A method for preparing a polyelectrolyte composite microsphere-based total heat exchange membrane

Abstract

The invention relates to the field of total heat exchange, and in particular to a method for preparing a polyelectrolyte complex microsphere-based total heat exchange membrane. The main preparation method is as follows: firstly, chitosan quaternary ammonium salt and sodium alginate in a certain mass ratio are dissolved in deionized water, heated and stirred until completely dissolved, to prepare a polyelectrolyte complex solution and let it stand for use; sodium polyacrylate is dissolved in deionized water, heated and stirred until completely dissolved, and let it stand for use; then the two solutions are mutually dissolved in proportion to obtain a casting liquid, and let it stand for use; finally, the casting liquid is coated on a polymer base membrane to make a total heat exchange membrane. The polyelectrolyte complex microsphere-based total heat exchange membrane prepared by the invention has good application prospects in the field of total heat exchange.

Description

Technical Field

[0001] The invention belongs to the field of fresh air full heat exchange, and in particular relates to a method for preparing a polyelectrolyte complex microsphere-based full heat exchange membrane. Technical Background

[0002] In recent years, with the improvement of people's living standards, air conditioners have entered thousands of households and become a necessity in our lives. However, due to the use of air conditioners, the space is closed, causing "air conditioning disease", and the indoor air quality has attracted more and more attention. On the other hand, according to survey statistics, the energy directly consumed by buildings is close to 1 / 3 of the total social energy consumption, of which heating and air conditioning energy consumption accounts for about 65%. In order to solve these problems, more and more people are committed to the innovation of traditional air conditioners: to ensure the circulation of indoor and outdoor air while reducing energy consumption as much as possible. At present, the total heat exchanger is the best way to solve the above problems. As an air conditioning auxiliary device, the total heat exchanger uses the heat energy of the exhaust air to be recycled and reused in the fresh air system for air supply, and uses efficient heat exchange elements to exchange heat between the exhaust air and the supply air. Only the outdoor fresh air is used as a cold source to take away the heat, and the outdoor air does not directly enter the room; the indoor air is sent back to the room after being cooled by heat exchange. It can effectively reduce the impact of the fresh air load on the indoor load. Avoid energy waste. Compared with the combination of ordinary ventilating fans and air conditioners, the combination of a heat exchanger and an air conditioner can significantly reduce the fluctuation of indoor temperature, making the air supply temperature closer to the room temperature and making the indoor people feel more comfortable. The high temperature exchange efficiency allows the air conditioner to maintain a comfortable room temperature while continuously bringing in fresh and clean air.

[0003] The heat exchange efficiency of the heat exchanger used in the current heat exchange energy-saving system is very low, resulting in the energy-saving efficiency of the heat exchange energy-saving system being far lower than that of the ventilation energy-saving system. Although the full heat exchanger has entered the industrial production stage, many products use paper membrane as the full heat exchange membrane. With the popularization of the full heat exchanger, the shortcomings of this membrane have gradually been exposed, such as easy to mold and no air blocking.

[0004] In view of this, new full heat exchange membranes have become a research hotspot. The research mainly focuses on the preparation of various full heat exchange membranes with excellent moisture permeability, high gas barrier properties, mildew resistance and flame retardancy through the compounding of different membrane materials and additives, so as to replace paper membranes and more effectively reduce air conditioning energy consumption and improve indoor air quality. For example, Chinese Patent Application No. 201910681871.7 discloses a formaldehyde-removing full heat exchange membrane and a preparation method thereof, wherein the exchange membrane comprises a porous base membrane and a polymer membrane containing a formaldehyde-removing material coated on the porous base membrane; Chinese Patent Application No. 202210442333.4 discloses an ultra-high gas barrier thin film composite polyamide full heat exchange membrane based on acid-base solution post-treatment and a preparation method thereof. Compared with the comparative example of washing and drying, the membrane has extremely low CO2 gas permeability and equally high moisture permeability and heat recovery efficiency; Chinese Patent Application No. 202010657696.0 discloses a method for preparing water-resistant full heat exchange paper, which comprises: adding a polymer film-forming substance and an antibacterial and mildew-proof material to a solvent to obtain a coating solution, applying the coating solution onto low-permeability paper with a screen roller, and drying to obtain a full heat exchange membrane. However, the "trade-off" effect between selectivity and permeability that is common in polymer membranes restricts their industrial production and application, and full heat exchange membranes are still in the research and development stage.

[0005] Based on the above, problems such as paper membranes being prone to mold and not air-tight, and the common "trade-off effect" between water vapor permeability and gas permeability of polymer membranes, lead to low exchange efficiency of total heat exchangers, and energy-saving efficiency is not as good as ventilation-type energy-saving systems. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method for preparing a polyelectrolyte complex microsphere-based total heat exchange membrane. Sodium alginate is a polyanion electrolyte, and quaternary ammonium salt chitosan is a polycation electrolyte. Since the two raw materials have different charges, the two polyelectrolytes form a polyelectrolyte complex when blended. Polyelectrolyte complex is a type of polymer with three-dimensional structure and performance, which has a high degree of hydrophilicity and can still maintain good mechanical strength in a swollen state. In this regard, polyelectrolyte complex microspheres are introduced into the preparation of the total heat exchange membrane to improve hydrophilicity, thereby improving water vapor permeability, and the polyelectrolyte complex has a three-dimensional structure, which extends the gas transmission path and improves the gas barrier property, thereby balancing the "trade-off" effect between the films. The main preparation method is as follows: first, a certain mass ratio of chitosan quaternary ammonium salt and sodium alginate are dissolved in deionized water and heated and stirred until completely dissolved, a certain mass of sodium polyacrylate is dissolved in deionized water and heated and stirred until completely dissolved, and then the two solutions are mutually dissolved in proportion to obtain a casting liquid. Finally, the casting liquid is applied to the polymer base membrane for a total heat exchange membrane. In the embodiment of the present invention, the prepared polyelectrolyte complex microsphere-based total heat exchange membrane is compared with the composite membrane only adding quaternary ammonium salt polymer or sodium alginate, and a method for preparing a polyelectrolyte complex microsphere-based total heat exchange membrane is provided. The specific steps are as follows:

[0007] Step 1: weigh chitosan quaternary ammonium salt and sodium alginate powder, dissolve them in deionized water, heat and stir until they are completely dissolved, wherein the mass ratio of chitosan quaternary ammonium salt to sodium alginate is 1-3:3-5.

[0008] Step 2: Weigh sodium polyacrylate powder and dissolve it in deionized water to prepare a sodium polyacrylate solution with a mass fraction of 3%-6%, heat and stir until it is completely dissolved, and then stand it for use;

[0009] Step 3: Mix the solutions of step 1 and step 2 in proportion, heat and stir to mix evenly, wherein the mass ratio of step 1 to step 2 is 3-1:1.

[0010] Step 4: Apply the solution in step 3 to the surface of the polymer film substrate using a laboratory knife coater, wherein the knife coating thickness is 1-5 μm.

[0011] The present invention achieves the following beneficial effects:

[0012] High water vapor transmission rate. In the present invention, by preparing a functional layer loaded with polyelectrolyte complex microspheres on the surface of the base film, the hydrophilicity of the film is improved, so that water vapor molecules can be quickly adsorbed on the surface of the functional layer, and then the water vapor molecules are conducted through dissolution-diffusion, thereby transferring energy, and reducing energy consumption as an air conditioning auxiliary device. Under the test conditions of 38°C and 90% RH, the water vapor transmission rate is as high as 5763.9g / (m 2 ·24h).

[0013] Thin thickness and high gas barrier property. The prepared polyelectrolyte complex solution is mixed with sodium polyacrylate solution and then coated on the surface of the substrate. The coating thickness is only 1-5 μm. The prepared polyelectrolyte complex exists not only on the surface of the functional layer but also inside it. The unique three-dimensional structure of the polyelectrolyte complex prolongs the transmission path of gas molecules. Under the test conditions of 23°C and 0.1MPa, the minimum air permeability is 31476l / m 2 / h / bar. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 ae is a schematic diagram of the water contact angle of Examples 1-5 of the present invention after stabilization for 10 seconds;

[0015] Figure 2 ab is a schematic diagram of the water contact angle of Comparative Example 1-2 of the present invention after stabilization for 10 seconds; DETAILED DESCRIPTION

[0016] Example 1

[0017] A polyelectrolyte complex microsphere-based total heat exchange membrane comprising the following steps:

[0018] Step 1: Weigh 1g chitosan quaternary ammonium salt and 5g sodium alginate powder and dissolve them in 100ml deionized water, heat and stir until completely dissolved.

[0019] Step 2: Weigh 3 g of sodium polyacrylate powder and dissolve it in 97 ml of deionized water, and heat and stir until it is completely dissolved.

[0020] Step 3: Mix the solutions of step 1 and step 2 in a ratio of 3:1, and heat and stir to mix evenly.

[0021] Step 4: Use a laboratory knife coater to apply the solution in step 3 to the surface of the polymer film substrate, with a coating thickness of 1 μm.

[0022] Example 2

[0023] Step 1: Weigh 2 g of chitosan quaternary ammonium salt and 4 g of sodium alginate powder and dissolve them in 100 ml of deionized water, and heat and stir until completely dissolved.

[0024] Step 2: Weigh 4 g of sodium polyacrylate powder and dissolve it in 96 ml of deionized water, and heat and stir until it is completely dissolved.

[0025] Step 3: Mix the solutions of step 1 and step 2 in a ratio of 2:1, and heat and stir to mix evenly.

[0026] Step 4: Use a laboratory doctor blade coater to apply the solution in step 3 onto the surface of the polymer film substrate, with a coating thickness of 2 μm.

[0027] Example 3

[0028] Step 1: Weigh 3 g of chitosan quaternary ammonium salt and 3 g of sodium alginate powder and dissolve them in 100 ml of deionized water, and heat and stir until completely dissolved.

[0029] Step 2: Weigh 5 g of sodium polyacrylate powder and dissolve it in 95 ml of deionized water, then heat and stir until completely dissolved.

[0030] Step 3: Mix the solutions of step 1 and step 2 in a ratio of 3:1, and heat and stir to mix evenly.

[0031] Step 4: Use a laboratory doctor blade coater to apply the solution in step 3 to the surface of the polymer film substrate, with a coating thickness of 3 μm.

[0032] Example 4

[0033] Step 1: Weigh 3 g of chitosan quaternary ammonium salt and 3 g of sodium alginate powder and dissolve them in 100 ml of deionized water, and heat and stir until completely dissolved.

[0034] Step 2: Weigh 6 g of sodium polyacrylate powder and dissolve it in 94 ml of deionized water, and heat and stir until it is completely dissolved.

[0035] Step 3: Mix the solutions of step 1 and step 2 in a ratio of 2:1, and heat and stir to mix evenly.

[0036] Step 4: Use a laboratory doctor blade coater to apply the solution in step 3 onto the surface of the polymer film substrate, with a coating thickness of 4 μm.

[0037] Example 5

[0038] Step 1: Weigh 2 g of chitosan quaternary ammonium salt and 6 g of sodium alginate powder and dissolve them in 100 ml of deionized water, and heat and stir until completely dissolved.

[0039] Step 2: Weigh 5 g of sodium polyacrylate powder and dissolve it in 95 ml of deionized water, then heat and stir until completely dissolved.

[0040] Step 3: Mix the solutions of step 1 and step 2 in a ratio of 1:1, and heat and stir to mix evenly.

[0041] Step 4: Apply the solution in step 3 to the surface of the polymer film substrate using a laboratory doctor blade coater, with a coating thickness of 5 μm.

[0042] Comparative Example 1

[0043] Step 1: Weigh 2 g of chitosan quaternary ammonium salt and dissolve it in 100 ml of deionized water, and heat and stir until it is completely dissolved.

[0044] Step 2: Weigh 5 g of sodium polyacrylate powder and dissolve it in 95 ml of deionized water, then heat and stir until completely dissolved.

[0045] Step 3: Mix the solutions of step 1 and step 2 in a ratio of 3:1, and heat and stir to mix evenly.

[0046] Step 4: Use a laboratory doctor blade coater to apply the solution in step 3 onto the surface of the polymer film substrate, with a coating thickness of 5 μm.

[0047] Comparative Example 2

[0048] Step 1: Weigh 3 g of sodium alginate powder and dissolve it in 100 ml of deionized water, then heat and stir until completely dissolved.

[0049] Step 2: Weigh 6 g of sodium polyacrylate powder and dissolve it in 94 ml of deionized water, and heat and stir until it is completely dissolved.

[0050] Step 3: Mix the solutions of step 1 and step 2 in a ratio of 3:1, and heat and stir to mix evenly.

[0051] Step 4: Apply the solution in step 3 to the surface of the polymer film substrate using a laboratory doctor blade coater, with a coating thickness of 4 μm.

[0052] Test method:

[0053] For the embodiments and comparative examples of the present invention, the water vapor permeability of the total heat exchange membrane was evaluated by the method of "GB / T 1037-2021 Plastic film and sheet water vapor permeability determination cup weight gain and weight loss method".

[0054] The gas barrier properties of the total heat exchange membrane were evaluated using the GB / T 1038.1-2022 Test method for gas permeability of plastic films and sheets - Part 1: Differential pressure method.

[0055] The test results of water vapor permeability, gas permeability and water contact angle of the polyelectrolyte complex microsphere-based total heat exchange membrane prepared by the method of the present invention are shown in Table 1.

[0056] Table 1 A polyelectrolyte complex microsphere-based total heat exchange membrane

[0057] Example Water vapor transmission rate g / (㎡·24h) <![CDATA[Gas permeability (l / m 2 / h / bar)]]> Water contact angle (°) Example 1 3287.3 90876 47 Example 2 3940.3 61870 38 Example 3 4783.1 41276 30 Example 4 5763.9 31476 21 Example 5 3674.9 81028 49 Comparative Example 1 2980.6 137651 57 Comparative Example 2 2347.8 421347 63

[0058] The water contact angle test of the polyelectrolyte complex microsphere-based total heat exchange membrane prepared by the method of the present invention is shown in the attached figure. Figure 1 a Figure 1 b Figure 1 c Figure 1 D Figure 1 e are schematic diagrams of the water contact angles of Examples 1, 2, 3, 4 and 5 of the present invention after stabilization for 10 seconds, Figure 2 a and Figure 2 b is a schematic diagram of the water contact angles of comparative examples 1 and 2 of the present invention after being stabilized for 10s; it can be seen from the figure that the water contact angle of Example 4 is the smallest, and the water contact angles of the embodiments are greater than those of the comparative examples, proving that the hydrophilicity of the embodiments is higher than that of the comparative examples.

[0059] Conclusion: By comparing Example 4 with Comparative Example 2 and Example 5 with Comparative Example 1, it can be concluded that the total heat exchange membrane loaded with polyelectrolyte complex microspheres has a higher water vapor permeability than the total heat exchange membrane prepared by adding sodium alginate hydrophilic polymer or quaternary ammonium salt hydrophilic polymer alone, and the gas barrier property is also improved. It is proved that the composite membrane prepared by using polyelectrolyte complex microspheres composed of chitosan quaternary ammonium salt and sodium alginate has efficient total heat exchange performance.

Claims

1. A method for preparing a polyelectrolyte complex microsphere-based total heat exchange membrane, characterized by the following steps: Step 1, weigh chitosan quaternary ammonium salt and sodium alginate powder in a mass ratio of 1-3:3-5, dissolve in deionized water, heat and stir until completely dissolved, prepare a polyelectrolyte complex solution, and let stand for use; Step 2: Weigh sodium polyacrylate powder and dissolve it in deionized water, heat and stir until it is completely dissolved to prepare a sodium polyacrylate solution with a concentration of 3%-6%, and let it stand for later use; Step 3, mixing the solutions of step 1 and step 2 according to a certain proportion, heating and stirring to mix evenly, preparing a casting solution, and letting it stand for later use; Step 4: Use a laboratory doctor blade to coat the solution in step 3 on the surface of the polymer membrane substrate, wherein the coating thickness is 1-5 μm, to obtain a full heat exchange membrane loaded with polyelectrolyte complex microspheres prepared on the surface of the substrate.

2. The preparation method according to claim 1, characterized in that: In the step three, the mass ratio of the solution of step one to that of step two is 3-1:1.

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