Preparation method and application of ultra-long room-temperature phosphorescent formaldehyde-free adhesive

Abstract

The invention belongs to the technical field of functional adhesives, and relates to a preparation method and application of an ultra-long room-temperature phosphorescent formaldehyde-free adhesive. The method comprises the following steps: by taking lignin as a basic component, sequentially reacting with epichlorohydrin and an amination reagent under an alkaline condition to obtain ammoniated modified lignin; meanwhile, dispersing a natural polyhydroxy polymer in water, performing light oxidation treatment, and embedding a phosphorescent light-emitting unit through a covalent bond to obtain a functional cross-linking agent; and finally, uniformly mixing the two products at room temperature to prepare the ultra-long room-temperature phosphorescent formaldehyde-free adhesive. According to the method, biomass molecules are taken as a main body of raw materials, the process conditions are mild, and the obtained adhesive forms a covalent bond and hydrogen bond dual rigid network after being heated and fully cured, so that the adhesive can reflect the ultra-long room-temperature phosphorescence characteristic under the excitation of ultraviolet light, has the functions of interface bonding and optical recognition, and can be applied to the field of light emitting devices. The method can be applied to anti-counterfeiting and tracing of wood composite materials and related interface systems.

Description

Technical Field

[0001] This invention belongs to the field of formaldehyde-free adhesives and optical information materials technology, specifically relating to a method for preparing and applying an ultra-long room temperature phosphorescent formaldehyde-free adhesive. Background Technology

[0002] Currently, adhesives commonly used in wood-based composites, paper-based composites, and other interfacial bonding systems are mostly represented by urea-formaldehyde resin, phenolic resin, or melamine-modified resin. Although these adhesives have a mature application base, they generally have problems with the release of free formaldehyde or potential formaldehyde, making it difficult to meet the requirements of green manufacturing, low volatile organic compound emissions, and sustainable development.

[0003] Lignin is a naturally abundant aromatic polymer with various active groups such as phenolic and aliphatic hydroxyl groups in its molecular structure, making it a potential raw material for formaldehyde-free biomass-based adhesives. Developing environmentally friendly adhesives based on lignin is of great significance for the preparation of environmentally friendly engineered wood products, wood-based composites, and paper-based composites. However, most existing lignin-based or other formaldehyde-free adhesives only focus on bonding performance and environmental friendliness, lacking functional designs for identifying the authenticity of end products, tracing their origin, and indicating their service status. This makes it difficult for consumers and users to easily identify the source of adhesive materials and the adhesive information used at the interface.

[0004] Room-temperature phosphorescent materials, which continue to emit light even after the excitation source is removed, show promising application prospects in fields such as optical identification, anti-counterfeiting traceability, information storage, and environmental response monitoring. Therefore, incorporating room-temperature phosphorescence into adhesive systems could potentially achieve the integration of adhesion and functional identification. However, simply blending phosphorescent materials presents system compatibility issues, making it difficult to achieve uniform phosphorescence and limiting its practicality.

[0005] Therefore, developing a lignin-based functional adhesive that combines formaldehyde-free bonding with stable ultra-long room temperature phosphorescence properties, has a relatively mild preparation process, and is suitable for composite material interface applications has significant research value and application significance. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing an ultra-long room temperature phosphorescent formaldehyde-free adhesive, in order to solve the problems of high formaldehyde release risk of existing adhesives, single function of biomass-based adhesives, and difficulty in synergistic integration of phosphorescent functional materials and adhesive systems.

[0007] To achieve the above objectives, this invention first uniformly disperses lignin in an alkaline aqueous phase to fully expose the phenolic hydroxyl groups within the aggregated structure. Then, by controlling the temperature and pH gradient, epichlorohydrin and diamine are sequentially introduced to modify the lignin, achieving efficient amination. Simultaneously, a suitable amount of aldehyde groups are introduced by dispersing a natural polyhydroxy polymer in water and undergoing a mild oxidation treatment under controlled conditions. The remaining hydroxyl groups are then used to anchor the phosphorescent luminescent units. Finally, the amination-modified lignin and the modified natural polyhydroxy polymer are mixed uniformly at room temperature to obtain the ultra-long room-temperature phosphorescent formaldehyde-free adhesive. After complete curing by heating, this adhesive exhibits ultra-long room-temperature phosphorescence properties under ultraviolet light excitation.

[0008] The objective of this invention and the technical problem it solves are achieved through the following technical solutions: A method for preparing an ultra-long room temperature phosphorescent formaldehyde-free adhesive, characterized by the following steps: Step 1, mixing lignin with water, adjusting the system to a first pH, then adding epichlorohydrin, and reacting at a first temperature to obtain a first product; Step 2, cooling the first product to a second temperature and adjusting it to a second pH, then adding an amination reagent, and reacting at the second temperature to obtain a second product; Step 3, dispersing a polyhydroxy polymer in water, heating it to a third temperature while continuously stirring, adding an oxidant, and reacting at the third temperature to obtain a third product; Step 4, lowering the temperature of the third product to a fourth temperature, slowly adding a phosphorescent luminescent unit, and stirring for 10–30 min to obtain a fourth product; Step 5, mixing the second product and the fourth product uniformly at room temperature to obtain an ultra-long room temperature phosphorescent formaldehyde-free adhesive.

[0009] The lignin mentioned in step 1 is at least one of sulfate lignin, pre-hydrolyzed lignin, organic solvent lignin, and lignin-rich fermentation residue; the mass ratio of lignin to water is 1:2~5; the first pH is 11.5~12.0; the ratio of epichlorohydrin added to lignin mass is 0.05~0.2:1.0; the first temperature is 80~90℃, and the reaction time is 0.5~1.5 h.

[0010] Preferably, the lignin in step 1 is at least one of sulfate lignin, lignin sulfonate, and pre-hydrolyzed lignin; the mass ratio of lignin to water is 1.0:3.0~4.0; the first pH is 11.5~11.8; the ratio of epichlorohydrin added to lignin mass is 0.1~0.15:1.0; the first temperature is 85~90 ℃, and the reaction time is 0.8~1.2 h.

[0011] Step 2: The second pH is 9.0~11.0; the amination agent is at least one of ethylenediamine, hexamethylenediamine, urea, and difunctional polyetheramine, and the ratio of the amount added to the lignin quality in step 1 is 0.1~0.4:1.0; the second temperature is 60~80 ℃, and the reaction time is 1.0~3.0 h.

[0012] Preferably, in step 2, the second pH is 9.5-10.5; the amination agent is at least one of ethylenediamine and difunctional polyetheramine, and the ratio of the amount added to the lignin quality in step 1 is 0.2-0.3:1.0; the second temperature is 65-75 °C, and the reaction time is 1.8-2.5 h.

[0013] The polyhydroxy polymer in step 3 is at least one of starch, guar gum, sodium alginate, carboxymethyl cellulose, and chitosan, and its mixing mass ratio with water is 0.05~0.3:1; the oxidant is at least one of 2,2,6,6-tetramethylpiperidine oxide, sodium hypochlorite, periodic acid, and hydrogen peroxide, and its addition amount is 0.01~0.10 of the polyhydroxy polymer; the third temperature is 35~60 °C, and the reaction time is 0.5~1.5 h.

[0014] Preferably, the polyhydroxy polymer in step 3 is at least one of starch, sodium alginate, and carboxymethyl cellulose, and its mixing mass ratio with water is 0.1~0.25:1; the oxidant is at least one of periodic acid and hydrogen peroxide, and its addition amount is 0.05~0.10 of the polyhydroxy polymer; the third temperature is 40~50 °C, and the reaction time is 0.8~1.2 h.

[0015] The fourth temperature in step 4 is 35~55 ℃; the phosphorescent unit is at least one pure organic room temperature phosphorescent monomer containing isocyanate group, epoxy group or silane group, and the addition amount is 0.05~0.2:1.0 in mass ratio with the polyhydroxy polymer in step 3; the stirring speed is 500~800 r / min and the stirring time is 10~30 min.

[0016] Preferably, the fourth temperature in step 4 is 40~50 ℃; the phosphorescent unit is at least one of pure organic room temperature phosphorescent monomers containing epoxy or silaneoxy groups, and the addition amount is in a mass ratio of 0.1~0.15:1.0 to the polyhydroxy polymer in step 3; the stirring speed is 600~700 r / min, and the stirring time is 15~25 min.

[0017] In step 5, the mass ratio of the second product to the fourth product is 1:0.5~2.0.

[0018] Preferably, in step 5, the mass ratio of the second product to the fourth product is 1:1.0~1.5.

[0019] The present invention also provides an ultra-long room temperature phosphorescent formaldehyde-free adhesive prepared by the above method, and the adhesive exhibits ultra-long room temperature phosphorescence characteristics after being fully cured by heating and under ultraviolet light excitation.

[0020] The application of the ultra-long room temperature phosphorescent formaldehyde-free adhesive in optical identification, anti-counterfeiting traceability, or environmental response monitoring in wood composite materials, paper-based composite materials, and related interfacial bonding systems.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses lignin and natural polyhydroxy polymers as the main raw materials to construct an adhesive system, which can significantly reduce the dependence on traditional petrochemical-based aldehyde-containing adhesives, and make the resulting product have both low-carbon and environmentally friendly properties and optical functional properties. At the same time, the preparation process of this invention is relatively mild and controllable, and the raw materials are widely available, which has good prospects for industrial application; (2) This invention adopts an aldehyde-free preparation route and constructs adhesives without using aldehyde crosslinking systems, which avoids the risk of formaldehyde release that may occur during the manufacturing, use and long-term service of adhesives from the source, and can meet the use requirements of various aldehyde-free application scenarios; (3) This invention achieves the synergistic construction of adhesive performance and phosphorescence function in the same adhesive system by aminated modification of lignin and mild oxidative activation and hydroxyl-mediated phosphorescence luminescence unit grafting of polyhydroxy polymers. The two types of biomacromolecules modified by functional groups can form more covalent linkage structures during the curing process of the adhesive, ensuring the bonding strength; at the same time, the oxygen and nitrogen atoms introduced into the system have strong hydrogen bonding ability, which can further form a second cross-linking strengthening structure that is different from covalent cross-linking. The above structural features are not only conducive to improving the bonding strength of the adhesive, but also can strengthen the rigid confinement of the phosphorescence luminescence center, reduce the non-radiative transition of triplet excitons, thereby endowing the cured adhesive with excellent room temperature phosphorescence performance; (4) After the adhesive obtained by the present invention is fully cured by heating, it can exhibit ultra-long room temperature phosphorescence characteristics under ultraviolet light excitation, thereby giving the bonding interface the potential for application of visual identification, anti-counterfeiting traceability and environmental response monitoring; (5) The adhesive layer formed after the adhesive is cured is bound to the bonded material throughout the entire service life, and cannot be easily covered or wiped off, which can support the traceability-level anti-counterfeiting requirements of artificial board products. Detailed Implementation

[0022] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the preparation method and application of an ultra-long room temperature phosphorescent formaldehyde-free adhesive proposed in this invention are further illustrated below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Non-substantial improvements and adjustments made by those skilled in the art under the guidance of this invention should all fall within the scope of protection of this invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment.

[0023] Unless otherwise specified, all raw materials, reagents, and instruments mentioned below are conventional commercially available products well-known to those skilled in the art; unless otherwise specified, all methods employed are methods known in the art. Unless otherwise defined, the technical or scientific terms used herein should be understood in the manner of those skilled in the art to which this invention pertains.

[0024] This invention proposes a method for preparing and applying an ultra-long room temperature phosphorescent formaldehyde-free adhesive. The key is to achieve the synergistic construction of adhesive performance and phosphorescence function in the same adhesive system by amination modification of lignin, mild oxidation activation of polyhydroxy polymers and grafting of hydroxyl-mediated phosphorescent units.

[0025] Specifically, this invention first uniformly disperses lignin in an alkaline aqueous phase to fully expose the phenolic hydroxyl groups within the aggregated structure. Then, by controlling the temperature and pH gradient, epichlorohydrin and diamine are sequentially introduced to modify the lignin, achieving efficient amination. Simultaneously, a suitable amount of aldehyde groups are introduced by dispersing a natural polyhydroxy polymer in water and undergoing a mild oxidation treatment under controlled conditions. The remaining hydroxyl groups are then used to anchor the phosphorescent units. Finally, the amination-modified lignin and the modified natural polyhydroxy polymer are mixed uniformly at room temperature to obtain the ultra-long room-temperature phosphorescent formaldehyde-free adhesive. After complete curing by heating, this adhesive exhibits ultra-long room-temperature phosphorescence properties under ultraviolet light excitation.

[0026] This invention employs a precise biomass macromolecule modification strategy to pre-place valence-donating binding sites in lignin and natural polyhydroxy polymers, enabling the formation of numerous covalently linked structures during adhesive curing and ensuring bonding strength. Simultaneously, by leveraging the hydrogen bonding capabilities of the oxygen and nitrogen atoms introduced into the system, a second layer of reinforcement is achieved for the covalently cross-linked structure. This not only increases the adhesive's bonding strength but also effectively enhances the rigid confinement effect on the phosphorescent emission centers embedded in the cross-linked structure, reducing non-radiative transitions of triplet excitons, thereby endowing the cured adhesive with excellent room-temperature phosphorescence properties.

[0027] Example 1 Step 1: Weigh 100 g of sulfate lignin and mix it with water at a mass ratio of 1:3. Adjust the pH of the system to 11.7, then add epichlorohydrin at a mass ratio of 0.12:1.0 to lignin. Keep the mixture at 87 °C for 1.0 h to obtain the first product.

[0028] Step 2: Cool the first product to 70 °C, adjust the pH of the system to 10.0, add ethylenediamine, the mass ratio of ethylenediamine added to lignin in step 1 is 0.25:1.0, and keep the reaction at 70 °C for 2.0 h to obtain the second product.

[0029] Step 3: Disperse starch in water at a mass ratio of starch to water of 0.15:1. Heat the mixture to 45 °C with continuous stirring, then add hydrogen peroxide at a mass ratio of 0.08 to starch. Keep the mixture at this temperature for 1.0 h to obtain the third product.

[0030] Step 4: Lower the temperature of the third product to 45 °C, slowly add a pure organic room temperature phosphorescent monomer containing epoxy groups, with the addition amount being 0.12:1 in mass ratio to the polyhydroxy polymer described in Step 3, and stir at 680 r / min for 20 min to obtain the fourth product.

[0031] Step 5: Mix the second product and the fourth product at a mass ratio of 1.0:1.1 at room temperature to obtain an ultra-long room temperature phosphorescent formaldehyde-free adhesive.

[0032] Flour (25% by weight) was added to the above adhesive to prepare the adhesive solution, which was then applied to 2.2 mm thick eucalyptus veneers at an application rate of 340 g / m² (double-sided). This resulted in the assembly of three-layer eucalyptus plywood sheets. The sheets were then hot-pressed at 120 ℃ and 1.0 MPa for 10 min to obtain three-layer eucalyptus plywood. The dry bond strength, Class II bond strength, formaldehyde release, and phosphorescence properties were then tested.

[0033] Example 2 Step 1: 100 g of pre-hydrolyzed lignin was selected and mixed with water at a mass ratio of 1:3.5. The pH of the system was adjusted to 11.7, and epichlorohydrin was added at a mass ratio of 0.13:1.0 to lignin. The reaction was carried out at 89 °C for 1.0 h to obtain the first product.

[0034] Step 2: Cool the first product to 70 °C, adjust the pH of the system to 9.8, add difunctional polyetheramine, the mass ratio of the difunctional polyetheramine added to the lignin in step 1 is 0.28:1.0, and keep the reaction at 73 °C for 2.2 h to obtain the second product.

[0035] Step 3: Disperse carboxymethyl cellulose in water at a mass ratio of 0.2:1.0. After heating to 35 °C with continuous stirring, add periodic acid at a mass ratio of 0.01 to carboxymethyl cellulose. Keep the mixture at 48 °C for 1.0 h to obtain the third product.

[0036] Step 4: Lower the temperature of the third product to 42 °C, slowly add a pure organic room temperature phosphorescent monomer containing silaneoxy groups, with the addition amount being 0.14:1 in mass ratio to the polyhydroxy polymer described in Step 3, and stir at 620 r / min for 20 min to obtain the fourth product.

[0037] Step 5: Mix the second product and the fourth product at a mass ratio of 1:1.3 at room temperature to obtain an ultra-long room temperature phosphorescent formaldehyde-free adhesive.

[0038] Flour (25% by weight) was added to the above adhesive to prepare the adhesive solution, which was then applied to 2.2 mm thick eucalyptus veneers at an application rate of 340 g / m² (double-sided). This resulted in the assembly of three-layer eucalyptus plywood sheets. The sheets were then hot-pressed at 120 ℃ and 1.0 MPa for 10 min to obtain three-layer eucalyptus plywood. The dry bond strength, Class II bond strength, formaldehyde release, and phosphorescence properties were then tested.

[0039] Example 3 Step 1: Pre-hydrolyzed lignin was selected and mixed with water at a mass ratio of 1:2.5. The pH of the system was adjusted to 12.0, and epichlorohydrin was added at a mass ratio of 0.17:1.0 to lignin. The reaction was carried out at 82 °C for 0.6 h to obtain the first product.

[0040] Step 2: Cool the first product to 62 °C, adjust the pH of the system to 10.8, add difunctional polyetheramine, the mass ratio of the difunctional polyetheramine added to the lignin in step 1 is 0.17:1.0, and keep the reaction at 78 °C for 1.5 h to obtain the second product.

[0041] Step 3: Disperse guar gum in water at a mass ratio of 0.28:1. Heat the mixture to 38 °C with continuous stirring, then add periodic acid. The mass ratio of ammonium persulfate to sodium alginate is 0.03. Keep the mixture at 55 °C for 1.4 h to obtain the third product.

[0042] Step 4: Lower the temperature of the third product to 33°C, slowly add a pure organic room temperature phosphorescent monomer containing epoxy groups, with the addition amount being 0.18:1 in mass ratio to the polyhydroxy polymer described in Step 3, and stir at 550 r / min for 28 min to obtain the fourth product.

[0043] Step 5: Mix the second product and the fourth product at a mass ratio of 1:1.8 at room temperature to obtain an ultra-long room temperature phosphorescent formaldehyde-free adhesive.

[0044] Flour (25% by weight) was added to the above adhesive to prepare the adhesive solution, which was then applied to 2.2 mm thick eucalyptus veneers at an application rate of 340 g / m² (double-sided). This resulted in the assembly of three-layer eucalyptus plywood sheets. The sheets were then hot-pressed at 120 ℃ and 1.0 MPa for 10 min to obtain three-layer eucalyptus plywood. The dry bond strength, Class II bond strength, formaldehyde release, and phosphorescence properties were then tested.

[0045] Table 1. Properties and phosphorescence characteristics of the adhesive-bonded boards prepared in the examples.

[0046] Note: The plywood strength in Table 1 is the test result of 14 specimens. The numerator is the average bond strength and the denominator is the minimum bond strength.

[0047] The bonding strength of the above-mentioned Class II plywood was tested according to the strength test method in GB / T 9846-2015 "Ordinary Plywood".

[0048] The three-layer eucalyptus plywood prepared in Examples 1 to 3 all exhibited excellent bonding strength, and the adhesive layer showed good room temperature phosphorescence emission performance, indicating that the patented technology has good practicality.

Claims

1. A method for preparing an ultra-long room temperature phosphorescent formaldehyde-free adhesive, characterized in that, Includes the following steps: Step 1. Mix lignin with water, adjust the system to the first pH, then add epichlorohydrin, and keep the reaction at the first temperature to obtain the first product; Step 2: Cool the first product to a second temperature and adjust it to a second pH, then add an amination reagent and keep the reaction at the second temperature to obtain the second product; Step 3: Disperse the polyhydroxy polymer in water, heat it to a third temperature while stirring continuously, add an oxidant, and keep it at the third temperature to obtain the third product; Step 4: Lower the temperature of the third product to a fourth temperature, slowly add the phosphorescent luminescent unit, stir for 10-30 min to obtain the fourth product; Step 5: Mix the second product and the fourth product evenly at room temperature to obtain an ultra-long room temperature phosphorescent formaldehyde-free adhesive.

2. The preparation method of an ultra-long room temperature phosphorescent formaldehyde-free adhesive according to claim 1, characterized in that, The lignin mentioned in step 1 is at least one of sulfate lignin, pre-hydrolyzed lignin, organic solvent lignin, lignin sulfonate, and lignin-rich fermentation residue; the mass ratio of lignin to water is 1.0:2.0~5.0; the first pH is 11.5~12.0; the ratio of epichlorohydrin added to lignin mass is 0.05~0.2:1.0; the first temperature is 80~90℃, and the reaction time is 0.5~1.5 h.

3. The preparation method of an ultra-long room temperature phosphorescent formaldehyde-free adhesive according to claim 1, characterized in that, Step 2: The second pH is 9.0~11.0; the amination agent is at least one of ethylenediamine, hexamethylenediamine, urea, and difunctional polyetheramine, and the ratio of the amount added to the lignin quality in step 1 is 0.1~0.4:1.0; the second temperature is 60~80 ℃, and the reaction time is 1.0~3.0 h.

4. The preparation method of an ultra-long room temperature phosphorescent formaldehyde-free adhesive according to claim 1, characterized in that, The polyhydroxy polymer in step 3 is at least one of starch, guar gum, sodium alginate, carboxymethyl cellulose, and chitosan, and its mixing mass ratio with water is 0.05~0.3:1; the oxidant is at least one of 2,2,6,6-tetramethylpiperidine oxide, sodium hypochlorite, periodic acid, and hydrogen peroxide, and its addition amount is 0.01~0.10 of the polyhydroxy polymer; the third temperature is 35~60 °C, and the reaction time is 0.5~1.5 h.

5. The preparation method of an ultra-long room temperature phosphorescent formaldehyde-free adhesive according to claim 1, characterized in that, The fourth temperature in step 4 is 35~55 ℃; the phosphorescent unit is at least one of pure organic room temperature phosphorescent monomers containing isocyanate groups, epoxy groups or silane groups, and the addition amount is 0.05~0.2:1 in mass ratio with the polyhydroxy polymer in step 3; the stirring speed is 500~800 r / min and the stirring time is 10~30 min.

6. The preparation method of an ultra-long room temperature phosphorescent formaldehyde-free adhesive according to claim 1, characterized in that, In step 5, the mass ratio of the second product to the fourth product is 1:0.5~2.

0.

7. The product prepared by the method according to any one of claims 1-6 is an ultra-long room temperature phosphorescent formaldehyde-free adhesive, and after the adhesive is fully cured by heating, it can exhibit ultra-long room temperature phosphorescence characteristics under ultraviolet light excitation.

8. The application of the ultra-long room temperature phosphorescent formaldehyde-free adhesive according to claim 7 in optical identification, anti-counterfeiting traceability or environmental response monitoring in wood composite materials, paper-based composite materials and related interfacial bonding systems.

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