Synthesis method of biomass organophosphorus flame-retardant environment-friendly amino resin adhesive

Abstract

The invention relates to the technical field of biomass organophosphorus flame-retardant environment-friendly amino resin adhesive synthesis, and discloses a biomass organophosphorus flame-retardant environment-friendly amino resin adhesive synthesis method, which comprises: drying an agricultural waste biomass raw material until the water content is less than or equal to 5%, crushing, and screening with a 80-120 mesh sieve to obtain biomass powder. According to the synthesis method of the biomass organophosphorus flame-retardant environment-friendly amino resin adhesive, a phosphorus-carbon synergistic flame-retardant system is constructed through biomass (agricultural wastes) and organophosphorus, and the oxygen index of the adhesive can be increased to be greater than or equal to 33.5% (far greater than 22% of pure amino resin and 30% of an inorganic flame retardant) without high addition amount; meanwhile, hydroxyl groups and carboxyl groups in the biomass and a resin matrix form hydrogen bonds, so that 30%-40% of bonding strength reduction caused by agglomeration of a traditional inorganic flame retardant is effectively avoided, and the normal bonding strength of the product is ensured to be greater than or equal to 1.9 MPa; and halogen flame retardants are abandoned, so that no toxic gases such as hydrogen bromide and dioxin are released during combustion.

Description

Technical Field

[0001] This invention relates to the field of biomass organophosphorus flame-retardant and environmentally friendly amino resin adhesive synthesis technology, specifically a method for synthesizing biomass organophosphorus flame-retardant and environmentally friendly amino resin adhesive. Background Technology

[0002] Amino resin adhesives (based on urea-formaldehyde resin and melamine-formaldehyde resin) occupy a core position in the wood processing field due to their fast curing speed, high bonding strength (normal bonding strength can reach 1.5-2.0MPa), and excellent boiling water resistance. According to industry data, they account for more than 70% of the market share of adhesives for engineered wood products. They are widely used in the production of particleboard, fiberboard, plywood and other products, supporting my country's annual production capacity demand of more than 300 million cubic meters of engineered wood products.

[0003] However, existing amino resin adhesives face three major technical bottlenecks that urgently need to be overcome: First, their flame retardant properties are inherently insufficient. The oxygen index of pure amino resin adhesives is generally below 22% (belonging to the category of flammable materials). Although this can be improved by adding flame retardants, traditional methods have significant drawbacks. When using inorganic flame retardants such as aluminum hydroxide and magnesium oxide, more than 30% needs to be added to raise the oxygen index to 30%. However, high addition amounts can easily lead to the agglomeration of flame retardant particles, resulting in poor compatibility with the resin matrix. This directly causes a 30% to 40% decrease in the adhesive's bonding strength, and the cured boards are prone to cracking and delamination. When using halogenated organic flame retardants (such as decabromodiphenyl ether), although the compatibility is better than that of inorganic flame retardants, they release toxic and harmful gases such as hydrogen bromide and dioxins during combustion. Therefore, there is an urgent need for a biomass organophosphorus flame-retardant and environmentally friendly amino resin adhesive synthesis method. Summary of the Invention

[0004] The purpose of this invention is to provide a method for synthesizing a biomass organophosphorus flame-retardant and environmentally friendly amino resin adhesive, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for synthesizing a biomass organophosphorus flame-retardant and environmentally friendly amino resin adhesive, comprising the following steps:

[0006] S1. Biomass raw material pretreatment: Agricultural waste biomass raw materials are dried to a moisture content of ≤5%, crushed and passed through an 80-120 mesh sieve to obtain biomass powder;

[0007] S2. Preparation of biomass organophosphorus flame retardant: The biomass powder obtained in step S1 and the organophosphorus reagent are added to the reaction vessel at a mass ratio of 1:(1.2-2.0). Under nitrogen protection, the mixture is stirred and reacted at 80-110℃ for 2-4 hours. After the reaction is completed, the mixture is cooled to room temperature, washed with ethanol 3-5 times, and vacuum dried to obtain the biomass organophosphorus flame retardant.

[0008] S3. Preparation of amino resin prepolymer: Add amino compound and aldehyde compound to reaction vessel at a molar ratio of 1:(1.5-2.5), adjust the pH of the system to 8.0-9.5, heat to 60-80℃ and stir for 1.5-3h to obtain amino resin prepolymer;

[0009] S4. Flame retardant modification and adhesive synthesis: The biomass organophosphorus flame retardant obtained in step S2 is added to the amino resin prepolymer obtained in step S3 at a ratio of 10% to 30% of the mass of the amino resin prepolymer. A catalyst is added to adjust the pH value of the system to 4.0-6.0. The temperature is raised to 70-90℃ and kept at the temperature for 1-2.5 hours. After the reaction is completed, an environmentally friendly solvent is added to adjust the solid content to 40%-60%. The mixture is cooled to room temperature to obtain the biomass organophosphorus flame retardant environmentally friendly amino resin adhesive.

[0010] Preferably, in step S2, the organophosphoric agent is a mixture of ammonium dihydrogen phosphate and dimethyl phosphite in a mass ratio of 1:(0.8-1.2).

[0011] Using a mixture of ammonium dihydrogen phosphate and dimethyl phosphite at a mass ratio of 1:(0.8-1.2) as an organophosphorus phosphate reagent, it can react better with biomass powder to generate biomass organophosphorus flame retardants with good flame retardant properties.

[0012] Preferably, in step S3, the amino compound is melamine, the aldehyde compound is formaldehyde, and the molar ratio of melamine to formaldehyde is 1:(2.0-2.2).

[0013] The amino compound is melamine, and the aldehyde compound is formaldehyde. The molar ratio of melamine to formaldehyde is 1:(2.0-2.2), which enables the reaction to produce a high-performance amino resin prepolymer, laying the foundation for the subsequent synthesis of high-quality adhesives.

[0014] Preferably, in step S4, the amount of biomass organophosphorus flame retardant added is 15% to 25% of the mass of the amino resin prepolymer.

[0015] The amount of biomass organophosphorus flame retardant added in step S4 is 15%-25% of the mass of amino resin prepolymer. This ensures that the adhesive has good flame retardant properties while also taking into account other properties of the adhesive, such as viscosity and stability.

[0016] Preferably, in step S2, the vacuum drying temperature is 50-60℃, the vacuum degree is -0.08 to -0.09 MPa, and the drying time is 3 to 5 hours.

[0017] The vacuum drying temperature is 50-60℃, the vacuum degree is -0.08 to -0.09MPa, and the drying time is 3-5 hours. Vacuum drying under these conditions can effectively remove moisture from biomass organophosphorus flame retardants, while avoiding the performance of flame retardants being affected by excessively high temperatures or excessively long drying times.

[0018] Preferably, in step S3, the reagent used to adjust the pH value of the system is an aqueous solution of sodium hydroxide or ammonia, wherein the mass concentration of the aqueous solution of sodium hydroxide is 10% to 20% and the mass concentration of the ammonia is 25% to 28%.

[0019] The reagents used to adjust the pH value of the system are sodium hydroxide aqueous solution or ammonia water. The mass concentration of sodium hydroxide aqueous solution is 10%-20%, and the mass concentration of ammonia water is 25%-28%. This can accurately adjust the pH value of the system to 8.0-9.5 to meet the requirements of the reaction.

[0020] Preferably, in step S4, the catalyst is citric acid, and the amount of citric acid added is 0.5% to 2.0% of the total mass of the amino resin prepolymer and the biomass organophosphorus flame retardant.

[0021] Citric acid is used as the catalyst, and the amount of citric acid added is 0.5%-2.0% of the total mass of amino resin prepolymer and biomass organophosphorus flame retardant. Citric acid, as a catalyst, can promote the reaction between the flame retardant and the amino resin prepolymer, which can make the reaction proceed smoothly, while not introducing too many impurities that affect the performance of the adhesive.

[0022] Preferably, in step S4, after adjusting the solid content, a filtration step is also included: using a 100-150 mesh filter to remove impurity particles from the system.

[0023] The purpose of using a 100-150 mesh filter is to remove impurities from the system, making the final biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive purer and improving the quality and stability of the adhesive.

[0024] Preferably, the agricultural waste biomass raw material is selected from at least one of straw, rice husk, and sawdust; the organophosphorus reagent is selected from at least one of ammonium dihydrogen phosphate, dimethyl phosphite, and triethyl phosphate; the amino compound is selected from at least one of urea, melamine, and benzoguanamine; the aldehyde compound is selected from at least one of formaldehyde, acetaldehyde, and furfural; the catalyst is selected from at least one of formic acid, acetic acid, and citric acid; and the environmentally friendly solvent is selected from at least one of deionized water and ethanol.

[0025] Agricultural waste biomass raw materials can be at least one of straw, rice husk, and sawdust; organophosphorus reagents can be at least one of ammonium dihydrogen phosphate, dimethyl phosphite, and triethyl phosphate; amino compounds can be at least one of urea, melamine, and benzoguanamine; aldehyde compounds can be at least one of formaldehyde, acetaldehyde, and furfural; catalysts can be at least one of formic acid, acetic acid, and citric acid; and environmentally friendly solvents can be at least one of deionized water and ethanol. This wide range of choices provides more flexibility and adaptability to the synthesis method, allowing for the selection of appropriate raw materials to synthesize adhesives based on actual conditions.

[0026] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0027] First, this invention constructs a "phosphorus-carbon" synergistic flame retardant system by combining biomass (agricultural waste) and organophosphorus compounds. This system can increase the oxygen index of the adhesive to ≥33.5% (far exceeding the 22% of pure amino resin and the 30% of inorganic flame retardants) without requiring high addition amounts. At the same time, the hydroxyl and carboxyl groups in the biomass form hydrogen bonds with the resin matrix, effectively avoiding the 30% to 40% decrease in bonding strength caused by the agglomeration of traditional inorganic flame retardants, ensuring that the product's normal bonding strength is ≥1.9MPa. Furthermore, it eliminates halogenated flame retardants, and no toxic gases such as hydrogen bromide and dioxins are released during combustion.

[0028] Secondly, this invention utilizes the hydroxyl groups abundant in biomass to actively adsorb formaldehyde remaining from the condensation reaction, reducing the free formaldehyde content of the product to ≤0.07%, thus solving the potential indoor air pollution problem at its source. At the same time, it transforms agricultural waste such as straw and rice husks into high-value-added flame-retardant functional raw materials, replacing some traditional chemical reagents. This not only reduces raw material costs but also reduces PM2.5 pollution and carbon emissions from open burning, thus balancing environmental, economic, and resource benefits. Attached Figure Description

[0029] Figure 1 This is a flowchart of a method for synthesizing a biomass organophosphorus flame-retardant and environmentally friendly amino resin adhesive. Detailed Implementation

[0030] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Specific Implementation

[0032] Example 1

[0033] Step S1 Biomass feedstock pretreatment

[0034] Agricultural waste wheat straw with an initial moisture content of 12% was placed in a 60℃ forced-air drying oven for 4 hours until the moisture content dropped to 3%. The dried straw was then crushed and passed through a 100-mesh standard sieve. The material passing through the sieve was collected to obtain biomass powder.

[0035] Step S2: Preparation of Biomass Organophosphorus Flame Retardant

[0036] Add 50g of the above-mentioned biomass powder to a 500mL four-necked reactor, then add the organophosphorus reagents: 30g of ammonium dihydrogen phosphate and 30g of dimethyl phosphite in a mass ratio of 1:1, and stir to mix evenly. Purge the air in the reactor with nitrogen three times, each time at a flow rate of 200mL / min for 5min. Then maintain the nitrogen atmosphere at a flow rate of 50mL / min, raise the temperature to 95℃, and stir the reaction at 300r / min for 3h. After the reaction is completed, allow it to cool naturally to room temperature, transfer the reaction product to a Buchner funnel, and wash it four times with 80mL of anhydrous ethanol each time until the washing liquid is neutral. Place the washed product in a vacuum drying oven and dry it for 4h at a temperature of 55℃ and a vacuum of -0.085MPa to obtain the biomass organophosphorus flame retardant.

[0037] Step S3: Preparation of amino resin prepolymer

[0038] Add 63g of melamine (an amino compound) and 110g of formaldehyde (a 37% aldehyde solution, 1.1mol, with a molar ratio of melamine to formaldehyde of 1:2.2) to a 1000mL three-necked flask. Add 20% sodium hydroxide aqueous solution dropwise while stirring to adjust the pH of the system to 8.8. Heat to 70℃ and stir at 250r / min for 2.5h, taking samples every 30min during the reaction. Stop the reaction when the system becomes transparent and viscous to obtain the amino resin prepolymer.

[0039] Step S4 Flame retardant modification and adhesive synthesis

[0040] The biomass organophosphorus flame retardant prepared in step S2 was added to the above-mentioned amino resin prepolymer at a rate of 20% of the prepolymer's mass. The prepolymer was weighed to be 160g, so 32g of flame retardant was added and stirred for 15 minutes. Then, citric acid catalyst was added at a rate of 1% of the total mass of the prepolymer and flame retardant, i.e., 1.92g. The pH of the system was adjusted to 5.0 by stirring. The temperature was raised to 80℃ and the reaction was maintained with stirring for 2 hours. After the reaction, deionized water was added to adjust the solid content of the system to 50% by weighing, and approximately 45mL of water was added. After the system cooled to room temperature, it was filtered through a 120-mesh nylon filter to remove a small amount of unreacted impurities, yielding a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive.

[0041] Example 2

[0042] Step S1

[0043] Rice husks with an initial moisture content of 10% were dried at 60℃ for 3 hours to a moisture content of 4%, then pulverized and passed through an 80-mesh sieve to obtain biomass powder.

[0044] Step S2

[0045] 50g of biomass powder, 25g of ammonium dihydrogen phosphate and 20g of dimethyl phosphite (mass ratio 1:0.8) were reacted under nitrogen protection at 90℃ with stirring for 2.5h. The mixture was washed three times with ethanol and dried under vacuum at 50℃ and -0.08MPa for 3.5h to obtain a flame retardant.

[0046] Step S3

[0047] 63g of melamine and 100g of formaldehyde solution were mixed, and the pH was adjusted to 8.5 with 25% ammonia water. The mixture was reacted at 75℃ for 2 hours to obtain a prepolymer.

[0048] Step S4

[0049] The flame retardant was added at 15% of the prepolymer mass, and the citric acid was added at 0.8% of the total mass. The pH was adjusted to 4.5, and the reaction was carried out at 85℃ for 1.5 hours. The solid content was adjusted to 45% with deionized water, and the mixture was filtered through a 100-mesh filter to obtain the adhesive.

[0050] Example 3

[0051] Step S1

[0052] Wood chips with an initial moisture content of 8% were dried at 55℃ for 5 hours until the moisture content decreased to 2%. After being pulverized, the chips were passed through a 120-mesh sieve to obtain biomass powder.

[0053] Step S2

[0054] 50g of biomass powder, 35g of ammonium dihydrogen phosphate and 35g of dimethyl phosphite (mass ratio 1:1.2) were reacted under nitrogen protection at 105℃ with stirring for 3.5h. The mixture was washed 5 times with ethanol and dried under vacuum at 60℃ and -0.09MPa for 5h to obtain a flame retardant.

[0055] Step S3

[0056] 63g of melamine and 105g of formaldehyde solution were mixed, and the pH was adjusted to 9.2 with 15% sodium hydroxide solution. The mixture was reacted at 65℃ for 3 hours to obtain the prepolymer.

[0057] Step S4

[0058] The flame retardant was added at 25% of the prepolymer mass, and the citric acid was added at 1.5% of the total mass. The pH was adjusted to 5.5, and the reaction was carried out at 75°C for 2.5 hours. Ethanol and deionized water were mixed at a ratio of 1:1 to adjust the solid content to 55%. The mixture was filtered through a 150-mesh filter to obtain the adhesive.

[0059] Comparative Example 1: No biomass organophosphorus flame retardant

[0060] Except for step S4, in which no biomass organophosphorus flame retardant is added, the remaining steps are as follows: S1 is omitted, and the remaining parameters of S3 and S4 are completely consistent with those of Example 1. Ordinary amino resin adhesive is prepared by using amino resin prepolymer, citric acid, and deionized water.

[0061] Comparative Example 2: Replacement of Traditional Inorganic Flame Retardants

[0062] In step S4, the biomass organophosphorus flame retardant in Example 1 is replaced with an equal mass of aluminum hydroxide, a traditional inorganic flame retardant. The remaining steps and parameters are the same as in Example 1, and an inorganic flame-retardant amino resin adhesive is prepared.

[0063] Performance testing

[0064] Oxygen index flame retardancy: Tested according to GB / T2406.2-2009 "Determination of flammability by oxygen index method for plastics - Part 2: Room temperature test", with the sample prepared as a standard strip of 100mm×10mm×4mm.

[0065] Bond strength: Tested according to GB / T14074-2021 "Test Methods for Adhesives and Resins for Wood Industry", with a substrate of poplar veneer (250mm×25mm×5mm) and an adhesive application rate of 150g / m². 2 The hot pressing conditions were 120℃, 1.0MPa, and 10min.

[0066] Free formaldehyde content: Tested according to GB18583-2008 "Limits of harmful substances in adhesives for interior decoration and renovation materials" using the acetylacetone spectrophotometric method.

[0067] Test Results

[0068]

[0069] Results Analysis

[0070] Flame retardancy: The oxygen index of Examples 1-3 was ≥33.5%, which was much higher than that of Comparative Example 121.8% (no flame retardant) and Comparative Example 230.3% (inorganic flame retardant). This indicates that biomass organophosphorus flame retardants can promote the formation of char layer by the carbon element in biomass through the "phosphorus-carbon" synergistic effect, while the phosphorus element inhibits the combustion chain reaction, thus significantly improving the flame retardant performance of the adhesive.

[0071] Bond strength: The bond strength of Examples 1-3 is ≥1.9MPa, which is higher than that of Comparative Examples 11.7MPa and 21.5MPa. This is because the biomass organophosphorus flame retardant has good compatibility with the amino resin prepolymer. The hydroxyl and carboxyl groups in the biomass form hydrogen bonds with the amino and hydroxyl groups in the resin, without destroying the cross-linking structure of the resin. In contrast, the inorganic flame retardant aluminum hydroxide is prone to agglomeration, which weakens the interfacial bonding force.

[0072] Environmental friendliness: The free formaldehyde content in Examples 1-3 is ≤0.07%, which is lower than the comparative example of 10.12%, because the hydroxyl groups in biomass can undergo an addition reaction with formaldehyde, reducing the release of free formaldehyde; at the same time, it meets the environmental protection requirement of "free formaldehyde ≤0.1%" in GB18583-2008.

[0073] In summary, this invention achieves a synergistic improvement in the "flame retardant-adhesive-environmental protection" of adhesives by combining biomass raw materials with organophosphorus compounds. Moreover, the raw materials are derived from agricultural waste, resulting in low cost and strong sustainability, making it suitable for fields such as wood processing and engineered wood product manufacturing.

[0074] 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, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing a biomass organophosphorus flame-retardant and environmentally friendly amino resin adhesive, comprising the following steps: S1. Biomass raw material pretreatment: Agricultural waste biomass raw materials are dried to a moisture content of ≤5%, crushed and passed through an 80-120 mesh sieve to obtain biomass powder; S2. Preparation of biomass organophosphorus flame retardant: The biomass powder obtained in step S1 and the organophosphorus reagent are added to the reaction vessel at a mass ratio of 1:(1.2-2.0). Under nitrogen protection, the mixture is stirred and reacted at 80-110℃ for 2-4 hours. After the reaction is completed, the mixture is cooled to room temperature, washed with ethanol 3-5 times, and vacuum dried to obtain the biomass organophosphorus flame retardant. S3. Preparation of amino resin prepolymer: Add amino compound and aldehyde compound to reaction vessel at a molar ratio of 1:(1.5-2.5), adjust the pH of the system to 8.0-9.5, heat to 60-80℃ and stir for 1.5-3h to obtain amino resin prepolymer; S4. Flame retardant modification and adhesive synthesis: The biomass organophosphorus flame retardant obtained in step S2 is added to the amino resin prepolymer obtained in step S3 at a ratio of 10% to 30% of the mass of the amino resin prepolymer. A catalyst is added to adjust the pH value of the system to 4.0-6.

0. The temperature is raised to 70-90℃ and kept at the temperature for 1-2.5 hours. After the reaction is completed, an environmentally friendly solvent is added to adjust the solid content to 40%-60%. The mixture is cooled to room temperature to obtain the biomass organophosphorus flame retardant environmentally friendly amino resin adhesive.

2. The method for synthesizing a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive according to claim 1, characterized in that: In step S2, the organophosphoric agent is a mixture of ammonium dihydrogen phosphate and dimethyl phosphite in a mass ratio of 1:(0.8-1.2).

3. The method for synthesizing a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive according to claim 1, characterized in that: In step S3, the amino compound is melamine, the aldehyde compound is formaldehyde, and the molar ratio of melamine to formaldehyde is 1:(2.0-2.2).

4. The method for synthesizing a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive according to claim 1, characterized in that: In step S4, the amount of biomass organophosphorus flame retardant added is 15% to 25% of the mass of the amino resin prepolymer.

5. The method for synthesizing a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive according to claim 1, characterized in that: In step S2, the vacuum drying temperature is 50-60℃, the vacuum degree is -0.08 to -0.09MPa, and the drying time is 3 to 5 hours.

6. The method for synthesizing a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive according to claim 1, characterized in that: In step S3, the reagent used to adjust the pH value of the system is an aqueous solution of sodium hydroxide or ammonia, wherein the mass concentration of the aqueous solution of sodium hydroxide is 10% to 20% and the mass concentration of the ammonia is 25% to 28%.

7. The method for synthesizing a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive according to claim 1, characterized in that: In step S4, the catalyst is citric acid, and the amount of citric acid added is 0.5% to 2.0% of the total mass of the amino resin prepolymer and the biomass organophosphorus flame retardant.

8. The method for synthesizing a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive according to claim 1, characterized in that: In step S4, after adjusting the solid content, a filtration step is also included: using a 100-150 mesh filter to remove impurity particles from the system.

9. The method for synthesizing a biomass organophosphorus flame-retardant environmentally friendly amino resin adhesive according to claim 1, characterized in that: The agricultural waste biomass raw material is selected from at least one of straw, rice husk, and sawdust; the organophosphorus reagent is selected from at least one of ammonium dihydrogen phosphate, dimethyl phosphite, and triethyl phosphate; the amino compound is selected from at least one of urea, melamine, and benzoguanamine; the aldehyde compound is selected from at least one of formaldehyde, acetaldehyde, and furfural; the catalyst is selected from at least one of formic acid, acetic acid, and citric acid; and the environmentally friendly solvent is selected from at least one of deionized water and ethanol.

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