Flexible structural color composite film with humidity response characteristic as well as preparation method and application of flexible structural color composite film

Abstract

The invention provides a flexible structural color composite film with a humidity response characteristic as well as a preparation method and application of the flexible structural color composite film. According to the invention, hydroxy propyl cellulose and D-glucose are simultaneously introduced into a cellulose nanocrystal suspension, and the composite membrane prepared by an evaporation-induced self-assembly method has the characteristics of ultrahigh flexibility, rapid humidity response and good cyclic response performance. The composite film can be applied to the fields of humidity visibility detection, intelligent packaging and the like. The raw materials selected by the invention are all from biomass materials, are green and environment-friendly, and are degradable; the preparation process of the structural color composite film is realized in a water environment, high temperature is not needed in the reaction process, and the preparation method has the characteristics of mild reaction conditions and simplicity in operation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional film material preparation, and particularly relates to a flexible structural color composite film with humidity response characteristics and a preparation method and application thereof. BACKGROUND

[0002] The color diversity of nature is divided into two categories: chemical color and structural color. Chemical color depends on the light absorption and reflection of specific pigment molecules, providing biological bodies with diversified color performance. However, they usually lack color durability and environmental friendliness. Structural color is a kind of color between natural light and microstructure optical interaction, and widely exists in nature, most of which involve nanoscale periodic photonic crystal structure or composite film interference mechanism. However, traditional photonic materials (such as silica and polystyrene colloidal crystals) face double challenges: on the one hand, they rely on high energy consumption preparation process, and on the other hand, they are based on non-renewable petroleum-based materials, which is difficult to meet the demand of sustainable development.

[0003] Among the many candidates of biomimetic structural color, cellulose nanocrystals (CNC) have attracted considerable attention due to their wide sustainable sources, excellent physicochemical properties and remarkable compatibility with biological bodies. At the same time, the optical transparency, thermal stability, crystallinity and high specific surface area of CNC enable them to exhibit special structural color. For example, cellulose nanocrystal suspension can form a composite film with cholesteric phase structure by evaporation-induced self-assembly at a certain concentration, which exhibits bright color in appearance. However, there are two difficulties in cellulose nanocrystal-based structural color composite films: 1. The flexibility of the composite film is not good, which affects the actual application field; 2. The rapid response ability to the environment is not strong, which limits its application range. SUMMARY

[0004] In order to improve the deficiencies existing in the prior art, the present application provides a flexible structural color composite film with humidity response characteristics and a preparation method and application thereof. The present application introduces hydroxypropyl cellulose and D-glucose into cellulose nanocrystal suspension at the same time, and the composite film prepared by the method of evaporation-induced self-assembly has the characteristics of super-high flexibility, rapid humidity response and good cycle response performance. The composite film can be applied in humidity visibility detection, intelligent packaging and other fields.

[0005] The purpose of the present application is achieved by the following technical scheme:

[0006] A preparation method of a flexible structural color composite film with humidity response characteristics, the method comprising the following steps:

[0007] (1) mixing cellulose nanocrystal suspension and hydroxypropyl cellulose solution to obtain a first mixed solution;

[0008] (2) adding glycerol into the first mixed solution to obtain a second mixed solution;

[0009] (3) adding a D-glucose solution into the second mixed solution to obtain a third mixed solution;

[0010] (4) forming a film by evaporative-induced self-assembly of the third mixed solution to obtain the structural color composite film.

[0011] According to an embodiment of the present application, in step (1), the cellulose nanocrystal suspension is a suspension of cellulose nanocrystals in water; the concentration of the cellulose nanocrystal suspension is 3-8 wt%, for example, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt%. The cellulose nanocrystal suspension can be prepared by a method known in the art or purchased through commercial channels.

[0012] According to an embodiment of the present application, in step (1), the cellulose nanocrystal has a length of 60-300 nm, such as 60 nm, 100 nm, 140 nm, 180 nm, 220 nm, 260 nm or 300 nm; and a diameter of 4-19 nm, such as 5 nm, 10 nm, 15 nm or 19 nm.

[0013] According to an embodiment of the present application, in step (1), the hydroxypropyl cellulose solution is an aqueous solution of hydroxypropyl cellulose; the concentration of the hydroxypropyl cellulose solution is 2-8 wt%, for example, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt%. The hydroxypropyl cellulose solution can be prepared by a method known in the art or purchased through commercial channels.

[0014] According to an embodiment of the present application, in step (1), the hydroxypropyl cellulose solution is first stirred and ultrasonically mixed before mixing, i.e. stirring at room temperature for 6-12 hours and then ultrasonic mixing for 5-10 minutes, with the power of ultrasonic mixing being 400-600 W.

[0015] According to an embodiment of the present application, in step (1), the mixing is ultrasonic stirring and mixing; for example, the hydroxypropyl cellulose solution is added to the cellulose nanocrystal suspension, ultrasonic mixing for 2-5 minutes and then stirring at room temperature for 12-24 hours, with the power of ultrasonic mixing being 300-500 W.

[0016] According to an embodiment of the present application, in step (1), the mass ratio of the cellulose nanocrystal to the hydroxypropyl cellulose is 96:4-80:20, for example, 96:4, 95:5, 90:10, 85:15 or 80:20.

[0017] According to an embodiment of the present application, in step (2), the glycerol is added to the first mixed solution as a plasticizer, and the introduction of the glycerol can not only improve the flexibility of the composite film, but also absorb moisture to some extent, thereby improving the humidity response sensitivity of the composite film.

[0018] According to an embodiment of the present application, in step (2), the glycerol is added dropwise to the first mixed solution, and the second mixed solution is obtained after uniform mixing.

[0019] According to an embodiment of the present application, in step (2), the mixing is stirring at room temperature for 6-12 hours.

[0020] According to an embodiment of the present application, in step (2), the mass ratio of the glycerol to the first mixed solution is 0.057-0.57:100, for example, 0.057:100, 0.06:100, 0.07:100, 0.08:100, 0.09:100, 0.1:100, 0.15:100, 0.2:100, 0.25:100, 0.3:100, 0.35:100, 0.4:100, 0.45:100, 0.5:100, 0.55:100 or 0.57:100.

[0021] According to an embodiment of the present application, in step (3), the D-glucose solution is an aqueous solution of D-glucose; the concentration of the D-glucose solution is 5-15 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%. The D-glucose solution can be prepared by a method known in the art or purchased through a commercial channel.

[0022] According to an embodiment of the present application, in step (3), the mass of the D-glucose accounts for 5%-50% of the total mass of the D-glucose, the cellulose nanocrystal and the hydroxypropyl cellulose, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%; that is, the D-glucose is 5-50 parts by mass, and the total mass of the D-glucose, the cellulose nanocrystal and the hydroxypropyl cellulose is 100 parts by mass.

[0023] According to an embodiment of the present application, in step (3), the mixing is stirring at room temperature for 6-12 hours.

[0024] According to an embodiment of the present application, in step (4), the film formation by the method of evaporation-induced self-assembly means that the third mixed solution is placed in a mold, and then the solvent in the third mixed solution is volatilized to form a film under the condition that the temperature is 15-25℃ and the dry humidity is 25-35%.

[0025] According to an embodiment of the present application, in step (4), the evaporation-induced self-assembly is carried out at a temperature of 15-25℃ and a humidity of 25-35%.

[0026] The present application also provides the flexible structural color composite film with humidity response prepared by the above method.

[0027] According to an embodiment of the present application, the structural color composite film comprises cellulose nanocrystals, hydroxypropyl cellulose and D-glucose.

[0028] According to an embodiment of the present application, the structural color composite film has a chiral nematic structure.

[0029] According to an embodiment of the present application, in the structural color composite film, the cellulose nanocrystals, the hydroxypropyl cellulose and the D-glucose are connected through hydrogen bonding.

[0030] According to an embodiment of the present application, the thickness of the structural color composite film is 0.08-0.12mm.

[0031] According to an embodiment of the present application, the inside of the structural color composite film presents a helical structure.

[0032] The present application also provides the use of the flexible structural color composite film with humidity response as described above in the fields of humidity visual detection, intelligent packaging, etc.

[0033] The present application has the following advantages:

[0034] 1) The raw materials used in the present application are all derived from biomass materials, which are green, environmentally friendly and biodegradable; the preparation process of the structural color composite film of the present application is realized in a water environment, and the reaction process does not require high temperature, which has the characteristics of mild reaction conditions and simple operation;

[0035] 2) The structural color composite film of the present application has ultra-high flexibility and humidity response performance, can quickly respond to changes in humidity in the environment, has good repeatability, and has commercial production potential;

[0036] 3) The composite film of the present application has bright structural color, and the inside of the film presents a helical structure; with the change of humidity, the pitch changes, thereby changing the color of the composite film; the composite film can quickly switch colors under different humidity, and has good reversibility;

[0037] 4) The composite film of the present application has excellent flexibility, the elongation at break is increased by 79 times, and can maintain a chiral nematic structure, which is easy to industrialize. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The stress-strain curve of the composite film prepared in Example 1-5 is shown in the figure.

[0039] Figure 2 Stress-strain curve of the composite film prepared for Comparative Example 1-2;

[0040] Figure 3 TEM image of the composite film prepared for Example 4;

[0041] Figure 4 Polarized light microscope image of the composite film prepared for Example 1;

[0042] Figure 5 Reflectance spectra of the composite films prepared for Examples 1-5;

[0043] Figure 6 Circular dichroism spectra of the composite films prepared for Examples 1-5;

[0044] Figure 7 Photos of the composite film prepared for Example 2 showing color at different humidity;

[0045] Figure 8 Reflectance spectra of the composite film prepared for Example 2 at different humidity;

[0046] Figure 9 Reversible humidity response of the composite film prepared for Example 2 in 10 consecutive cycles between 32% and 86% relative humidity.

[0047] Figure 10 Humidity response range (determined at 32% and 86% relative humidity) of the composite films prepared for Example 2 and Comparative Example 1-3 based on the shift of the peak of UV-Vis reflectance. DETAILED DESCRIPTION

[0048] The preparation method of the present application will be further described in detail below in connection with specific examples. It should be understood that the following examples are only illustratively and explain the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology achieved based on the above description of the present application is covered within the scope intended to be protected by the present application.

[0049] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0050] The cellulose nanocrystal suspension used in the following examples is a suspension formed by cellulose nanocrystals in water; the hydroxypropyl cellulose solution used in the following examples is an aqueous solution of hydroxypropyl cellulose; the D-glucose solution used in the following examples is an aqueous solution of D-glucose.

[0051] Example 1:

[0052] 1) Take 33.25 ml of cellulose nanocrystal suspension with a mass concentration of 3 wt%, disperse 1.75 g of hydroxypropyl cellulose solution with a mass concentration of 3 wt% in the above solution by ultrasonic wave, and add 0.04 ml of glycerol as a plasticizer drop by drop, and stir the mixed solution to be uniform.

[0053] 2) Add 1.17 g of D-glucose solution with a mass concentration of 10 wt% to the above mixed solution and mix well.

[0054] 3) The mixed solution is formed into a film by the method of evaporation-induced self-assembly (temperature 15-25°C, humidity 25-35%), to obtain a cellulose nanocrystal / hydroxypropyl cellulose / D-glucose composite film (denoted as CHG10), with a film thickness of 0.08-0.1 mm.

[0055] Example 2:

[0056] 1) Take 33.25 ml of cellulose nanocrystal suspension with a mass concentration of 3 wt%, disperse 1.75 g of hydroxypropyl cellulose solution with a mass concentration of 3 wt% in the above solution by ultrasonic wave, and add 0.04 ml of glycerol as a plasticizer drop by drop, and stir the mixed solution to be uniform.

[0057] 2) Add 2.63 g of D-glucose solution with a mass concentration of 10 wt% to the above mixed solution and mix well.

[0058] 3) The mixed solution is formed into a film by the method of evaporation-induced self-assembly (temperature 15-25°C, humidity 25-35%), to obtain a cellulose nanocrystal / hydroxypropyl cellulose / D-glucose composite film (denoted as CHG20), with a film thickness of 0.08-0.1 mm.

[0059] Example 3:

[0060] 1) Take 33.25 ml of cellulose nanocrystal suspension with a mass concentration of 3 wt%, disperse 1.75 g of hydroxypropyl cellulose with a mass concentration of 3 wt% in the above solution by ultrasonic wave, and add 0.04 ml of glycerol as a plasticizer drop by drop, and stir the mixed solution to be uniform.

[0061] 2) Add 4.5 g of D-glucose solution with a mass concentration of 10 wt% to the above mixed solution and mix well.

[0062] 3) The mixed solution is formed into a film by the method of evaporation-induced self-assembly (temperature 15-25°C, humidity 25-35%), to obtain a cellulose nanocrystal / hydroxypropyl cellulose / D-glucose composite film (denoted as CHG30), with a film thickness of 0.08-0.11 mm.

[0063] Example 4:

[0064] 1) Take 33.25 ml of cellulose nanocrystal suspension with a mass concentration of 3 wt%, disperse 1.75 g of hydroxypropyl cellulose with a mass concentration of 3 wt% in the above solution by ultrasonic wave, and add 0.04 ml of glycerol as a plasticizer drop by drop, and stir the mixed solution to be uniform.

[0065] 2) Add 7 g of D-glucose solution with a mass concentration of 10 wt% to the above mixed solution and mix well.

[0066] 3) The mixed solution is formed into a film by the method of evaporation-induced self-assembly (temperature 15-25°C, humidity 25-35%), to obtain a cellulose nanocrystal / hydroxypropyl cellulose / D-glucose composite film (marked as CHG40), with a film thickness of 0.09-0.12 mm.

[0067] Example 5:

[0068] 1) Take 33.25 ml of cellulose nanocrystal suspension with a mass concentration of 3 wt%, disperse 1.75 g of hydroxypropyl cellulose with a mass concentration of 3 wt% in the above solution by ultrasonic wave, and add 0.04 ml of glycerol as a plasticizer drop by drop, and stir the mixed solution to be uniform.

[0069] 2) Add 10.5 g of D-glucose solution with a mass concentration of 10 wt% to the above mixed solution and mix well.

[0070] 3) The mixed solution is formed into a film by the method of evaporation-induced self-assembly (temperature 15-25°C, humidity 25-35%), to obtain a cellulose nanocrystal / hydroxypropyl cellulose / D-glucose composite film (marked as CHG50), with a film thickness of 0.09-0.12 mm.

[0071] Comparative Example 1:

[0072] 1) Take 33.25 ml of cellulose nanocrystal suspension with a mass concentration of 3 wt%, disperse 1.75 g of hydroxypropyl cellulose with a mass concentration of 3 wt% in the above solution by ultrasonic wave, and add 0.04 ml of glycerol as a plasticizer drop by drop, and stir the mixed solution to be uniform.

[0073] 2) The mixed solution is formed into a film by the method of evaporation-induced self-assembly (temperature 15-25°C, humidity 25-35%), to obtain a cellulose nanocrystal / hydroxypropyl cellulose composite film (marked as CNC / HPC), with a film thickness of 0.09-0.11 mm.

[0074] Comparative Example 2:

[0075] 1) Take 33.25 ml of cellulose nanocrystal suspension with a mass concentration of 3 wt%, and add 0.04 ml of glycerol as a plasticizer drop by drop, and stir the mixed solution to be uniform.

[0076] 2) 7 g of a D-glucose solution with a mass concentration of 10 wt% was added to the above mixture and mixed evenly.

[0077] 3) The mixture was formed into a film by an evaporation-induced self-assembly method (temperature 15-25°C, humidity 25-35%), to obtain a cellulose nanocrystal / D-glucose composite film (denoted as CNC / Glu40), with a film thickness of 0.09-0.11 mm.

[0078] Comparative Example 3:

[0079] 1) 33.25 ml of a cellulose nanocrystal suspension with a mass concentration of 3 wt% was added dropwise to 0.04 ml of glycerol as a plasticizer, and the mixed solution was stirred until uniform.

[0080] 2) The mixture was formed into a film by an evaporation-induced self-assembly method (temperature 15-25°C, humidity 25-35%), to obtain a cellulose nanocrystal composite film (denoted as CNC), with a film thickness of 0.08-0.10 mm.

[0081] Test Example 1

[0082] The above-prepared composite films were subjected to ultraviolet-visible-near infrared (UV-vis-NIR), mechanical property, and humidity response performance tests, and the test results are shown in Figures 1-10 .

[0083] Figure 1 The stress-strain curve of the composite film prepared in Example 1-5 is shown in Figure 2 The stress-strain curve of the composite film prepared in Comparative Examples 1-3 is shown in The mechanical properties of the composite films of Examples 1-5 and Comparative Examples 1-3 were evaluated by tensile testing, and it can be seen from Figure 1 and Figure 2 that, compared with the pure CNC film, the elongation at break of the composite films of Examples 1-5 was significantly improved, thanks to the hydrogen bond synergy between cellulose nanocrystals (CNC), hydroxypropyl cellulose (HPC), and D-glucose (Glu). With the increase of the Glu content from 10% to 50%, the elongation at break of the composite films of Examples 1-5 increased from 2.6±0.1% to 58.8±4.3%. It can be seen that, compared with the pure CNC film, the composite film of the present application exhibits unique plasticity, which may be due to the presence of hydroxypropyl cellulose and D-glucose, which improves energy dissipation.

[0084] Compared with the composite film CNC / HPC of Comparative Example 1 or the composite film CNC / Glu40 of Comparative Example 2, the flexibility of the composite film of Examples 1-5 is obviously improved, which is mainly attributed to the plasticization between CNC, HPC and Glu, the formation of appropriate hydrogen bonds, and the synergistic effect in the system is more conducive to improving the flexibility of the composite film. When co-assembled with HPC, CNC does not cause obvious inelastic deformation, and the elongation at break of the prepared binary composite film CNC / HPC is 1.1±0.2%. After further adding Glu in the binary composite film CNC / HPC, obvious yield and gradually enhanced ductility appear, and the composite film CHG40 of Example 4 has both flexibility and good optical performance, and the elongation at break thereof is about 25.3±2.5%.

[0085] Figure 3 The electron microscope image of the composite film prepared in Example 4; from Figure 3 It can be seen that, by observing the SEM image of the cross section of the composite film, it can be confirmed that the chiral nematic structure is retained in the composite film.

[0086] Figure 4 The polarizing microscope image of the composite film prepared in Example 1; from Figure 4 It can be seen that the composite film shows very obvious birefringence under the polarizing microscope, and the fingerprint texture area is clear.

[0087] Figure 5 The reflection spectrum of the composite film prepared in Examples 1-5 and Comparative Example 3; from Figure 5 It can be seen that the spectral peak of the pure CNC film is relatively narrow, mainly concentrated in the range of 300-600 nm, and the highest point is near 410 nm, indicating that the pure CNC film has strong selective reflection to the light in the range of 300-600 nm. With the increase of the content of Glu (from 10% to 50%), the maximum reflection wavelength of the composite film increases from 530 to 906 nm. Among them, the reflection wavelength of the CHG50 composite film exceeds the visible spectrum. In addition, the spectral peak gradually becomes wide, and its intensity also decreases with the addition of Glu, indicating that the helical structure is gradually destroyed.

[0088] Figure 6 The circular dichroism spectrum of the composite film prepared in Examples 1-5 and Comparative Example 3; from Figure 6 It can be seen that the composite film also shows strong positive signals in the circular dichroism (CD) spectrum, indicating that the composite film is a left-handed structure. The composite film of the present application shows a positive CD peak similar to that of the pure CNC film, and with the increase of the addition amount of Glu from 10% to 50%, the CD peak shows a significant red shift from 491 nm to 826 nm. It is similar to the law shown in the UV-vis-NIR spectrum, which further proves that the chiral nematic structure is retained in the composite film.

[0089] Figure 7 Photos of the composite film prepared in Example 2 showing color at different humidity; from Figure 7 It can be seen that the color of the composite film red-shifts with increasing humidity.

[0090] Figure 8 Reflectance spectra of the composite film prepared in Example 2 at different humidity; from Figure 8 It can be seen that the color of the composite film at different humidity is characterized by UV-vis-NIR spectra. The results show that the peak wavelength of the composite film increases from 604 nm to 768 nm as the humidity increases from 32% to 86%, which is consistent with the results of Figure 7 .

[0091] Figure 9 Reversible humidity response of the composite film prepared in Example 2 in 10 consecutive cycles between 32% and 86% relative humidity; from Figure 9 It can be seen that to test the humidity cycle responsiveness of the composite film, it is alternately exposed to 32% and 86% humidity for 10 times. The peak of the reflected wavelength shown by the UV-vis-NIR spectra shows a repeatable and reversible change, indicating that the composite film has excellent stability and reversibility.

[0092] Figure 10 Humidity response range (determined at 32% and 86% relative humidity) of the composite films prepared in Example 2 and Comparative Examples 1-3 based on the peak shift of UV-visible spectrum reflectance; from Figure 10 It can be seen that to determine the humidity response of the composite film, the optical shift of the humidity response of the film is tested at 32% and 86% relative humidity, and the results show that the composite film prepared in Example 2 has a wider humidity response range (Δλ≈164 nm), which is better than the humidity response range of the composite films prepared in Comparative Examples 1-3, i.e. the humidity response performance of the ternary film is better than that of the pure CNC film and the binary films (CNC / HPC, CNC / Glu).

[0093] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a flexible structural color composite film with humidity responsive property, the method comprising the following steps: (1) mixing a cellulose nanocrystal suspension and a hydroxypropyl cellulose solution to obtain a first mixture; (2) adding glycerol to the first mixture, and mixing uniformly to obtain a second mixture; (3) adding a D-glucose solution to the second mixture, and mixing uniformly to obtain a third mixture; (4) forming a film from the third mixture by an evaporation-induced self-assembly method to prepare the structural color composite film.

2. The production method according to claim 1, wherein, In step (1), the cellulose nanocrystal suspension is a suspension of cellulose nanocrystals in water; the concentration of the cellulose nanocrystal suspension is 3-8 wt%; and / or, in step (1), the hydroxypropyl cellulose solution is an aqueous solution of hydroxypropyl cellulose; the concentration of the hydroxypropyl cellulose solution is 2-8 wt%.

3. The production method according to claim 1 or 2, wherein In step (1), the mass ratio of the cellulose nanocrystal and the hydroxypropyl cellulose is 96:4-80:

20.

4. The production process according to any one of claims 1 to 3, wherein In step (2), the mass ratio of the glycerol to the first mixture is 0.057-0.57:

100.

5. The production process according to any one of claims 1 to 4, wherein In step (3), the D-glucose solution is an aqueous solution of D-glucose; the concentration of the D-glucose solution is 5-15 wt%.

6. The production process according to any one of claims 1 to 5, wherein In step (3), the mass of the D-glucose accounts for 5%-50% of the total mass of D-glucose, cellulose nanocrystal and hydroxypropyl cellulose.

7. The method of making according to any one of claims 1-6, wherein, In step (4), the evaporation-induced self-assembly conditions are: temperature 15-25℃, humidity 25-35%. 8.The flexible structural color composite film with humidity responsive property prepared by the method of any one of claims 1-7.

9. The flexible structural color composite film of claim 8, wherein, The structural color composite film comprises cellulose nanocrystal, hydroxypropyl cellulose and D-glucose. 10.Use of the flexible structural color composite film with humidity responsive property of any one of claims 8-9 in the field of humidity visual detection and intelligent packaging.

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