CN107022102B

CN107022102B - Preparation method of monodisperse mesoporous silica, nano composite foaming agent, preparation method and application

Info

Publication number: CN107022102B
Application number: CN201710287285.5A
Authority: CN
Inventors: 郭灿雄; 梅莉
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2017-04-27
Filing date: 2017-04-27
Publication date: 2022-12-13
Anticipated expiration: 2037-04-27
Also published as: CN107022102A

Abstract

The invention provides a preparation method of monodisperse mesoporous silica, a nano composite foaming agent, a preparation method and application. Preparing silica sol by using elemental silicon powder as a silicon source, adjusting the particle size of the silica sol by supplementing silicon powder and sodium hydroxide solution, and synthesizing urea-formaldehyde resin/SiO by polymerizing the silica sol through a polymerization-induced colloid condensation method ₂ And (4) compounding the microspheres, and calcining to obtain the monodisperse mesoporous silica. The nano composite foaming agent is prepared by compounding monodisperse mesoporous silica and azodicarbonamide. The composite foaming agent prepared by the invention has small particle size and high loading amount of chemical foaming agent, so that microcellular foam plastic with better foaming quality can be obtained, and the composite foaming agent has wide application prospect.

Description

Preparation method of monodisperse mesoporous silica, nano composite foaming agent, preparation method and application

Technical Field

The invention relates to the field of foaming agents, mainly relates to the field of nano composite foaming agents, and particularly relates to a composite foaming agent, a foamed product, and preparation methods and applications thereof.

Background

The silica microspheres are widely applied to chromatographic column fillers, coatings, catalysts and the like due to the characteristics of high mechanical strength, good stability and easy dispersion in solvents. Meanwhile, the silicon dioxide microspheres also have the advantages of nontoxicity, hydrophilicity, easy functionalization of surface hydroxyl groups and the like, and have potential application values in the fields of biological detection and medicine. The porous silica microspheres with uniform particle size and controllable pore size are the most commonly used carrier materials in the nano mesoporous composite material.

Microcellular foams mean cell sizes of 0.1 to 10 μm with cell densities of 10 ⁹ -10 ¹⁵ Per cm ³ . The microporous foamed plastic has high impact strength which is more than 5 times that of the traditional foamed plastic, high toughness and high rigidity-weight ratio which is 8-9 times of the fatigue life of the common porous plastic, high thermal stability and great potential application value due to the unique property of the microporous foamed plastic.

At present, two types of foaming agents are mainly used for preparing the foam plastics, one type is a physical foaming agent, the other type is a chemical foaming agent, and most of the foaming agents adopt the physical foaming agent for foaming. At present, in the foaming of a physical foaming agent, the supercritical fluid is increasingly regarded as the production of microcellular foam plastics. Supercritical fluid refers to a fluid state between two phases, gas and liquid, at a temperature and pressure both above the critical value. The density and solvating power of the supercritical fluid are close to those of liquid, the viscosity and diffusion coefficient are close to those of gas, the physical and chemical properties of the fluid near the critical point are extremely sensitive to the change of temperature and pressure, and the properties of the fluid can be adjusted by pressure under the condition of not changing the chemical composition. However, this method requires strict conditions, and requires control of pressure, temperature, and depressurization rate, etc. during the experiment. When the chemical foaming agent is used for preparing the foam plastic, the compatibility of the chemical foaming agent in a polymer matrix is lower than that of the physical foaming agent, and agglomeration is easy to occur.

The composite foaming agent in the patent application 200710064945.X is a foaming agent compounded by utilizing the adsorption effect of silicon dioxide, the composite foaming agent is easy to agglomerate, and foam plastics produced by utilizing the foaming agent have larger cell size and uneven distribution.

Patent application 201010176081.2 discloses a nanocomposite blowing agent based on porous inorganic materials: after the porous inorganic material is modified, the object of the composite foaming agent is dissolved in a certain quantitative solvent, and is compounded with the modified porous inorganic material, and after a period of time, the nano composite foaming agent is prepared by separation and drying. Although the patent can solve the problem of agglomeration of the foaming agent to a certain extent, the foaming efficiency of the nano composite foaming agent still needs to be improved.

Disclosure of Invention

The technical problem solved by the invention is as follows: although the existing composite foaming agent can solve the problem that the size of a foam hole is difficult to control to a certain extent, the composite effect of the existing foaming agent is still to be improved, nucleation points on the composite foaming agent are still to be improved, and the foaming efficiency and the foaming quality are still to be further improved. The epoxy resin needs a foaming agent to have certain compatibility with the epoxy resin, and the foaming agent has smaller particles and higher dispersity, so that the foamed plastic with smaller cells can be obtained.

The purpose of the invention is: the silicon dioxide is used as a main body, the nano composite foaming agent is provided, and the composite process of the silicon dioxide and the organic foaming agent is optimized by synthesizing the monodisperse mesoporous silicon dioxide, so that the composite efficiency and the dispersing performance of the foaming agent are improved, and the foaming efficiency and the foaming quality are further improved.

In order to solve the technical problems, the inventor provides a nano composite foaming agent, which contains a chemical foaming agent and mesoporous silica, wherein the mesoporous silica is prepared by taking elemental silicon powder as a silicon source to prepare silica sol, and the size of the silica sol particle is adjusted by supplementing silicon powder and a sodium hydroxide solution, so that the obtained silica with controllable pore size is obtained.

The invention also provides a preparation method of the nano composite foaming agent, which comprises the following steps: mixing and contacting the mesoporous silica with a chemical foaming agent in the presence of an organic solvent, and fully washing.

In the present invention, the term "mesoporous" refers to pores having an average pore diameter of between 2 and 50nm, that is, mesoporous refers to a material having an average pore diameter of between 2nm and 50nm; the term "nanocomposite" refers to spherical particles in which the filler material size is on the micron scale, but the pore size is on the nanometer scale, in a composite filler phase material.

The invention also provides an application of the nano composite foaming agent in preparing a foaming product and microcellular foam.

Specifically, the invention provides the following technical scheme:

the invention provides a nano composite foaming agent, wherein the nano composite foaming agent contains monodisperse mesoporous silica and azodicarbonamide.

The nanocomposite blowing agent preferably has a particle size of the monodisperse mesoporous silica of 1 to 7 μm, preferably 3 to 5 μm.

Any one of the above nanocomposite blowing agents is preferable, wherein the maximum value of the pore volume of the mesoporous silica corresponds to a pore diameter of 5 to 12nm, preferably 10 to 12nm.

Preferably, any one of the nanocomposite foaming agents described above, wherein the mass ratio of the monodisperse mesoporous silica to the azodicarbonamide is 5: (2-4), preferably in a mass ratio of 5:3.

any of the above-mentioned nanocomposite blowing agents is preferred, wherein the particle size of the nanocomposite blowing agent is 3 to 20 μm, preferably 3 to 10 μm.

The invention also provides a preparation method of any one of the nano composite foaming agents, which comprises the following steps:

step (1): preparing silica sol by using elemental silicon powder as a silicon source, and adjusting the particle size of the silica sol by supplementing silicon powder and a sodium hydroxide solution;

step (2): synthesizing the urea-formaldehyde resin/SiO 2 composite microspheres from the target product silica sol obtained in the step (1) by a polymerization-induced colloid condensation method, and calcining to obtain monodisperse mesoporous silica, wherein the urea-formaldehyde resin/SiO 2 composite microspheres are preferably synthesized by diluting the target product silica sol and then by the polymerization-induced colloid condensation method. The dilution is preferably with water.

And (3): adding the monodisperse mesoporous silica into an aqueous solution of dimethyl sulfoxide containing azodicarbonamide to obtain a mixed solution, and carrying out solid-liquid separation on the mixed solution to obtain the nano composite foaming agent, wherein the aqueous solution of dimethyl sulfoxide containing azodicarbonamide is heated before adding the silica, or the obtained mixed solution is heated.

The preparation method is preferable, wherein the size of the silica sol particle of the target product obtained in the step (1) is 20-50nm.

In any one of the above production methods, the sodium hydroxide solution in the step (1) preferably has a mass concentration of 0.5%.

Preferably, in any of the above preparation methods, the mass concentration range of the diluted silica sol in the step (2) is: 7.5% -15%, preferably 7.5% -10%.

In any of the above preparation methods, preferably, in the step (2), when the urea resin/SiO 2 composite microspheres are synthesized by polymerization-induced colloid aggregation, the urea and formaldehyde raw materials are added in a molar ratio of 1: (1.1-2.0), and the preferred molar ratio is 1.

In any of the above production methods, preferably, the step (2) of calcining includes the steps of:

step (1): heating the temperature from room temperature to a first calcining temperature, and preserving the temperature for 30-60min;

step (2): heating the temperature from the first calcining temperature to the second calcining temperature, and preserving the heat for 30-60min;

step (3): heating the second calcining temperature to a third calcining temperature, and preserving heat for 1-3h;

step (4): heating the third calcining temperature to a fourth calcining temperature;

step (5): heating the fourth calcining temperature to the fifth calcining temperature, and preserving the heat for 1-3h;

wherein the first calcining temperature is 90-120 ℃, the second calcining temperature is 180-220 ℃, the third calcining temperature is 250-300 ℃, the fourth calcining temperature is 330-400 ℃, and the fifth calcining temperature is 500-600 ℃.

In any of the above-mentioned production methods, preferably, the calcination temperature-increasing rates are respectively:

step (1): 1-7 ℃/min, preferably 3-5 ℃/min;

step (2): 1-5 ℃/min, preferably 2-3 ℃/min;

step (3): 1-10 ℃/min, preferably 1-3 ℃/min;

step (4): 1-5 ℃/min, preferably 1-2 ℃/min;

step (5): 3-10 deg.C/min, preferably 3-5 deg.C/min.

In any of the above production methods, it is preferable that the concentration of the azodicarbonamide in the aqueous dimethyl sulfoxide solution containing the azodicarbonamide in the step (3) is 0.03 to 0.05mol/L, preferably 0.04mol/L.

In any of the above production methods, washing with ethanol is preferably performed a plurality of times.

The invention also provides the nano composite foaming agent prepared by any one of the preparation methods.

The invention also provides a foamed product which is obtained by foaming the nano composite foaming agent, the curing agent and the epoxy resin raw material.

The foamed product preferably comprises the following components in percentage by weight: (2-4): (5-7): 100, preferably the weight ratio of (3-4): (6-7): 100.

the above foamed article is preferably wherein the foamed article is an epoxy resin microcellular foam.

The invention also provides application of the nano composite foaming agent in the field of foaming agents.

The invention also provides a preparation method of the monodisperse mesoporous silica, which comprises the following steps: step (1): preparing silica sol by using elemental silicon powder as a silicon source, and adjusting the particle size of the silica sol by supplementing silicon powder and a sodium hydroxide solution;

step (2): diluting the silica sol obtained in the step (1), synthesizing urea resin/SiO 2 composite microspheres from the diluted silica sol by a polymerization-induced colloid condensation method, and calcining to obtain the monodisperse mesoporous silica. The dilution is preferably with water.

Preferably, the method for preparing the monodisperse mesoporous silica comprises the step (1) of obtaining silica sol particles with the size of 20-50nm.

Preferably, the method for preparing the monodisperse mesoporous silica includes the step (1) in which the sodium hydroxide solution has a mass concentration of 0.5%.

Preferably, in the method for preparing the monodisperse mesoporous silica, the mass concentration range of the diluted silica sol in the step (2) is as follows: 7.5% -15%, preferably 7.5% -10%.

Preferably, in the step (2), in the synthesis of the urea-formaldehyde resin/SiO 2 composite microspheres by polymerization-induced colloid aggregation, the molar ratio of urea to formaldehyde is 1: (1.1-2.0), preferably the molar ratio is 1.

In the method for preparing the monodisperse mesoporous silica, the calcination in the step (2) preferably includes the steps of:

step (2): heating the temperature from the first calcining temperature to the second calcining temperature, and preserving the temperature for 30-60min;

Preferably, the preparation method of the monodisperse mesoporous silica comprises the following steps:

step (1): 1-7 ℃/min, preferably 3-5 ℃/min;

step (2): 1-5 ℃/min, preferably 2-3 ℃/min;

step (3): 1-10 ℃/min, preferably 1-3 ℃/min;

step (4): 1-5 ℃/min, preferably 1-2 ℃/min;

step (5): 3-10 deg.C/min, preferably 3-5 deg.C/min.

The invention has the beneficial effects that:

in the nano composite foaming agent, the size of silicon dioxide is uniform, and the size distribution of the prepared composite foaming agent particles is narrow; the mesoporous silica has larger mesoporous pore canals, excellent dispersibility and good sphericity, and the agglomeration of the nano-composite foaming agent in the drying process is reduced by introducing the chemical foaming agent into the mesoporous silica with larger pore diameter and uniform dispersion and washing, so that the agglomeration phenomenon of the washed nano-composite foaming agent is obviously improved.

Because the silicon dioxide has good dispersibility and a washing process is introduced in the process of preparing the composite foaming agent, the composite foaming agent has more uniform particle size and better dispersibility.

The nano composite foaming agent provided by the invention has small particle size, the pore size of the silicon dioxide enables the foaming agent loading amount to be improved, and the prepared foam plastic has smaller cells and higher cell density, so that the microporous foam plastic with better foaming quality can be obtained.

The foaming agent disclosed by the invention is high in decomposition temperature, is not easy to foam in advance, is applied to epoxy resin, and is relatively uniform and compact in size of obtained foam holes in a foaming process.

The silicon dioxide prepared by the method has uniform size, complete particles and good sphericity;

the invention adjusts the aperture size of the silicon dioxide by changing the size of the silica sol particles, and the aperture of the silicon dioxide is controllable.

Drawings

FIGS. 1-a,1-b,1-c are transmission electron microscope images of silica sol particles. The test conditions were: acceleration voltage: 200kv, magnification: 50000, camera length: 0mm, film number: 001. scale in the figure: 100nm.

FIG. 1-a is a transmission electron microscope photograph of primary particle silica sol particles according to example 1 of the present invention.

FIG. 1-b is a TEM image of 2 silicon-supplemented silica sol particles according to example 2 of the present invention.

FIG. 1-c is a TEM image of 4 silicon-supplemented silica sol particles according to example 3 of the present invention.

FIGS. 2-a to 2-e are scanning electron micrographs of mesoporous silica in examples, under the test conditions of voltage: 20kv, magnification: 1000. scale in the figure: 50 μm.

FIG. 2-a is a scanning electron microscope photograph of the mesoporous silica in example 4.

FIG. 2 b is a scanning electron microscope photograph of the mesoporous silica in example 5.

FIG. 2-c is a scanning electron microscope photograph of the mesoporous silica in example 6.

FIG. 2 d is a scanning electron microscope photograph of the mesoporous silica in example 7.

FIG. 2-e is a scanning electron microscope photograph of the mesoporous silica of example 8.

Figure 3 is a graph of the pore size distribution of silica according to an embodiment of the present invention,

wherein a is the pore size distribution curve of the silica described in example 4 of the present invention;

wherein b is the pore size distribution curve of the silica described in example 5 of the present invention;

wherein c is the pore size distribution curve of the silica described in example 6 of the present invention;

wherein d is the pore size distribution curve of the silica described in example 7 of the present invention;

wherein e is the pore size distribution curve of the silica described in example 8 of the present invention.

FIG. 4 is a thermogravimetric plot of a nanocomposite blowing agent according to an embodiment of the present invention,

wherein a is the thermogravimetric curve of the nanocomposite foaming agent described in example 9 of the invention;

wherein b is the thermogravimetric curve of the nanocomposite blowing agent described in example 10 of the present invention;

wherein c is the thermogravimetric curve of the nanocomposite blowing agent described in example 11 of the present invention.

FIG. 5-a is a scanning electron micrograph of the nanocomposite blowing agent of example 11 of the present invention, with test conditions of voltage: 20kv, magnification: 500, scale in the figure: 100 μm.

FIG. 5-b is a scanning electron micrograph of the nanocomposite blowing agent of example 12 of the present invention, under test conditions of voltage: 20kv, magnification: 500, scale in the figure: 100 μm.

FIG. 6 is a thermogravimetric plot of a nanocomposite blowing agent according to an embodiment of the present invention,

wherein a is the thermogravimetric curve of the nanocomposite blowing agent described in example 13 of the present invention;

wherein b is the thermogravimetric curve of the nanocomposite blowing agent described in example 14 of the present invention.

FIG. 7 is a scanning electron microscope image of the foam blown with epoxy resin with nanocomposite blowing agent of example 15, with test conditions of voltage: 20kv, magnification: 40, scale in the figure: 1mm.

Detailed Description

As described above, the present invention aims to: provides a nano composite foaming agent which takes mesoporous silicon dioxide as a main body and an organic foaming agent as an object.

In a preferred embodiment, the preparation process of the nanocomposite foaming agent of the present invention is as follows:

preparation of mesoporous silica:

obtaining mesoporous silicon dioxide by a polymerization-induced colloid condensation method, soaking single-substance silicon powder in hot water at 70 ℃ for 10 minutes for activation, and centrifuging to obtain activated single-substance silicon powder. And then adding 200g of sodium hydroxide solution with the mass concentration of 0.5% into a three-neck flask, heating to 60-80 ℃, adding activated silicon powder, stirring to react for 12-24h, separating the reaction mixture, wherein the separated solution is the primary particles of the silica sol. The primary particles of the silica sol obtained are used as mother liquor, the same steps as the preparation of the primary particles are adopted, and silica sol with different particle sizes is obtained by supplementing silica powder and sodium hydroxide solution with the mass fraction of 0.5%. The amount of the supplemented elemental silicon powder and the amount of the supplemented sodium hydroxide solution can be equal to or different from the amount of the corresponding raw material elemental silicon powder and the raw material sodium hydroxide solution in the mother liquor. The size of the silica sol particles is adjusted by supplementing simple substance silicon powder and sodium hydroxide, wherein the supplementing times can be adjusted according to the particle size.

The concentration of sodium hydroxide is important, and when the concentration is too high, the silica sol becomes gel when the pH is adjusted to 1.5, and the concentration is too low, so that the silica powder cannot be hydrolyzed sufficiently.

The silica sol is diluted to a mass concentration of 7.5-15% with deionized water and the pH of the silica sol is adjusted to 1.5-2.0 with a hydrochloric acid solution (37% concentrated hydrochloric acid to water volume ratio 1:1). Then accurately measuring silica sol, adding a newly prepared urea and formaldehyde solution (wherein the molar ratio of urea to formaldehyde is 1.6) under the stirring condition, reacting for 10-15min, and standing for 20-24h to obtain white precipitate. Centrifuged to discardSupernatant, washing the obtained white precipitate with water and anhydrous ethanol for 3 times, respectively, and drying the hybrid microsphere obtained in the above process at 60-80 deg.C for 5.0-10h to obtain urea-formaldehyde resin/SiO ₂ Compounding the microspheres, and calcining to obtain the mesoporous silica microspheres.

And analyzing and testing the obtained mesoporous silica microspheres. Weighing 0.1 g of mesoporous silica microsphere sample, vacuumizing and degassing for 3h at 200 ℃, weighing, placing in liquid nitrogen (77K) for cooling, measuring the adsorption capacity of the mesoporous silica microsphere sample to nitrogen at different pressure points under 77K, and obtaining the pore volume, specific surface, pore size distribution and other information of the sample through secondary calculation. The specific surface area of the measured mesoporous silica sample is calculated by a BET model, and the pore size distribution is calculated by a BJH model. And obtaining the pore volume and pore size distribution information of the mesoporous silica microspheres.

Preparing a nano composite foaming agent:

the nano composite foaming agent is prepared by impregnating silicon dioxide and azodicarbonamide of the invention: dissolving a chemical foaming agent in a dimethyl sulfoxide aqueous solution in the presence of dimethyl sulfoxide and water, uniformly stirring, adding deionized water with the same amount as the dimethyl sulfoxide, heating to 60-80 ℃, adding mesoporous silica, stirring and soaking for 24 hours, washing an obtained sample with a detergent, and drying to obtain the mesoporous silica embedded nano composite foaming agent. Wherein the detergent comprises a mixed solution and ethanol, wherein each mixed solution contains 25mL of absolute ethanol, 25mL of dimethyl sulfoxide and 0.05g to 0.09g of azodicarbonamide.

Preparing the foamed plastic:

at the temperature of 100-130 ℃, 0.2-0.4g of the nano composite foaming agent is added into 10g of epoxy resin, after uniform stirring, 0.5-0.7mL of curing agent diethylenetriamine is added, after rapid stirring, the mixture is moved into an oven at the temperature of 60 ℃ for continuous curing for 12h. Thereby obtaining the epoxy resin microcellular foam plastic.

The nanocomposite blowing agents of the present invention, methods of making and using the same are further illustrated by the following specific examples.

The reagents and instrumentation used in the following examples were from the following sources:

the activated silicon powder used in the following examples was activated by immersing 100g of elemental silicon powder in hot water at 70 ℃ for 10 minutes to obtain activated silicon powder for later use.

EXAMPLE 1 preparation of silica Sol (Primary particles)

Adding 200g of 0.5% sodium hydroxide solution into a three-neck flask, heating to 70 ℃, adding 21g of activated silicon powder, stirring for reaction for 12 hours, centrifuging the reaction mixture, and separating to obtain the silica sol primary particle silica sol with the mass concentration of 10%.

As shown in FIG. 1-a, the primary particle size of the silica sol was 15nm.

Example 2 preparation of silica Sol (example 1 silica Sol 2 silicon additions)

Taking 50mL of the mother liquor as the silica sol obtained in example 1, heating 5.25g of elemental silicon powder subjected to the 1 st supplementary activation and 50g of sodium hydroxide solution with the mass fraction of 0.5% in the mother liquor to 70 ℃, stirring for reaction for 12 hours, and centrifuging the reaction mixture to obtain the silica sol. Taking the silica sol as mother liquor, adding 11.5g of elemental silicon powder subjected to the 2 nd supplementary activation and 100g of sodium hydroxide solution with the mass fraction of 0.5% into the mother liquor, heating the mixture to 70 ℃, stirring the mixture for reaction for 12 hours, and centrifuging the reaction mixture to obtain the silica sol, wherein the mass concentration of the silica sol is as follows: 20 percent.

As shown in FIG. 1-b, the silica sol primary particle size was 25nm.

Example 3 preparation of silica Sol (example 1 silica Sol was subjected to silica supplementation 4 times)

Taking 50mL of mother liquor as the mother liquor, taking 5.25g of elemental silicon powder subjected to the 3 rd supplementary activation and 50g of sodium hydroxide solution with the mass fraction of 0.5% into the mother liquor, heating the mother liquor to 70 ℃, stirring the mother liquor to react for 12 hours, centrifuging the reaction mixture to obtain silica sol, taking the silica sol as the mother liquor, heating the mother liquor, taking 11.5g of elemental silicon powder subjected to the 4 th supplementary activation and 100g of sodium hydroxide solution with the mass fraction of 0.5% into the mother liquor, heating the mother liquor to 70 ℃, stirring the mother liquor to react for 12 hours, centrifuging the reaction mixture to obtain the silica sol, wherein the mass concentration of the silica sol is as follows: 30 percent.

As shown in FIG. 1-c, the silica sol primary particle size was 45nm.

Example 4 preparation of silica

The silica sol prepared in example 1 was adjusted to a pH of 1.5 with a hydrochloric acid solution (37% concentrated hydrochloric acid to water volume ratio 1:1). Then, 39mL of silica sol was accurately weighed, 3.78mL of newly prepared urea and formaldehyde solutions (molar ratio of urea to formaldehyde was 1.6) were added to each of the silica sol and the formaldehyde solutions under stirring, and after a reaction time of 10min, the mixture was allowed to stand for 20 hours to obtain a white precipitate. Centrifuging to remove supernatant, washing the obtained white precipitate with water and ethanol for 3 times, and drying the hybrid microsphere obtained in the above process at 60 deg.C for 5.0h to obtain urea-formaldehyde resin/SiO ₂ Compounding the microspheres, and calcining to obtain the mesoporous silica microspheres. The calcination procedure was as follows: (1) Heating the temperature from room temperature to 100 ℃, wherein the heating rate is 5 ℃/min, and keeping the temperature for 60min; (2) Raising the temperature to 200 ℃ again, and keeping the temperature for 1h at the temperature raising rate of 2 ℃/min; (3) Heating to 270 deg.C at a rate of 1 deg.C/min, and maintaining for 2h; (4) And raising the temperature to 350 ℃ again, raising the temperature at the rate of 2 ℃/min, finally raising the temperature to 550 ℃ at the rate of 5 ℃/min, and preserving the temperature for 2h.

As shown in FIG. 2-a, the mesoporous silica particles have a size of 1-3 μm, and as shown in the pore size distribution diagram of the silica of FIG. 3-a, the maximum pore volume corresponds to a pore size of 5nm. The silica particles prepared by means of the primary particles of the silica sol are of smaller size and smaller pore size.

Example 5 preparation of silica

The difference from example 4 is that: silica was prepared using the silica sol obtained in example 2.

As shown in FIG. 2-b, the mesoporous silica particles have a size of 1-3 μm, and as shown by the pore size distribution diagram of the silica in FIG. 3-b, the maximum pore volume corresponds to a pore size of 8nm. The silica sol prepared by silica sol obtained by silica supplementation for 2 times has smaller particle size, and the particle size of the silica sol is increased to a certain extent after silica supplementation for 2 times, so that the pore diameter of the final silica is increased compared with that of the embodiment 4.

Example 6 preparation of silica

The silica sol prepared in example 3 was diluted to 15% with deionized water and the pH of the silica sol was adjusted to 2.0 with a hydrochloric acid solution (37% concentrated hydrochloric acid to water volume ratio 1:1). Then, 39mL of silica sol was accurately weighed, 3.78mL of newly prepared urea and formaldehyde solution (molar ratio of urea to formaldehyde was 1.1) was added under stirring, and after 15min of reaction, the mixture was allowed to stand for 24 hours to obtain a white precipitate. Centrifuging to remove supernatant, washing the obtained white precipitate with water and ethanol for 3 times, respectively, and drying the hybrid microsphere obtained by the above process at 80 deg.C for 10 hr to obtain urea-formaldehyde resin/SiO ₂ Compounding the microspheres, and calcining to obtain the mesoporous silica microspheres. The calcination procedure was as follows: (1) Heating the temperature from room temperature to 90 ℃, wherein the heating rate is 10 ℃/min, and keeping the temperature for 60min; (2) Raising the temperature to 180 ℃ again, wherein the temperature raising rate is 1 ℃/min, and keeping the temperature for 1h; (3) Heating to 250 deg.C at a heating rate of 10 deg.C/min, and maintaining for 2 hr; (4) And raising the temperature to 350 ℃, raising the temperature rate to 1 ℃/min, finally raising the temperature to 550 ℃ at the temperature rise rate of 3 ℃/min, and preserving the heat for 2h.

As shown in FIG. 2-c, the mesoporous silica particles have a size of 3 to 5 μm. As shown by the pore size distribution of the silica of FIG. 3-c, the maximum pore volume corresponds to a pore size of 11.8nm. At the same time, the particle size and pore size of the silica increased compared to examples 4 and 5 due to the calcination process change and the larger difference of the silica sol particles used.

Example 7 preparation of silica

The silica sol prepared in example 3 was diluted to 10% with deionized water and the pH of the silica sol was adjusted to 1.5 with a hydrochloric acid solution (37% concentrated hydrochloric acid to water volume ratio of 1.6). Then, 39mL of silica sol was accurately weighed, 3.78mL of newly prepared urea and formaldehyde solution (molar ratio of urea to formaldehyde was 1.6) was added under stirring, and after 15min of reaction, the mixture was allowed to stand for 24 hours to obtain a white precipitate. Centrifuged and discardedCleaning the obtained white precipitate with water and ethanol for 3 times, respectively, and drying the hybrid microsphere obtained in the above process at 80 deg.C for 10 hr to obtain urea-formaldehyde resin/SiO ₂ Compounding the microspheres, and calcining to obtain the mesoporous silica microspheres. The calcination procedure was as follows: (1) Heating the temperature from room temperature to 100 ℃, wherein the heating rate is 5 ℃/min, and keeping the temperature for 60min; (2) Raising the temperature to 200 ℃ again, wherein the temperature raising rate is 2 ℃/min, and keeping the temperature for 1h; (3) Heating to 270 deg.C at a heating rate of 1 deg.C/min, and maintaining for 2 hr; (4) And raising the temperature to 350 ℃, raising the temperature at the rate of 2 ℃/min, finally raising the temperature to 550 ℃, raising the temperature at the rate of 5 ℃/min, and keeping the temperature for 2 hours.

As shown in FIG. 2 d, the size of the mesoporous silica particles is 3-5 μm, and the silica prepared in this example has uniform size distribution, monodispersity and good sphericity. As shown by the pore size distribution of the silica in fig. 3-d, the pore volume maximum corresponds to a pore size of 12nm.

EXAMPLE 8 preparation of silica

The silica sol prepared in example 3 was diluted to 7.5% with deionized water and the pH of the silica sol was adjusted to 1.0 with a hydrochloric acid solution (37% concentrated hydrochloric acid to water volume ratio of 1. Then, 39mL of silica sol was accurately weighed, 3.78mL of newly prepared urea and formaldehyde solution (molar ratio of urea to formaldehyde was 1. Centrifuging to remove supernatant, washing the obtained white precipitate with water and ethanol for 3 times, respectively, and drying the hybrid microsphere obtained by the above process at 80 deg.C for 10 hr to obtain urea-formaldehyde resin/SiO ₂ Compounding the microspheres, and calcining to obtain the mesoporous silica microspheres. The calcination procedure was as follows: (1) Heating the temperature from room temperature to 120 ℃, wherein the heating rate is 3 ℃/min, and keeping the temperature for 60min; (2) Raising the temperature to 200 ℃ again, wherein the temperature raising rate is 5 ℃/min, and keeping the temperature for 1h; (3) Heating to 270 deg.C at a heating rate of 1 deg.C/min, and maintaining for 2 hr; (4) And raising the temperature to 350 ℃, raising the temperature at the rate of 2 ℃/min, finally raising the temperature to 550 ℃, raising the temperature at the rate of 5 ℃/min, and keeping the temperature for 2 hours.

As shown in FIG. 2-e, the mesoporous silica particles have a size of 2-4 μm, and as shown in the pore size distribution diagram of the silica of FIG. 3-e, the maximum pore volume corresponds to a pore size of 11.6nm.

EXAMPLE 9 preparation of nanocomposite blowing agent

1.8g of Azodicarbonamide (AC) was weighed out and dissolved in 150mL of dimethyl sulfoxide (DMSO) and stirred magnetically until homogeneous. Adding 150mL of deionized water, and heating to 60 ℃. 3.0g of the mesoporous silica prepared in example 4 was weighed and added to the above solution, and the solution was immersed for 24 hours and centrifuged to obtain a nanocomposite blowing agent. Washing with ethanol for three times, and drying to obtain the nano composite foaming agent AC/SiO ₂ As can be seen from the thermogravimetric graph of the nanocomposite blowing agent a in fig. 4, the mass fraction of AC in the composite blowing agent is 22.8%, and the amount of AC supported by the composite blowing agent is relatively low because the silica particles and the pore size used are small.

EXAMPLE 10 preparation of nanocomposite blowing agent

The difference from example 9 is that: silica was prepared using the silica sol obtained in example 5. From the thermogravimetric graph of the b nanocomposite blowing agent in fig. 4, it is seen that the mass fraction of AC in the composite blowing agent is 26.4%, and the amount of AC supported by the composite blowing agent is increased.

EXAMPLE 11 preparation of nanocomposite blowing agent

The difference from example 10 is that: silica was prepared using the silica sol obtained in example 7. As can be seen from the thermogravimetric graph of the c nanocomposite blowing agent in fig. 4, the mass fraction of AC in the composite blowing agent was 31.7%, and the amount of AC supported by the composite blowing agent reached the maximum, and the silica prepared in example 7 was more suitable for supporting the AC blowing agent. As can be seen from the scanning electron micrograph of the nanocomposite foaming agent in FIG. 5-a, AC/SiO ₂ The composite foaming agent has the particle size of 3-10 microns and is monodisperse, and the agglomeration of the composite foaming agent can be effectively reduced and the particle size of the composite foaming agent is reduced by washing with ethanol.

EXAMPLE 12 preparation of nanocomposite blowing agent

The difference from example 11 is that: prepared composite foaming agent AC/SiO ₂ And directly drying without washing by ethanol. As can be seen from the scanning electron micrograph of the nanocomposite foaming agent in FIG. 5-b, AC/SiO ₂ The particle size of the composite foaming agent is 3-20 mu m, and the unwashed composite foaming agent has larger particle size and appears to a certain degreeAnd (3) agglomeration.

EXAMPLE 13 preparation of nanocomposite blowing agent

The difference from example 11 is that: the Azodicarbonamide (AC) was weighed to give a mass of 1.2g. From the thermogravimetric graph of the nanocomposite blowing agent a in fig. 6, the mass fraction of AC in the composite blowing agent is 23%, which is that the concentration of AC in the solution is too small, so that the amount of AC carried by the composite blowing agent is not high.

EXAMPLE 14 preparation of nanocomposite blowing agent

The difference from example 11 is that: the azodicarbonamide was weighed to give a mass of 2.0g. From the thermogravimetry of b nanocomposite blowing agent in fig. 6, it is seen that the mass fraction of AC in the blowing agent is 27%, and the concentration of AC in the solution is too high, which in turn decreases the amount of AC carried by the composite blowing agent.

Example 15 foamed article

This example illustrates the use of the nanocomposite blowing agent of the present invention in the preparation of microcellular foams. At 125 ℃, the nano composite foaming agent is added into 10g of epoxy resin, and the curing agent diethylenetriamine is added for normal pressure foaming experiment. The influence of the amount of the nanocomposite foaming agent and the amount of the curing agent added on the foaming results was investigated.

Measuring the diameter of the cells and counting the number of the cells by using Nano Measurer software to carry out SEM image of the sample, calculating the average cell diameter, and then calculating according to a formula rho _c ＝(nM ² /A) ^3/2 Calculating cell density, wherein p _c Is cell density (pieces/cm) ³ ) N is the number of cells in the statistical area, M is the magnification factor, and A is the statistical area.

TABLE 1 statistics of foam clinker cell diameter and density prepared from foaming agent and curing agent with different addition amounts

The results are shown in Table 1. As can be seen from Table 1, the optimum conditions were 0.3g of the nanocomposite blowing agent and 0.3g of the curing agent at 125 ℃0.6g of foam prepared in epoxy resin. As shown in FIG. 7, the average cell diameter was the smallest, the average cell diameter was 59.9 μm, the cell density was the largest, and the cell density was 3.5X 10 ⁵ 。

Claims

1. A nano composite foaming agent is characterized in that the nano composite foaming agent is composed of monodisperse mesoporous silica and azodicarbonamide, wherein the particle size of the monodisperse mesoporous silica is 3-5 mu m; the maximum value of the pore volume of the mesoporous silicon dioxide corresponds to the pore diameter of 10-12nm; the particle size of the nano composite foaming agent is 3-10 mu m, and the mass ratio of the monodisperse mesoporous silica to the azodicarbonamide is 5:2-4,

wherein the monodisperse mesoporous silica is prepared by a method comprising the following steps:

step (1): preparing silica sol by taking elemental silicon powder as a silicon source, and adjusting the particle size of the silica sol by supplementing silicon powder and a sodium hydroxide solution; the size of the target product silica sol particles obtained in the step (1) is 45-50nm;

step (2): diluting the target product silica sol obtained in the step (1), and synthesizing urea-formaldehyde resin/SiO by a polymerization-induced colloid condensation method ₂ The composite microspheres are prepared by adding raw material urea and raw material formaldehyde in a molar ratio of 1: (1.1-2.0), calcining to obtain monodisperse mesoporous silica;

in the presence of an organic solvent, mixing and contacting the obtained mesoporous silica with azodicarbonamide serving as a chemical foaming agent, and fully washing to obtain the nano composite foaming agent;

the step (2) of calcining comprises the following procedures:

2. The method of preparing the nanocomposite blowing agent of claim 1, comprising the steps of:

step (2): synthesizing the target product silica sol obtained in the step (1) into urea-formaldehyde resin/SiO by a polymerization-induced colloid condensation method ₂ The composite microspheres are prepared by adding raw material urea and raw material formaldehyde in a molar ratio of 1: (1.1-2.0), calcining to obtain monodisperse mesoporous silica;

and (3): adding the monodisperse mesoporous silica into an aqueous solution of dimethyl sulfoxide containing azodicarbonamide to obtain a mixed solution, and carrying out solid-liquid separation on the mixed solution to obtain a nano composite foaming agent, wherein the aqueous solution of dimethyl sulfoxide containing azodicarbonamide is heated before adding the silica, or the obtained mixed solution is heated;

wherein the step (2) of calcining comprises the following steps:

3. The preparation method according to claim 2, wherein in the step (2), the urea resin/SiO is synthesized by polymerization-induced colloid condensation after the silica sol of the target product is diluted ₂ And (3) compounding the microspheres.

4. The preparation method according to claim 3, wherein the mass concentration range of the diluted silica sol in the step (2) is as follows: 7.5 to 15 percent.

5. The production method according to claim 3, wherein the mass concentration of the diluted silica sol in the step (2) is in the range of 7.5 to 10%.

6. The production method according to any one of claims 2 to 5, wherein in the step (2), urea resin/SiO is synthesized by polymerization-induced colloid coagulation ₂ When the microspheres are compounded, the molar ratio of the added raw material urea to the added raw material formaldehyde is 1.6.

7. The production method according to any one of claims 2 to 5, wherein the calcination temperature increase rates in the step (2) are respectively:

step (1): 1-7 ℃/min;

step (2): 1-5 ℃/min;

step (3): 1-10 ℃/min;

step (4): 1-5 ℃/min;

step (5): 3-10 ℃/min.

8. The preparation method according to claim 6, wherein the calcination temperature rise rates in the step (2) are respectively:

step (1): 1-7 ℃/min;

step (2): 1-5 ℃/min;

step (3): 1-10 ℃/min;

step (4): 1-5 ℃/min;

step (5): 3-10 ℃/min.

9. The production method according to any one of claims 2 to 5, wherein the calcination temperature increase rates in the step (2) are respectively:

step (1): 3-5 ℃/min;

step (2): 2-3 ℃/min;

step (3): 1-3 ℃/min;

step (4): 1-2 ℃/min;

step (5): 3-5 ℃/min.

10. The preparation method according to claim 6, wherein the calcination temperature rise rates in the step (2) are respectively:

step (1): 3-5 ℃/min;

step (2): 2-3 ℃/min;

step (3): 1-3 ℃/min;

step (4): 1-2 ℃/min;

step (5): 3-5 ℃/min.

11. The production process according to any one of claims 2 to 5, wherein the concentration of the azodicarbonamide in the aqueous dimethyl sulfoxide solution containing the azodicarbonamide in the step (3) is 0.03 to 0.05mol/L.

12. The production process according to claim 6, wherein the concentration of the azodicarbonamide in the aqueous dimethyl sulfoxide solution containing the azodicarbonamide in the step (3) is 0.03 to 0.05mol/L.

13. The production process according to claim 7, wherein the concentration of the azodicarbonamide in the aqueous dimethyl sulfoxide solution containing the azodicarbonamide in the step (3) is 0.03 to 0.05mol/L.

14. The production process according to claim 8, wherein the concentration of the azodicarbonamide in the aqueous dimethyl sulfoxide solution containing the azodicarbonamide in the step (3) is 0.03 to 0.05mol/L.

15. The production process according to any one of claims 2 to 5, wherein the concentration of the azodicarbonamide in the aqueous dimethyl sulfoxide solution containing the azodicarbonamide in the step (3) is 0.04mol/L.

16. The production method according to any one of claims 2 to 5, wherein the nanocomposite blowing agent obtained in the step (3) is further washed with ethanol a plurality of times.

17. The production method according to claim 6, wherein the nanocomposite blowing agent obtained in the step (3) is further washed with ethanol a plurality of times.

18. The production method according to claim 7, wherein the nanocomposite blowing agent obtained in the step (3) is further washed with ethanol a plurality of times.

19. The production method according to claim 8, wherein the nanocomposite blowing agent obtained in the step (3) is further washed with ethanol a plurality of times.

20. The production method according to claim 9, wherein the nanocomposite blowing agent obtained in the step (3) is further washed with ethanol a plurality of times.

21. The production method according to claim 11, wherein the nanocomposite blowing agent obtained in the step (3) is further washed with ethanol a plurality of times.

22. A nanocomposite blowing agent, characterized by being produced by the production method according to any one of claims 2 to 21.

23. A foamed article obtained by foaming a raw material comprising the nanocomposite blowing agent according to claim 1 or 22, a curing agent and an epoxy resin.

24. The foamed article of claim 23, wherein the nanocomposite blowing agent, curing agent, and epoxy resin are in a weight ratio of: (2-4): (5-7): 100.

25. the foamed article of claim 24, wherein the nanocomposite blowing agent, curing agent, and epoxy resin are in a weight ratio of: (3-4): (6-7): 100.

26. the foamed article of any of claims 23-25, wherein the foamed article is an epoxy resin microcellular foam.

27. Use of a nanocomposite blowing agent according to claim 1 or claim 22 in the field of foamed articles.