Biomass formaldehyde-free resin adhesive film as well as preparation method and application thereof

Abstract

The invention discloses a biomass formaldehyde-free resin adhesive film as well as a preparation method and application thereof, and belongs to the technical field of wood adhesives. The adhesive film is prepared by taking sodium carboxymethyl cellulose and tris (2-aminoethyl) amine as raw materials, mixing, heating, reacting and curing to prepare a film, and soaking in a tannic acid solution. When the adhesive film is applied to plywood bonding, wood veneers can be activated through an oxidizing agent solution, then the adhesive film and the activated veneers are assembled, and hot-pressing curing is conducted after pre-pressing. The raw materials of the adhesive film are green and non-toxic, formaldehyde release is avoided, the preparation process is simple, and the prepared plywood is high in bonding strength, good in water resistance and easy to store and transport and has good application prospects in the field of artificial boards.

Description

Technical Field

[0001] This invention relates to the field of wood adhesive technology, specifically to a biomass formaldehyde-free resin film, its preparation method, and its application. Background Technology

[0002] Engineered wood products are an important area for the efficient utilization of wood resources and are widely used in furniture, decoration and other industries. In engineered wood product production, adhesives are the key materials that connect wood units and determine the performance of the board. Traditional formaldehyde-based adhesives (urea-formaldehyde resin, phenolic resin, etc.) have long dominated the market due to their low raw material costs and high initial bond strength. However, with the upgrading of environmental protection requirements and the iteration of production needs, their inherent drawbacks have become a significant bottleneck for the development of the industry.

[0003] From an environmental and safety perspective, the synthesis of traditional formaldehyde-based adhesives relies on formaldehyde monomers, and the reaction cannot be completely converted, resulting in the continuous release of formaldehyde into the manufactured engineered wood products during use. Excessive indoor formaldehyde concentrations can irritate the respiratory and nervous systems, and long-term exposure may cause health problems such as allergies and weakened immune function, making it one of the main sources of indoor air pollution. Although the industry has reduced release through methods such as adding formaldehyde scavengers and optimizing reaction ratios, achieving "zero formaldehyde" remains difficult, and the additional processing steps increase production costs, weakening product competitiveness.

[0004] From the perspective of production and application convenience, traditional formaldehyde-based adhesives are mostly liquid, which presents key problems such as short shelf life and inconvenient transportation. Liquid adhesives are easily affected by temperature and humidity, resulting in stratification and deterioration. They typically have a shelf life of only 1-3 months and require low-temperature and light-proof storage, increasing warehousing costs. There is also a risk of leakage during transportation, requiring special sealed containers, making logistics costs significantly higher than for solid materials. Furthermore, liquid adhesives require on-site mixing, demanding strict requirements on mixing ratio accuracy and application thickness. Improper operation can easily lead to uneven bonding of boards, affecting product qualification rates.

[0005] From a process complexity perspective, the synthesis of traditional formaldehyde-based adhesives requires strict control of high-temperature and high-pressure reaction conditions, relies on corrosion-resistant specialized equipment, and has a long reaction cycle, high energy consumption, and large equipment investment, making it difficult for small and medium-sized wood-based panel enterprises to afford. While some formaldehyde-free adhesives (such as polyurethane adhesives and isocyanate adhesives) solve environmental protection issues, their raw materials rely on petrochemical products, resulting in high costs. Furthermore, their curing is sensitive to humidity, requiring complex curing equipment that is not compatible with the existing production lines of most enterprises.

[0006] Biomass-based formaldehyde-free adhesives have been a research hotspot in recent years, but they still have significant shortcomings: most biomass raw materials (such as soybean protein and starch) require graft copolymerization and cross-linking modification to improve bonding strength, and the modification process requires the use of chemical reagents and harsh reaction conditions; although some adhesives are environmentally friendly, they must be used immediately after production and cannot be stored for long periods, and they are easily damaged during transportation, making it difficult to achieve large-scale supply. In addition, existing biomass adhesives generally have poor water resistance, requiring precise control of temperature and time during hot pressing, resulting in low adaptability and failing to meet the hot water resistance requirements of plywood.

[0007] In summary, the engineered wood products industry urgently needs to develop an adhesive solution that is environmentally friendly, has a simple process, and is convenient to store and transport. Summary of the Invention

[0008] To address the issues of poor water resistance and formaldehyde release in plywood adhesives, the present invention aims to provide a method for preparing a biomass formaldehyde-free resin film, specifically comprising the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare sodium carboxymethyl cellulose solution.

[0009] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a tri(2-aminoethyl)amine solution and adjust the pH.

[0010] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution. Pour the mixed solution into a mold for film laying, heat to react and cure to obtain a composite film.

[0011] (4) Soak the composite film in tannic acid solution for 2-6 hours to obtain biomass formaldehyde-free resin film.

[0012] Preferably, the mass percentage concentration of sodium carboxymethyl cellulose solution in step (1) of the present invention is 1%-5%.

[0013] Preferably, the mass percentage concentration of the tri(2-aminoethyl)amine solution in step (2) of the present invention is 50%.

[0014] Preferably, in step (2) of the present invention, adjusting the pH specifically involves adjusting the pH to 5-6 using hydrochloric acid with a concentration of 12 mol / L.

[0015] Preferably, in step (3) of the present invention, the volume ratio of sodium carboxymethyl cellulose solution and tris(2-aminoethyl)amine solution is 1:1-4:1.

[0016] Preferably, the heating reaction and curing conditions in step (3) of the present invention are: heating reaction at 50-80℃ for 6-12h.

[0017] Preferably, in step (4) of the present invention, the mass percentage concentration of the tannic acid solution is 10%-30%, and the pH of the tannic acid solution is 6-7.

[0018] Another object of the present invention is to provide a biomass formaldehyde-free resin film.

[0019] Another object of the present invention is to provide an application of biomass formaldehyde-free resin film in plywood bonding, specifically including the following steps: (1) Activation of wood surface: Prepare an aqueous solution of oxidant, apply the aqueous solution of oxidant to the surface of wood veneer for activation, and obtain activated wood veneer.

[0020] (2) Pre-pressing: The formaldehyde-free biomass resin film is assembled with the activated wood veneer and pre-pressed to obtain a pre-pressed sample.

[0021] (3) Hot pressing curing: The pre-pressed sample is hot-pressed and cured to obtain plywood.

[0022] Preferably, the oxidant in step (1) of the present invention is any one of sodium periodate, potassium permanganate, hydrogen peroxide, and peracetic acid.

[0023] Preferably, the mass percentage concentration of the oxidant aqueous solution in step (1) of the present invention is 8%.

[0024] Preferably, the wood veneer in step (1) of the present invention is any one of poplar, eucalyptus, birch and beech.

[0025] Preferably, the pre-compression condition in step (2) of the present invention is: pre-compression for 0.5 h at a pressure of 1 MPa at room temperature.

[0026] Preferably, the hot-press curing conditions in step (3) of the present invention are: hot-press curing for 5-8 minutes under the conditions of hot-pressing pressure of 1-2 MPa and hot-pressing temperature of 140-180℃.

[0027] Unless otherwise specified, all reagents used in this invention are commercially available analytical grade reagents.

[0028] Compared with the prior art, the present invention provides a biomass formaldehyde-free resin film, its preparation method and application, which has the following beneficial effects: (1) The resin film prepared by the present invention has no formaldehyde release, which meets the requirements of environmental protection regulations and green home furnishing.

[0029] (2) The preparation method of the present invention has mild reaction conditions, simple steps, no complex and harsh conditions such as high temperature and high pressure, only conventional equipment is required, no complicated devices are needed, which significantly reduces the technical threshold and equipment investment for production, and can be mass-produced.

[0030] (3) The solid resin film prepared by the present invention is not easily affected by temperature and humidity, and its storage period is much longer than that of traditional liquid adhesives; there is no risk of leakage, and it can be stacked and packaged, which reduces transportation costs.

[0031] (4) The plywood prepared using the resin film of the present invention exhibits excellent hot water resistance and bonding strength, fully meeting the requirements of relevant national standards (such as GB / T 17657-2022) for bonding strength and water resistance of artificial boards. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the biomass formaldehyde-free resin film of the present invention in plywood bonding.

[0033] Figure 2 This is a schematic diagram of the molecular structure of the composite film of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 1%.

[0036] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0037] (3) A mixed solution was obtained by mixing sodium carboxymethyl cellulose solution and tris(2-aminoethyl)amine solution, with a volume ratio of sodium carboxymethyl cellulose solution to tris(2-aminoethyl)amine solution of 1:1; the mixed solution was poured into a mold for film laying and placed in an oven, and heated at 60°C for 12 hours to obtain a composite film (the molecular structure of the composite film is as follows). Figure 2 (As shown).

[0038] (4) Soak the composite film in a tannic acid solution with a mass percentage concentration of 20% for 2 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness of 0.2 mm).

[0039] The biomass formaldehyde-free resin film prepared above was used for plywood bonding, and the bonding method was as follows: Figure 1 As shown, the specific steps are as follows: (1) Activation of wood surface: Prepare an 8% sodium periodate aqueous solution by mass percentage, and apply the sodium periodate aqueous solution to the surface of poplar veneer for activation to obtain activated poplar veneer.

[0040] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated poplar veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain the pre-compressed sample.

[0041] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 8 minutes under a hot pressing pressure of 2MPa and a hot pressing temperature of 160℃ to obtain plywood.

[0042] Example 2 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 3%.

[0043] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5.5 with 12 mol / L hydrochloric acid.

[0044] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 2:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 60°C for 12 hours to obtain a composite film.

[0045] (4) Soak the composite film in a tannic acid solution with a mass percentage concentration of 20% for 2 hours (the pH of the tannic acid solution can be adjusted to 6.5 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness of 0.4 mm).

[0046] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an 8% potassium permanganate aqueous solution by mass percentage, and apply the potassium permanganate aqueous solution to the surface of poplar veneer for activation, thereby obtaining activated poplar veneer.

[0047] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated poplar veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain the pre-compressed sample.

[0048] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 6 minutes under a hot pressing pressure of 2MPa and a hot pressing temperature of 180℃ to obtain plywood.

[0049] Example 3 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 3%.

[0050] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 6 with 12 mol / L hydrochloric acid.

[0051] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 3:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 60°C for 12 hours to obtain a composite film.

[0052] (4) Soak the composite film in a tannic acid solution with a mass percentage concentration of 20% for 2 hours (the pH of the tannic acid solution can be adjusted to 7 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness of 0.6 mm).

[0053] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an 8% hydrogen peroxide aqueous solution by mass percentage, and apply the hydrogen peroxide aqueous solution to the surface of poplar veneer for activation to obtain activated poplar veneer.

[0054] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated poplar veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain the pre-compressed sample.

[0055] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 8 minutes under a hot pressing pressure of 2MPa and a hot pressing temperature of 140℃ to obtain plywood.

[0056] Example 4 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 5%.

[0057] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0058] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 4:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 60°C for 12 hours to obtain a composite film.

[0059] (4) Soak the composite film in a 10% tannic acid solution for 4 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness 0.85 mm).

[0060] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an 8% peracetic acid aqueous solution and apply the peracetic acid aqueous solution to the surface of poplar veneer for activation to obtain activated poplar veneer.

[0061] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated poplar veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain the pre-compressed sample.

[0062] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 6 minutes under the conditions of hot pressing pressure of 1.5MPa and hot pressing temperature of 160℃ to obtain plywood.

[0063] Example 5 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 2%.

[0064] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0065] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 1:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 80°C for 8 hours to obtain a composite film.

[0066] (4) Soak the composite film in a 30% tannic acid solution for 6 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness 0.4 mm).

[0067] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an 8% sodium periodate aqueous solution by mass percentage, and apply the sodium periodate aqueous solution to the surface of eucalyptus veneer for activation to obtain activated eucalyptus veneer.

[0068] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated eucalyptus veneer were assembled and pre-compressed at room temperature and 1 MPa for 0.5 h to obtain the pre-compressed sample.

[0069] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 7 minutes under a hot pressing pressure of 1 MPa and a hot pressing temperature of 180℃ to obtain plywood.

[0070] Example 6 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 2%.

[0071] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0072] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 2:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 50°C for 10 hours to obtain a composite film.

[0073] (4) Soak the composite film in a 30% tannic acid solution for 2 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness 0.8 mm).

[0074] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an 8% sodium periodate aqueous solution by mass percentage, and apply the sodium periodate aqueous solution to the surface of beech veneer for activation to obtain activated beech veneer.

[0075] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated beech veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain the pre-compressed sample.

[0076] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 6 minutes under a hot pressing pressure of 1MPa and a hot pressing temperature of 160℃ to obtain plywood.

[0077] Example 7 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 2%.

[0078] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0079] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 3:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 60°C for 8 hours to obtain a composite film.

[0080] (4) Soak the composite film in a tannic acid solution with a mass percentage concentration of 20% for 2 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness of 0.4 mm).

[0081] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an aqueous solution of sodium periodate with a mass percentage concentration of 8%, and apply the sodium periodate aqueous solution to the surface of birch veneer for activation to obtain activated birch veneer.

[0082] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated birch veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain a pre-compressed sample.

[0083] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 8 minutes under a hot pressing pressure of 2MPa and a hot pressing temperature of 140℃ to obtain plywood.

[0084] Example 8 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 2%.

[0085] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0086] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 4:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 50°C for 6 hours to obtain a composite film.

[0087] (4) Soak the composite film in a tannic acid solution with a mass percentage concentration of 20% for 2 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness of 0.6 mm).

[0088] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an 8% sodium periodate aqueous solution by mass percentage, and apply the sodium periodate aqueous solution to the surface of the wood veneer for activation to obtain activated wood veneer.

[0089] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated wood veneer were assembled and pre-compressed at room temperature and 1 MPa for 0.5 h to obtain the pre-compressed sample.

[0090] (3) Hot pressing curing: The pre-pressed sample is hot-pressed and cured for 5 minutes under a hot pressing pressure of 2MPa and a hot pressing temperature of 160℃ to obtain plywood.

[0091] Comparative Example 1 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 1%.

[0092] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0093] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 4:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 60°C for 12 hours to obtain a composite film.

[0094] (4) Soak the composite film in a tannic acid solution with a mass percentage concentration of 20% for 2 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness of 0.2 mm).

[0095] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Pre-compression: Formaldehyde-free biomass resin film and poplar veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain pre-compressed sample.

[0096] (2) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 8 minutes under a hot pressing pressure of 2MPa and a hot pressing temperature of 160℃ to obtain plywood.

[0097] Comparative Example 2 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 1%.

[0098] (2) Dissolve tri(2-aminoethyl)amine in water to prepare a 50% tri(2-aminoethyl)amine solution, and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0099] (3) Mix sodium carboxymethyl cellulose solution and tri(2-aminoethyl)amine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to tri(2-aminoethyl)amine solution of 0.5:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 60°C for 12 hours to obtain a composite film.

[0100] (4) Soak the composite film in water for 2 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness 0.2 mm).

[0101] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an 8% sodium periodate aqueous solution by mass percentage, and apply the sodium periodate aqueous solution to the surface of poplar veneer for activation to obtain activated poplar veneer.

[0102] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated poplar veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain the pre-compressed sample.

[0103] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 8 minutes under a hot pressing pressure of 2MPa and a hot pressing temperature of 160℃ to obtain plywood.

[0104] Comparative Example 3 A method for preparing a biomass formaldehyde-free resin film specifically includes the following steps: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution with a mass percentage concentration of 1%.

[0105] (2) Dissolve ethylenediamine in water to prepare a 50% ethylenediamine solution and adjust the pH to 5 with 12 mol / L hydrochloric acid.

[0106] (3) Mix sodium carboxymethyl cellulose solution and ethylenediamine solution to obtain a mixed solution with a volume ratio of sodium carboxymethyl cellulose solution to ethylenediamine solution of 5:1; pour the mixed solution into a mold for film laying and place it in an oven, and heat it at 60°C for 12 hours to obtain a composite film.

[0107] (4) Soak the composite film in a tannic acid solution with a mass percentage concentration of 20% for 2 hours (the pH of the tannic acid solution can be adjusted to 6 by NaOH) to obtain a biomass formaldehyde-free resin film (thickness of 0.2 mm).

[0108] The biomass formaldehyde-free resin film prepared above is used for plywood bonding. The specific steps are as follows: (1) Activation of wood surface: Prepare an 8% sodium periodate aqueous solution by mass percentage, and apply the sodium periodate aqueous solution to the surface of poplar veneer for activation to obtain activated poplar veneer.

[0109] (2) Pre-compression: The formaldehyde-free biomass resin film and the activated poplar veneer were assembled and pre-compressed for 0.5 h at room temperature and 1 MPa pressure to obtain the pre-compressed sample.

[0110] (3) Hot pressing curing: The pre-pressed sample was hot-pressed and cured for 8 minutes under a hot pressing pressure of 2MPa and a hot pressing temperature of 160℃ to obtain plywood.

[0111] The plywood prepared in Examples 1-8 and Comparative Examples 1-3 were subjected to physical and mechanical property tests on a universal testing machine according to the requirements of the national standard GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The main tests were on the bonding strength and water resistance of the plywood. The specific steps are as follows: The plywood was cut into 24 specimens and divided into 3 equal parts for testing. The dry strength, 3-hour warm water (63℃) wet strength (the specimen was immersed in 63℃ water for 3 hours), and 3-hour boiling water wet strength (the specimen was immersed in boiling water for 3 hours) were tested. The test results are shown in Table 1.

[0112] Table 1 Note: / indicates that the interface bonding has failed and the wood board has fallen off the adhesive film.

[0113] As shown in Table 1, the dry bonding strength of Examples 1-8 of this invention all exceed 2.30 MPa, with the highest reaching 3.41 MPa (Example 5), which is much higher than that of Comparative Examples 1-3, and no peeling occurred. This indicates that the adhesive film prepared by this invention has excellent cohesive strength and interfacial bonding strength with wood, and can meet the requirements for use in engineered wood products. The plywood prepared in Examples 1-8 of this invention maintains high strength in both hot water and boiling water, fully meeting the strength requirements of Class II plywood (water-resistant plywood) in the national standard GB / T 17657-2022. This indicates that the adhesive layer has excellent resistance to damp heat aging and durability. Furthermore, the method of this invention has a wide process window and good operability, and is suitable for different types of wood (poplar, eucalyptus, beech, birch, etc.) and different production conditions.

[0114] The high strength and water resistance of the adhesive film of this invention originate from the unique cross-linking network design. The carboxyl groups of sodium carboxymethyl cellulose and the primary amino groups of tris(2-aminoethyl)amine form amide bonds through electrostatic interaction and heating, constructing a preliminary cross-linking network and giving the adhesive film basic strength. The abundant phenolic hydroxyl groups in tannic acid form strong hydrogen bonds with unreacted amino and carboxyl groups in the adhesive film network, and can further undergo Schiff base reaction, significantly increasing the cross-linking density. During hot pressing, tannic acid undergoes oxidative polymerization. Through the synergy of these three factors, a more stable and hydrophobic interpenetrating network structure of the adhesive film is constructed.

[0115] After the wood veneer is activated by an oxidant, the cellulose / hemicellulose on its surface is oxidized to generate a large number of highly active aldehyde groups. During the hot pressing process, these aldehyde groups covalently bond with the abundant active groups (amine groups, phenolic hydroxyl groups of tannic acid, and quinone groups) in the adhesive film to form stable covalent bonds. Furthermore, under the hot pressing conditions, the adhesive film's bulk network is further cured, tannic acid is oxidized and polymerized, and interfacial chemical bonds are generated simultaneously. These reactions promote each other and work synergistically to ultimately construct a continuous and dense three-dimensional cross-linked network from the adhesive film to the wood interface, thereby achieving a bonding strength and durable water resistance far exceeding that of physical adsorption.

[0116] In summary, this invention successfully prepared a high-performance biomass formaldehyde-free adhesive by constructing a basic network using multifunctional tris(2-aminoethyl)amine and sodium carboxymethyl cellulose, followed by secondary reinforcement with natural polyphenolic tannins, and combined with an oxidation activation strategy on the wood surface. Essentially, it constructs a highly cohesive, interfacially bonded, and highly cross-linked adhesive system through the synergistic chemical action of multiple components and steps, achieving high-strength and water-resistant bonding while being environmentally friendly (formaldehyde-free).

[0117] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a biomass formaldehyde-free resin film, characterized in that, Specifically, the following steps are included: (1) Dissolve sodium carboxymethyl cellulose in water to prepare a sodium carboxymethyl cellulose solution; (2) Dissolve tri(2-aminoethyl)amine in water to prepare a tri(2-aminoethyl)amine solution, and adjust the pH. (3) Mix sodium carboxymethyl cellulose solution and tris(2-aminoethyl)amine solution to obtain a mixed solution. Pour the mixed solution into a mold for film laying, heat to react and cure to obtain a composite film. (4) Soak the composite film in tannic acid solution for 2-6 hours to obtain biomass formaldehyde-free resin film.

2. The method for preparing a formaldehyde-free biomass resin film according to claim 1, characterized in that, The mass percentage concentration of the sodium carboxymethyl cellulose solution in step (1) is 1%-5%.

3. The method for preparing a formaldehyde-free biomass resin film according to claim 1, characterized in that, The mass percentage concentration of the tri(2-aminoethyl)amine solution in step (2) is 50%; the pH adjustment specifically involves adjusting the pH to 5-6 with 12 mol / L hydrochloric acid.

4. The method for preparing a formaldehyde-free biomass resin film according to claim 1, characterized in that, In step (3), the volume ratio of sodium carboxymethyl cellulose solution and tris(2-aminoethyl)amine solution in the mixed solution is 1:1-4:1; the heating reaction and curing conditions are: heating reaction at 50-80℃ for 6-12h.

5. The method for preparing a formaldehyde-free biomass resin film according to claim 1, characterized in that, The tannic acid solution in step (4) has a mass percentage concentration of 10%-30% and a pH of 6-7.

6. The biomass formaldehyde-free resin film prepared by the method according to any one of claims 1-5.

7. The application of the biomass formaldehyde-free resin film according to claim 6 in plywood bonding, characterized in that, Specifically, the following steps are included: (1) Activation of wood surface: Prepare an aqueous solution of oxidant, apply the aqueous solution of oxidant to the surface of wood veneer for activation, and obtain activated wood veneer; (2) Pre-pressing: The formaldehyde-free biomass resin film is assembled with the activated wood veneer and pre-pressed to obtain a pre-pressed sample; (3) Hot pressing curing: The pre-pressed sample is hot-pressed and cured to obtain plywood.

8. The application of the biomass formaldehyde-free resin film according to claim 7 in plywood bonding, characterized in that, The oxidant mentioned in step (1) is any one of sodium periodate, potassium permanganate, hydrogen peroxide, and peracetic acid; the mass percentage concentration of the aqueous solution of the oxidant is 8%; and the wood veneer is any one of poplar, eucalyptus, birch, and beech.

9. The application of the biomass formaldehyde-free resin film according to claim 7 in plywood bonding, characterized in that, The pre-compression conditions in step (2) are: pre-compressed for 0.5 h at a pressure of 1 MPa at room temperature.

10. The application of the biomass formaldehyde-free resin film according to claim 7 in plywood bonding, characterized in that, The conditions for hot pressing curing in step (3) are: hot pressing curing for 5-8 minutes under the conditions of hot pressing pressure of 1-2 MPa and hot pressing temperature of 140-180℃.

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