CN110372886B

CN110372886B - Chitosan/polysulfonyl betaine double-network self-healing hydrogel and preparation method thereof

Info

Publication number: CN110372886B
Application number: CN201910576595.8A
Authority: CN
Inventors: 张静; 冯杰; 沈彪
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Zhejiang University of Technology ZJUT
Priority date: 2019-06-28
Filing date: 2019-06-28
Publication date: 2021-12-17
Anticipated expiration: 2039-06-28
Also published as: CN110372886A

Abstract

A chitosan/polysulfonyl betaine double-network self-healing hydrogel and a preparation method thereof relate to the field of hydrogels, the hydrogel is of a double-network structure and is formed by mutually penetrating a first network and a second network, the first network is a physical cross-linked network formed by chitosan and multi-valence negative ions through coordination, the second network is a polysulfonyl betaine physical cross-linked network, and the first network is inserted into the second network; according to the invention, chitosan and multi-valence negative ions are selected to form a first network, polysulfonyl betaine is selected as a second network, micelles are used as physical cross-linking points of the second network of the polysulfonyl betaine to cross-link the second network, so that the first network and the second network are mutually interpenetrated, and the hydrogel is endowed with a double-network structure, so that the hydrogel has excellent mechanical properties and self-healing capability, and has the advantages of large resistance change rate under strain, high sensitivity, wider test range as a strain sensor, and wide application prospect.

Description

Chitosan/polysulfonyl betaine double-network self-healing hydrogel and preparation method thereof

Technical Field

The invention relates to the field of hydrogel, in particular to chitosan/polysulfonyl betaine double-network self-healing hydrogel and a preparation method thereof.

Background

In the last few years, a large number of advanced intelligent electronic devices have been developed, such as electronic skins, nano-robots, actuator elements based on flexible materials, stretchable sensors. In practical applications, the electronic devices are required to withstand mechanical deformation such as bending, folding, twisting and stretching, which puts higher demands on the stability and durability of the materials. A strain gauge is a sensor that converts mechanical deformation of an object into an output signal according to changes in resistance and capacitance, and a resistance strain gauge is the most common sensing element and converts mechanical deformation into resistance change. These sensors can conform to complex surfaces and are therefore widely used in monitoring human/machine activity, human health, the environment, etc. Conventional resistive strain gages tend to be composed of metal models and semiconductor piezoresistors, and despite their low production cost, there are limitations in the brittle fracture, rigidity of the metal, and durability and stretchability of the semiconductor material. Therefore, the hydrogel material which is conductive, good in fatigue resistance and good in mechanical property and self-healing property is prepared by a simple and convenient method, and has great research significance.

The hydrogel is a high polymer material with a 3D network structure and adjustable physical and chemical properties. Hydrogels can store a large amount of water between networks by crosslinking hydrophilic polymer chains, and by virtue of their excellent water retention and network structure similar to human tissues, hydrogels have become a research focus in recent years. With the intensive research on hydrogels, self-healing hydrogels have attracted much attention. The self-healing hydrogel can pass through a self-healing mechanism after being damaged externally so as to keep the integrity of a network structure and the mechanical property of the hydrogel and ensure that the self-healing hydrogel can be stably used for a long time. Self-healing hydrogels are mostly achieved by means of the reconstruction of physical cross-linking points through reversible interactions between polymer backbones, such as hydrogen bonds, hydrophilic-hydrophobic interactions, ionic coupling interactions, and the like. However, in many cases, the self-healing properties of physical crosslinking and higher mechanical properties cannot be achieved simultaneously, since the self-healing capacity of hydrogels needs to be satisfied: three conditions of reversible fragmentation, dynamic non-covalent interaction and mobile polymer chains, high mechanical strength requires strong and stable chemical crosslinking or covalent crosslinking, which limits the movement of the polymer chains and reduces the self-healing ability of the polymer chains, for example, a method for rapidly preparing carboxymethyl cellulose-based luminescent self-healing hydrogel disclosed in Chinese patent document No. CN105504312B, which synthesizes citric acid (PCAD) compounds having blue-green fluorescence by solid phase reaction, and then Al is added³⁺The aqueous solution of the cross-linking agent is dripped into the transparent carboxymethyl cellulose solution to synthesize the self-healing material with excellent self-healing propertyCan be made into hydrogel, but has a breaking strength of only 13 kPa at most.

Disclosure of Invention

The invention provides a chitosan/polysulfonyl betaine double-network self-healing hydrogel and a preparation method thereof, aiming at solving the problems that the existing physically crosslinked hydrogel cannot obtain good self-healing performance and high mechanical performance at the same time and the like.

The main objects of the present invention include: 1. preparing the double-network hydrogel with good self-healing performance and excellent mechanical performance; 2. the hydrogel has a larger resistance change rate under strain, and the sensitivity is improved; 3. the preparation process is simplified, and the preparation method is simple, efficient and environment-friendly.

In order to achieve the purpose, the invention adopts the following technical scheme:

the utility model provides a chitosan/polysulfonate betaine dual-network self-healing hydrogel, the aquogel is dual-network structure, and it is run through each other by first network and second network and forms, first network is the physics crosslinked network that is formed through coordination by chitosan and polyvalent anion, the second network is by the micelle that surfactant agent and hydrophobic alkyl ester formed as the physics crosslink point, and the polysulfonate betaine physics crosslinked network that forms with sulfonic acid betaine methyl methacrylate copolymerization, first network alternates in the second network.

In the invention, the first network is a physical cross-linked network formed by chitosan and multi-valence negative ions through coordination, wherein N-glucose-amine units on chitosan molecules can generate chelation with the multi-valence negative ions, so that the multi-valence negative ions can be simultaneously combined with a plurality of N-glucose-amine units through coordination, thereby forming the physical cross-linked network, and after the breakage, ion cross-linking points on the first network can also form coordination and complexation again, thereby having good self-healing effect.

The second network of the invention is a polysulfonate betaine physical crosslinking network formed by the copolymerization of micelles formed by a surfactant and hydrophobic alkyl ester and sulfobetaine methyl methacrylate as physical crosslinking points, firstly, the surfactant is dispersed in water to form micelles, and hydrophobic chain segments in the hydrophobic alkyl ester are inserted into micelles, wherein the chain segments with double bonds face outwards, and are copolymerized with the sulfobetaine methyl methacrylate to form the polysulfonate betaine physical crosslinking network under the action of an initiator and ultraviolet light, therefore, the self-healing can be realized by reconstructing the physical crosslinking points through reversible hydrophilic-hydrophobic interaction force, when the hydrogel is subjected to external force, the micelles formed by the surfactant and the hydrophobic alkyl ester are damaged, at the moment, the physical crosslinking points are damaged, but the hydrogel can be rapidly self-assembled to form micelles again, the mechanical property is basically recovered, and the self-healing effect is achieved.

According to the invention, a first network formed by chitosan and multi-valence negative ions and a physical crosslinking network of polysulfonate betaine are mutually interpenetrated and wound to form a double-network hydrogel, wherein the first network is rigid and fragile, and the first network is rapidly subjected to crosslinking point damage when the hydrogel is impacted, so that energy is dispersed, and the second network which is soft and good in deformability provides ductility of the hydrogel to prevent aggregation and enlargement of micro-crack damage, so that the hydrogel has excellent mechanical properties.

In addition, multiple polyelectrolytes exist in the hydrogel, and multi-valence negative ions are used as charge carriers and migrate in a high molecular medium by virtue of the chain motion of the polyelectrolytes to realize electric conduction. Besides the resistance change caused by the size change of the hydrogel under different strains, the pore size of the hydrogel network is reduced due to stretching of the hydrogel network, the ion transfer is blocked, the resistance is further changed, and the resistance change rate of the hydrogel under the strains is larger.

A preparation method of chitosan/polysulfonyl betaine double-network self-healing hydrogel comprises the following preparation steps:

1) preparing a mixed solution of chitosan, sulfobetaine methyl methacrylate, a surfactant, hydrophobic alkyl ester and an initiator;

2) deoxidizing the mixed solution, and removing bubbles in the mixed solution to obtain a pre-polymerization solution;

3) injecting the pre-polymerization solution into a light-transmitting mold, irradiating the pre-polymerization solution by ultraviolet light for reaction, and obtaining pre-gel after the reaction is finished;

4) and (3) soaking the pre-gel in a multivalent anion solution to obtain the chitosan/polysulfonyl betaine double-network self-healing hydrogel.

Compared with the traditional preparation method, the preparation method is simpler, more efficient and more environment-friendly, and can not cause waste of raw materials.

Preferably, the concentration of the chitosan is 0.015-0.07 g/mL; the concentration of the sulfobetaine methyl methacrylate is 1.5-3 mol/L; the amount of the initiator is 1 to 4mol percent of the sulfobetaine methyl methacrylate; the dosage of the surfactant is 4-10 wt%; the dosage of the hydrophobic alkyl ester is 3-6 mol% of the sulfobetaine methyl methacrylate; the solvent includes water.

In the preparation process, the proportion of raw materials is strictly controlled, and the self-healing performance is reduced due to the over-high or over-low dosage of the chitosan, the sulfobetaine methyl methacrylate and the hydrophobic alkyl ester.

Preferably, the surfactant is a cationic surfactant, including cetyltrimethylammonium chloride; the hydrophobic alkyl ester comprises octadecyl methacrylate; the initiator comprises alpha-ketoglutaric acid.

Since the chitosan surface in the first network is positively charged in the present invention, the present invention requires the use of a surfactant with a positively charged surface, such as cetyltrimethylammonium chloride; if the surfactant with the negatively charged surface is selected, the positive and negative charges can generate electrostatic action to cause the chitosan network to be crosslinked in advance, so that the surfactant cannot form micelles and cannot serve as physical crosslinking points of a second network, the double-network structure is seriously influenced, and the subsequent ionic crosslinking of the chitosan is influenced, so that the mechanical property and the self-healing property of the hydrogel are also influenced.

Preferably, the chitosan has a molecular weight of less than 10000 Da; the deacetylation degree of the chitosan is more than or equal to 90%.

In the invention, the chitosan with small molecular weight has better solubility, and the chitosan has high deacetylation degree, more amino groups on the molecular chain and stronger coordination with multi-valence negative ions.

Preferably, the oxygen removal is performed by introducing nitrogen or inert gas to reduce oxygen solubility; the method for removing the bubbles in the mixed solution is ultrasonic.

The mode that adopts nitrogen gas and inert gas to let in and reduce oxygen solubility is safe, environmental protection, and can not cause any harmful effects to the mixed solution, and the bubble in the mixed solution can high-efficiently be got rid of to the supersound.

Preferably, in step 3): the light-transmitting mold comprises a silicon rubber sheet glass mold with pores, and the thickness of the silicon rubber sheet is less than or equal to 2 mm; the ultraviolet light with the wavelength of 340-400nm is selected during the ultraviolet light irradiation reaction; the reaction time of the ultraviolet irradiation is 4-10 h.

Under the irradiation of ultraviolet light within the wavelength range of 340-400nm, the zwitterionic monomer sulfobetaine methyl methacrylate has enough energy to initiate the reaction, and the wavelength of the ultraviolet light is preferably 365 nm.

Preferably, in step 4): the multi-valence state negative ion solution comprises multi-valence state acid radical ions; the multivalent acid radical ions comprise citrate radical ions and sulfate radical ions, and the soaking time is 1-24 h.

Therefore, the invention has the following beneficial effects: (1) the preparation method is simple, efficient and environment-friendly; (2) according to the invention, chitosan and multi-valence negative ions are selected to form a first network, polysulfonyl betaine is selected as a second network, micelles are used as physical cross-linking points of the second network of the polysulfonyl betaine to cross-link the second network, so that the first network and the second network are mutually interpenetrated, and the hydrogel is endowed with a double-network structure, so that the hydrogel has excellent mechanical properties and self-healing capability, and has the advantages of large resistance change rate under strain, high sensitivity, wider test range as a strain sensor, and wide application prospect.

Drawings

FIG. 1 is a stress-strain curve diagram of a two-network hydrogel prepared in examples 1-2 of the present invention.

FIG. 2 shows the recovery rate of the performance of the double-network hydrogel prepared in examples 1-2 of the present invention after standing at room temperature for 24 h.

FIG. 3 shows the recovery rate of the performance of the double-network hydrogel prepared in example 2 of the present invention after standing at 40 ℃.

FIG. 4 shows the recovery rate of the performance of the double-network hydrogel prepared in example 2 of the present invention after standing at 60 ℃.

FIG. 5 shows the recovery rate of the performance of the double-network hydrogel prepared in example 2 of the present invention after standing at 100 ℃.

FIG. 6 is a graph of the strain-resistance change rate of the double-network hydrogel prepared in example 2 of the present invention.

FIG. 7 is a resistance change rate curve of the double-network hydrogel prepared in example 2 of the present invention under different bending angles of a simulated joint.

Detailed Description

The invention is further described with reference to specific embodiments.

Examples 1 to 7:

1) preparing a mixed solution of chitosan (the molecular weight is less than 10000Da), sulfobetaine methyl methacrylate, hexadecyl trimethyl ammonium chloride, octadecyl methacrylate and an initiator alpha-ketoglutaric acid;

2) deoxidizing the mixed solution, and ultrasonically removing bubbles in the mixed solution to obtain a pre-polymerization solution;

Wherein, the deacetylation degree of the chitosan in the embodiment 1-5 is 95%, nitrogen is introduced during oxygen removal, and the multivalent anion solution is a saturated sodium citrate solution; the deacetylation degree of chitosan described in examples 6-7 was 90%, argon gas was introduced during oxygen removal, and the multivalent anion solution was a saturated sodium sulfate solution. Also, the respective mass formulations in examples 1-7, step 1) are shown in table 1, where α -ketoglutaric acid and stearyl methacrylate are used in relative mole percent (mol%) with respect to the sulfobetaine methyl methacrylate and cetyltrimethylammonium chloride is used in mass percent (wt%) with respect to the total mass.

Table 1: examples 1-7, step 1) the ratios of the substances.

Specific preparation parameters in examples 1-7, step 3), step 4) are shown in table 2.

Table 2: examples 1-7, step 3), step 4) specific preparation parameters.

Comparative examples 1 to 6: the difference from example 2 is that the respective mass ratios of step 1) in comparative examples 1 to 6 are shown in Table 3.

Table 3: the material ratios of the step 1) in the comparative examples 1 to 6.

After the preparation, the performance of the hydrogels prepared in the examples and comparative examples was tested, and the performance test included the following aspects: and (3) testing mechanical properties: a hydrogel sample strip with the length of 40mm and the width of 10mm is prepared by a glass mold with the thickness of 1mm, and a double-network hydrogel sample strip with the gauge length of 16mm, the width of 4mm and the thickness of 1mm is prepared by a dumbbell-shaped cutter. 3 sample bars are taken to carry out a mechanical tensile test on an Instron 5966 universal material testing machine, the tensile speed is 100mm/min, and the mechanical properties are measured.

Testing self-healing performance: and cutting the soaked double-network hydrogel from the middle, then naturally lapping the hydrogel together, and self-healing the hydrogel for a corresponding time under a certain condition. And then, testing the mechanical properties of the self-healing hydrogel by using a universal material testing machine. Setting parameters and testing the tensile mechanical property. Wherein the performance recovery rate is the ratio of the tensile strength of the double-network hydrogel after self-healing to the tensile strength of the initial hydrogel.

And (3) resistance change test: and measuring the resistance of the hydrogel soaked in the salt solution by using an interactive digital instrument. The samples tested were dumbbell-shaped bars of 16mm by 4mm by 2 mm. Under the voltage of 1V, two poles of a power supply are connected to two ends of the hydrogel sample strip, the hydrogel is stretched to different strains, and the resistance of the hydrogel in different strains can be automatically recorded by an instrument, so that a resistance-strain curve graph is obtained. Wherein the relative resistance change of the double-network hydrogel with certain strain is obtained by the following formula, wherein R₀R 'is the initial resistance, R' is the resistance under certain strain, and Δ R is the difference between the resistance under certain strain and the initial resistance.

The stress-strain curves of the double-network hydrogels prepared in examples 1 and 2 are shown in fig. 1, and the hydrogels prepared in soaking times of 1, 2, 4, 8, 12 and 24h respectively correspond to A, B, C, D, E, F curves in the graph, and it can be seen that the tensile strength of the hydrogel increases and then decreases with the increase of the soaking time, the tensile strength of the hydrogel prepared in soaking time of 8h is the maximum and reaches 0.08MPa, and the elongation at break reaches 2800%.

The performance recovery rate of the double-network hydrogel prepared in the example 1-2 after standing at room temperature for 24 hours is shown in fig. 2, and it can be seen in the figure that the double-network hydrogel has excellent self-healing performance, the performance recovery rate of the double-network hydrogel increases and then decreases with the increase of the soaking time, and the performance recovery rate of the double-network hydrogel prepared when the soaking time is 2 hours is the highest and is 91.1%.

Fig. 3 and 4 show the performance recovery rates of example 2 after standing for 2, 4 and 8 hours at 40 ℃ and 60 ℃, respectively, and fig. 5 shows the performance recovery rates of example 2 after standing for 0.5, 1, 1.5 and 2 hours at 100 ℃, which shows that the performance recovery rates are obviously increased and the self-healing performance is better along with the extension of the standing time at the same standing temperature, the performance recovery rate reaches 78% after standing for 8 hours at 40 ℃, and the performance recovery rate reaches 87% after standing for 8 hours at 60 ℃; the performance recovery rate reaches 89% after standing for 2 hours at 100 ℃.

The strain-resistance change rate curve of the double-network hydrogel prepared in example 2 is shown in fig. 6, which shows that the resistance change rate of the double-network hydrogel at 50% strain is greater than 80%, and the resistance change rate at 25% strain reaches 30%.

The resistance change rate curve of the double-network hydrogel prepared in example 2 at different bending angles of the simulated joint is shown in fig. 7, and it can be seen that the resistance change rate is obviously improved as the bending angle of the joint is increased, the resistance change rate is about 40% when the bending angle is 90 degrees, and the resistance change rate is more than 50% when the bending angle is 135 degrees.

The self-healing effect of the double-network hydrogel prepared in example 2 and the comparative example is shown in table 4.

Table 4: the self-healing effect of the double-network hydrogel prepared in example 2 and the comparative example is good.

	Self-healing effect
		Example 2	Is excellent in
Comparative example 1	Is poor
		Comparative example 2	Can not self-heal
Comparative example 3	Is poor
		Comparative example 4	Can not self-heal
Comparative example 5	Can not self-heal
		Comparative example 6	Is poor

It can be seen from the comparison of example 2 with the comparative example that too high or too low amounts of chitosan, sulfobetaine methyl methacrylate and hydrophobic alkyl ester lead to a decrease in the self-healing performance.

The large number of detection results show that the double-network hydrogel prepared by the technical scheme of the invention has excellent mechanical property and self-healing property, has higher relative resistance change rate and high sensitivity when being deformed, and has high application value in the fields of flexible electronic equipment, strain sensors and the like.

Claims

1. The chitosan/polysulfonyl betaine double-network self-healing hydrogel is characterized in that the hydrogel is of a double-network structure and is formed by mutually penetrating a first network and a second network, the first network is a physical cross-linked network formed by chitosan and multi-valence negative ions through coordination, and the multi-valence negative ions comprise citrate ions and sulfate ions; the second network is a polysulfonate betaine physical crosslinking network formed by copolymerizing micelles formed by a surfactant and hydrophobic alkyl ester and sulfobetaine methyl methacrylate as physical crosslinking points, and the surfactant is a cationic surfactant; the first network is inserted in the second network; in the preparation process of the hydrogel, chitosan, sulfobetaine methyl methacrylate, a surfactant, hydrophobic alkyl ester and an initiator are prepared into a mixed solution and then are crosslinked, wherein in the mixed solution, the concentration of the chitosan is 0.015-0.07g/mL, the concentration of the sulfobetaine methyl methacrylate is 1.5-3mol/L, and the dosage of the hydrophobic alkyl ester is 3-6 mol% of the sulfobetaine methyl methacrylate.

2. A method for preparing the chitosan/polysulfonyl betaine double-network self-healing hydrogel according to claim 1, wherein the method comprises the following steps:

1) preparing a mixed solution of chitosan, sulfobetaine methyl methacrylate, a surfactant, hydrophobic alkyl ester and an initiator; the surfactant is a cationic surfactant; in the mixed solution, the concentration of chitosan is 0.015-0.07g/mL, the concentration of sulfobetaine methyl methacrylate is 1.5-3mol/L, and the dosage of hydrophobic alkyl ester is 3-6 mol% of the sulfobetaine methyl methacrylate;

4) and (3) soaking the pre-gel in a multivalent anion solution, wherein the multivalent anion solution comprises multivalent acid radical ions, and the multivalent acid radical ions comprise citrate ions and sulfate ions, so that the chitosan/polysulfonyl betaine double-network self-healing hydrogel is obtained.

3. The method for preparing the chitosan/polysulfonyl betaine double-network self-healing hydrogel according to claim 2, wherein the step 1) comprises the following steps: the amount of the initiator is 1 to 4mol percent of the sulfobetaine methyl methacrylate; the dosage of the surfactant is 4-10 wt%; the solvent of the mixed solution includes water.

4. The method for preparing the chitosan/polysulfonyl betaine double-network self-healing hydrogel according to claim 2 or 3, wherein in step 1): the surfactant comprises cetyl trimethyl ammonium chloride; the hydrophobic alkyl ester comprises octadecyl methacrylate; the initiator comprises alpha-ketoglutaric acid.

5. The method for preparing the chitosan/polysulfonyl betaine double-network self-healing hydrogel according to claim 2, wherein in step 1): the molecular weight of the chitosan is less than 10000 Da; the deacetylation degree of the chitosan is more than or equal to 90%.

6. The method for preparing the chitosan/polysulfonyl betaine double-network self-healing hydrogel according to claim 2, wherein in step 2): the oxygen removal is carried out in a mode of introducing nitrogen or inert gas to reduce the oxygen solubility; the method for removing the bubbles in the mixed solution is ultrasonic.

7. The method for preparing the chitosan/polysulfonyl betaine double-network self-healing hydrogel according to claim 2, wherein in step 3): the light-transmitting mold comprises a silicon rubber sheet glass mold with pores, and the thickness of the silicon rubber sheet is less than or equal to 2 mm; the ultraviolet light with the wavelength of 340-400nm is selected during the ultraviolet light irradiation reaction; the reaction time of the ultraviolet irradiation is 4-10 h.

8. The method for preparing the chitosan/polysulfonyl betaine double-network self-healing hydrogel according to claim 2, wherein in step 4): the soaking time of the pre-gel in the multi-valence state anion solution is 1-24 h.