Modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde glue and preparation method thereof

Abstract

The invention relates to the technical field of adhesive preparation, in particular to modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde glue and a preparation method thereof. According to the technical scheme, the modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde glue is prepared from the following raw materials in parts by weight: 100 parts of urea-formaldehyde resin prepolymer; 8 to 25 parts of modified gelatin; 0.5 to 1.5 parts of nano copper doped manganese dioxide; the modified gelatin is gelatin subjected to protease enzymolysis treatment, and the average molecular weight of the modified gelatin is 3,000-60,000 Da; the nano-copper doped manganese dioxide is a mesoporous material with the copper doping amount of 3-10 mol%; after the adhesive is hot-pressed and cured, the formaldehyde release amount of a prepared artificial board is smaller than or equal to 0.025 mg / m, the dry-state bonding strength is larger than or equal to 0.80 MPa, through the three-stage synergistic effect of weak acid initial process source control, modified gelatin in-situ capture and nano-catalyst oxidative conversion, formaldehyde is inhibited and eliminated from the source to the process in an all-around mode, and the prepared artificial board is stable in formaldehyde release amount and high in bonding strength. And the technical bottleneck that the conventional urea-formaldehyde glue is difficult to stably reach the ENF level is solved.

Description

Technical Field

[0001] This invention relates to the field of adhesive preparation technology, and more particularly to a modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive and its preparation method. Background Technology

[0002] Urea-formaldehyde resin is one of the most widely used adhesives in the wood industry, mainly used in the production of engineered wood products (such as plywood, particleboard and medium-density fiberboard). Its advantages include low cost, high bonding strength and fast curing speed.

[0003] Currently, the main methods to reduce formaldehyde release from UF adhesives include: reducing the molar ratio of formaldehyde to urea, adding urea in stages, adding formaldehyde scavengers (such as melamine, urea derivatives, etc.), and adjusting the pH value of the synthesis process. However, these methods often lead to the following problems: reducing the amount of formaldehyde or adding certain scavengers can result in insufficient cross-linking density of the adhesive, affecting the mechanical properties of the final board. Although the traditional alkali, acid, and alkali process is mature and stable, a large amount of free formaldehyde is generated in the initial alkaline stage, making it difficult to achieve the ENF level. While the early "strong acid initiation" process can reduce formaldehyde, it results in low bonding strength and a narrow process window due to the rapid reaction and uneven structure, making it difficult to industrialize. Some scavengers only temporarily adsorb formaldehyde and are prone to re-release in humid and hot environments, resulting in unstable long-term environmental performance. Summary of the Invention

[0004] To overcome the problem that traditional methods of reducing formaldehyde dosage or adding certain scavenging agents can lead to insufficient colloidal crosslinking density, affecting the mechanical properties of the final board, traditional alkali, acid and alkali processes, although mature and stable, generate a large amount of free formaldehyde in the initial alkaline stage, making it difficult to achieve ENF level. While the early "strong acid initiation" process can reduce formaldehyde, it suffers from low bonding strength and a narrow process window due to the rapid reaction and uneven structure, making it difficult to industrialize. Some scavenging agents only temporarily adsorb formaldehyde and are prone to re-release in humid and hot environments, resulting in unstable long-term environmental performance.

[0005] The technical solution of this invention is as follows: a modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive, comprising the following components by weight percentage: 100 parts of urea-formaldehyde resin prepolymer; 8-25 parts of modified gelatin; 0.5-1.5 parts of nano-copper-doped manganese dioxide; the modified gelatin is gelatin treated with protease hydrolysis, with an average molecular weight of 3,000-60,000 Da; the nano-copper-doped manganese dioxide is a mesoporous material with a copper doping content of 3-10 mol%; after the adhesive is cured by hot pressing, the formaldehyde release of the prepared artificial board is ≤0.025 mg / m³, and the dry bonding strength is ≥0.80 MPa.

[0006] Preferably, the method for preparing modified gelatin includes the following steps:

[0007] Step 1: Dissolve gelatin in deionized water to prepare a solution with a mass concentration of 8% to 20%.

[0008] Step 2: Add protease and hydrolyze at 40–60°C and pH 6.0–9.0 for 0.5–3 hours. The amount of protease added is 0.05%–8% of the dry weight of gelatin.

[0009] Step 3: After enzymatic hydrolysis, heat to 75-85℃ and maintain for 10-30 minutes to inactivate the enzyme, then dry to obtain powder.

[0010] Preferably, the preparation method of nano-copper doped manganese dioxide is a hydrothermal method, which includes the following steps:

[0011] Step 1: Prepare an aqueous solution of potassium permanganate as an oxidizing agent solution;

[0012] Step 2: Prepare a mixed aqueous solution containing divalent manganese salt and divalent copper salt as a reducing agent solution;

[0013] Step 3: Add the reducing agent solution dropwise to the oxidizing agent solution to react and obtain the precursor mixture;

[0014] Step four: The precursor mixture is subjected to a hydrothermal reaction, and the reaction product is washed and dried to obtain nano-copper-doped manganese dioxide.

[0015] Preferably, the urea-formaldehyde resin prepolymer is prepared by a weak acid-initiated synthesis process, which includes initiating a polycondensation reaction at a pH of 4.5 to 5.8 and adding urea and formaldehyde in stages during the reaction.

[0016] A method for preparing modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive, comprising the above-described modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive, the steps of which are as follows;

[0017] Step 1: Prepare urea-formaldehyde resin prepolymer using a weak acid-initiated synthesis process, specifically as follows:

[0018] Add the first portion of formaldehyde, adjust the pH to alkaline, add the first portion of urea, and initiate the initial hydroxymethylation reaction;

[0019] Adjust the pH of the system to 4.5–5.8, add the second part of urea and some modified gelatin, and carry out a weak acid polycondensation reaction;

[0020] Add the remaining formaldehyde and the third part of urea, and continue to polymerize to the target viscosity;

[0021] Adjust the pH to alkaline, add the fourth part of urea for post-stabilization treatment, and then cool down before discharging.

[0022] Step 2: Mix the urea-formaldehyde resin prepolymer obtained in Step 1 with the remaining modified gelatin, nano-copper doped manganese dioxide, and optional curing accelerator to obtain urea-formaldehyde adhesive.

[0023] Preferably, in step one, the reaction temperature is controlled at 85-98°C, and the weak acid polycondensation reaction is carried out until the viscosity is 12-18 seconds.

[0024] According to step one, the reaction is carried out at pH 4.5–5.8 and temperature 85–95°C until the viscosity reaches 18–28 seconds.

[0025] Preferably, the reactor includes a prepolymerization reaction unit, comprising a reactor equipped with stirring, temperature control, and pH online monitoring devices; a post-mixing unit, comprising a high-speed dispersion device connected to the reactor; a raw material supply unit, for quantitatively supplying formaldehyde, urea, modified gelatin, and nano-copper-doped manganese dioxide to the reactor and the post-mixing unit; and a control system, for automatically controlling the feeding, temperature, pH, and mixing parameters of the reaction process.

[0026] Preferably, the application of a modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive in the preparation of engineered wood panels.

[0027] Preferably, it is manufactured through gluing, laying, and hot pressing processes; the hot pressing process parameters are: temperature 110~200℃, pressure 1.0~2.0 MPa, time 0.3~1.2 min / mm board thickness; the formaldehyde emission of the artificial board is ≤0.025 mg / m³.

[0028] The beneficial effects of this invention are:

[0029] Through the three-level synergistic effect of weak acid starting process source control, modified gelatin in-situ capture and nano-catalyst oxidation conversion, formaldehyde is inhibited and eliminated from the source to the process in an all-round way. The formaldehyde release of the resulting artificial board is stable, which not only meets but exceeds the national ENF level, but also meets the world's most stringent environmental protection requirements, and solves the technical bottleneck that traditional urea-formaldehyde glue is difficult to stably reach the ENF level.

[0030] Bio-based enzymatically modified gelatin is used as a highly efficient formaldehyde scavenger and reinforcing agent, replacing or partially replacing traditional chemical additives such as melamine. The raw materials are renewable, non-toxic, and biodegradable, reducing the environmental impact throughout the product's lifecycle. The introduction of modified gelatin not only captures formaldehyde, but its active groups also actively participate in the cross-linking network, enhancing the cohesiveness of the adhesive layer and its interfacial bonding with wood. Formic acid generated by the nano-catalyst promotes deep curing of the resin.

[0031] This invention creatively combines two functional materials: enzymatically hydrolyzed gelatin and copper-doped manganese dioxide nanoparticles. The former is responsible for chemical adsorption and structural enhancement, while the latter is responsible for catalytic oxidation and promoting curing. The complementary functions and synergistic effects are achieved by employing a weak acid initiation and segmented temperature-controlled synthesis process, which cleverly balances the reaction rate and molecular structure. This reduces free formaldehyde while constructing a more rational polymer network, laying the foundation for high performance. Detailed Implementation

[0032] The present invention will be further described below with reference to embodiments.

[0033] Example 1: A method for preparing modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive, comprising the following steps:

[0034] Step 1: Prepare modified gelatin;

[0035] Weigh 100g of gelatin (bone glue, Brookfield viscosity 150mPa·s), dissolve it in 900g of deionized water at 50℃ to prepare a 10% solution, add 2.0g of alkaline protease (Novozymes Alcalase 2.4L, enzyme activity 2.4AU / g), and enzymatically hydrolyze it at pH 8.0 and 50℃ for 90 minutes.

[0036] The solution was then heated to 85°C and held for 15 minutes to inactivate the enzyme. Subsequently, the solution was spray-dried (inlet air temperature 175°C, outlet air temperature 85°C) to obtain modified gelatin powder with an average molecular weight of approximately 15 kDa.

[0037] Step 2: Prepare copper-doped manganese dioxide nanoparticles;

[0038] Dissolve 0.632 g of potassium permanganate in 40 mL of deionized water to obtain solution A;

[0039] Dissolve 1.014 g of manganese sulfate monohydrate and 0.148 g of copper nitrate trihydrate together in 20 mL of deionized water to obtain solution B;

[0040] Under magnetic stirring, solution B was added dropwise to solution A within 10 minutes. After stirring for another 30 minutes, the mixture was transferred to a 100 mL polytetrafluoroethylene-lined reactor and hydrothermally reacted at 150 °C for 18 hours.

[0041] After centrifugation, water washing, and alcohol washing, the product was dried at 60°C for 12 hours and then ground to obtain nano-manganese dioxide powder with a copper doping content of approximately 5 mol%.

[0042] Step 3: Prepare urea-formaldehyde resin prepolymer;

[0043] 324 g of a 37% formaldehyde solution (F1, 40% of the total amount of formaldehyde) was added to a 2-liter glass reactor equipped with an anchor stirrer, condenser, thermometer and pH electrode (Mettler-Toledo InPro3253i).

[0044] Adjust the pH to 8.1 with a 20% sodium hydroxide solution, add 120g of urea (U1, 35% of the total amount of urea), heat to 90℃ at a uniform rate over 40 minutes, and keep at 90℃ for 30 minutes. Then adjust the pH of the system to 5.1 with a 10% formic acid solution.

[0045] Add 85.7 g of urea (U2, 25% of the total amount of urea) and 15 g of the modified gelatin powder prepared in the first step, maintain the temperature at 89℃±1℃ for reaction, and monitor the viscosity using an online viscometer (Bolefe DV3T, SC4-21 rotor). When the viscosity reaches 14 seconds (corresponding to about 15 mPa·s, 25℃), proceed to the next step.

[0046] Quickly add 486 g of formaldehyde solution with a mass fraction of 37% (F2, 60% of the total mass of formaldehyde) and 68.6 g of urea (U3, 20% of the total mass of urea), control the system temperature at 93℃±1℃, and continue the reaction until the viscosity reaches 21 seconds.

[0047] The pH was then adjusted to 7.9 using a 20% sodium hydroxide solution. 68.6 g of urea (U4, 20% of the total urea mass) was added, the temperature was lowered to 70°C, and the reaction was maintained at this temperature for 30 minutes. Finally, the mixture was cooled to 35°C and discharged to obtain a urea-formaldehyde resin prepolymer with a solid content of approximately 55%.

[0048] Step 4: Prepare the finished adhesive;

[0049] Take 1000g of the urea-formaldehyde resin prepolymer obtained in the third step and place it in a high-speed disperser (Shanghai Weite, speed adjustable). While stirring at 500rpm, add 5g of nano-copper-doped manganese dioxide powder obtained in the second step and 1.5g of ammonium chloride (as a curing accelerator).

[0050] Then increase the speed to 1500 rpm and continue stirring for 30 minutes until evenly dispersed to obtain the urea-formaldehyde resin of this embodiment.

[0051] In the process of application, the adhesive was used to prepare three-layer poplar plywood with a veneer thickness of 1.5 mm and an application rate (single side) of 120 g / m². The adhesive was then aged for 15 minutes after application.

[0052] After assembly, the blanks are fed into a hot press. The hot pressing process is as follows: hot pressing temperature 120℃, unit pressure 1.2MPa, and hot pressing time 4.5 minutes (i.e., 3min / mm plate thickness).

[0053] After hot pressing, the boards are cooled, cut, and cured before performance testing. The test results show that the dry bonding strength of the plywood is 0.82 MPa and the formaldehyde emission is 0.023 mg / m³, meeting the ENF standard.

[0054] Example 2: Based on Example 1, a preparation system and process with precise online monitoring and optimization are added.

[0055] Based on Example 1, this embodiment introduces a preparation system with precise online monitoring and feedback control, and modifies the catalyst.

[0056] Including the following improvements:

[0057] Firstly, in the preparation of copper-doped manganese dioxide nanoparticles, 0.1 g of cetyltrimethylammonium bromide was added as a structure-directing agent in solution B. The hydrothermal reaction conditions were changed to 160℃ for 24 hours, resulting in a catalyst with a nanowire morphology and a larger specific surface area. + / (Cu + +Cu² + The ratio, as determined by XPS, is approximately 0.35.

[0058] Secondly, a dedicated production system is adopted. The core of this system is a 50-liter jacketed stainless steel reactor, equipped with: a high-precision pH control subsystem, an online viscosity and temperature integrated monitoring module, and a segmented temperature control module. The high-precision pH control subsystem uses a Mettler Toledo InPro4800i smart electrode linked with two metering pumps (KNFLab, Germany), controlled by a Siemens S7-1200 PLC, which can realize dynamic closed-loop control of pH value during the reaction process with an accuracy of ±0.05. The online viscosity and temperature integrated monitoring module is equipped with a Hydromotion VISCOpro1600 online viscometer and a Pt100 platinum resistance temperature sensor, and the data is uploaded to the control system in real time. The segmented temperature control module is connected to three independent high-precision circulating oil baths (Huber, Germany), which are preset with four program segments of 90℃, 89℃, 93℃ and 70℃, respectively. The PLC automatically switches according to the process steps, with a temperature control accuracy of ±0.5℃.

[0059] The preparation process parameters were optimized: the reaction temperature of the weak acid polycondensation stage (pH 5.1) was precisely controlled at 89.0℃, and the target viscosity was set at 15 seconds; the temperature of the secondary polycondensation stage was precisely controlled at 93.0℃, and the target viscosity was set at 22 seconds; the proportions of other materials were the same as in Example 1.

[0060] During operation, the automated system ensures extremely consistent reaction conditions. In the preparation of the finished adhesive, a vacuum degassing device is used in the high-speed dispersion stage to ensure bubble-free dispersion of the nanomaterials. In application, it is used to prepare 18mm thick particleboard with an adhesive application rate of 11% (solid adhesive / oven-dry particleboard). Isocyanate is used as a reinforcing agent (added at 1% of the adhesive solids). The hot-pressing process employs a two-stage pressurization: first, preheating at 1.5MPa and 130℃ for 1 minute; then pressing at 1.8MPa and 155℃ for 6.3 minutes; finally, depressurizing to 0.8MPa and holding the pressure for 1 minute. The resulting particleboard has an internal bond strength of 0.78MPa, a formaldehyde release of only 0.019mg / m³, and batch-to-batch variation of less than 5%, demonstrating excellent stability.

[0061] Example 3: Based on Example 1, a composite fiber reinforcement system and a high-temperature rapid curing process are added.

[0062] Based on Example 1, this embodiment introduces a composite fiber reinforcement system and adjusts the formula and process for high-temperature rapid curing.

[0063] In the final adhesive formulation stage, in addition to adding 5 grams of nano-copper doped manganese dioxide and 1.5 grams of ammonium chloride, 3 grams of cellulose nanofibers (CNF, solid content 2%) with a length of 1 mm and 2 grams of ultrafine aluminosilicate fibers (average diameter 5 μm, aspect ratio of about 50) surface-treated with silane coupling agent (KH-550) were added. These fibers were dispersed with the adhesive solution at 1500 rpm for 30 minutes to form a micro-reinforcing network.

[0064] This adhesive is designed for high-strength plywood requiring rapid production. The hot-pressing process employs a high-temperature, short-time strategy: the hot-pressing temperature is set at 185°C, the unit pressure is 1.6 MPa, and the hot-pressing time is shortened to 2.1 minutes (i.e., 1.4 min / mm board thickness, suitable for 1.5mm veneer three-layer boards). The extremely high hot-pressing temperature causes the catalytic activity of nano-copper doped manganese dioxide to reach its peak in a very short time, while the composite fiber network can effectively inhibit adhesive layer cracking and maintain dimensional stability under rapid heating and pressure.

[0065] During the process, due to the extremely fast curing speed, the post-application aging time is more strictly controlled, shortened to 8 minutes. Plywood produced using this method achieves a bond strength of 0.95 MPa and a formaldehyde emission of 0.021 mg / m³. Furthermore, after a boiling water resistance test (28 hours), the plywood retained 75% of its strength, demonstrating excellent durability.

[0066] The above working principles can be summarized as follows:

[0067] The working principle of the urea-formaldehyde resin of this invention is based on a three-level synergistic regulation mechanism. First, in the synthesis stage, the weak acid initiation process (pH 5.1) promotes the formation of more stable methylene and ether bonds, thereby reducing the content of easily hydrolyzed hydroxymethyl groups from the molecular structure and reducing the potential risk of formaldehyde release.

[0068] Secondly, in adhesive systems, enzymatically modified gelatin, due to its rich content of amino and carboxyl groups and other active groups, can "capture" free formaldehyde diffused from the wood surface and inside the adhesive layer in situ through Schiff base reaction and hydrogen bonding adsorption after application and in the early stage of hot pressing.

[0069] Finally, in the core stage of hot-press curing, the nano-copper-doped manganese dioxide dispersed in the adhesive layer plays a crucial role: its abundant oxygen vacancies and the mixed valence state of copper, driven by thermal energy, efficiently catalyze the reaction of residual and previously weakly adsorbed formaldehyde with oxygen in the air, oxidizing it to formic acid. The newly generated formic acid immediately lowers the local pH of the adhesive layer, feeding back and accelerating the acidic curing condensation reaction of the urea-formaldehyde resin itself, forming a more dense and cross-linked cured network;

[0070] This process of capture, oxidation, and acid-catalyzed self-reinforcement forms a virtuous cycle, which not only completely eliminates formaldehyde but also simultaneously improves the mechanical strength and water resistance of the final adhesive joint. The online monitoring system in Example 2 ensures the precise repeatability of this chemical process, while the composite fiber in Example 3 physically enhances the toughness and thermal shock resistance of the adhesive layer, enabling this synergistic mechanism to remain stable under more demanding process conditions.

[0071] Based on Example 1 and another example (Example 2 or 3), the scope of protection of the present invention is not limited to specific parameters and materials. For example, the protease can also be a neutral protease or a complex protease; the carrier of the nanocatalyst can also be based on manganese dioxide, combined with semiconductor materials such as titanium dioxide or zinc oxide to enhance the photocatalytic auxiliary effect.

[0072] The fiber reinforcement system can also be made of aramid pulp or carbon nanotubes. All urea-formaldehyde resin adhesives and their products that adopt the triple synergistic technology concept of "weak acid starting synthesis process", "enzymatic gelatin modification" and "nano copper-based catalyst oxidation" of this invention, and obtain them by adjusting the raw material ratio, process parameters or introducing auxiliary functional materials, fall within the scope of protection claimed in the claims of this invention.

[0073]

[0074] Key parameters and performance of the examples and comparative examples

[0075] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive, characterized in that, The product is made from the following raw materials in parts by weight: 100 parts urea-formaldehyde resin prepolymer; 8-25 parts modified gelatin; 0.5-1.5 parts nano-copper-doped manganese dioxide; the modified gelatin is gelatin treated with protease hydrolysis, with an average molecular weight of 3,000-60,000 Da; the nano-copper-doped manganese dioxide is a mesoporous material with a copper doping content of 3-10 mol%; after the adhesive is cured by hot pressing, the formaldehyde release of the prepared artificial board is ≤0.025 mg / m³, and the dry bonding strength is ≥0.80 MPa.

2. The modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive according to claim 1, characterized in that, The preparation method of modified gelatin includes the following steps: Step 1: Dissolve gelatin in deionized water to prepare a solution with a mass concentration of 8% to 20%. Step 2: Add protease and hydrolyze at 40–60°C and pH 6.0–9.0 for 0.5–3 hours. The amount of protease added is 0.05%–8% of the dry weight of gelatin. Step 3: After enzymatic hydrolysis, heat to 75-85℃ and maintain for 10-30 minutes to inactivate the enzyme, then dry to obtain powder.

3. The modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive according to claim 1, characterized in that: The preparation method of copper-doped manganese dioxide nanoparticles is a hydrothermal method, which includes the following steps: Step 1: Prepare an aqueous solution of potassium permanganate as an oxidizing agent solution; Step 2: Prepare a mixed aqueous solution containing divalent manganese salt and divalent copper salt as a reducing agent solution; Step 3: Add the reducing agent solution dropwise to the oxidizing agent solution to react and obtain the precursor mixture; Step four: The precursor mixture is subjected to a hydrothermal reaction, and the reaction product is washed and dried to obtain nano-copper-doped manganese dioxide.

4. The modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive according to claim 1, characterized in that: Urea-formaldehyde resin prepolymer is prepared by a weak acid-initiated synthesis process, which includes initiating a polycondensation reaction at a pH of 4.5–5.8 and adding urea and formaldehyde in stages during the reaction.

5. A method for preparing modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive, characterized in that, The modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive according to claims 1-4 are comprising the following steps: Step 1: Prepare urea-formaldehyde resin prepolymer using a weak acid-initiated synthesis process, specifically as follows: Add the first portion of formaldehyde, adjust the pH to alkaline, add the first portion of urea, and initiate the initial hydroxymethylation reaction; Adjust the pH of the system to 4.5–5.8, add the second part of urea and some modified gelatin, and carry out a weak acid polycondensation reaction; Add the remaining formaldehyde and the third part of urea, and continue to polymerize to the target viscosity; Adjust the pH to alkaline, add the fourth part of urea for post-stabilization treatment, and then cool down before discharging. Step 2: Mix the urea-formaldehyde resin prepolymer obtained in Step 1 with the remaining modified gelatin, nano-copper doped manganese dioxide, and optional curing accelerator to obtain urea-formaldehyde adhesive.

6. The method for preparing modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive according to claim 5, characterized in that: In step one, the reaction temperature is controlled at 85-98℃, and the weak acid polycondensation reaction is carried out until the viscosity is 12-18 seconds. According to step one, the reaction is carried out at pH 4.5–5.8 and temperature 85–95°C until the viscosity reaches 18–28 seconds.

7. A dedicated production system for the preparation method of modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive according to claim 6, characterized in that: It includes a prepolymerization reaction unit, including a reactor equipped with stirring, temperature control and pH online monitoring devices; a post-mixing unit, including a high-speed dispersion device connected to the reactor; a raw material supply unit, for quantitatively supplying formaldehyde, urea, modified gelatin and nano-copper doped manganese dioxide to the reactor and the post-mixing unit; and a control system, for automatically controlling the feeding, temperature, pH and mixing parameters of the reaction process.

8. The application of the modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive according to claims 1 to 4 in the preparation of artificial boards.

9. A type of engineered wood panel, characterized in that, It is made by using a modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive as described in any one of claims 1 to 4, or by the preparation method of a modified gelatin and copper-doped manganese dioxide low-formaldehyde urea-formaldehyde adhesive as described in any one of claims 5 to 6, through a process of applying adhesive, laying, and hot pressing; the hot pressing process parameters are: temperature 110 to 200℃, pressure 1.0 to 2.0 MPa, time 0.3 to 1.2 min / mm board thickness; the formaldehyde release of the artificial board is ≤0.025mg / m³.

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