reaction raw materials are cross-linked with each other to form a new target system.

[0112] The photos of the products at different stages during the reaction of Example 1 are shown in Figure 10 , wherein the CSU sample is CSU, the CSUG sample is CSUG, and the target adhesive is CSUG-Gly prepared in Example 1.

[0113] Three-layer plywood preparation process parameters:

[0114] Veneer material: fast-growing poplar, thickness 1.5mm, moisture content 8% to 9%;

[0115] Glue application amount: 190 / m 2 (single-sided), the glue used was the product prepared in Example and Comparative Example respectively;

[0116] Hot pressing process parameters: hot pressing temperature 160℃, hot pressing time 5min, theoretical pressure 1.5MPa.

[0117] The three-layer plywood prepared was tested for dry and wet bonding strength according to the relevant methods in the latest GB / T9846-2015 standard. The wet strength test specimen treatment method is: soak the prepared sample in cold water at room temperature for 24 hours; soak the prepared sample in hot water at 63°C for 3 hours, take it out and wipe off the moisture on the surface of the specimen for testing. The test results are shown in Table 1, and the bonding strength test results of the plywood prepared in Examples 1 to 3 and Comparative Examples 1, 2 and Comparative Examples 5 and 6 are shown in Table 1. Figure 11 .

[0118] Table 1 Plywood bonding strength test results

[0119]

[0120]

[0121] From Table 1, Figure 11 It can be seen that compared with UG resin, the plywood prepared from the CSUG-Gly resin synthesized in the examples of the present invention shows significant changes and improvements in dry bond strength, cold water wet bond strength, and hot water wet bond strength. Although the water resistance of the resin varies somewhat under different ratios, it is higher than the 0.7 MPa requirement for Class II plywood in the national standard. Compared with the CSUG resin synthesized without the introduction of glycerol in Comparative Example 2, it also has a significant advantage in water resistance. Although the functional groups contained in the examples and CSUG resins are basically the same, the changes in the components and distribution of the resin system structure will lead to different effects. The process conditions and implementation steps of the present invention have more obvious effects and outstanding advantages.

[0122] In the three examples, the varying Gly to U ratios resulted in varying amounts of Gly added to the three systems, resulting in varying water resistance strengths. This approach can meet the practical needs of different applications. Adjusting the amount of Gly incorporated to meet varying levels of water resistance requirements facilitates cost control and performance matching.

[0123] The plywood prepared in Comparative Examples 7 and 8 did not meet the requirements, so it was more appropriate to control the molar ratio of CS to U at 1: (5-6).

[0124] The mechanical properties of the plywood in Comparative Examples 5 and 6 are poor. The hot water-resistant wet bonding strength of the plywood prepared in Comparative Examples 5 and 6 is about 0.5 MPa, and the dry bonding strength of the plywood decreases sharply. In addition, the increased amount of propylene glycol in Comparative Example 6 also increases the cost of the adhesive.

[0125] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a highly water-resistant glyoxal-based copolymer resin for wood gluing, characterized in that: It is obtained by the co-condensation reaction of chitosan, urea, glyoxal and glycerol.

2. The method for preparing the highly water-resistant glyoxal-based copolymer resin for wood bonding according to claim 1, wherein: The following steps are involved: At room temperature, urea is added to a chitosan-acetic acid-water mixture and stirred to obtain a chitosan-urea copolymer product; Mixing the chitosan-urea copolymer product with a glyoxal aqueous solution, adjusting the pH value to be weakly alkaline, and heating and keeping the mixture warm to obtain a chitosan-urea-glyoxal copolymer product; The chitosan-urea-glyoxal copolymer product is mixed and stirred with glycerol at room temperature to obtain the highly water-resistant glyoxal-based copolymer resin for wood bonding.

3. The method for preparing the highly water-resistant glyoxal-based copolymer resin for wood bonding according to claim 2, wherein: The molar ratio of chitosan to urea in the chitosan-acetic acid-water mixture is 1:(5-6).

4. The method for preparing the highly water-resistant glyoxal-based copolymer resin for wood bonding according to claim 2, wherein: The mass concentration of the glyoxal aqueous solution is 40%.

5. The method for preparing the highly water-resistant glyoxal-based copolymer resin for wood bonding according to claim 2, wherein: The molar ratio of glyoxal to urea in the glyoxal aqueous solution is 1.25:

1.

6. The method for preparing the highly water-resistant glyoxal-based copolymer resin for wood gluing according to claim 2, wherein: Use alkaline solution to adjust the pH to 7.5-8.5; The alkaline solution is selected from sodium hydroxide aqueous solution and / or potassium hydroxide aqueous solution.

7. The method for preparing the highly water-resistant glyoxal-based copolymer resin for wood gluing according to claim 2, wherein: The heating and insulation reaction is carried out in two stages. The first heating and insulation is carried out at a temperature of 80° C. for 1 hour, and the second heating and insulation is carried out at a temperature of 90° C. for 2 hours.

8. The method for preparing the highly water-resistant glyoxal-based copolymer resin for wood gluing according to claim 2, wherein: The molar ratio of the urea to the glycerol is 1:(0.1-0.2).

9. A highly water-resistant glyoxal-based copolymer resin for wood bonding, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the highly water-resistant glyoxal-based copolymer resin according to claim 9 in wood gluing.

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