Primary formaldehyde-free adhesive as well as preparation method and application thereof

Abstract

The invention discloses a native formaldehyde-free adhesive as well as a preparation method and application thereof, and belongs to the field of application of an environment-friendly artificial board preparation technology. The polyamino polymer resin with a branched structure and an amino-terminated end is prepared by using polybasic carboxylic acid containing three or more carboxyl groups and regulating and designing aliphatic carboxylic acid and an amino-containing monomer in a polyamide polyamine epichlorohydrin resin polymerization process; and preparing the native formaldehyde-free adhesive with low-temperature soybean meal or oil-tea meal. According to the method, high-density free amino groups and active imino groups are introduced by regulating and controlling the feeding ratio and the feeding batch, controlling the monomer polymerization speed and the like, so that formaldehyde is expected to be continuously absorbed and fixed in the gluing and using processes, and long-acting formaldehyde control of the artificial board glued by the bio-based protein adhesive is realized. Studies prove that the prepared artificial board achieves efficient adsorption of free formaldehyde in space, and the concentration of free formaldehyde in the human settlement environment is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly engineered wood products, and in particular to a formaldehyde-free virgin formaldehyde-free adhesive with a branched structure of polyamine polyamide resin and its application. Background Technology

[0002] Most adhesives used in my country's wood-based panel industry are synthetic resin adhesives, with urea-formaldehyde resin, phenolic resin, and melamine-urea-formaldehyde resin (collectively known as "three-formaldehyde adhesives") dominating the market. However, these adhesives inevitably release free formaldehyde during production and use, becoming one of the main sources of indoor air pollution and posing a potential threat to human health.

[0003] Studies have shown that formaldehyde release from engineered wood products made with aldehyde-based adhesives (hereinafter referred to as "aldehyde-based boards") exhibits a clear pattern: formaldehyde release is high in the initial stages of use, gradually decreasing and stabilizing over time. However, even after long-term use, aldehyde-based boards continue to release trace amounts of formaldehyde, which is usually difficult to reduce to zero, leading to persistent indoor formaldehyde concentrations and potential accumulation exceeding standards. Furthermore, the severity of formaldehyde pollution is closely related to the formaldehyde carrying capacity of the indoor environment. Formaldehyde carrying capacity refers to the ratio of the surface area of ​​formaldehyde-releasing sources such as furniture to the volume of the indoor space. A higher carrying capacity results in a greater total formaldehyde release, further increasing the indoor formaldehyde concentration. Simultaneously, indoor formaldehyde pollution is not caused by a single source but is the result of the combined effects of multiple formaldehyde-releasing sources (such as furniture, flooring, and decorative materials). This cumulative effect is closely related to the formaldehyde carrying capacity. When the indoor carrying capacity is high, the formaldehyde release from each source accumulates, often leading to indoor formaldehyde concentrations significantly exceeding national standards (such as E0 and E1 levels), posing a greater risk to human health.

[0004] Currently, methods for treating formaldehyde pollution mainly include ventilation dilution and adsorption or decomposition using chemical reagents (such as formaldehyde adsorbents). For example, CN112619640A, an activated manganese adsorbent, can adsorb low concentrations of formaldehyde gas, but it has drawbacks such as high cost and strong environmental dependence. Similarly, CN116966747A is another example; this device can effectively adsorb formaldehyde carried by freshly produced engineered wood products, but it still cannot solve the problem of subsequent accumulation of trace amounts of formaldehyde. Furthermore, while ventilation is the most common and inexpensive treatment method, its effectiveness is highly dependent on external environmental conditions. To fundamentally solve the formaldehyde release problem, reducing or replacing the use of formaldehyde-based adhesives has become one of the key research directions. In recent years, biomass adhesives developed based on renewable resources have gradually attracted attention. Among them, protein-based adhesives are particularly favored due to their wide availability of raw materials, environmental friendliness, and lack of formaldehyde release. Examples include CN113249086A, CN117757426A, and CN114686121A. Although the formaldehyde problem has been improved in the prepared adhesives, the issue of trace formaldehyde accumulation in the later stages still cannot be resolved. In other words, existing technologies cannot fundamentally solve the impact of the cumulative effect of formaldehyde on air quality. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention prepares a multi-amino polymer resin with branched structure and amino-terminated ends by regulating and designing amino-containing monomers in the polymerization process of polyamide polyamine epichlorohydrin resin, and uses it in virgin formaldehyde-free adhesives. By regulating the feed ratio, feed batch, and controlling the monomer polymerization rate, high-density free amino and active imino groups are introduced to continuously absorb and fix formaldehyde during bonding and use, thereby achieving long-term formaldehyde control in engineered wood panels bonded with the above-mentioned modified protein-based adhesives.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] On the one hand, this invention provides a PAE resin modifier. By optimizing the feeding ratio and preparation process of PAE resin, a water-soluble resin rich in active amino and imino groups is prepared and used to enhance protein-based adhesives. This improves the water-resistant bonding strength of the bonded engineered wood panels and enhances the adsorption and fixation of formaldehyde during use. This is of great significance for fundamentally solving the impact of the cumulative effect of formaldehyde on indoor air quality.

[0008] Specifically, the PAE resin modifier is prepared from the following raw materials in parts by weight: 100 parts water; 24 parts polycarboxylic acid; 15-65 parts polyethylene polyamine; 15-25 parts epichlorohydrin; 0.4-0.9 parts catalyst; and 0.5-2.5 parts acid.

[0009] The polycarboxylic acid is citric acid, aminotriacetic acid, or ethylenediaminetetraacetic acid; the polyethylene polyamine is diethylenetriamine, triethylenetetraamine, or tetraethylenepentamine; the catalyst is selected from p-toluenesulfonic acid and / or EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide); the acid is one or more of hydrochloric acid, sulfuric acid, and formic acid; the molar ratio of the carboxyl group in the polycarboxylic acid to the amino group in the polyethylene polyamine is 1-1.5:1.

[0010] Preferably, the PAE resin modifier is prepared from the following raw materials in parts by weight: 100 parts water; 24 parts citric acid; 19-29 parts diethylenetriamine; 25 parts epichlorohydrin; 0.43-0.53 parts p-toluenesulfonic acid; and 1 part hydrochloric acid.

[0011] Preferably, the molar ratio of amino groups in diethylenetriamine is 1.0 times, 1.1 times, 1.2 times, 1.3 times, 1.4 times, and 1.5 times that of carboxyl groups in citric acid, respectively; and the amount of p-toluenesulfonic acid added is 1% of the total mass of the polycarboxylic acid monomer and the polyethylenepolyamine monomer.

[0012] On the other hand, the present invention provides a method for preparing the above-mentioned PAE resin modifier. First, an amino-terminated polyamide polyamine intermediate is prepared using polycarboxylic acids and excess polyethylene polyamine as raw materials; then, the above-mentioned polyamide polyamine intermediate is reacted with epichlorohydrin to prepare an amino-terminated polyamide polyamine epichlorohydrin (PAE) resin modifier; specifically including:

[0013] Step 1: Weigh the raw materials according to the proportions;

[0014] Step 2: Preheat the polyethylene polyamine to 50°C, then add 1 / 2 of the polycarboxylic acid and stir until fully dissolved;

[0015] Step 3: Add 1 / 4 of the polycarboxylic acid to the solution from Step 2 and stir until fully dissolved; then add the remaining polycarboxylic acid and heat to 80-85℃;

[0016] Step 4: Stop heating, add the catalyst p-toluenesulfonic acid and accelerate stirring to promote further polycondensation reaction (the process will continue to be exothermic); observe the thermometer, and immediately raise the temperature to 160-175℃ and keep it for 3 hours after the exothermic reaction is completed to evaporate the moisture in the system, and obtain the amino-terminated polyamide polyamine prepolymer.

[0017] Step 5: After the prepolymer has cooled naturally to 45-50℃, adjust the solid content to 50% with water, and add epichlorohydrin monomer dropwise while stirring over 20 minutes. Then raise the temperature to 65℃ and continue stirring for 2.5 hours to obtain PAE resin. Adjust the solid content to 12.5%-45% with distilled water and adjust the pH of the solution to 5-6 with acid. Preferably, the stirring conditions are mechanical stirring at a speed of 400-800 rpm.

[0018] This invention introduces excess polyethylenepolyamine to end the active amino groups in the prepared polyamide polyamine epichlorohydrin (PAE) resin, resulting in a high imino content in the molecular chain. The three-step citric acid feeding method ensures complete polymerization of citric acid, leading to a uniform molecular weight distribution and high degree of polymerization in the prepared resin. Preheating of the polyethylenepolyamine promotes its initial polymerization with citric acid, accelerating and optimizing the dehydration polymerization reaction. The resulting PAE resin modifier is comparable to PAE resins with a high epichlorohydrin feed ratio, reducing the subsequent use of epichlorohydrin while maintaining the same expected performance of the PAE resin.

[0019] Furthermore, the present invention also provides a virgin formaldehyde-free adhesive, comprising the above-mentioned PAE resin modifier, specifically composed of the following components by weight: 100 parts water; 20-35 parts PAE resin modifier; 30-45 parts protein raw material; wherein the protein raw material is low-temperature soybean meal or camellia oil meal, the particle size of the protein raw material is 70-500 mesh, and the protein content in the protein raw material is above 43 wt%.

[0020] Preferably, the solid content of the PAE resin modifier is 12.5%.

[0021] The present invention also provides a method for preparing the above-mentioned virgin formaldehyde-free adhesive, comprising:

[0022] (1) Weigh out the protein raw materials, PAE resin modifier and water according to the weight parts of each raw material;

[0023] (2) Dissolve the PAE resin modifier in water and stir until homogeneous;

[0024] (3) Add the protein raw material to the above solution and stir until homogeneous to obtain protein-based adhesive.

[0025] Preferably, the stirring conditions in steps (2)-(3) are mechanical stirring with a speed of 300-600 rpm, a stirring temperature of 20-35℃, and a stirring time of 10-30 minutes.

[0026] The prepared protein-based adhesive has a solid content of 30-50%wt, a viscosity (25℃) of 1000-3500mPa·s, and an active period of 15-30 days.

[0027] The introduction of high-density free amino and active imino groups into the adhesive of this invention enables the modified protein-based adhesive to continuously absorb and fix formaldehyde during bonding and use, achieving long-term formaldehyde control in engineered wood panels bonded with the modified protein-based adhesive. Simultaneously, the polyamino PAE resin can achieve physical and chemical cross-linking with the protein group through a highly active cationic nitrogen-containing heterocyclic butanol structure, significantly improving the water resistance and bonding strength of the protein-based adhesive-bonded panels. Furthermore, by using polycarboxylic acids with three or more carboxyl groups to replace dicarboxylic acids, the protein-based adhesive modified with the branched polyamino PAE resin and the three-layer plywood prepared from it exhibit optimal water resistance, bonding strength, and formaldehyde adsorption and degradation capabilities. When the molar ratio of carboxyl groups in the polycarboxylic acid to amino groups in the polyethylenepolyamine is 1:1.3, the protein-based adhesive modified with the polyamino PAE resin and the three-layer plywood prepared from it exhibit optimal formaldehyde adsorption and degradation capabilities and water resistance, bonding strength. Protein-based adhesives modified with branched polyamino PAE resin prepared from citric acid and diethylenetriamine, and the three-layer plywood prepared from them, exhibit the best water-resistant bonding strength and formaldehyde adsorption and degradation capabilities.

[0028] The present invention also provides an application of the above-mentioned virgin formaldehyde-free adhesive in the fields of wood, bamboo, furniture, printed matter, decoration, and construction; in particular, the present invention also includes wood products, bamboo products, printed matter, decorations, buildings, etc. containing the above-mentioned virgin formaldehyde-free adhesive, such as plywood, particleboard, medium-density fiberboard and blockboard and other artificial boards.

[0029] The method for preparing engineered wood panels using the above-mentioned virgin formaldehyde-free adhesive includes:

[0030] S1 Veneer: Poplar (400mm×400mm×1.5mm), moisture content 8-12%;

[0031] S2 Glue Application: Glue is applied to both sides of the core board, with a coating amount of 170-225g / m². 2 ;

[0032] S3 assembly: Three veneers are assembled in a direction perpendicular to the grain of adjacent veneers;

[0033] S4 hot pressing: hot pressing temperature 120℃, hot pressing pressure 1.0MPa, hot pressing time 6min, holding time 1min.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The virgin formaldehyde-free adhesive of this invention and the engineered wood panels manufactured from it do not release formaldehyde. Furthermore, the introduction of high-density free amino and active imino groups into the adhesive allows the modified protein-based adhesive to continuously absorb and fix formaldehyde during bonding and use, achieving long-term formaldehyde control in engineered wood panels bonded with the modified protein-based adhesive. Simultaneously, engineered wood panels prepared with the virgin formaldehyde-free adhesive exhibit excellent bonding performance, significantly improved water-resistant bonding strength, meeting the national Class II plywood standard requirements, and possess sufficient processing toughness. The panels do not crack during post-processing, resulting in high processing quality and applicability to the production of plywood, particleboard, medium-density fiberboard, and blockboard. These engineered wood panels can degrade and adsorb indoor formaldehyde, thereby addressing the environmental and health problems caused by formaldehyde.

[0036] The main raw material of this invention, low-temperature soybean meal, is a byproduct of agricultural product processing. It is widely available and renewable. It can not only solve the problem of resource utilization of agricultural byproducts and the high cost of biomass adhesives, but also solve the problem of excessive dependence on fossil resources by synthetic adhesives. It meets the requirements of environmental protection and sustainable development and has important economic and social benefits.

[0037] The preparation method of the virgin formaldehyde-free adhesive of this invention is simple and easy to implement, and is suitable for industrial production of engineered wood products. Detailed Implementation

[0038] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0039] The reagents and materials used in this invention, unless otherwise specified, are all commercially available. The low-temperature soybean meal has a particle size of 70-500 mesh and a protein content of 43 wt% or more; the high-temperature soybean meal has a particle size of 70-500 mesh and a protein content of 40%.

[0040] This invention provides a virgin formaldehyde-free adhesive, its preparation method, and its application. Specific embodiments are as follows.

[0041] Example 1

[0042] A PAE resin modifier, comprising the following components in parts by weight:

[0043] The PAE resin modifier prepared by mixing 100 parts water, 24 parts citric acid, 19 parts diethylenetriamine, 25 parts epichlorohydrin, 0.43 parts p-toluenesulfonic acid, and 1 part hydrochloric acid is named S1-19. The preparation method of the above PAE resin modifier is as follows:

[0044] (1) Preheat the so-called diethylenetriamine to 50°C, add 1 / 2 of the citric acid (12 parts), stir to dissolve and react fully, and the stirring conditions are mechanical stirring at a speed of 300 rpm;

[0045] (2) After the citric acid has fully dissolved, add half of the total 1 / 4 citric acid (6 parts) and stir rapidly to dissolve it. Immediately after dissolution, add the remaining 1 / 4 citric acid (6 parts) and heat to 80-85℃. The stirring conditions are mechanical stirring at a speed of 500 rpm;

[0046] (3) Stop heating when the temperature reaches above 80℃, add p-toluenesulfonic acid and stir to promote further polycondensation reaction (the process will continue to exothermic); observe the thermometer, and immediately raise the temperature to 160℃ and maintain it for 3 hours after the exothermic reaction is completed to evaporate the moisture in the system, thus obtaining the amino-terminated polyamide polyamine prepolymer. The stirring conditions are mechanical stirring at a speed of 500 rpm;

[0047] (4) When the prepolymer is cooled to 45-50℃, add 50 parts of water to adjust the solid content to 50%, and add 25 parts of weighed epichlorohydrin monomer dropwise while stirring over 20 minutes. Then raise the temperature to 65℃ and continue stirring for 2.5 hours to obtain PAE resin. Add the remaining 50 parts of water to adjust the solid content to 12.5%, and finally add 1 part of hydrochloric acid to adjust the pH of the solution to 5-6. The stirring conditions are mechanical stirring at 800 rpm to obtain S1-19.

[0048] A virgin formaldehyde-free adhesive is made from the following raw materials in the indicated weight ratios: 100 parts water; 30 parts of the above-mentioned PAE resin modifier; and 35 parts of low-temperature soybean meal.

[0049] The preparation method of the above-mentioned virgin formaldehyde-free adhesive is as follows:

[0050] (1) Weigh out the low-temperature soybean meal, PAE resin modifier and water;

[0051] (2) Dissolve the PAE resin modifier in water and stir evenly (mechanical stirring at room temperature, speed 600 rpm, time 30 minutes).

[0052] (3) Add low-temperature soybean meal to the above solution and stir until homogeneous to obtain biomass protein adhesive.

[0053] This invention utilizes the biomass protein adhesive prepared above to prepare three-layer plywood, as detailed below:

[0054] (1) Veneer: Poplar (400mm×400mm×1.5mm), moisture content 10%;

[0055] (2) Applying adhesive: Apply adhesive to both sides of the core board, with an adhesive application rate of 180g / m². 2 ;

[0056] (3) Assembly: Three veneers are assembled in a direction where the grain of adjacent veneers is perpendicular;

[0057] (4) Hot pressing: hot pressing temperature 120℃, hot pressing pressure 1.0MPa, hot pressing time 6min, holding time 1min.

[0058] The inventors also named the PAE resin modifiers prepared with diethylenetriamine in amounts of 21, 23, 25, 27, and 29 parts, and p-toluenesulfonic acid in amounts of 0.45, 0.47, 0.49, 0.51, and 0.53 parts, respectively, as S1-21, S1-23, S1-25, S1-27, and S1-29.

[0059] The above-mentioned modifiers were used to prepare virgin formaldehyde-free adhesives, and three-layer plywood was prepared using them.

[0060] This invention tests the properties of the PAE resin modifier prepared by the above method and the plywood prepared accordingly. The molecular weight of the PAE resin modifier prepared with different diethylenetriamine contents is determined by gel permeation chromatography (GPC). The wet shear strength of the plywood, the toughness of the virgin formaldehyde-free adhesive layer, and the formaldehyde adsorption capacity of the plywood are also tested. Specific test methods are as follows.

[0061] The specific test method for the wet shear strength of plywood is as follows:

[0062] (1) Sample preparation: In accordance with the national standard GB / T 9846-2015, the prepared plywood was placed in a ventilated place for 24 hours and then cut into 100mm×25mm specimens with a bonding area of ​​25mm×25mm. Before the test, the specimens were placed in water at 63±0.5℃ for 3 hours.

[0063] (2) Tensile test: The maximum load force (N) of the plywood adhesive layer breaking was tested using a universal testing machine at a speed of 100 mm / min. Strength data of 6 samples were obtained for each plywood, and the average value was taken. The test results are shown in Table 1.

[0064] The test method for the toughness of the adhesive layer of virgin formaldehyde-free adhesives is as follows:

[0065] The adhesive layer toughness of the above-mentioned virgin formaldehyde-free adhesive was calculated based on the area integral of the tensile stress-strain curve of the wet shear strength of the above-mentioned plywood. The test results are expressed as bonding work, and the test results are shown in Table 1.

[0066] The test method for formaldehyde adsorption by plywood is as follows:

[0067] (1) Sample preparation: Cut the plywood prepared above into rectangular samples with a specification of 150mm×50mm, ensuring that the surface is free from damage, oil stains and coating interference;

[0068] (2) Pretreatment: The sample was placed in a constant temperature and humidity chamber and equilibrated for 168±2h at a temperature of 25±2℃ and a relative humidity of 50±5% to eliminate the influence of the environment in the early stage; then, the sample was transferred to a desiccator and left to stand for 24h to ensure that there was no free moisture residue on the surface.

[0069] (3) Test chamber configuration: A stainless steel sealed environment chamber conforming to ISO 16000-9 standard (volume 1.0±0.02m³) is adopted. 3 The cabin is equipped with temperature and humidity sensors (accuracy ±0.5℃, ±3%RH) and circulating fans (wind speed 0.1-0.3m / s) to ensure a uniform environment.

[0070] (4) Formaldehyde release and adsorption test:

[0071] a. Background value calibration: After 24 hours of empty cabin operation, the formaldehyde concentration inside the cabin is <0.01 mg / m³. 3 Considered qualified;

[0072] b. Initial formaldehyde release: Inject 0.1% formaldehyde solution (analytical grade, GB / T 685-2016) into the chamber at a rate of 10 mL / m³. 3 Calculate the injection volume, and allow it to stand in a sealed container for (24±0.5) hours until the concentration stabilizes (fluctuation ≤5% in 3 consecutive samplings).

[0073] c. Adsorption stage: The pretreated sample is vertically suspended in the center of the chamber, and the temperature is maintained at (23±0.5)℃, the humidity at (50±3)%, and the air exchange rate is <0.05h⁻¹. The gas in the chamber is collected every 60 minutes until the concentration change rate is ≤2% for 3 consecutive times, which is considered as adsorption equilibrium.

[0074] (5) Gas sampling and analysis:

[0075] a. Phenol reagent spectrophotometry (GB / T 18204.2-2014) was used. 10L of gas was collected using an atmospheric sampler (flow rate 0.5L / min ± 2%), and the absorbance was measured at a wavelength of 630 nm after color development.

[0076] b. Calculate the formaldehyde concentration using the standard curve method (accurate to 0.001 mg / m³). Each set of data was measured in triplicate, and the arithmetic mean was taken.

[0077] (6) Adsorption performance calculation:

[0078] Formaldehyde adsorption capacity is calculated using the following formula:

[0079]

[0080] Q: Formaldehyde adsorption capacity (%)

[0081] C0: Initial formaldehyde concentration (mg / m³) 3 );

[0082] C e Adsorption equilibrium concentration (mg / m³) 3 );

[0083] Each group of samples was tested three times, with a relative standard deviation (RSD) of ≤5%. The test results are shown in Table 1.

[0084] Table 1

[0085]

[0086] As shown in Table 1, the plywood prepared by using citric acid and diethylenetriamine as modifiers in the preparation of virgin formaldehyde-free adhesives exhibits high wet shear strength and formaldehyde adsorption capacity exceeding 56.5%, with a maximum of 76.3%, demonstrating that the method of this invention can effectively control formaldehyde levels over a long period. Furthermore, the bonding work of the prepared plywood is above 0.62 J, indicating high processing toughness and ease of subsequent processing. The best performance is observed when the molar ratio of carboxyl groups to amino groups is 1:1.3.

[0087] Example 2

[0088] In this embodiment, diethylenetriamine was replaced with triethylenetetramine. The specific amounts of each component are shown in Table 2 below, and the other conditions are the same as in Example 1. The prepared PAE resin modifiers were named S2-27, S2-30, S2-33, S2-36, S2-38, and S2-41, respectively.

[0089] Table 2

[0090]

[0091] The PAE resin modifier, virgin formaldehyde-free adhesive and plywood prepared in Example 2 were prepared under the same conditions as in Example 1. The specific performance test results are shown in Table 3.

[0092] Table 3

[0093]

[0094] Table 3 shows that replacing diethylenetriamine with triethylenetetramine, resulting in a carboxyl to amino group ratio of 1:1 to 1:1.5, significantly reduced the wet shear strength and bonding work of the prepared plywood, and also reduced the formaldehyde adsorption to some extent. Furthermore, the best performance was observed when the molar ratio of carboxyl to amino groups was 1:1.3.

[0095] Example 3

[0096] In this embodiment, hydrochloric acid was replaced with an equal mass of formic acid, and the other conditions were the same as in Example 2. The prepared PAE resin modifiers were named S3-27, S3-30, S3-33, S3-36, S3-38, and S3-41, respectively.

[0097] The PAE resin modifier, virgin formaldehyde-free adhesive, and plywood prepared in Example 3 were prepared under the same conditions as in Example 1. The specific performance test results are shown in Table 4.

[0098] Table 4

[0099]

[0100] As shown in Table 4, replacing hydrochloric acid with an equal mass of formic acid resulted in a decrease in the performance of the plywood compared to Example 2.

[0101] To further illustrate the beneficial effects of the present invention, the following comparative examples were constructed.

[0102] Comparative Example 1

[0103] A PAE resin modifier, with the same component dosage as in Example 1 S1-25;

[0104] This comparative example provides a polyamide polyamine resin modifier, the synthesis steps of which are as follows:

[0105] (1) Pour the so-called diethylenetriamine into a four-necked flask, add half of the required total amount of citric acid (12 parts), stir to dissolve and react fully, and the stirring conditions are mechanical stirring at a speed of 300 rpm;

[0106] (2) After the citric acid has fully dissolved, add half (6 parts) of the remaining total citric acid and stir rapidly to dissolve it. Immediately after dissolution, add the remaining citric acid (6 parts) and heat to 80-85℃. The stirring conditions are mechanical stirring at a speed of 500 rpm;

[0107] (3) Stop heating when the temperature reaches above 80℃, add p-toluenesulfonic acid and stir to promote further polycondensation reaction (the process will continue to exothermic); observe the thermometer, and immediately raise the temperature to 160℃ and maintain it for 3 hours after the exothermic reaction is completed to evaporate the moisture in the system, thus obtaining the amino-terminated polyamide polyamine prepolymer. The stirring conditions are mechanical stirring at a speed of 500 rpm;

[0108] (4) When the prepolymer is cooled to 45-50℃, add 50 parts of distilled water to adjust the solid content to 50%, and add 25 parts of weighed epichlorohydrin monomer dropwise while stirring over 20 minutes. Then raise the temperature to 65℃ and continue stirring for 2.5 hours to obtain PAE resin. Add the remaining 50 parts of distilled water to adjust the solid content to 12.5%, and finally add 1 part of hydrochloric acid to adjust the pH of the solution to 5-6. The stirring conditions are mechanical stirring at 800 rpm.

[0109] The remaining conditions are the same as in Example 1.

[0110] Comparative Example 2

[0111] A PAE resin modifier, with the same component dosage as in Example 1 S1-25;

[0112] The preparation method of the above-mentioned modifier includes the following synthesis steps:

[0113] (1) Preheat the so-called diethylenetriamine to 50°C, add the so-called citric acid (24 parts), stir to dissolve it, and then raise the temperature to 80-85°C. The stirring conditions are mechanical stirring at a speed of 500 rpm.

[0114] (2) Stop heating when the temperature reaches above 80℃, add p-toluenesulfonic acid and stir to promote further polycondensation reaction (the process will continue to exothermic); observe the thermometer, and immediately raise the temperature to 160℃ and maintain it for 3 hours after the exothermic reaction is completed to evaporate the moisture in the system, thus obtaining the amino-terminated polyamide polyamine prepolymer. The stirring conditions are mechanical stirring at a speed of 500 rpm;

[0115] (3) When the prepolymer is cooled to 45-50℃, add 50 parts of distilled water to adjust the solid content to 50%, and add 25 parts of weighed epichlorohydrin monomer dropwise while stirring over 20 minutes. Then raise the temperature to 65℃ and continue stirring for 2.5 hours to obtain PAE resin. Add the remaining 50 parts of distilled water to adjust the solid content to 12.5%, and finally add 1 part of hydrochloric acid to adjust the pH of the solution to 5-6. The stirring conditions are mechanical stirring at 800 rpm.

[0116] The remaining conditions are the same as in Example 1.

[0117] Comparative Example 3

[0118] In this comparative example, the low-temperature soybean meal used in the preparation process of the virgin formaldehyde-free adhesive was replaced with an equal mass of high-temperature soybean meal, and the other conditions were the same as in Example 1.

[0119] Comparative Example 4

[0120] A polyamide polyamine resin modifier, with the same component dosage as in Example 2 S2-36;

[0121] This comparative example provides a polyamide polyamine resin modifier, the synthesis steps of which are as follows:

[0122] (1) Pour the triethylenetetramine into a four-necked flask, add half of the required total amount of citric acid (12 parts), stir to dissolve and react fully, and use mechanical stirring at a speed of 300 rpm.

[0123] (2) After the citric acid has fully dissolved, add half (6 parts) of the remaining total citric acid and stir rapidly to dissolve it. Immediately after dissolution, add the remaining citric acid (6 parts) and heat to 80-85℃. The stirring conditions are mechanical stirring at a speed of 500 rpm;

[0124] (3) Stop heating when the temperature reaches above 80℃, add p-toluenesulfonic acid and stir to promote further polycondensation reaction (the process will continue to exothermic); observe the thermometer, and immediately raise the temperature to 160℃ and maintain it for 3 hours after the exothermic reaction is completed to evaporate the moisture in the system, thus obtaining the amino-terminated polyamide polyamine prepolymer. The stirring conditions are mechanical stirring at a speed of 500 rpm;

[0125] (4) When the prepolymer is cooled to 45-50℃, add 50 parts of distilled water to adjust the solid content to 50%, and add 25 parts of weighed epichlorohydrin monomer dropwise while stirring over 20 minutes. Then raise the temperature to 65℃ and continue stirring for 2.5 hours to obtain PAE resin. Add the remaining 50 parts of distilled water to adjust the solid content to 12.5%, and finally add 1 part of hydrochloric acid to adjust the pH of the solution to 5-6. The stirring conditions are mechanical stirring at 800 rpm.

[0126] The remaining conditions are the same as in Example 2.

[0127] Comparative Example 5

[0128] A polyamide polyamine resin modifier, with the same component dosage as in Example 2 S2-36;

[0129] The synthesis steps of the above-mentioned polyamide polyamine resin modifier are as follows:

[0130] (1) Preheat the triethylenetetramine to 50°C, add the citric acid (24 parts), stir to dissolve, then heat to 80-85°C, and stir mechanically at 500 rpm.

[0131] (2) Stop heating when the temperature reaches above 80℃, add p-toluenesulfonic acid and stir to promote further polycondensation reaction (the process will continue to exothermic); observe the thermometer, and immediately raise the temperature to 160℃ and maintain it for 3 hours after the exothermic reaction is completed to evaporate the moisture in the system, thus obtaining the amino-terminated polyamide polyamine prepolymer. The stirring conditions are mechanical stirring at a speed of 500 rpm;

[0132] (3) When the prepolymer is cooled to 45-50℃, add 50 parts of distilled water to adjust the solid content to 50%, and add 25 parts of weighed epichlorohydrin monomer dropwise while stirring over 20 minutes. Then raise the temperature to 65℃ and continue stirring for 2.5 hours to obtain PAE resin. Add the remaining 50 parts of distilled water to adjust the solid content to 12.5%, and finally add 1 part of hydrochloric acid to adjust the pH of the solution to 5-6. The stirring conditions are mechanical stirring at 800 rpm.

[0133] The remaining conditions are the same as in Example 2.

[0134] Comparative Example 6

[0135] In this comparative example, the low-temperature soybean meal used in the preparation process of the virgin formaldehyde-free adhesive was replaced with an equal mass of high-temperature soybean meal, and the other conditions were the same as in Example 2.

[0136] Comparative Example 7

[0137] In this comparative example, citric acid was replaced with an equal mass of adipic acid, diethylenetriamine was used in an amount of 22 parts, p-toluenesulfonic acid was used in an amount of 0.46 parts, and the other conditions were the same as in Example 1 S1-25.

[0138] Comparative Example 8

[0139] In this comparative example, citric acid was replaced with an equal mass of adipic acid, triethylenetetramine was used in 31 parts, p-toluenesulfonic acid was used in 0.55 parts, and the other conditions were the same as in Example 2 S2-36.

[0140] Comparative Example 9

[0141] In this comparative example, the amount of diethylenetriamine was 35 parts, the amount of p-toluenesulfonic acid was 0.59 parts, and the other conditions were the same as in Example 1.

[0142] In Examples 1-3 above, the bonding performance and formaldehyde adsorption performance were optimal when the ratio of carboxyl groups to amino groups was 1:1.3. In Comparative Examples 1-8 above, the molar ratio of polycarboxyl groups to amino groups was 1:1.3, and in Comparative Example 9, the molar ratio of carboxyl groups to amino groups of polyamines was 1:1.8. The optimal detection results of Examples 1-3 and the detection results of Comparative Examples 1-9 are shown in Table 5.

[0143] Table 5

[0144]

[0145] As shown in Table 5, the protein-based adhesive prepared using the polyamino PAE modifier provided by this invention exhibits significantly improved water resistance and enhanced wet shear strength, meeting the requirements for Class II plywood. Furthermore, the engineered wood products prepared with the virgin formaldehyde-free adhesive provided by this invention demonstrate excellent formaldehyde adsorption, offering advantages such as environmental friendliness and irreversible reaction, effectively preventing secondary pollution. This is primarily because the polycarboxylic acid and polyethylenepolyamine, through condensation polymerization, provide active reaction sites for the grafted epichlorohydrin monomer. The condensation polymer and epichlorohydrin monomer further form a highly active cationic nitrogen-containing butanol-structured polyamino PAE resin. This nitrogen-containing butanol structure, along with the active groups (-NH2, -COOH) in the protein-based molecules, forms a stable covalent cross-linked network structure through a ring-opening reaction, preventing water molecule intrusion and thus improving the water resistance of the virgin formaldehyde-free adhesive and the bonding strength of the plywood. In the adhesive crosslinking system used to prepare engineered wood products, the -NH2 in the polyamine-terminated PAE resin undergoes an affinity addition reaction with indoor formaldehyde to generate hydroxymethyl derivatives, thereby achieving the purpose of adsorbing and degrading indoor formaldehyde.

[0146] The inventors also replaced citric acid with aminotriacetic acid, and the relevant examples are as follows.

[0147] Example 4

[0148] In this embodiment, citric acid was replaced with an equal mass of aminotriacetic acid. The specific amounts of each component are shown in Table 6 below, and the other conditions are the same as in Example 1. The prepared PAE resin modifiers were named S4-19, S4-21, S4-23, S4-25, S4-27, and S4-29, respectively.

[0149] Table 6

[0150]

[0151] The PAE resin modifier, virgin formaldehyde-free adhesive, and plywood prepared in Example 4 were prepared under the same conditions as in Example 1. The specific performance test results are shown in Table 7.

[0152] Table 7

[0153]

[0154] As shown in Table 7, replacing citric acid with an equal mass of aminotriacetic acid significantly reduced the performance of the plywood, but it still met the national standard requirements for Class II plywood.

[0155] Example 5

[0156] In this embodiment, citric acid was replaced with an equal mass of aminotriacetic acid. The specific amounts of each component are shown in Table 8 below, and the other conditions are the same as in Example 2. The prepared PAE resin modifiers were named S5-27, S5-30, S5-33, S5-36, S5-38, and S5-41, respectively.

[0157] Table 8

[0158]

[0159] The PAE resin modifier, virgin formaldehyde-free adhesive, and plywood prepared in Example 5 were prepared under the same conditions as in Example 1. The specific performance test results are shown in Table 9.

[0160] Table 9

[0161]

[0162] As shown in Table 9, the performance of PAE resin modifiers prepared from aminotriacetic acid and triethylenetetramine is slightly improved compared with that of PAE resin modifiers prepared from aminotriacetic acid and diethylenetriamine when used in virgin formaldehyde-free adhesives, but the improvement effect is not significant.

[0163] Example 6

[0164] In this embodiment, hydrochloric acid was replaced with an equal mass of formic acid, and the other conditions were the same as in Example 5. The prepared PAE resin modifiers were named S6-27, S6-30, S6-33, S6-36, S6-38, and S6-41, respectively.

[0165] The PAE resin modifier, virgin formaldehyde-free adhesive and plywood prepared in Example 6 were prepared under the same conditions as in Example 1. The specific performance test results are shown in Table 10.

[0166] Table 10

[0167]

[0168] As shown in Table 10, replacing hydrochloric acid with formic acid does not significantly alter the performance compared to Example 5.

[0169] Comparative Example 10

[0170] A PAE resin modifier, with the same component dosage as in Example 4 S4-25;

[0171] The preparation method of the PAE resin modifier in this comparative example is the same as that in Comparative Example 1;

[0172] The remaining conditions are the same as in Example 4.

[0173] Comparative Example 11

[0174] A PAE resin modifier, with the same component dosage as in Example 4 S4-25;

[0175] The preparation method of the PAE resin modifier in this comparative example is the same as that in comparative example 2;

[0176] The remaining conditions are the same as in Example 4.

[0177] Comparative Example 12

[0178] In this comparative example, the low-temperature soybean meal used in the preparation process of the virgin formaldehyde-free adhesive was replaced with an equal mass of high-temperature soybean meal, and the other conditions were the same as in Example 4.

[0179] Comparative Example 13

[0180] In this comparative example, the amount of diethylenetriamine was 35 parts, the amount of p-toluenesulfonic acid was 0.59 parts, and the other conditions were the same as in Example 4.

[0181] In Examples 4-6 above, the bonding performance and formaldehyde adsorption performance were optimal when the ratio of carboxyl groups to amino groups was 1:1.3. In Comparative Examples 10-12, the molar ratio of carboxyl groups to amino groups was 1:1.3, and in Comparative Example 13, the molar ratio of carboxyl groups to amino groups was 1:1.8. The optimal detection results of Examples 4-6 and the detection results of Comparative Examples 10-13 are shown in Table 11.

[0182] Table 11

[0183]

[0184] As shown in Table 11, replacing citric acid with aminotriacetic acid resulted in a deterioration in the performance of the plywood. However, the wet shear strength of the plywood still met the requirements for Class II plywood, and it exhibited excellent formaldehyde adsorption performance.

[0185] The inventors also replaced citric acid with ethylenediaminetetraacetic acid, and the relevant examples are as follows.

[0186] Example 7

[0187] In this embodiment, citric acid was replaced with an equal mass of ethylenediaminetetraacetic acid. The specific amounts of each component are shown in Table 12 below, and the other conditions are the same as in Example 1. The prepared PAE resin modifiers were named S7-17, S7-19, S7-20, S7-22, S7-24, and S7-25, respectively.

[0188] Table 12

[0189]

[0190] The PAE resin modifier, virgin formaldehyde-free adhesive and plywood prepared in Example 7 were prepared under the same conditions as in Example 1. The specific performance test results are shown in Table 13.

[0191] Table 13

[0192]

[0193] As shown in Table 13, replacing citric acid with an equal mass of ethylenediaminetetraacetic acid significantly reduced the performance of the plywood compared to Example 1.

[0194] Example 8

[0195] In this embodiment, diethylenetriamine was replaced with triethylenetetramine. The specific amounts of each component are shown in Table 14 below, and the other conditions are the same as in Example 1. The prepared PAE resin modifiers were named S8-24, S8-26, S8-29, S8-31, S8-34, and S8-36, respectively.

[0196] Table 14

[0197]

[0198] The PAE resin modifier, virgin formaldehyde-free adhesive and plywood prepared in Example 8 were prepared under the same conditions as in Example 1. The specific performance test results are shown in Table 15.

[0199] Table 15

[0200]

[0201] As shown in Table 15, replacing diethylenetriamine with triethylenetetramine improved the performance of the plywood compared to Example 7, but the improvement was not significant.

[0202] Example 9

[0203] In this embodiment, hydrochloric acid was replaced with an equal mass of formic acid, and the other conditions were the same as in Example 8. The prepared PAE resin modifiers were named S9-24, S9-26, S9-29, S9-31, S9-34, and S9-36, respectively.

[0204] The PAE resin modifier, virgin formaldehyde-free adhesive and plywood prepared in Example 9 were prepared under the same conditions as in Example 1. The specific performance test results are shown in Table 16.

[0205] Table 16

[0206]

[0207] As shown in Table 16, replacing hydrochloric acid with formic acid resulted in a decrease in the performance of the plywood compared to Example 8.

[0208] Comparative Example 14

[0209] A PAE resin modifier, with the same component dosage as in Example 7 S7-22;

[0210] The preparation method of the PAE resin modifier in this comparative example is the same as that in Comparative Example 1;

[0211] The remaining conditions are the same as in Example 7.

[0212] Comparative Example 15

[0213] A PAE resin modifier, with the same component dosage as in Example 7 S7-22;

[0214] The preparation method of the PAE resin modifier in this comparative example is the same as that in comparative example 2;

[0215] The remaining conditions are the same as in Example 7.

[0216] Comparative Example 16

[0217] In this comparative example, the low-temperature soybean meal used in the preparation process of the virgin formaldehyde-free adhesive was replaced with an equal mass of high-temperature soybean meal, and the other conditions were the same as in Example 7.

[0218] Comparative Example 17

[0219] In this comparative example, the amount of diethylenetriamine was 30 parts, the amount of p-toluenesulfonic acid was 0.54 parts, and the other conditions were the same as in Example 7.

[0220] In Examples 7-9 above, the bonding performance and formaldehyde adsorption performance were optimal when the ratio of carboxyl groups to amino groups was 1:1.3. In Comparative Examples 14-16 above, the molar ratio of carboxyl groups to amino groups was 1:1.3, and in Comparative Example 17, the molar ratio of carboxyl groups to amino groups was 1:1.8. The optimal detection results of Examples 7-9 and the detection results of Comparative Examples 14-17 are shown in Table 17.

[0221] Table 17

[0222]

[0223] As shown in Table 17, replacing citric acid with ethylenediaminetetraacetic acid (EDTA) resulted in plywood with inferior performance compared to plywood made with citric acid, but superior performance compared to plywood made with ethylenediaminetetraacetic acid (EDTA). However, the wet shear strength of the plywood still met the requirements for Class II plywood, and it exhibited excellent formaldehyde adsorption performance.

[0224] In summary, by introducing an excess of polyethylene polyamine, the prepared polyamide polyamine epichlorohydrin (PAE) resin can be end-capped with active amino groups, which enables the modified protein-based adhesive to continuously absorb and fix formaldehyde during bonding and use, thus achieving long-term formaldehyde control in engineered wood panels bonded with the aforementioned biomass protein adhesive.

[0225] The above description is a preferred embodiment of the present invention. For those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A PAE resin modifier, characterized in that, It is prepared from the following raw materials in parts by weight: 100 parts water; 24 parts polycarboxylic acid; 15-65 parts polyethylene polyamine; 15-25 parts epichlorohydrin; 0.4-0.9 parts catalyst; 0.5-2.5 parts acid; The polycarboxylic acid is citric acid, aminotriacetic acid, or ethylenediaminetetraacetic acid; the polyethylene polyamine is diethylenetriamine, triethylenetetraamine, or tetraethylenepentamine; the catalyst is p-toluenesulfonic acid and / or (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; the acid is one or more of hydrochloric acid, sulfuric acid, and formic acid; the molar ratio of the carboxyl group in the polycarboxylic acid to the amino group in the polyethylene polyamine is 1:1-1.

5.

2. The PAE resin modifier according to claim 1, characterized in that, It is prepared from the following raw materials in parts by weight: 100 parts water; 24 parts citric acid; 19-29 parts diethylenetriamine; 25 parts epichlorohydrin; 0.43-0.53 parts p-toluenesulfonic acid; and 1 part hydrochloric acid.

3. The PAE resin modifier according to claim 2, characterized in that, The amount of p-toluenesulfonic acid added is 1% of the total mass of polyethylene polyamine and polycarboxylic acid.

4. The method for preparing the PAE resin modifier according to any one of claims 1-3, characterized in that, include: Step 1: Weigh the raw materials according to the proportions; Step 2: Preheat the polyethylene polyamine to 50°C, then add 1 / 2 of the polycarboxylic acid and stir until fully dissolved; Step 3: Add 1 / 4 of the polycarboxylic acid to the solution from Step 2 and stir until fully dissolved; then add the remaining polycarboxylic acid and heat to 80-85℃; Step 4: Stop heating, add catalyst and stir to make the reaction complete, then immediately raise the temperature to 160-175℃ and keep it for 3 hours to evaporate the water in the system, and obtain amino-terminated polyamide polyamine prepolymer; Step 5: When the above prepolymer cools naturally to 45-50℃, adjust the solid content to 50% with water, and add epichlorohydrin monomer dropwise while stirring over 20 minutes. Then raise the temperature to 65℃ and continue stirring for 2.5 hours to obtain PAE resin. Adjust the solid content to 12.5%-45% with water and adjust the pH of the solution to 5-6 with acid.

5. A virgin formaldehyde-free adhesive, characterized in that, Includes the PAE resin modifier according to any one of claims 1-3.

6. The virgin formaldehyde-free adhesive according to claim 5, characterized in that, It is composed of the following components by weight: 100 parts water; 20-35 parts PAE resin modifier; 30-45 parts protein raw material; wherein the protein raw material is low-temperature soybean meal or camellia oil meal, the particle size of the protein raw material is 70-500 mesh, and the protein content in the protein raw material is above 43 wt%.

7. The method for preparing the virgin formaldehyde-free adhesive according to claim 5 or 6, characterized in that, include: (1) Weigh out the protein raw materials, PAE resin modifier and water according to the weight parts of each raw material; (2) Dissolve the PAE resin modifier in water and stir until homogeneous; (3) Add the protein raw material to the above solution and stir until homogeneous to obtain protein-based adhesive.

8. The method for preparing the virgin formaldehyde-free adhesive according to claim 7, characterized in that, The stirring conditions in steps (2)-(3) are mechanical stirring, with a speed of 300-600 rpm, a stirring temperature of 20-35℃, and a stirring time of 10-30 minutes.

9. The method for preparing the virgin formaldehyde-free adhesive according to claim 7, characterized in that, The protein-based adhesive has a solids content of 30-50%wt, a viscosity (25℃) of 1000-3500mPa·s, and an active period of 15-30 days.

10. The application of the virgin formaldehyde-free adhesive according to claim 5 or 6, characterized in that, Applications of the virgin formaldehyde-free adhesive in wood products, bamboo products, printed materials, decorations, and buildings.

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