A PNIPAM / KCA hydrogel and its preparation method

Abstract

The present invention belongs to the field of polymer materials, and specifically relates to a PNIPAM / KCA hydrogel and a preparation method thereof. Preparation method: Using N-isopropylacrylamide (NIPAM) as a polymerization monomer, N,N'-methylenebisacrylamide (BIS) as a cross-linking agent, and ammonium persulfate (APS) as a reaction initiator, reacting in a nitrogen environment to prepare a PNIPAM hydrogel. Then, K-type carrageenan (KCA) is added to the PNIPAM hydrogel, and the mixture is stirred at 40 °C to generate a PNIPAM / KCA hydrogel. The present invention can achieve effective control of PNIPAM gel microspheres, realize the uniform dispersion of PNIPAM polymers in the gel system, and can inhibit the agglomeration and sedimentation behavior of gel microspheres in the PNIPAM hydrogel, and improve the light transmittance at low temperatures.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and particularly relates to a PNIPAM / KCA hydrogel and a preparation method thereof. Background Art

[0002] In China, building energy consumption accounts for up to 40% of the primary energy consumption. The application of energy-saving technologies in building design has become the focus of energy decision-making and energy-saving improvement. Among many building components, the window system is the weakest link in terms of building insulation and airtightness. Approximately 60% of the energy is lost through window conduction, convection, and radiation. Optimizing and improving the regulation of indoor light and heat by windows is an effective way to improve energy utilization efficiency and comfort.

[0003] Since solar radiation is the main source of indoor heat, 47% of its energy is distributed in the near-infrared band (750−2500 nm). If there is an energy-saving intelligent window that can automatically sense the surrounding environmental temperature and intelligently regulate near-infrared light, it will help improve the energy-saving and cooling effect of buildings. Currently, traditional responsive materials usually have low transparency and a narrow range of solar transmittance, while new thermochromic hydrogels have strong sunlight modulation ability and are suitable for the research of color-changing intelligent windows, showing good potential application prospects in energy-saving buildings and greenhouses.

[0004] Poly(N-isopropylacrylamide) (PNIPAM) is a common thermochromic hydrogel with hydrophilic amide groups and hydrophobic isopropyl groups. The PNIPAM hydrogel prepared by the traditional emulsion polymerization method has strong diffusivity, which optimizes the slow phase change rate of the hydrogel-based intelligent window, but reduces the light transmittance at low temperatures. In order to improve the performance of existing hydrogel materials, the synthesis method involved in this application utilizes the porous 3D network structure of KCA (carrageenan) to effectively control PNIPAM gel microspheres, achieve uniform dispersion of PNIPAM polymers in the gel system, and inhibit the aggregation and sedimentation behavior of gel microspheres in the PNIPAM hydrogel, thereby improving the light transmittance at low temperatures. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to overcome the defects in the prior art and provide a PNIPAM / KCA thermochromic hydrogel. In this hydrogel, KCA has a porous 3D network structure, which can effectively control PNIPAM microspheres, achieve uniform dispersion of PNIPAM in the gel system, and promote short response time of water molecule diffusion characteristics. At the same time, the light transmittance of the PNIPAM / KCA hydrogel in a low-temperature environment is significantly higher than that of the PNIPAM hydrogel. The KCA / PNIPAM hydrogel has excellent sunlight modulation ability, rapid response speed, and excellent performance stability, which has far-reaching significance for building energy conservation.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned PNIPAM / KCA thermochromic hydrogel: Prepare a PNIPAM hydrogel. The polymerization monomer is N-isopropylacrylamide (NIPAM), the cross-linking agent is N,N'-methylenebisacrylamide (BIS), and the reaction initiator is ammonium persulfate (APS). To avoid the combination of oxygen and chain radicals during the polymerization and terminate the polymerization, the reaction process is carried out in a nitrogen environment. Then, K-carrageenan (KCA) is added to the PNIPAM hydrogel, and the mixture is stirred at 40 °C to form a gel.

[0007] A method for preparing a PNIPAM / KCA hydrogel specifically includes the following steps:

[0008] (1) Prepare an aqueous solution containing 2.667% N-isopropylacrylamide monomer and 0.467% N,N'-methylenebisacrylamide. After stirring and dissolving, it is the first monomer solution. Prepare an aqueous solution containing 12.281% N-isopropylacrylamide monomer and 0.589% N,N'-methylenebisacrylamide. After stirring and dissolving, it is the second monomer solution.

[0009] (2) Add a certain amount of distilled water and the first monomer solution to a four-necked flask, and then introduce nitrogen to blow out the air. While continuously stirring the four-necked flask, add a certain amount of 4.156% sodium dodecyl sulfate (SDS) solution. Subsequently, add an appropriate amount of 10% ammonium persulfate (APS) aqueous solution and continuously stir for a period of time to initiate the emulsion polymerization reaction.

[0010] (3) In the solution obtained in step (2), slowly drop the second monomer with a peristaltic pump and continuously react for a certain time to obtain a PNIPAM hydrogel.

[0011] (4) Prepare an aqueous solution of carrageenan, place it in an oil bath at 50 °C and stir and swell for 1 h, then raise the temperature to 75 °C and stir for another 1 h. The magnetic stirrer speed is 400 r / min, and then cool it to 40 °C to obtain a carrageenan solution.

[0012] (5) Mix the PNIPAM hydrogel prepared in step (3) and the carrageenan solution prepared in step (4) in a certain proportion and stir for a period of time. Collect the product to obtain a PNIPAM / KCA thermochromic hydrogel.

[0013] Preferably, in step (2), the amounts of distilled water and the first monomer solution added to the four-necked flask are 100 ml and 15 ml respectively.

[0014] Preferably, the amount of 4.156% sodium dodecyl sulfate (SDS) solution added in step (2) is 1 ml; the amount of 10% ammonium persulfate (APS) aqueous solution added later is 0.8 ml, and the stirring time is 1 min.

[0015] Preferably, the amount of the second monomer solution added in step (3) is 25 ml, and the reaction time is 2 h.

[0016] Preferably, the content of carrageenan in the prepared carrageenan aqueous solution in step (4) is 0.5%.

[0017] Preferably, the mixing ratio of the PNIPAM hydrogel and the carrageenan solution in step (5) is 1:4, the rotation speed of the magnetic stirrer is 500 r / min, and the stirring time is 1 h.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0019] The present invention prepares the PNIPAM / KCA hydrogel by dispersing PNIPAM microspheres into a carrageenan (KCA) matrix. KCA is an environmentally friendly material that constructs a 3D network structure in the gel, and the PNIPAM microspheres are uniformly and stably dispersed in this network structure. At the same time, the network structure of KCA has a steric hindrance effect, which can not only effectively prevent the aggregation of PNIPAM microspheres, ensure the number of PNIPAM scattering centers, and thus optimize its sunlight modulation ability, but also increase the water retention of the system and achieve excellent stability. Description of the Drawings

[0020] Figure 1 are the scanning electron microscope images of the PNIPAM hydrogel and the PNIPAM / KCA hydrogel

[0021] Figure 2 are the visible light transmittance diagrams of the PNIPAM hydrogel and the PNIPAM / KCA hydrogel at 18 °C and 38 °C respectively

[0022] Figure 3 is the variable-temperature linear transmittance test diagram of the PNIPAM hydrogel and the PNIPAM / KCA hydrogel. Detailed Embodiments

[0023] The present invention discloses a PNIPAM / KCA composite hydrogel and a preparation method thereof. The present invention will be further described in detail below in conjunction with examples and drawings, but the implementation manners of the present invention are not limited thereto. Those skilled in the art can draw on the content of this article and appropriately modify the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The following described examples are only a part of the examples of the present invention, rather than all the examples. The method and product of the present invention have been described through preferred examples, and those related can obviously make changes or appropriate alterations and combinations to the methods described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0024] In the examples of the present invention, those not specified under specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. The raw materials, reagents, etc. without indicating the manufacturer can be obtained as conventional products through commercial purchase. Unless otherwise specified, the reagents involved in the examples of the present invention are all commercially available products and can be obtained through commercial channels.

[0025] Example 1

[0026] (1) Preparation of PNIPAM hydrogel:

[0027] Prepare an aqueous solution containing 2.667% N-isopropylacrylamide monomer and 0.467% N,N'-methylenebisacrylamide. After stirring and dissolving, it is the first monomer. Prepare an aqueous solution containing 12.281% N-isopropylacrylamide monomer and 0.589% N,N'-methylenebisacrylamide. After stirring and dissolving, it is the second monomer. Add 100 ml of distilled water and 15 ml of the first monomer solution to a four-necked flask, and then introduce nitrogen to blow out the air. While continuously stirring the four-necked flask, add 1 ml of 4.156% sodium dodecyl sulfate (SDS) solution. Subsequently, add 0.8 ml of 10% ammonium persulfate (APS) aqueous solution and continuously stir for 1 min to initiate the emulsion polymerization reaction. Then, slowly drip 25 ml of the second monomer with a peristaltic pump and continuously react for 2 h. Finally, obtain the PNIPAM hydrogel.

[0028] (2) Preparation of PNIPAM / KCA hydrogel:

[0029] Prepare an aqueous solution containing 0.5% carrageenan, place it in a 50 °C oil bath and stir for swelling for 1 h, then raise the temperature to 75 °C and stir for another 1 h. The magnetic stirrer speed is 400 r / min, and then cool it down to 40 °C to obtain the carrageenan solution. Mix the prepared PNIPAM hydrogel and the carrageenan solution in a volume ratio of 1:4 and stir for 1 h. The magnetic stirrer speed is 500 r / min. Collect the product to obtain the PNIPAM / KCA thermochromic hydrogel.

[0030] Figure 1 It is the observation result diagram of the scanning electron microscope of the PNIPAM hydrogel and the PNIPAM / KCA hydrogel prepared in this example. It can be seen from the figure that the PNIPAM hydrogel after mixing with KCA has obtained a porous structure. The porous 3D network structure of KCA effectively controls the PNIPAM microspheres, realizes the uniform dispersion of PNIPAM in the gel system, and promotes the short response time of the water molecule diffusion characteristics.

[0031] Figure 2 It is the visible light transmittance diagram of the PNIPAM hydrogel and the PNIPAM / KCA hydrogel prepared in this example measured by an ultraviolet-visible spectrometer. As can be seen from the figure, the light transmittance of the PNIPAM hydrogel is significantly lower than that of the PNIPAM / KCA hydrogel in any visible light band. This is because the porous 3D network structure of KCA effectively inhibits the aggregation and sedimentation behavior of the PNIPAM microspheres. Therefore, the light transmittance of the PNIPAM / KCA hydrogel is significantly higher than that of the PNIPAM hydrogel.

[0032] Figure 3 It is the test diagram of the visible straight-line transmittance of the PNIPAM hydrogel and the PNIPAM / KCA hydrogel prepared in this example measured by spectrophotometry. It can be observed and calculated from the transmittance hysteresis regression curve that the LCST values of the PNIPAM hydrogel and the PNIPAM / KCA hydrogel are close. It can be seen that the porous 3D network structure generated by the addition and mixing of KCA has no significant effect on the LCST value of the PNIPAM hydrogel.

[0033] Example 2

[0034] (1) Preparation of PNIPAM hydrogel:

[0035] Prepare an aqueous solution containing 2.667% N-isopropylacrylamide monomer and 0.467% N,N'-methylenebisacrylamide. After stirring and dissolving, it is the first monomer. Prepare an aqueous solution containing 12.281% N-isopropylacrylamide monomer and 0.589% N,N'-methylenebisacrylamide. After stirring and dissolving, it is the second monomer. Add 100 ml of distilled water and 15 ml of the first monomer solution to a four-necked flask, and then pass nitrogen to blow out the air. While continuously stirring the four-necked flask, add 1 ml of 4.156% sodium dodecyl sulfate (SDS) solution. Subsequently, add 0.8 ml of 10% ammonium persulfate (APS) aqueous solution and continuously stir for 1 min to initiate the emulsion polymerization reaction. Then, slowly drip 25 ml of the second monomer with a peristaltic pump and continuously react for 2 h. Finally, obtain the PNIPAM hydrogel.

[0036] (2)Preparation of PNIPAM / KCA hydrogel:

[0037] Prepare an aqueous solution containing 0.5% carrageenan, place it in a 50 °C oil bath and stir and swell for 1 h, then heat to 75 °C and stir for another 1 h. The magnetic stirrer speed is 400 r / min, and then cool to 40 °C to obtain the carrageenan solution. Mix the prepared PNIPAM hydrogel and the carrageenan solution in a volume ratio of 1:5 and stir for 1 h. The magnetic stirrer speed is 500 r / min. Collect the product to obtain the PNIPAM / KCA thermochromic hydrogel.

[0038] Example 3

[0039] (1)Preparation of PNIPAM hydrogel:

[0040] Prepare an aqueous solution containing 2.667% N-isopropylacrylamide monomer and 0.467% N,N'-methylenebisacrylamide. After stirring and dissolving, it is the first monomer. Prepare an aqueous solution containing 12.281% N-isopropylacrylamide monomer and 0.589% N,N'-methylenebisacrylamide. After stirring and dissolving, it is the second monomer. Add 100 ml of distilled water and 20 ml of the first monomer solution to a four-necked flask, and then pass nitrogen to blow out the air. While continuously stirring the four-necked flask, add 1 ml of 4.156% sodium dodecyl sulfate (SDS) solution. Subsequently, add 0.8 ml of 10% ammonium persulfate (APS) aqueous solution and continuously stir for 1 min to initiate the emulsion polymerization reaction. Then, slowly drip 20 ml of the second monomer with a peristaltic pump and continuously react for 2 h. Finally, obtain the PNIPAM hydrogel.

[0041] (2)Preparation of PNIPAM / KCA hydrogel:

[0042] Prepare an aqueous solution containing 0.5% carrageenan, place it in an oil bath at 50 °C and stir for swelling for 1 h, then raise the temperature to 75 °C and stir for another 1 h, with the magnetic stirrer rotating at 400 r / min. Subsequently, cool it down to 40 °C to obtain the carrageenan solution. Mix the prepared PNIPAM hydrogel and the carrageenan solution in a volume ratio of 1:4 and stir for 1 h, with the magnetic stirrer rotating at 500 r / min. Collect the product to obtain the PNIPAM / KCA thermochromic hydrogel.

[0043] Example 4

[0044] (1) Preparation of PNIPAM hydrogel:

[0045] Mix 1.64 g of N-isopropylacrylamide (NIPAM), 0.004 g of N,N'-methylenebisacrylamide (BIS) and 120 ml of distilled water in a two-necked flask, and stir (at a speed of 300 r / min) in an oil bath at 50 °C for 30 min to dissolve. Then, add 1 ml of 10% ammonium persulfate (APS) solution as an initiator, and blow out the air in the device with nitrogen. Finally, react at a temperature of 70 °C for 30 min to obtain the PNIPAM hydrogel.

[0046] (2) Preparation of PNIPAM / KCA hydrogel:

[0047] Weigh 0.25 g of KCA and disperse it in a beaker containing 50 ml of distilled water, stir and swell at 50 °C for 1 h, then raise the temperature to 75 °C and stir to dissolve for 1 h, with a rotation speed of 300 r / min. After dissolution, cool it down to 40 °C. Then, mix the prepared PNIPAM solution and the KCA solution in a volume ratio of 1:4 and stir for 1 h, with a rotation speed of 500 r / min. Finally, collect the product to obtain the PNIPAM / KCA thermochromic hydrogel.

[0048] The above examples are only for illustrating the technical concept and characteristics of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit and essence of the present invention should be covered by the protection scope of the present invention.

Claims

1. A preparation method of a PNIPAM / KCA hydrogel, characterized in that, Specifically, it includes the following steps: (1) Prepare an aqueous solution containing 2.667% N-isopropylacrylamide monomer and 0.467% N,N'-methylenebisacrylamide. After stirring and dissolving, it becomes the first monomer solution; Prepare an aqueous solution containing 12.281% N-isopropylacrylamide monomer and 0.589% N,N-methylenebisacrylamide. After stirring and dissolving, it becomes the second monomer solution; (2) Add 100 ml of distilled water and 15 ml of the first monomer solution to a four-necked flask, and then introduce nitrogen to blow out the air. While continuously stirring the four-necked flask, add 1 ml of 4.156% sodium dodecyl sulfate solution. Subsequently, add 0.8 ml of 10% ammonium persulfate aqueous solution and continuously stir for 1 min to initiate the emulsion polymerization reaction; (3) In the solution obtained in step (2), slowly drip 25 ml of the second monomer with a peristaltic pump and continue the reaction for 2 h to obtain PNIPAM hydrogel; (4) Prepare an aqueous solution of carrageenan, place it in a 50 °C oil bath and stir and swell for 1 h, then raise the temperature to 75 °C and stir for another 1 h. The magnetic stirrer speed is 400 r / min, and then cool it to 40 °C to obtain the carrageenan solution; (5) Mix the PNIPAM hydrogel prepared in step (3) and the carrageenan solution prepared in step (4) in a certain proportion and stir for a period of time; Collect the product to obtain the PNIPAM / KCA thermochromic hydrogel; the mixing ratio of the PNIPAM hydrogel to the carrageenan solution is 1:

4.

2. The preparation method according to claim 1, wherein In step (4), the content of carrageenan in the prepared aqueous solution of carrageenan is 0.5%.

3. The preparation method according to claim 1, wherein, In step (5), the rotation speed of the magnetic stirrer for stirring is 500 r / min, and the stirring time is 1 h.

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