Sulfonated modified starch / polyacrylic acid / graphene composite hydrogel as well as preparation method and application thereof

Abstract

The invention discloses a preparation method and application of sulfonated modified starch / polyacrylic acid / graphene composite hydrogel, sodium periodate and sulfamic acid are used for sequentially carrying out aldehyde oxidation modification and sulfonated modification on starch, acrylic acid and N, N-methylene bisacrylamide are subjected to free radical polymerization in a modified starch solution to form gel, and the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is prepared. Then the sulfonated modified starch is mixed with graphene to obtain sulfonated modified starch / polyacrylic acid / graphene composite hydrogel, and an interpenetrating polymerization network formed between polyacrylic acid and a modified starch copolymer exists in the prepared hydrogel, so that the hydrogel has good mechanical strength. Meanwhile, the prepared hydrogel also has a dual-conductive network formed by a sulfonic acid group and graphene, so that the hydrogel has stable and sensitive electric signal sensing performance. The method disclosed by the invention has the characteristics that the raw materials are easy to obtain, the cost is relatively low, and the preparation process is unique and simple; and the prepared hydrogel has wide application in the aspects of flexible wearable electronic devices and flexible electronic materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials of polymer materials and graphene, and particularly relates to a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel, a preparation method thereof and an application thereof. Background Art

[0002] With the continuous progress of modern intelligent human wearable sensor technology, the demand for flexible electrolytes with high stretchability, good compressibility and high-efficiency ion transport ability is increasing day by day. As an excellent material for wearable strain sensors, compared with common metal and non-metal materials, the unique three-dimensional network structure of conductive hydrogels endows them with excellent stretchability and flexibility, making them have significant advantages in the manufacture of flexible electronic devices. In addition, hydrogels also have good environmental adaptability and broad application prospects. Sensors based on hydrogels have developed into a large and continuously innovative family of intelligent sensing devices and are widely used in many fields.

[0003] In fact, hydrogels are essentially polymer networks with strong hydrophilicity, good biocompatibility and high water swelling ability, which can convert chemical energy into mechanical energy and have excellent characteristics of responding to external stimuli. Especially natural polymer-based hydrogels, in addition to high safety, good biocompatibility and strong sustainability, can easily achieve conductivity by adding electrolytes, attracting more and more researchers' attention. However, natural polymer-based hydrogels usually have the problem of low stretchability. Essentially, hydrogels are polymer networks with outstanding hydrophilicity, good biocompatibility and high water swelling characteristics, which can convert chemical energy into mechanical energy and have outstanding ability to react to external stimuli. Especially natural polymer-based hydrogels, which not only have high safety, excellent biocompatibility and sustainability, but also can simply achieve conductivity by adding electrolytes, making them receive more and more attention from scientific researchers. However, natural polymer-based hydrogels generally have poor stretchability. Summary of the Invention

[0004] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel, a preparation method thereof and an application thereof. Periodic acid is used for the unique oxidation of starch to prepare dialdehyde starch, and then modified starch with Schiff base structure and carboxyl group is prepared with sulfamic acid. Free radical polymerization of acrylic acid and cross-linking reaction with N,N-methylenebisacrylamide are carried out in the modified starch solution, and then compounded with graphene to form a hydrogel double conductive network with a double network structure, which has sensitive electrical signal sensing performance, so as to solve the problems of poor mechanical strength, weak intermolecular interaction in the gel network and lack of conductivity of pure starch-based hydrogels. To achieve the above object, the present invention is implemented by the following technical solutions: The present invention discloses a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel, and the structural formula of the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is as follows: The present invention also discloses a preparation method of the above-mentioned sulfonated modified starch / polyacrylic acid / graphene composite hydrogel, which comprises the following steps: Step 1, by mass, take 15-20 parts of corn starch, add 160-180 parts of deionized water and stir, then add 3-6 parts of sodium periodate, adjust its pH to 3.3-4.5 with 20% hydrochloric acid solution, and react at 25-30 °C in the dark for 4-6 hours. The obtained product is filtered by suction and washed with 30-40 parts of deionized water and 40-50 parts of acetone. The washed product is vacuum dried at 55-60 °C for 4-8 hours to obtain dialdehyde corn starch; Step 2, add 1-3 parts of dialdehyde starch to a mixed solution of 30-40 parts of deionized water and 20-30 parts of ethanol, add 0.01-0.2 parts of sulfamic acid at 25-30 °C, and stir and react for 3-5 hours. Add 50-70 ml of ethanol to the product, and use a rotary evaporator to evaporate the water at 40-70 °C. Finally, a milky white solid is obtained, which is sulfonated modified starch; Step 3, add 0.1-2.0 parts of the sulfonated modified starch obtained in Step 2 to 20-30 parts of deionized water and stir to dissolve. Add 0.01-0.04 parts of N,N-methylenebisacrylamide and 0.01-0.04 parts of azobisisobutyronitrile and continue to react. Slowly add 3-6 parts of acrylic acid and then continue to stir for 30-40 minutes. Add 0.01-0.04 parts of graphene, and the above solution is treated with nitrogen for 10-15 minutes to ensure an anaerobic state. Irradiate under ultraviolet light for 60-120 minutes to obtain a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel.

[0005] Preferably, the starch used in Step 1 is corn starch.

[0006] Preferably, the purity of sodium periodate, sulfamic acid, N,N-methylenebisacrylamide, azobisisobutyronitrile, and acrylic acid is greater than 99%.

[0007] Preferably, the composite hydrogel can be used as a conductive and signal sensing material and device for sensors in flexible wearable electronic devices.

[0008] The present invention also discloses the application of the above-mentioned sulfonated modified starch / polyacrylic acid / graphene composite hydrogel in conductive sensing.

[0009] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a preparation method and application of a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel. In this method, periodic acid and sulfamic acid are used to modify corn starch successively. Using acrylic acid as the polymerization monomer, N,N'-methylenebisacrylamide as the cross-linking agent, and azobisisobutyronitrile as the initiator, a composite hydrogel is prepared in a solution containing the modified starch, and then graphene is introduced to prepare a modified starch / polyacrylic acid / graphene double-crosslinked network cement gel, which has good mechanical strength. At the same time, a double conductive network is formed in the prepared hydrogel, so it has stable and sensitive electrical signal sensing performance. The method of the present invention has the characteristics of easy availability of raw materials, low cost, and unique and simple preparation process. The prepared hydrogel has a wide range of uses in flexible wearable electronic devices and flexible electronic materials. The sulfonated modified starch / polyacrylic acid / graphene composite hydrogel of the present invention has good conductive sensing performance, and the best GF = 4.1. The corn starch natural biomass used in the present invention is sold at 4.2 yuan / 500g in the market, and acrylic acid is 13 yuan / 500g, which has the advantages of being cheap and easy to obtain. It can replace hundreds of thousands of expensive medical sensors in life, and the total cost of each detection is 2 yuan, so it has great economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the synthesis route of the sulfonated modified starch of the present invention; Figure 2 It is a schematic diagram of the preparation process of the sulfonated modified starch / polyacrylic acid hydrogel of the present invention; Figure 3 It is a schematic diagram of the conductive network structure of the composite hydrogel of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0011] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0012] It should be noted that the terms "first", "second", etc. in the specification, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0013] The present invention discloses a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel and a preparation method thereof. The method uses sodium periodate, aminosulfonic acid and corn starch as raw materials, acrylic acid and N,N-methylenebisacrylamide as cross-linking agents, and azobisisobutyronitrile as an initiator. Based on the principle of free radical polymerization, graphene is finally introduced to significantly improve the conductivity of the hydrogel, and a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is prepared by physical cross-linking and chemical cross-linking.

[0014] Specifically, it includes the following steps: Step 1, by mass, take 15-20 parts of corn starch, add 160-180 parts of deionized water and stir, then add 3-6 parts of sodium periodate, adjust its pH to 3.3-4.5 with 20% hydrochloric acid solution, and react at 25-30 °C in the dark for 4-6 hours. The obtained product is filtered by suction and washed with 30-40 parts of deionized water and 40-50 parts of acetone. The washed product is vacuum dried at 55-60 °C for 4-8 hours to obtain dialdehyde corn starch; Step 2, add 1-3 parts of dialdehyde starch to a mixed solution of 30-40 parts of deionized water and 20-30 parts of ethanol, add 0.01-0.2 parts of aminosulfonic acid at 25-30 °C, and stir and react for 3-5 hours. Add 50-70 ml of ethanol to the product, and use a rotary evaporator to evaporate the water at 40-70 °C. Finally, a milky white solid is obtained, which is sulfonated modified starch; Step 3, add 0.1-2.0 parts of the sulfonated modified starch obtained in Step 2 to 20-30 parts of deionized water and stir to dissolve, add 0.01-0.04 parts of N,N-methylenebisacrylamide and 0.01-0.04 parts of azobisisobutyronitrile and continue to react. Slowly add 3-6 parts of acrylic acid and then continue to stir for 30-40 minutes. Add 0.01-0.04 parts of graphene, and the above solution is treated with nitrogen for 10 minutes to ensure an anaerobic state. Irradiate with ultraviolet light for 60 minutes to obtain a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel.

[0015] Preferably, the starch is corn starch.

[0016] Preferably, the purity of sodium periodate, sulfamic acid, N,N-methylenebisacrylamide, azobisisobutyronitrile, and acrylic acid is greater than 99%.

[0017] Preferably, the composite hydrogel glue can be used for sensors in flexible wearable electronic devices.

[0018] Example 1 Step 1: By mass, take 15 parts of corn starch, add 170 parts of deionized water and stir, then add 3.3 parts of sodium periodate, adjust its pH to 3.5 with 20% hydrochloric acid solution, react in the dark at 27°C for 7 hours, filter the obtained product, and wash it with 30 parts of deionized water and 40 parts of acetone. Dry the washed product in vacuo at 55°C for 5 hours to obtain dialdehyde corn starch; Step 2: Add 1 part of dialdehyde starch to a mixed solution of 35 parts of deionized water and 20 parts of ethanol, add 0.05 part of sulfamic acid at 25°C, and stir and react for 4 hours. Add 60 mL of ethanol to the product, and use a rotary evaporator to evaporate the water at 55°C. Finally, obtain a milky white solid, which is sulfonated modified starch; Step 3: Add 1.0 part of the sulfonated modified starch obtained in Step 2 to 20 parts of deionized water and stir to dissolve. Add 0.01 part of N,N-methylenebisacrylamide and 0.02 part of azobisisobutyronitrile and continue to react. Slowly add 4 parts of acrylic acid and then continue to stir for 30 minutes. Add 0.02 part of graphene, and subject the above solution to nitrogen treatment for 10 minutes to ensure an anaerobic state. Irradiate under ultraviolet light for 70 minutes to obtain a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel.

[0019] A sulfonated modified starch / polyacrylic acid / graphene composite hydrogel prepared by the above preparation method has remarkable application properties and characteristics, namely, electrical conduction and sensing ability. When the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is used to test an electrochemical workstation, its strain sensitivity (GF) is 2.

[0020] Example 2 Step 1: By mass, take 15 parts of corn starch, add 170 parts of deionized water and stir, then add 3.3 parts of sodium periodate, adjust its pH to 3.3 with 20% hydrochloric acid solution, react in the dark at 25°C for 5 hours, filter the obtained product, and wash it with 30 parts of deionized water and 45 parts of acetone. Dry the washed product in vacuo at 55°C for 5 hours to obtain dialdehyde corn starch; Step 2: Add 2 parts of dialdehyde starch into a mixed solution of 40 parts of deionized water and 20 parts of ethanol. Add 0.05 part of sulfamic acid at 25°C and stir for 4 hours. Add 60 mL of ethanol to the product, and use a rotary evaporator to evaporate the water at 45°C. Finally, a milky white solid is obtained, which is sulfonated modified starch. Step 3: Dissolve 0.2 part of the sulfonated modified starch obtained in Step 2 in 20 parts of deionized water by stirring. Add 0.01 part of N,N'-methylenebisacrylamide and 0.02 part of azobisisobutyronitrile and continue the reaction. Slowly add 4 parts of acrylic acid and then stir for 30 minutes. Add 0.02 part of graphene, and subject the above solution to nitrogen treatment for 10 minutes to ensure an anaerobic state. Irradiate under ultraviolet light for 60 minutes to obtain a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel.

[0021] A sulfonated modified starch / polyacrylic acid / graphene composite hydrogel prepared by the above preparation method has remarkable application performance and characteristics, namely, conductive sensing ability. When the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is used to test an electrochemical workstation, its gauge factor (GF) is 3.5.

[0022] Example 3 Step 1: By mass, take 20 parts of corn starch, add 170 parts of deionized water and stir, then add 4 parts of sodium periodate. Adjust its pH to 4 with 20% hydrochloric acid solution, and react in the dark at 25 - 30°C for 4 hours. Filter the obtained product and wash it with 30 parts of deionized water and 40 parts of acetone. Dry the washed product in vacuum at 55°C for 5 hours to obtain dialdehyde corn starch. Step 2: Add 2 parts of dialdehyde starch into a mixed solution of 30 parts of deionized water and 25 parts of ethanol. Add 0.05 part of sulfamic acid at 25°C and stir for 4 hours. Add 50 mL of ethanol to the product, and use a rotary evaporator to evaporate the water at 50°C. Finally, a milky white solid is obtained, which is sulfonated modified starch. Step 3: Dissolve 0.5 part of the sulfonated modified starch obtained in Step 2 in 20 parts of deionized water by stirring. Add 0.02 part of N,N'-methylenebisacrylamide and 0.01 part of azobisisobutyronitrile and continue the reaction. Slowly add 3 parts of acrylic acid and then stir for 30 minutes. Add 0.01 part of graphene, and subject the above solution to nitrogen treatment for 15 minutes to ensure an anaerobic state. Irradiate under ultraviolet light for 80 minutes to obtain a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel.

[0023] A sulfonated modified starch / polyacrylic acid / graphene composite hydrogel prepared by the above preparation method has remarkable application performance and characteristics, namely, conductive sensing ability. When the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is used to test an electrochemical workstation, its gauge factor (GF) is 3.

[0024] Example 4 Step 1: Take 20 parts by mass of corn starch, add 180 parts of deionized water and stir. Then add 6 parts of sodium periodate, adjust its pH to 4.5 with 20% hydrochloric acid solution, and react in the dark at 30 °C for 6 hours. The obtained product is subjected to suction filtration and washed with 40 parts of deionized water and 50 parts of acetone. The washed product is vacuum dried at 60 °C for 6 hours to obtain dialdehyde corn starch; Step 2: Add 3 parts of dialdehyde starch to a mixed solution of 40 parts of deionized water and 30 parts of ethanol, add 0.08 part of sulfamic acid at 30 °C, and stir and react for 4 hours. Add 70 mL of ethanol to the product, and use a rotary evaporator to evaporate the water at 70 °C. Finally, a milky white solid is obtained, which is sulfonated modified starch; Step 3: Add 0.8 part of the sulfonated modified starch obtained in Step 2 to 30 parts of deionized water and stir to dissolve. Add 0.04 part of N,N-methylenebisacrylamide and 0.02 part of azobisisobutyronitrile and continue to react. Slowly add 6 parts of acrylic acid and then continue to stir for 40 minutes. Add 0.04 part of graphene, and the above solution is treated with nitrogen for 15 minutes to ensure an anaerobic state. Irradiate under ultraviolet light for 120 minutes to obtain a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel.

[0025] A sulfonated modified starch / polyacrylic acid / graphene composite hydrogel prepared by the above preparation method has significant application performance and characteristics, namely, conductive sensing ability. When the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is used to test an electrochemical workstation, its strain sensitivity (GF) is 4.

[0026] Example 5 Step 1: Take 20 parts by mass of corn starch, add 180 parts of deionized water and stir. Then add 6 parts of sodium periodate, adjust its pH to 3.3 with 20% hydrochloric acid solution, and react in the dark at 25 °C for 5 hours. The obtained product is subjected to suction filtration and washed with 30 parts of deionized water and 40 parts of acetone. The washed product is vacuum dried at 60 °C for 5 hours to obtain dialdehyde corn starch; Step 2: Add 1 part of dialdehyde starch to a mixed solution of 30 parts of deionized water and 20 parts of ethanol, add 0.08 part of sulfamic acid at 25 °C, and stir and react for 5 hours. Add 60 mL of ethanol to the product, and use a rotary evaporator to evaporate the water at 50 °C. Finally, a milky white solid is obtained, which is sulfonated modified starch; Step 3: Add 1.0 part of the sulfonated modified starch obtained in Step 2 to 30 parts of deionized water and stir to dissolve. Then add 0.02 part of N,N-methylenebisacrylamide and 0.04 part of azobisisobutyronitrile and continue the reaction. Slowly add 6 parts of acrylic acid and then continue stirring for 30 minutes. Add 0.02 part of graphene, and subject the above solution to nitrogen treatment for 15 minutes to ensure an anaerobic state. Irradiate under ultraviolet light for 120 minutes to obtain a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel.

[0027] A sulfonated modified starch / polyacrylic acid / graphene composite hydrogel prepared by the above preparation method has remarkable application performance and characteristics, namely, its conductive sensing ability. When the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is used to test an electrochemical workstation, its strain sensitivity (GF) is 4.5.

[0028] Control Example By mass, add 0.2 part of starch to 10 parts of distilled water, stir until clear, then add 0.04 part of N,N-methylenebisacrylamide and 0.08 part of azobisisobutyronitrile and continue the reaction. Slowly add 3 parts of acrylic acid and then continue stirring for 30 minutes. Irradiate under ultraviolet light for 30 minutes to obtain a starch hydrogel.

[0029] This control example did not perform sulfonation modification and graphene composite, but only used ordinary starch to prepare the hydrogel. When the starch hydrogel is used to test an electrochemical workstation, its strain sensitivity (GF) is 0.5, which is significantly lower than that of the examples of the present invention.

[0030] The comparison of the hydrogel strain sensitivity (GF) results of the above examples and the control example is shown in Table 1.

[0031] Table 1. Comparison of hydrogel strain sensitivity (GF) results The strain sensitivity (GF) of the sulfonated modified starch / polyacrylic acid / graphene composite hydrogels in Examples 1 to 5 is 2 to 4.5, the tensile strength is 0.03 to 0.06 MPa, the swelling ratio is 77.8% to 79.1%, and the response time is 210 to 230 ms. The strain sensitivity (GF) of the control example is 0.5, the tensile strength is 0.01 MPa, the swelling ratio is 83.5%, and there is no response time. This shows that the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel of the present invention has excellent strain sensitivity and mechanical properties and can be used as a strain sensor in motion and health detection instruments.

[0032] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel, characterized in that, It includes the following steps: Step 1: By mass fraction (the same hereinafter), take 15 - 20 parts of starch, add 160 - 180 parts of deionized water and stir, then add 3 - 6 parts of sodium periodate, adjust its pH to 3.3 - 4.5 with 20% hydrochloric acid solution, react in the dark at 25 - 30 °C for 4 - 6 hours. The obtained product is filtered by suction and washed with 30 - 40 parts of deionized water and 40 - 50 parts of acetone. The washed product is dried in vacuum at 55 - 60 °C for 4 - 8 hours to obtain dialdehyde starch. Step 2: Take 1 - 3 parts of the dialdehyde starch prepared in Step 1 and add it to a mixed solution of 30 - 40 parts of deionized water and 20 - 30 parts of ethanol. Add 0.01 - 0.2 parts of amidosulfonic acid at 25 - 30 °C and stir for 3 - 5 hours. Add 50 - 70 mL of ethanol to the product, and use a rotary evaporator to evaporate the water at 40 - 70 °C. Finally, a milky white solid is obtained, which is sulfonated modified starch. Step 3: Add 0.1 - 2.0 parts of the sulfonated modified starch obtained in Step 2 to 20 - 30 parts of deionized water and stir to dissolve. Add 0.01 - 0.04 parts of N,N - methylenebisacrylamide and 0.01 - 0.04 parts of azobisisobutyronitrile and continue the reaction. Slowly add 3 - 6 parts of acrylic acid and then continue to stir for 30 - 40 minutes. Add 0.01 - 0.04 parts of graphene. The above solution is treated with nitrogen for 10 - 15 minutes to ensure an anaerobic state. Irradiate under ultraviolet light for 60 - 120 minutes to obtain a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel.

2. The preparation method of a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel according to claim 1, wherein, The starch used in Step 1 is corn starch.

3. The preparation method of a sulfonated modified starch / polyacrylic acid / graphene composite hydrogel according to claim 2, characterized in that, The purity of the sodium periodate, amidosulfonic acid, N,N - methylenebisacrylamide, azobisisobutyronitrile, and acrylic acid is greater than 99%.

4. A sulfonated modified starch / polyacrylic acid / graphene composite hydrogel prepared by the preparation method as described in claims 1 - 3.

5. The sulfonated modified starch / polyacrylic acid / graphene composite hydrogel according to claim 4, wherein The structural formula of the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel is as follows: 。 6. The application of the sulfonated modified starch / polyacrylic acid / graphene composite hydrogel prepared by the preparation method as described in claim 1, characterized in that the composite hydrogel is used in a sensor for a flexible wearable electronic device.

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