Multi-response cellulose nanocrystals-composite film and preparation method thereof
11421041 · 2022-08-23
Assignee
Inventors
Cpc classification
C08L1/04
CHEMISTRY; METALLURGY
B82Y30/00
PERFORMING OPERATIONS; TRANSPORTING
B82Y40/00
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
The disclosure discloses a multi-response cellulose nanocrystals-composite film and a preparation method thereof, belonging to the technical field of functional materials. The multi-response cellulose nanocrystals-composite film of the disclosure includes cellulose nanocrystals, a deep eutectic solvent and anthocyanins. The deep eutectic solvent is composed of choline chloride and biological sugar. A mass ratio of the choline chloride to the biological sugar is 1-20:1-6. A mass ratio of the cellulose nanocrystals to the deep eutectic solvent to the anthocyanins is 10:0-10:1, and the amount of the deep eutectic solvent is not 0. The preparation method of the composite film of the disclosure is simple and easy to operate, and has the advantages of mild conditions and short time consumption. The multi-response film prepared in the disclosure has humidity and pH detection functions, has the advantages of good flexibility, good reversibility, excellent stability, etc., and can be used as a flexible humidity and pH sensor.
Claims
1. A multi-response cellulose nanocrystals-composite film, comprising: cellulose nanocrystals, a deep eutectic solvent, and anthocyanins, wherein the deep eutectic solvent is composed of choline chloride and biological sugar; wherein a mass ratio of the cellulose nanocrystals to the deep eutectic solvent to the anthocyanins is 10:0-10:1; and wherein an amount of the deep eutectic solvent is not 0.
2. The multi-response cellulose nanocrystals-composite film according to claim 1, wherein a mass ratio of the choline chloride to the biological sugar is 1-20:1-6.
3. The multi-response cellulose nanocrystals-composite film according to claim 1, wherein the biological sugar comprises glucose and sucrose.
4. The multi-response cellulose nanocrystals-composite film according to claim 1, wherein a preparation method of the deep eutectic solvent comprises: mixing the choline chloride and the biological sugar at the mass ratio of 1-20:1-6, and stirring the mixture at 70° C. to 90° C. for 8 hours to 12 hours to obtain a colorless transparent solution, that is, the deep eutectic solvent.
5. The multi-response cellulose nanocrystals-composite film according to claim 2, wherein the mass ratio of the choline chloride to the biological sugar is 2:1.
6. A method for preparing the multi-response cellulose nanocrystals-composite film according to claims 1, comprising the following steps: carrying out acid hydrolysis on microcrystalline cellulose to obtain a cellulose nanocrystals suspension; concentrating the cellulose nanocrystals suspension to obtain a cellulose nanocrystals concentrated suspension; adding the deep eutectic solvent and the anthocyanins to the cellulose nanocrystals concentrated suspension, uniformly mixing the mixture to obtain a film forming solution; film casting the film forming solution, and drying to obtain the multi-response cellulose nanocrystals-composite film.
7. The method according to claim 6, wherein the acid hydrolysis is performed after the microcrystalline cellulose is added to a sulfuric acid solution, wherein a mass/volume ratio of the microcrystalline cellulose to the sulfuric acid solution is 10 g to 20 g:100 mL, and wherein the sulfuric acid solution has a concentration of 60 wt % to 65 wt %.
8. The method according to claim 6, wherein the cellulose nanocrystals suspension has a concentration of 0.5 wt % to 0.8 wt %.
9. The method according to claim 6, wherein the concentrated suspension is a suspension concentrated to a solid content of 5 wt % to 8 wt %.
10. The method according to claim 6, wherein the film casting is casting the film forming solution on a polytetrafluoroethylene tray, and a film thickness is 50 μm to 60 μm.
11. The method according to claim 6, wherein the multi-response is humidity and pH dual-response, and the humidity is in a range of a relative humidity (RH) of 30% to 95%; and wherein the pH is in a range of 2 to 12.
12. A flexible humidity and pH dual-response sensor, comprising the multi-response cellulose nanocrystals-composite film according to claim 1.
13. The multi-response cellulose nanocrystals-composite film according to claim 1, wherein the biological sugar comprises glucose or sucrose.
Description
BRIEF DESCRIPTION OF FIGURES
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DETAILED DESCRIPTION
(10) Preferred examples of the disclosure will be described below. It should be understood that the examples are intended to better explain the disclosure and are not intended to limit the disclosure.
(11) Test Methods:
(12) Tensile Strength and Elongation at Break:
(13) Under the conditions of 25° C. and a humidity RH of 60%, the composite film is subjected to mechanical strength testing using a BZ2.5/TNIS Zwick material tester (Zwick, Germany). The specimen size is 15×100 mm, the chuck distance is 50 mm, the tensile speed is 50 mm/min, and each specimen is tested at least 5 times.
(14) Color Parameter Testing:
(15) An image of the film is taken using an RX100 III camera, and color parameters of the film are measured using a portable colorimeter 6 (Xrite2600d, MI, 101, USA).
Example 1
(16) A method for preparing a multi-response cellulose nanocrystals-composite film includes the following steps:
(17) (1) Acid hydrolysis was carried out after 11 g of microcrystalline cellulose was added to 100 mL of a sulfuric acid solution having a concentration of 64 wt % to obtain a cellulose nanocrystals suspension having a concentration of 0.5 wt %. Then the cellulose nanocrystals suspension was evaporated at room temperature to obtain a cellulose nanocrystals concentrated suspension with a solid content of 5 wt % (the amount of cellulose nanocrystals (CNC) in the concentrated suspension was 1 g).
(18) (2) 0.1 g of anthocyanins (Anth) and different amounts (0, 0.2, 0.4, 0.6, 0.8 and 1.0 g) of deep eutectic solvent (DES) were added to the cellulose nanocrystals concentrated suspension. Each of the mixtures was stirred uniformly at room temperature to obtain a film forming solution. A preparation method of the deep eutectic solvent included: choline chloride and glucose at a mass ratio of 2:1 were mixed, and the mixture was heated and stirred in an 80° C. oil bath pan for 10 h to obtain a colorless transparent solution, that is, the deep eutectic solvent.
(19) (3) The film forming solution was cast on a polytetrafluoroethylene tray, and drying was carried out at room temperature for 24 h to obtain the multi-response cellulose nanocrystals-composite film, respectively marked as CNC/Anth, CNC/Anth/DES.sub.0.2, CNC/Anth/DES.sub.0.4. CNC/Anth/DES.sub.0.6, CNC/Anth/DES.sub.0.8 and CNC/Anth/DES.sub.1.0.
(20) The obtained multi-response cellulose nanocrystals-composite films were subjected to performance testing. The test results are as follows:
(21) Table 1 shows test results of color parameters and mechanical properties of response films with different amounts of the deep eutectic solvent added. As can be seen from Table 1, due to high rigidity of the CNC, the CNC/Anth film is very brittle, so it is difficult to carry out measurements by in-plane tensile testing. As the DES content increases, the tensile strength of the response film decreases, and the elongation at break increases. The reason is that the plasticizing effect of DES makes the movement of CNC molecules unrestricted, thereby leading to the increase in the elongation at break of the CNC composite film. As the DES content increases, the film color gradually changes from purple to light red.
(22) TABLE-US-00001 TABLE 1 Color parameters and mechanical properties of response films with different amounts of deep eutectic solvent added Tensile Elongation Thickness strength at break Color parameters Film (μm) (MPa) (%) Color L* a* b* CNC/Anth 52.8 — — Purple 53.27 25.31 −26.56 CNC/Anth/DES.sub.0.2 52.6 9.036 1.326 Light 60.97 16.10 −26.01 purple CNC/Anth/DES.sub.0.4 52.9 7.25 2.716 Light 65.31 1.34 −13.42 blue CNC/Anth/DES.sub.0.6 53.2 4.974 4.375 Yellow 68.73 −1.25 17.19 CNC/Anth/DES.sub.0.8 53.0 2.172 6.124 Orange 70.67 6.59 21.99 CNC/Anth DES.sub.1.0 54.1 1.051 7.341 Light 67.90 14.67 15.30 red Notes: “—” means that the measurement cannot be carried out by in-plane tensile testing.
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(24) Saturated salt solutions of CaCl.sub.2, K.sub.2CO.sub.3 and NaCl and distilled water were placed in closed vessels to control different humidity conditions (30% RH, 50% RH, 75% RH and 95% RH). 2 cm×2 cm CNC/Anth, CNC/Anth/DES.sub.0.2, CNC/Anth/DES.sub.0.4, CNC/Anth/DES.sub.0.6, CNC/Anth/DES.sub.0.8 and CNC/Anth/DES.sub.1.0 response films were placed into the above vessels, then the vessels were sealed, and the water absorption rate of the film was calculated by weighing the humidity response films. Water absorption rate (%)=(weight of film after water absorption−weight of original film)/weight of original film×100%.
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(26) Taking the CNC/Anth/DES.sub.0.4 film as an example, under different humidity conditions, the color changes of the multi-response cellulose nanocrystals-composite film are shown in Table 2. As can be seen from Table 2, as the relative humidity increases from 30% to 95%, the CNC/Anth/DES.sub.0.4 composite film shows a higher L* value, which indicates that the composite film has higher luminance. The a* value decreases from 1.34 to −8.12 and the b* increases from −13.42 to 13.97, which indicates that as the relative humidity increases, the red color decreases and the yellow color increases. Besides, the ΔE* value of the composite film is greater than 9, which indicates that the color difference between the composite films under different humidity conditions is very obvious and easy to distinguish with naked eyes.
(27) TABLE-US-00002 TABLE 2 Color changes of CNC/Anth/DES.sub.0.4 film under different humidity conditions Color parameters Humidity (%) Color L* a* b* ΔE 30 Light blue 65.31 1.34 −13.42 — 50 Cyan 66.09 −15.18 −7.81 17.45 75 Light green 69.84 −13.91 6.88 15.21 95 Yellow-green 70.01 −8.12 13.97 9.15 Notes: — means no need for comparison, and ΔE means the color difference between adjacent humidities.
(28) A 2 cm×2 cm CNC/Anth/DES.sub.0.4 film was placed under the humidity condition of 30% RH, the color of the CNC/Anth/DES.sub.0.4 film was recorded and the color parameters of the CNC/Anth/DES.sub.0.4 film were measured. Then the film was placed under the humidity condition of 95% RH, the color of the CNC/Anth/DES.sub.0.4 film was recorded and the color parameters of the CNC/Anth/DES.sub.0.4 film were measured. The above operations were repeated ten times or more. The CNC/Anth/DES.sub.0.4 film was stored under 25° C. and 30% RH. Every other week, the CNC/Anth/DES.sub.0.4 film was tested for humidity response, and the color and parameter values of the CNC/Anth/DES.sub.0.4 film were recorded.
(29) The cycling stability of the CNC/Anth/DES.sub.0.4 film is shown in
(30) A 2 cm×2 cm CNC/Anth/DES.sub.0.4 film was placed in buffer solutions with different pH values, the color of the CNC/Anth/DES.sub.0.4 film was recorded, and the color parameters of the CNC/Anth/DES.sub.0.4 film were measured, as shown in Table 3.
(31) TABLE-US-00003 TABLE 3 Color changes of CNC/Anth/DES.sub.0.4 film under different pH conditions pH Original 2 4 6 8 10 12 Color Yellow Green Light Yellow- Brown Yellow- Green green brown green L* 68.73 63.56 70.43 56.98 45.51 58.41 46.15 a* −1.25 −21.12 −18.01 −3.24 10.37 −6.53 −25.10 b* 17.19 16.00 11.23 15.76 6.62 21.73 17.05 ΔE — 20.57 8.93 20.48 20.01 26.08 22.74 Notes: “—” means no need for comparison, and ΔE is the color difference between adjacent pH values.
Comparative Example 1
(32) The deep eutectic solvent in Example 1 was adjusted to choline chloride and glycerin, the amount was 0.4 g, the rest was the same as in Example 1, and a composite film was obtained.
Comparative Example 2
(33) The deep eutectic solvent in Example 1 was adjusted to choline chloride, the amount was 0.4 g, the rest was the same as in Example 1, and a composite film was obtained.
Comparative Example 3
(34) The deep eutectic solvent in Example 1 was adjusted to glucose, the amount was 0.4 g, the rest was the same as in Example 1, and a composite film was obtained.
Comparative Example 4
(35) The ratio of the choline chloride to the glucose in Example 1 was adjusted to 1:2, the amount was 0.4 g, the rest was the same as in Example 1, and a composite film was obtained.
Comparative Example 5
(36) The amount of the cellulose nanocrystals (CNC) used in Example 1 was adjusted to 0.5 g, the rest was the same as in Example 1, and a composite film was obtained.
(37) The composite films obtained in Comparative Examples 1 to 5 were subjected to performance testing. The test results are as follows.
(38) As can be seen from Table 4, the addition of the choline chloride leads to a decrease in both the tensile strength and the elongation at break of the composite film. When the choline chloride/glycerin are used as the deep eutectic solvent, the tensile strength of the composite film slightly increases, but during the storage process of the composite film, the glycerin is easily separated out from the composite film, which makes the composite film easily become aged and brittle. When the glucose is added, due to the rigidity of the CNC, the strength testing cannot be carried out. When the ratio of the choline chloride to the glucose is 1:2, the tensile strength of the composite film slightly increases, and the elongation at break slightly decreases. When the CNC content is 0.5 g, the thickness of the composite film decreases, the tensile strength decreases, and the elongation at break increases.
(39) TABLE-US-00004 TABLE 4 Color parameters and mechanical properties of composite films obtained in Comparative Examples 1 to 5 Tensile Elongation Comparative Thickness strength at break Color parameters Example (μm) (MPa) (%) Color L* a* b* 1 52.9 6.89 2.502 Light 64.23 1.52 −13.10 blue 2 52.4 5.78 2.110 Blue 48.94 14.10 −52 3 52.8 — — Light 56.45 15.98 −25.47 purple 4 52.9 7.29 2.620 Blue 48.25 6.97 −30.24 5 26 3.21 1.46 Purplish 52.58 29.31 −20.78 red Notes: “—” means that the measurement cannot be carried out by in-plane tensile testing.
(40) As can be seen from Table 5, the color difference of the films prepared in Comparative Examples 1 to 4 under different humidity conditions is less than the color difference of the CNC/Anth/DES.sub.0.4 film. Moreover, the color difference of the films obtained in Comparative Example 2 and Comparative Example 3 under higher humidity conditions is less than 5, so they cannot meet the requirements of intelligent colorimetry. The film prepared in Comparative Example 5 has no humidity response effect. Due to the low CNC content, no photon structure can be formed in the self-assembly process, so the film cannot respond to humidity.
(41) TABLE-US-00005 TABLE 5 Color changes ΔE of composite films obtained in Comparative Examples 1 to 5 under different humidity conditions Comparative Comparative Comparative Comparative Comparative Humidity Example Example Example Example Example (%) 1 2 3 4 5 30 — — — — — 50 13.10 10.21 6.12 15.10 — 75 7.85 6.52 4.56 12.24 — 95 5.01 4.81 4.78 6.19 — Notes: “—” means no color change, and ΔE means the color difference between adjacent humidities.
(42) As can be seen from Table 6, the color difference of the composite films prepared in Comparative Examples 1 to 5 under different pH conditions is small, so they cannot meet the requirements of intelligent colorimetry.
(43) TABLE-US-00006 TABLE 6 Color changes ΔE of composite films obtained in Comparative Examples 1 to 5 under different pH conditions Comparative Comparative Comparative Comparative Comparative Example Example Example Example Example pH 1 2 3 4 5 Original — — — — — 2 14.29 15.36 2.11 16.24 5.42 4 4.35 4.79 2.43 5.12 3.51 6 3.27 4.21 1.89 4.57 2.99 8 3.01 3.97 1.62 4.61 3.12 10 4.65 4.65 4.26 4.97 2.74 12 5.24 5.66 5.31 6.25 6.23 Notes: “—” means no need for comparison, and ΔE means the color difference between adjacent pH values.