A fluorescent transparent wood material and its preparation method

Abstract

The present invention discloses a fluorescent transparent wood material and a preparation method thereof. The preparation method includes introducing an aggregation-induced emission material into the wood material through in-situ polymerization doping of polymers. The fluorescent transparent wood obtained by this method has good transparency and a high quantum yield.

Description

Technical Field

[0001] The present invention relates to a fluorescent transparent wood material and a preparation method thereof, belonging to the technical field of transparent wood materials. Background Art

[0002] In the past few decades, due to severe resource shortages and environmental problems caused by petroleum-based materials, bio-based materials prepared from renewable materials have developed vigorously. Currently, biofibers, biopolymers, and bio-based composites are widely used in industries such as fashion, household products, and automobiles. Bio-based materials have a wide range of sources, including plants, animals, or other living organisms. Wood, as one of the most abundant biological materials on Earth, has attracted great attention in advanced materials and manufacturing. Inspired by the inherent physical and chemical properties of wood, functional wood materials have developed rapidly. In recent years, through modification strategies (physical, chemical, or combined modification), the unique hierarchical structure of wood has been adjusted, and the components in the natural wood structure have been increased or decreased to endow wood materials with improved or new properties and functions, enabling their application in aspects such as construction, water treatment, solar steam power generation, and optical applications. Among them, by utilizing the waveguide effect caused by the anisotropic cell structure of wood, combining with fluorescent dyes, and then filling with polymers, fluorescent transparent wood laser materials can be prepared. However, most of these fluorescent dyes have aggregation-caused quenching effects (ACQ), which affect the fluorescence properties of the composite materials.

[0003] Aggregation-induced emission (AIE) is a photophysical behavior related to the aggregation of chromophores. Some molecules emit weakly in good solvents, but as a large amount of poor solvents are added, the molecules begin to aggregate, and the luminescence of the mixed system becomes very strong. These phenomena are related to the restriction of intramolecular motion (RIM). In the solution state, active intramolecular motions, such as rotation and vibration, dissipate the energy of the excited state through non-radiative decay pathways, so that the luminescent body does not emit light. However, in the solid state, intramolecular motion is hindered or the RIM process is activated, thus transforming the lumophore into a strong emitter. AIE molecules usually have good photophysical and chemical stabilities and can maintain their fluorescence properties in different environments. At the same time, compared with traditional fluorescent dyes, the fluorescence properties of AIE molecules are not affected by their aggregation states. AIE molecules have the potential to be prepared into fluorescent transparent wood materials.

[0004] However, at present, in the existing technologies, the fluorescence performance of the fluorescent transparent wood materials prepared by using fluorescent dyes is not very satisfactory.

[0005] The present invention provides a preparation method of a fluorescent transparent wood material, which can effectively solve the above problems.

[0006] The present invention is implemented as follows:

[0007] A preparation method of a fluorescent transparent wood material, which introduces an aggregation-induced emission material into the wood material through in-situ polymerization doping of polymers.

[0008] As a further improvement, the chemical structural formula of the aggregation-induced emission material is as follows:

[0009]

[0010] Among them, the R, R·, R··, and R··· groups are each independently selected from one of hydrogen, heteroatoms, alkyl groups, unsaturated alkyl groups, heteroalkyl groups, cycloalkyl groups, heterocycloalkyl groups, aryl groups, or heteroaryl groups.

[0011] As a further improvement, the chemical structural formula of the aggregation-induced emission material is as follows:

[0012]

[0013] As a further improvement, it includes the following steps:

[0014] S1. Remove lignin from the wood material.

[0015] S2. Add a polymer into a container to obtain a prepolymer solution.

[0016] S3. Dissolve fluorescent dye molecules in an organic solvent to obtain a dye mother liquor, and slowly drop the dye mother liquor into the prepolymer solution to obtain a dye-doped pre-polymer solution.

[0017] S4. Immerse the wood material in the pre-polymer solution under vacuum for vacuum infiltration.

[0018] S5. Heat and cure the wood material that has undergone vacuum infiltration to obtain the fluorescent transparent wood material.

[0019] As a further improvement, the wood material is balsa wood.

[0020] As a further improvement, the polymer is one or more of polyvinyl alcohol, epoxy resin, polyethylene glycol, or polymethyl methacrylate.

[0021] As a further improvement, the concentration of the fluorescent dye molecules in the dye mother liquor is 0.0001 wt% - 0.2 wt%; the volume ratio of the dye mother liquor to the prepolymer solution is 1:30 - 50.

[0022] As a further improvement, the time for vacuum infiltration is 25 - 35 min, and the number of times is more than 3 times.

[0023] As a further improvement, the temperature for heat curing is 65 - 75 °C, and the time is 3.5 - 4.5 h.

[0024] A fluorescent transparent wood material prepared by the above method.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. The present invention uses aggregation-induced emission molecules as fluorescent dyes, without considering the influence of dye aggregation on the fluorescence properties of the material; there is no quenching effect caused by aggregation (ACQ), and the fluorescence characteristics of the composite material are strong.

[0027] 2. The present invention uses balsa wood as the raw material, the raw material source is wide, and the preparation process is simple and easy. The obtained fluorescent transparent wood has good transparency.

[0028] 3. The present invention uses wood materials as raw materials, fills them with polymers, and after doping with AIE dyes, the obtained fluorescent transparent wood has a high quantum yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0030] Figure 1 is a schematic flow chart of the present invention for making fluorescent transparent wood.

[0031] Figure 2 is a macroscopic photograph of the fluorescent transparent wood of the present invention.

[0032] Figure 3 is the fluorescence performance diagram of the transparent wood doped with TPE dye provided in Example 1 of the present invention. Among them, Figure 3 A is the fluorescence diagram of the transparent wood doped with TPE dye under ultraviolet light; Figure 3 B is the fluorescence excitation and emission spectrum diagram of the transparent wood doped with TPE dye; Figure 3 C is the fluorescence imaging analysis diagram of the transparent wood doped with TPE dye.

[0033] Figure 4 is the fluorescence performance diagram of the transparent wood doped with TBPE-4TA dye provided in Example 2 of the present invention. Among them, Figure 4 A is the fluorescence diagram of the transparent wood doped with TBPE-4TA dye under ultraviolet light; Figure 4 B is the fluorescence excitation and emission spectrum diagram of the transparent wood doped with TBPE-4TA dye; Figure 4 C is the fluorescence imaging analysis diagram of the transparent wood doped with TBPE-4TA dye provided in Example 2 of the present invention.

[0034] Figure 5 It is the fluorescence performance diagram of the transparent wood doped with TPE-4TA dye provided in Embodiment 3 of the present invention. Among them, Figure 5 A is the fluorescence diagram of the transparent wood doped with TPE-4TA dye under ultraviolet light; Figure 5 B is the fluorescence excitation and emission spectrum diagram of the transparent wood doped with TPE-4TA dye provided in Embodiment 3 of the present invention; Figure 5 C is the fluorescence imaging analysis diagram of the transparent wood doped with TPE-4TA dye provided in Embodiment 3 of the present invention.

[0035] Figure 6 It is the fluorescence diagram of the transparent wood of TBPE-4TA dye provided in Comparative Example 3 of the present invention under ultraviolet light. Detailed implementation manners

[0036] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0037] The embodiments of the present invention provide a preparation method of a fluorescent transparent wood material, which introduces an aggregation-induced emission material into the wood material through in-situ polymerization doping of polymers. In the embodiments of the present invention, when introducing AIEgens into the wood framework structure, a wood nanocomposite with unique fluorescent transparency properties is prepared by using the characteristics of high fluorescence efficiency and strong anti-photobleaching ability of AIEgens in the solid state. Compared with the application of traditional dyes, when doping AIEgens, there is no need to consider the dispersion problem, and even if less AIEgens are used, a bulk wood material with higher brightness can still be obtained. This composite material inherits the functions of the AIE material and combines the porosity, biocompatibility and mechanical properties of the wood itself, and the interaction can produce new performance advantages, such as the luminescence efficiency of the dye being greatly improved.

[0038] In some embodiments, the chemical structural formula of the aggregation-induced emission material is as follows:

[0039]

[0040] Among them, the R, R′, R″ and R‴ groups are each independently selected from one of hydrogen, heteroatom, alkyl, unsaturated alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl or heteroaryl.

[0041] The above tetraphenylethylene derivatives, which are simple molecules composed of four benzene rings and one carbon-carbon double bond, exhibit extremely wonderful aggregation-induced emission (AIE) luminescence behavior and have excellent fluorescence luminescence properties when infiltrated into wood.

[0042] In some embodiments, the chemical structural formula of the aggregation-induced emission material is as follows:

[0043]

[0044] In some embodiments, it includes the following steps:

[0045] S1. Remove lignin from the wooden material. Lignin is the main reason for the color of raw wood. At the same time, due to its rich functional groups and amorphous network structure, lignin binds to hemicellulose at the molecular scale and physically contacts fibers at the nano and micro scales, and is an important filler and binder. Therefore, removing lignin has two functions. One is bleaching, which removes the color of the raw wood and makes the wood chips white. The other is that while removing lignin, the anisotropy and hierarchical porous structure of natural wood are maintained, but more nanopores appear inside the cell wall, which is more conducive to the filling of polymers. If lignin is not removed, the polymer cannot be completely filled into the wood pores, and the resulting product has low transparency and is not beautiful. In addition, lignin may interfere with the aggregation-induced emission performance of the wooden material.

[0046] S2. Add a polymer into a container to obtain a prepolymer solution.

[0047] S3. Dissolve fluorescent dye molecules in an organic solvent to obtain a dye mother liquor, and slowly drop the dye mother liquor into the prepolymer solution to obtain a dye-doped pre-polymer solution.

[0048] S4. Immerse the wooden material in the pre-polymer solution under vacuum for vacuum infiltration.

[0049] S5. Heat and cure the vacuum-infiltrated wooden material to obtain the fluorescent transparent wooden material.

[0050] In the embodiments of the present invention, the wood material is used as the raw material, filled with a polymer, and a tetraphenylethylene derivative is used as the fluorescent dye; when the fluorescent dye exists alone in an aqueous solution, due to the free rotation of its tetraphenylethylene fluorescent group, the excitation energy can be annihilated through non-radiative transition, resulting in the probe being unable to emit strong fluorescence; however, when the fluorescent dye and the polymer are filled into the wood framework structure together, the rigid environment inside the composite material restricts the rotation of the tetraphenylethylene group, resulting in the dye being able to emit strong fluorescence. The wood material, polymer filling, and tetraphenylethylene derivative fluorescent dye play a synergistic effect, improving the fluorescence performance of the wood material.

[0051] In some embodiments, the removal of lignin in step S1 includes the following steps:

[0052] (1) Place the wood chips in an oven at 90 - 110 °C for 24 hours to remove the moisture in the wood sample.

[0053] (2) Immerse the dried wood chips from step (1) in a sodium chlorite solution, and then gradually add glacial acetic acid dropwise to adjust the pH to 4.4 - 4.8; keep the solution boiling gently, and when the wood sample gradually changes from yellow to white, end the dropwise addition reaction and take out the sample.

[0054] (3) Rinse the sample after the reaction in step (2) repeatedly with hot distilled water to remove the chemicals.

[0055] (4) Keep the sample washed in step (3) in ethanol for later use.

[0056] In some embodiments, the wood material is preferably balsa wood, but not limited thereto. Balsa wood is widely sourced, and the preparation process is simple and easy. The obtained fluorescent transparent wood has good transparency.

[0057] In some embodiments, the polymer is one or several of polyvinyl alcohol, epoxy resin, polyethylene glycol, or polymethyl methacrylate. Poly methyl methacrylate is preferred. When the polymer is polyvinyl alcohol or polyethylene glycol, a prepolymer solution can be obtained by dissolving it in water or other solvents during use. When the polymer is epoxy resin, it can be simply understood as the commonly used AB glue, and a prepolymer solution can be obtained by mixing the two. When the polymer is polymethyl methacrylate, an initiator azobisisobutyronitrile needs to be added, and pre-polymerize for 15 - 20 minutes in a nitrogen atmosphere at 70 - 80 °C, and then cool to room temperature to slow down the polymerization reaction to obtain the prepolymer solution.

[0058] In some embodiments, the concentration of the fluorescent dye molecules in the dye mother liquor is 0.0001 wt% - 0.2 wt%; the volume ratio of the dye mother liquor to the prepolymer solution is 1:30 - 50. By doping different concentrations of fluorescent dyes, a series of fluorescent transparent wood materials with different fluorescence properties are prepared.

[0059] In some embodiments, the time of vacuum infiltration is 25 - 35 min, and the number of times is more than 3 times. Repeat 3 times to achieve a complete infiltration effect.

[0060] In some embodiments, the temperature of heat curing is 65 - 75 °C, and the time is 3.5 - 4.5 h.

[0061] An embodiment of the present invention provides a fluorescent transparent wood material prepared by the above method.

[0062] Example 1

[0063] Removal of lignin: Immerse the dried wood chips in sodium chlorite solution, add glacial acetic acid drop by drop to adjust the pH of the solution to 4.6, keep the solution slightly boiling. When the sample gradually changes from yellow to white, end the reaction and take out the sample, and rinse it with hot distilled water to remove most of the chemicals. Keep the washed sample in ethanol for later use.

[0064] Synthesis of blue fluorescent luminescent transparent wood material: In a two-necked round-bottom flask, add methyl methacrylate (MMA) and 0.3 wt% azobisisobutyronitrile (AIBN) as an initiator. The mixture is pre-polymerized at 75 °C under nitrogen for 15 min. Then cool the mixture to room temperature in an ice-water bath to stop the reaction. Dissolve the fluorescent dye molecule tetraphenylethylene TPE (0.004, 0.4, 4.0 and 40.0 mg) in dry DMF (1 mL) to obtain 0.0001 wt%, 0.001 wt%, 0.01 wt% and 0.1 wt% dye mother solutions. Slowly drip 1 mL of the mother solution into 40 mL of the mixture with a syringe to prepare a fluorescent precursor solution. Then, in a vacuum chamber, immerse the delignified wood chips (10 mm * 10 mm * 1 mm) in 40 mL of the pre-polymerized solution for 30 minutes. The above vacuum infiltration process is repeated three times. Finally, sandwich the polymer-infiltrated wood between two glass slides and wrap it with aluminum foil and place it in an oven, heat it at 70 °C for 4 hours to complete the curing process, and obtain transparent blue fluorescent wood.

[0065] Place the transparent wood on the paper printed with letters. The transparent wood material is placed in the center of each photo, and a blank space for letters is left around the outer circle. Its macroscopic photo is as Figure 2 shown. From Figure 2 it can be seen that the transparent wood material prepared in Example 1 shows good transparency.

[0066] Test the fluorescence performance of the transparent blue fluorescent wood as Figure 3 shown. Figure 3A shows the fluorescence photographs of transparent wood doped with TPE dyes under ultraviolet light. From left to right, the concentrations of fluorescent dye molecules are 0.0001 wt%, 0.001 wt%, 0.01 wt% and 0.1 wt% in sequence, and their fluorescence quantum yields Ф F (The excitation spectra and emission spectra of the standard sample and transparent wood are measured using an integrating sphere, and their fluorescence quantum yields are calculated through the formula quantum yield = (number of quanta of the generated product) / (number of quanta absorbed)) are 7%, 22%, 61% and 78% in sequence, indicating that it has visible blue fluorescence to the naked eye, and the fluorescence brightness increases with the increase of the dye concentration. Figure 3 B reveals the fluorescence excitation and emission spectra of transparent wood doped with TPE dyes (measured by a steady-state / transient fluorescence spectrometer), indicating that with the increase of the dye concentration, the emission wavelength of the transparent wood redshifts from 452 nm to 476 nm. Figure 3 C images the transparent wood doped with TPE dyes through a laser scanning confocal microscope. The confocal fluorescence imaging analysis reveals the internal structure of the fluorescent transparent wood material, and the cavity structure inside the wood is clearly visible.

[0067] Example 2

[0068] The fluorescent dye is TBPE-4TA (0.004, 0.4, 4.0 and 40.0 mg), and transparent green fluorescent wood is obtained. Others are the same as in Example 1.

[0069] Test the fluorescence properties of the transparent blue fluorescent wood as Figure 4 shown. Figure 4 A shows the fluorescence photographs of transparent wood doped with TBPE-4TA dyes under ultraviolet light. From left to right, the concentrations of fluorescent dye molecules are 0.0001 wt%, 0.001 wt%, 0.01 wt% and 0.1 wt% in sequence, and their fluorescence quantum yields Ф F (The test method is the same as in Example 1) are 18%, 45%, 64% and 71% in sequence, indicating that it has visible blue-green fluorescence to the naked eye, and the fluorescence brightness increases with the increase of the dye concentration. Figure 4 B reveals the fluorescence excitation and emission spectra of transparent wood doped with TBPE-4TA dyes (measured by a steady-state / transient fluorescence spectrometer), indicating that with the increase of the dye concentration, the emission wavelength of the transparent wood redshifts from 466 nm to 493 nm. Figure 4 C images the transparent wood doped with TBPE-4TA dyes through a laser confocal scanning microscope. The confocal fluorescence imaging analysis reveals the internal structure of the fluorescent transparent wood material, and the fiber orientation on the wood surface is clearly visible.

[0070] Example 3

[0071] The fluorescent dye was TPE-4TA (0.004, 0.4, 4.0 and 40.0 mg), and transparent green fluorescent wood was obtained. Other operations were the same as in Example 1.

[0072] The fluorescence properties of the transparent blue fluorescent wood were tested as Figure 5 shown. Figure 5 A shows the fluorescence photos of the transparent wood doped with TPE-4TA dye under ultraviolet light. From left to right, the concentrations of the fluorescent dye molecules are 0.0001 wt%, 0.001 wt%, 0.01 wt% and 0.1 wt% in sequence, and their fluorescence quantum yields Ф F (The testing method was the same as in Example 1) were 15%, 33%, 68% and 99% in sequence, indicating that it had visible blue-green fluorescence, and with the increase of the dye concentration, the fluorescence brightness increased; Figure 5 B reveals the fluorescence excitation and emission spectra of the transparent wood doped with TPE-4TA dye (measured by a steady-state / transient fluorescence spectrometer), indicating that with the increase of the dye concentration, the emission wavelength of the transparent wood redshifts from 466 nm to 493 nm; Figure 5 C images the transparent wood doped with TPE-4TA dye by a laser confocal scanning microscope. The confocal fluorescence imaging analysis reveals the internal structure of the fluorescent transparent wood material and can perform three-dimensional imaging on the inside of the wood.

[0073] Comparative Example 1

[0074] The fluorescent luminescent transparent wood material was not prepared, and only the fluorescence properties of the fluorescent dye with the same concentration as in Example 2 were tested (the testing method was the same as in Example 1). The test results are shown in Table 1.

[0075] Table 1

[0076]

[0077] The experimental results of Examples 1-3 and Comparative Example 1 show that due to the in-situ polymerization curing and the effective effect of the microenvironment filled in the wood on the doped aggregation-induced emission dye, the luminescence efficiency of the dye can usually be greatly improved. When the amount of the dye used is small (> one ten-thousandth), the quantum yield reaches > 60%, while the quantum yield of the dye under the same concentration is < 2%.

[0078] Comparative Example 2

[0079] The lignin was not removed, and other operations were the same as in Example 2. The experimental results show that the polymer could not be filled into the inside of the wood, and the fluorescent transparent wood material could not be prepared.

[0080] Comparative Example 3

[0081] In a two-necked round-bottom flask, methyl methacrylate (MMA) and 0.3 wt% azobisisobutyronitrile (AIBN) were added as initiators. The mixture was pre-polymerized under nitrogen at 75 °C for 15 min. Then the mixture was cooled to room temperature in an ice-water bath to stop the reaction. Fluorescent dye molecules TBPE-4TA (0.004, 0.4, 4.0 and 40.0 mg) were dissolved in dry DMF (1 mL) to obtain dye mother solutions with concentrations of 0.0001 wt%, 0.001 wt%, 0.01 wt% and 0.1 wt%. 1 mL of the mother solution was slowly added dropwise to 40 mL of the mixture using a syringe to prepare a fluorescent precursor solution. The fluorescent precursor solution was placed in an oven and heated at 70 °C for 4 hours to complete the curing process, obtaining a transparent blue fluorescent material. Its fluorescence properties were directly tested (the testing method was the same as in Example 1), and the test results are as Figure 6 shown. That is, the fluorescent dye was only mixed with the polymer without penetrating into the wood.

[0082] As Figure 6 can be seen, from left to right, the concentrations of the fluorescent dye molecules are 0.0001 wt%, 0.001 wt%, 0.01 wt% and 0.1 wt% in turn, and their fluorescence quantum yields Ф F are 1%, 9%, 35% and 70% in turn. It can be seen from this that under the condition of the same concentration of fluorescent dye molecules, after the polymerization of the fluorescent dye, wood and polymer, their fluorescence properties are significantly better than those of the material formed by the polymerization of the fluorescent dye and polymer.

[0083] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a fluorescent transparent wood material, characterized in that, By introducing aggregation-induced emission (AIE) materials into wood materials through in-situ polymerization doping of polymers, using wood materials as raw materials, filling them with polymers, and preparing them with tetraphenylethylene derivatives as fluorescent dyes; It includes the following steps: S1. Remove lignin from the wood material; S2. Add polymers into a container to obtain a prepolymer solution; S3. Dissolve fluorescent dye molecules in an organic solvent to obtain a dye mother liquor, and slowly add the dye mother liquor dropwise into the prepolymer solution to obtain a dye-doped pre-polymer solution; S4. Immerse the wood material in the pre-polymer solution under vacuum for vacuum infiltration; S5. Heat and cure the vacuum-infiltrated wood material to obtain the fluorescent transparent wood material.

2. The preparation method of the fluorescent transparent wood material according to claim 1, characterized in that, The chemical structural formula of the aggregation-induced emission material is as follows: ； Wherein, both the R and R' groups are selected from one of hydrogen, heteroatoms, alkyl groups, unsaturated alkyl groups, heteroalkyl groups, cycloalkyl groups, heterocycloalkyl groups, aryl groups or heteroaryl groups.

3. The preparation method of the fluorescent transparent wood material according to claim 2, characterized in that, The chemical structural formula of the aggregation-induced emission material is as follows: 。 4. The preparation method of the fluorescent transparent wood material according to claim 1, characterized in that, The wood material is balsa wood.

5. The preparation method of the fluorescent transparent wood material according to claim 1, characterized in that, The polymer is one or more of polyvinyl alcohol, epoxy resin, polyethylene glycol or polymethyl methacrylate.

6. The preparation method of the fluorescent transparent wood material according to claim 1, wherein, The concentration of the fluorescent dye molecules in the dye mother liquor is 0.0001 wt% - 0.2 wt%; the volume ratio of the dye mother liquor to the prepolymer solution is 1:30 - 50.

7. The preparation method of the fluorescent transparent wood material according to claim 1, characterized in that, In step S4, the time of the vacuum infiltration is 25 - 35 min, and the number of times is more than 3 times.

8. The preparation method of the fluorescent transparent wood material according to claim 1, wherein, In step S5, the temperature of the heat curing is 65 - 75 °C, and the time is 3.5 - 4.5 h.

9. A fluorescent transparent wood material prepared by the method according to any one of claims 1 to 8.

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