Preparation method and application of hyperbranched polyamide amine supported flame-retardant adhesive

Abstract

This invention relates to the technical field of flame-retardant adhesives, and discloses a method for preparing and applying a hyperbranched polyamide amine-supported flame-retardant adhesive, comprising the following steps: (1) preparation of ADP / MPP@PAMAM; (2) pre-curing a mixture of ADP / MPP@PAMAM, 1,2-diaminobenzene, and 4,6-dihydroxyisophthalic acid, and grafting the resulting product with perfluorohexyl ethyl acrylate to obtain a composite flame retardant; (3) mixing polyether polyol, the composite flame retardant, and a wetting agent as component A, and polymeric MDI as component B, and mixing to obtain a flame-retardant adhesive. This invention uses hyperbranched polyamide amine as a carrier to successively support the ADP and MPP composite flame-retardant system, thereby improving the dispersion stability of the flame retardant. At the same time, it carries out a modification reaction, breaking through the thermal decomposition limit of ADP and the hygroscopic bottleneck of MPP. The resulting composite flame retardant is suitable for the hot pressing process of artificial boards.

Description

Technical Field

[0001] This invention relates to the technical field of flame retardant adhesives, and in particular to a method for preparing and applying a hyperbranched polyamide amine supported flame retardant adhesive. Background Technology

[0002] As a core material in building decoration, furniture manufacturing, and other fields, the flame retardant performance of engineered wood products directly affects fire safety during use. Halogen-free flame retardant technology, with its advantages of low smoke, low toxicity, and environmental friendliness, has become the mainstream development direction in the field of engineered wood flame retardancy. Among numerous halogen-free flame retardant systems, the composite system of aluminum diethyl phosphite (ADP) and melamine polyphosphate (MPP) exhibits high flame retardant potential due to its synergistic flame retardant effect, and is considered a highly promising halogen-free flame retardant solution for engineered wood products, attracting widespread attention in the industry. For example, patent CN111117101A discloses a high-toughness, high-flame-retardant PVC wood-plastic composite material and its preparation method. Its raw materials include: PVC resin, plant powder, processing modifier ACR-401, foaming agent, heat stabilizer, modified linear low-density polyethylene, attapulgite, halloysite, nano-barium sulfate, polyacrylonitrile-based carbon fiber, and a composite flame retardant; the composite flame retardant is a mixture of sepiolite, boron phosphate, melamine polyphosphate, ammonium octamolate, and aluminum diethyl phosphite.

[0003] However, in practical applications, the ADP and MPP compound system faces three major technical bottlenecks, severely restricting its industrial application in the engineered wood products sector. First, ADP suffers from significant thermal stability defects. The hot-pressing process in engineered wood product manufacturing typically involves temperatures between 180-200℃, while ADP's decomposition temperature is only around 180℃. If the hot-pressing temperature exceeds its decomposition temperature, ADP will decompose prematurely during the hot-pressing stage, failing to form an effective flame-retardant protective layer and directly losing its flame-retardant function. Second, MPP exhibits extremely high hygroscopicity. With a water absorption rate exceeding 5%, MPP readily absorbs moisture from the environment when applied to engineered wood products, causing the boards to swell and deform. It also leads to deterioration of the internal adhesive layer, compromising the structural integrity and stability of the board. Third, compatibility and migration issues are prominent problems. ADP is hydrophobic, while MPP is hydrophilic. The two have a large difference in polarity, which makes them prone to phase separation during the compounding process, resulting in a significant reduction in synergistic flame retardant efficiency of more than 30%. At the same time, when the amount of the compounded flame retardant system exceeds 15wt%, the flame retardant components tend to migrate to the interface of the wood-based panel, which not only further weakens the flame retardant effect, but also causes the bonding strength of the panel to decrease by 40%, failing to meet the basic performance requirements of the wood-based panel.

[0004] To address the aforementioned issues, existing technologies primarily employ silane modification for improvement. However, such solutions can only address a single technical problem, such as either enhancing the thermal stability of ADP or improving the hygroscopicity of MPP. They cannot simultaneously overcome the triple obstacles of thermal decomposition, hygroscopicity, and migration, making it difficult to fundamentally resolve the application defects of the compound system. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing and applying a hyperbranched polyamide amine-supported flame-retardant adhesive. By using hyperbranched polyamide amine (PAMAM) as a carrier, a flame-retardant system composed of aluminum diethyl phosphite (ADP) and melamine polyphosphate (MPP) is successively supported, improving the dispersion stability of the flame retardant. Simultaneously, a modification reaction is carried out, and the surface-synthesized polybenzoxazole can prevent ADP from prematurely decomposing and failing in large quantities during the hot-pressing process. The grafted and modified perfluorohexyl ethyl acrylate can solve the hygroscopic problem of MPP, breaking through the thermal decomposition limit of ADP and the hygroscopic bottleneck of MPP. The resulting composite flame retardant is suitable for high-temperature and high-pressure processes of engineered wood products.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a hyperbranched polyamide amine supported flame retardant adhesive, comprising the following steps: (1) Disperse hyperbranched polyamidoamine in ethanol, adjust the pH to 4-5, add aluminum diethylphosphite and heat to react; after the reaction is complete, add melamine polyphosphate and sonicate, evaporate the solvent to obtain ADP / MPP@PAMAM; (2) After mixing ADP / MPP@PAMAM and 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid, a pre-curing reaction was carried out. The resulting product was grafted with perfluorohexyl ethyl acrylate in toluene. The solvent was evaporated to obtain a composite flame retardant. (3) Mix polyether polyol, composite flame retardant and wetting agent as component A, and polymeric MDI as component B. Mix component A and component B to obtain flame retardant adhesive.

[0007] This invention utilizes hyperbranched polyamide amine (PAMAM) as a carrier to sequentially immobilize a flame-retardant system composed of aluminum diethyl phosphite (ADP) and melamine polyphosphate (MPP). Under acidic conditions, the amino groups (-NH2) on the PAMAM surface are protonated to -NH3. +MPP forms a strong electrostatic bond with the anion of ADP. Subsequently, due to the triazine ring (electron-deficient) in the melamine structure of MPP, the tertiary amine structure of PAMAM acts as an electron-rich donor, and its lone pair electrons can form n-π interactions with the π* orbitals of the triazine ring, similar to the electron donor-acceptor effect of π-π stacking. Simultaneously, the hydrophobic cavity inside PAMAM provides spatial constraint, strengthening this supramolecular force, stably encapsulating the triazine ring of MPP internally, shielding its hydrophilic groups, and suppressing hygroscopicity. This solves the compatibility problem when ADP and MPP are combined, achieving synergistic immobilization on the PAMAM support, resulting in higher flame retardant dispersibility and reduced agglomeration. If MPP is immobilized first and then ADP, MPP may hinder the electrostatic bonding of ADP due to steric hindrance, leading to uneven dispersion and decreased compatibility, ultimately affecting the synergistic flame retardant effect and the efficiency of MPP hydrophobic modification.

[0008] Subsequently, ADP / MPP@PAMAM is mixed with a polybenzoxazole (PBO) precursor (1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid) and subjected to a pre-curing reaction. The precursor undergoes a preliminary polycondensation reaction, followed by dehydration condensation to obtain a prepolymer. The resulting viscous prepolymer is bonded to the ADP / MPP@PAMAM surface through hydrogen bonds and interaction forces, making it less prone to detachment during subsequent grafting reactions. Furthermore, this prepolymer undergoes a high-temperature cyclization and dehydration reaction during subsequent hot pressing of the substrate, transforming from a prepolymer into a polybenzoxazole with a rigid ladder-like structure. Essentially, this involves the condensation and ring-closure of carboxyl and ortho-amine groups to form an oxazole ring, requiring no additional catalyst; the hot pressing environment provides the activation energy to promote the reaction. As a highly efficient thermal barrier and physical encapsulation layer, polybenzoxazole significantly delays the transfer of heat to the internal ADP, thereby preventing premature decomposition and failure of ADP during the hot pressing process. In addition, polybenzoxazole will carbonize at high temperatures to form a nitrogen-containing carbonized layer. This carbonized layer also contains phosphorus and nitrogen elements from flame retardants, which work together to form a strong expansion flame retardant barrier, effectively isolating heat and oxygen and improving the flame retardant effect.

[0009] Furthermore, perfluorohexyl ethyl acrylate (PFHEA) is covalently grafted and hydrogen-bonded with PAMAM and pre-cured products, increasing the contact angle of the composite flame retardant particles and improving their hydrophobicity, thereby reducing the water absorption rate of MPP. The fluorinated composite flame retardant remains compatible with polyether polyols through van der Waals forces, and the wetting agent further synergistically improves interfacial dispersibility; therefore, the hydrophobic modification does not lead to a decrease in compatibility.

[0010] Therefore, this invention, after immobilizing the ADP and MPP composite flame-retardant system, overcomes the limitations of ADP thermal decomposition and MPP hygroscopicity through in-situ surface polymerization and graft modification, resulting in a composite flame retardant suitable for high-temperature and high-pressure processes in engineered wood products. Simultaneously, the polyether polyol, as the main resin and reactant in the adhesive, provides hydroxyl groups, reacting with polymeric MDI to form a polyurethane network, constituting the adhesive matrix and used to disperse the composite flame retardant. The polymeric MDI, acting as a curing agent and adhesion promoter, reacts with the hydroxyl groups in the formulation and the hydroxyl amino groups in the wood, improving bonding strength.

[0011] Preferably, in step (1), the mass ratio of the hyperbranched polyamide amine to diethyl aluminum hypophosphite is 10:3-4; the mass ratio of the diethyl aluminum hypophosphite to melamine polyphosphate is calculated according to a P:N molar ratio of 1:2; and the hyperbranched polyamide amine is a third-generation hyperbranched polyamide amine (PAMAM G3.0) or a fourth-generation hyperbranched polyamide amine (PAMAM G4.0).

[0012] In low-generation systems, the cavity is too small to effectively encapsulate MPP, while in high-generation systems, the cavity is too large, resulting in loose encapsulation and exposure of the hydrophilic groups of MPP. Furthermore, it allows for sufficient protonation bonding of ADP, avoiding excessive steric hindrance.

[0013] ADP and MPP are immobilized with PAMAM at a phosphorus-nitrogen ratio (P / N) of 1:2. This ratio generates a dense phosphorus-nitrogen cross-linked char layer during combustion. Compared with conventional physical blending methods, it can achieve a significant improvement in flame retardant efficiency with a lower addition amount.

[0014] Preferably, in step (1), the ratio of hyperbranched polyamide amine to ethanol is 10g:50-100mL.

[0015] Preferably, in step (1), the heating reaction is carried out at 50-60℃ for 1-3 hours; the ultrasonic treatment is carried out for 1-2 hours.

[0016] Preferably, in step (2), the mass ratio of the hyperbranched polyamide amine to the mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid is 10:2-3; and the mass ratio of 1,2-diaminobenzene to 4,6-dihydroxyisophthalic acid in the mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid is 1:1.2-1.5.

[0017] Preferably, in step (2), the pre-curing is performed at 100-120℃ for 30-60 minutes.

[0018] Preferably, in step (2), the mass ratio of the hyperbranched polyamide amine to perfluorohexyl ethyl acrylate is 10:1-3; the ratio of the amount of perfluorohexyl ethyl acrylate to toluene is 1-3 g:200mL; and the grafting reaction is carried out at 70-80℃ for 2-4 hours.

[0019] Preferably, in step (3), the mass percentage of the polyether polyol and the composite flame retardant is 60-80%: 20-40%, and the total mass percentage is 100%; the mass ratio of component A to component B is 100: 30-40.

[0020] Preferably, in step (3), the polyether polyol is polypropylene glycol with an average molecular weight of 2000-4000; the mass of the wetting agent is 0.2-0.5% of the total mass of the polyether polyol and the composite flame retardant; and the wetting agent is a polyether-modified polysiloxane wetting agent.

[0021] Secondly, the present invention provides an application of the flame-retardant adhesive prepared by the above preparation method in artificial boards, comprising: applying the flame-retardant adhesive to wood shavings, and then laying and hot-pressing them to obtain artificial boards.

[0022] Preferably, the amount of glue applied is 10-13% of the dry weight of the wood shavings; the hot pressing is performed at 180-200℃ and 2-4MPa.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) By using hyperbranched polyamide amine (PAMAM) as a carrier, a flame retardant system of aluminum diethyl phosphite (ADP) and melamine polyphosphate (MPP) is successively immobilized, achieving molecular-level dispersion and long-term stability (no migration) of ADP and MPP, and achieving GB 8624 B1 level flame retardancy at low addition levels; (2) Polybenzoxazole was synthesized in situ on the surface of ADP / MPP@PAMAM. As an efficient thermal barrier and physical encapsulation layer, polybenzoxazole significantly delayed the transfer of heat to the internal ADP, thereby avoiding the premature decomposition and failure of ADP in the hot pressing process. (3) Surface grafting modified perfluorohexyl ethyl acrylate increases the contact angle of the composite flame retardant particles, improves their hydrophobicity, and avoids the expansion and deformation of the board caused by the hygroscopicity of MPP. (4) Polyether polyols, as the main resin and reactants of the adhesive, provide hydroxyl groups and react with polymeric MDI to generate a polyurethane network, which constitutes the matrix of the adhesive and is used to disperse composite flame retardants; polymeric MDI, as a curing agent and adhesion promoter, reacts with the hydroxyl groups in the formulation and the hydroxyl amino groups of wood to improve the bonding strength. Detailed Implementation

[0024] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0025] 1. Flame-retardant adhesives The preparation of hyperbranched polyamide amine supported flame retardant adhesives includes the following steps: (1) Hyperbranched polyamidoamine (3rd generation hyperbranched polyamidoamine PAMAM G3.0 or 4th generation hyperbranched polyamidoamine PAMAM G4.0) was dispersed in ethanol, with a ratio of hyperbranched polyamidoamine to ethanol of 10 g: 50-100 mL, and the pH was adjusted to 4-5; aluminum diethyl phosphite (ADP) was added, with a mass ratio of hyperbranched polyamidoamine to aluminum diethyl phosphite of 10:3-4, and the reaction was heated at 50-60℃ for 1-3 h; after the reaction was completed, melamine polyphosphate (MPP) was added and ultrasonically treated for 1-2 h, with the mass ratio of aluminum diethyl phosphite to melamine polyphosphate calculated according to a P:N molar ratio of 1:2; then the solvent was evaporated and dried to obtain ADP / MPP@PAMAM; (2) A mixture of ADP / MPP@PAMAM and 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid (mass ratio of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid is 1:1.2-1.5) is stirred and mixed at a mass ratio of 10:2-3, and then subjected to a pre-curing reaction at 100-120℃ for 30-60 min. The resulting product is added to toluene along with perfluorohexyl ethyl acrylate (PFHEA), with a mass ratio of hyperbranched polyamide amine to perfluorohexyl ethyl acrylate of 10:1-3 and a volume ratio of perfluorohexyl ethyl acrylate to toluene of 1-3 g:200 mL. The grafting reaction is carried out at 70-80℃ for 2-4 h. After that, the solvent is evaporated and dried to obtain the composite flame retardant. (3) Mix polyether polyol, composite flame retardant and wetting agent as component A. The mass percentage of polyether polyol and composite flame retardant is 60-80%: 20-40%, and the total mass percentage is 100%. The mass of wetting agent is 0.2-0.5% of the total mass of polyether polyol and composite flame retardant. Use polymeric MDI (NCO%=30-33%) as component B. Mix component A and component B in a mass ratio of 100:30-40 to obtain flame retardant adhesive.

[0026] 2. Artificial boards The flame-retardant adhesive prepared above is applied to wood shavings at a rate of 10-13% of the dry weight of the wood shavings. After being laid out, the wood shavings are hot-pressed at 180-200℃ and 2-4 MPa to obtain the engineered wood product. Example 1

[0027] (1) Take 10 g of fourth-generation hyperbranched polyamide amine (PAMAM G4.0) and disperse it in 100 mL of ethanol. Adjust the pH to 4.0 with dilute hydrochloric acid, add 3.6 g of aluminum diethylphosphite (ADP), and react at 60 °C for 2 h. After the reaction is complete, ADP@PAMAM is obtained. Add 4.8 g of melamine polyphosphate (MPP) to it and sonicate for 1 h. Then evaporate the solvent and dry to obtain ADP / MPP@PAMAM.

[0028] (2) After mixing ADP / MPP@PAMAM with 2 g of polybenzoxazole precursor (a mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid in a mass ratio of 1:1.2), pre-curing was carried out by stirring at 120°C for 30 min. Finally, the pre-cured product was added to 200 mL of toluene with 1.5 g of perfluorohexyl ethyl acrylate (PFHEA) and grafted at 70°C for 3 h. The solvent was then evaporated and dried to obtain the composite flame retardant (FR-PAMAM).

[0029] (3) Mix polyether polyol (PPG-3000), composite flame retardant (FR-PAMAM), and wetting agent BYK-333 in a mass ratio of 70:30:0.3 as component A, and polymeric MDI (NCO %=31 %) as component B. Mix component A and component B in a mass ratio of 100:35 to obtain the flame-retardant adhesive.

[0030] (4) Apply flame retardant adhesive to pine wood shavings at a rate of 10% of the dry weight of the pine wood shavings. After laying, hot press at 190℃ and 3.0 MPa for 6 minutes (18 mm thick) to obtain the engineered wood board. Example 2

[0031] (1) Take 10 g of third-generation hyperbranched polyamide amine (PAMAM G3.0) and disperse it in 100 mL of ethanol. Adjust the pH to 4.0 with dilute hydrochloric acid, add 3.2 g of aluminum diethylphosphite (ADP), and react at 60 °C for 2 h. After the reaction is complete, ADP@PAMAM is obtained. Add 4.3 g of melamine polyphosphate (MPP) to it and sonicate for 1 h. Then evaporate the solvent and dry to obtain ADP / MPP@PAMAM.

[0032] (2) After mixing ADP / MPP@PAMAM with 2 g of polybenzoxazole precursor (a mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid in a mass ratio of 1:1.2), pre-curing was carried out by stirring at 120°C for 30 min. Finally, the pre-cured product was added to 200 mL of toluene with 1.5 g of perfluorohexyl ethyl acrylate (PFHEA) and grafted at 70°C for 3 h. The solvent was then evaporated and dried to obtain the composite flame retardant (FR-PAMAM).

[0033] (3) Polyether polyol (PPG-3000), composite flame retardant (FR-PAMAM), and wetting agent BYK-333 are mixed in a mass ratio of 60:40:0.3 as component A, and polymeric MDI (NCO %=31 %) is used as component B. Component A and component B are mixed in a mass ratio of 100:40 to obtain the flame-retardant adhesive.

[0034] (4) Apply flame retardant adhesive to pine wood shavings at a rate of 10% of the dry weight of the pine wood shavings. After laying, hot press at 190℃ and 3.0 MPa for 6 minutes (18 mm thick) to obtain the engineered wood board. Example 3

[0035] (1) Take 10 g of fourth-generation hyperbranched polyamide amine (PAMAM G4.0) and disperse it in 100 mL of ethanol. Adjust the pH to 4.0 with dilute hydrochloric acid, add 3.6 g of aluminum diethylphosphite (ADP), and react at 60 °C for 2 h. After the reaction is complete, ADP@PAMAM is obtained. Add 4.8 g of melamine polyphosphate (MPP) to it and sonicate for 1 h. Then evaporate the solvent and dry to obtain ADP / MPP@PAMAM.

[0036] (2) After mixing ADP / MPP@PAMAM with 2.5 g of polybenzoxazole precursor (a mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid in a mass ratio of 1:1.2), pre-curing was carried out by stirring at 120°C for 30 min. Finally, the pre-cured product was added to 200 mL of toluene with 1.5 g of perfluorohexyl ethyl acrylate (PFHEA) and grafted at 70°C for 3 h. The solvent was then evaporated and dried to obtain the composite flame retardant (FR-PAMAM).

[0037] (3) Mix polyether polyol (PPG-3000), composite flame retardant (FR-PAMAM), and wetting agent BYK-333 in a mass ratio of 65:35:0.5 as component A, and polymeric MDI (NCO %=31 %) as component B. Mix component A and component B in a mass ratio of 100:30 to obtain the flame-retardant adhesive.

[0038] (4) Apply flame retardant adhesive to pine wood shavings at a rate of 10% of the dry weight of the pine wood shavings. After laying, hot press at 190℃ and 3.0 MPa for 6 minutes (18 mm thick) to obtain the engineered wood board.

[0039] Comparative Example 1 The difference from Example 1 is that the flame retardant is physically blended.

[0040] (1) Polyether polyol (PPG-3000), composite flame retardant (a mixture of ADP and MPP in a mass ratio of 3:4), and wetting agent BYK-333 are mixed in a mass ratio of 70:30:0.3 as component A, and polymeric MDI (NCO %=31 %) is mixed as component B. Component A and component B are mixed in a mass ratio of 100:35 to obtain the flame-retardant adhesive.

[0041] (2) Apply flame retardant adhesive to pine wood shavings at a rate of 10% of the dry weight of the pine wood shavings. After laying, hot press at 190℃ and 3.0 MPa for 6 minutes (18 mm thick) to obtain the engineered wood board.

[0042] Comparative Example 2 The difference from Example 1 is that 5th generation hyperbranched polyamide amine is used.

[0043] (1) Take 10 g of fifth-generation hyperbranched polyamide amine (PAMAM G5.0) and disperse it in 100 mL of ethanol. Adjust the pH to 4.0 with dilute hydrochloric acid, add 3.6 g of aluminum diethylphosphite (ADP), and react at 60 °C for 2 h. After the reaction is complete, ADP@PAMAM is obtained. Add 4.8 g of melamine polyphosphate (MPP) to it and sonicate for 1 h. Then evaporate the solvent and dry to obtain ADP / MPP@PAMAM.

[0044] (2) After mixing ADP / MPP@PAMAM with 2 g of polybenzoxazole precursor (a mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid in a mass ratio of 1:1.2), pre-curing was carried out by stirring at 120°C for 30 min. Finally, the pre-cured product was added to 200 mL of toluene with 1.5 g of perfluorohexyl ethyl acrylate (PFHEA) and grafted at 70°C for 3 h. The solvent was then evaporated and dried to obtain the composite flame retardant (FR-PAMAM).

[0045] (3) Mix polyether polyol (PPG-3000), composite flame retardant (FR-PAMAM), and wetting agent BYK-333 in a mass ratio of 70:30:0.3 as component A, and polymeric MDI (NCO %=31 %) as component B. Mix component A and component B in a mass ratio of 100:35 to obtain the flame-retardant adhesive.

[0046] (4) Apply flame retardant adhesive to pine wood shavings at a rate of 10% of the dry weight of the pine wood shavings. After laying, hot press at 190℃ and 3.0 MPa for 6 minutes (18 mm thick) to obtain the engineered wood board.

[0047] Comparative Example 3 The difference from Example 1 is that the order in which ADP and MPP are added is changed.

[0048] (1) Take 10 g of fourth-generation hyperbranched polyamide amine (PAMAM G4.0) and disperse it in 100 mL of ethanol. Add 4.8 g of melamine polyphosphate (MPP) and sonicate for 1 h. Adjust the pH to 4.0 with dilute hydrochloric acid, add 3.6 g of aluminum diethylphosphite (ADP), and react at 60 °C for 2 h. After the reaction is complete, evaporate the solvent and dry to obtain ADP / MPP@PAMAM.

[0049] (2) After mixing ADP / MPP@PAMAM with 2 g of polybenzoxazole precursor (a mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid in a mass ratio of 1:1.2), pre-curing was carried out by stirring at 120°C for 30 min. Finally, the pre-cured product was added to 200 mL of toluene with 1.5 g of perfluorohexyl ethyl acrylate (PFHEA) and grafted at 70°C for 3 h. The solvent was then evaporated and dried to obtain the composite flame retardant (FR-PAMAM).

[0050] (3) Mix polyether polyol (PPG-3000), composite flame retardant (FR-PAMAM), and wetting agent BYK-333 in a mass ratio of 70:30:0.3 as component A, and polymeric MDI (NCO %=31 %) as component B. Mix component A and component B in a mass ratio of 100:35 to obtain the flame-retardant adhesive.

[0051] (4) Apply flame retardant adhesive to pine wood shavings at a rate of 10% of the dry weight of the pine wood shavings. After laying, hot press at 190℃ and 3.0 MPa for 6 minutes (18 mm thick) to obtain the engineered wood board.

[0052] Comparative Example 4 The difference from Example 1 is that no polybenzoxazole precursor was added.

[0053] (1) Take 10 g of fourth-generation hyperbranched polyamide amine (PAMAM G4.0) and disperse it in 100 mL of ethanol. Adjust the pH to 4.0 with dilute hydrochloric acid, add 3.6 g of aluminum diethylphosphite (ADP), and react at 60 °C for 2 h. After the reaction is complete, ADP@PAMAM is obtained. Add 4.8 g of melamine polyphosphate (MPP) to it and sonicate for 1 h. Then evaporate the solvent and dry to obtain ADP / MPP@PAMAM.

[0054] (2) Add ADP / MPP@PAMAM and 1.5 g of perfluorohexyl ethyl acrylate (PFHEA) to 200 mL of toluene and perform a grafting reaction at 70 °C for 3 h. Then evaporate the solvent and dry to obtain the composite flame retardant (FR-PAMAM).

[0055] (3) Mix polyether polyol (PPG-3000), composite flame retardant (FR-PAMAM), and wetting agent BYK-333 in a mass ratio of 70:30:0.3 as component A, and polymeric MDI (NCO %=31 %) as component B. Mix component A and component B in a mass ratio of 100:35 to obtain the flame-retardant adhesive.

[0056] (4) Apply flame retardant adhesive to pine wood shavings at a rate of 10% of the dry weight of the pine wood shavings. After laying, hot press at 190℃ and 3.0 MPa for 6 minutes (18 mm thick) to obtain the engineered wood board.

[0057] Comparative Example 5 The difference from Example 1 is that the mass ratio of polyether polyol and composite flame retardant exceeds the specified range.

[0058] (1) Take 10 g of fourth-generation hyperbranched polyamide amine (PAMAM G4.0) and disperse it in 100 mL of ethanol. Adjust the pH to 4.0 with dilute hydrochloric acid, add 3.6 g of aluminum diethylphosphite (ADP), and react at 60 °C for 2 h. After the reaction is complete, ADP@PAMAM is obtained. Add 4.8 g of melamine polyphosphate (MPP) to it and sonicate for 1 h. Then evaporate the solvent and dry to obtain ADP / MPP@PAMAM.

[0059] (2) After mixing ADP / MPP@PAMAM with 2 g of polybenzoxazole precursor (a mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid in a mass ratio of 1:1.2), pre-curing was carried out by stirring at 120°C for 30 min. Finally, the pre-cured product was added to 200 mL of toluene with 1.5 g of perfluorohexyl ethyl acrylate (PFHEA) and grafted at 70°C for 3 h. The solvent was then evaporated and dried to obtain the composite flame retardant (FR-PAMAM).

[0060] (3) Mix polyether polyol (PPG-3000), composite flame retardant (FR-PAMAM), and wetting agent BYK-333 in a mass ratio of 50:50:0.3 as component A, and polymeric MDI (NCO %=31 %) as component B. Mix component A and component B in a mass ratio of 100:35 to obtain the flame-retardant adhesive.

[0061] (4) Apply flame retardant adhesive to pine wood shavings at a rate of 10% of the dry weight of the pine wood shavings. After laying, hot press at 190℃ and 3.0 MPa for 6 minutes (18 mm thick) to obtain the engineered wood board.

[0062] Performance testing: Flame retardancy: Tested according to standard GB 8624.

[0063] Limiting Oxygen Index (LOI): Tested according to standard GB / T 2406.2.

[0064] Internal bond strength: Tested according to standard GB / T 17657.

[0065] Aging resistance: After treatment in an environment of 70℃ and 95%RH for 168 hours, the flame retardancy rating and internal bond strength were tested again.

[0066] 24-hour water absorption thickness swelling rate: Tested according to standard GB / T 17657-2022 24-hour water absorption thickness swelling rate - Method 1.

[0067] Table 1 As shown in Table 1, compared with the physically blended ADP / MPP flame retardant adhesive in Comparative Example 1, the flame retardant adhesive prepared by this invention can achieve B1 flame retardancy, limiting oxygen index (LOI) ≥32%, internal bond strength ≥0.60 MPa, and moisture absorption ≤3.0%. Furthermore, no flame retardant is released after accelerated aging, maintaining B1 flame retardancy and retaining >90% of the internal bond strength. In contrast, the final flame retardant in Comparative Example 1 was only physically blended, leading to ADP hot-pressing decomposition and MPP moisture migration, resulting in the failure of both flame retardancy and bonding strength.

[0068] In Comparative Example 2, the hyperbranched polyamide amine (PAMAM) used was of an excessively high generation, resulting in a loose cavity and poor coating and shielding effect on the MPP. This affected the dispersibility of the flame retardant, making it prone to migration in subsequent processes. Furthermore, due to the poor coating effect of the PMAM carrier on the MPP cavity, the subsequent hydrophobic surface modification of perfluorohexyl ethyl acrylate could not effectively improve the hygroscopicity of the MPP, thus affecting the flame retardancy and bonding strength.

[0069] In Comparative Example 3, the loading order of the flame retardant was reversed, with MPP loaded first and then ADP loaded. MPP may hinder the electrostatic bonding of ADP due to steric hindrance, resulting in uneven dispersion and decreased compatibility between the two, weakening the synergistic effect and ultimately affecting the flame retardant and hydrophobic modification effect of MPP.

[0070] In Comparative Example 4, without the addition of PBO precursor, ADP decomposed prematurely during the hot-pressing stage due to the lack of a protective shell, resulting in a complete loss of its flame-retardant function. Meanwhile, PBO, generated through in-situ polymerization of the precursor, exhibits synergistic flame-retardant properties by forming a carbonized layer at high temperatures. Therefore, without the addition of PBO precursor, the flame-retardant performance of Comparative Example 4 was significantly reduced.

[0071] In Comparative Example 5, the composite flame retardant was added in excessive amounts, and the proportion of polyether polyol added was too low. Excessive particles damaged the integrity of the adhesive layer, resulting in substandard mechanical strength. At the same time, poor curing led to increased moisture absorption.

[0072] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a hyperbranched polyamide amine supported flame retardant adhesive, characterized in that, Includes the following steps: (1) Disperse hyperbranched polyamidoamine in ethanol, adjust the pH to 4-5, add aluminum diethylphosphite and heat to react; after the reaction is complete, add melamine polyphosphate and sonicate, evaporate the solvent to obtain ADP / MPP@PAMAM; (2) After mixing ADP / MPP@PAMAM and 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid, a pre-curing reaction was carried out. The resulting product was grafted with perfluorohexyl ethyl acrylate in toluene. The solvent was evaporated to obtain a composite flame retardant. (3) Mix polyether polyol, composite flame retardant and wetting agent as component A, and polymeric MDI as component B. Mix component A and component B to obtain flame retardant adhesive.

2. The method for preparing the hyperbranched polyamide amine supported flame retardant adhesive according to claim 1, characterized in that, In step (1), the mass ratio of the hyperbranched polyamide amine to diethyl aluminum hypophosphite is 10:3-4; the mass ratio of the diethyl aluminum hypophosphite to melamine polyphosphate is calculated according to a P:N molar ratio of 1:2; the hyperbranched polyamide amine is a third-generation hyperbranched polyamide amine or a fourth-generation hyperbranched polyamide amine.

3. The method for preparing the hyperbranched polyamide amine supported flame retardant adhesive according to claim 1 or 2, characterized in that, In step (1), the heating reaction is carried out at 50-60℃ for 1-3 hours; the ultrasonic treatment takes 1-2 hours.

4. The method for preparing the hyperbranched polyamide amine supported flame retardant adhesive according to claim 1, characterized in that, In step (2), the mass ratio of the hyperbranched polyamide amine to the mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid is 10:2-3; and the mass ratio of 1,2-diaminobenzene to 4,6-dihydroxyisophthalic acid in the mixture of 1,2-diaminobenzene and 4,6-dihydroxyisophthalic acid is 1:1.2-1.

5.

5. The method for preparing the hyperbranched polyamide amine supported flame retardant adhesive according to claim 1, characterized in that, In step (2), the pre-curing is performed at 100-120℃ for 30-60 minutes.

6. The method for preparing the hyperbranched polyamide amine supported flame retardant adhesive according to claim 1, 4, or 5, characterized in that, In step (2), the mass ratio of the hyperbranched polyamide amine to perfluorohexyl ethyl acrylate is 10:1-3; the ratio of the amount of perfluorohexyl ethyl acrylate to toluene is 1-3 g:200mL; and the grafting reaction is carried out at 70-80℃ for 2-4 hours.

7. The method for preparing the hyperbranched polyamide amine supported flame retardant adhesive according to claim 1, characterized in that, In step (3), the mass percentage of the polyether polyol and the composite flame retardant is 60-80%: 20-40%, and the total mass percentage is 100%; the mass ratio of component A to component B is 100: 30-40.

8. The method for preparing the hyperbranched polyamide amine supported flame retardant adhesive according to claim 1 or 7, characterized in that, In step (3), the polyether polyol is polypropylene glycol; the mass of the wetting agent is 0.2-0.5% of the total mass of the polyether polyol and the composite flame retardant; and the wetting agent is a polyether-modified polysiloxane wetting agent.

9. The application of a flame-retardant adhesive prepared by the method according to any one of claims 1-8 in engineered wood products, characterized in that, include: Flame-retardant adhesive is applied to wood shavings, which are then laid out and hot-pressed to obtain engineered wood panels.

10. The application according to claim 9, characterized in that, The amount of adhesive applied is 10-13% of the dry weight of the wood shavings; the hot pressing is carried out at 180-200℃ and 2-4MPa.

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