WOOD-BASED BIOMIMETIC ARTIFICIAL MUSCLE AND PREPARATION METHOD AND APPLICATION THEREOF

Abstract

The invention relates to a wood-based biomimetic artificial muscle and preparation method and application thereof. The biomimetic artificial muscle comprises a wood-based cellulose skeleton, and polyvinyl alcohol and at least one ionic polymer filled in the wood-based cellulose skeleton. The preparation method includes S1: slicing wood, and subjecting the obtained wood slices to ammonia treatment and delignification in sequence; S2: soaking in the solution of citric acid and/or citrate; S3: preparing water solution of an ionic polymer and DMSO water solution of polyvinyl alcohol separately, and mixing to obtain polymer solution; S4: subjecting the treated wood slices to vacuum treatment, filling the polymer solution into the container, releasing vacuum, and pressurizing to infiltrate the polymer into the wood slices until saturation; S5: freezing the wood slices in a refrigerator and thawing; and S6: repeating S5 for 5-10 times, washing the wood slices, and drying. The inventive biomimetic artificial muscle obtained by physical crosslinking not only has the same elasticity and electrostriction as the polymer, but also maintains the strength of the wood-based skeleton.

Claims

1. A wood-based biomimetic artificial muscle, comprising a wood-based cellulose skeleton, and polyvinyl alcohol and at least one ionic polymer filled in the wood cellulose skeleton.

2. The wood-based biomimetic artificial muscle in claim 1, wherein the molecular weight of polyvinyl alcohol is 27,000-205,000.

3. The wood-based biomimetic artificial muscle in claim 1, wherein the molecular weight of polyvinyl alcohol is 67,000-145,000.

4. The wood-based biomimetic artificial muscle in claim 1, wherein the ionic polymer is selected from polyacrylic acid, polymethacrylic acid, sodium polyacrylate and/or sodium polymethacrylate; and the molecular weight of polyacrylic acid, polymethacrylic acid, sodium polyacrylate or sodium polymethacrylate is preferably 2,000-125,000.

5. The wood-based biomimetic artificial muscle in claim 1, wherein the mass ratio of the wood-based cellulose skeleton to polyvinyl alcohol is 100:10-20.

6. The wood-based biomimetic artificial muscle in claim 1, wherein the mass ratio of the wood-based cellulose skeleton to the ionic polymer is 100:20-40.

7. The wood-based biomimetic artificial muscle in claim 1, wherein the wood cellulose skeleton comprises citric acid and/or citrate.

8. The wood-based biomimetic artificial muscle in claim 7, wherein the mass ratio of the wood-based cellulose skeleton to the total of citric acid and citrate is 100:5-10.

9. The wood-based biomimetic artificial muscle in claim 7, wherein citrate is trisodium citrate.

10. A preparation method of wood-based biomimetic artificial muscles, including the following steps: Step S1: slicing wood, and subjecting the obtained wood slices to ammonia treatment and delignification in sequence; Step S2: soaking in solution of citric acid and/or citrate; Step S3: preparing water solution of the ionic polymer and dimethyl sulfoxide water solution of polyvinyl alcohol separately, and mixing to obtain polymer solution; Step S4: subjecting the treated wood slices to vacuum treatment in a container, filling the polymer solution into the container, releasing vacuum, and pressurizing to infiltrate the polymer into the wood slices until saturation; Step S5: freezing the wood slices in a refrigerator and thawing; and Step S6: repeating Step S5 for 5-10 times, washing the wood slices and drying.

11. The method in claim 10, wherein the wood in Step S1 is poplar, birch, cork wood and/or pine.

12. The method in claim 10, wherein the ammonia treatment in Step S1 includes soaking the wood slices in 10-25 wt % ammonia water for 5-60 min.

13. The method in claim 10, wherein: the delignification treatment in Step S1 includes boiling the wood slices in sodium hydroxide-sodium sulfite water solution at 85-100 C. for 2-4 h, and washing in deionized water; and the concentration of sodium hydroxide is 0.01-5 mol/L and that of sodium sulfite is 0.01-3 mol/L.

14. The method in claim 10, wherein in Step S2, the citrate is trisodium citrate, the soaking temperature is 25-50 C., the soaking time is 1-60 min, and the total of citric acid and citrate accounts for 1-10 wt % of the solution of citric acid and/or citrate.

15. The method in claim 10, wherein: the water solution of the ionic polymer in Step S3 is 10-60 wt % polyacrylic acid water solution, polymethacrylic acid water solution, sodium polyacrylate water solution or sodium polymethacrylate water solution; and the mass fraction of polyvinyl alcohol in the dimethyl sulfoxide water solution of polyvinyl alcohol is 10-60%.

16. The method in claim 10, wherein the dimethyl sulfoxide water solution of polyvinyl alcohol is prepared by adding polyvinyl alcohol as solute into 20-50 wt % dimethyl sulfoxide water solution as solvent, and standing in a water bath at 70-90 C. until polyvinyl alcohol is fully dissolved.

17. The method in claim 10, wherein in Step S3, the volume ratio of the water solution of the ionic polymer to the dimethyl sulfoxide water solution of polyvinyl alcohol is 2-4:1.

18. The method in claim 10, wherein in Step S4, the vacuum treatment includes treating under 0.6-0.8 MPa for 1 min-1 h, holding for 1-20 min after vacuum release, pressurizing to 0.6-3 MPa and holding the pressure for 10 min-6 h.

19. The method in claim 10, wherein in Step S5, the freezing temperature ranges from 60 C. to 5 C., the freezing time lasts for 10-20 h, and the thawing time lasts for 6-10 h.

20. The method in claim 10, wherein in Step S6, the washing includes soaking in distilled water to wash for 3-5 times, and the drying includes drying at 45-60 C. for 10-24 h.

21. A biomimetic robot, comprising machine joints, artificial muscles and a control module, wherein the artificial muscle is a wood-based biomimetic artificial muscle comprising a wood-based cellulose skeleton, and polyvinyl alcohol and at least one ionic polymer filled in the wood-based cellulose skeleton.

Description

BRIEF DESCRIPTION OF FIGURES

[0045] Hereinafter, a brief introduction to the drawings required in the specific embodiments of the present invention or the description of prior arts is given, in order to clearly illustrate the specific embodiments or the technical solutions in prior arts. In all the drawings, similar elements or parts are generally marked by similar reference numerals. Each element or part is not necessarily drawn to its actual scale in the drawings.

[0046] FIG. 1 is an electron micrograph of the delignified wood slice obtained in Step S1 of the method for preparing a wood-based biomimetic artificial muscle provided in Example 1 of the present invention;

[0047] FIG. 2 is an electron micrograph of the biomimetic artificial muscle obtained in Step S6 of the method for preparing a wood-based biomimetic artificial muscle provided in Example 1 of the present invention;

[0048] FIG. 3 is an infrared spectrum comparison chart between the delignified wood slice obtained in Step S1 and the wood-based biomimetic artificial muscle obtained in Step S6 in Example 1;

[0049] FIG. 4 is a bending state diagram of an artificial muscle varying over time under the condition of an electric field intensity of 10 V/cm;

[0050] FIG. 5 is a state diagram of the bending angle of an artificial muscle changing with electric field intensity;

[0051] FIG. 6 is a stress-strain curve diagram of a wood-based biomimetic artificial muscle prepared in Examples 1-4 of the present invention; and

[0052] FIG. 7 is a tensile strength comparison diagram of a wood-based biomimetic artificial muscle prepared in Examples 1-4 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] It should be noted that, unless otherwise specified, the technical or scientific terms used in this application should receive the ordinary meanings understood by those skilled in the art of the invention.

[0054] The ionic polymers mainly comprise electrolyte polymers, carbon nanocomposites, ionic polymers and electroconductive polymers. Examples of the ionic polymers and the electroconductive polymers are highlighted in the embodiments.

[0055] The electroconductive polymers are formed from polymers having conjugated bonds by chemical or electrochemical doping, and have electrical conductivity ranging from insulator to conductor. Under electrochemical stimulation, the electroconductive polymers structurally expand in an oxidation state and contract upon change into random coils in a reduction state, thereby realizing their motions and actions under the large deformation.

[0056] The ionic polymers undergo local swelling and contraction due to the migrating motions of the polymer ions and electrolyte ions in an electric field environment to change the ion concentration inside the polymers, thereby driving the materials to deform.

[0057] The embodiments of the invention provide a preparation method of wood-based biomimetic artificial muscle, including: [0058] Step S1: slicing wood, and subjecting the obtained wood slices to ammonia treatment and delignification in sequence. [0059] The wood can be selected from poplar, birch, cork wood or pine, and the wood slices with even lengths, smooth cuts and uniform thicknesses can be obtained in the slicing process. [0060] The ammonia treatment specifically includes soaking the wood slices in 10-25% ammonia water for 5-60 min. [0061] The ammonia treatment realizes softening of the wood slices which have lost their surface and internal moisture due to standing for long time, to thereby facilitate the subsequent delignification. [0062] Lignin is an amorphous aromatic polymer widely found in plants and containing oxophenylpropanol or its derivative structural units in its molecular structure. It is one of the components forming the cell walls of plant and plays the role in connecting cells. In order to make the polymer well infiltrate into the wood subsequently, the invention adopts delignification to provide a sufficient space for the polymer, so that the wood and the polymer are well combined together. [0063] The delignification process in the embodiments of the invention employs alkaline solution and specifically includes boiling the wood slices in sodium hydroxide-sodium sulfite water solution at 85-100 C. for 2-4 h, and washing in deionized water, wherein the concentration of sodium hydroxide is 0.01-5 mol/L and that of sodium sulfite is 0.01-3 mol/L. [0064] Step S2: soaking the wood slices in citric acid solution or citrate (trisodium citrate) solution at 25-50 C. for 1-60 min. [0065] Generally, wood comprises cellulose 40-50%, hemicellulose 10-30% and lignin 20-30%. The delignified wood slices may undergo a decline in strength, so the invention has the wood slices soaked in citric acid or citrate to affect the movement of cellulose and hemicellulose molecular chains, thereby strengthening the skeleton structure inside the molecules, remarkably improving the mechanical properties and stability of the wood slices and reducing moisture absorption. [0066] The citric acid or citrate accounts for 1-10 wt % of the citric acid solution or citrate solution. [0067] Step S3: preparing ionic polymer solution and DMSO water solution of PVA separately, and mixing to obtain polymer solution. [0068] The ionic polymer solution is 10-60 wt % PAA water solution, sodium polyacrylate water solution or sodium polymethacrylate water solution containing purified water or distilled water as solvent. [0069] The mass fraction of the DMSO water solution of PVA is 10-60%. [0070] The DMSO water solution of PVA is prepared by adding PVA as solute into 20-50 wt % DMSO water solution as solvent, and standing in a water bath container at 70-90 C. until PVA is fully dissolved. [0071] In Step S3, the volume ratio of the ionic polymer solution to the DMSO water solution of PVA is 2-4:1. [0072] The ionic polymer is premixed with PVA in the embodiments of the invention, so that PVA will uniformly infiltrate into the wood in the subsequent impregnation process to thereby improve the mechanical properties of the whole wood slices. [0073] Step S4: subjecting the treated wood slices to vacuum treatment under 0.6-0.8 MPa for 1 min-1 h in a container, filling the polymer solution obtained in Step S3 into the container, releasing vacuum, and pressurizing to infiltrate the polymer into the wood slices until saturation. [0074] In Step S4, the pressure is increased to 0.6-3 MPa 1-20 min after vacuum release, and held for 10 min-6 h. [0075] Whether the wood is saturated with the polymer or not is determined by the volume expanding situation of the wood. [0076] Step S5: freezing the wood slices at 60-5 C. in a refrigerator for 12 h and thawing at a room temperature for 6-10 h. [0077] Step S6: repeating Step S5 for 5-10 times, washing the wood slices, and drying at 45-60 C. for 10-24 h. [0078] The washing is performed by soaking in distilled water for 3-5 times

[0079] The invention adopts the cyclic freezing-thawing process with no initiator or crosslinker but simply physical crosslinking to obtain the biomimetic artificial muscle, which not only has the same elasticity and electrostriction as the polymer, but also maintains the strength of the wood-based skeleton.

[0080] When applied with an electric field, the wood-based biomimetic artificial muscle prepared by the invention has its swelling balance in electrolyte solution so broken that free ions in the artificial muscle move away from electrodes against the friction within the artificial muscle and at the artificial muscle interface. At the same time, the fixed charge position of the polymer chain is relatively stable, and the uniform distribution of ions is disturbed due to the movement of the free ions. Thus, an ion gradient is formed between the electrodes and affects the uniform structure and mechanical properties of the artificial muscle, which further induces the swelling pressure to move towards a nonequilibrium state of the electric field. As a result, the swelling pressure of the positive electrode in the artificial muscle is higher than that of the negative electrode, so that the artificial muscle is bent towards the negative electrode.

[0081] Hereinafter, embodiments of the invention will be illustrated in details in conjunction with the accompanying drawings. The following embodiments are only used to clearly illustrate the technical solution of the invention, and therefore are merely examples, and should not be used to limit the protection scope of the invention.

[0082] The molecular weight of PAA used in the following embodiments is about 5,000, and that of PVA is about 67,000.

Example 1

[0083] S1: slicing poplar, soaking the obtained wood slices in 25% ammonia water for 5 min, boiling in sodium hydroxide-sodium sulfite water solution at 100 C. for 2 h, and washing in deionized water, wherein the concentration of sodium hydroxide is 5 mol/L and that of sodium sulfite is 3 mol/L.

[0084] S2: soaking the wood slices in 1 wt % citric acid solution at 50 C. for 60 min.

[0085] S3: preparing 60 wt % PAA water solution.

[0086] PVA as solute is added into 50 wt % DMSO water solution as solvent and then fully dissolved via a water bath container at 70 C., wherein the mass fraction of PVA in the DMSO water solution is 60%.

[0087] The PAA water solution is mixed with the DMSO water solution of PVA at a volume ratio of 2:1 to obtain polymer solution.

[0088] S4: subjecting the wood slices to vacuum treatment under 0.6 MPa for 30 min in a container, filling the polymer solution in the container, releasing the vacuum, holding for 10 min, pressurizing to 3 MPa and holding the pressure for 10 min until the wood is saturated with the polymer.

[0089] S5: freezing the wood slices at 60 C. in a refrigerator for 12 h, and thawing at a room temperature for 10 h.

[0090] S6: repeating the step S5 for 10 times, soaking the wood slices in distilled water to wash for 5 times, and drying at 60 C. for 12 h to obtain the wood-based biomimetic artificial muscle.

[0091] FIG. 1 is an electron micrograph of a delignified wood slice obtained in Step S1 of the method for preparing a wood-based biomimetic artificial muscle provided in Example 1 of the present invention; FIG. 2 is an electron micrograph of the biomimetic artificial muscle obtained in Step S6 of the method for preparing a wood-based biomimetic artificial muscle provided in Example 1 of the present invention. With reference to FIG. 1 and FIG. 2, it can be seen that PVA and PAA fully infiltrate into the wood slices and are well linked with them after repeated freezing and thawing.

[0092] FIG. 3 is an infrared spectrum comparison chart between the delignified wood slice obtained in Step S1 and the wood-based biomimetic artificial muscle obtained in Step S6 in Example 1.

[0093] With reference to FIG. 3, the absorption peak of the hydroxyl groups of the delignified wood slice is at 3410 cm.sup.1, while that of the wood-based biomimetic artificial muscle is at 3345 cm.sup.1. Such a movement of the absorption peak to the low wavenumber means that the hydroxyl groups of PVA molecules, those in the wood slices and the carboxyl or carboxyl derivative groups of the ionic polymer form strong hydrogen bonds during the combination process of the polymer and the wood slices. Compared with the infrared spectrum of the delignified wood slices, in the infrared spectrum of the wood-based biomimetic artificial muscle derived from the carboxyl groups of PAA, CO stretching vibration occurs at 1705 cm.sup.1, the peak at 1461 cm.sup.1 results from CH.sub.2 vibration, and COH stretching vibration at 1060-1155 cm.sup.1 gets enhanced, because of PVA. All these chemical bond changes indicate that PVA and PAA are combined on the delignified wood slices, and these formed hydrogen bonds play the role of physical crosslinking in the wood-based biomimetic artificial muscle, to thereby form the wood-based biomimetic artificial muscle with good strength.

Example 2

[0094] S1: slicing cork wood, soaking the obtained wood slices in 20% ammonia water for 40 min, boiling in sodium hydroxide-sodium sulfite water solution at 85 C. for 2.5 h, and washing in deionized water, wherein the concentration of sodium hydroxide is 4 mol/L and that of sodium sulfite is 2 mol/L.

[0095] S2: soaking the wood slices in 2 wt % citric acid solution at 40 C. for 40 min.

[0096] S3: preparing 30 wt % sodium polyacrylate water solution.

[0097] PVA as solute is added into 30 wt % DMSO water solution as solvent and then fully dissolved via a water bath container at 80 C., wherein the mass fraction of PVA in the DMSO water solution is 30%.

[0098] The sodium polyacrylate water solution is mixed with the DMSO water solution of PVA at a volume ratio of 3:1 to obtain polymer solution.

[0099] S4: subjecting the wood slices to vacuum treatment under 0.8 MPa for 1 min in a container, filling the polymer solution in the container, releasing the vacuum, holding for 20 min, pressurizing to 2 MPa and holding the pressure for 1 h until the wood is saturated with the polymer.

[0100] S5: freezing the wood slices in a refrigerator at 38 C. for 12 h, and thawing at a room temperature for 8 h.

[0101] S6: repeating the step S5 for 10 times, soaking the wood slices in distilled water to wash for 3 times, and drying at 50 C. for 12 h to obtain the wood-based biomimetic artificial muscle.

Example 3

[0102] S1: slicing pine, soaking the obtained wood slices in 15% ammonia water for 30 min, boiling in sodium hydroxide-sodium sulfite water solution at 90 C. for 3 h, and washing in deionized water, wherein the concentration of sodium hydroxide is 1 mol/L and that of sodium sulfite is 1 mol/L.

[0103] S2: soaking the wood slices in 5 wt % trisodium citrate solution at 25 C. for 30 min.

[0104] S3: preparing 20 wt % sodium polymethacrylate water solution.

[0105] PVA as solute is added into 25 wt % DMSO water solution as solvent and then fully dissolved via a water bath container at 80 C., wherein the mass fraction of PVA in the DMSO water solution is 30%.

[0106] The sodium polymethacrylate water solution is mixed with the DMSO water solution of PVA at a volume ratio of 2:1 to obtain polymer solution.

[0107] S4: subjecting the wood slices to vacuum treatment under 0.8 MPa for 1 h in a container, filling the polymer solution in the container, releasing the vacuum, holding for 1 min, pressurizing to 1 MPa and holding the pressure for 3 h until the wood is saturated with the polymer.

[0108] S5: freezing the wood slices in a refrigerator at 20 C. for 12 h, and thawing at a room temperature for 7 h.

[0109] S6: repeating the step S5 for 8 times, soaking the wood slices in distilled water to wash for 4 times, and drying at 60 C. for 12 h to obtain the wood-based biomimetic artificial muscle.

Example 4

[0110] S1: slicing birch, soaking the obtained wood slices in 10% ammonia water for 60 min, boiling in sodium hydroxide-sodium sulfite water solution at 95 C. for 4 h, and washing in deionized water, wherein the concentration of sodium hydroxide is 0.01 mol/L and that of sodium sulfite is 0.01 mol/L.

[0111] S2: soaking the wood slices in 10 wt % trisodium citrate solution at 50 C. for 1 min.

[0112] S3: preparing 10 wt % polymethacrylic acid water solution.

[0113] PVA as solute is added into 20 wt % DMSO water solution as solvent and then fully dissolved via a water bath container at 90 C., wherein the mass fraction of PVA in the DMSO water solution is 10%.

[0114] The polymethacrylic acid water solution is mixed with the DMSO water solution of PVA at a volume ratio of 4:1 to obtain polymer solution.

[0115] S4: subjecting the wood slices to vacuum treatment under 0.7 MPa for 10 min in a container, filling the polymer solution in the container, releasing the vacuum, holding for 10 min, pressurizing to 0.6 MPa and holding the pressure for 6 h until the wood is saturated with the polymer.

[0116] S5: freezing the wood slices in a refrigerator at 5 C. for 12 h, and thawing at a room temperature for 6 h.

[0117] S6: repeating the step S5 for 5 times, soaking the wood slices in distilled water to wash for 5 times, and drying at 45 C. for 12 h to obtain the wood-based biomimetic artificial muscle.

Electric Field Response Test on Wood-Based Biomimetic Artificial Muscles

[0118] The biomimetic artificial muscle prepared in Example 1 is cut into a shape with a length of 30 mm and a width of 5 mm, then soaked in deionized water and finally fixed between two graphite electrodes of a test device. The distance between the graphite electrodes is adjustable, and the test device is loaded with 2 wt % sodium sulfate solution and externally connected with a DC voltage and current stabilized power source. When the electric field intensity is adjusted as required, the power switch is turned on to record the bending conditions of the artificial muscle in different electric fields.

[0119] FIG. 4 is a bending state diagram of an artificial muscle varying over time under the condition of an electric field intensity of 10 V/cm. With reference to FIG. 4, it can be seen that the artificial muscle gradually deflects over time until its bending angle reaches 90 degrees, which takes 14 s.

[0120] FIG. 5 is a state diagram of the bending angle of an artificial muscle changing with electric field intensity. With reference to FIG. 5, the time for the artificial muscle to bend to 90 degrees gradually decreases along with the increase in the electric field intensity.

Mechanical Strength Test on Wood-Based Biomimetic Artificial Muscles

[0121] The wood-based artificial muscles prepared in Examples 1-4 are cut into a shape with a length of 40 mm, width of 5 mm and thickness of 2 mm separately, to obtain five samples for each example, and a test on tensile strength is carried out by use of a miniature mechanical test machine.

[0122] FIG. 6 and FIG. 7 are tensile property diagrams of the wood-based artificial muscles in Examples 1-4. The strengths of the wood-based muscles in Examples 1 and 2 are 25.68 and 23.45, respectively. Such a difference mainly arises from the wood variety and, more specifically, poplar has higher strength than cork wood. In addition, the ratio of sodium polyacrylate to PVA in Example 2 is 3:1. In the artificial muscle of the present invention, it is the wood and PVA that play the role in enhancing the mechanical strength. As a result, the tensile strength in Example 1 is higher than that in Example 2. Likewise, the ratio of sodium polyacrylate to PVA in Example 4 is 4:1, so the tensile strength in Example 4 is the lowest.

[0123] Unless otherwise stated specifically, the numerical values elaborated in these embodiments do not limit the scope of the present invention. In all the examples shown and described herein, any specific value, unless otherwise specified, should be construed as exemplary only, but not as a limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, but not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made on the technical solutions recorded in the foregoing embodiments, or equivalent replacements can be made on some or all of the technical features. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and should be covered by the scope of the claims and the specification of the present invention.