Weak acid-polyol-based adhesive, and preparation method and application thereof

Abstract

The present application relates to the technical field of adhesive, in particular to a weak acid-polyol-based adhesive as well as a preparation method and application thereof.The weak acid-polyol-based adhesive provided by the present application is a green, environmentally friendly and formaldehyde-free adhesive prepared by using specific weak acid and polyol as a matrix, using ferric chloride hexahydrate or tetrabutyl titanate as a catalyst, and using diphenyl methane diisocyanate or epoxy resin as a curing agent.The adhesive has simple and easily available raw materials and high solid content.The adhesive can be used for preparing plywood under the condition of 110-130 DEG C pressing plate, which can ensure the bonding strength of the pressing plate without affecting the brittleness of the plate.In addition, the adhesive can improve the hot pressing efficiency, improve the phenomenon of glue lump and still be used after being placed for more than one month, and has high bonding quality.Therefore, the adhesive can be used to prepare plywood with excellent comprehensive performance, which is beneficial to the preparation and application of high-quality plywood.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a weak acid-polyol-based adhesive, its preparation method, and its application. Background Technology

[0002] As a renewable natural resource, wood is increasingly widely used in the field of engineered wood products. Plywood, one of the three major types of engineered wood products, is a sheet material made by rotary cutting logs into veneers or slicing timber into thin sheets, and then gluing them together with adhesives. Plywood improves wood utilization, is a major way to conserve wood, and is a commonly used material in furniture making. It is also widely used in aircraft, ships, trains, automobiles, construction, and packaging. The widespread application of plywood in industry is inseparable from the use of wood adhesives, and the increasing demand for plywood has further promoted the development of wood adhesives.

[0003] Traditional petrochemical-based thermosetting resin adhesives remain the most widely used adhesives on the market due to their economic advantages and performance. However, the formaldehyde release from traditional petroleum-based adhesives has a significant impact on human health and the environment. Therefore, developing sustainable and environmentally friendly formaldehyde-free adhesives has become a key research focus in the engineered wood products industry.

[0004] Currently, technicians have developed a series of adhesives made from environmentally friendly materials. However, in the application of plywood manufacturing, conventional adhesives still have the following problems that need to be solved: 1) high curing temperature and long curing time; 2) high hot pressing temperature, low bonding strength of the pressed boards, and easy to affect the brittleness of the boards; 3) easy to clump together and difficult to store.

[0005] Therefore, developing a new type of environmentally friendly adhesive to comprehensively solve the above problems is crucial for promoting the rational application of plywood and improving wood performance. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the present invention aims to provide a weak acid-polyol-based adhesive. This adhesive is environmentally friendly and formaldehyde-free. When used in plywood, it can be hot-pressed at 110–130°C without affecting the brittleness of the board. It has a fast curing speed and high curing strength, resulting in plywood with excellent overall performance. At the same time, this adhesive can improve the problem of glue clumping and can still be used after being left for more than a month, making it suitable for use in the plywood industry.

[0007] Meanwhile, the present invention also aims to provide a method for preparing the above-mentioned weak acid-polyol-based adhesive.

[0008] Meanwhile, the present invention also aims to provide applications of the above-mentioned weak acid-polyol-based adhesives.

[0009] Meanwhile, the present invention also aims to provide a plywood.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A weak acid-polyol-based adhesive is mainly prepared from the following raw materials in parts by weight: 25-35 parts weak acid, 16-24 parts polyol, 3-5 parts catalyst, 10-15 parts curing agent, and 40-50 parts water.

[0012] Wherein, the weak acid is lactic acid or oxalic acid; the polyol is polyvinyl alcohol or polypropylene glycol; the catalyst is ferric chloride hexahydrate or tetrabutyl titanate; and the curing agent is diphenylmethane diisocyanate or epoxy resin.

[0013] The solid content and viscosity of the adhesive are within a reasonable range, ensuring that the adhesive can be hot-pressed at a temperature of 110–130°C without affecting the brittleness of the board. As a preferred embodiment of the present invention, the solid content of the weak acid-polyol-based adhesive is 50%–60%, and the viscosity is 20,000–40,000 mPa·s.

[0014] As a preferred embodiment of the present invention, the weak acid-polyol-based adhesive is mainly prepared from the following raw materials in parts by weight: 32.7 parts weak acid, 17.3 parts polyol, 5 parts catalyst, 10 parts curing agent, and 45 parts water; wherein, the weak acid is lactic acid; the polyol is polyvinyl alcohol; the catalyst is ferric chloride hexahydrate; and the curing agent is diphenylmethane diisocyanate.

[0015] Alternatively, the weak acid-polyol-based adhesive is mainly prepared from the following raw materials in parts by weight: 25.3 parts weak acid, 21.7 parts polyol, 3 parts catalyst, 12.5 parts curing agent, and 50 parts water; wherein the weak acid is oxalic acid; the polyol is polypropylene glycol; the catalyst is tetrabutyl titanate; and the curing agent is epoxy resin.

[0016] This invention does not impose any particular limitation on the type of water used in the adhesive raw materials; any type of water known to those skilled in the art for preparing adhesives may be used. As a preferred embodiment of this invention, the water is distilled water.

[0017] As a preferred embodiment of the present invention, the polyvinyl alcohol is polyvinyl alcohol 1799; the polypropylene glycol is polypropylene glycol 400; and the epoxy resin is epoxy resin T31.

[0018] The preparation method of the above-mentioned weak acid-polyol-based adhesive includes the following steps:

[0019] Step 1: Mix the weak acid, polyol and water, and stir at a low speed to react;

[0020] Step 2: Add the catalyst to the system after the low-speed stirring reaction in Step 1, and carry out the high-speed stirring reaction.

[0021] Step 3: Add curing agent to the system after high-speed stirring reaction in step 2, and stir until uniform to obtain the weak acid-polyol-based adhesive.

[0022] As a preferred embodiment of the present invention, the temperature of the low-speed stirring reaction is 80-90℃, the reaction time is 0.5-1h, and the stirring speed is 100-150r / min; the temperature of the high-speed stirring reaction is 90-110℃, the reaction time is 1-2h, and the stirring speed is 300-400r / min.

[0023] The above-mentioned weak acid-polyol-based adhesives are used as adhesives in the preparation of plywood.

[0024] A type of plywood is prepared by hot pressing a board material with the aforementioned weak acid-polyol-based adhesive; the board material includes a veneer and a core board.

[0025] As a preferred embodiment of the present invention, the method for preparing the plywood includes the following steps:

[0026] The weak acid-polyol-based adhesive is evenly applied to one side of two veneers. Then, the core board is placed on the glued side of one veneer, and the glued side of the other glued veneer is placed on the core board, keeping the wood grain direction perpendicular to each other, to complete the assembly. The assembled board is then hot-pressed to obtain the plywood.

[0027] As a preferred embodiment of the present invention, the double-sided application amount of the weak acid-polyol-based adhesive is 180-220 g / m². 2 The hot pressing temperature is 110–130℃, the pressure is 1–1.5 MPa, and the time is 8–12 min.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The weak acid-polyol-based adhesive provided by this invention uses weak acid and polyol as a matrix, ferric chloride hexahydrate or tetrabutyl titanate as a catalyst, and diphenylmethane diisocyanate or epoxy resin as a curing agent. This results in a green, environmentally friendly, formaldehyde-free adhesive suitable for the existing plywood industry, effectively avoiding formaldehyde release. Furthermore, the raw materials for this adhesive are simple and readily available, with a high solids content, allowing for pressing at 110–130°C without affecting the brittleness of the plywood, thus ensuring bonding strength. In addition, this adhesive improves hot-pressing efficiency, reduces glue clumping, and remains usable even after more than a month. Plywood made with this adhesive exhibits excellent overall performance and overcomes the drawbacks of conventional plywood adhesives, such as high curing temperatures and long curing times, improving bonding speed and quality. It has promising application prospects in the plywood field.

[0030] This invention provides a method for preparing a weak acid-polyol-based adhesive. The adhesive matrix is ​​constructed using a specific weak acid and polyol. During synthesis, tetrabutyl titanate or ferric chloride hexahydrate is used as a catalyst to catalyze the esterification reaction of the weak acid and polyol. Further, during curing, epoxy resin or diphenylmethane diisocyanate is used to improve the curing rate and strength, resulting in a novel weak acid-polyol-based green adhesive. This adhesive has a moderate viscosity and a solid content of 50%–60%. The prepared adhesive can be hot-pressed at relatively low temperatures (110–130°C) without affecting the brittleness of the substrate. Furthermore, the method uses readily available and simple raw materials, and the process is straightforward. No formaldehyde is generated during the reaction, making it environmentally friendly.

[0031] The plywood prepared using the above-mentioned adhesive of this invention has a formaldehyde emission level ≤0.4 mg / L, which meets the requirements for E0 grade plywood in the group standard T / CNFPIA 1001-2019 "Formaldehyde Emission Limits for Wood-based Panels". Furthermore, the bond strength is >0.7 MPa, meeting the requirements for Class II plywood in the national standard GB / T 9846-2015 "Ordinary Plywood". Therefore, the adhesive of this invention is very suitable for use in the plywood industry. Detailed Implementation

[0032] The technical solutions and effects of the present invention will be clearly and completely described below with reference to specific embodiments and test examples. However, those skilled in the art should understand that the embodiments are only used to illustrate the technical solutions of the present invention and should not be regarded as limiting the scope of protection of the present invention. Unless otherwise specified, the test methods used in the following embodiments are conventional methods; unless otherwise specified, the raw materials used are items commonly used in the art, publicly available, or commercially obtainable.

[0033] In this invention, there are no special limitations on the types of polyvinyl alcohol, polypropylene glycol, and epoxy resin, as long as the adhesive performance is guaranteed. Preferably, in the following examples, the polyvinyl alcohol is polyvinyl alcohol 1799; the polypropylene glycol is polypropylene glycol 400; and the epoxy resin is epoxy resin T31.

[0034] This invention does not impose any particular limitation on the type of water used in the adhesive raw materials; any type of water known to those skilled in the art for preparing adhesives may be used. Preferably, in the following embodiments, the water is distilled water.

[0035] Example 1

[0036] This embodiment provides a weak acid-polyol-based adhesive, mainly prepared from the following raw materials in parts by weight: 32.7 parts lactic acid, 17.3 parts polyvinyl alcohol, 5 parts ferric chloride hexahydrate, 10 parts diphenylmethane diisocyanate, and 45 parts water. The solid content of this weak acid-polyol-based adhesive is 55%, and its tested viscosity is 38344 mPa·s.

[0037] This embodiment also provides a method for preparing the above-mentioned weak acid-polyol-based adhesive, including the following steps:

[0038] Step 1: Mix lactic acid, polyvinyl alcohol and water, and react at 90°C with low-speed stirring (150 r / min) for 1 hour.

[0039] Step 2: Add ferric chloride hexahydrate to the system after the reaction in Step 1, and react at 100°C with high-speed stirring (400 r / min) for 1 hour;

[0040] Step 3: Add diphenylmethane diisocyanate to the system after the reaction in Step 2, and stir until homogeneous to obtain the weak acid-polyol-based adhesive of this embodiment.

[0041] This embodiment also provides the application of the above-mentioned weak acid-polyol-based adhesive in the preparation of plywood.

[0042] This embodiment also provides a plywood prepared by hot pressing the aforementioned weak acid-polyol-based adhesive with the board material; the board material includes veneers and core boards. The preparation method of the plywood includes the following steps: uniformly applying the weak acid-polyol-based adhesive to one side of two veneers, then placing the core board on the glued side of one veneer, and then placing the glued side of another glued veneer on the core board, keeping the wood grain directions perpendicular to each other to complete the assembly; then hot pressing the assembled board material using a hot press to obtain the plywood, which can be used after being left at room temperature. The double-sided adhesive application rate is 200 g / m². 2 The hot pressing temperature was 130℃, the pressure was 1.3MPa, and the time was 10min.

[0043] Example 2

[0044] This embodiment provides a weak acid-polyol-based adhesive, mainly prepared from the following raw materials in parts by weight: 25.3 parts oxalic acid, 21.7 parts polypropylene glycol, 3 parts tetrabutyl titanate, 12.5 parts epoxy resin, and 50 parts water. The solid content of this weak acid-polyol-based adhesive is 50%, and its tested viscosity is 23752 mPa·s.

[0045] This embodiment also provides a method for preparing the above-mentioned weak acid-polyol-based adhesive, including the following steps:

[0046] Step 1: Mix oxalic acid, polypropylene glycol and water, and react at 80°C with low-speed stirring (100 r / min) for 0.5 hours;

[0047] Step 2: Add tetrabutyl titanate to the system after the reaction in Step 1, and react at 95°C with high-speed stirring (300 r / min) for 1.5 hours;

[0048] Step 3: Add epoxy resin to the system after the reaction in Step 2, and stir until uniform to obtain the weak acid-polyol-based adhesive of this embodiment.

[0049] This embodiment also provides the application of the above-mentioned weak acid-polyol-based adhesive in the preparation of plywood.

[0050] This embodiment also provides a plywood prepared by hot pressing the aforementioned weak acid-polyol-based adhesive with the board material; the board material includes veneers and core boards. The preparation method of the plywood includes the following steps: uniformly applying the weak acid-polyol-based adhesive to one side of two veneers, then placing the core board on the glued side of one veneer, and then placing the glued side of another glued veneer on the core board, keeping the wood grain directions perpendicular to each other to complete the assembly; then hot pressing the assembled board material using a hot press to obtain the plywood, which can be used after being left at room temperature. The double-sided adhesive application rate is 220 g / m². 2 The hot pressing temperature was 110℃, the pressure was 1.4MPa, and the time was 12min.

[0051] Experimental Example 1: Catalyst Test

[0052] This experiment investigated the effects of different types and amounts of catalysts used to prepare adhesives on the mechanical properties (dry shear strength, dry wood breakage rate, wet shear strength, and wet wood breakage rate) of plywood after application. In each experimental group, the adhesive composition and preparation process were the same as in Example 1, except for the type or amount of catalyst. The process conditions for preparing plywood using the adhesive were also the same as in Example 1. After preparation, the performance of the plywood from each experimental group was tested. Table 1 shows the effect of different types of catalysts on plywood performance when the catalyst dosage is 5 parts. Table 2 shows the effect of different catalyst dosages on plywood performance when ferric chloride hexahydrate is used as the catalyst.

[0053] Table 1. Effect of catalyst type on plywood properties

[0054]

[0055] Table 2. Effect of catalyst dosage on plywood properties

[0056]

[0057] As shown in Tables 1 and 2, Example 1 of this invention utilizes ferric chloride hexahydrate as a catalyst, and when the addition amount is 5 parts, it catalyzes the esterification reaction of weak acid and polyol, achieving the best bonding strength (0.85 MPa) with a moderate wood breakage rate. This effectively prevents board breakage and does not significantly affect the brittleness of the board. Furthermore, further testing revealed that the bonding strength of the plywood obtained in Example 2 is 0.76 MPa, both meeting the requirements for Class II plywood in the national standard GB / T 9846-2015 "Ordinary Plywood".

[0058] Test Example 2: Hot Press Test

[0059] This experiment investigated the effects of different hot-pressing temperatures and times on the dry shear strength, dry wood breakage rate, wet shear strength, and wet wood breakage rate of plywood. During plywood preparation, except for changes in hot-pressing temperature and time, other raw material composition and process parameters were the same as in Example 1. The hot-pressing temperature and time settings and test results are shown in Table 3.

[0060] Table 3. Effects of hot-pressing temperature and time on plywood properties

[0061]

[0062] Table 3 shows that the shear strength of plywood increases with increasing hot-pressing temperature and time. At a hot-pressing temperature of 110℃, it already meets the requirements of the national standard GB / T 9846-2015 (≥0.7MPa). Furthermore, considering that excessively high temperatures can damage the wood structure, causing breakage, and that the wood is prone to carbonization during hot pressing, affecting its color and increasing its susceptibility to breakage, the final determined hot-pressing conditions are 110–130℃ for 10 minutes.

[0063] Test Example 3: Formaldehyde Release Test

[0064] This test example follows the desiccator method (4.61) in the national standard GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels" to determine the formaldehyde release of plywood in Examples 1 and 2. The test procedure is as follows: 300-500 mL of distilled water is placed at the bottom of a glass desiccator. A stainless steel wire sample holder is placed inside, and ten plywood specimens (150 mm long and 50 mm wide) are placed on the stainless steel wire support mesh. The formaldehyde released from the specimens is collected. A formaldehyde calibration solution and an acetylacetone-ammonium acetate solution are prepared. 25 mL of the formaldehyde solution is accurately pipetted into a 100 mL Erlenmeyer flask with a stopper, and 25 mL of the acetylacetone-ammonium acetate solution is measured. The flask is then stoppered and shaken well. The solution is then heated in a water bath at (65±2)℃ for 10 min, and then stored in a dark place at 20℃ for (60±5) min. The absorbance of the solution is measured at a wavelength of 412 nm using a spectrophotometer. The same method was used to determine the background mass concentration of formaldehyde. The concentration of the formaldehyde solution was then calculated using the formula.

[0065] The concentration of the formaldehyde solution is calculated according to formula (1), accurate to 0.01 mg / L:

[0066] c = f × (A) S - A b ) × 1800 / A (1)

[0067] Where, c represents the formaldehyde mass concentration, in milligrams per liter (mg / L); f is the slope of the standard curve, in milligrams per milliliter (mg / mL); A s A represents the absorbance of the formaldehyde solution. b A represents the absorbance of the blank solution; A is the surface area of ​​the specimen, in square centimeters (cm²). 2 The results are shown in Table 4.

[0068] Table 4. Formaldehyde Emission Rates of Plywood

[0069]

[0070] As shown in Table 4, the plywood prepared using the weak acid-polyol-based adhesive of the present invention has a formaldehyde emission of ≤0.4mg / L, which meets the requirements of the group standard T / CNFPIA 1001-2019 "Formaldehyde Emission Limits for Wood-based Panels" for E0 grade plywood.

[0071] Test Example 4: Storage Test

[0072] This experiment investigated the effect of different storage times of the adhesive on the performance of plywood. Specifically, the weak acid-polyol-based adhesive from Example 1 was stored for 7, 14, 21, 28, and 35 days. Then, following the plywood process in Example 1, three-layer plywood was prepared and its mechanical strength was tested. The results are shown in Table 5.

[0073] Table 5. Effect of adhesive storage days on plywood performance

[0074]

[0075]

[0076] Table 5 shows that the weak acid-polyol green adhesive, stored for more than one month, can still be used, and the plywood prepared from it meets the requirements of Class II plywood in the national standard GB / T 9846-2015 "Ordinary Plywood". This indicates that the adhesive of the present invention is not prone to clumping, has high bonding strength, and the plywood produced has excellent overall performance.

[0077] In summary, the weak acid-polyol-based adhesive provided by this invention is a green, environmentally friendly, formaldehyde-free adhesive prepared using weak acid and polyol as a matrix, suitable for the existing plywood industry, and can effectively avoid the problem of formaldehyde release. Furthermore, the raw materials for this adhesive are simple and readily available, with a high solids content, and it can be used for pressing at 110–130°C, ensuring the bonding strength of the pressed boards without affecting the brittleness of the boards. In addition, this adhesive improves hot pressing efficiency, reduces glue clumping, and remains usable even after being stored for more than a month. Plywood made with this adhesive exhibits excellent overall performance and overcomes the shortcomings of conventional plywood adhesives, such as high curing temperatures and long curing times, improving bonding speed and quality, and showing promising application prospects in the plywood field.

Claims

1. A weak acid-polyol-based adhesive, characterized in that, It is mainly prepared from the following raw materials in parts by weight: 25-35 parts weak acid, 16-24 parts polyol, 3-5 parts catalyst, 10-15 parts curing agent, and 40-50 parts water; Wherein, the weak acid is lactic acid; the polyol is polyvinyl alcohol; the catalyst is ferric chloride hexahydrate; and the curing agent is diphenylmethane diisocyanate.

2. The weak acid-polyol-based adhesive according to claim 1, characterized in that, The weak acid-polyol-based adhesive has a solid content of 50% to 60% and a viscosity of 20,000 to 40,000 mPa•s.

3. The weak acid-polyol-based adhesive according to claim 1, characterized in that, The weak acid-polyol-based adhesive is mainly prepared from the following raw materials in parts by weight: 32.7 parts weak acid, 17.3 parts polyol, 5 parts catalyst, 10 parts curing agent, and 45 parts water.

4. The weak acid-polyol-based adhesive according to claim 1 or 3, characterized in that, The polyvinyl alcohol is polyvinyl alcohol 1799.

5. A method for preparing a weak acid-polyol-based adhesive as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Mix the weak acid, polyol and water, and stir at a low speed to react; Step 2: Add the catalyst to the system after the low-speed stirring reaction in Step 1, and carry out a high-speed stirring reaction; Step 3: Add curing agent to the system after high-speed stirring reaction in step 2, and stir until uniform to obtain the weak acid-polyol-based adhesive.

6. The method for preparing the weak acid-polyol-based adhesive according to claim 5, characterized in that, The low-speed stirring reaction is carried out at a temperature of 80-90℃, a reaction time of 0.5-1h, and a stirring speed of 100-150r / min; the high-speed stirring reaction is carried out at a temperature of 90-110℃, a reaction time of 1-2h, and a stirring speed of 300-400r / min.

7. The application of a weak acid-polyol-based adhesive as described in any one of claims 1 to 4, characterized in that, Its application as an adhesive in the preparation of plywood.

8. A type of plywood, characterized in that, The material is prepared by hot pressing a weak acid-polyol-based adhesive as described in any one of claims 1 to 4 with a board material; the board material includes a veneer and a core board.

9. The plywood according to claim 8, characterized in that, The method for preparing the plywood includes the following steps: The weak acid-polyol-based adhesive is evenly applied to one side of two veneers. Then, the core board is placed on the glued side of one veneer, and the glued side of the other glued veneer is placed on the core board, keeping the wood grain direction perpendicular to each other, to complete the assembly. The assembled board is then hot-pressed to obtain the plywood.

10. The plywood according to claim 9, characterized in that, The double-sided sizing amount of the weak acid-polyol-based adhesive is 180-220 g / m 2 ; the temperature of the hot pressing is 110-130℃, the pressure is 1-1.5 MPa, and the time is 8-12 min.

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