CN115819696B - Low free formaldehyde melamine formaldehyde resin with antibacterial property and preparation method thereof - Google Patents

Abstract

The invention discloses a low free formaldehyde melamine formaldehyde resin with antibacterial property and a preparation method thereof. And (3) selecting paraformaldehyde and melamine as raw materials to obtain melamine formaldehyde resin prepolymer solution, and regulating the pH value by utilizing guanidine phosphate urea solution to obtain novel melamine formaldehyde resin powder. And then adding cysteine to reduce the content of free formaldehyde in the obtained powder. Zinc acetate is used as a zinc source by a hydrothermal method and a chemical deposition method, a structure inducer is added, and a layer of zinc oxide is coated on the outer wall of melamine formaldehyde powder. The invention creatively proposes to utilize the guanidyl urea phosphate solution to adjust the pH value of the melamine formaldehyde resin prepolymer solution, and simultaneously, the guanidyl urea phosphate can be grafted with the melamine formaldehyde resin, so that the impact resistance of the powder is improved. By a hydrothermal method, a layer of nano zinc oxide grows on the outer wall of the melamine formaldehyde microsphere, so that the antibacterial performance of the powder is integrally improved.

Description

A low-free formaldehyde melamine formaldehyde resin with antibacterial properties and its preparation method

Technical Field

The invention relates to a low-free-formaldehyde melamine-formaldehyde resin with antibacterial performance and a preparation method thereof.

Background Art

Melamine formaldehyde resin (MF) is an amino resin formed by the polycondensation reaction of formaldehyde and melamine. The reaction process can be roughly divided into two stages. In the first stage, melamine and formaldehyde are subjected to a hydroxymethylation reaction to obtain a melamine resin prepolymer liquid. At this time, a mixture of polymethylol melamine prepolymers is obtained. In the second stage, methylol melamine undergoes a further polycondensation reaction to generate a series of different oligomers. Generally, two types of bridge bonds are generated, namely methylene bridge bonds and methylene ether bridge bonds. Under acidic conditions, the hydroxymethylated oligomers cross-link to form infusible and insoluble substances. Melamine formaldehyde resin can be degraded in an acid solution with a low pH value and can pass through the small holes in the cavity wall of the core-shell microspheres to form melamine formaldehyde resin microspheres. Generally speaking, in the hydroxylation process, in order to make the reaction rate gentle and controllable, the hydroxylation is carried out under alkaline conditions. At the same time, in order to meet the requirements of the molecular weight of the MF prepolymer in the subsequent powder preparation, the pH of the system is adjusted to a weak acid after a period of hydroxymethylation. Melamine-formaldehyde resin microspheres are a new type of polymer material with simple and easy-to-obtain raw materials, low cost, large specific surface area and regular and orderly structure.

Melamine formaldehyde resin microspheres have flame retardancy, chemical corrosion resistance, etc., and are widely used, but they have almost no antibacterial properties. Zinc oxide is a common inorganic antibacterial agent. Under ultraviolet light, the valence band of nano-ZnO produces charged holes. These holes react with oxygen, hydroxyl groups and water adsorbed on the surface of the material to produce hydroxyl free radicals and active oxygen ions with reducing effects, thereby stimulating oxygen in the air and water to become active oxygen. Active oxygen has extremely strong oxidizing activity. They can react with organic matter in a variety of microorganisms, such as hydroxyl groups, to destroy the proliferation ability of bacterial cells, thereby inhibiting or killing bacteria.

However, there is an obvious interface between zinc oxide and melamine formaldehyde powder, and zinc oxide cannot be coated on the surface of melamine formaldehyde resin powder by simply mixing the two substances. Common methods for changing the surface of a substance include: photolithography, vapor deposition, sol-gel, hydrothermal, electrochemical, template, etc. The present invention grows zinc oxide on the surface of melamine formaldehyde resin powder by hydrothermal and chemical deposition.

Summary of the invention

The object of the present invention is to provide a melamine formaldehyde resin powder with low free formaldehyde and antibacterial properties and a preparation method thereof. The melamine formaldehyde resin powder is different from the traditional melamine formaldehyde resin powder in structure, has low free formaldehyde content and has antibacterial properties.

In order to achieve the above object, the present invention adopts the following technical solution:

A method for preparing a melamine-formaldehyde resin powder with low free formaldehyde and antibacterial properties comprises the following steps:

1) Take 50 mL of deionized water, adjust the pH to 8.5-9 with alkali, add it into a three-necked flask with stirring and condensation, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, react for 1 hour, and obtain a melamine formaldehyde resin prepolymer solution.

2) When the test precipitation ratio is 2:2 (i.e., after aspirating 2 mL of the reaction solution into a clean test tube and adding 2 mL of ice water, the sample becomes turbid and does not become clear after shaking), add guanidine phosphate urea solution to the melamine formaldehyde resin prepolymer solution, adjust the pH to 4-5, raise the temperature to 80°C, and react for 2 hours.

3) Add a certain amount of cysteine, stir for 1 hour, cool, filter, and dry to obtain melamine formaldehyde resin powder.

4) Weigh a certain mass of the melamine formaldehyde resin powder obtained in step 3), add anhydrous zinc acetate, sodium citrate, urea and water, stir at 40° C. for 1 hour, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95° C. for 8 hours, filter and dry to obtain the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties.

In step 1), the substances used for adjusting the alkalinity include: sodium hydroxide, triethanolamine, triethylamine, and ethylenediamine.

In step 1), melamine is added in batches at a ratio of 3:1:1, and the interval between each addition is 10 minutes.

In step 2), the guanidinyl urea phosphate solution is prepared by weighing 1 g of guanidinyl urea phosphate and dissolving it in 120 mL of deionized water.

In step 3), after cysteine is added, its concentration is 1wt%-5wt%.

In step 4), melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 15-25g: 9g: 2g: 1L.

In the present invention, sodium citrate is a structural inducing agent, and urea provides alkaline conditions for hydrothermal growth.

The principle of the present invention is as follows: Guanidinyl urea phosphate is a substance similar to a pH buffer, composed of three groups: urea, phosphoric acid and guanidine. The pH of its aqueous solution is 4-5 at room temperature, and the pH value does not change with the temperature, which can just meet the weak acid condition required for the later cross-linking of the melamine formaldehyde resin of the present invention. At the same time, the substance has an amino group, which can react with the melamine formaldehyde resin prepolymer, increase the distance between triazine rings, reduce the cross-linking density of the molecule, and improve the flexibility.

As an amino acid derivative, the amino group on cysteine molecules can easily react with formaldehyde to generate stable and harmless compounds, which can be used to eliminate free formaldehyde. Cysteine has high reactivity and will not produce secondary pollution during the reaction.

The formation of the zinc oxide layer of the present invention is mainly divided into three steps: hydrolysis, nucleation, and growth. Urea is decomposed by heat, and the generated ammonia is mixed with solvent water to generate ammonium ions and hydroxide ions, providing an alkaline environment for the reaction; zinc acetate provides zinc ions and acetate ions for the reaction; sodium citrate is a structural inducer, and hydrolysis to generate citrate ions is helpful for nucleation. Zinc ions are grafted onto the outer wall of the powder under the action of the structural inducer and the hydroxyl groups of the melamine formaldehyde resin powder itself, and then begin to grow on the surface under the joint action of citrate, acetate, and hydroxide. The zinc ions on the surface of the microspheres and the hydroxide generated by hydrolysis generate zinc hydroxide and tetrahydroxy zinc ions. As the reaction proceeds, the zinc hydroxide and tetrahydroxy zinc ions decompose to generate zinc oxide, and a structure of zinc oxide-coated melamine formaldehyde resin powder is obtained.

The beneficial effects of the present invention are:

1. Paraformaldehyde is used to replace the traditional formaldehyde solution. Paraformaldehyde is solid and depolymerizes in water to become small molecules, which reduces the free formaldehyde to a certain extent.

2. By adding melamine in batches, the amount of free formaldehyde can be reduced to a certain extent.

3. Guanidine urea phosphate is not only a new type of pH regulating substance that can adjust the acidity of the resin solution, but also can react with melamine formaldehyde resin oligomers to obtain a new type of melamine formaldehyde resin powder with good compression resistance.

4. Cysteine can react with free formaldehyde to reduce the free formaldehyde content.

5. Using zinc acetate as a zinc source, a layer of zinc oxide is coated on the outer wall of the melamine formaldehyde resin microspheres by a hydrothermal method. Zinc oxide, as a common antibacterial agent, can greatly improve the antibacterial properties of melamine formaldehyde resin powder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a SEM image of a low-free-formaldehyde melamine-formaldehyde resin powder having antibacterial properties according to Example 1;

FIG2 is a SEM image of the low free formaldehyde melamine formaldehyde resin powder of Comparative Example 3;

FIG3 is an infrared image of guanidinium urea phosphate and the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties in Example 1;

FIG. 4 is an XRD diagram of the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties of Example 1.

DETAILED DESCRIPTION

The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these embodiments.

Example 1

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 0.5 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry at 80 °C.

(5) Weigh a certain mass of the powder obtained in step (4), add anhydrous zinc acetate, sodium citrate, urea and water in a ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 20g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C to obtain the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties.

Example 2

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 1 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry at 80 °C.

(5) Weigh a certain mass of the powder obtained in step (4), add anhydrous zinc acetate, sodium citrate, urea and water in a ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 20g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C to obtain the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties.

Example 3

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 1.5 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry at 80 °C.

(5) Weigh a certain mass of the powder obtained in step (4), add anhydrous zinc acetate, sodium citrate, urea and water in a ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 20g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C to obtain the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties.

Example 4

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 2 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry at 80 °C.

(5) Weigh a certain mass of the powder obtained in step (4), add anhydrous zinc acetate, sodium citrate, urea and water in a ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 20g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C to obtain the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties.

Example 5

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 2.5 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry at 80 °C.

(5) Weigh a certain mass of the powder obtained in step (4), add anhydrous zinc acetate, sodium citrate, urea and water in a ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 20g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C to obtain the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties.

Example 6

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 1.5 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry at 80 °C.

(5) Weigh a certain mass of the powder obtained in step (4), add anhydrous zinc acetate, sodium citrate, urea and water in a ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 15g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C to obtain the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties.

Example 7

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 1.5 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry at 80 °C.

(5) Weigh a certain mass of the powder obtained in step (4), add anhydrous zinc acetate, sodium citrate, urea and water in a ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 25g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C to obtain the low free formaldehyde melamine formaldehyde resin powder with antibacterial properties.

Comparative Example 1 (Compared with Example 3, without adding cysteine)

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Weigh a certain mass of the powder obtained in step (3), add anhydrous zinc acetate, sodium citrate, urea and water in the ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 20g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C.

Comparative Example 2 (Compared with Example 3, guanidine urea phosphate was not used, and dilute sulfuric acid was used to adjust the pH of the system)

(1) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(2) When the test precipitation ratio is 2:2, adjust the pH to 4 with dilute sulfuric acid, raise the temperature to 80°C, and react for 2 hours.

(3) Add 1.5 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry at 80 °C.

(4) Weigh a certain mass of the powder obtained in step (3), add anhydrous zinc acetate, sodium citrate, urea and water in the ratio of melamine formaldehyde resin powder: anhydrous zinc acetate: sodium citrate: urea: water = 5g: 20g: 9g: 2g: 1L, stir at 40°C for 1h, pour into a polytetrafluoroethylene reactor, perform hydrothermal reaction at 95°C for 8h, filter with suction, and dry at 80°C.

Comparative Example 3 (Compared with Example 3, zinc oxide is not coated)

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 1.5 g of cysteine, stir for 1 hour, cool to room temperature, filter, and dry to obtain low free formaldehyde melamine formaldehyde resin powder.

Comparative Example 4 (Compared with Example 3, nano zinc oxide was added by blending using a physical method)

(1) Preparation of guanidine urea phosphate solution: Weigh 1 g of guanidine urea phosphate and dissolve it in 120 mL of deionized water. Stir at room temperature for 15 min.

(2) Take 50 mL of deionized water with a measuring cylinder, adjust the pH to 8.5 with alkali, add the water to a three-necked flask with stirring and condensing, add 3.7 g of paraformaldehyde, raise the temperature to 70°C, wait for the solution to become clear, add 2.6 g of melamine, and react for 1 h.

(3) When the test precipitation ratio is 2:2, add guanidine phosphate urea solution, adjust the pH to 4, raise the temperature to 80℃, and react for 2h.

(4) Add 1.5 g of cysteine, stir for 1 h, cool to room temperature, filter, and dry.

(5) Weigh a certain amount of the novel melamine formaldehyde resin powder obtained in step (4), and mix it evenly with a certain amount of nano zinc oxide at room temperature, melamine formaldehyde resin powder: nano zinc oxide = 5 g: 8.85 g.

In order to measure the free formaldehyde content in the melamine formaldehyde powder prepared in the examples and comparative examples, a spectrophotometric method was used. The method is as follows: weigh 150 mg of modified or unmodified powder, add 100 mL of distilled water, stir at 40 ° C for 1 hour, and filter to obtain a formaldehyde extraction solution. Weigh 37.5 g of anhydrous ammonium acetate, 0.75 mL of acetic acid, and 0.5 mL of acetylacetone solution, and use a 250 mL volumetric flask to make up the volume to obtain an acetylacetone solution. Take 5 mL of the extract and 5 mL of the acetylacetone solution, color in a colorimetric dish at 40 ° C for 30 minutes, use an ultraviolet spectrophotometer, and test the absorbance at 410 nm. The content of free formaldehyde in the powder is deduced through the standard curve of formaldehyde content.

Table 1 shows the free formaldehyde content of melamine formaldehyde resin powder prepared with different cysteine concentrations. Examples 1-5 correspond to cysteine concentrations of 1%-5%, respectively, and Comparative Example 1 does not add cysteine.

Table 1 Test results of free formaldehyde content

As can be seen from Table 1, the free formaldehyde content of the obtained material was detected by ultraviolet spectrophotometer. The results show that the addition of cysteine can significantly reduce the content of free formaldehyde in the powder, and the addition of cysteine at different concentrations has different effects on the elimination of formaldehyde. Within the concentration range of the present invention, when the concentration is 3%, the content of free formaldehyde is the lowest, but if the concentration continues to increase, it will be found that the effect decreases. This is because when the concentration of cysteine is too high, cysteine and melamine formaldehyde resin will produce a coupling negative effect, making the structure of melamine formaldehyde resin unstable, decomposing it into small molecules again, and releasing formaldehyde. At the same time, from an economic perspective, the concentration of cysteine is not suitable to be too high.

The antibacterial performance test of Examples 3, 6, 7 and Comparative Examples 3 and 4 uses fluorescent Escherichia coli. Take the nutrient agar culture of Escherichia coli from the third to the eighth generation, dilute the strain concentration to about 10 ⁵ cfu/mL with 0.03 mol/L phosphate buffer, and obtain a prefabricated bacterial suspension. Weigh 0.5g of the powder to be tested, put it into a three-necked flask, add 95mL of PBS containing 0.1% Tween 80, mix well, and then add 5mL of the prefabricated bacterial suspension. Fix the three-necked flask on a constant temperature shaker, shake at 150r/min at 37°C, measure the liquid luminescence value at intervals, and calculate the antibacterial rate.

Table 2 shows the antibacterial performance test of the powders obtained in some embodiments and comparative examples

As can be seen from Table 2, after zinc oxide coating, the antibacterial properties of each embodiment are improved. The antibacterial property of Example 7 is the best. After culturing in the culture medium for 10 minutes, the antibacterial property has reached 86.18%. After 50 minutes, the antibacterial rate reaches 99.97%. At the same time, it can be seen that with the increase of the amount of zinc oxide added, the antibacterial property gradually improves. Comparative Example 4 Simply physically mix the nano zinc oxide powder and the melamine formaldehyde resin powder. From the results, although the antibacterial property is improved, it is not as good as the effect of coating by hydrothermal method. The reason is that when the powder obtained by physical mixing is tested for antibacterial property, only the bacteria that come into contact with the nano zinc oxide powder can be inactivated, and the bacteria that come into contact with the melamine formaldehyde resin powder are not quickly inactivated. The melamine formaldehyde resin powder coated with nano zinc oxide has its own outer wall modified, and has antibacterial property, which increases the contact area with the bacteria, and the antibacterial property is significantly improved.

Table 3 shows the impact strength test of Example 3 and Comparative Example 2. The obtained powder was pressed into 80mm*10mm*2mm strips at 200°C and 5MPa by hot pressing. It can be seen from Table 3 that the powder prepared by using guanidine urea phosphate has stronger impact strength than the powder prepared by using sulfuric acid as pH regulator in conventional synthesis.

Table 3 Impact strength test table

FIG1 is a scan of the low-free-formaldehyde melamine formaldehyde resin powder with antibacterial properties of Example 1, illustrating that the melamine formaldehyde resin powder is spherical in shape, has an uneven surface, and is attached with a layer of mesh material, which is zinc oxide.

FIG2 is a scanned image of the low free formaldehyde melamine formaldehyde resin powder of Comparative Example 3, in which it is observed that the particles are partially bonded to each other and are in a full spherical shape.

Figure 3 is an infrared image of guanidinourea phosphate and melamine formaldehyde resin powder with antibacterial properties. In guanidinourea phosphate, 3000 cm ^-1 -3500 cm ^-1 is the stretching vibration of OH, 2500-3000 is υ (-CH2-), 1639 cm ^-1 is υ (O = P-OH), 1265 cm ^-1 is υ (P = O), and 1118 cm ^-1 is the stretching vibration of PO. The absorption peak of melamine formaldehyde resin powder with antibacterial properties at 1618 cm ^-1 is the stretching vibration absorption peak of the primary amine bond, 3410 cm ^-1 is the stretching vibration absorption peak of the secondary amine NH, the broad peak at 1500 cm ^-1 -1600 cm -1 is the combination of the vibration absorption peak of the triazine ring and υ (O = P-OH), and the three absorption peaks of 1557 cm ^-1 , 1350 cm ^-1 , and 810 cm ^-1 are the skeleton vibration absorption peaks of the triazine ring. The symmetric and antisymmetric stretching vibration absorption peaks of COC are at 1152 cm ^-1 and 992 cm ^-1 , while υ(PO) appears at 1004 cm ^-1 .

Figure 4 is the XRD pattern of zinc oxide/melamine formaldehyde resin powder. According to JCPDS standard card no. 36-1451, the diffraction angles of 33.8°, 38.1°, and 59.2° respectively represent the characteristic absorption peaks of (001), (101), and (110) of the wurtzite crystal form of zinc oxide. The diffraction peaks within the diffraction range less than 30° are consistent with the diffraction peaks of layered basic zinc acetate (Zn ₅ (OH) ₈ Ac _2· 2H ₂ O). 7.11°, 14.14°, and 21.36° correspond to the (001), (002), and (003) crystal planes, respectively. At the same time, 33.07°, 58.67°, and 69.2° correspond to the (100), (110), and (200) crystal planes.

The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims (4)

1. A method for preparing a low free formaldehyde melamine formaldehyde resin with antibacterial property, which is characterized by comprising the following steps:

1) Measuring 50mL of deionized water, regulating the pH to 8.5-9 with alkali, adding the deionized water into a three-neck flask with stirring and condensation, adding 3.7g of paraformaldehyde, heating to 70 ℃, adding 2.6g of melamine after the solution is clarified, and reacting for 1h to obtain melamine formaldehyde resin prepolymer solution;

2) Adding guanidine urea phosphate solution into melamine formaldehyde resin prepolymer solution, regulating pH to 4-5, heating to 80 ℃ and reacting for 2h;

3) Adding a certain amount of cysteine, stirring for 1h, cooling, performing suction filtration and drying to obtain melamine formaldehyde resin powder;

4) Weighing a certain mass of the powder obtained in the step 3), adding anhydrous zinc acetate, sodium citrate, urea and water, stirring at 40 ℃ for 1h, pouring into a polytetrafluoroethylene reaction kettle, performing hydrothermal reaction at 95 ℃ for 8h, performing suction filtration, and drying to obtain the low free formaldehyde melamine formaldehyde resin with antibacterial property;

In step 4), melamine formaldehyde resin powder, anhydrous zinc acetate, sodium citrate, urea, water=5 g, 15-25g, 9g, 2g, 1l.

2. The method according to claim 1, wherein the method for preparing the guanidyl urea phosphate solution comprises: 1g of guanidyl urea phosphate was weighed and dissolved in 120mL of deionized water to prepare the product.

3. The process according to claim 1, wherein the final concentration of cysteine added in step 3) is 1% to 5% by weight.

4. A low free formaldehyde melamine formaldehyde resin with antibacterial properties prepared by the preparation method as claimed in any one of claims 1 to 3.