CN1793277A - Process for preparing compound forming phase changing material of polyethyldiol/silicon dioxide - Google Patents

Abstract

The invention provides a preparation method of polyethylene glycol/silicon dioxide composite shape-setting phase change material, comprising (1) adding polyethylene glycol powder into silica sol to dissolve, and then adding accelerator solution dropwise to cause sol-gelation The gel reacts to form a three-dimensional network gel; (2) the gel obtained in step (1) is dried and crushed to make a powder; (3) the powder obtained in step (2) is dehydrated and added to make the surface hydrophobic Modified modifiers. The obtained product has a high phase transition latent heat of 60-140kJ/kg, good shapeability, no leakage of polyethylene glycol when the temperature is 20-50°C higher than the phase transition temperature, and stable performance. It can be popularized and applied in the fields of warm textiles and building energy-saving walls.

Description

Preparation method of polyethylene glycol/silica composite shape-setting phase change material

Technical field

The invention relates to thermal energy storage and utilization materials, in particular to a preparation method of polyethylene glycol/silicon dioxide composite shape-changing materials.

Background technique

Phase change materials release or absorb the latent heat of phase change during the phase transition process, so as to achieve energy storage and release and alleviate the contradiction between energy supply and demand imbalance, and have broad application prospects. Traditional phase change materials undergo solid-liquid transformation during melting, so they need to be packaged in special containers, which not only increases the cost, but also increases the thermal resistance between the heat transfer medium and the phase change material, thereby reducing heat exchange efficiency. Shape-setting phase change materials are one of the most effective ways to solve the above problems. The shape-setting phase change material is a composite phase change material, which is mainly composed of a support material (carrier matrix) and a phase change material (working substance). The carrier matrix can fix the working substance with latent heat of phase change in it, and when the phase change occurs, it can still maintain its original shape. Because the shape-setting phase change material can be directly in contact with the heat transfer medium, the cost can be greatly reduced and the heat exchange efficiency can be improved.

Shape-setting phase change materials are mainly aimed at solid-liquid phase change materials, which can be divided into inorganic, organic and mixed types according to the working substances. Inorganic types such as crystalline hydrated salts, molten salts, etc., are characterized by latent heat of phase change and high thermal conductivity; organic types such as paraffin, polyethylene glycol, carboxylic acid, etc. Because inorganic phase change materials have defects such as supercooling, precipitation and corrosion; therefore, the working substances of shape-setting phase change materials are mainly organic. As far as the carrier matrix is concerned, it can be divided into two categories: organic and inorganic. Organic polymers such as high-density polyethylene (HDPE), thermoplastic elastomer styrene-butadiene triblock copolymer (SBS), etc., have the advantages of good shapeability and easy processing; when used for a long time, there are mainly material aging, work Problems such as phase separation between substance and matrix; inorganic matrix such as expanded graphite has high porosity and low density, and the prepared inorganic/organic composite shape-changing material has the characteristics of good thermal conductivity and high energy storage density, but it is porous under pressure The matrix is easy to be crushed, deformed and poorly set.

Contents of Invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing a polyethylene glycol/silica composite shape-setting phase change material with good shape setting, high heat storage capacity, stable performance, and processability. The prepared The material can be used in industries such as thermal control materials for electronic components, heat storage and temperature control textiles, and building energy-saving walls.

The preparation method of polyethylene glycol/silicon dioxide composite shape-changing material of the present invention comprises the following steps:

(1) adding the polyethylene glycol powder to dissolve in the silica sol, then adding the accelerator solution dropwise, a sol-gel reaction occurs to form a three-dimensional network gel;

(2) drying the gel obtained in step (1), smashing it into powder;

(3) Dewatering the powder obtained in step (2), adding a modifying agent to make its surface hydrophobically modified.

The modified powder can be made into polyethylene glycol/silicon dioxide composite shape-setting phase-change material blocks in various shapes by using a tablet press.

In step (1), the number average molecular weight of the polyethylene glycol is preferably 1,000-20,000. Different molecular weights have slightly different melting points, and the higher the molecular weight, the higher the melting point. In practical applications, it is desired that the phase transition melting range be as large as possible so that the phase transition of the composite phase change material can occur in a wider temperature range. Therefore, polyethylene glycols with different molecular weights should be selected for mixing. Another advantage of the combination of high and low molecular weight is that it can enhance the entanglement between polyethylene glycol molecules with different chain lengths, resulting in better compounding effect.

Exploratory experiments have proved that the mixing effect of polyethylene glycol with a number average molecular weight of 3000-6000 and polyethylene glycol with a number average molecular weight of 10000-20000 at a ratio of 0.5-1/1 is the best.

In the step (1), the raw material of the supporting matrix silica is silica sol, and since it contains a small amount of sodium ions, the sol is slightly alkaline, and its pH value is preferably in the range of 8-9.5. The concentration of the selected silica sol is preferably 15-30% by weight; if the concentration is low, the water content of the obtained gel will be high and the drying time will be long; if the concentration is high, it is not conducive to the dispersion of polyethylene glycol in the silica sol.

Exploratory experiments prove that the silica sol concentration with the best effect is 20-25% by weight.

In step (1), it is best to control the silicon dioxide content in the obtained gel to be 10-50%. If the silica content is low, polyethylene glycol will leak out from the silica network, which will make the final material unsatisfactory in setting effect; if the silica content is high, the restriction effect on the polyethylene glycol chain segment will be enhanced, so that The movement of polyethylene glycol chain segments is seriously hindered, so the crystallization rate of polyethylene glycol is significantly reduced, so that the latent heat of phase change of the final material is low.

It is proved by experiments that the silicon dioxide content in the gel is in the optimum range of 10-30% by weight.

In step (1), due to the stability of the silica sol, it is difficult to rapidly generate a sol-gel reaction to form a gel. In order to speed up the reaction process, a certain amount of accelerator needs to be added. The selected accelerators are weak acids or soluble high-value salts; weak acids such as acetic acid, formic acid or lactic acid; soluble high-value salts such as calcium chloride, magnesium chloride, aluminum chloride, aluminum sulfate or aluminum nitrate.

Because the essence of the accelerator is to destroy the stable structure of the electric double layer of the silica sol, so that the silica particles coagulate. The higher the anion and cation charges in the accelerator, the more conducive to electrical neutralization, so it is better to choose soluble salts with higher anion and cation charges, such as aluminum sulfate or aluminum chloride. The dosage of the accelerator preferably accounts for 0.01-0.1‰ weight of the total amount of polyethylene glycol and silica sol. If the addition amount is small, the sol-gel reaction will be slow, if the addition amount is large, the sol-gel rate will be fast, and the compounding effect will be poor.

Exploratory experiments prove that the accelerator dosage with the best effect is 0.01-0.05‰ weight of the total amount of polyethylene glycol and silica sol.

The drying method in step (2) may be to air-dry the gel in an oven at 80° C. for 24 to 48 hours, cool to room temperature, take out, mash and stir to obtain a powder.

In step (3), since the surface of the powder obtained in step (2) contains hydroxyl groups and is sensitive to moisture, surface hydrophobic treatment is required. The modifier used is preferably a silane coupling agent. The general formula of silane coupling agent is RSiX ₃ , where R is an active group that has an affinity with polyethylene glycol, such as aminopropyl, etheroxypropyl, acyloxypropyl, and X is a hydrolyzable alkoxy, halogen wait. For example, aminopropyltriethoxysilane (KH-550), glycidyloxypropyltrimethoxysilane (KH-560) or methacryloxypropyltrimethoxysilane (KH-570), etc. The amount of modifier used is 0.1-1.5% by weight of the powder, preferably 0.5-1.0% by weight.

The modification process in the present invention should adopt a dry modification method. When most of the moisture in the powder is removed, the residual moisture will first hydrolyze the X group of the silane coupling agent into silanol and silicon dioxide on the surface of the silica. The hydroxyl group and the terminal hydroxyl group of polyethylene glycol are condensed to form Si-O-Si and C-O-Si bonds, or the coupling agent molecules are associated to form a network structure, covering the surface of the powder, so as to achieve the purpose of hydrophobic modification.

Therefore, the water removal in step (3) is to evacuate the powder at 40°C for 2 to 4 hours to remove most of the water, and then add a modifier to hydrophobically modify it under nitrogen protection at a temperature of 90°C to obtain this product. Invented composite shape-setting phase-change materials.

The working principle of the invention is as follows: through the sol-gel reaction of silica sol, the silica with high specific surface area and multi-microporous network structure can be obtained. Through the capillary adsorption of micropores, the hydrophilic polyethylene glycol phase change material can be adsorbed in the porous skeleton of silica; Strong hydrogen bonds are formed between hydroxyl groups (CH ₂ -OH), which further enhances the interaction between the two, so polyethylene glycol can be firmly embedded in the silica network. When solid-liquid phase transition occurs, Polyethylene glycol fluid will not leak from the skeleton. When polyethylene glycol is dissolved in silica sol, due to the relative stability of silica sol, the sol-gel reaction rate is slow, and it is necessary to add accelerators, such as weak acids or soluble high-priced salts, to promote the formation of composite gels. Since silanol and alkoxy groups remain on the surface of polyethylene glycol/silica powder, they are sensitive to moisture in the air and are easily adsorbed on the surface. Therefore, a silane coupling agent needs to be added to remove active hydroxyl groups.

Compared with the prior art, the present invention has the following advantages and effects: (1) large latent heat and good energy storage effect; (2) good shape-setting performance. Good setting effect; (3) High stability, because silica is a high-temperature-resistant and corrosion-resistant support matrix, it has strong stability. When it is compounded with polyethylene glycol, it will increase due to capillary adsorption and hydrogen bonding. The mutual containment of the two is eliminated, and the sol-gel process is adopted, and the components are evenly dispersed.

Description of drawings

Fig. 1 is the thermomechanical analysis figure (embodiment 1) of Polyethylene Glycol and Polyethylene Glycol/silica composite shape-changing material;

Figure 2 is a polarized light microscope picture of polyethylene glycol and composite shape-changing material (embodiment 1), wherein Figure 2a is a polarized light microscope picture of polyethylene glycol at 60°C, and Figure 2b is a polarized light microscope picture of polyethylene glycol at 64°C The polarized light microscope picture of Figure 2c is the polarized light microscope picture of polyethylene glycol at 68°C, and Figure 2d is the polarized light microscope picture of the composite shaped material at 60-120°C;

Fig. 3 is the transmission electron microscope figure (embodiment 1) of composite shape-setting phase-change material;

Fig. 4 is the DSC curve (embodiment 1) of polyethylene glycol and polyethylene glycol/silicon dioxide composite shape-changing material;

Fig. 5 shows the stability test results of the polyethylene glycol/silica composite shape-changing material (Example 1, 2, 3).

Detailed ways

Example 1

Steps: (1) At room temperature, in a 1.5L glass beaker, add 500g of 20% silica sol (pH value = 9), and slowly add polyethylene glycol (PEG5000/PEG10000 = 1/2) under strong stirring with a CNC mixer 400g of powder, after the polyethylene glycol powder is completely dissolved, slowly add 1% aluminum sulfate solution dropwise according to the ratio of 0.01‰ of the total amount of composite phase-change and shape-setting materials, and continue stirring until all gels are formed. Transfer the beaker containing the gel into a blast drying oven, dry at a constant temperature of 80°C for 36 hours, cool to room temperature, take out the dried gel, mash it in a mortar, transfer it to a beaker, and stir it vigorously to obtain Powder. (2) Transfer the powder into a 1L four-necked flask equipped with a stirrer, nitrogen tube, reflux tube, and dropping funnel, and vacuumize at 40°C for 3 hours while stirring, then heat the oil bath to 90°C, and open the water condensation return pipe , nitrogen protection, according to the proportion of 1% of the total weight of the powder, silane coupling agent K560 was added dropwise, and after 3 hours of treatment, the temperature was lowered, stirring was stopped, reflux, and nitrogen was passed to obtain an inorganic-organic composite phase change material.

Fig. 1 is the thermomechanical analysis (TMA) diagram of polyethylene glycol and polyethylene glycol/silica composite shape-setting phase change material (Example 1).

For the polyethylene glycol sample, a phase transition occurs during the thermal melting process, with an initial melting temperature of 69.89°C and a maximum melting rate (-429.9μm/°C) at 78.61°C. Its deformation (-6449μm) is basically equal to the thickness of the sample before the phase transition, that is, the sample is completely melted. For the polyethylene glycol/silica sample, due to the formation of porous network structure silica and the physical cross-linking (hydrogen bond) between silanol and alcoholic hydroxyl groups, polyethylene glycol is firmly confined in the two in silicon oxide. During heating, although a phase transition occurred, it exhibited a different melting behavior than polyethylene glycol. Its initial melting temperature is 81.25°C, and its maximum melting rate is at 84.58°C, with a value of -8.992μm/°C. Compared with polyethylene glycol, its melting rate is much slower. Similarly, the deformation of the polyethylene glycol/silica sample is much smaller, only -65.035 μm, which is 1.008% of the deformation of polyethylene glycol. It can be seen that even at a temperature above 80°C higher than the melting point of polyethylene glycol (tested by DSC, the test end temperature is 150°C), polyethylene glycol can still be kept from flowing out of the composite material, showing excellent performance. shape performance.

The shape-setting effect of silica on polyethylene glycol was further confirmed by polarizing microscopy. Fig. 2 is a polarizing microscope image of polyethylene glycol and polyethylene glycol/silica composite shape-setting phase change material (Example 1). It can be seen that for the pure polyethylene glycol product, at 60 ° C, it shows obvious spherulite crystal orientation without melting. When the temperature rises to 64 ° C, the polyethylene glycol part melts, and when it reaches near the melting point (68 °C), the polyethylene glycol is completely dissolved and bubbles are generated. After adding silica as a shaping component, even at a temperature nearly 30°C (110°C) higher than the melting point of polyethylene glycol (65-68°C), it still does not flow, indicating that the silica in the composite material has a good shaping effect.

Fig. 3 is an electron micrograph of polyethylene glycol/silica composite shape-changing material (Example 1). It can be seen that the size of the composite particles is in the nanometer range, and there is no agglomeration phenomenon, which shows that the components of the material obtained in the present invention are evenly distributed.

Fig. 4 DSC curves of polyethylene glycol and polyethylene glycol/silica composite shape-setting phase change material (Example 1). It can be seen from Figure 5 that the polyethylene glycol phase change material has a relatively high heat storage capacity (187.3J/g), and the phase change temperature is 67.18°C. After compounding, the melting enthalpy of the composite shape-setting phase change material is still high (137.7J/g), and the migration of silicon dioxide only plays a role in setting the shape, but the addition of silicon dioxide causes defects in the crystallization of polyethylene glycol, thus compounding The phase change latent heat and phase change temperature (66.93℃) of the shape-setting phase change material decreased slightly.

Example 2

Steps: (1) In a 1.5L glass beaker, add 600g of 15% silica sol (pH value = 8), and slowly add 360g of polyethylene glycol (PEG5000/PEG10000 = 1/1) powder under strong stirring of a CNC mixer, After the polyethylene glycol powder is completely dissolved, slowly add 0.1M acetic acid dropwise at a rate of 0.05‰ of the total amount of the composite phase-change shape-setting material, and continue stirring until all gels are formed. Transfer the beaker containing the gel into a blast drying oven, dry at a constant temperature of 80°C for 48 hours, cool to room temperature, take out the dried gel, mash it in a mortar, transfer it to a beaker, and stir it vigorously to obtain Powder;

(2) Transfer the powder into a 1L four-necked flask equipped with a stirrer, nitrogen tube, reflux tube, and dropping funnel, and vacuumize at 40°C for 3 hours while stirring, then heat the oil bath to 90°C, and open the water condensation return pipe , Nitrogen protection, according to the proportion of 0.5% of the total weight of the powder, dropwise add silane coupling agent K570, after 3 hours of treatment, lower the temperature, stop stirring, reflux, and pass nitrogen to obtain the composite shape-setting phase change material of the present invention.

Example 3

Steps: (1) at room temperature, in a 1.5L glass beaker, add 500g of 30% silica sol (pH value = 8.5), slowly add polyethylene glycol ((PEG3000/PEG15000 = 1/2 )) powder 350g, after the polyethylene glycol powder is completely dissolved, slowly add 1% calcium chloride solution dropwise according to the ratio of 0.03‰ of the total amount of the composite phase change shape-setting material, and continue to stir until it is completely gelled. Transfer the beaker containing the gel into a blast drying oven, dry at a constant temperature of 80°C for 24 hours, cool to room temperature, take out the dried gel, mash it in a mortar, transfer it to a beaker, and stir it vigorously to obtain Powder.

(2) Transfer the powder into a 1L four-necked flask equipped with a stirrer, nitrogen tube, reflux tube, and dropping funnel, and vacuumize at 40°C for 3 hours while stirring, then heat the oil bath to 90°C, and open the water condensation return pipe , nitrogen protection, according to the proportion of 1.5% of the total weight of the powder, silane coupling agent K550 was added dropwise, and after 3 hours of treatment, the temperature was lowered, the stirring was stopped, reflux, and nitrogen was passed to obtain an inorganic-organic composite phase change material.

The bulk products (Example 1, Example 2, Example 3) were subjected to heat storage and heat release tests, and the stability of the composite shape-changing material is shown in FIG. 5 .

Three kinds of materials pass through about 1000 times of cycle tests, and their phase transition latent heat rate of change is respectively: 3.5% (embodiment 3), 5.5% (embodiment 1), 6.8% (embodiment 2), show good stability sex.

Example 4

Steps: (1) In a 1.5L glass beaker, add 300g of 25% silica sol (pH value = 9.5), and slowly add 600g of polyethylene glycol (PEG1000/PEG10000 = 1/2) powder under strong stirring with a CNC mixer, After the polyethylene glycol powder is completely dissolved, slowly add 0.1M formic acid dropwise at a ratio of 0.04‰ of the total amount of composite phase-change shape-setting materials, and continue stirring until all gels are formed. Transfer the beaker containing the gel into a blast drying oven, dry at a constant temperature of 80°C for 30 hours, cool to room temperature, take out the dried gel, mash it in a mortar, transfer it to a beaker, and stir it vigorously to obtain Powder;

(2) Transfer the powder into a 1L four-neck flask equipped with a stirrer, nitrogen tube, reflux tube, and dropping funnel, and vacuumize at 40°C for 2 hours while stirring, then heat the oil bath to 90°C, and open the water condensation reflux tube , Nitrogen protection, according to the proportion of 1.0% of the total weight of the powder, dropwise add silane coupling agent K550, after 3 hours of treatment, lower the temperature, stop stirring, reflux, and pass nitrogen to obtain the composite shape-setting phase change material of the present invention.

Example 5

Steps: (1) In a 1.5L glass beaker, add 500g of 30% silica sol (pH value = 9), and slowly add 200g of polyethylene glycol (PEG3000/PEG10000 = 1/1) powder under strong stirring of a CNC mixer, After the polyethylene glycol powder is completely dissolved, slowly add 0.1M lactic acid dropwise at a ratio of 0.03‰ of the total amount of the composite phase-change shape-setting material, and continue stirring until all gels are formed. Transfer the beaker containing the gel into a blast drying oven, dry at a constant temperature of 80°C for 24 hours, cool to room temperature, take out the dried gel, mash it in a mortar, transfer it to a beaker, and stir it vigorously to obtain Powder;

(2) Transfer the powder into a 1L four-neck flask equipped with a stirrer, nitrogen tube, reflux tube, and dropping funnel, and vacuumize at 40°C for 2 hours while stirring, then heat the oil bath to 90°C, and open the water condensation reflux tube , Nitrogen protection, according to the proportion of 0.8% of the total weight of the powder, dropwise add silane coupling agent K570, after 3 hours of treatment, lower the temperature, stop stirring, reflux, and pass nitrogen to obtain the composite shape-setting phase change material of the present invention.

Example 6

Steps: (1) In a 1.5L glass beaker, add 400g of 25% silica sol (pH value = 9), and slowly add 300g of polyethylene glycol (PEG5000/PEG10000 = 1/2) powder under strong stirring of a CNC mixer, After the polyethylene glycol powder is completely dissolved, slowly add 1% aluminum nitrate solution dropwise at a ratio of 0.02‰ of the total amount of the composite phase-change shape-setting material, and continue stirring until it is completely gelled. Transfer the beaker containing the gel into a blast drying oven, dry at a constant temperature of 80°C for 36 hours, cool to room temperature, take out the dried gel, mash it in a mortar, transfer it to a beaker, and stir it vigorously to obtain Powder;

(2) Transfer the powder into a 1L four-necked flask equipped with a stirrer, nitrogen tube, reflux tube, and dropping funnel, and vacuumize at 40°C for 3 hours while stirring, then heat the oil bath to 90°C, and open the water condensation return pipe , Nitrogen protection, according to the proportion of 0.8% of the total weight of the powder, dropwise add silane coupling agent K560, after 3 hours of treatment, lower the temperature, stop stirring, reflux, and pass nitrogen to obtain the composite shape-setting phase change material of the present invention.

Example 7

Steps: (1) In a 1.5L glass beaker, add 500g of 20% silica sol (pH value = 8.), and slowly add 360g of polyethylene glycol (PEG3000/PEG15000 = 1/1) powder under strong stirring with a CNC mixer , after the polyethylene glycol powder is completely dissolved, slowly add 1% magnesium chloride solution dropwise at a rate of 0.02‰ of the total amount of composite phase change shape-setting materials, and continue stirring until all gels are formed. Transfer the beaker containing the gel into a blast drying oven, dry at a constant temperature of 80°C for 48 hours, cool to room temperature, take out the dried gel, mash it in a mortar, transfer it to a beaker, and stir it vigorously to obtain Powder;

(2) Transfer the powder into a 1L four-necked flask equipped with a stirrer, nitrogen tube, reflux tube, and dropping funnel, and vacuumize at 40°C for 3 hours while stirring, then heat the oil bath to 90°C, and open the water condensation return pipe , Nitrogen protection, according to the proportion of 1.0% of the total weight of the powder, dropwise add silane coupling agent K550, after 3 hours of treatment, lower the temperature, stop stirring, reflux, and pass nitrogen to obtain the composite shape-setting phase change material of the present invention. Table 1 shows the DSC test results of composite shape-setting phase change materials with different ratios.

When the silica content is less than 10%, the capillary adsorption of the silica pores and the hydrogen bond with polyethylene glycol are not enough to offset the segmental movement of polyethylene glycol when it melts, and it will melt and leak out, that is, it cannot be easily Good shape. When the silicon dioxide content is above 50%, the restriction on polyethylene glycol is too strong, its crystalline segment is severely damaged, and its melting enthalpy cannot be displayed in DSC. Therefore, the content of shaped silicon dioxide is in the range of 10 to 50%. . The effect is preferably 10-30%, which not only has a good setting effect, but also has a high melting latent heat value.

Table 1 sample Silica% polyethylene glycol/dioxide ΔHm(kJ/kg) Melting temperature Tm(℃) Crystallinity 12345678 010202530405060 100/090/1080/2075/2570/3060/4050/5040/60 187.3165.2137.7124.3120.657.0557.15- 67.1867.0166.9366.0365.5963.1755.54- 100% 85.857 3.45% 66.14% 62.76% 30.92% 30.51% -

Claims (9)

1, a kind of preparation method of polyethylene glycol/silicon dioxide composite shape-changing material, is characterized in that comprising the steps: (1) adding the polyethylene glycol powder to dissolve in the silica sol, and then adding the accelerator solution dropwise, a sol-gel reaction occurs to form a three-dimensional network gel; (2) drying the gel obtained in step (1), smashing it into powder; (3) Dewatering the powder obtained in step (2), and adding a modifying agent to modify its surface hydrophobically. 2. The method according to claim 1, characterized in that in step (1), the number-average molecular weight of the polyethylene glycol is 1000-20000, which is obtained by mixing polyethylene glycols with different molecular weights. 3. The method according to claim 1 or 2, characterized in that in step (1), the pH value of the silica sol is 8-9.5, the concentration is 15-30% by weight, and the silica content in the obtained gel is Controlled at 10-50% by weight. 4. The method according to claim 3, characterized in that in step (1), the accelerator selected is weak acid acetic acid, formic acid or lactic acid, or the soluble high-valent salt calcium chloride, magnesium chloride, aluminum chloride, aluminum sulfate or For aluminum nitrate, the amount of accelerator accounts for 0.01-0.1 ‰ weight of the total amount of polyethylene glycol and silica sol. 5. The method according to claim 4, characterized in that in step (1), the polyethylene glycol powder is composed of polyethylene glycol with a number average molecular weight of 3000-6000 and 10000-20000 in the amount of 0.5-1 /1 mixed to obtain; the silica sol concentration is 20-25% by weight; the silicon dioxide content in the gel is controlled at 10-30% by weight; 6. The method according to claim 5, characterized in that the drying described in step (2) is to air-dry the gel in an oven at 80°C for 24-48 hours, cool to room temperature, take it out, mash and stir to obtain a powder . 7. The method according to claim 6, characterized in that in step (3), the water removal is to vacuumize the powder at 40°C for 2-4 hours, and then add modified sex agent. 8. The method according to claim 7, characterized in that in step (3), the modifier used is a silane coupling agent whose general formula is RSiX3, wherein R is a compound having an affinity with polyethylene glycol The active group aminopropyl, etheroxypropyl or acyloxypropyl, X is a hydrolyzable alkoxyl group or a halogen; its dosage accounts for 0.1-1.5% by weight of the powder. 9. The method according to claim 8, characterized in that the silane coupling agent is aminopropyltriethoxysilane (KH-550), glycidyl etheroxypropyltrimethoxysilane (KH-560) Or methacryloxypropyltrimethoxysilane (KH-570); its dosage is 0.5-1.0% by weight of the powder.

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