Formaldehyde-free flame-retardant solid wood composite floor and modified lignin-based flame-retardant adhesive

Abstract

This invention provides a formaldehyde-free flame-retardant solid wood composite flooring and a modified lignin-based flame-retardant adhesive. The flame-retardant adhesive comprises 20-30 parts by weight of ethanol lignin, 20-30 parts by weight of hydroxide, 10-20 parts by weight of phytate, 30-60 parts by weight of crosslinking agent, 30-50 parts by weight of high-temperature soybean meal powder, and 0.1-0.2 parts by weight of tackifier. The invention also provides a preparation method. First, amino-rich hydroxide and phytate are grafted onto ethanol lignin to obtain hydroxide / phytate ethanol lignin. Next, the obtained hydroxide / phytate ethanol lignin is mixed with the crosslinking agent and high-temperature soybean meal powder. Finally, the tackifier is added, and the mixture is mechanically stirred to prepare the modified lignin-based flame-retardant adhesive. The flame-retardant adhesive provided by this invention is formaldehyde-free, exhibits excellent flame-retardant properties, good coating performance, good water resistance, and great application potential.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant materials technology, and particularly relates to a formaldehyde-free flame retardant solid wood composite floor and a modified lignin-based flame retardant adhesive. Background Technology

[0002] Lignin is an abundant renewable biomass resource and the second largest natural polymer material, widely found in plant resources such as wood, sorghum, and corn cobs. In biomass structures, lignin has an amorphous structure and a certain degree of viscosity, making it suitable for direct use as an adhesive. In natural plants, lignin acts like an adhesive, distributed around fibers and between fine fibers within the fibers, forming a strong skeletal structure. The char layer formed when lignin gum is heated acts as a condensed phase, isolating oxygen and preventing the diffusion of combustible gases, thus inhibiting thermal decomposition and combustion reactions. However, lignin, when used alone as a flame retardant, suffers from poor flame retardant efficiency.

[0003] Patent CN201811117318 discloses a lignin-based formaldehyde-free adhesive and its preparation method. This lignin-based formaldehyde-free adhesive is not synthesized using formaldehyde as a raw material, significantly reducing the formaldehyde release from engineered wood products pressed with this adhesive, which is beneficial to the environment and human health. However, it does not modify the lignin for flame retardancy. Currently, there are no relevant literature reports on the preparation of flame-retardant adhesives using flame-retardant modified lignin. Summary of the Invention

[0004] One objective of this invention is to provide a method for preparing a modified lignin-based flame-retardant adhesive. First, an amino-rich hydroxide / phytate is grafted onto ethanol lignin to obtain hydroxide / phytate ethanol lignin. Second, the obtained hydroxide / phytate ethanol lignin is mixed with a crosslinking agent and high-temperature soybean meal powder. Finally, a tackifier is added, and the mixture is mechanically stirred to prepare the modified lignin-based flame-retardant adhesive. The specific steps are as follows:

[0005] 1) 20-30 parts by weight of hydroxide and 10-20 parts by weight of phytate are suspended in 100-120 parts by weight of water, ultrasonically dispersed, and then transferred to a reaction vessel. Then 10-15 parts by weight of tetraethyl orthosilicate are added, and the mixture is heated to 45-50°C and reacted for 10-15 hours under mechanical stirring. Then 10-15 parts by weight of 3-aminopropyltriethoxysilane are added, heated to 60-65°C, and kept at that temperature for 2-3 hours to obtain a hydroxide / phytate particle suspension with amino groups on the surface.

[0006] 2) Add 20-30 parts by weight of ethanol lignin to the suspension in step 1), then add 35-55 parts by weight of glyoxal solution to the system, heat to 60-70℃, react for 4-6 hours to obtain hydroxide / phytate lignin suspension. After cooling to room temperature, adjust the pH value to 9.5-10.5 with sodium hydroxide solution, add 30-50 parts by weight of high-temperature soybean meal powder, 30-60 parts by weight of crosslinking agent and 0.1-0.5 parts by weight of thickener, and mechanically stir to obtain modified lignin-based flame retardant adhesive.

[0007] In some embodiments, the hydroxide is one or more of aluminum hydroxide, magnesium hydroxide, and iron hydroxide. During combustion, the hydroxide decomposes upon heating, releasing water vapor that lowers the combustion temperature and dilutes oxygen in the air, thereby slowing down the combustion process. Simultaneously, the metal ions in the hydroxide fill the char layer formed by lignin, stabilizing the char layer. Furthermore, the hydroxide itself has a strong smoke-suppressing effect, working synergistically with lignin to reduce smoke release and improve flame-retardant performance.

[0008] In some embodiments, the phytate is one or more of iron phytate, zinc phytate, and magnesium phytate. The phytate is rich in phosphorus, which plays a catalytic role in carbon formation during combustion, accelerating the formation of the carbon layer.

[0009] In some embodiments, the tetraethyl orthosilicate and 3-aminopropyltriethoxysilane are crosslinked with hydroxide and phytate to obtain hydroxide / phytate with an amino-rich surface.

[0010] In some embodiments, the ethanol lignin is bioethanol lignin. Biomass ethanol lignin is inexpensive and readily available, and has not undergone high temperature, high pressure, or acid and alkali treatment, thus preserving its natural properties well. It has high reactivity. The phenolic hydroxyl groups on the ethanol lignin undergo the Mannich reaction with metal oxides rich in amine groups, branching the amine-rich hydroxide / phytate on the surface onto the lignin, thereby increasing the flame retardant effect of the lignin. At the same time, the ethanol lignin hydroxyl and hydroxymethyl groups undergo dehydration condensation with the hydrogen on the hydroxymethyl group or secondary amine group in the crosslinking agent molecule to form a network structure of ether bonds or phenylamides.

[0011] In some embodiments, the crosslinking agent is a polyamide polyamine epichlorohydrin resin solution with a solid content between 10% and 12.5%. In an alkaline environment, polyamide polyamine epichlorohydrin can crosslink with the hydroxyl and hydroxymethyl groups on lignin to form an ether bond or phenylamide network structure, thereby improving water resistance.

[0012] In some embodiments, the high-temperature soybean meal powder is further activated in an alkaline environment, increasing the number of polar groups. The hydroxyl groups of ethanol lignin interact with the active groups in polyamide polyamine epichlorohydrin resin and the polar groups of soybean meal powder. The cross-linked network structure formed by the reaction can effectively prevent moisture intrusion, improve the water resistance of the adhesive, and thus improve the bonding performance and water resistance of the flame retardant adhesive system.

[0013] In some embodiments, the tackifier is sodium polyacrylate, which further improves the tack of the modified lignin-based flame retardant adhesive and solves the problems of inability to apply adhesive and uneven application during the adhesive application process.

[0014] The modified lignin-based flame-retardant adhesive provided by this invention solves the problems of poor compatibility and poor bonding performance between adhesives and flame retardants caused by the addition of flame retardants. Furthermore, this invention improves the flame-retardant effect of the adhesive by grafting amine-rich hydroxides / phytates onto ethanol lignin, achieving a synergistic effect between the strong smoke suppression of metal ions and the catalytic char formation of lignin by phosphorus. The adhesive used in this invention is formaldehyde-free, and the use of high-temperature soybean meal powder and sodium polyacrylate enhances the bonding and water resistance of the system, enabling the system's impregnation and peel performance to meet the requirements of the national standard for solid wood composite flooring.

[0015] Another objective of this invention is to provide a formaldehyde-free flame-retardant engineered wood flooring and its preparation method. The formaldehyde-free flame-retardant engineered wood flooring includes a paint coating layer, a surface veneer, a flame-retardant adhesive layer, a flame-retardant multi-layer substrate layer, a flame-retardant adhesive layer, and a back panel. The flame-retardant multi-layer substrate layer is composed of eucalyptus veneer and flame-retardant adhesive assembled into a plywood substrate for engineered wood flooring. The preparation method includes the following steps:

[0016] I. Preparation of Modified Lignin-Based Flame-Retardant Adhesives

[0017] 1) Suspend 20-30 parts by weight of hydroxide and 10-20 parts by weight of phytate in 100-120 parts by weight of water, disperse by ultrasonication, and transfer to a reaction vessel. Then add 10-15 parts by weight of tetraethyl orthosilicate and react at 45-50°C for 10-15 hours under mechanical stirring. Then add 10-15 parts by weight of 3-aminopropyltriethoxysilane, heat to 60-65°C, and keep warm for 2-3 hours to obtain a hydroxide / phytate particle suspension with amino groups on the surface.

[0018] 2) Add 20-30 parts by weight of ethanol lignin to the suspension in step 1), then add 20-40 parts by weight of glyoxal solution to the system, heat to 60-70℃, react for 4-6 hours to obtain hydroxide / phytate lignin suspension. After cooling to room temperature, adjust the pH value to 9.5-10.5 with sodium hydroxide solution, add 30-50 parts by weight of high-temperature soybean meal powder, 30-60 parts by weight of crosslinking agent and 0.1-0.5 parts by weight of thickener, and mechanically stir to obtain modified lignin-based flame retardant adhesive.

[0019] II. Preparation of Formaldehyde-Free Flame-Retardant Solid Wood Composite Flooring

[0020] 1) The modified lignin-based flame retardant adhesive prepared in step one is applied to the surface of eucalyptus veneer. The veneer is then assembled in a cross-hatched manner according to the multi-layer plywood used for solid wood composite flooring. After cold pressing and hot pressing, a flame retardant multi-layer substrate layer is formed.

[0021] 2) After the flame-retardant multilayer substrate layer is balanced, the modified lignin-based flame-retardant adhesive prepared in step one is applied. The top surface is bonded to the top board and the bottom surface is bonded to the bottom board. After assembly, the formaldehyde-free flame-retardant solid wood composite flooring is produced through processes such as cold pressing, hot pressing, curing, slicing, sanding, grooving, and painting.

[0022] In some specific embodiments, the single-sided coating amount of the flame-retardant multilayer substrate modified lignin-based flame-retardant adhesive in step two (1) is 110–120 g / m². 2 The process conditions are cold pressing followed by hot pressing. The unit pressure for cold pressing is 0.7±0.1 MPa, and the cold pressing time is 40–50 min. Hot pressing employs a three-stage process, with the first stage using a unit pressure of 0.8–1.0 MPa / m. 2 The hot-pressing time is 15-16 minutes, and the unit pressure of the second stage of hot pressing is 0.3-0.4 MPa / m. 2 The hot-pressing time is 1-2 minutes, and the unit pressure of the third stage of hot pressing is 0.2-0.3 MPa / m. 2 1. Hot pressing time: 1-2 min; 2) In step 2), the coating amount on the surface plate is 100-110 g / m². 2 The unit pressure for cold pressing is 0.7±0.1 MPa, and the cold pressing time is 40–50 min. The unit pressure for hot pressing is 0.7–0.8 MPa / m. 2 Hot pressing time: 300-360 seconds.

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

[0024] 1. This invention creatively uses bioethanol lignin, a renewable resource, as the raw material for adhesives and a flame retardant component, achieving efficient utilization of renewable resources and conforming to the national environmental protection policy under the dual-carbon background.

[0025] 2. This invention grafts amine-rich hydroxide / phytate onto bioethanol lignin. During combustion, the hydroxide stabilizes the lignin char layer and has a strong smoke-suppressing effect, working synergistically with lignin to reduce smoke release. Meanwhile, the phytate is rich in phosphorus, which catalyzes char formation during combustion, accelerating the formation of the char layer and improving the flame retardant effect. This avoids problems such as poor compatibility and poor bonding strength caused by adding flame retardants to adhesives.

[0026] 3. This invention uses polyamide polyamine epichlorohydrin resin as a crosslinking agent, and adds high-temperature soybean meal powder as a reinforcing agent and sodium polyacrylate as a tackifier. This allows the interaction between ethanol lignin and the active groups in polyamide polyamine epichlorohydrin resin and the polar groups in soybean protein to form a crosslinked network structure that can effectively prevent moisture intrusion, improve the water resistance of the adhesive, and thus improve the impregnation and peeling performance of the flame retardant adhesive system.

[0027] 4. The formaldehyde-free flame-retardant solid wood composite flooring obtained by this invention does not release free formaldehyde, thus eliminating formaldehyde release at the source. It also has good impregnation and peeling performance, good water resistance, flame retardant performance reaching B1(C) level, and low smoke emission. Detailed Implementation

[0028] The following detailed description of specific embodiments further illustrates the present invention, and the advantages and features of the present invention will become clearer as a result of the description. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Various modifications, combinations, or refinements can be made to the technical solutions of the present invention without departing from the essence of the present invention, but all such modifications, combinations, or refinements fall within the scope of protection claimed by the present invention.

[0029] Unless otherwise specified, all materials, equipment, and instruments used in the following embodiments are commercially available. In this invention, "parts" refers to parts by weight.

[0030] Example 1

[0031] The first step is to prepare a modified lignin-based flame-retardant adhesive.

[0032] 1) 30 parts by weight of aluminum hydroxide and 20 parts by weight of ferric phytate were suspended in 100 parts by weight of water, ultrasonically dispersed, and then transferred to a reaction vessel. Then 10 parts by weight of tetraethyl orthosilicate were added, and the mixture was heated to 50°C and reacted for 10 hours under mechanical stirring. Then 15 parts by weight of 3-aminopropyltriethoxysilane were added, heated to 65°C, and kept at that temperature for 2 hours to obtain a suspension of aluminum hydroxide / ferric phytate particles with amino groups on the surface.

[0033] 2) Add 20 parts by weight of ethanol lignin to the suspension in step 1), then add 35 parts by weight of glyoxal solution to the system, heat to 70°C, react for 6 hours to obtain aluminum hydroxide / ferric phytate lignin suspension. After cooling to room temperature, adjust the pH value to 10 with sodium hydroxide solution, add 50 parts by weight of high-temperature soybean meal powder, 60 parts by weight of crosslinking agent and 0.1 parts by weight of thickener, and mechanically stir to obtain modified lignin-based flame retardant adhesive.

[0034] The second step is to prepare formaldehyde-free flame-retardant solid wood composite flooring.

[0035] 1) Apply the modified lignin-based flame-retardant adhesive prepared in step one to the surface of eucalyptus veneer, with a single-sided coating amount of 120 g / m². 2 Solid wood composite flooring is made by assembling multi-layer plywood with each layer arranged in a cross-hatching pattern, and then cold-pressing and hot-pressing to form a flame-retardant multi-layer substrate. The cold-pressing unit pressure is 0.7±0.1MPa, and the cold-pressing time is 40–50 minutes. A three-stage hot-pressing process is used, with the first stage having a unit pressure of 0.8–1.0MPa / m². 2 The hot-pressing time is 15–16 minutes, and the unit pressure of the second stage of hot pressing is 0.3–0.4 MPa / m. 2 The hot-pressing time is 1-2 minutes, and the unit pressure of the third stage of hot pressing is 0.2-0.3 MPa / m. 2 Hot pressing time: 1-2 minutes;

[0036] 2) After the flame-retardant multilayer substrate layer is balanced, the modified lignin-based flame-retardant adhesive prepared in step one is applied, with a coating amount of 110 g / m². 2 The upper surface is bonded with a top plate, and the lower surface is bonded with a bottom plate. After assembly, the blanks undergo cold pressing, hot pressing, curing, slicing, sanding, grooving, and painting processes. The cold pressing unit pressure is 0.7±0.1 MPa, and the cold pressing time is 40–50 min. The hot pressing unit pressure is 0.7–0.8 MPa / m. 2 Hot pressing time: 300s.

[0037] Example 2

[0038] The first step is to prepare a modified lignin-based flame-retardant adhesive.

[0039] 1) 30 parts by weight of magnesium hydroxide and 20 parts by weight of zinc phytate were suspended in 100 parts by weight of water, ultrasonically dispersed, and then transferred to a reaction vessel. Then 10 parts by weight of tetraethyl orthosilicate were added, and the mixture was heated to 50°C and reacted for 10 hours under mechanical stirring. Then 15 parts by weight of 3-aminopropyltriethoxysilane were added, heated to 65°C, and kept at that temperature for 2 hours to obtain a magnesium hydroxide / zinc phytate particle suspension with amino groups on the surface.

[0040] 2) Add 20 parts by weight of ethanol lignin to the suspension in step 1), then add 35 parts by weight of glyoxal solution to the system, heat to 70°C, react for 6 hours to obtain magnesium hydroxide / zinc phytate lignin suspension. After cooling to room temperature, adjust the pH value to 10 with sodium hydroxide solution, add 50 parts by weight of high-temperature soybean meal powder, 60 parts by weight of crosslinking agent and 0.1 parts by weight of thickener, and mechanically stir to obtain modified lignin-based flame retardant adhesive.

[0041] The second step is to prepare formaldehyde-free flame-retardant solid wood composite flooring.

[0042] 1) Apply the modified lignin-based flame-retardant adhesive prepared in step one to the surface of eucalyptus veneer, with a single-sided coating amount of 120 g / m². 2 Solid wood composite flooring is made by assembling multi-layer plywood with each layer arranged in a crisscross pattern. The layers are then cold-pressed and hot-pressed to form a flame-retardant multi-layer substrate. The cold-pressing process involves a unit pressure of 0.7 MPa and a cold-pressing time of 50 minutes. The hot-pressing process employs a three-stage method, with the first stage using a unit pressure of 0.8 MPa / m². 2 The hot pressing time is 16 minutes, and the unit pressure of the second stage of hot pressing is 0.4 MPa / m. 2 Hot pressing time 2 minutes, third stage hot pressing unit pressure 0.2 MPa / m 2 Hot pressing time: 2 minutes;

[0043] 2) After the flame-retardant multilayer substrate layer is balanced, the modified lignin-based flame-retardant adhesive prepared in step one is applied, with a coating amount of 110 g / m². 2 The upper surface is bonded with a top plate, and the lower surface is bonded with a bottom plate. After assembly, the blanks undergo cold pressing, hot pressing, curing, slicing, sanding, grooving, and painting processes. The cold pressing unit pressure is 0.7 MPa, and the cold pressing time is 40 minutes. The hot pressing unit pressure is 0.8 MPa / m. 2 Hot pressing time: 300s.

[0044] Comparative Example 1

[0045] The first step is to prepare lignin-based flame-retardant adhesives.

[0046] 1) 20 parts of ethanol lignin were dissolved in 100 parts of aqueous solution and ultrasonically dissolved to obtain an ethanol lignin solution; the pH value was adjusted to 10 with sodium hydroxide solution, and 50 parts by weight of high-temperature soybean meal powder, 60 parts by weight of crosslinking agent and 0.1 parts by weight of thickener were added and mechanically stirred to obtain a lignin-based flame retardant adhesive.

[0047] The second step is to prepare formaldehyde-free flame-retardant solid wood composite flooring.

[0048] 1) The modified lignin-based flame-retardant adhesive prepared in step one is applied to the surface of eucalyptus veneer, with a single-sided coating amount of 120 g / m². The layers of multi-layer plywood for engineered wood flooring are assembled in a crisscross pattern, and then cold-pressed and hot-pressed to form a flame-retardant multi-layer substrate layer. The cold-pressing unit pressure is 0.7 MPa, and the cold-pressing time is 50 min. The hot-pressing adopts a three-stage hot-pressing method, with the first stage having a unit pressure of 0.8 MPa / m². 2 The hot pressing time is 16 minutes, and the unit pressure of the second stage of hot pressing is 0.4 MPa / m. 2 Hot pressing time 2 minutes, third stage hot pressing unit pressure 0.2 MPa / m 2 Hot pressing time: 2 minutes;

[0049] 2) After balancing, the flame-retardant multilayer substrate is coated with the modified lignin-based flame-retardant adhesive prepared in step one, with a coating amount of 110 g / m². The top surface is bonded to the top panel, and the bottom surface is bonded to the bottom panel. After assembly, it undergoes cold pressing, hot pressing, curing, shaving, sanding, grooving, and painting processes. The cold pressing unit pressure is 0.7 MPa, and the cold pressing time is 40 min. The hot pressing unit pressure is 0.8 MPa / m². 2 Hot pressing time: 300s.

[0050] Comparative Example 2

[0051] The first step is to prepare a modified lignin-based flame-retardant adhesive.

[0052] 1) 10 parts aluminum hydroxide, 5 parts ferric phytate and 20 parts ethanol lignin were ultrasonically suspended in 100 parts water. The pH value was adjusted to 10 with sodium hydroxide solution. 50 parts high-temperature soybean meal powder, 60 parts crosslinking agent and 0.1 parts thickener were added and mechanically stirred to obtain modified lignin-based flame retardant adhesive.

[0053] The second step is to prepare formaldehyde-free flame-retardant solid wood composite flooring.

[0054] 1) Apply the modified lignin-based flame-retardant adhesive prepared in step one to the surface of eucalyptus veneer, with a single-sided coating amount of 120 g / m². 2 Solid wood composite flooring is made by assembling multi-layer plywood with each layer arranged in a crisscross pattern. The layers are then cold-pressed and hot-pressed to form a flame-retardant multi-layer substrate. The cold-pressing process involves a unit pressure of 0.7 MPa and a cold-pressing time of 50 minutes. The hot-pressing process employs a three-stage method, with the first stage using a unit pressure of 0.8 MPa / m². 2 The hot pressing time is 16 minutes, and the unit pressure of the second stage of hot pressing is 0.4 MPa / m. 2 Hot pressing time 2 minutes, third stage hot pressing unit pressure 0.2 MPa / m 2 Hot pressing time: 2 minutes;

[0055] 2) After balancing, the flame-retardant multilayer substrate is coated with the modified lignin-based flame-retardant adhesive prepared in step one, with a coating amount of 110 g / m². The top surface is bonded to the top panel, and the bottom surface is bonded to the bottom panel. After assembly, it undergoes cold pressing, hot pressing, curing, shaving, sanding, grooving, and painting processes. The cold pressing unit pressure is 0.7 MPa, and the cold pressing time is 40 min. The hot pressing unit pressure is 0.8 MPa / m². 2 Hot pressing time: 300s.

[0056] Comparative Example 3

[0057] The first step is to prepare a modified lignin-based flame-retardant adhesive.

[0058] 1) 30 parts by weight of aluminum hydroxide and 20 parts by weight of ferric phytate were suspended in 100 parts by weight of water, ultrasonically dispersed, and then transferred to a reaction vessel. Then 10 parts by weight of tetraethyl orthosilicate were added, and the mixture was heated to 50°C and reacted for 10 hours under mechanical stirring. Then 15 parts by weight of 3-aminopropyltriethoxysilane were added, heated to 65°C, and kept at that temperature for 2 hours to obtain a suspension of aluminum hydroxide / ferric phytate particles with amino groups on the surface.

[0059] 2) Add 20 parts by weight of ethanol lignin to the suspension in step 1), then add 30 parts by weight of glyoxal solution to the system, heat to 70℃, and react for 6 hours to obtain an aluminum hydroxide / ferric phytate lignin suspension. After cooling to room temperature, adjust the pH to 10 with sodium hydroxide solution, add 50 parts by weight of high-temperature soybean meal powder and 60 parts by weight of crosslinking agent, and mechanically stir to obtain a modified lignin-based flame-retardant adhesive. This adhesive has no tackiness, poor coating performance, and cannot complete the adhesive application process. The impregnation peeling and formaldehyde release of flame-retardant solid wood composite flooring were tested according to GBT 18103-2013 "Solid Wood Composite Flooring". The combustion performance and smoke production characteristics of the flame-retardant solid wood composite flooring specimens were tested according to GBT 20284-2006 "Single Combustion Test of Building Materials or Products". The results are shown in the table below.

[0060] Table 1

[0061]

[0062] As shown in Table 1, compared with Example 1, Comparative Example 1, without the addition of metal hydroxide and phytate, showed a decrease in all product combustion performance indicators, with the critical radiative flux decreasing from 8.9 kW / m². 2 It becomes 3.2kW / m 2Within 20 seconds, the flame tip height changed from less than 150mm to greater than 150mm, and the total flue gas concentration changed from 247 / %×min to 768 / %×min, failing to reach the B1(B) combustion rating. This is because the absence of water vapor released by the thermal decomposition of aluminum hydroxide failed to lower the combustion temperature, dilute the oxygen in the air, and slow down the combustion process; and the absence of ferrous phytate hindered the formation and stability of the char layer, resulting in the substrate not forming an effective protective effect.

[0063] Compared with Example 1, although aluminum hydroxide and ferric phytate were added in Comparative Example 2, they were not subjected to amination treatment. As a result, aluminum hydroxide and ferric phytate affected the water resistance of the adhesive, resulting in failure of immersion peeling. At the same time, aluminum hydroxide and ferric phytate were not mixed evenly with the adhesive, resulting in a significant decrease in combustion performance.

[0064] Compared with Example 1, Comparative Example 3 and Example 1 both added aluminum hydroxide and ferrous phytate to modify lignin, and both aluminum hydroxide and ferrous phytate were amination and grafted onto lignin. However, Comparative Example 3 did not add sodium polyacrylate as a tackifier, which resulted in the adhesive failing to complete the application.

[0065] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A formaldehyde-free flame-retardant solid wood composite flooring, characterized in that, This formaldehyde-free, flame-retardant engineered wood flooring is obtained through the following preparation method: I. Preparation of Modified Lignin-Based Flame-Retardant Adhesives 1) 20-30 parts by weight of hydroxide and 10-20 parts by weight of phytate are suspended in 100-120 parts by weight of water, ultrasonically dispersed, and then transferred to a reaction vessel. 10-15 parts by weight of tetraethyl orthosilicate are then added, and the mixture is heated to 45-50°C and reacted for 10-15 hours under mechanical stirring. 10-15 parts by weight of 3-aminopropyltriethoxysilane are then added, and the mixture is heated to 60-65°C and held for 2-3 hours to obtain a hydroxide / phytate particle suspension rich in amino groups on the surface. The hydroxide is one or more of aluminum hydroxide, magnesium hydroxide, and iron hydroxide, and the phytate is one or more of iron phytate, magnesium phytate, and zinc phytate. 2) Add 20-30 parts by weight of ethanol lignin to the suspension in step 1), then add 20-40 parts by weight of glyoxal solution to the system, heat to 60-70℃, react for 4-6 hours to obtain hydroxide / phytate lignin suspension. After cooling to room temperature, adjust the pH value to 9.5-10.5 with sodium hydroxide solution, add 30-50 parts by weight of high-temperature soybean meal powder, 30-60 parts by weight of crosslinking agent and 0.1-0.5 parts by weight of thickener, and mechanically stir to obtain modified lignin-based flame retardant adhesive; II. Preparation of Formaldehyde-Free Flame-Retardant Solid Wood Composite Flooring 1) Apply the modified lignin-based flame-retardant adhesive obtained in step one to the surface of eucalyptus veneer, and assemble each layer of multi-layer plywood for solid wood composite flooring in a crisscross pattern. After cold pressing and hot pressing, a flame-retardant multi-layer substrate layer is formed. 2) After the flame-retardant multilayer substrate layer is balanced, the modified lignin-based flame-retardant adhesive prepared in step one is applied. The top surface is bonded to the top panel and the bottom surface is bonded to the bottom panel. After assembly, the formaldehyde-free flame-retardant solid wood composite flooring is produced through cold pressing, hot pressing, curing, slicing, sanding, grooving, and painting processes.

2. The formaldehyde-free flame-retardant solid wood composite flooring as described in claim 1, characterized in that, Ethanol lignin is bioethanol lignin.

3. The formaldehyde-free flame-retardant solid wood composite flooring as described in claim 1, characterized in that, The sodium hydroxide solution has a mass concentration of 20% to 30%.

4. The formaldehyde-free flame-retardant solid wood composite flooring as described in claim 1, characterized in that, The glyoxal solution has a mass fraction between 30% and 47%.

5. The formaldehyde-free flame-retardant solid wood composite flooring as described in claim 1, characterized in that, The crosslinking agent is a polyamide polyamine epichlorohydrin resin solution with a solid content of 10-12.5%.

6. The formaldehyde-free flame-retardant solid wood composite flooring as described in claim 1, characterized in that, The thickener is sodium polyacrylate.

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