CN110918011A

CN110918011A - SiO (silicon dioxide)2Preparation method and application of/glass fiber composite aerogel

Info

Publication number: CN110918011A
Application number: CN201911252984.1A
Authority: CN
Inventors: 徐淑艳; 王亚; 潘雅婷
Original assignee: Northeast Forestry University
Current assignee: Northeast Forestry University
Priority date: 2019-12-09
Filing date: 2019-12-09
Publication date: 2020-03-27

Abstract

SiO (silicon dioxide)₂The invention discloses a preparation method and application of glass fiber composite aerogel, and relates to SiO₂The invention discloses a preparation method and application of glass fiber composite aerogel, and aims to solve the problem of the existing SiO₂The aerogel is easy to break due to poor formability and is difficult to serve as a filling material to keep the chilled and fresh products fresh, and the method comprises the following steps: preparing a wet gel; then modifying, cleaning the modified wet gel with n-hexane, and drying to obtain SiO₂A glass fiber composite aerogel. The composite aerogel has good forming effect, the hydrophobic angles are all about 120 degrees, and the specific surface area is 552.8023-828.5978m²The heat insulation performance is excellent between the temperature of the water and the volume of the water, and the fresh-keeping effect is obvious. The invention is applied to the field of preparation of heat-insulating and safety materials.

Description

SiO (silicon dioxide)2Preparation method and application of/glass fiber composite aerogel

Technical Field

The invention relates to SiO₂A preparation method and application of glass fiber composite aerogel.

Background

Silicon dioxide (SiO)₂) The aerogel is a multifunctional material, is a nano porous amorphous light solid material, has a framework formed by stacking 1-100 nm nano-sized particles, and has excellent performances of high specific surface area, very low density, extremely low heat conductivity coefficient, low dielectric constant and the like. As a mesoporous material, SiO₂Thermal insulation, catalysis and sound insulation of aerogel^[5]And the like, and has very wide application prospect. SiO 2₂Aerogel is a material with a porous three-dimensional structure, has developed pores, has a lowest density which can reach one sixth of the air density, and is a solid material with the lowest density known at present.

SiO₂The aerogel is made of SiO in the shape of sphere₂A porous network material consisting of particles. Since the pores are filled with air, heat is generated in SiO₂The aerogel is continuously consumed, and the heat conduction and radiation processes are hindered due to SiO₂The thermal convection conductivity is also reduced by the small pore size in the aerogel, and thus the SiO₂The aerogel has very low heat conductivity coefficient, is an excellent heat-insulating material, and is applied to the fields of buildings and the like. At present, cold chain logistics are rapidly developed, and a novel material with excellent low thermal conductivity is urgently needed for the preservation of cold and fresh products, so that SiO₂The aerogel also has very wide application prospect in the transportation package for keeping the fresh of the cold and fresh products. But SiO₂Aerogel is easily broken due to its poor formability, and is in a powdery state when lightly pressed by fingers, so that it is difficult to keep a chilled product fresh as a filling material.

Disclosure of Invention

The invention aims to solve the problem of the prior SiO₂The problem that the aerogel is difficult to serve as a filling material to keep the chilled products fresh due to the poor formability of the aerogel is provided_2/A preparation method and application of glass fiber composite aerogel.

The invention relates to SiO₂The preparation method of the glass fiber composite aerogel comprises the following steps:

firstly, preparing a mixed solution of ethyl orthosilicate, ethanol and water, stirring for 5-10 min, then adding hydrochloric acid with the concentration of 0.5-2mol/L until the pH value of the solution is 3-4, and continuing to stir for 5-10 min; stirring in a water bath at the temperature of 30-40 ℃ for 20-30 h, adding N, N-dimethylformamide, stirring, adjusting the pH value of the solution to 7-8, adding pretreated glass fiber, and standing to obtain wet gel; wherein the molar ratio of the ethyl orthosilicate to the ethanol to the water is 1 (6-9) to 4; the mass content of the glass fiber in the wet gel is 1-7%;

standing and aging the wet gel at room temperature for 22-26 h, then aging the wet gel in an ethanol water solution for 22-26 h at the temperature of 45-55 ℃, and then aging the wet gel in a mixed solution of ethyl orthosilicate and ethanol for 22-26 h; then, exchanging for 3 times by using normal hexane within 45-50 h at the temperature of 45-55 ℃; performing surface modification by using trimethylchlorosilane/normal hexane at the temperature of 45-55 ℃ to obtain modified wet gel; trimethylchlorosilane/trimethylchlorosilane in n-hexane is 5% to 13% of the volume of n-hexane;

thirdly, cleaning the modified wet gel with n-hexane for 4 times within 20-30 h, drying at room temperature for 22-26 h, then drying at 60 ℃ for 4h, at 80 ℃ for 4h, at 120 ℃ for 1h and at 150 ℃ for 1h in sequence to obtain SiO₂A glass fiber composite aerogel.

SiO of the invention₂The glass fiber composite aerogel is applied to preparing heat-insulating and safety materials.

Toughness depends on the ability of the material to absorb impact energy and resist crack propagation. There are four cases of fiber toughening mechanisms: (1) the crack bends and deflects, bypassing the fiber and deflecting at the surface. The tensile stress decreases after the crack deflects and the path grows, requiring more energy to be absorbed. (2) The fiber is debonded, the fiber diameter, the fiber critical length or the fiber tensile strength are increased, and the energy required in the fiber debonding process is increased, so that the toughening effect is achieved. (3) And (3) pulling out the fibers, namely, under the action of an external force, after the fibers are debonded, the fibers slide out along the interface of the matrix, the microcracks effectively prevent the cracks from expanding, and the external force does work to require energy, so that the toughness of the composite aerogel is improved. (4) And (4) fiber bridging, namely bridging the two sides of the crack by fibers to generate compressive stress which is counteracted with the external stress, so that the toughness of the composite aerogel is increased. The glass fiber plays a skeleton role in the composite aerogel to support the whole system, so that the formability of the composite aerogel is improved. The fibers and the aerogel are complicated in interlacing, and when the aerogel receives impact load, the phenomena of fiber debonding, fiber pulling-out and the like occur, so that impact energy is absorbed.

The invention has the beneficial effects that:

(1) the forming effect of the composite aerogel gradually becomes better along with the increase of the content of the glass fiber, and the forming property is best when the content of the glass fiber is 5 percent and 7 percent.

(2) The glass fiber does not affect the amorphous structure of the aerogel.

(3)SiO₂The excellent thermal insulation performance of the aerogel mainly depends on the three-dimensional network nanostructure. In order to obtain excellent heat insulating properties, it is necessary to prepare SiO having a high specific surface area and a uniform internal structure₂The specific surface area of the aerogel, the composite aerogel of the invention is 552.8023-828.5978m²Between the/g, there is no correlation between the addition of the glass fiber and the specific surface area. SiO under microscopic level₂The aerogel is supported by the glass fiber and plays a role of a bracket. SiO 2₂The aerogel still has a three-dimensional network structure and more uniform pores.

(4)SiO₂The glass fiber composite aerogel has hydrophobicity, the doping amount of the glass fiber has no influence on the hydrophobic effect, and the hydrophobic angles are all about 120 degrees.

(5)SiO₂The glass fiber composite aerogel has obvious fresh-keeping effect.

Drawings

FIG. 1 is a photograph of a glass fiber after pretreatment in the examples;

FIG. 2 is a graph showing the appearance and appearance of sample 1 in example;

FIG. 3 is a graph showing the appearance and appearance of sample 2 in example;

FIG. 4 is a graph showing the appearance and appearance of sample 3 in example;

FIG. 5 is a graph showing the appearance and appearance of sample 4 in example;

FIG. 6 is a top view of sample 3 in the example;

FIG. 7 is a side view of sample 3 in the example;

FIG. 8 is a top view of sample No. 4 in the example;

FIG. 9 is a side view of sample No. 4 in the example;

FIG. 10 is an infrared spectrum of samples 1 to 4 in example;

FIG. 11 is a scanning electron micrograph of sample 1 in example;

FIG. 12 is a scanning electron micrograph of sample 2 in example;

FIG. 13 is a scanning electron micrograph of sample 3 in example;

FIG. 14 is a scanning electron micrograph of sample 4 in example;

FIG. 15 is a high-power scanning electron micrograph of sample 1 in example;

FIG. 16 is a high-power scanning electron micrograph of sample 2 in example;

FIG. 17 is a high-power scanning electron micrograph of sample 3 in example;

FIG. 18 is a high-power scanning electron micrograph of sample 4 in example;

FIG. 19 is a hydrophobic pattern of sample 1 in example;

FIG. 20 is a hydrophobic pattern of sample 2 in example;

FIG. 21 is a hydrophobic pattern of sample 3 in the examples;

FIG. 22 is a hydrophobic pattern of sample 4 in the examples;

FIG. 23 shows SiO production of control example₂Physical diagrams of aerogels;

FIG. 24 is SiO production of control example₂An X-ray diffraction spectrum of the aerogel;

FIG. 25 is SiO production of control example₂Scanning electron micrographs of aerogels;

FIG. 26 is SiO production of control example₂A hydrophobic pattern of the aerogel;

fig. 27 is a graph of the score of the salmon appearance in example 5;

fig. 28 is a graph of the salmon odor score in example 5;

FIG. 29 is a graph showing the evaluation scores of salmon in example 5;

fig. 30 is a graph of the sensory total scores of salmon in example 5;

fig. 31 shows the juice loss rate of salmon in example 5.

Detailed Description

The first embodiment is as follows: this embodiment is a SiO₂The preparation method of the glass fiber composite aerogel comprises the following steps:

The volume ratio of water to ethanol in the ethanol water solution is 1:5, and the volume ratio of ethyl orthosilicate to ethanol in the mixed solution of ethyl orthosilicate and ethanol is 1: 5; the surface modification is carried out by using trimethylchlorosilane/n-hexane at the temperature of 45-55 ℃, namely, the aged wet gel is placed in the trimethylchlorosilane/n-hexane for soaking for 72 hours.

The beneficial effects of the embodiment are as follows:

(2) The glass fiber does not affect the amorphous structure of the aerogel.

(3)SiO₂The excellent thermal insulation performance of the aerogel mainly depends on the three-dimensional network nanostructure. In order to obtain excellent heat insulating properties, it is necessary to prepare SiO having a high specific surface area and a uniform internal structure₂AerogelThe specific surface area of the composite aerogel is 552.8023-828.5978m²Between the/g, there is no correlation between the addition of the glass fiber and the specific surface area. SiO under microscopic level₂The aerogel is supported by the glass fiber and plays a role of a bracket. SiO 2₂The aerogel still has a three-dimensional network structure and more uniform pores.

(5)SiO₂The glass fiber composite aerogel has obvious fresh-keeping effect.

The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: in the first step, the molar ratio of the ethyl orthosilicate to the ethanol to the water is 1:8: 4. The rest is the same as the first embodiment.

The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: the concentration of the hydrochloric acid in the first step is 1 mol/L. The others are the same as in the first or second embodiment.

The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: in the first step, analytically pure ammonia water with the mass concentration of 25% is used for adjusting the pH value of the solution to 7-8. The rest is the same as one of the first to third embodiments.

The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: the wet gel obtained in step one is left to stand until the gel is inclined at 45 degrees and does not flow. The rest is the same as one of the first to fourth embodiments.

The sixth specific implementation mode: the present embodiment is different from the first to fifth embodiments in that: soaking the glass fiber in hydrochloric acid with the mass concentration of 36-38% for 4h, pouring out the liquid, soaking in 0.01mol/L NaOH solution for 1h, washing, placing in an electric heating blast constant-temperature drying oven, and drying at 100 ℃ for 12h to obtain the pretreated glass fiber. The rest is the same as the first to fifth embodiments.

The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: in the first step, the mass content of the glass fiber in the wet gel is 5%. The rest is the same as one of the first to sixth embodiments.

The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: in the first step, the length of the glass fiber is 3-5 mm. The rest is the same as one of the first to seventh embodiments.

The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: trimethylchlorosilane represents 10% by volume of n-hexane. The rest is the same as the first to eighth embodiments.

The detailed implementation mode is ten: SiO of the present embodiment₂The glass fiber composite aerogel is applied to preparing heat-insulating and safety materials.

The effect of the invention is demonstrated by the following examples:

example 1: this example is a SiO₂The preparation method of the glass fiber composite aerogel comprises the following steps:

firstly, preparing a mixed solution of ethyl orthosilicate, ethanol and water, stirring for 10min, then adding hydrochloric acid with the concentration of 1mol/L until the pH value of the solution is 3-4, and continuing stirring for 30 min; stirring in a water bath at 35 ℃ for 24 hours, adding N, N-dimethylformamide, continuously stirring, adjusting the pH value of the solution to 7-8 by using ammonia water, adding pretreated glass fiber, and standing to obtain wet gel; wherein the molar ratio of the ethyl orthosilicate to the ethanol to the water is 1:8: 4; the mass content of the glass fiber in the wet gel is 1 percent; standing the wet gel obtained in the step one until the wet gel is inclined at 45 degrees and does not flow; the pretreatment method of the glass fiber comprises the following steps: soaking the glass fiber in hydrochloric acid with the mass concentration of 36-38% for 4h, pouring out the liquid, soaking in 0.01mol/L NaOH solution for 1h, washing, placing in an electric heating blast constant-temperature drying oven, and drying at 100 ℃ for 12h to obtain pretreated glass fiber;

standing and aging the wet gel at room temperature for 24h, then aging the wet gel in an ethanol water solution for 24h at 50 ℃, and then aging the wet gel in a mixed solution of tetraethoxysilane and ethanol for 24 h; then exchanging with n-hexane for 3 times within 48h at the temperature of 50 ℃; then soaking the gel in trimethylchlorosilane/normal hexane for 72h at the temperature of 50 ℃ to carry out surface modification to obtain modified wet gel; trimethylchlorosilane/trimethylchlorosilane in n-hexane is 10% by volume of n-hexane;

thirdly, washing the modified wet gel with n-hexane for 4 times within 24h, then drying at room temperature for 24h, then drying at 60 ℃ and 80 ℃ for 4h respectively, and drying at 120 ℃ and 150 ℃ for 1h respectively to obtain SiO₂The/glass fiber composite aerogel, noted as sample 1.

Example 2 SiO₂The preparation method of the glass fiber composite aerogel comprises the following steps:

firstly, preparing a mixed solution of ethyl orthosilicate, ethanol and water, stirring for 10min, then adding hydrochloric acid with the concentration of 1mol/L until the pH value of the solution is 3-4, and continuing stirring for 30 min; stirring in a water bath at 35 ℃ for 24 hours, adding N, N-dimethylformamide, continuously stirring, adjusting the pH value of the solution to 7-8 by using ammonia water, adding pretreated glass fiber, and standing to obtain wet gel; wherein the molar ratio of the ethyl orthosilicate to the ethanol to the water is 1:8: 4; the mass content of the glass fiber in the wet gel is 3 percent; standing the wet gel obtained in the step one until the wet gel is inclined at 45 degrees and does not flow; the pretreatment method of the glass fiber comprises the following steps: soaking the glass fiber in hydrochloric acid with the mass concentration of 36-38% for 4h, pouring out the liquid, soaking in 0.01mol/L NaOH solution for 1h, washing, placing in an electric heating blast constant-temperature drying oven, and drying at 100 ℃ for 12h to obtain pretreated glass fiber;

thirdly, washing the modified wet gel with n-hexane for 4 times within 24h, then drying at room temperature for 24h, then drying at 60 ℃ and 80 ℃ for 4h respectively, and drying at 120 ℃ and 150 ℃ for 1h respectively to obtain SiO₂The/glass fiber composite aerogel, noted as sample 2.

Example 3 SiO₂The preparation method of the glass fiber composite aerogel comprises the following steps:

firstly, preparing a mixed solution of ethyl orthosilicate, ethanol and water, stirring for 10min, then adding hydrochloric acid with the concentration of 1mol/L until the pH value of the solution is 3-4, and continuing stirring for 30 min; stirring in a water bath at 35 ℃ for 24 hours, adding N, N-dimethylformamide, continuously stirring, adjusting the pH value of the solution to 7-8 by using ammonia water, adding pretreated glass fiber, and standing to obtain wet gel; wherein the molar ratio of the ethyl orthosilicate to the ethanol to the water is 1:8: 4; the mass content of the glass fiber in the wet gel is 5 percent; standing the wet gel obtained in the step one until the wet gel is inclined at 45 degrees and does not flow; the pretreatment method of the glass fiber comprises the following steps: soaking the glass fiber in hydrochloric acid with the mass concentration of 36-38% for 4h, pouring out the liquid, soaking in 0.01mol/L NaOH solution for 1h, washing, placing in an electric heating blast constant-temperature drying oven, and drying at 100 ℃ for 12h to obtain pretreated glass fiber;

thirdly, washing the modified wet gel with n-hexane for 4 times within 24h, then drying at room temperature for 24h, drying at 60 ℃ and 80 ℃ for 4h respectively, and drying at 120 ℃ and 150 ℃ for 1h respectively to obtain SiO₂The/glass fiber composite aerogel, noted as sample 3.

Example 4 SiO₂The preparation method of the glass fiber composite aerogel comprises the following steps:

firstly, preparing a mixed solution of ethyl orthosilicate, ethanol and water, stirring for 10min, then adding hydrochloric acid with the concentration of 1mol/L until the pH value of the solution is 3-4, and continuing stirring for 30 min; stirring in a water bath at 35 ℃ for 24 hours, adding N, N-dimethylformamide, continuously stirring, adjusting the pH value of the solution to 7-8 by using ammonia water, adding pretreated glass fiber, and standing to obtain wet gel; wherein the molar ratio of the ethyl orthosilicate to the ethanol to the water is 1:8: 4; the mass content of the glass fiber in the wet gel is 7 percent; standing the wet gel obtained in the step one until the wet gel is inclined at 45 degrees and does not flow; the pretreatment method of the glass fiber comprises the following steps: soaking the glass fiber in hydrochloric acid with the mass concentration of 36-38% for 4h, pouring out the liquid, soaking in 0.01mol/L NaOH solution for 1h, washing, placing in an electric heating blast constant-temperature drying oven, and drying at 100 ℃ for 12h to obtain pretreated glass fiber;

thirdly, washing the modified wet gel with n-hexane for 4 times within 24h, then drying at room temperature for 24h, then drying at 60 ℃ and 80 ℃ for 4h respectively, and drying at 120 ℃ and 150 ℃ for 1h respectively to obtain SiO₂The/glass fiber composite aerogel, designated as sample 4.

Fig. 1 is a picture of pretreated glass fibers, fig. 2 to fig. 5 are appearance graphs of samples 1 to 4, fig. 2 is a appearance graph of a composite aerogel with a glass fiber content of 1%, it can be visually seen that a complete sheet-shaped or block-shaped composite aerogel is not formed, and the formability is poor because the glass fiber content is low and is not enough to be uniformly distributed and cannot support a material surface layer. Fig. 3 shows that at a glass fiber content of 3%, the composite aerogel gradually became a block, but the edges did not form a complete block. Moldability was better than 1%. Fig. 4 and 5 show that the composite aerogel can be formed into a complete block at 5% and 7%, respectively, and the aerogel and the glass fiber are well overlapped at the edge position, so that the formability is optimal, and the glass fiber plays a supporting role in the composite aerogel. When the content of the glass fiber is 1%, a plurality of collapsed and unlapped glass fibers are arranged on the surface; at a glass fiber content of 3%, there is relatively less surface collapse and less glass fibers that are not overlapped; at the glass fiber contents of 5% and 7%, the surface was hardly collapsed, and the state of glass fiber and aerogel lap joint was good. However, the longer the time in the gel stage at a content of 7% may be because the number of layers where the fibers are spread alternately is large, which may hinder the occurrence of gel.

FIGS. 6 and 7 are a top view and a side view of sample No. 3; fig. 8 and 9 are a top view and a side view of sample 4. From fig. 6 and 7, it can be seen that the whole body is blocky, the structure is complete, a little glass fiber is not built on the aerogel at the edge, the rest part of the glass fiber is well wrapped by the aerogel, the glass fiber plays a supporting role in the composite aerogel, and the good formability is demonstrated. It can be seen from fig. 8 and 9 that the surface is not smooth with a content of 5%, because in the sol-gel stage, the solution is deposited downwards, the content of 7% of glass fibers is more, and a little more glass fibers are not well mixed with the solution on the surface of the gel, so that the surface is rough, and the edges have glass fibers which are not built up with the aerogel, so that the integral formability is better.

FIG. 10 is an infrared spectrum of samples 1 to 4, and it can be seen from FIG. 10 that the absorption peaks of the 4 curves are substantially uniform. At 2964cm^-1、847cm^-1Absorption peaks exist nearby, which indicates that Si-CH exists₃Because the composite aerogel is subjected to surface modification treatment, the composite aerogel has hydrophobicity. At 3435cm^-1Antisymmetric stretching vibration in the form of-OH, such as physically adsorbed water and chemically bound water on the surface layer and in the pores of the aerogel can be removed by high-temperature heat treatment, and SiO₂The aerogel-OH number will be reduced, and the peak will be obviously reduced, at 1631cm^-1Bending vibration at position of H-O-H at 1087cm^-1Antisymmetric stretching vibration at 455cm of Si-O-Si^-1Bending vibration of Si-O-Si is treated. The 4 curves are very similar and no new groups are generated or reduced, since the main component of the glass fiber is also SiO₂And glass fiber and SiO₂The physical combination between the two does not damage SiO₂Structural features of the aerogel itself.

FIGS. 11-14 are scanning electron micrographs of samples 1-4 at low magnification showing that the glass fibers and SiO are clearly visible at a 100um viewing angle₂In the combined state of the aerogel, the glass fiber plays a skeleton role in the composite aerogel to support the whole system, so that the formability of the composite aerogel is improved. The fibers and the aerogel are complicated in interlacing, and when the aerogel receives impact load, the phenomena of fiber debonding, fiber pulling-out and the like occur, so that impact energy is absorbed. Fig. 15-18 are high-power scanning electron microscope images of samples 1-4, at 20000 times of viewing angle, the fine and uniform pores of the aerogel can be observed, it can be seen that the content of the glass fiber has no obvious relationship with the structure of the aerogel, and the aerogel is still in the nanometer three-dimensional network structure.

FIGS. 19-22 show the hydrophobicity angles of samples 1-4, where it can be clearly seen that the aerogels having been surface-modified all have excellent hydrophobicity. The contact angles of samples 1 to 4 were about 121 °, 123 °, 127 °, and 110 °, respectively, and the addition amount of the glass fiber had little influence on the hydrophobic angle.

The specific surface area and BJH pore size distribution curves for samples 1-4 were determined by ASAP2020 type specific surface area Analyzer, passing through N at 77k₂Adsorption test the samples were subjected to a high temperature pre-heat treatment at 120 ℃ prior to testing. The pore size distribution is calculated in a BJH degassing stage, and the specific surface area is calculated by test software automatically by adopting a BET algorithm value. The results are shown in Table 1.

TABLE 1 SiO₂Specific surface area and average pore diameter of/glass fiber composite aerogel

As shown in the table, SiO₂The specific surface area of the glass fiber composite aerogel is 552.8023-828.5978m²Between the points of the content and the content of the SiO particles, the addition of the glass fiber has no great influence on the specific surface area of the composite aerogel, and the verification that the glass fiber cannot damage the original SiO is carried out again₂The structure of the aerogel is still a three-dimensional nano network structure. The average pore diameter of the composite aerogel is within 9nm, and when the content of the glass fiber is 5%, the average pore diameter is the largest.

Control group SiO₂Glass fiber compositeThe preparation method of the composite aerogel comprises the following steps:

firstly, preparing a mixed solution of ethyl orthosilicate, ethanol and water, stirring for 10min, then adding hydrochloric acid with the concentration of 2mol/L until the pH value of the solution is 3-4, and continuing stirring for 30 min; stirring in a water bath at 35 ℃ for 24 hours, adding N, N-dimethylformamide, continuously stirring, adjusting the pH value of the solution to 7-8, and standing to obtain wet gel; wherein the molar ratio of the ethyl orthosilicate to the ethanol to the water is 1:8: 4;

standing and aging the wet gel at room temperature for 24h, then aging the wet gel in an ethanol water solution for 24h at 50 ℃, and then aging the wet gel in a mixed solution of tetraethoxysilane and ethanol for 24 h; then exchanging with n-hexane for 3 times within 48h at the temperature of 50 ℃; then carrying out surface modification by using trimethylchlorosilane/normal hexane at the temperature of 50 ℃ to obtain modified wet gel; trimethylchlorosilane/trimethylchlorosilane in n-hexane is 8% by volume of n-hexane;

thirdly, washing the modified wet gel with n-hexane for 4 times within 24h, then drying at room temperature for 24h, then drying at 60 ℃ and 80 ℃ for 4h respectively, and drying at 120 ℃ and 150 ℃ for 1h respectively to obtain SiO₂An aerogel.

SiO prepared from control group₂FIG. 23 shows the physical diagram of the aerogel, which shows SiO₂The aerogel is light blue and semitransparent in the air, has poor strength and is easy to break, and can be crushed by lightly pressing with fingers. The crushed aerogel powder is loosely piled together to be flocculent, which shows that the aerogel powder has extremely low density and large specific surface area and becomes light blue under the irradiation of sunlight.

FIG. 24 is SiO₂X-ray diffraction pattern of aerogel. Modified SiO₂The aerogel consists of SiO₂The composition shows that a sample has a steamed bun-like diffuse diffraction peak with a shape of 20-25 degrees at 2 theta through X-ray diffraction, and the intensity of the peak is relatively low, which shows that the composition of the sample is disordered amorphous SiO₂. Explanation of the SiO finally prepared₂The structure of the aerogel is amorphous and non-crystalline.

FIG. 25 is SiO₂Scanning Electron microscopy of aerogels, SiO₂The aerogel is lightThe structure is a light nanoscale three-dimensional network framework structure, clear pores can be seen from the figure, the particle size is small, the pores are uniformly distributed, and the structure has a better three-dimensional network framework structure. When the aerogel is prepared by using ethyl orthosilicate, ethanol and water in a high molar ratio, a large amount of water is enclosed in a space structure of the aerogel in a gelling stage, the particles are not tightly connected, and a three-dimensional framework is extremely easy to damage in the solvent replacement and solvent evaporation processes. When the molar ratio of the mixed solution is lower, the three-dimensional frameworks are built more densely, the solvent replacement is not easy to carry out, and the frameworks are easy to close together during normal-pressure graded drying, so that the aerogel is seriously shrunk.

FIG. 26 is SiO₂The hydrophobic angle of the aerogel is schematically shown, and spherical water drops which do not wet the surface of the aerogel are clearly seen in the figure. The contact angle of the sample was about 121 °. The hydrophobic angle of the sample subjected to surface modification is more than 90 degrees, and the SiO subjected to surface modification₂The aerogels are all hydrophobic.

SiO calculation Using multiple samples₂The aerogel has specific surface area and average pore diameter of 515.4025-924.9138m²Between/g.

In summary, as the content of the glass fiber increases, the forming effect of the composite aerogel gradually becomes better, and the forming performance is best when the content of the glass fiber is 5% and 7%. The glass fiber does not affect the amorphous structure of the aerogel. The specific surface area of the composite aerogel is 552.8023-828.5978m²Between the/g, there is no correlation between the addition of the glass fiber and the specific surface area. SiO under microscopic level₂The aerogel is supported by the glass fiber and plays a role of a bracket. SiO 2₂The aerogel still has a three-dimensional network structure and more uniform pores. SiO 2₂The glass fiber composite aerogel has hydrophobicity, the doping amount of the glass fiber has no influence on the hydrophobic effect, and the hydrophobic angle is about 120 degrees.

Example 5 verification of SiO prepared in examples 1-4 Using this example₂The application of the glass fiber composite aerogel in the fresh keeping of salmon. Washing fresh salmon with distilled water, sucking water from the surface of salmon with sterile filter paper, weighing about 40g fish blocks, and recordingAnd (4) placing the data in a packaging box, and then placing the data in a refrigerator at 4 ℃ for fresh keeping.

Examples 1-4 preparation of SiO₂The glass fiber composite aerogel is wrapped by a preservative film to prevent surface substances from falling off, covers the upper part of a purchased fresh salmon packing box, is wound by the preservative film and is fixed by a rubber band to be sealed, and is respectively marked as A1, A3, A5 and A7, and the control group is marked as K. Immediately after the salmon is packaged in groups, sensory evaluation, juice loss rate, TVB-N value, TBA value and color difference value are carried out on the salmon at 0d, and data are recorded, wherein the specific method for measuring is as follows.

1. Sensory evaluation

Samples of salmon from the experimental group were taken out, placed in a clean mortar, and visually observed, smelled through the nose, touched, and the like, one by one in table 2. Observing the appearance, color, organization structure, texture, smell and the like, forming a sensory evaluation group by a plurality of sensory evaluators, carrying out sensory evaluation on the salmon sample through sensory evaluation training, and giving out a comprehensive score, wherein each score is 10 points full.

TABLE 2 Salmon sensory Scoring criteria

Salmon can produce a lot of enzymes and bacteria after dying, and gives off odor mainly because the fish is easy to rot to produce bacteria, and in the process of fresh keeping, because of the loss of water, the elasticity of the fish meat is worse and worse, and the color is darker and darker. Sensory evaluation is a method for discriminating fish quality by five senses such as human vision, smell, touch, and the like.

The fresh salmon has fresh fish flavor, high surface glossiness, compact fish meat, clear texture and high elasticity, the depression immediately disappears after the fingers press the salmon, and the three aspects of the appearance, the smell and the texture of the salmon are regularly observed and subjected to sensory evaluation in the process of refrigeration and preservation at 4 ℃. As shown in fig. 27 to 30, it can be seen that the salmon showed a tendency to decline in three aspects of appearance, smell and texture as the number of days for preservation increased, with the decline in K groups being most pronounced and the slow decline rates remaining in the remaining groups. As can be seen from fig. 27-30, the sensory index of group a7 was in a more favorable sensory state than the other groups, indicating that group a7 was the sample that caused the least sensory change. The index scores in group a5 were slightly lower than those in group a7, but much higher than those in the remaining three groups.

Meanwhile, the K group and the A1 group have the largest change, the K group of salmon has rough feeling on the surface of the 3 rd group and has slight fishy smell, the elasticity of the fish tissue is poor at the 5 th group, the fish has fishy smell, the smell changes seriously at the 7 th group, the strong fishy smell and ammonia smell are presented, and meanwhile, the surfaces of the fish are observed to be soft and sticky, the juice is turbid, the meat is soft and inelastic, and the salmon is not suitable for eating. The A3 group fish sample has little sensory change in the first 3d, has slight fishy smell in the 5d, and has obvious quality reduction.

2. Determination of juice loss Rate

Weighing salmon meat before experiment, carrying out original weight before cold preservation, then sucking the effluent of the salmon meat after preservation, weighing the rest weight, and calculating the juice loss rate of the salmon meat according to the following formula:

in the formula: g₁-weight of salmon meat before refrigeration;

g₂-the weight of the salmon meat at the end of the cold storage period.

Fig. 31 reflects the liquid loss of salmon during the preservation period, and it can be seen from the graph that the liquid loss rate of each salmon sample group shows a trend of increasing with the increase of the experimental days. In comparison, the juice loss of the sample wrapped with the composite aerogel is less than that of the sample wrapped with the preservative film.

Table 3 shows that the liquid juice loss rate of salmon is relatively slow, and increases to 3.61%, and the change of A3 group and A5 group is also slow, but slightly higher than that of a7 group, and the change of two groups respectively increases to 4.47% and 4.39%, and the change of a1 group is faster, and increases to 4.85%, but is better than 6.36% of a K group, and the change of the K group is large, and the liquid juice loss rate of salmon is about twice as high as that of the a7 group with optimal fresh-keeping property, as can be seen from table 3. Also, as can be seen from fig. 27, the change curves of juice loss of the groups a1, A3, a5 and a7 from the 1d to the 7d are gradually increased.

As salmon undergoes a series of physicochemical changes during cold storage, its juice loss changes. The degree of putrefaction is proved to be large by intense change, and small by slow change. Therefore, in five groups of fresh-keeping tests, the salmon has the largest corruption degree of K group and the salmon has the smallest corruption degree of A7 group, the A7 group basically keeps fresh, and the salmon has signs of corruption compared with the A1, A3 and A5 groups, but the corruption degree is not large.

TABLE 3 Salmon juice loss Rate

3. Determination of volatile basic Nitrogen (TVB-N)

The method refers to the regulation of GB 5009.228-2016 national food safety standard 'determination of volatile basic nitrogen in food', and the determination is carried out according to the principle of an automatic Kjeldahl azotometer method. TVB-N is a basic nitrogen-containing substance such as ammonia and amines generated by decomposition of protein by the action of enzymes and bacteria during putrefaction of fish meat. The substance has volatility, is evaporated in an alkaline solution, is absorbed by a boric acid absorption solution, and is titrated by a standard hydrochloric acid solution to calculate the content of volatile basic nitrogen. The measurement was performed using an automatic kjeldahl apparatus model K1100, and the volatile basic nitrogen content in the sample was calculated according to the following formula.

The calculation method comprises the following steps:

X＝(V₁-V₂)*c*14*100/m

in the formula: x is the content of volatile basic nitrogen in the sample, and the unit is mg/100 g;

V₁-the sample consumes the volume of hydrochloric acid standard titration solution in mL;

V₂reagent blank consuming saltVolume of acid standard titration solution, unit mL;

c, the concentration of the hydrochloric acid standard titration solution is unit mol/L;

m is sample mass in g;

reference is made to GB 2710 and 1996 "hygienic Standard for fresh (frozen) poultry meat": the primary freshness is less than or equal to 15mg/100g, the secondary freshness is less than or equal to 20mg/100g, and the deteriorated meat is more than 20mg/100 g.

TVB-N is an expression form that enzymes and aerobic microorganisms are easily generated in aquatic products to destroy meat quality structures, and proteins are decomposed to generate ammonia, amines and other alkaline nitrogen-containing substances, so that the TVB-N has volatility and causes loss of the proteins, and is an important index for identifying freshness of the aquatic products.

As can be seen from Table 4, the TVB-N values of salmon were all below 15mg/100g and were maintained at first-class freshness between 0 th and 6 th days of freshness preservation. However, at 7d, the TVB-N values of the K-, A1-and A3-groups increased greatly, the K-and A1-groups had reached a secondary freshness of 17.64mg/100g and 15.88mg/100g, respectively, and the A3-group was 14.87mg/100g at the edge of the primary and secondary freshness. The freshness of the groups A5 and A7 was maintained at first grade, 11.38mg/100g and 9.75mg/100g, respectively, and the difference between the growth of the 7d and 0d group, the TVB-N growth value of the K group was 3 times that of the A7 group, indicating that the spoilage degree of the K group was large and the spoilage degree of the A7 group was relatively small. The TVB-N value of group A5, group 7d, is between the 5 th and 6 th of group K, and the TVB-N value of group A7, group 7d, is between the 3 rd and 4 th of group K, so that the fresh-keeping effect of group A7 is prolonged by about 3d compared with that of a normal preservative film.

TABLE 4 Salmon TVB-N value (mg/100g)

4. Determination of Thiobabituric acid (TBA)

The TBA value reflects the degree of oxidation of fat, since TBA reacts with Malondialdehyde (MAD), a product of oxidative degradation of lipids. Taking 10g of salmon sample, mincing, adding 25mL of distilled water, stirring uniformly, adding 25mL of 10% trichloroacetic acid solution, stirring uniformly, and centrifuging in a centrifuge for 10min at the rotating speed of 8000 r/min. Filtering, taking 4mL of filtrate, adding 1mL of 0.04moL/L TBA solution, and mixing uniformly. Storing in boiling water bath for 20min, taking out, cooling to room temperature, measuring absorbance at wavelength of 532nm and 600nm, and determining TBA value in mg/kg by mass fraction of Malondialdehyde (MAD).

The TBA value is reflected in the color change produced by the reaction of malondialdehyde with thiobarbituric acid, which finally gives a red mixture. And then measuring the absorbance value of the red mixture to obtain the content of malondialdehyde, and finally calculating to obtain the fat oxidation degree.

As can be seen from Table 5, the initial value of TBA is low, 0.158mg/kg, the TBA value of the salmon in the five groups is greatly changed, and the value of 7d is increased by about 4 times compared with that of 0 d. But the values of the groups of the same time period are slightly different. The TBA values of the A3 group, the A5 group and the A7 group at 7d are all smaller than the value of the K group, which indicates that the composite aerogel coated on the surface has an inhibiting effect on the oxidation of fat.

TABLE 5 TBA values (mg/kg) of Salmon

5. Determination of the colour difference value

The values of L, a and b were determined using a CR-410 type colorimeter (side head Φ 15mm) CIE-LAB system. The colorimeter is started and preheated for 5min, fish meat is taken and spread below a lens, the values of L, a and b of each group of samples are measured, and the average value is taken repeatedly twice.

The flesh color of the fresh salmon is generally red or fresh orange, and when the salmon is sold, the color is a very important factor influencing the purchase of consumers. The two numerical values of L and a visually reflect the color of the salmon, L represents the brightness, and the larger the numerical value is, the brighter the numerical value is; a represents red and green, and represents red bias when the value is positive, and the red is more obvious when the value is larger.

The luminance values L and the redness values a in the salmon color difference values are shown in tables 6 and 7. In the preservation process, the brightness value and the redness value of the salmon fluctuate and the whole salmon is in a descending trend. The brightness value decreases gradually and the redness value decreases sharply. The decrease in the brightness value is caused by the gradual change of the flesh color to a dark color, and the decrease in the redness value is caused by the oxidation and destruction of carotenoid substances such as astaxanthin, which is an orange color-developing substance. The brightness value of the A7 group remained the highest in the five groups all the time, and the reduction value was not large, and was only 10.29, which indicates that the flesh color of the salmon meat of the A7 group remained fresh all the time, and the brightness value of the K group was reduced most obviously, by 24.17, and the reduction value was as much as twice that of the A7 group. The flesh color of the K group of salmon meat is darkened and is no longer fresh, thus seriously affecting the purchase of consumers. The brightness values of the A1, A3 and A5 groups are maintained at a better value, and the flesh color is fresher. The embodiment of each group of data is just consistent with the scoring result of the sensory evaluation of the salmon.

Table 6 salmon brightness values L

Table 7 salmon redness values a

Analyzing each index, namely the K groups have the lowest sensory score, the largest juice loss, the largest TVB-N value increase, the fish meat reaches the second-level freshness, and the color difference shows that the meat color is dark; the indexes of the A1 group, the A3 group and the A5 group are all superior to those of the K group, the sensory score of the A7 group is highest, the juice loss rate is minimum, the TVB-N value is minimum to increase, the fish meat keeps first-level freshness, the increase value is small, the color difference shows that the fish meat is normal in luster and brightness, the fish meat is rich in elasticity when touched by fingers, and the effect of wrapping and preserving the fish meat by using the composite aerogel is obvious.

From the examples, it can be seen that the forming effect of the composite aerogel gradually becomes better with the increase of the glass fiber content, and the forming property is best when the glass fiber content is 5% and 7%. The glass fiber does not affect the amorphous structure of the aerogel. The specific surface area of the composite aerogel is 552.8023-828.5978m²Between the/g, there is no correlation between the addition of the glass fiber and the specific surface area. SiO under microscopic level₂Aerogel is by glassThe glass fiber supports the bracket and plays a role of a bracket. SiO 2₂The aerogel still has a three-dimensional network structure and more uniform pores. SiO 2₂The glass fiber composite aerogel has hydrophobicity, the doping amount of the glass fiber has no influence on the hydrophobic effect, and the hydrophobic angles are all about 120 degrees. SiO 2₂The glass fiber composite aerogel has obvious fresh-keeping effect.

Claims

1. SiO (silicon dioxide)₂The preparation method of the glass fiber composite aerogel is characterized by comprising the following steps:

firstly, preparing a mixed solution of ethyl orthosilicate, ethanol and water, stirring for 5-10 min, then adding hydrochloric acid with the concentration of 0.5-2mol/L until the pH value of the solution is 3-4, and continuing to stir for 5-10 min; then stirring in a water bath at the temperature of 30-40 ℃ for 20-30 h, adding N, N-dimethylformamide, stirring, adjusting the pH value of the solution to 7-8, then adding pretreated glass fiber, and standing to obtain wet gel; wherein the molar ratio of the ethyl orthosilicate to the ethanol to the water is 1 (6-9) to 4; the mass content of the pretreated glass fiber in the wet gel is 1-7%;

2. An SiO as claimed in claim 1₂The preparation method of the/glass fiber composite aerogel is characterized in that the molar ratio of ethyl orthosilicate, ethanol and water in the step one is 1:8: 4.

3. An SiO as claimed in claim 1₂The preparation method of the/glass fiber composite aerogel is characterized in that the concentration of hydrochloric acid in the step one is 1 mol/L.

4. An SiO as claimed in claim 1₂The preparation method of the/glass fiber composite aerogel is characterized in that in the step one, analytically pure ammonia water with the mass concentration of 25% is used for adjusting the pH value of the solution to be 7-8.

5. An SiO as claimed in claim 1₂The preparation method of the/glass fiber composite aerogel is characterized in that the wet gel obtained in the step one is kept still until the wet gel inclines to 45 degrees and does not flow.

6. An SiO as claimed in claim 1₂The preparation method of the glass fiber composite aerogel is characterized in that the glass fiber pretreatment method in the first step is as follows: soaking the glass fiber in hydrochloric acid with the mass concentration of 36-38% for 4h, pouring out the liquid, soaking in 0.01mol/L NaOH solution for 1h, washing, placing in an electric heating blast constant-temperature drying oven, and drying at 100 ℃ for 12h to obtain the pretreated glass fiber.

7. An SiO as claimed in claim 1₂The preparation method of the glass fiber composite aerogel is characterized in that in the step one, the mass content of the glass fiber in the wet gel is 5%.

8. An SiO as claimed in claim 1₂The preparation method of the glass fiber composite aerogel is characterized in that the length of the glass fiber in the step one is 3-5 mm.

9. An SiO as claimed in claim 1₂The preparation method of the glass fiber composite aerogel is characterized in that the volume of the trimethylchlorosilane is 10 percent of that of the normal hexane.

10. SiO as prepared in claim 1₂Application of/glass fiber composite aerogel, which is characterized in that SiO₂The glass fiber composite aerogel is used for preparing heat-insulating and safety materials.