Preparation method for rapidly curing ENF-grade urea-formaldehyde resin

Abstract

The invention provides a preparation method for rapidly curing ENF-grade urea-formaldehyde resin, which comprises the following steps: step 1, adding formaldehyde, a first batch of urea, polyvinyl alcohol and lignin into a reaction kettle, adding an alkali catalyst to adjust the pH value to be alkaline, heating, and carrying out heat preservation reaction to generate a hydroxymethyl compound; step 2, adding an acid catalyst to adjust the pH to be acidic, adding a second batch of urea, reacting to preset viscosity, and adding an alkali catalyst to adjust the pH to be weakly alkaline; step 3, adding melamine, carrying out heat preservation reaction to a predetermined state, adding a third batch of urea, and finally reducing the molar ratio of formaldehyde to urea to 1.0-1.05; then adding a nano SiOO dispersion liquid, cooling, adding a formaldehyde treating agent and a carboxyl-terminated polymer, naturally cooling, and discharging; the nano silicon dioxide is added as a curing accelerator, so that the thermal conductivity can be improved, the heat transfer is accelerated, the curing speed of the resin is increased, and the gelation time is shortened by 40% or above.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, and in particular to a rapidly curing E NF Preparation method of grade urea-formaldehyde resin. Background Technology

[0002] Urea-formaldehyde resin (UF) is a primary adhesive in the manufacture of engineered wood products due to its low cost and high bonding strength. However, it has two major drawbacks: slow curing speed, which prolongs hot-pressing time and reduces production efficiency; and high formaldehyde emission, making it difficult to meet E5 standards. NF The product meets the environmental protection standard requirement (formaldehyde emission ≤ 0.025 mg / m³).

[0003] Existing technologies accelerate adhesive curing by adding curing accelerators (such as ammonium chloride, formaldehyde, and other acidic curing agents), but this also increases formaldehyde emissions. Reducing the F / U (formaldehyde / urea) molar ratio can decrease formaldehyde emissions, but this leads to slower curing speed and reduced bond strength. Therefore, existing methods cannot simultaneously achieve rapid curing and E (formaldehyde / urea) bonding. NF To achieve environmental protection standards, innovative formulas and processes are urgently needed. Summary of the Invention

[0004] This invention proposes a rapid curing E NF A method for preparing grade urea-formaldehyde resin is proposed to address the issue that existing methods for preparing urea-formaldehyde resin, as mentioned in the background section, cannot simultaneously achieve rapid curing and E-grade urea-formaldehyde resin preparation. NF The issue of environmental protection requirements.

[0005] The technical solution of this invention is implemented as follows: A fast-curing E NF The preparation method of grade urea-formaldehyde resin includes the following steps: Step 1: Add formaldehyde, the first batch of urea, polyvinyl alcohol and lignin to the reaction vessel, add an alkaline catalyst to adjust the pH to alkaline, raise the temperature and keep it at the temperature to produce hydroxymethyl compounds; Step 2: Add an acid catalyst to adjust the pH to acidic, add the second batch of urea and react to the predetermined viscosity, then add an alkaline catalyst to adjust the pH to weakly alkaline; Step 3: Add melamine and keep it at a constant temperature until the desired reaction is reached. Add the third batch of urea to reduce the final molar ratio of formaldehyde to urea to 1.0-1.05. Then add nano-SiO2 dispersion, cool down, add formaldehyde treatment agent and carboxyl-terminated polymer, and discharge the material after natural cooling.

[0006] Preferably, in step one, the weight ratio of each raw material is as follows: formaldehyde 300-370 parts, first batch of urea 92-124 parts, polyvinyl alcohol 1-1.5 parts, lignin 5-10 parts. The molar ratio of formaldehyde to urea is 2.0-2.2.

[0007] Preferably, in step one, the pH value after adding an alkaline catalyst is adjusted to 8.5-9.0, and the temperature is raised to 88℃-92℃ and kept at that temperature for 45 minutes to generate a stable hydroxymethyl compound.

[0008] Preferably, in step two, the pH value after adjusting with an acid catalyst is 4.5-5.0; The weight of the second batch of urea added is 60-100 parts.

[0009] Preferably, in step two, adding the second batch of urea and reacting to the predetermined viscosity means that after the reaction temperature is 90-95℃ and the reaction time is 40-60min, the reaction solution exhibits a stringy state in water at 45℃. After the reaction is complete, adjust the pH value to 7.5-8.0.

[0010] Preferably, in step three, the weight of melamine added is 4-10 parts, the heat preservation reaction temperature is 85°C, and the predetermined state is that the reaction solution can be drawn into threads without breaking in water at 55°C; the weight of the third batch of urea is 44-50 parts. Add 1.5-3 parts by weight of nano-SiO2 dispersion, and after cooling to 60°C, add formaldehyde treatment agent and carboxyl-terminated polymer. Allow the mixture to cool naturally to 45-60°C before discharging. The weight of the carboxyl-terminated polymer is 1-1.5 parts.

[0011] Preferably, in step one, the polyvinyl alcohol is PVA-1799 and the lignin is bamboo lignin; The alkaline catalyst is a 30% sodium hydroxide solution, a 20% potassium hydroxide solution, triethanolamine, or a 17% ammonia solution.

[0012] Preferably, in step two, the acid catalyst is a 20% ammonium chloride solution, a 5% citric acid solution, a 10% oxalic acid solution, a 5% phosphoric acid solution, or a 15% formic acid solution.

[0013] Preferably, in step three, the formaldehyde treatment agent is a 17% ammonia solution, 5% ammonium carbamate, 8% glycerol, or 5% carbohydrazine; the terminal carboxyl polymer is a 2% solution.

[0014] Preferably, the synthesis process of the end-carboxyl polymer is as follows: 500 g of 0.5 mol citric acid is added to a four-necked flask equipped with a water separator, mechanical stirrer, reflux condenser and thermometer. At the same time, 0.12 mol polyol is added to the four-necked flask. After stirring evenly, a certain amount of phthalic acid is added to the reaction vessel. The speed of mechanical stirring is controlled at 300-320 r / min. After heating to 120℃, melt polymerization is carried out. During the polymerization process, the vacuum degree of the reaction system is controlled at 0.1-0.12 MPa by a vacuum pump. By controlling the reaction time to 2-4 h, the end-carboxyl hyperbranched polymer is prepared.

[0015] By adopting the above technical solution, the beneficial effects of the present invention are as follows: 1. This invention improves thermal conductivity and accelerates heat transfer by adding nano-silica as a curing accelerator, thereby increasing the curing speed of the resin and shortening the gel time by more than 40%. 2. The bamboo lignin of this invention contains a large number of phenolic hydroxyl groups, which can react with formaldehyde to form polyphenol hydroxymethylphenol polymers, improving the mechanical properties and water resistance of the resin. Simultaneously, lignin is a renewable and biodegradable material with advantages of low cost and high yield. The resulting modified urea-formaldehyde resin utilizes a triple capture process involving melamine, bamboo lignin, and formaldehyde treatment agent, resulting in free formaldehyde in the resin ≤0.06%, and formaldehyde release from medium-density fiberboard below 0.025 mg / m³ (E NF class); 3. The PVA of this invention can enhance the flexibility of the adhesive layer, the internal bonding strength of medium density fiberboard reaches more than 0.5 MPa, and the wood breakage rate of ecological board reaches more than 95%. 4. The end-carboxyl polymer of the present invention contains a large number of carboxyl groups, which form stable chemical bonds with polyhydroxymethyl groups, extending the resin's shelf life to more than 30 days. 5. This invention is applicable to the manufacturing of ecological boards, bamboo-based engineered wood panels, and multi-layer boards; it is also applicable to continuous press production lines for fiberboard and particleboard. 6. This invention employs a triple technology coupling of "segmented polycondensation + nano-thermal conduction + multi-stage formaldehyde capture", which breaks through the contradiction between the curing speed and environmental performance of urea-formaldehyde resin and has significant industrial application value. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1This is a diagram illustrating the synthesis mechanism of the carboxyl-terminated polymer of this invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] A fast-curing E NF The preparation method of grade urea-formaldehyde resin includes the following steps: Step 1: First, add formaldehyde, the first batch of urea, polyvinyl alcohol, and lignin to the reactor. The weight ratio of each raw material is as follows: formaldehyde 300-370 parts, the first batch of urea 92-124 parts, polyvinyl alcohol 1-1.5 parts, and lignin 5-10 parts. At this stage, the initial molar ratio of formaldehyde to urea needs to be controlled at 2.0-2.2. PVA-1799 is preferred for the polyvinyl alcohol, and bamboo lignin is preferred for the lignin. After the materials are added, add an alkaline catalyst to adjust the pH to 8.5-9.0. The alkaline catalyst can be selected from one of the following: 30% sodium hydroxide solution, 20% potassium hydroxide solution, triethanolamine, or 17% ammonia water. After adjusting the pH, raise the temperature to 88℃-92℃ and maintain the reaction at this temperature for 45 minutes to generate a stable hydroxymethyl compound.

[0020] Step Two: After the heat preservation in Step One is completed, add an acid catalyst to adjust the pH value to an acidic environment, preferably 4.5-5.0. The acid catalyst can be selected from one of the following: 20% ammonium chloride solution, 5% citric acid solution, 10% oxalic acid solution, 5% phosphoric acid solution, or 15% formic acid solution. Subsequently, add a second batch of urea, with a weight ratio of 60-100 parts. Control the reaction temperature at 90-95℃ and maintain the reaction for 40-60 minutes. During this process, the viscosity of the reaction solution needs to be monitored. When the reaction solution exhibits a stringy state in water at 45℃, it is considered to have reached the predetermined viscosity. At this point, immediately add an alkaline catalyst to adjust the pH value to 7.5-8.0, making the reaction solution weakly alkaline.

[0021] Step 3: After adjusting the pH to weakly alkaline, add 4-10 parts of melamine and maintain the temperature at 85℃ for a continuous reaction until the reaction solution can be drawn into threads without breaking in 55℃ water. Then add a third batch of urea, 44-50 parts by weight, adjusting the amount of feed to reduce the total molar ratio of formaldehyde to urea in the final resin to 1.0-1.05, thereby reducing the free formaldehyde content. Next, add 1.5-3 parts of nano-SiO2 dispersion to the reaction solution to enhance resin performance using its nano-effect. Cool the reaction solution to 60℃ and add the formaldehyde treatment agent and the previously synthesized carboxyl-terminated polymer. The formaldehyde treatment agent is preferably one of 17% ammonia solution, 5% ammonium carbamate, 8% glycerol, or 5% carbamate; the amount of the carboxyl-terminated polymer (2% solution) added is 1-1.5 parts. Finally, allow the reaction to cool naturally to 45-60℃ before discharging to obtain the finished product, rapidly cured E. NF Grade urea-formaldehyde resin.

[0022] The above-mentioned carboxyl-terminated polymer (carboxyl-terminated hyperbranched polymer) is synthesized as follows: 500 g of 0.5 mol citric acid is added to a four-necked flask equipped with a water separator, mechanical stirrer, reflux condenser, and thermometer. At the same time, 0.12 mol of polyol (e.g., ethylene glycol, glycerol) is added to the four-necked flask. After stirring evenly, a certain amount of phthalic acid is added to the reaction vessel. The mechanical stirring speed is controlled at 300-320 r / min. After heating to 120℃, melt polymerization is carried out. During the polymerization process, the vacuum degree of the reaction system is controlled at 0.1-0.12 MPa by a vacuum pump. The reaction time is controlled at 2-4 h to prepare the carboxyl-terminated hyperbranched polymer.

[0023] The following specific embodiments are given to further illustrate the preparation method of this application.

[0024] Example 1

[0025] Raw material ratio (parts by weight): 37% formaldehyde solution: 300 parts; Urea (industrial grade): First batch 105 samples (initial F / U = 2.1), second batch 60 samples, third batch 46 samples; 6 parts melamine, 5 parts lignin, and 1 part carboxyl-terminated polymer; 1 part PVA-1799, 1.5 parts nano SiO2 (20nm), 1 part formaldehyde scavenger; Preparation steps: (1) Add 300 parts of formaldehyde and 1 part of PVA to the reaction vessel and stir. Add 30% sodium hydroxide solution to adjust the pH to 8.5-8.0, and turn on the steam to raise the temperature to 40℃. (2) Add 105 parts of the first batch of urea, 6 parts of melamine, and 5 parts of lignin, and slowly heat to 92℃ (40 min - 60 min), and keep the temperature for 60 min. (3) Add formic acid to adjust pH to 4.8-5.1, and keep the reaction at the temperature until the viscosity reaches the standard (the reaction at the temperature is about 60 minutes, and the mixture can be drawn into threads in 45-degree water). (4) Add triethanolamine to adjust pH to 7.5-8.0, add 60 parts of the second batch of urea, keep warm at 90℃ for 30 min, add 46 parts of the third batch of urea, 1.5 parts of nano SiO2 dispersion and 1 part of end-carboxyl polymer, let it cool naturally to 60 degrees, add 1 part of ammonium carbamate, stir and keep warm for 20 min, let it cool naturally to 45 degrees and discharge.

[0026] Example 2

[0027] Raw material ratio (parts by weight): 37% formaldehyde solution: 370 parts; Urea (industrial grade): First batch 96 samples (initial F / U = 2.3), second batch 65 samples, third batch 44 samples; 4 parts melamine, 6 parts lignin, and 1.5 parts carboxyl-terminated polymer; 1 part PVA-1799, 2 parts nano-SiO2 (20nm), 1.5 parts formaldehyde scavenger. Preparation steps: (1) Add 370 parts of formaldehyde and 1 part of PVA to the reaction vessel and stir. Add triethanolamine to adjust the pH to 8.5-8.0 and turn on the steam to raise the temperature to 40℃. (2) Add 96 parts of the first batch of urea, 4 parts of melamine, and 6 parts of lignin, and slowly heat to 92℃ (40 min - 60 min), and keep the temperature for 60 min. (3) Add 5% citric acid solution to adjust pH to 4.8-4.6, and keep the reaction at the temperature until the viscosity reaches the standard (the reaction at the temperature takes about 45 minutes, and the mixture can be drawn into threads in 50-degree water). (4) Add 17% ammonia water to adjust the pH to 7.5-8.0, add 65 parts of the second batch of urea, keep the reaction at 90℃ for 50 min, add 44 parts of the third batch of urea, 2 parts of nano SiO2 dispersion, and 1.5 parts of end-carboxyl polymer, let the reaction cool naturally to 60 degrees, add 1.5 parts of 5% carbohydrazine, stir and keep the reaction at 20 min, let the reaction cool naturally to 45 degrees and then discharge.

[0028] Example 3

[0029] Raw material ratio (parts by weight): 37% formaldehyde solution: 370 parts; Urea (industrial grade): First batch 124 samples (initial F / U = 2.2), second batch 100 samples, third batch 44 samples; 8 parts melamine, 7 parts lignin, and 2 parts carboxyl-terminated polymer; 1 part PVA-1799, 3 parts nano-SiO2 (20nm), 1 part formaldehyde scavenger Preparation steps: (1) Add 370 parts of formaldehyde and 1 part of PVA to the reaction vessel and stir. Add 20% potassium hydroxide solution to adjust the pH to 8.5-8.0 and heat to 45℃. (2) Add 124 parts of the first batch of urea, 8 parts of melamine, and 7 parts of lignin, and slowly heat to 95℃ (40 min - 60 min), and keep the temperature for 60 min. (3) Add 10% oxalic acid solution to adjust pH to 4.9-5.2, and keep the reaction at the temperature until the viscosity reaches the standard (the reaction at the temperature is about 90 minutes, and the mixture can be drawn into threads in 40-degree water). (4) Add 17% ammonia water to adjust the pH to 7.5-8.0, add 100 parts of the second batch of urea, keep the reaction at 90℃ for 50 min, add 44 parts of the third batch of urea, 3 parts of nano SiO2 dispersion, and 2 parts of end-carboxyl polymer, let the reaction cool naturally to 60 degrees, add 0.5 parts of 5% ammonium carbamate and 0.5 parts of 8% glycerol, stir and keep the reaction at 20 min, let the reaction cool naturally to 45 degrees and then discharge.

[0030] Example 4

[0031] Raw material ratio (parts by weight): 37% formaldehyde solution: 300 parts; Urea (industrial grade): First batch 92 parts (initial F / U = 2.4), second batch 80 parts, third batch 50 parts; 10 parts melamine, 10 parts lignin, 2 parts carboxyl-terminated polymer; PVA-1799 1.5 parts, nano SiO2 (20nm) 2 parts, formaldehyde scavenger: 2 parts Preparation steps: (1) Add 300 parts of 37% formaldehyde and 1.5 parts of PVA to the reaction vessel and stir. Add 30% sodium hydroxide solution to adjust the pH to 8.5-8.0 and heat to 45℃. (2) Add 92 parts of the first batch of urea, 10 parts of melamine, and 10 parts of lignin, and slowly heat to 90℃ (40 min - 60 min), and keep the temperature for 60 min. (3) Add 20% formic acid solution to adjust pH to 4.8-5.1, and keep it warm until the viscosity reaches the standard (keep it warm for about 70 minutes, and draw it into threads in 45-degree water). (4) Add triethanolamine to adjust pH to 7.5-7.0, add 80 parts of the second batch of urea, keep warm at 90℃ for 50 min, add 50 parts of the third batch of urea, 2 parts of nano SiO2 dispersion, and 2 parts of end-carboxyl polymer, let it cool naturally to 60 degrees, add 1 part of 5% ammonium carbamate and 1 part of 8% glycerol, stir and keep warm for 30 min, let it cool naturally to 45 degrees and then discharge.

[0032] Performance testing (compared to international standards) The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a fast curing E NF grade urea-formaldehyde resin, characterized in that, The method comprises the following steps: Step 1: formaldehyde, the first batch of urea, polyvinyl alcohol and lignin are added into a reaction kettle, an alkali catalyst is added to adjust the pH value to alkaline, and then the reaction is carried out after being heated and kept warm to generate a hydroxymethyl compound; Step 2: an acid catalyst is added to adjust the pH value to acidic, the second batch of urea is added and reacted to a predetermined viscosity, and then an alkali catalyst is added to adjust the pH value to weak alkaline; Step 3: melamine is added to keep warm and react to a predetermined state, the third batch of urea is added to reduce the molar ratio of formaldehyde to urea to 1.0-1.05, then a nano-SiO2 dispersion liquid is added, a formaldehyde treatment agent and a carboxyl-terminated polymer are added after being cooled, and then the product is discharged after being naturally cooled.

2. A fast curing E NF Process for the preparation of a urea-formaldehyde resin of the E grade, characterized in that, In step 1, the weight ratio of each raw material is as follows: formaldehyde 300-370 parts, the first batch of urea 92-124 parts, polyvinyl alcohol 1-1.5 parts and lignin 5-10 parts. The molar ratio of formaldehyde to urea is 2.0-2.

2.

3. The method for preparing a rapidly curing ENF-grade urea-formaldehyde resin according to claim 1, characterized in that, In step 1, the pH value after being adjusted by the alkali catalyst is 8.5-9.0, and the reaction is carried out after being heated to 88-92℃ for 45 minutes to generate a stable hydroxymethyl compound.

4. A fast curing E NF Process for the preparation of a urea-formaldehyde resin of the E grade, characterized in that, In step 2, the pH value after being adjusted by the acid catalyst is 4.5-5.

0. The weight ratio of the second batch of urea is 60-100 parts.

5. A fast curing E NF Process for the preparation of a urea-formaldehyde resin of the first stage, characterized in that, In step 2, the second batch of urea is added and reacted to a predetermined viscosity, which means that the reaction liquid appears a state of continuous thread in 45℃ water after being kept warm for 40-60 minutes at a reaction temperature of 90-95℃. The pH value is adjusted to 7.5-8.0 after the reaction is completed.

6. A fast curing E NF Process for the preparation of a urea-formaldehyde resin of the first stage, characterized in that, In step 3, the weight ratio of melamine is 4-10 parts, the reaction temperature is 85℃, the predetermined state is that the reaction liquid appears a state of continuous thread in 55℃ water, and the weight ratio of the third batch of urea is 44-50 parts. The weight ratio of the nano-SiO2 dispersion liquid is 1.5-3 parts, and the formaldehyde treatment agent and the carboxyl-terminated polymer are added after being cooled to 60℃, and then the product is discharged after being naturally cooled to 45-60℃, wherein the weight ratio of the carboxyl-terminated polymer is 1-1.5 parts.

7. A fast curing E NF Process for the preparation of a urea-formaldehyde resin of the first grade, characterized in that, In step 1, the polyvinyl alcohol is PVA-1799, and the lignin is bamboo lignin. The alkali catalyst is a 30% sodium hydroxide solution, a 20% potassium hydroxide solution, triethanolamine or a 17% ammonia solution.

8. A fast curing E NF Process for the preparation of a urea-formaldehyde resin of the first stage, characterized in that, The acid catalyst in step 2 is a 20% ammonium chloride solution, a 5% citric acid solution, a 10% oxalic acid solution, a 5% phosphoric acid solution or a 15% formic acid solution.

9. A fast curing E NF Process for the preparation of a urea-formaldehyde resin of the first stage, characterized in that, The formaldehyde treatment agent in step 3 is a 17% ammonia solution, 5% ammonium carbamate, 8% butanetriol or 5% carbohydrazide; and the carboxyl-terminated polymer is a 2% solution.

10. A fast curing E NF Process for the preparation of a urea-formaldehyde resin of the E grade, characterized in that, The synthesis process of the carboxyl-terminated polymer is as follows: 500 grams of 0.5 mol citric acid is added into a four-necked flask equipped with a water separator, mechanical stirring, a reflux condenser and a thermometer, 0.12 mol polyol is added into the four-necked flask, the mixture is stirred uniformly, a certain amount of phthalic acid is added into the reaction kettle, the stirring speed is controlled to be 300-320 r / min, and then the reaction is carried out after being heated to 120℃ for melting polymerization. The vacuum degree of the reaction system is controlled by a vacuum pump during the polymerization process, and is 0.1-0.12 MPa, and the reaction time is controlled to be 2-4 h, so as to prepare the carboxyl-terminated hyperbranched polymer.

Images