CN117757394A - Urea-formaldehyde resin adhesive and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of adhesive preparation, and particularly discloses a urea-formaldehyde resin adhesive and a preparation method thereof. The urea-formaldehyde resin adhesive provided by the invention comprises formaldehyde aqueous solution, urea, polyvinyl alcohol, modified straw, an anti-aging agent, a curing agent, modified starch and 4-methylbenzenesulfonic acid. The urea-formaldehyde resin adhesive provided by the invention synthesizes urea-formaldehyde resin by taking formaldehyde aqueous solution and urea as main components, and adds specific modified straw and modified starch, wherein a three-dimensional reticular macromolecular crosslinking structure is formed between the components through crosslinking reaction, so that the cementing strength and water resistance of the urea-formaldehyde resin adhesive are improved, the content of free formaldehyde can be further reduced, the problem of overhigh formaldehyde release in the prior art is fundamentally solved, the usability is good, the process is simple, the operation is easy, and the urea-formaldehyde resin adhesive is suitable for batch production.

Description

A kind of urea-formaldehyde resin adhesive and preparation method thereof

Technical field

The present invention relates to the technical field of adhesive preparation, and in particular to a urea-formaldehyde resin adhesive and a preparation method thereof.

Background technique

At present, there are many ways to reduce the formaldehyde emission of artificial boards, such as: using low-formaldehyde or formaldehyde-free adhesives to replace traditional urea-formaldehyde resin; adding formaldehyde adsorbents to the board to adsorb and fix formaldehyde; choosing a process with low formaldehyde emission Certified boards. However, alternative adhesives are usually more expensive and inferior to urea-formaldehyde resins in terms of performance and cost; formaldehyde adsorbents usually need to be replaced periodically, increasing maintenance costs, and the performance of the adsorbents is also susceptible to temperature and humidity; after low formaldehyde Emissions-certified panels are more expensive, have complex preparation processes, and are in limited supply. To sum up, although the above measures can reduce the formaldehyde content in artificial boards to a certain extent, they still have problems such as high cost or difficulty in mass production. Therefore, it is of great significance to provide a urea-formaldehyde resin adhesive that has good water resistance, low formaldehyde content, and high bonding strength.

Contents of the invention

In view of this, the present invention provides a urea-formaldehyde resin adhesive and a preparation method thereof. The present invention uses formaldehyde aqueous solution and urea as the main components to synthesize the urea-formaldehyde resin, and adds specific modified straw and modified starch. The components are cross-linked. The reaction forms a three-dimensional network of macromolecular cross-linked structures, which improves the bonding strength and water resistance of the urea-formaldehyde resin adhesive, further reduces the content of free formaldehyde, and fundamentally solves the problem of excessive formaldehyde release in the existing technology.

In order to solve the above technical problems, the technical solution provided by the present invention is:

The first aspect of the present invention provides a urea-formaldehyde resin adhesive, which includes the following components by mass: 200-250 parts of formaldehyde aqueous solution, 143-160 parts of urea, 2-5 parts of polyvinyl alcohol, and 10 parts of modified straw. -15 parts, 5-7 parts of antioxidant, 12-14 parts of curing agent, 10-15 parts of modified starch and 12-18 parts of 4-methylbenzenesulfonic acid;

Wherein, the mass concentration of the formaldehyde aqueous solution is 36.5%-37.5%;

The modified straw is straw modified by sodium hydroxide aqueous solution, sodium dodecyl benzene sulfonate and sodium dodecyl sulfate;

The modified starch is starch modified by hydrochloric acid aqueous solution and sodium persulfate.

Compared with the prior art, the urea-formaldehyde resin adhesive provided by the present invention uses formaldehyde aqueous solution and urea as the main components to synthesize urea-formaldehyde resin, and also adds modified straw and modified starch. Among them, the straw modified by adding specific components makes the modification The modified straw has excellent specific surface area and is loaded with a large number of reactive groups, which can react with free formaldehyde in urea-formaldehyde resin and reduce the content of free formaldehyde in the board; specific modified straw and urea-formaldehyde resin have excellent binding force and can be used in 4-formaldehyde resin. Under the action of benzene sulfonic acid, it can also be combined in the network structure of urea-formaldehyde resin. The hydroxyl groups in the modified straw and the dimethylol urea and oligomers in the urea-formaldehyde resin form an acetal structure, further improving the urea-formaldehyde resin adhesive. Water resistance and cementing strength; modified starch has a large number of active hydroxyl groups and other active groups, among which the active hydroxyl groups can react with formaldehyde to reduce the content of free formaldehyde in the board, and the active groups can also cross-link with urea-formaldehyde resin , greatly improving the bonding strength of urea-formaldehyde resin adhesive.

The present invention uses formaldehyde aqueous solution and urea as main components to synthesize urea-formaldehyde resin, and adds specific modified straw and modified starch. Each component forms a three-dimensional network macromolecular cross-linked structure through a cross-linking reaction, which improves the efficiency of the urea-formaldehyde resin. The bonding strength and water resistance of the adhesive can further reduce the content of free formaldehyde, fundamentally solving the problem of excessive formaldehyde release in the existing technology.

Preferably, the preparation of the modified straw includes the following steps:

S1. Add sodium hydroxide aqueous solution to the straw, soak at 30°C-40°C, filter, wash, and dry to obtain primary modified straw;

S2. Add sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and water to the primary modified straw, soak at 50°C-60°C, filter, wash with water, and dry to obtain the modified straw. .

In the present invention, after first using sodium hydroxide to modify the straw, the fiber tissue becomes fluffy and the surface will be damaged to a certain extent, thereby increasing the specific surface area of the straw. Furthermore, the primary modified straw is soaked in a specific surfactant. , the straw modified by sodium hydroxide has excellent specific surface area, the surfactant can be loaded more in the straw, providing a large number of active groups, which react with the free formaldehyde in the urea-formaldehyde resin, thereby reducing the concentration of free formaldehyde in the board. content; due to the excellent binding force between modified straw and urea-formaldehyde resin, it can also be combined in the network structure of urea-formaldehyde resin. The hydroxyl groups in the modified straw and the dimethylolurea and oligomers in the urea-formaldehyde resin form acetal. structure to further improve the water resistance and bonding strength of urea-formaldehyde resin adhesive.

Further preferably, in S1, the particle size of the straw is 15nm-30nm.

Further preferably, in S1, the mass concentration of the sodium hydroxide aqueous solution is 10%-12%.

Further preferably, in S1, the mass ratio of the straw and sodium hydroxide aqueous solution is 1: (8-10).

Further preferably, in S1, the soaking time is 4h-5h.

Further preferably, in S2, the mass ratio of straw, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and water is 1: (1.8-2.0): (1.3-1.5): (22-26 ).

Further preferably, in S2, the soaking time is 12h-18h.

Preferably, the preparation of the modified starch includes the following steps:

Step 1. Disperse starch in water, then add hydrochloric acid aqueous solution, and react at 50°C-55°C to obtain a primary modified starch aqueous emulsion;

Step 2: Add sodium persulfate to the primary modified starch aqueous emulsion, react at 60°C-70°C, and dry to obtain modified starch.

The present invention first uses hydrochloric acid aqueous solution to modify starch, which is beneficial to acidolysis of hydrochloric acid starch and provides more active groups; further, by selecting sodium persulfate as an oxidant to react with the primary modified starch, the active hydroxyl groups can be Oxidized to carboxyl groups, it can react with formaldehyde and reduce the content of free formaldehyde in the board; the active groups in modified starch can also cross-link with urea-formaldehyde resin, greatly improving the bonding strength of urea-formaldehyde resin adhesive.

Further preferably, in step 1, the reaction time is 5h-8h.

Further preferably, in step 1, the mass ratio of starch and water is 1: (8-10).

Further preferably, in step 1, the mass concentration of the hydrochloric acid aqueous solution is 1%-3%.

Further preferably, in step 1, the mass ratio of the starch and hydrochloric acid aqueous solution is 1: (0.04-0.07).

Further preferably, in step 2, the reaction time is 3h-5h.

Further preferably, in step 2, the mass ratio of the primary modified starch aqueous emulsion and sodium persulfate is 1: (0.1-0.15).

Preferably, the antioxidant is antioxidant AW.

Preferably, the curing agent is ammonium chloride.

A second aspect of the present invention provides a preparation method for the above-mentioned modified urea-formaldehyde resin adhesive, which includes the following steps:

Step a. Weigh each component according to the mass ratio, adjust the pH of the weighed formaldehyde aqueous solution to 7-7.5, then add polyvinyl alcohol, incubate at 50°C-60°C for 20min-30min, and then add 30%- 40% urea is reacted at 80℃-90℃ for 60min-70min to obtain the first reaction system;

Step b. Adjust the pH of the first reaction system to 4-5, then add 30%-40% urea, and react at 95°C-100°C for 50min-80min to obtain the second reaction system;

Step c. Adjust the pH of the second reaction system to 7-7.5, then add remaining urea, and react at 50°C-58°C for 30min-40min to obtain urea-formaldehyde resin;

Step d. Mix the urea-formaldehyde resin, modified straw, antioxidant, modified starch and 4-methylbenzenesulfonic acid evenly at 100°C-120°C, then react at 40°C-50°C, and the reaction is completed Then add a curing agent and mix evenly to obtain the urea-formaldehyde resin adhesive.

Further preferably, in step d, the reaction time is 50min-80min.

The urea-formaldehyde resin adhesive provided by the invention uses formaldehyde aqueous solution and urea as main components to synthesize urea-formaldehyde resin, and adds specific modified straw and modified starch. The components form a three-dimensional network macromolecular cross-linked structure through cross-linking reactions. , improves the bonding strength and water resistance of urea-formaldehyde resin adhesive, can further reduce the content of free formaldehyde, and fundamentally solves the problem of excessive formaldehyde release in the existing technology. It has good performance, simple process, easy operation, and is suitable for Mass production.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with examples. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

Example 1

This embodiment provides a urea-formaldehyde resin adhesive, including the following components by mass: 200 parts of formaldehyde aqueous solution with a mass concentration of 37%, 143 parts of urea, 2 parts of polyvinyl alcohol, 7 parts of modified straw, 7 parts of antioxidant, cured 12 parts of agent, 15 parts of modified starch and 12 parts of 4-methylbenzenesulfonic acid;

Wherein, the preparation of the modified straw includes the following steps:

S1. Add a sodium hydroxide aqueous solution with a mass concentration of 12% to the straw with a particle size of 15 nm, soak it at 40°C for 4 hours, filter, wash, and dry to obtain primary modified straw; among them, the ratio of the straw and the sodium hydroxide aqueous solution is The mass ratio is 1:8;

S2. Add sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and water to the primary modified straw, and soak at 50°C for 12 hours to obtain the modified straw; wherein, straw, dodecane The mass ratio of sodium benzene sulfonate and sodium dodecyl sulfate is 1:2.0:1.5:22;

Among them, the preparation of modified starch includes the following steps:

Step 1. Disperse starch in water, then add a hydrochloric acid aqueous solution with a mass concentration of 1%, and react at 55°C for 5 hours to obtain a primary modified starch aqueous emulsion; wherein, the mass ratio of starch to water is 1:8, and the starch and The mass ratio of hydrochloric acid aqueous solution is 1:0.04;

Step 2. Add sodium persulfate to the primary modified starch aqueous emulsion, react at 70°C for 3 hours, and dry to obtain modified starch; wherein, the mass ratio of the primary modified starch aqueous emulsion and sodium persulfate is 1: 0.15;

This embodiment also provides a preparation method for the above-mentioned urea-formaldehyde resin adhesive, which includes the following steps:

(1) Weigh each component according to the mass ratio, adjust the pH of the weighed formaldehyde aqueous solution to 7-7.5, then add polyvinyl alcohol, keep it at 60°C for 30 minutes, then add 40% urea, and heat at 90°C React for 60 minutes to obtain the first reaction system;

(2) Adjust the pH of the first reaction system to 4-5, then add 40% urea, and react at 95°C for 50 minutes to obtain the second reaction system;

(3) Adjust the pH of the second reaction system to 7-7.5, then add remaining urea, and react at 50°C for 40 minutes to obtain urea-formaldehyde resin;

(4) Mix the urea-formaldehyde resin, modified straw, antioxidant, modified starch and 4-methylbenzenesulfonic acid evenly at 100°C, and then react at 50°C for 50 minutes. After the reaction is completed, add the curing agent and mix evenly. , to obtain urea-formaldehyde resin adhesive.

Example 2

This embodiment provides a urea-formaldehyde resin adhesive, including the following components by mass: 250 parts of formaldehyde aqueous solution with a mass concentration of 37%, 160 parts of urea, 5 parts of polyvinyl alcohol, 10 parts of modified straw, 5 parts of antioxidant, cured 14 parts of agent, 10 parts of modified starch and 18 parts of 4-methylbenzenesulfonic acid;

Wherein, the preparation of the modified straw includes the following steps:

S1. Add a sodium hydroxide aqueous solution with a mass concentration of 10% to the straw with a particle size of 30 nm, soak it at 30°C for 5 hours, filter, wash, and dry to obtain primary modified straw; among them, the ratio of the straw and the sodium hydroxide aqueous solution is The mass ratio is 1:10;

S2. Add sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and water to the primary modified straw, and soak at 60°C for 18 hours to obtain the modified straw; wherein, straw, dodecane The mass ratio of sodium benzene sulfonate and sodium dodecyl sulfate is 1:1.8:1.3:26;

Among them, the preparation of modified starch includes the following steps:

Step 1. Disperse starch in water, then add a hydrochloric acid aqueous solution with a mass concentration of 3%, and react at 50°C for 8 hours to obtain a primary modified starch aqueous emulsion; wherein, the mass ratio of starch to water is 1:10, and the mass ratio of starch and water is 1:10. The mass ratio of hydrochloric acid aqueous solution is 1:0.07;

Step 2. Add sodium persulfate to the primary modified starch aqueous emulsion, react at 60°C for 5 hours, and dry to obtain modified starch; wherein, the mass ratio of the primary modified starch aqueous emulsion and sodium persulfate is 1: 0.1;

This embodiment also provides a preparation method for the above-mentioned urea-formaldehyde resin adhesive, which includes the following steps:

(1) Weigh each component according to the mass ratio, adjust the pH of the weighed formaldehyde aqueous solution to 7-7.5, then add polyvinyl alcohol, keep it at 50°C for 20 minutes, then add 30% urea, and heat at 80°C React for 70 minutes to obtain the first reaction system;

(2) Adjust the pH of the first reaction system to 4-5, then add 30% urea, and react at 100°C for 80 minutes to obtain the second reaction system;

(3) Adjust the pH of the second reaction system to 7-7.5, then add remaining urea, and react at 58°C for 40 minutes to obtain urea-formaldehyde resin;

(4) Mix the urea-formaldehyde resin, modified straw, antioxidant, modified starch and 4-methylbenzenesulfonic acid evenly at 120°C, and then react at 40°C for 80 minutes. After the reaction is completed, add the curing agent and mix Evenly, the urea-formaldehyde resin adhesive is obtained.

Example 3

This embodiment provides a urea-formaldehyde resin adhesive, including the following components by mass: 220 parts of formaldehyde aqueous solution with a mass concentration of 37%, 150 parts of urea, 3 parts of polyvinyl alcohol, 9 parts of modified straw, 6 parts of antioxidant, cured 13 parts of agent, 12 parts of modified starch and 16 parts of 4-methylbenzenesulfonic acid;

Wherein, the preparation of the modified straw includes the following steps:

S1. Add a sodium hydroxide aqueous solution with a mass concentration of 11% to the straw with a particle size of 20 nm, soak it at 35°C for 4.5 hours, filter, wash, and dry to obtain primary modified straw; among which, the straw and sodium hydroxide aqueous solution The mass ratio is 1:9;

S2. Add sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and water to the primary modified straw, and soak at 55°C for 16 hours to obtain the modified straw; wherein, straw, dodecane The mass ratio of sodium benzene sulfonate and sodium dodecyl sulfate is 1:1.9:1.4:25;

Among them, the preparation of modified starch includes the following steps:

Step 1. Disperse the starch in water, then add a hydrochloric acid aqueous solution with a mass concentration of 2%, and react at 55°C for 6 hours to obtain a primary modified starch aqueous emulsion; wherein, the mass ratio of starch to water is 1:9, and the starch and The mass ratio of hydrochloric acid aqueous solution is 1:0.05;

Step 2. Add sodium persulfate to the primary modified starch aqueous emulsion, react at 63°C for 4 hours, and dry to obtain modified starch; wherein, the mass ratio of the primary modified starch aqueous emulsion and sodium persulfate is 1: 0.13;

This embodiment also provides a preparation method for the above-mentioned urea-formaldehyde resin adhesive, which includes the following steps:

(1) Weigh each component according to the mass ratio, adjust the pH of the weighed formaldehyde aqueous solution to 7-7.5, then add polyvinyl alcohol, keep it at 55°C for 25 minutes, then add 35% urea, and heat at 85°C React for 65 minutes to obtain the first reaction system;

(2) Adjust the pH of the first reaction system to 4-5, then add 35% urea, and react at 98°C for 60 minutes to obtain the second reaction system;

(3) Adjust the pH of the second reaction system to 7-7.5, then add remaining urea, and react at 55°C for 35 minutes to obtain urea-formaldehyde resin;

(4) Mix the urea-formaldehyde resin, modified straw, antioxidant, modified starch and 4-methylbenzenesulfonic acid evenly at 110°C, and then react at 45°C for 70 minutes. After the reaction is completed, add the curing agent and mix evenly. , to obtain urea-formaldehyde resin adhesive

Comparative example 1

The difference between this comparative example and Example 1 is that sodium dodecylbenzene sulfonate is replaced by an equal amount of vinyltrimethoxysilane, and the remaining components and steps are the same as in Example 1.

Comparative example 2

The difference between this comparative example and Example 1 is that sodium persulfate is replaced by an equal amount of hydrogen peroxide, and the remaining components and steps are the same as in Example 1.

The urea-formaldehyde resin adhesive provided in Examples 1-3 and Comparative Examples 1-2 was tested, in which the formaldehyde release amount was tested in accordance with GBT 17657-2013 "Physical and Chemical Performance Test of Artificial Panels and Decorative Artificial Panels";

The bonding strength is tested in accordance with GB/T 9846-2015 "Ordinary Plywood";

Water resistance test: The bonding strength of the board is measured according to the provisions of GB/T 9846-2015 after the board is prepared into strips and soaked in 70°C hot water for 3 hours;

The specific test results are shown in Table 1:

Table 1

Test items Formaldehyde release (mg/L) Cement strength (MPa) Cement strength after soaking in hot water for 3 hours (MPa) Example 1 0.21 1.39 0.92 Example 2 0.23 1.28 0.87 Example 3 0.18 1.32 0.88 Comparative example 1 0.42 0.82 Ungluing the board Comparative example 2 0.63 0.69 Ungluing the board

As can be seen from Table 1, the formaldehyde release amount of the urea-formaldehyde resin adhesive provided in Examples 1-3 of the present invention is as low as 0.18 mg/L, the cementing strength can reach 1.39MPa, and the cementing strength after soaking in hot water for 3 hours can also reach 0.92MPa; the present invention Using urea-formaldehyde resin as the main component, and adding specific modified straw and modified starch, the three components form a three-dimensional network macromolecular cross-linked structure through cross-linking reactions, which improves the bonding strength and water resistance of the urea-formaldehyde resin adhesive. It has good performance, can further reduce the content of free formaldehyde, and fundamentally solves the problem of excessive formaldehyde release in the existing technology. It has good performance, simple process, easy operation, and is suitable for mass production.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (10)

1. The urea-formaldehyde resin adhesive is characterized by comprising the following components in parts by weight: 200-250 parts of formaldehyde aqueous solution, 143-160 parts of urea, 2-5 parts of polyvinyl alcohol, 7-10 parts of modified straw, 5-7 parts of anti-aging agent, 12-14 parts of curing agent, 10-15 parts of modified starch and 12-18 parts of 4-methylbenzenesulfonic acid;

wherein the mass concentration of the formaldehyde aqueous solution is 36.5% -37.5%;

the modified straw is modified by sodium hydroxide aqueous solution, sodium dodecyl benzene sulfonate and sodium dodecyl sulfate;

the modified starch is hydrochloric acid aqueous solution and sodium persulfate modified starch.

2. The urea-formaldehyde resin adhesive as set forth in claim 1, wherein the preparation of the modified straw comprises the steps of:

s1, adding a sodium hydroxide aqueous solution into straw, soaking at 30-40 ℃, filtering, washing with water, and drying to obtain primary modified straw;

s2, adding sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and water into the primary modified straw, soaking at 50-60 ℃, filtering, washing with water, and drying to obtain the modified straw.

3. The urea-formaldehyde resin adhesive according to claim 2, wherein in S1, the particle size of the straw is 15nm-30nm; and/or

In S1, the mass concentration of the sodium hydroxide aqueous solution is 10% -12%; and/or

In S1, the mass ratio of the straw to the sodium hydroxide aqueous solution is 1 (8-10); and/or

In S1, the soaking time is 4-5 h.

4. The urea-formaldehyde resin adhesive as set forth in claim 2, wherein in S2, the mass ratio of the straw, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and water is 1 (1.8-2.0): (1.3-1.5): (22-26); and/or

And S2, soaking for 12-18 hours.

5. The urea-formaldehyde resin adhesive as set forth in claim 1, wherein the preparation of the modified starch comprises the steps of:

step 1, dispersing starch in water, then adding hydrochloric acid aqueous solution, and reacting at 50-55 ℃ to obtain primary modified starch aqueous emulsion;

and step 2, adding sodium persulfate into the primary modified starch aqueous emulsion, reacting at 60-70 ℃, and drying to obtain modified starch.

6. The urea-formaldehyde resin adhesive according to claim 5, wherein in step 1, the reaction time is 5h to 8h; and/or

In the step 1, the mass ratio of the starch to the water is 1 (8-10); and/or

In the step 1, the mass concentration of the hydrochloric acid aqueous solution is 1% -3%; and/or

In the step 1, the mass ratio of the starch to the aqueous solution of hydrochloric acid is 1 (0.04-0.07).

7. The urea-formaldehyde resin adhesive according to claim 5, wherein in step 2, the reaction time is 3h to 5h; and/or

In the step 2, the mass ratio of the primary modified starch aqueous emulsion to the sodium persulfate is 1 (0.1-0.15).

8. The urea-formaldehyde resin adhesive according to claim 1, wherein the anti-aging agent is an anti-aging agent AW; and/or

The curing agent is ammonium chloride.

9. A method for preparing the urea-formaldehyde resin adhesive as set forth in any one of claims 1 to 8, comprising the steps of:

step a, weighing the components according to the mass ratio, regulating the pH value of the weighed formaldehyde aqueous solution to 7-7.5, then adding polyvinyl alcohol, preserving heat at 50-60 ℃ for 20-30 min, then adding 30-40% of urea, and reacting at 80-90 ℃ for 60-70 min to obtain a first reaction system;

step b, regulating the pH value of the first reaction system to be 4-5, then adding 30% -40% of urea, and reacting at 95-100 ℃ for 50-80 min to obtain a second reaction system;

step c, regulating the pH value of the second reaction system to 7-7.5, then adding the rest urea, and reacting at 50-58 ℃ for 30-40 min to obtain urea-formaldehyde resin;

and d, uniformly mixing the urea-formaldehyde resin, the modified straw, the anti-aging agent, the modified starch and the 4-methylbenzenesulfonic acid at the temperature of 100-120 ℃, then reacting at the temperature of 40-50 ℃, and adding a curing agent after the reaction is completed, and uniformly mixing to obtain the urea-formaldehyde resin adhesive.

10. The method for preparing urea-formaldehyde resin adhesive according to claim 9, wherein in the step d, the reaction time is 50min-80min.