Flexible Cellulose Nanocrystal Composite Film and Its Preparation Method and Application

Abstract

This application relates to the technical field of functional polymer composite membranes, and provides a method for preparing a time-dependent and repeatedly erasable and rewritable flexible cellulose nanocrystal composite membrane, which includes the following steps: Step S1: Prepare a cellulose nanocrystal thin film with structural color; Step S2: Prepare a time-dependent and repeatedly erasable and rewritable flexible cellulose nanocrystal composite membrane; and optionally Step S3: Prepare a quaternary ammonium salt-treated time-dependent and repeatedly erasable and rewritable flexible cellulose nanocrystal composite membrane. This application also relates to a time-dependent and repeatedly erasable and rewritable flexible cellulose nanocrystal composite membrane, an information storage material, an anti-counterfeiting and encryption material, and an anti-counterfeiting and encryption method. The flexible cellulose nanocrystal composite membrane described herein has good flexibility and mechanical properties, distinct and uniform structural color, and can enhance or disappear its fluorescence by adjusting the pH value, realizing the function of repeated writing or erasure.

Description

Technical Field

[0001] This application relates to the technical field of functional polymer composite films, in particular to a flexible cellulose nanocrystal composite film with time-dependence and repeatable erasing ability for information storage and anti-counterfeiting, and its preparation method and application. Background Art

[0002] Nowadays, the rapidly increasing information content has brought urgent information security problems. How to effectively protect information from being stolen, tampered with or forged during various transmission processes in daily life is an issue that has received increasing attention. This situation not only strengthens the demand of modern society for new materials and technologies for information anti-counterfeiting encryption and secure storage, but also requires more diversified new anti-counterfeiting materials and technologies.

[0003] In recent years, researchers have been committed to preparing new optical anti-counterfeiting encryption and secure storage materials with different functions through different construction strategies to ensure information security. Among them, information functional materials with both structural color and fluorescence have become a research hotspot due to their unique performance advantages and have great potential for wide application in information anti-counterfeiting and storage technologies. As a green and environmentally friendly natural polymer, cellulose nanocrystal (CNC) has the advantages of rich reserves, degradability and renewability, and is an ideal photonic crystal for constructing structural color materials. The water-dispersed CNC suspension can spontaneously assemble into a chiral cholesteric phase structure at an appropriate concentration and retain this structure in the dried solid film. Thus, the CNC-based film can not only reflect visible light of a specific wavelength, but also serve as a chiral environment for the luminescent body to generate circularly polarized light. Furthermore, the chiral cholesteric phase structure of the CNC-based film has excellent stimulus-responsive characteristics. For example, under stimuli such as stress, solvent, moisture, pH, light, electricity, magnetism, heat, etc., its helical pitch P can change, resulting in corresponding changes in its structural color and circularly polarized luminescence. This provides favorable conditions for the development of adjustable CNC-based information security materials. However, due to its crystalline six-membered ring polysaccharide molecular chain structure and abundant hydrogen bond interactions, the solid film of CNC usually has the defect of being hard and brittle, which is difficult to meet the objective use requirements.

[0004] Combining fluorescence with structural color is the main method to break the single optical mode of CNC-based thin films, which can increase the difficulty of information decoding and enhance the level of information security. So far, various typical stimulus-responsive fluorescent materials that achieve fluorescence or color changes through stimuli such as light, heat, stress, pH, ions, etc. have been developed and used for information encryption and anti-counterfeiting. Although these materials show great application potential in anti-counterfeiting and information encryption, most of them can only achieve constant fluorescence characteristics and are difficult to be regulated in the time dimension. On the other hand, under the condition of the presence or removal of specific external stimuli, the writing and erasing of the information stored in information security functional materials are also important issues. However, most of the reported erasable materials rely on chemical reactivity or are based on gel material systems, and their rewritability and sensitivity are limited.

[0005] Therefore, it is necessary to develop an information security storage material with rapid response, simple preparation, mild conditions, and repeatable erasure. To sum up, based on CNC, it is of great practical significance to develop a flexible structural color-fluorescent functional material with time dependence and repeatable erasure for information recording, storage, encryption, and anti-counterfeiting. Summary of the Invention

[0006] The purpose of this application is to provide a time-dependent and repeatable erasable flexible cellulose nanocrystal composite film and its preparation method and application. Specifically, by introducing a cross-linking agent and a surfactant into cellulose nanocrystals, the cellulose nanocrystal composite film has good flexibility and distinct and uniform structural color, and by introducing coumarin compounds, the flexible cellulose nanocrystal composite film has fluorescence characteristics. The fluorescence can be enhanced or disappeared by adjusting the pH value, realizing the function of repeatable writing or erasure.

[0007] To solve the above technical problems, this application provides the following technical solutions.

[0008] In the first aspect, this application provides a preparation method of a time-dependent and repeatable erasable flexible cellulose nanocrystal composite film, and the preparation method includes the following steps:

[0009] Step S1: Prepare a cellulose nanocrystal film with structural color

[0010] Mix the required weights of a water-dispersed cellulose nanocrystal suspension, a first cross-linking agent, a first surfactant, a coumarin compound, and a first photoinitiator to form a uniform mixed suspension, and obtain a cellulose nanocrystal film with structural color after drying;

[0011] Step S2: Prepare a time-dependent and repeatable erasable flexible cellulose nanocrystal composite film

[0012] The cellulose nanocrystal film with structural color obtained in step S1 is placed under ultraviolet light for the first cross-linking reaction to obtain the time-dependent and repeatable erasable flexible cellulose nanocrystal composite film.

[0013] In an embodiment of the first aspect, the preparation method further includes the following steps:

[0014] Step S3: Prepare a quaternary ammonium salt-treated time-dependent and repeatable erasable flexible cellulose nanocrystal composite film

[0015] The time-dependent and repeatable erasable flexible cellulose nanocrystal composite film obtained in step S2 is soaked in a soaking solution, and then placed under ultraviolet light for the second cross-linking reaction to obtain a quaternary ammonium salt-treated time-dependent and repeatable erasable flexible cellulose nanocrystal composite film;

[0016] Wherein, the soaking solution is made of a second cross-linking agent, a quaternary ammonium salt-based ionic liquid, a second photoinitiator, and an aqueous mixed solvent.

[0017] In an embodiment of the first aspect, in step S1, the water-dispersed cellulose nanocrystal suspension is prepared from cellulose by a mature sulfuric acid hydrolysis method, and its mass fraction in the total mass of the raw materials added in this step is 50%-90%. Preferably, the mass fraction of the water-dispersed cellulose nanocrystal suspension in the total mass of the raw materials added in this step is 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or the range or sub-range between any two of them.

[0018] Preferably, in step S1, the first cross-linking agent is one or both of polyethylene glycol diacrylate and polyethylene glycol dimethacrylate, the average relative molecular mass of the first cross-linking agent is 200 g / mol - 4000 g / mol, and its mass fraction in the total mass of the raw materials added in this step is 5% - 30%. Preferably, the average relative molecular mass of the first cross-linking agent is 200 g / mol, 500 g / mol, 1000 g / mol, 1500 g / mol, 2000 g / mol, 2500 g / mol, 3000 g / mol, 3500 g / mol, 4000 g / mol or the range or sub-range between any two of them. Preferably, the mass fraction of the first cross-linking agent in the total mass of the raw materials added in this step is 5%, 10%, 15%, 20%, 25%, 30% or the range or sub-range between any two of them.

[0019] Preferably, in step S1, the first surfactant is at least one of alkyl sulfates with 8 - 18 carbon atoms, alkyl sulfonates with 8 - 18 carbon atoms, and alkyl benzene sulfonates with 8 - 18 carbon atoms, and the mass fraction thereof in the total mass of the raw materials added in this step is 0% - 8%. The number of carbon atoms in the alkyl group of the first surfactant is 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18. Preferably, the mass fraction of the first surfactant in the total mass of the raw materials added in this step is 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8% or the range or sub - range between any two of these values.

[0020] Preferably, in step S1, the first photoinitiator is any commercially available general ultraviolet photoinitiator, and the mass fraction thereof in the total mass of the raw materials added in this step is 0.5% - 4.5%. The mass fraction of the first photoinitiator in the total mass of the raw materials added in this step is 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5% or the range or sub - range between any two of these values.

[0021] In one embodiment of the first aspect, in step S1, the coumarin - type compound is one or more of the compounds represented by the following structural formulas (I) - (IV), and the mass fraction thereof in the total mass of the raw materials added in this step is 0.5% - 7.5%:

[0022] 。

[0023] Preferably, the mass fraction of the coumarin - type compound in the total mass of the raw materials added in this step is 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5% or the range or sub - range between any two of these values.

[0024] In an embodiment of the first aspect, in step S3, the second crosslinking agent is one or both of polyethylene glycol diacrylate and polyethylene glycol dimethacrylate. The average relative molecular mass of the second crosslinking agent is 200 g / mol - 4000 g / mol, and the mass fraction thereof in the total mass of the raw materials added in this step is 0.5% - 5%. Preferably, the mass fraction of the second crosslinking agent in the total mass of the raw materials added in this step is 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0% or the range or sub-range between any two of them.

[0025] Preferably, in step S3, the second photoinitiator is any commercially available general ultraviolet photoinitiator, and the mass fraction thereof in the total mass of the raw materials added in this step is 0.1% - 1%. Preferably, the mass fraction of the second photoinitiator in the total mass of the raw materials added in this step is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or the range or sub-range between any two of them.

[0026] Preferably, in step S3, the aqueous mixed solvent is a mixture of water and dimethyl sulfoxide.

[0027] In an embodiment of the first aspect, in step S3, the quaternary ammonium salt ionic liquid is one or both of acrylate quaternary ammonium salt and methacrylate quaternary ammonium salt. The mass fraction thereof in the total mass of the raw materials added in this step is 10% - 60%. The structure of the quaternary ammonium salt ionic liquid is shown as follows:

[0028] ;

[0029] Wherein, m is an integer from 1 to 4, R 1 is H or methyl, R 2 , R 3 and R 4 are methyl, ethyl, propyl, butyl, benzyl, and R 2 , R 3 and R 4 can be the same or different, and X is chlorine or bromine.

[0030] In an embodiment of the first aspect, in step S3, the soaking time is 6 - 72 hours. Preferably, reduced pressure or vacuum soaking is adopted.

[0031] Preferably, when performing the second crosslinking reaction, the ultraviolet light irradiation time does not exceed 0.5 hours.

[0032] In a second aspect, the present application provides a time-dependent and repeatedly erasable flexible cellulose nanocrystal composite film, which is prepared by the preparation method as described in the first aspect.

[0033] In a third aspect, the present application provides an information storage material, which comprises the time-dependent and repeatedly erasable flexible cellulose nanocrystal composite film as described in the second aspect.

[0034] In a fourth aspect, the present application provides an anti-counterfeiting and encryption material, which comprises the time-dependent and repeatedly erasable flexible cellulose nanocrystal composite film as described in the second aspect.

[0035] In a fifth aspect, the present application provides an anti-counterfeiting and encryption method, which includes the following steps: storing the information to be hidden on the anti-counterfeiting material as described in the fourth aspect, then infiltrating the anti-counterfeiting and encryption material with an alkaline solution, and displaying the information to be hidden under ultraviolet light.

[0036] Compared with the prior art, the positive effects of the present invention are as follows: The flexible cellulose nanocrystal composite film (which can also be called a flexible structural color-fluorescent composite film) of the present invention has good flexibility and mechanical properties, and the structural color is distinct and uniform. On the one hand, when infiltrated with a dilute alkali solution, it can exhibit obvious time-dependent blue fluorescence under ultraviolet light. When further infiltrated with a dilute acid solution, the fluorescence immediately disappears, showing the characteristics of repeated writing / erasing. On the other hand, when the flexible structural color-fluorescent composite film is irradiated with ultraviolet light by using a mask method, the template pattern can be transferred onto the film to achieve a photo-induced pattern. Therefore, the flexible structural color-fluorescent composite film as described above in the present invention can be used as a new type of cellulose nanocrystal-based information storage and encryption anti-counterfeiting functional material. Description of the Drawings

[0037] The following drawings detail the exemplary embodiments disclosed in the present application. Wherein the same reference numerals represent similar structures in several views of the drawings. Those of ordinary skill in the art will understand that these embodiments are non-limiting and exemplary embodiments, and the drawings are only for the purpose of illustration and description, and are not intended to limit the scope of the present application. Embodiments in other ways may also achieve the inventive intent in the present application. It should be understood that the drawings are not drawn to scale.

[0038] Figure 1 Photographs of the flexible structural color-fluorescent composite films prepared in Example 1 and Example 2 of the present invention;

[0039] Figure 2 Photographs of the flexible structural color-fluorescent composite films prepared in Examples 3-5 of the present invention;

[0040] Figure 3Reflection spectra and stress-strain curves of the flexible structural color-fluorescent composite films prepared in Example 1 and Example 2 of the present invention;

[0041] Figure 4 Photos and fluorescence spectra of repeated writing / erasing of the flexible structural color-fluorescent composite film prepared in Example 2 of the present invention under ultraviolet light;

[0042] Figure 5 Alkali direct writing patterns of the flexible structural color-fluorescent composite films prepared in Example 1 and Example 2 of the present invention under ultraviolet light;

[0043] Figure 6 Optical QR code information storage of the flexible structural color-fluorescent composite film prepared in Example 1 of the present invention;

[0044] Figure 7 Schematic diagram of information storage, encryption and anti-counterfeiting of the flexible structural color-fluorescent composite film prepared in Example 2 of the present invention under ultraviolet light. Detailed implementation manners

[0045] Unless otherwise specified, implied from the context or in accordance with the convention of the prior art, all parts and percentages in this application are based on weight, and the test and characterization methods used are synchronized with the filing date of this application. Where applicable, any patents, patent applications or published content referred to in this application are incorporated herein by reference in their entirety, and their equivalent family patents are also incorporated by reference, especially the definitions of synthetic techniques, products and processing designs, polymers, comonomers, initiators or catalysts in the art disclosed in these documents. If the definition of a specific term disclosed in the prior art is inconsistent with any definition provided in this application, the definition of the term provided in this application shall prevail.

[0046] The numerical ranges in this application are approximate values, so unless otherwise stated, they may include values outside the range. The numerical range includes all values from the lower limit value to the upper limit value increased by 1 unit, provided that there is an interval of at least 2 units between any lower value and any higher value. For example, if it is stated that a component, physical or other property (such as molecular weight, melt index, etc.) is from 100 to 1000, it means that all individual values, such as 100, 101, 102, etc., and all sub-ranges, such as 100 to 166, 155 to 170, 198 to 200, etc., are clearly listed. For ranges containing values less than 1 or fractions greater than 1 (such as 1.1, 1.5, etc.), 1 unit is appropriately regarded as 0.0001, 0.001, 0.01 or 0.1. For ranges containing single-digit numbers less than 10 (such as 1 to 5), 1 unit is usually regarded as 0.1. These are only specific examples of what is intended to be expressed, and all possible combinations of the values between the lowest and highest values listed are considered to be clearly recited in this application. It should also be noted that the terms "first", "second", etc. in this text do not limit the order of precedence, but are only used to distinguish substances with different structures.

[0047] When used with respect to chemical compounds, unless explicitly stated, the singular includes all isomeric forms, and vice versa (e.g., "hexane" includes, individually or collectively, all isomers of hexane). Additionally, unless explicitly stated, a noun described by "a", "an" or "the" also includes its plural forms.

[0048] The terms "comprising", "including", "having" and their derivatives do not exclude the existence of any other components, steps or processes, and are independent of whether these other components, steps or processes are disclosed in this application. To remove any doubt, unless explicitly stated, all compositions using the terms "comprising", "including", or "having" in this application may contain any additional additives, excipients or compounds. In contrast, except for those necessary for the operating performance, the term "consisting essentially of" excludes any other components, steps or processes from the scope described below any such term. The term "consisting of" does not include any component, step or process not specifically described or listed. Unless explicitly stated, the term "or" refers to the individual members listed or any combination thereof.

[0049] In modern society, the demand for the diversity and security of information transmission is increasing, which has given rise to the rapid development of new materials and technologies for information storage, encryption, and anti-counterfeiting. Seeking more diverse information storage and encryption anti-counterfeiting functional materials is the fundamental solution to address information security issues. Based on this, the present invention provides a flexible cellulose nanocrystal composite film with time-dependence and repeatable writing / erasing capabilities (hereinafter referred to as the flexible structural color-fluorescent composite film), and the flexible structural color-fluorescent composite film is made of CNC, polyethylene glycol diacrylate PEGDA (polyethylene glycol dimethacrylate PEGDMA), surfactant, coumarin compounds, photoinitiator, (and / or) acrylate quaternary ammonium salt (methacrylate quaternary ammonium salt). PEGDA or PEGDMA mainly plays a cross-linking role and endows the structural color-fluorescent composite film with excellent flexibility. The surfactant can adjust the dispersibility and compatibility of the system, enabling the film to have a uniform iridescent structural color. Due to the inherent fluorescence sensitivity of coumarin compounds to pH, the flexible structural color-fluorescent composite film has excellent direct writing and erasing capabilities. In addition, as an ionic liquid, when acrylate quaternary ammonium salt (methacrylate quaternary ammonium salt) is compounded into the film, the resulting film has better hydrophilicity. When writing, the aqueous solution can quickly and uniformly penetrate into the film, thereby inhibiting the internal stress deformation caused by the uneven diffusion of water in the film.

[0050] In the composition of the flexible structural color-fluorescent composite film, the CNC is prepared from cellulose by a mature sulfuric acid hydrolysis method, and its mass fraction is not less than 50% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt).

[0051] In the composition of the flexible structural color-fluorescent composite film, the PEGDA and PEGDMA have an average relative molecular mass of 200 g / mol to 4000 g / mol, and a mass fraction of 5% to 30% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt), and their structural formulas are shown as follows:

[0052] 。

[0053] In the composition of the flexible structural color-fluorescent composite film, the surfactant is alkyl sulfate, alkyl sulfonate, alkyl benzene sulfonate, and its mass fraction is 0% to 8% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt), and the alkyl group is an alkyl group with 8 to 18 carbon atoms.

[0054] In the composition of the flexible structural color-fluorescent composite film, the coumarin compound is any one of the following structural formulas (I) to (IV), and its mass fraction is 0.5% to 7.5% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt):

[0055] 。

[0056] In the composition of the flexible structural color-fluorescent composite film, the photoinitiator is any commercially available general ultraviolet photoinitiator, and its mass fraction is 0.5% to 4.5% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt).

[0057] In the composition of the flexible structural color-fluorescent composite film, the acrylate quaternary ammonium salt and methacrylate quaternary ammonium salt have the following structures:

[0058] ;

[0059] Among them, m is an integer from 1 to 4, R 1 is H or methyl, and R 2 , R 3 and R 4 are methyl, ethyl, propyl, butyl, benzyl, and R 2 , R 3 and R 4 can be the same or different, and X is chlorine or bromine.

[0060] In addition, the present invention also provides a preparation method of the flexible structural color-fluorescent composite film having time-dependence and repeatable writing / erasing ability as described above. The method includes the following steps:

[0061] (1) Add the water-dispersed CNC suspension, polyethylene glycol diacrylate PEGDA (polyethylene glycol dimethacrylate PEGDMA), surfactant, coumarin compound, and photoinitiator into a sealable container according to the required mass, and then perform magnetic stirring at room temperature until the coumarin compound is completely dissolved (or fully dispersed) to form a uniform mixed suspension;

[0062] (2) Pour the uniformly stirred mixed suspension into a petri dish, and naturally place the petri dish at room temperature until the mixed suspension is completely dried into a film with structural color;

[0063] (3) Place the obtained film with structural color under ultraviolet light for cross-linking reaction to form a cross-linked flexible structural color-fluorescent composite film I;

[0064] (4) Prepare an immersion solution with a certain concentration by taking the required mass of polyethylene glycol diacrylate PEGDA (polyethylene glycol dimethacrylate PEGDMA), acrylate quaternary ammonium salt (methacrylate quaternary ammonium salt), photoinitiator, dimethyl sulfoxide DMSO, and water;

[0065] (5) Immerse the crosslinked flexible structural color-fluorescent composite film I obtained in step (3) in the immersion solution;

[0066] (6) After the immersion is completed, take out the film, rinse the surface with ethanol, and then place it under ultraviolet light for a secondary crosslinking reaction to obtain a quaternary ammonium salt-treated crosslinked flexible structural color-fluorescent composite film II.

[0067] As the preparation method of the flexible structural color-fluorescent composite film described in the present invention, in the step (1), the water-dispersed CNC suspension is prepared from cellulose by a mature sulfuric acid hydrolysis method, and its mass fraction is not less than 50% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt);

[0068] As the preparation method of the flexible structural color-fluorescent composite film described in the present invention, in the step (1), PEGDA and PEGDMA, with an average relative molecular mass of 200 g / mol to 4000 g / mol, and a mass fraction of 5% to 30% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt), and their structural formulas are shown as follows:

[0069] .

[0070] As the preparation method of the flexible structural color-fluorescent composite film described in the present invention, in the step (1), the surfactant is alkyl sulfate, alkyl sulfonate, or alkyl benzene sulfonate, with a mass fraction of 0% to 8% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt), and the alkyl is an alkyl group with 8 to 18 carbon atoms.

[0071] As the preparation method of the flexible structural color-fluorescent composite film described in the present invention, in the step (1), the coumarin compound is any one of the following structural formulas (I) to (IV), and its mass fraction is 0.5% to 7.5% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt):

[0072] .

[0073] As the preparation method of the flexible structural color-fluorescent composite film described in the present invention, in the step (1), the photoinitiator is any commercially available general ultraviolet photoinitiator, and its mass fraction is 0.5% to 4.5% (excluding the mass of acrylate quaternary ammonium salt or methacrylate quaternary ammonium salt).

[0074] As the preparation method of the flexible structural color-fluorescent composite film described in the present invention, in the step (3), the ultraviolet irradiation time is related to the light intensity and is not specifically limited, as long as the film can be crosslinked and has good flexibility.

[0075] As the preparation method of the flexible structural color-fluorescent composite film of the present invention, in the step (4), PEGDA and PEGDMA, with an average relative molecular mass of 200 g / mol to 4000 g / mol and a mass fraction of 0.5% to 5%, have the structural formulas as shown below:

[0076] .

[0077] As the preparation method of the flexible structural color-fluorescent composite film of the present invention, in the step (4), acrylate quaternary ammonium salt and methacrylate quaternary ammonium salt, with a mass fraction of 10% to 60%, have the structures as shown below:

[0078] ;

[0079] Among them, m is an integer from 1 to 4, R 1 is H or methyl, and R 2 , R 3 and R 4 are methyl, ethyl, propyl, butyl, benzyl, and R 2 , R 3 and R 4 can be the same or different, and X is chlorine or bromine.

[0080] As the preparation method of the flexible structural color-fluorescent composite film of the present invention, in the step (4), the photoinitiator is any commercially available general ultraviolet photoinitiator, with a mass fraction of 0.1% to 1%.

[0081] As the preparation method of the flexible structural color-fluorescent composite film of the present invention, in the step (4), except for PEGDA and PEGDMA, acrylate quaternary ammonium salt and methacrylate quaternary ammonium salt, and photoinitiator, the remaining components are DMSO and / or water, and the ratio between the two is not limited.

[0082] As the preparation method of the flexible structural color-fluorescent composite film of the present invention, in the step (5), the soaking time is 6 to 72 hours, and reduced pressure (even vacuum) soaking can be adopted as needed.

[0083] As the preparation method of the flexible structural color-fluorescent composite film of the present invention, in the step (6), the ultraviolet light irradiation time does not exceed 0.5 hours.

[0084] As the preparation method of the flexible structural color-fluorescent composite film of the present invention, the steps (4) to (6) can be discarded according to actual needs, and the film I obtained in the step (3) and / or the film II obtained in the step (6) are both the flexible structural color-fluorescent composite film of the present invention.

[0085] The flexible structural color-fluorescent composite film of the present invention has good flexibility and mechanical properties, and the structural color is distinct and uniform. On the one hand, when infiltrated with a dilute alkali solution, it can exhibit obvious time-dependent blue fluorescence under ultraviolet light. After further infiltrating with a dilute acid solution, the fluorescence immediately disappears, showing the characteristics of repeatable writing / erasing. On the other hand, when irradiating the flexible structural color-fluorescent composite film with ultraviolet light by using a mask method, the template pattern can be transferred onto the film to achieve photoinduced patterning. Therefore, the flexible structural color-fluorescent composite film as described above in the present invention can be used as a new type of CNC-based information storage and encryption anti-counterfeiting functional material application.

[0086] Example

[0087] The technical solutions of the present application will be clearly and completely described below in combination with the embodiments of the present application. Unless otherwise specified, the reagents and raw materials used can be purchased through commercial channels. The experimental methods without specific conditions specified in the following examples are carried out according to conventional methods and conditions, or selected according to the product instructions.

[0088] Example 1

[0089] Take 50 g of a CNC suspension with a mass concentration of about 2.1% in a glass bottle with a lid. Add 1 g of PEGDA with a mass concentration of 25% (average relative molecular mass of 1000 g / mol), 1 g of sodium dodecyl sulfate with a mass concentration of 5%, 0.05 g of a coumarin compound (structural formula IV as described above), and 0.025 g of photoinitiator I2959. Then cover the bottle cap and magnetically stir at room temperature until the coumarin compound is completely dissolved. Thereafter, pour the mixed suspension into a plastic petri dish with a diameter of about 115 mm and naturally volatilize at room temperature until it is completely dried into a film with structural color. Finally, place the plastic petri dish with the structural color film under ultraviolet light of 365 nm for cross-linking reaction for 15 min to obtain the flexible structural color-fluorescent composite film I.

[0090] Example 2

[0091] Take 50 g of a CNC suspension with a mass concentration of approximately 2.1% in a glass bottle with a lid. Add 1 g of PEGDA with a mass concentration of 25% (average relative molecular mass of 1000 g / mol), 1 g of sodium dodecyl sulfate with a mass concentration of 5%, 0.05 g of a coumarin compound (structural formula IV as described above), and 0.025 g of photoinitiator I2959. Cover the bottle cap and magnetically stir at room temperature until the coumarin compound is completely dissolved. Then pour the mixed suspension into a plastic petri dish with a diameter of approximately 115 mm and allow it to naturally evaporate at room temperature until it is completely dry to form a film with structural color. Thereafter, place the plastic petri dish with the structural color film under ultraviolet light of 365 nm for a crosslinking reaction for 15 min to obtain the crosslinked flexible structural color-fluorescent composite film I. Additionally, take 50 g of acrylate quaternary ammonium salt with a mass concentration of 80% (structural formula as described above, m is 2, R 1 is H, R 2 , R 3 and R 4 are all methyl, and X is chlorine), 6.25 g of PEGDA with a mass concentration of 25% (average relative molecular mass of 1000 g / mol), 0.625 g of photoinitiator I2959, and 37.6 g of DMSO and 12.4 g of water to prepare a uniform immersion solution. Further, immerse the crosslinked flexible structural color-fluorescent composite film I in this immersion solution for 24 h, maintaining the vacuum degree not higher than -0.095 MPa. After immersion, rinse the film surface with ethanol and then irradiate it with ultraviolet light of 365 nm for 5 min. Thus, the described flexible structural color-fluorescent composite film II is obtained.

[0092] Example 3

[0093] Take 50 g of a CNC suspension with a mass concentration of approximately 2.1% in a glass bottle with a lid. Add 1 g of PEGDA with a mass concentration of 25% (average relative molecular mass of 1000 g / mol), 1 g of sodium octyl sulfate with a mass concentration of 5%, 0.01 g of a coumarin compound (structural formula III as described above), and 0.025 g of photoinitiator I2959. Cover the bottle cap and magnetically stir at room temperature until the coumarin compound is completely dissolved. Then pour the mixed suspension into a plastic petri dish with a diameter of approximately 115 mm and allow it to naturally evaporate at room temperature until it is completely dry to form a film with structural color. Thereafter, place the plastic petri dish with the structural color film under ultraviolet light of 365 nm for a crosslinking reaction for 15 min to obtain the crosslinked flexible structural color-fluorescent composite film I. Additionally, take 50 g of acrylate quaternary ammonium salt with a mass concentration of 80% (structural formula as described above, m is 2, R 1 is H, R 2 , R 3 and R 4All are methyl groups, X is chlorine), 6.25 g of PEGDA with a mass concentration of 25% (average relative molecular mass is 1000 g / mol), 0.625 g of photoinitiator I2959, 37.6 g of DMSO, and 12.4 g of water were formulated into a uniform immersion solution. Further, the crosslinked flexible structural color-fluorescent composite film I was immersed in this immersion solution for 24 h, keeping the vacuum degree not higher than -0.095 MPa. After immersion, the surface of the film was rinsed with ethanol, and then irradiated with 365 nm ultraviolet light for 5 min. Thus, the flexible structural color-fluorescent composite film II was obtained.

[0094] Example 4

[0095] Take 50 g of a CNC suspension with a mass concentration of about 2.1% in a glass bottle with a lid. Add 1 g of PEGDMA with a mass concentration of 25% (average relative molecular mass is 1000 g / mol), 1 g of sodium dodecyl sulfate with a mass concentration of 5%, 0.01 g of a coumarin compound (structural formula II as described above), and 0.025 g of photoinitiator I2959. Cover the bottle cap and magnetically stir at room temperature until the coumarin compound is completely dissolved. Then pour the mixed suspension into a plastic petri dish with a diameter of about 115 mm and naturally evaporate it at room temperature until it is completely dry to form a film with structural color. Thereafter, place the plastic petri dish with the structural color film on it under 365 nm ultraviolet light for a crosslinking reaction for 15 min to obtain the crosslinked flexible structural color-fluorescent composite film I.

[0096] Example 5

[0097] Take 50 g of a CNC suspension with a mass concentration of about 2.1% in a glass bottle with a lid. Add 1 g of PEGDMA with a mass concentration of 25% (average relative molecular mass is 1000 g / mol), 1 g of sodium dodecylbenzenesulfonate with a mass concentration of 5%, 0.01 g of a coumarin compound (structural formula I as described above), and 0.025 g of photoinitiator I2959. Cover the bottle cap and magnetically stir at room temperature until the coumarin compound is completely dissolved. Then pour the mixed suspension into a plastic petri dish with a diameter of about 115 mm and naturally evaporate it at room temperature until it is completely dry to form a film with structural color. Thereafter, place the plastic petri dish with the structural color film on it under 365 nm ultraviolet light for a crosslinking reaction for 15 min to obtain the crosslinked flexible structural color-fluorescent composite film I. Additionally, take 50 g of a methacrylate quaternary ammonium salt with a mass concentration of 80% (structural formula as described above, m is 2, R 1 is methyl, R 2 、R 3 and R 4All are methyl groups, X is chlorine), 6.25 g of PEGDMA with a mass concentration of 25% (average relative molecular mass of 1000 g / mol), 0.625 g of photoinitiator I2959, 37.6 g of DMSO, and 12.4 g of water were formulated into a uniform immersion solution. Further, the cross-linked flexible structural color-fluorescent composite film I was immersed in this immersion solution for 24 h, maintaining the vacuum degree not higher than -0.095 MPa. After immersion, the film surface was rinsed with ethanol and then irradiated with 365 nm ultraviolet light for 5 min. Thus, the flexible structural color-fluorescent composite film II was obtained.

[0098] Example 6

[0099] The basic properties of the flexible structural color-fluorescent composite film of the present invention.

[0100] The reflection spectra, stress-strain curves, and fluorescence spectra of the flexible structural color-fluorescent composite films prepared in Example 1 and Example 2 were respectively tested. The testing methods were as follows:

[0101] The reflection spectrum was obtained by testing in the reflection mode of a Lambda 750S type ultraviolet-visible-near-infrared spectrophotometer from PerkinElmer, USA. The testing wavelength range was 380 nm to 850 nm, and the data interval was 1 nm;

[0102] The stress-strain curve was obtained by testing with a universal electronic testing machine from MTS Systems, USA at room temperature;

[0103] The fluorescence spectrum was obtained by testing with a Fluorolog-QM type visualization steady-state and transient fluorescence spectrum measurement system from HORIBA, Japan. The excitation wavelength was 365 nm, the testing wavelength range was 400 nm to 600 nm, and the data interval was 1 nm.

[0104] The test results are shown in Appendix Figure 3 and Appendix Figure 4 as shown.

[0105] From Appendix Figure 1 and Appendix Figure 2 It can be seen that the preparation method of the present invention can obtain a flexible structural color-fluorescent composite film with uniform structural color and good apparent state. The film has distinct colors, can be directly written or pattern-drawn, and has good flexibility for folding.

[0106] From (a) in Appendix Figure 3 it can be seen that the flexible structural color-fluorescent composite film has obvious reflection peaks, which is consistent with its distinct colors; after being immersed twice in the acrylate quaternary ammonium salt solution, the reflection peaks are slightly red-shifted, proving that the acrylate quaternary ammonium salt has penetrated into the film interior, resulting in an increase in its helical pitch P. From AppendixFigure 3 As can be seen from Fig. (b), the flexible structural color-fluorescent composite film has an elongation at break exceeding 15%, and the tensile strength is about 15 MPa; after secondary immersion, the tensile strength increases significantly to about 24 MPa. Although the elongation at break decreases, it still has an elongation at break of about 10%. As shown in the appendix Figure 4 As can be seen, when infiltrated with an alkaline solution, the flexible structural color-fluorescent composite film exhibits obvious blue fluorescence under ultraviolet light excitation. When infiltrated with an acidic solution again, the blue fluorescence intensity decreases, and there is no obvious characteristic peak in the fluorescence spectrum. This indicates that the film can be directly written on with an alkaline solution, and the written content can be quickly erased with an acidic solution, and this process can be repeated. Further, as shown in the appendix Figure 5 shows the alkaline direct-write fluorescence pattern of the flexible structural color-fluorescent composite film, and the fluorescence intensity of the obtained pattern first increases and then decays, which proves the time-dependent fluorescence characteristics of the flexible structural color-fluorescent composite film. Based on the above performance results, it can be concluded that the flexible structural color-fluorescent composite film has good flexibility, distinct structural colors, and time-dependent blue fluorescence performance, and can be quickly and repeatedly erased by acid and alkaline solutions. This means it has the potential to be applied in the fields of information storage and anti-counterfeiting encryption.

[0107] Example 7

[0108] Application of the flexible structural color-fluorescent composite film of the present invention

[0109] As shown in the appendix Figure 6 and as shown in the appendix Figure 7 show application examples of the flexible structural color-fluorescent composite film as a functional material for information storage and anti-counterfeiting encryption. As can be seen from the appendix Figure 6 It can be found that by using the mask method, a two-dimensional code pattern with graphic and text information recorded can be transferred onto the flexible structural color-fluorescent composite film by ultraviolet light. This two-dimensional code can be directly scanned and recognized by a mobile phone to obtain the recorded two-dimensional code information, indicating that the flexible structural color-fluorescent composite film can be used for information storage. As can be seen from the appendix Figure 7 It can be known that the ciphertext is hidden onto the flexible structural color-fluorescent composite film by using binary coding. After infiltration with an alkaline solution, the coded ciphertext can be clearly identified under ultraviolet light, and then the encrypted information can be extracted by decoding. This example shows that the flexible structural color-fluorescent composite film can be used as an information anti-counterfeiting encryption material.

[0110] The above description of the embodiments is to enable those of ordinary skill in the art to understand and apply this application. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, this application is not limited to the embodiments herein, and all improvements and modifications made by those skilled in the art within the scope and spirit of this application based on the disclosure of this application are within the scope of this application.

Claims

1. A method for preparing a time-dependent and rewritable flexible cellulose nanocrystal composite film, characterized in that: The preparation method comprises the following steps: Step S1: preparing a cellulose nanocrystal film with structural color; A water-dispersible cellulose nanocrystal suspension, a first crosslinking agent, a first surfactant, a coumarin compound and a first photoinitiator of required weight are mixed to form a uniform mixed suspension, and a cellulose nanocrystal film with structural color is obtained after drying; the coumarin compound is one or more of the compounds described in the following structural formulas (I) to (IV): ； Step S2: preparing a time-dependent and rewritable flexible cellulose nanocrystal composite film; placing the structurally colored cellulose nanocrystal film obtained in step S1 under ultraviolet light for a first crosslinking reaction to obtain the time-dependent and repeatedly erasable flexible cellulose nanocrystal composite film; Step S3: preparing a time-dependent and rewritable flexible cellulose nanocrystal composite film treated with quaternary ammonium salt; Soaking the time-dependent and repeatedly erasable flexible cellulose nanocrystal composite membrane obtained in step S2 with an immersion liquid for 6 to 72 hours, and then placing it under ultraviolet light for a second crosslinking reaction, and the ultraviolet light irradiation time does not exceed 0.5 hours, to obtain a quaternary ammonium salt-treated time-dependent and repeatedly erasable flexible cellulose nanocrystal composite membrane; Wherein, the soaking liquid is made of a second cross-linking agent, a quaternary ammonium salt ionic liquid, a second photoinitiator and an aqueous mixed solvent, the mass fraction of the second cross-linking agent in the total mass of the raw materials added in this step is 0.5% to 5%; the mass fraction of the second photoinitiator in the total mass of the raw materials added in this step is 0.1% to 1%; the mass fraction of the quaternary ammonium salt ionic liquid in the total mass of the raw materials added in this step is 10% to 60%, and the structure of the quaternary ammonium salt ionic liquid is shown as follows: ； wherein m is 2, R1 is H, R2, R3 and R4 are methyl, and X is chlorine or bromine; In the composition of the flexible cellulose nanocrystal composite film, excluding the mass of the quaternary ammonium salt ionic liquid, the mass fraction of the cellulose nanocrystals is not less than 50%, the mass fraction of the first cross-linking agent and the second cross-linking agent is 5%~30%, the mass fraction of the first surfactant is 0%~8%, the mass fraction of the coumarin compound is 0.5%~7.5%, and the mass fraction of the first photoinitiator and the second photoinitiator is 0.5%~4.5%.

2. The preparation method according to claim 1, characterized in that In step S1, a water-dispersed cellulose nanocrystal suspension is prepared from cellulose by a well-established sulfuric acid hydrolysis method.

3. The preparation method according to claim 1 or 2, characterized in that: In step S1, the first cross-linking agent is one or both of polyethylene glycol diacrylate and polyethylene glycol dimethacrylate, and the average relative molecular mass of the first cross-linking agent is 200 g / mol-4000 g / mol; In step S1, the first surfactant is at least one of an alkyl sulfate having 8 to 18 carbon atoms, an alkyl sulfonate having 8 to 18 carbon atoms, and an alkylbenzene sulfonate having 8 to 18 carbon atoms; In step S1, the first photoinitiator is any commercially available universal ultraviolet photoinitiator.

4. The preparation method according to claim 1 or 2, characterized in that: In step S3, the second cross-linking agent is one or both of polyethylene glycol diacrylate and polyethylene glycol dimethacrylate, and the average relative molecular mass of the second cross-linking agent is 200 g / mol-4000 g / mol; In step S3, the second photoinitiator is any commercially available universal ultraviolet photoinitiator; In step S3, the aqueous mixed solvent is a mixture of water and dimethyl sulfoxide.

5. The preparation method according to claim 1 or 2, characterized in that: In step S3, reduced pressure or vacuum immersion is adopted.

6. A time-dependent and rewritable flexible cellulose nanocrystal composite film, which is prepared by the preparation method according to any one of claims 1 to 5.

7. An information storage material comprising the time-dependent and repeatedly erasable flexible cellulose nanocrystal composite film as claimed in claim 6.

8. An anti-counterfeiting encryption material comprising the time-dependent and repeatedly erasable flexible cellulose nanocrystal composite film as claimed in claim 6.

9. An anti-counterfeiting encryption method, characterized in that: The anti-counterfeiting encryption method comprises the following steps: storing the information to be hidden on the anti-counterfeiting encryption material as claimed in claim 8, then soaking the anti-counterfeiting encryption material with an alkaline solution, and displaying the information to be hidden under ultraviolet light.

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