Performance-adjustable aramid nanofiber reinforced polyvinyl alcohol hydrogel and preparation method thereof

Abstract

The invention discloses a performance-adjustable aramid nanofiber reinforced polyvinyl alcohol hydrogel and a preparation method thereof, and the preparation method comprises the following steps: S1, through a high-speed shearing sequential control method, realizing the conversion of aramid fibers from a micron level to a nano level; s2, dissolving and dispersing aramid fibers by using a mixed acid system to obtain an ANFs stock solution, dropwise adding deionized water into an ice bath, and centrifuging to obtain an ANFs aqueous dispersion system; s3, PVA, TA and ANFs are heated and stirred, and a uniform PVA / ANFs-TA mixed solution is obtained; the preparation method comprises the following steps: mixing a PVA solution with ANFs-TA, adding a borax solution into the mixed solution, heating, pouring into a mold to obtain PVA / ANFs-TA hydrogel, and adjusting the concentration of TA to obtain super-stretched hydrogel (TA 2%) and self-repairing hydrogel (TA 0.8%). The prepared self-repairing hydrogel solves the problems that a single hydrogel material is insufficient in mechanical strength and limited in self-repairing capacity; the super-stretching hydrogel can realize 50000% super-stretching rate and underwater long-term adhesion.

Description

TECHNICAL FIELD

[0001] The present application relates to an adjustable performance aramid nanofiber reinforced polyvinyl alcohol hydrogel and a preparation method thereof, and belongs to the technical field of hydrogel preparation. BACKGROUND

[0002] Aramid nanofiber is a nanometer scale fiber composed of aromatic polyamide molecules, with a diameter of 10-100 nm and an aspect ratio of about 3000. It has a large specific surface area, high surface energy, good dispersibility, high water retention rate, and excellent flame retardant performance. It can be efficiently compounded with a polymer matrix through physical / chemical / self-assembly, etc. It can also be prepared into aramid nanofiber-based materials with different properties and applications through different preparation methods and morphology control, solving the pain points in the production and application of traditional aramid fibers.

[0003] Polyvinyl alcohol (PVA) is a water-soluble polymer material with high transparency, adhesion and moisture resistance. Due to its unique physical and chemical properties, PVA is widely used in pharmaceutical, food, cosmetic and other fields, especially as a film-forming material, playing an important role in various fields such as medicine, food packaging, coatings and adhesives.

[0004] Tannic acid (TA) is a natural polyphenol antibacterial small molecule with antioxidant, antibacterial, anti-inflammatory and biodegradable effects. At the same time, a large number of phenolic groups can provide multiple interaction sites, including hydrogen bonds, ionic bonds, coordination bonds and hydrophobic interactions, which can be used as a hydrogel crosslinking agent.

[0005] Aramid nanofiber (anfs) currently has problems such as long preparation cycle and protonation when encountering water. Moreover, it does not have self-repairing effect, which affects the service life of actual application. In view of the above problems, the present application aims to realize the preparation of hydrogels with different properties by adjusting the concentration of TA. By adjusting the concentration of TA, super-stretching hydrogel (TA 2%) and self-repairing hydrogel (TA 0.8%) can be obtained. SUMMARY

[0006] In view of the deficiencies of the prior art, the first purpose of the present application is to provide a preparation method of an adjustable performance aramid nanofiber reinforced polyvinyl alcohol hydrogel, comprising the following steps: S1: aramid pretreatment By using the high-speed shearing time control method, the gradient transformation of aramid fibers from micron to nanometer is realized within 25 min, and aramid nanofibers are obtained; By high-speed shearing time control method (mechanical crushing → structure dissociation → chemical recombination → size convergence), the homogenization process of reducing the diameter from 12 μm to 400-600 nm is completed within 25 min, and the gradient conversion problem of aramid fiber from micron to nanometer is solved. This aims to provide a fast and repeatable preparation scheme of aramid nanofiber (ANFs) to overcome the defects of low efficiency and uneven size of traditional methods, and to provide high specific surface area for subsequent nanocomposites.

[0007] S2: Preparation of ANFs aqueous dispersion system The aramid nanofiber is dissolved and dispersed by a mixed acid system, stirred for 20 h, and then diluted with deionized water in an ice bath, and then centrifuged to obtain an ANFs aqueous dispersion system; By a mixed acid (sulfuric acid / nitric acid) dissolution and ice bath dilution process combined with centrifugation technology, a uniform ANFs aqueous dispersion is obtained. The problem of stable dispersion of aramid nanofiber in water phase is solved, and at the same time, the process is optimized by SEM, TEM, FT-IR and XRD characterization means to ensure the controllability of the structure, morphology and size (such as nanometer network structure) of ANFs, so as to improve its compatibility and reinforcing effect in composite materials.

[0008] S3: Preparation of PVA / ANFs-TA hydrogel PVA, TA and ANFs are heated and stirred at 90°C for 6h to obtain a uniform PVA / ANFs-TA mixed solution; then borax solution is added to the PVA / ANFs-TA mixed solution, heated and stirred at 90°C for 2h, and then poured into a mold to obtain a PVA / ANFs-TA hydrogel.

[0009] Preferably, the mixed acid system in step S2 is sulfuric acid and nitric acid with a volume ratio of 3:1.

[0010] Preferably, the mass ratio of borax to PVA / ANFs-TA mixed solution in step S3 is 1:1, and the mass concentration of the borax solution is 1%.

[0011] Preferably, in the PVA / ANFs-TA mixed solution in step S3, the mass concentration of PVA is 20%, the mass concentration of TA is 2%, and the mass concentration of ANFs is 0.26%, to obtain an aramid nanofiber-based super-stretching hydrogel.

[0012] By using the above technical solution, a two-step method is used to quickly develop an ANFs / PVA-TA-BS multi-network synergistic system, so that the super-stretching hydrogel realizes a super-stretching rate of 50000% and long-term underwater adhesion.

[0013] Preferably, in the PVA / ANFs-TA mixed solution in step S3, the mass concentration of PVA is 20%, the mass concentration of TA is 0.8%, and the mass concentration of ANFs is 0.26%, so that the obtained PVA / ANFs-TA hydrogel is a self-repairing hydrogel.

[0014] Preferably, the method further comprises: S4: Preparation of PVA / AgNWs conductive layer hydrogel S41: PVA and TA with a mass ratio of 3:0.4 are heated and stirred at 90℃ for 6h to obtain a uniform PVA-TA mixed solution; S42: 0.28g of AgNWs is mixed with 6 wt% of the PVA-TA aqueous solution to obtain a conductive PVA-TA / AgNWs hydrogel dispersion, and the PVA concentration in the dispersion is 6 wt%.

[0015] Preferably, in step S42, AgNWs is replaced by Mxene, LM or a mixture of the two.

[0016] Preferably, in step S5, the repeated freeze-thawing is specifically as follows: the mold containing the conductive PVA-TA / AgNWs and PVA / ANFs-TA base layer hydrogel is placed in a-20℃ refrigerator for freezing for 12h, and then thawed at room temperature for 12h, and the freeze-thawing cycle is repeated for 3 times.

[0017] By adopting the technical scheme, through designing the double-layer structure of the PVA / ANFs-TA base layer and the PVA-TA / AgNWs conductive layer, the problems of insufficient mechanical strength and limited self-repairing capability of a single hydrogel material are solved.

[0018] (1) Base layer preparation: PVA, tannic acid (TA), ANFs and borax (BS) are combined to realize self-repairing through hydrogen bonds and dynamic borate ester bonds (physical cross-linking is strengthened through freeze-thawing cycles).

[0019] (2) Conductive layer preparation: silver nanowires (AgNWs) are integrated to provide conductivity, and volume control is used to ensure the uniform thickness between layers. This aims to realize the synergy of high mechanical strength (enhanced by ANFs), fast self-repairing (affected by TA and BS) and high conductivity (provided by AgNWs), so as to improve the durability and functionality of the hydrogel.

[0020] The second object of the present application provides an aramid nanofiber-based super-stretching hydrogel prepared by the above method.

[0021] The third object of the present application provides a self-repairing aramid nanofiber / polyvinyl alcohol multilayer hydrogel prepared by the above method.

[0022] The present application has the following beneficial effects: (1) The application enhances the mechanical properties of PVA, gives it self-repairing properties, adds a conductive layer, and makes it have good application in the field of flexible wearable devices.

[0023] (2) The application provides a rapid and repeatable preparation scheme for aramid nanofiber (ANFs) to overcome the defects of low efficiency and uneven size of traditional methods, and provides high specific surface area for subsequent nanocomposites.

[0024] (3) The application solves the problems of insufficient mechanical strength and limited self-repairing ability of single hydrogel material by designing a double-layer structure of PVA / ANFs-TA base layer and PVA / AgNWs conductive layer.

[0025] (4) The application uses a two-step method to quickly develop ANFs / PVA-TA-BS multi-network synergistic system, so that the super-stretching hydrogel realizes 50000% super-stretching rate and long-term underwater adhesion. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The application is an ANFs fiber diameter diagram.

[0027] Figure 2 The application is a mechanical property comparison diagram of the product before and after self-repairing of Example 1.

[0028] Figure 3 The application is the self-repairing process of the product prepared in Example 1.

[0029] Figure 4 The application is a self-repairing process diagram of the product prepared in Example 1.

[0030] Figure 5 The application is a diagram of the product prepared in Example 1 as a strain sensor to monitor human motion.

[0031] Figure 6 The application is an adhesion effect diagram of the product prepared in Example 2.

[0032] Figure 7 The application is an underwater adhesion diagram of the product prepared in Example 2.

[0033] Figure 8 The application is a super-stretching schematic diagram of the product prepared in Example 2. DETAILED DESCRIPTION

[0034] In order to make the technical means, creative features, purposes and effects of the application easy to understand, the application is further described below in combination with specific embodiments.

[0035] Example 1 A self-repairing aramid nanofiber / polyvinyl alcohol multilayer hydrogel, comprising the following steps: S1: Aramid fiber pretreatment Through high-speed shearing time control method, the gradient conversion of aramid fiber from micron level to nanometer level is realized within 25 min, for reference Figure 1 ; S2: Preparation of ANFs aqueous dispersion system The aramid fiber is dissolved and dispersed by a mixed acid system, stirred for 20 h, an ANFs stock solution is obtained, and then deionized water is gradually added dropwise in an ice bath for dilution, and then centrifuged to obtain an ANFs aqueous dispersion system. S3: Preparation of PVA / ANFs-TA hydrogel PVA, TA and ANFs are heated and stirred at 90°C for 6h to obtain a uniform PVA / ANFs-TA mixed solution; then borax solution is added to the PVA / ANFs-TA mixed solution, heated and stirred at 90°C for 2h, and then poured into a mold to obtain a PVA / ANFs-TA hydrogel.

[0036] S4: Preparation of PVA / AgNWs conductive layer hydrogel S41: PVA and TA with a mass ratio of 3:0.4 are heated and stirred at 90°C for 6h to obtain a uniform PVA-TA mixed solution. S42: 0.28g AgNWs and 6 wt% PVA-TA aqueous solution are mixed to obtain a conductive PVA-TA / AgNWs hydrogel dispersion, and the PVA concentration in the dispersion is 6 wt%.

[0037] S5: The conductive PVA-TA / AgNWs hydrogel dispersion obtained in step S4 is directly poured on the PVA / ANFs-TA base layer hydrogel, and repeated freezing and thawing to obtain a self-repairing aramid nanofiber / polyvinyl alcohol multilayer hydrogel.

[0038] S5: The conductive PVA-TA / AgNWs hydrogel obtained in step S4 is directly poured on the PVA / ANFs-TA base layer hydrogel, and repeated freezing and thawing to obtain a self-repairing aramid nanofiber / polyvinyl alcohol multilayer hydrogel.

[0039] In this embodiment, the mixed acid system in step S2 is sulfuric acid and nitric acid with a volume ratio of 3:1.

[0040] In this embodiment, the mass ratio of borax to PVA / ANFs-TA mixed solution in step S3 is 1:1, and the mass concentration of the borax solution is 1%.

[0041] In this embodiment, the mass concentration of PVA in the PVA / ANFs-TA mixed solution in step S3 is 20%, the mass concentration of TA is 0.8%, and the mass concentration of ANFs is 0.26%, and the obtained PVA / ANFs-TA hydrogel is a self-repairing hydrogel.

[0042] In this embodiment, the repeated freezing and thawing in step S5 is specifically as follows: the mold containing the conductive PVA-TA / AgNWs hydrogel and the PVA / ANFs-TA hydrogel is placed in a-20℃ refrigerator for freezing for 12h, and then thawed at room temperature for 12h, and the above freezing and thawing cycle is repeated for 3 times.

[0043] Embodiment 2 An aramid nanofiber-based super-stretching hydrogel, comprising the following steps: S1: Aramid pretreatment By high-speed shearing time control method, the gradient transformation of aramid fibers from micron level to nanometer level is realized within 25min; S2: Preparation of ANFs aqueous dispersion system The aramid fibers are dissolved and dispersed by a mixed acid system, stirred for 20h to obtain an ANFs stock solution, then gradually added with deionized water for dilution in an ice bath, and then centrifuged to obtain an ANFs aqueous dispersion system; S3: Preparation of PVA / ANFs-TA hydrogel PVA, TA and ANFs are heated and stirred at 90℃ for 6h to obtain a uniform PVA / ANFs-TA mixed solution; then a borax solution is added to the PVA / ANFs-TA mixed solution, heated and stirred at 90℃ for 2h, and then poured into a mold to obtain a PVA / ANFs-TA hydrogel.

[0044] In this embodiment, the mixed acid system in step S2 is sulfuric acid and nitric acid with a volume ratio of 3:1.

[0045] In this embodiment, the mass ratio of borax to PVA / ANFs-TA mixed solution in step S31 is 1:1, and the mass concentration of the borax solution is 1%.

[0046] In this embodiment, the mass concentration of PVA in the PVA / ANFs-TA mixed solution in step S31 is 20%, the mass concentration of TA is 2%, and the mass concentration of ANFs is 0.26%, and the obtained aramid nanofiber-based super-stretching hydrogel is obtained.

[0047] Embodiment 3 The difference from embodiment 1 is that AgNWs in step S42 is replaced by Mxene.

[0048] Embodiment 4 The difference from Example 1 is that the AgNWs in step S42 are replaced by LM.

[0049] Example 3 The difference from Example 1 is that the AgNWs in step S42 are replaced by Mxene and LM, with a mass ratio of 1:1.

[0050] Test Example 1 Test group: Example 1.

[0051] Test method: (1) Mechanical properties: an electronic universal material testing machine was used to evaluate the mechanical properties of the hydrogel.

[0052] (2) Self-healing: the hydrogel sample (20 mm × 10 mm × 5 mm) was subjected to tensile testing at a rate of 50 mm / min. Until the two pieces were broken, the self-healing was observed.

[0053] (3) Based on the performance of PVA / ANFS-TA composite multilayer hydrogel, it was used as a strain sensor to monitor human motion.

[0054] The specific method is: the electrical signal of the sample is recorded using an electrochemical workstation. At each end of the hydrogel, two conductive copper pieces connected by wires constitute a strain or pressure sensor unit. The gel unit is attached to the human finger, wrist, throat, neck and other parts, and the electrochemical workstation is used to monitor the real-time motion and physiological state of the human body in real time, and record the change of electrical signal.

[0055] The sensitivity (GF) of the hydrogel is calculated by the following formula: GF= ( ∆R / R0) / ε×100% Where: ΔR- change of hydrogel resistance after loading strain or pressure; R0- initial resistance of hydrogel; ε- strain.

[0056] Test results: Reference Figure 2 The mechanical properties of the hydrogel were tested. But after being pulled apart at room temperature, it quickly repaired itself. The PACLPM hydrogel still had a strength of 1.7 Mpa and a strain of 350% after repair, proving its good self-repairing property.

[0057] Reference Figure 3 Using a surgical blade to gently cut the hydrogel sample, no pressure is needed. The optical microscope photo records the process of physical contact self-healing of the cut hydrogel sample at room temperature.

[0058] Reference Figure 4The hydrogel sample was stretched until it broke into two pieces, and the cross-section was immediately connected. After 3 s at 25℃, the spliced sample could be repaired, stretched again without breaking, showing excellent tensile and self-repairing properties of the hydrogel.

[0059] As a flexible strain sensor, the hydrogel is suitable for real-time identification and monitoring of human motion. By combining the hydrogel with copper foil tape and assembling it on key parts of the human body such as the elbow and knee, it can effectively monitor and identify motion signals at different parts. As shown in FIG. 6, under different motion intensities, the peak value and frequency of the ΔR / R0 signal show significant differences, but the ΔR / R0 signal always has good repeatability and reversibility. Figure 5

[0060] Test Example 2 Test Group: Example 2.

[0061] Test Method: (1) Super-elongation: Take a super-elongated hydrogel with a diameter of 1 cm and a length of 1 cm, and stretch it to a length of 600 cm by pulling one end of each person.

[0062] (2) Underwater stability: Use the super-elongated hydrogel based on aramid nanofiber as an adhesive to coat between two pieces of cotton and glass, and after drying, it can be tightly adhered and soaked in water for 1 month.

[0063] Test Results: (1) Super-elongation: 60000% elongation, refer to Figure 8 .

[0064] (2) Underwater stability: The glass / cotton cloth adhesive body did not fall off after soaking in water for 1 month, and still maintained effective adhesion effect, refer to Figure 6 and Figure 7 .

[0065] Test Example 3 The product prepared in Example 2 was adhered to cotton, glass, and wood, respectively, and the adhesion was measured at 0 days, 7 days, 15 days, and 30 days, respectively. See Table 1 for details.

[0066] Table 1 Change of adhesion of product prepared in Example 2 with time

[0067] ​The foregoing merely illustrates the principles of the application and application of its leading features. This application is not limited to the exact details shown above and described herein, and obvious modifications will occur to those skilled in the art. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and without intent that the application be limited to the subjects shown or described, the scope of the application being indicated by the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.

[0068] Furthermore, it should be understood that although the description above is based on embodiments, not every embodiment contains only one independent technical solution, and the description above is only for the sake of clarity, and those skilled in the art should understand the description as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for preparing a aramid nanofiber-reinforced polyvinyl alcohol hydrogel with tunable properties, characterized in that, Includes the following steps: S1: Aramid pretreatment By using a high-speed shearing time-controlled method, the gradient transformation of aramid fibers from the micron to the nanometer scale was achieved within 25 minutes, resulting in aramid nanofibers. S2: Preparation of ANFs Aqueous Dispersion System Aramid nanofibers were dissolved and dispersed using a mixed acid system and stirred for 20 hours to obtain an ANF stock solution. Deionized water was gradually added dropwise in an ice bath to dilute the solution, and then centrifuged to obtain an ANF aqueous dispersion system. S3: Preparation of PVA / ANFs-TA hydrogel PVA, TA, and ANFs were heated and stirred at 90°C for 6 hours to obtain a homogeneous PVA / ANFs-TA mixed solution. Then, borax solution was added to the PVA / ANFs-TA mixed solution, and the mixture was heated and stirred at 90°C for 2 hours. Finally, the mixture was poured into a mold to obtain a PVA / ANFs-TA hydrogel.

2. The method for preparing a performance-tunable aramid nanofiber reinforced polyvinyl alcohol hydrogel as described in claim 1, characterized in that, The mixed acid system in step S2 is sulfuric acid and nitric acid in a volume ratio of 3:

1.

3. The method for preparing a performance-tunable aramid nanofiber reinforced polyvinyl alcohol hydrogel as described in claim 1, characterized in that, In step S3, the mass ratio of borax to PVA / ANFs-TA mixed solution is 1:1, and the mass concentration of the borax solution is 1%.

4. The method for preparing a performance-tunable aramid nanofiber reinforced polyvinyl alcohol hydrogel as described in claim 1, characterized in that, In step S3, the PVA / ANFs-TA mixed solution has a PVA mass concentration of 20%, a TA mass concentration of 2%, and an ANFs mass concentration of 0.26%, resulting in an ultra-stretched hydrogel based on aramid nanofibers.

5. The method for preparing a performance-tunable aramid nanofiber reinforced polyvinyl alcohol hydrogel as described in claim 1, characterized in that, In step S31, the PVA / ANFs-TA mixed solution has a PVA mass concentration of 20%, a TA mass concentration of 0.8%, and an ANFs mass concentration of 0.26%, resulting in a self-healing PVA / ANFs-TA hydrogel.

6. The method for preparing a performance-tunable aramid nanofiber reinforced polyvinyl alcohol hydrogel as described in claim 5, characterized in that, Also includes: S4: Preparation of PVA / AgNWs conductive layer hydrogel; S41: PVA and TA in a mass ratio of 3:0.4 are heated at 90℃ and stirred for 6 hours to obtain a homogeneous PVA-TA mixed solution; S42: Mix 0.28g AgNWs and 6 wt% PVA-TA aqueous solution to obtain a conductive PVA-TA / AgNWs hydrogel dispersion with a PVA concentration of 6 wt%. S5: The conductive PVA-TA / AgNWs hydrogel dispersion obtained in step S4 is directly poured onto the PVA / ANFs-TA base hydrogel, and the mixture is repeatedly frozen and thawed to obtain a self-healing aramid nanofiber / polyvinyl alcohol multilayer hydrogel.

7. The method for preparing a performance-tunable aramid nanofiber reinforced polyvinyl alcohol hydrogel as described in claim 6, characterized in that, In step S42, AgNWs is replaced with Mxene, LM, or a combination of both.

8. The method for preparing a performance-tunable aramid nanofiber reinforced polyvinyl alcohol hydrogel as described in claim 6, characterized in that, The repeated freeze-thaw cycle in step S5 is as follows: the mold containing conductive PVA-TA / AgNWs hydrogel and PVA / ANFs-TA hydrogel is placed in a -20℃ freezer and frozen for 12 hours, then thawed at room temperature for 12 hours, and the above freeze-thaw cycle is repeated 3 times.

9. An ultrastretched hydrogel based on aramid nanofibers prepared by the method according to any one of claims 1-4.

10. A self-healing aramid nanofiber / polyvinyl alcohol multilayer hydrogel prepared by the method according to any one of claims 1-3 and 5-8.

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