Adhesive for plywood

Abstract

The invention belongs to the technical field of adhesives, and particularly relates to an adhesive for plywood. The adhesive for the plywood is prepared from the following components in percentage by mass: 55-65% of matrix resin, 3-7% of a reinforcing component, 0.3-0.5% of a curing system, 5-15% of a plasticizer and the balance of deionized water, totaling 100%, wherein the matrix resin is prepared from epoxidized soybean oil acrylate and a bio-based polyurethane prepolymer through a reaction; the bio-based polyurethane prepolymer is prepared from decarboxylated hydroxyalkylated cashew nut shell oil and isophorone diisocyanate through a reaction, and the hydroxyl value in the decarboxylated hydroxyalkylated cashew nut shell oil is 180 to 220 mg KOH / g. According to the adhesive for the plywood, through the synergistic effect of multiple components, the comprehensive performance of the plywood is remarkably improved, the requirements of environment-friendly plywood are met, and the adhesive has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and in particular relates to an adhesive for plywood. Background Art

[0002] Plywood is an important part of the wood-based panel industry. Formaldehyde-based synthetic resins are commonly used as adhesives in traditional plywood production, mainly urea-formaldehyde resins and their modified products, but the formaldehyde they release is the main source of formaldehyde pollution in indoor air pollution. Solving the formaldehyde release problem and producing environmentally friendly green plywood products are the key to the survival and development of the plywood industry.

[0003] In the prior art, there are disclosed formaldehyde-free plywood adhesives. For example, patent CN113831892B discloses an adhesive for formaldehyde-free plywood, a preparation method and plywood containing the same. The adhesive adopts polyvinyl alcohol modified by monocarboxyl-modified silicone oil, which reduces the regularity of the polyvinyl alcohol molecular chain and the number of carboxyl groups in the dosage form. At the same time, the incompatibility of the monocarboxyl-modified silicone oil segment with polyisocyanate and the steric hindrance effect are utilized to reduce the reaction activity of the modified polyvinyl alcohol with polyisocyanate at room temperature, thereby extending the drying time of the adhesive and increasing the service life of the adhesive.

[0004] It is undeniable that the adhesive disclosed in the patent can indeed achieve the above-mentioned effects, but it still has certain shortcomings: the hydroxyl group of polyvinyl alcohol (PVA) is reduced after being modified with monocarboxyl-modified silicone oil, and the chemical crosslinking density with polyisocyanate (PMDI) is insufficient; and it only relies on the reaction of -NCO of PMDI and -OH of PVA to generate linear urethane bonds, and the crosslinking point density is low, and an interpenetrating network cannot be formed. This will, to a certain extent, lead to limited wet bonding strength, that is, limited water resistance, and the adhesive layer may swell after being eroded by water, which will lead to a decrease in bonding strength. Summary of the invention

[0005] The purpose of the present invention is to provide an adhesive for plywood to solve the problems existing in the prior art in the background technology.

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

[0007] An adhesive for plywood, which is prepared by, by mass percentage, 55-65% of a base resin, 3-7% of a reinforcing component, 0.3-0.5% of a curing system, 5-15% of a plasticizer, and deionized water supplemented to 100%;

[0008] The base resin is formed by reacting epoxy soybean oil acrylate with a bio-based polyurethane prepolymer in a mass ratio of 1-2:1, and the bio-based polyurethane prepolymer is formed by reacting decarboxylated hydroxyalkylated cashew nut shell oil with isophorone diisocyanate in a molar ratio of 1:2.0-2.5 via a catalyst, and the hydroxyl value of the decarboxylated hydroxyalkylated cashew nut shell oil is 180-220 mg KOH / g;

[0009] The reinforcing component is nanocellulose modified by a silane coupling agent;

[0010] The curing system is graphene oxide loaded with ammonium persulfate;

[0011] The plasticizer is citrate.

[0012] Furthermore, the preparation method of the decarboxylated hydroxyalkylated cashew nut shell oil is: heating the cashew nut shell oil to 180° C. under vacuum, maintaining decarboxylation for 2 hours, adding propylene oxide, adding 1% of the total mass of the reactants as a boron trifluoride-ether complex catalyst, and catalyzing the reaction at 80° C. for 4 hours to obtain the decarboxylated hydroxyalkylated cashew nut shell oil; wherein the molar ratio of cashew nut shell oil to propylene oxide is 1:2.

[0013] Furthermore, the preparation method of the bio-based polyurethane prepolymer is as follows: the decarboxylation hydroxyalkylated cashew nut shell oil is vacuum dried at 100° C. for 2 hours and then mixed evenly with isophorone diisocyanate, the temperature is raised to 75° C. under nitrogen protection, 0.05% of the total mass of the reactants as a dibutyltin dilaurate catalyst is added, the reaction is carried out at 75° C. and 500 rpm until the isophorone diisocyanate group content drops to 9.0%, stirring is stopped and the temperature is lowered to 40° C., and then acetone is added to dilute the viscosity to 2200-2800 mPa·s, thereby obtaining a bio-based polyurethane prepolymer.

[0014] Furthermore, the preparation method of the silane coupling agent modified nanocellulose is as follows: the silane coupling agent and the ethanol / water mixture are uniformly mixed in a mass ratio of 1:9, acetic acid is added to adjust the pH to 4.0, and magnetic stirring is performed in a 40°C water bath for 1 hour to fully hydrolyze the silane to form silanol; a 2% nanocellulose water suspension is mixed with the hydrolyzed silane coupling agent solution in a mass ratio of 10:1, ultrasonically dispersed for 30 minutes at a power of 300W and a frequency of 40kHz, reacted in a 60°C water bath with magnetic stirring for 4 hours, centrifuged at 8000rpm for 15 minutes to remove unreacted silane, washed with ethanol three times, and vacuum dried at 60°C for 24 hours to obtain the silane coupling agent modified nanocellulose; wherein the particle size of the nanocellulose is 20-40nm.

[0015] Furthermore, the preparation method of the graphene oxide loaded with ammonium persulfate is as follows: adding graphene oxide to deionized water, ultrasonically dispersing for 30 minutes under the conditions of a power of 300 W and a frequency of 40 kHz to obtain a graphene oxide aqueous suspension with a concentration of 5 mg / mL; adding ammonium persulfate to the graphene oxide aqueous suspension, stirring at 500 rpm for 2 hours, and vacuum freeze-drying the mixed solution at -50°C to obtain the graphene oxide loaded with ammonium persulfate; wherein the mass ratio of the ammonium persulfate to the graphene oxide is 1:1, the flake thickness of the graphene oxide is 1-3 nm, and the specific surface area is 800-1200 m 2 / g; the loading rate of the graphene oxide is 89-95%.

[0016] The present invention also provides a method for preparing the adhesive for plywood, comprising the following steps:

[0017] S1. Epoxidized soybean oil acrylate and bio-based polyurethane prepolymer were added into a container and stirred at 60°C and 500 rpm for 45 min;

[0018] S2. Add silane coupling agent to modify nanocellulose and disperse it ultrasonically at a power of 300 W and a frequency of 40 kHz for 60 min;

[0019] S3. Add graphene oxide loaded with ammonium persulfate and stir at 500 rpm for 20 min;

[0020] S4. Add citrate and deionized water to adjust the viscosity to 1300-1700 mPa·s.

[0021] The present invention also provides a plywood. The preparation method of the plywood is as follows: the adhesive for the plywood is applied between two adjacent layers of veneer wood, and the plywood is cured at 90° C. for 20 minutes under 0.8 MPa to obtain the plywood.

[0022] Furthermore, the single-layer wood is a poplar veneer with a moisture content of 6-9%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The hydroxyl group of the epoxy soybean oil acrylate of the present invention reacts with the isocyanate group of the bio-based polyurethane prepolymer to generate a carbamate bond, thereby forming a primary cross-linked network. In addition, the acrylate double bonds of the epoxy soybean oil acrylate undergo free radical polymerization under the initiation of graphene oxide-loaded ammonium persulfate to form a secondary cross-linked network, thereby forming an interpenetrating network structure. In this way, the interface bonding is enhanced by two-component cross-linking, thereby significantly improving the bonding strength (especially the dry bonding strength); the silane coupling agent-modified nanocellulose increases the interface bonding force, effectively blocks water erosion, and thus improves the wet bonding strength. At the same time, the reinforcing component improves the water resistance of the plywood. Through the synergistic effect of the base resin and the reinforcing component, the bonding strength under dry, wet and boiling conditions is significantly improved. This multi-component synergistic effect can provide higher initial bonding ability and stronger water resistance;

[0025] The synergistic use of silane coupling agent-modified nanocellulose and graphene oxide-loaded ammonium persulfate significantly reduced the immersion peeling rate and water absorption thickness expansion rate, and improved the water resistance of plywood.

[0026] The addition and uniform dispersion of nanocellulose improves the bending resistance, while the use of graphene oxide-loaded ammonium persulfate enhances the rigidity of the glue layer and optimizes the static bending strength and elastic modulus of the plywood, thereby improving the overall mechanical properties.

[0027] In summary, the adhesive for plywood of the present invention significantly improves the comprehensive performance of plywood through the synergistic effect of multiple components, meets the demand for environmentally friendly green plywood, and has broad application prospects. DETAILED DESCRIPTION

[0028] The following is a clear and complete description of the technical solution of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the following examples, the epoxidized soybean oil acrylate is EBECRYL 5848 epoxidized soybean oil acrylate.

[0030] 1. Materials and Methods

[0031] 1.1 Preparation of bio-based polyurethane prepolymer

[0032] S1. The cashew nut shell liquid was heated to 180°C under vacuum and maintained for 2 h to remove the carboxylic acid groups and release carbon dioxide to increase the reaction activity;

[0033] S2. Add propylene oxide (the molar ratio of cashew nut shell oil to propylene oxide is 1:2), add a catalyst boron trifluoride-ether complex (the amount added is 1% of the total mass of the reactants), and catalyze the reaction at 80°C for 4h to obtain decarboxylated hydroxyalkylated cashew nut shell oil, and the hydroxyl value is measured to reach 200mg KOH / g;

[0034] S3. The decarboxylation hydroxyalkylated cashew nut shell oil was vacuum dried at 100°C for 2h (water content was less than 0.05%), then mixed evenly with isophorone diisocyanate, heated to 75°C under nitrogen protection, added with a catalyst dibutyltin dilaurate (the amount added was 0.05% of the total mass of the reactants), reacted at 75°C and 500rpm for 3.5h (during the reaction, the isophorone diisocyanate group content was measured every 30min; at 3.5h, the isophorone diisocyanate group content dropped to about 9.0%), stopped stirring and cooled to 40°C;

[0035] S4. Acetone was added to dilute the viscosity to 2600 mPa·s (25° C.), thereby obtaining a bio-based polyurethane prepolymer, which was recorded as Bio-PU.

[0036] 1.2 Preparation of silane coupling agent modified nanocellulose

[0037] S1. The silane coupling agent and the ethanol / water mixture (the volume of ethanol and water is 4:1) are mixed evenly in a mass ratio of 1:9, acetic acid is added to adjust the pH to 4.0, and magnetic stirring is performed in a 40°C water bath for 1 hour to fully hydrolyze the silane to form silanol;

[0038] S2. Mix nanocellulose dry powder with a diameter of 20 nm with deionized water in proportion, homogenize at 35°C, 1000rpm for 30 minutes, then high-pressure homogenize at 100MPa, 35°C, 1000rpm for 30 minutes, and cycle 5 times; finally, ultrasonically disperse at a power of 500W and a frequency of 20kHz for 30 minutes to obtain a nanocellulose aqueous suspension with a concentration of 2%; take a portion of it without modification for the subsequent control test.

[0039] S3. A 2% aqueous suspension of nanocellulose was mixed with a hydrolyzed silane coupling agent solution in a mass ratio of 10:1, and ultrasonically dispersed for 30 min at a power of 300 W and a frequency of 40 kHz to promote condensation of silanol with the surface hydroxyl groups of nanocellulose;

[0040] S4. React in a 60℃ water bath with magnetic stirring for 4h, and centrifuge at 8000rpm for 15min to remove unreacted silane;

[0041] S5. After washing with ethanol three times, vacuum drying was performed at 60° C. for 24 h to obtain the silane coupling agent-modified nanocellulose, which was recorded as CNF-KH550.

[0042] 1.3 Preparation of graphene oxide loaded with ammonium persulfate

[0043] S1. Graphene oxide (sheet thickness of 1-3nm, specific surface area of ​​800-1200m 2 / g) was added into deionized water, and ultrasonically dispersed for 30 min at a power of 300 W and a frequency of 40 kHz to obtain a graphene oxide aqueous suspension with a concentration of 5 mg / mL;

[0044] S2. Add ammonium persulfate (the mass ratio of ammonium persulfate to graphene oxide is 1:1) and stir at 500 rpm for 2 h;

[0045] S3. The mixed solution was freeze-dried at -50°C in vacuum for 24 hours to obtain the graphene oxide loaded with ammonium persulfate. The loading rate of the graphene oxide was measured to be 92.4%, recorded as GO-APS.

[0046] 1.4 Preparation of plywood

[0047] S1. Add the base resin into the container, stir at 60°C and 500 rpm for 45 min; add the reinforcing component, and ultrasonically disperse it at a power of 300 W and a frequency of 40 kHz for 60 min; add the curing system, and stir and mix at 500 rpm for 20 min; add citrate and deionized water, and adjust the viscosity to 1500 mPa·s (25°C) to obtain an adhesive; the raw material formula for the preparation of the adhesive is shown in Table 1;

[0048] S2. Apply adhesive between two adjacent layers of poplar veneer (moisture content 8%), with a coating amount of 220g / m 2 , 0.8MPa, 90℃, cured for 20min, to obtain plywood. Samples were taken to measure the properties of the plywood. The test reference is shown in Table 2, and the test results are shown in Table 3.

[0049] Table 1 Raw material formula for adhesive preparation

[0050]

[0051] Note: In Table 1, ESOA is epoxidized soybean oil acrylate; Bio-PU is the bio-based polyurethane prepolymer prepared in "1.1"; CNF-KH550 is the silane coupling agent modified nanocellulose prepared in "1.2"; GO-APS is the graphene oxide loaded with ammonium persulfate prepared in "1.3".

[0052] Table 2 Test criteria and methods

[0053]

[0054]

[0055] Table 3 Effects of different adhesives on the properties of poplar plywood

[0056]

[0057] As can be seen from Tables 1-3, in terms of bonding strength, the dry bonding strength of C6 (4.8MPa) is 37.1% higher than that of the optimal control group C5 (3.5MPa), indicating that the synergistic cross-linking of the two-component matrix (ESOA+Bio-PU) significantly enhances the interface bonding; the wet bonding strength of C6 (3.6MPa) is 63.6% higher than that of C4 (2.2MPa), and the Si-OC covalent bond of silane-modified nanocellulose (CNF-KH550) blocks moisture erosion; the bonding strength of C6 after boiling water (2.9MPa) is 81.3% higher than that of C4 (1.6MPa), and the slow release of free radicals by graphene oxide (GO-APS) optimizes the water resistance of the cross-linked network.

[0058] In terms of water resistance, the immersion peeling rate of C6 (10.5%) is 48.5% lower than that of C4 (20.4%), and the interface bonding strength is significantly enhanced; the water absorption thickness expansion rate of C6 (4.3%) is 72.1% lower than that of C1 (15.4%), and the adhesive fills the pores of the wood to inhibit water absorption and expansion.

[0059] In terms of mechanical properties, the static bending strength (42.7MPa) is 27.8% higher than that of C4 (33.4MPa), and the uniform dispersion of nanocellulose improves the bending resistance; the elastic modulus of C6 (5.1GPa) is 30.8% higher than that of C4 (3.9GPa), the rigidity of the adhesive layer is enhanced, and the deformation resistance is optimized.

[0060] In summary, the epoxy soybean oil acrylate of the present invention provides high reactivity, while the bio-based polyurethane prepolymer enhances the mechanical properties and water resistance of the material through cross-linking reaction, and enhances the interface bonding through two-component cross-linking, thereby significantly improving the bonding strength (especially the dry bonding strength); the silane coupling agent-modified nanocellulose increases the interface bonding force, effectively blocks water erosion, and thus improves the wet bonding strength. At the same time, the reinforcing component improves the water resistance of the plywood. Through the synergistic effect of the base resin and the reinforcing component, the bonding strength under dry, wet and boiling conditions is significantly improved. This multi-component synergistic effect can provide higher initial bonding ability and stronger water resistance;

[0061] The synergistic use of silane coupling agent-modified nanocellulose and graphene oxide-loaded ammonium persulfate significantly reduced the immersion peeling rate and water absorption thickness expansion rate, and improved the water resistance of plywood.

[0062] The addition and uniform dispersion of nanocellulose improves the bending resistance, while the use of graphene oxide-loaded ammonium persulfate enhances the rigidity of the glue layer and optimizes the static bending strength and elastic modulus of the plywood, thereby improving the overall mechanical properties.

[0063] In summary, the adhesive for plywood of the present invention significantly improves the comprehensive performance of plywood through the synergistic effect of multiple components, meets the demand for environmentally friendly green plywood, and has broad application prospects.

Claims

1. An adhesive for plywood, characterized in that: In terms of mass percentage, the adhesive for plywood is prepared by 55-65% of base resin, 3-7% of reinforcing component, 0.3-0.5% of curing system, 5-15% of plasticizer and deionized water added to 100%; The base resin is formed by reacting epoxy soybean oil acrylate with a bio-based polyurethane prepolymer in a mass ratio of 1-2:1, and the bio-based polyurethane prepolymer is formed by reacting decarboxylated hydroxyalkylated cashew nut shell oil with isophorone diisocyanate in a molar ratio of 1:2.0-2.5 via a catalyst, and the hydroxyl value of the decarboxylated hydroxyalkylated cashew nut shell oil is 180-220 mg KOH / g; The reinforcing component is nanocellulose modified by a silane coupling agent; The curing system is graphene oxide loaded with ammonium persulfate; The plasticizer is citrate.

2. The adhesive for plywood according to claim 1, characterized in that: The preparation method of the decarboxylated hydroxyalkylated cashew nut shell oil comprises: heating the cashew nut shell oil to 180° C. under vacuum, maintaining decarboxylation for 2 hours, adding propylene oxide, adding a boron trifluoride-ether complex catalyst of 1% of the total mass of the reactants, and catalytically reacting at 80° C. for 4 hours to obtain the decarboxylated hydroxyalkylated cashew nut shell oil; wherein the molar ratio of the cashew nut shell oil to the propylene oxide is 1:

2.

3. The adhesive for plywood according to claim 1, characterized in that: The preparation method of the bio-based polyurethane prepolymer comprises: drying the decarboxylation hydroxyalkylated cashew nut shell oil at 100° C. in vacuum for 2 hours, uniformly mixing the mixture with isophorone diisocyanate, heating the mixture to 75° C. under nitrogen protection, adding a dibutyltin dilaurate catalyst of 0.05% of the total mass of the reactants, reacting the mixture at 75° C. and 500 rpm until the isophorone diisocyanate group content decreases to 9.0%, stopping stirring and cooling the mixture to 40° C., and then adding acetone to dilute the viscosity to 2200-2800 mPa·s, thereby obtaining the bio-based polyurethane prepolymer.

4. The adhesive for plywood according to claim 1, characterized in that: The preparation method of the silane coupling agent modified nanocellulose is as follows: uniformly mixing the silane coupling agent and the ethanol / water mixed solution at a mass ratio of 1:9, adding acetic acid to adjust the pH to 4.0, and magnetically stirring in a 40°C water bath for 1 hour to fully hydrolyze the silane to form silanol; mixing a 2% nanocellulose water suspension with the hydrolyzed silane coupling agent solution at a mass ratio of 10:1, ultrasonically dispersing for 30 minutes under the conditions of a power of 300W and a frequency of 40kHz, magnetically stirring in a 60°C water bath for 4 hours, centrifuging at 8000rpm for 15 minutes to remove unreacted silane, washing with ethanol three times, and vacuum drying at 60°C for 24 hours to obtain the silane coupling agent modified nanocellulose; wherein the particle size of the nanocellulose is 20-40nm.

5. The adhesive for plywood according to claim 1, characterized in that: The preparation method of the graphene oxide loaded with ammonium persulfate is as follows: adding graphene oxide to deionized water, ultrasonically dispersing for 30 minutes under the conditions of a power of 300 W and a frequency of 40 kHz, to obtain a graphene oxide water suspension with a concentration of 5 mg / mL; adding ammonium persulfate to the graphene oxide water suspension, stirring at 500 rpm for 2 hours, and vacuum freeze-drying the mixed solution at -50°C to obtain the graphene oxide loaded with ammonium persulfate; wherein the mass ratio of the ammonium persulfate to the graphene oxide is 1:1, the graphene oxide has a sheet thickness of 1-3 nm, and a specific surface area of ​​800-1200 m 2 / g; the loading rate of the graphene oxide is 89-95%.

6. A method for preparing the adhesive for plywood according to claim 1, characterized in that: The following steps are involved: S1. Epoxidized soybean oil acrylate and bio-based polyurethane prepolymer were added into a container and stirred at 60°C and 500 rpm for 45 min; S2. Add silane coupling agent to modify nanocellulose and disperse it ultrasonically at a power of 300 W and a frequency of 40 kHz for 60 min; S3. Add graphene oxide loaded with ammonium persulfate and stir at 500 rpm for 20 min; S4. Add citrate and deionized water to adjust the viscosity to 1300-1700 mPa·s.

7. A plywood, characterized in that: The preparation method of the plywood is as follows: applying the adhesive for plywood according to claim 1 between two adjacent layers of veneer wood, and curing at 90° C. for 20 minutes under 0.8 MPa to obtain the plywood.

8. The plywood according to claim 1, characterized in that: The single-layer wood is a poplar veneer with a moisture content of 6-9%.

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