A stretch-color-changing flexible cellulose liquid crystal composite film, its preparation method and application

Abstract

This invention discloses a stretchable, color-changing flexible cellulose liquid crystal composite film and its preparation method, belonging to the field of materials technology. The stretchable, color-changing flexible cellulose liquid crystal composite film of this invention uses nanocrystalline cellulose as a matrix, polyethylene glycol diacrylate and polyhydroxyethyl acrylate as fillers, and glucose as a plasticizer, and is obtained through self-assembly. The stretchable, color-changing flexible cellulose liquid crystal composite film prepared by this invention has good flexibility, can be bent or folded arbitrarily, and its elongation at break is greatly improved. Simultaneously, the composite film also has a distinct cholesteric structure, exhibiting a strong structural color, and produces a significant color change when subjected to tensile deformation. Furthermore, the CNC matrix, as a natural polymer, has excellent renewability and is environmentally friendly, conforming to the concepts of sustainable development and green chemistry.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a stretch-color-changing flexible cellulose liquid crystal composite film, its preparation method, and its application. Background Technology

[0002] Cellulose is the world's most abundant and widely used renewable polymer, and is considered the most influential green material in human society. For thousands of years, cellulose has been extensively used in the forms of wood and plant fibers in many fields such as textiles, papermaking, agriculture, and biomedicine. With social development, people have gained a deeper understanding of cellulose and have extracted nanoscale cellulose from nature.

[0003] Nanocrystalline cellulose (CNC), as a type of nanocellulose material, possesses excellent mechanical properties, abundant reaction sites, and good biocompatibility. Furthermore, CNC suspensions can be self-assembled through evaporation to obtain CNC liquid crystal films with a cholesteric helical structure. These liquid crystal films are one-dimensional photonic crystals that selectively reflect specific wavelengths of light, thus exhibiting vibrant and bright structural colors. This unique optical property makes CNC liquid crystal films highly promising for applications in optical devices, optical anti-counterfeiting, sensing and detection, and liquid crystal displays.

[0004] In practical applications, to meet the diverse needs of CNC liquid crystal films, researchers have modified them using various methods to endow them with diverse functions to adapt to different application scenarios. However, due to the rigidity of CNC particles, CNC films exhibit poor flexibility and are prone to breakage during use, severely limiting their application scope. Therefore, developing a flexible CNC composite film and functionally modifying it is urgently needed. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a stretch-color-changing flexible cellulose liquid crystal composite film.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution, including mixing nanocrystalline cellulose (CNC) suspension, polyethylene glycol diacrylate (PEGDA) solution, plasticizer and photoinitiator, stirring in the dark, and evaporating and self-assembling under constant temperature and humidity for 3 to 5 days to generate a CNC composite film, and then subjecting it to ultraviolet light treatment to induce the molecular chains in the film to form a PEGDA network, thereby obtaining a CNC / PEGDA-Glu liquid crystal film;

[0009] The CNC / PEGDA-Glu liquid crystal film was immersed in a hydroxyethyl acrylate (HEA) solution containing a photoinitiator and a crosslinking agent, allowing it to fully absorb the HEA monomer and BIS crosslinking agent. Then, it was placed under ultraviolet light for photopolymerization to form a hydroxyethyl acrylate (PHEA-bis) network structure. Finally, the film was dried to remove internal moisture, thus preparing the CNC liquid crystal composite film (CNC / PEGDA / PHEA-Glu liquid crystal film).

[0010] The polyethylene glycol diacrylate has a mass fraction of 10-55% relative to the nanocrystalline cellulose matrix; the volume ratio of hydroxyethyl 2-acrylate to water in the hydroxyethyl 2-acrylate solution is 1:0.25-4.

[0011] In a preferred embodiment of the method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film of the present invention, the plasticizer includes one or more of glucose (Glu), glycerol, citric acid, and phthalate, and the content of the plasticizer is 0-35 wt% of CNC.

[0012] In a preferred embodiment of the method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film of the present invention, the photoinitiator includes one or more of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone (photoinitiator 2959), 2-hydroxy-2-methyl-1-phenylacetone (photoinitiator 1173), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), and 1-hydroxycyclohexylphenyl ketone (184), and the amount of the photoinitiator used is 0.5 to 2.0 wt% of PEGDA and HEA, respectively.

[0013] In a preferred embodiment of the method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film of the present invention, the self-assembly temperature is 20-30°C, the humidity is 40-60%RH, and the time is 3-5 days.

[0014] In a preferred embodiment of the method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film of the present invention, the film is immersed in HEA solution for 18-24 hours at a temperature of 35-45°C.

[0015] In a preferred embodiment of the method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film of the present invention, the crosslinking agent includes one or more of N,N-methylenebisacrylamide (BIS), divinylbenzene (DVB), or diisocyanate compounds, and the content of the crosslinking agent is 0.5 to 1.5 wt% of HEA.

[0016] In a preferred embodiment of the method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film of the present invention, the content of the crosslinking agent is 1 wt% of HEA.

[0017] In a preferred embodiment of the method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film of the present invention, the ultraviolet light irradiation treatment includes an irradiation intensity of 50W, an ultraviolet light wavelength of 365nm, a distance of 10-15cm between the light source and the film, and an irradiation time of 15-30min.

[0018] As a preferred embodiment of the preparation method of the stretch-color-changing flexible cellulose liquid crystal composite film of the present invention, the preparation method of the CNC includes: mixing microcrystalline cellulose with sulfuric acid solution for acid hydrolysis reaction, adding deionized water to terminate the acid hydrolysis reaction, taking the lower layer solution after standing, centrifuging to collect the solid, dispersing it in water to form a nanocellulose suspension, then placing it in a dialysis bag for dialysis to make the pH of the suspension neutral, and ultrasonically dispersing it to obtain the CNC suspension; wherein, the concentration of sulfuric acid solution is 64 wt%; the mass ratio of microcrystalline cellulose to sulfuric acid solution is 1:8-10; the temperature of the acid hydrolysis reaction is 45-50℃, and the acid hydrolysis time is 60-75 min.

[0019] The purpose of this invention is to overcome the shortcomings of the prior art and provide a flexible cellulose liquid crystal composite film that changes color when stretched.

[0020] The purpose of this invention is to overcome the shortcomings of the prior art and provide an application of cellulose liquid crystal composite film in the fields of deformation sensing, deformation detection, damage monitoring and optics.

[0021] Beneficial effects of this invention:

[0022] (1) The stretchable color-changing flexible cellulose liquid crystal composite film prepared by the present invention has good flexibility and can be bent or folded arbitrarily, and the elongation at break is greatly improved.

[0023] (2) The composite membrane prepared by the present invention also has an obvious cholesteric structure, strong structural color, and obvious color change when subjected to stretching deformation.

[0024] (3) The CNC matrix used in this invention is a natural polymer with excellent renewability and no pollution to the environment, which is in line with the concept of sustainable development and green chemistry. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0026] Figure 1 The image shows the color change of the CNC / PEGDA / PHEA-Glu liquid crystal composite film during the stretching process.

[0027] Figure 2 SEM images of the CNC / PEGDA / PHEA-Glu liquid crystal composite film under different stretching conditions.

[0028] Figure 3 The image shows the color changes of CNC / PEGDA-Glu liquid crystal composite films with different PEGDA contents in aqueous solution.

[0029] Figure 4 SEM images of CNC / PEGDA-Glu liquid crystal composite films with different PEGDA contents after immersion in aqueous solution and drying. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0033] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0034] The sulfuric acid used in this embodiment was 95wt% concentrated sulfuric acid, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.; the microcrystalline cellulose, polyethylene glycol diacrylate, and anhydrous glucose used in this embodiment were purchased from Sinopharm Chemical Reagent Co., Ltd.; the hydroxyethyl acrylate used in this embodiment was purchased from Beijing Innocare Technology Co., Ltd.; the N,N-methylenebisacrylamide used in this embodiment was purchased from Sigma-Aldrich Ltd.; and the 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone used in this embodiment was purchased from Shanghai Maclean Biochemical Co., Ltd.

[0035] The materials obtained in the embodiments of the present invention were subjected to performance testing according to the following method:

[0036] Scanning electron microscopy (SEM) analysis: SEM analysis is mainly used to observe the microstructure of thin films. After sputtering the thin film with gold, a scanning voltage of 3kV was selected, and observations were performed at different magnifications.

[0037] Tensile properties: The film was cut into dumbbell-shaped strips, 12 mm long and 2 mm wide, with 5 strips cut for each sample group. The film strips were subjected to tensile testing on a universal testing machine at a tensile rate of 10 mm / min.

[0038] Water absorption test: For each sample, 15mm × 15mm film squares were cut and dried in a 40℃ oven until their weight became constant. Then, they were placed in an aqueous solution to reach water absorption equilibrium, and the change in the mass of the film squares was recorded during this process. The water absorption rate was calculated using the following formula, where w0 is the initial mass of the film and w1 is the mass of the film after water absorption.

[0039] Water absorption rate (%) = [(w1-w0) / w0] × 100%.

[0040] Example 1

[0041] This embodiment provides a method for preparing a cellulose liquid crystal composite film, specifically as follows:

[0042] (1) Preparation of nanocellulose (CNC): CNC was prepared using sulfuric acid hydrolysis. 17g of microcrystalline cellulose and 150mL of sulfuric acid solution (64wt%) were added to a three-necked flask and stirred vigorously at 45℃ for 70min to hydrolyze the microcrystalline cellulose. After stirring, 1500mL of deionized water was added to terminate the hydrolysis reaction. The solution was allowed to stand for 12h to allow complete separation. The supernatant was discarded, and the lower milky white solution was centrifuged (10000r / min, 10min). The resulting white gelatinous solid was washed several times with water and then added to a dialysis bag along with an appropriate amount of deionized water. Dialysis was performed at room temperature for 5–7 days until the pH of the solution stabilized at approximately 6.5. Finally, the dialyzed solution was subjected to ultrasonic treatment (400w, 5min) in an ultrasonic cell disruptor to obtain the CNC suspension. The solid content of the CNC suspension was controlled to 2.5% using a rotary evaporator for convenient subsequent use.

[0043] (2) Preparation of CNC / PHEA-Glu liquid crystal film: Polyethylene glycol diacrylate (PEGDA) solution, glucose (Glu), and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone (photoinitiator 2959) were simultaneously added to 16 ml of CNC suspension and magnetically stirred for 30 min under light-protected conditions. The contents of PEGDA and Glu were 25 wt% and 5 wt% of CNC, respectively, and the amount of photoinitiator 2959 added was 1 wt% of PEGDA. The mixture was kept at a constant temperature and humidity of 25℃ and 50%RH for 4.5 days for evaporation and self-assembly to obtain CNC / PEGDA-Glu film. The film was then subjected to ultraviolet light irradiation for 30 min (50W, 365nm, height 10cm) to initiate the formation of a PEGDA network in the molecular chains of the film, thus obtaining the CNC / PEGDA-Glu liquid crystal film.

[0044] (3) Preparation of CNC / PEGDA / PHEA-Glu liquid crystal film: The CNC / PEGDA-Glu liquid crystal film was immersed in a hydroxyethyl acrylate (HEA) solution containing photoinitiator 2959 and BIS crosslinking agent (V HEA ∶V H2OThe mixture was prepared by soaking the HEA monomer and BIS crosslinking agent in a 1:1 ratio (photoinitiator 2959 content is 1 wt% of HEA) at 40℃ for 24 hours to allow for full absorption of HEA monomer and BIS crosslinking agent. The composite film in the solution was then photopolymerized again using ultraviolet light (50W, 365nm, height 10cm, 15min) to form a polyhydroxyethyl acrylate (PHEA-bis) network structure. Finally, the composite film was peeled from the gel and dried in a 40℃ oven to remove internal moisture, thus obtaining the CNC / PEGDA / PHEA-Glu liquid crystal composite film, i.e., a flexible cellulose liquid crystal composite film.

[0045] When the CNC composite film has a high stretch length, it will have obvious color changes during the stretching deformation process. Figure 1 The experiment demonstrates that the color of the CNC / PEGDA / Glu-25%Glu film changes with increasing stretching during the stretching process, gradually transforming from a pale red to an orange-yellow, and finally turning blue before reaching maximum stretching deformation. This indicates that during stretching, the maximum light reflection wavelength of the film gradually shifts to blue, and the color change range essentially covers the entire visible light spectrum, making it easily observable by the human eye.

[0046] Figure 2 The results show that when the film is subjected to only 10% tensile strain, it appears dark red overall, and the SEM image shows that the pitch of the film at this point is similar to the initial pitch (633 nm). When the tensile strain increases to 60%, the film turns reddish-yellow, and the pitch decreases to 509 nm. When the strain increases to 110%, the film turns bluish-green, and the pitch decreases to 377 nm. These phenomena indicate that the color change of the film is due to the compression of the cholesteric helical structure during stretching, leading to a decrease in pitch. Combined with Bragg's law, the decrease in pitch causes a reduction in the wavelength of the maximum selectively reflected light, i.e., a blue shift in color. This characteristic holds promise for applications in tensile sensing and tensile detection.

[0047] Example 2

[0048] The difference between this embodiment and Embodiment 1 is that the V in the HEA solution is adjusted. HEA :V H2O The ratio was 4:1, and the rest of the preparation process was the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0049] Example 3

[0050] The difference between this embodiment and Embodiment 1 is that the V in the HEA solution is adjusted. HEA :V H2O=3:1, and the rest of the preparation process is the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0051] Example 4

[0052] The difference between this embodiment and Embodiment 1 is that the V in the HEA solution is adjusted. HEA :V H2O =2:1, and the rest of the preparation process is the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0053] Example 5

[0054] The difference between this embodiment and Embodiment 1 is that the V in the HEA solution is adjusted. HEA :V H2O =1:0, and the rest of the preparation process is the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0055] Example 6

[0056] The difference between this embodiment and Embodiment 1 is that the V in the HEA solution is adjusted. HEA :V H2O =1:2, and the rest of the preparation process is the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0057] Example 7

[0058] The difference between this embodiment and Embodiment 1 is that the V in the HEA solution is adjusted. HEA :V H2O =1:3, and the rest of the preparation process is the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0059] Example 8

[0060] The difference between this embodiment and Embodiment 1 is that the V in the HEA solution is adjusted. HEA :V H2O =1:4, and the rest of the preparation process is the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0061] Example 9

[0062] The difference between this embodiment and Embodiment 1 is that the V in the HEA solution is adjusted. HEA :V H2O =0:1, and the rest of the preparation process is the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0063] The performance of the materials prepared in the above embodiments was tested, and the comparison results with those of Example 1 are shown in Table 1.

[0064] Table 1. Effects of HEA solutions with different volume ratios on film absorbance and mechanical properties.

[0065]

[0066] As shown in the table above, the absorption of monomers and water by the CNC / PEGDA-Glu film varies with different concentrations of HEA solution. The mass change of the film after immersion reflects the total mass of HEA monomers and water molecules absorbed by the film. After immersion and drying, the water molecules inside the film are removed, and the mass change of the film at this time represents the mass of HEA monomers absorbed by the film. Table 1 shows that the mass of the film after immersion in pure aqueous solution is 255.4% of the initial value, which is much greater than the 148.5% after immersion in pure HEA solution. This is because although HEA has a hydrophilic hydroxyl group at one end, its other end has a hydrophobic acrylate bond, which hinders the entry of HEA monomers into the film, resulting in a lower swelling degree of the film in pure HEA solution. Aqueous solution, as a dispersant for CNC, has good compatibility with CNC and can penetrate well into the film, significantly increasing the absorption capacity of the film in aqueous solution. Therefore, as the water content in the solution increases, the absorption capacity of the film also gradually increases.

[0067] After soaking and dehydrating the CNC / PEGDA-Glu film, it was found that the film's monomer absorption in pure HEA solution was low. However, after adding a certain amount of water molecules to the solution, the film's absorption of HEA monomers showed a trend of first increasing and then decreasing. HEA :V H2O At a 1:1 ratio, the monomer uptake reaches its maximum of 184.9%. This is because in the HEA aqueous solution, water molecules first enter the membrane, causing it to swell. Simultaneously, the aqueous solution, as a good solvent for HEA, can introduce a large amount of HEA monomers into the membrane, acting as a bridge between the CNC and HEA, thus improving their compatibility. Therefore, adding a certain amount of water molecules to the solution enhances the membrane's ability to absorb HEA monomers. However, when the water content in the solution is too high, the concentration of HEA monomers is too low, causing the membrane to reach swelling equilibrium at a low concentration, which is not conducive to the membrane's uptake of HEA molecules. Therefore, the membrane at V... HEA :V H2O In a 1:1 solution, the HEA monomer uptake reaches its maximum. Without compromising the CNC film structure, a higher content of the flexible network in the film results in lower tensile strength and higher elongation at break. If the film contains more monomers, the content of the subsequently formed flexible network will also be higher. Therefore, the V in this invention...HEA :V H2O The best technical effect can be obtained when the ratio is 1:1.

[0068] Example 10

[0069] The difference between this embodiment and Embodiment 1 is that the amount of PEGDA added is adjusted to 10 wt% of CNC, while the rest of the preparation process is the same as in Embodiment 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0070] Example 11

[0071] The difference between this embodiment and Embodiment 1 is that the amount of PEGDA added is adjusted to 15wt% of CNC, while the rest of the preparation process is the same as in Embodiment 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0072] Example 12

[0073] The difference between this embodiment and Embodiment 1 is that the amount of PEGDA added is adjusted to 35 wt% of CNC, while the rest of the preparation process is the same as in Embodiment 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0074] Example 13

[0075] The difference between this embodiment and Embodiment 1 is that the amount of PEGDA added is adjusted to 45 wt% of CNC, while the rest of the preparation process is the same as in Embodiment 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0076] Example 14

[0077] The difference between this embodiment and Embodiment 1 is that the amount of PEGDA added is adjusted to 55 wt% of CNC, while the rest of the preparation process is the same as in Embodiment 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0078] The performance of the materials prepared in the above embodiments was tested, and the results compared with those of Example 1 are shown in Table 2.

[0079] Table 2. Effects of PEGDA content on film absorbance and mechanical properties

[0080]

[0081] The proportion of the PEGDA network in the CNC / PEGDA / PHEA-Glu liquid crystal composite film also affects the film's absorption of HEA monomers. As shown in Table 2, with the increase of PEGDA content in the film, the mass change of the film in the HEA solution first increases and then decreases, reaching a maximum of 276.1% when the PEGDA content is 25%. This is because when the PEGDA content inside the film is too high, the dense network structure greatly hinders the swelling of the film, making it difficult for monomers and water molecules to enter the film, thus reducing the film's absorption. Conversely, when the PEGDA network content is low, the network structure is too sparse, reducing the film's water resistance, causing excessive swelling and even dissolution, resulting in some CNC molecules redispersing into the solution. This can be seen from the mass change of the film after immersion in aqueous solution and drying. Figure 3 This can be seen from the following: After immersing and drying the film in an aqueous solution, the film mass decreased significantly, reaching only 78.2% of the initial mass, indicating that some film components were redispersed in the aqueous solution. However, as the PEGDA content in the film increased, the mass of the film after immersion and drying gradually approached the initial value. Simultaneously, if the PEGDA content in the film is low, excessive swelling can disrupt the internal chiral nematic structure, causing the film to lose its structural color characteristics. This can be observed from the color change of the film in HEA solution. Figure 3 ) and SEM images ( Figure 4 As can be seen from the data, when the PEGDA content is low (10%), the structural color characteristics of the film basically disappear after immersion, and there is obvious whitening at the film edges. This indicates that the cholesteric structure of the film is destroyed, and CNC molecules begin to redisperse in the solution. As the PEGDA content in the film increases, the structural color characteristics gradually recover, indicating that the PEGDA network structure at this point can effectively control the ingress of solution during film swelling, protecting the film structure from damage. Figure 4 As shown in the SEM image, the internal cholesteric structure of the film is significantly disrupted, with the originally regular chiral arrangement becoming distorted and deformed. However, after increasing the PEGDA content, the film returns to its initial morphology. Table 2 shows that when the PEGDA content is 25%, the film achieves its maximum uptake of the monomer HEA, while maintaining good structural color characteristics in solution. Without compromising the structural color of the CNC film, a higher content of the flexible network in the film results in lower tensile strength and higher elongation at break. If the film contains more monomers, the content of the subsequently formed flexible network will also be higher. Therefore, the preferred PEGDA content is 25%.

[0082] Example 15

[0083] The difference between this embodiment and Example 1 is that the content of Glu is adjusted to 2wt%, while the rest of the preparation process is the same as in Example 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0084] Example 16

[0085] The difference between this embodiment and Embodiment 1 is that the content of Glu is adjusted to 15wt%, while the rest of the preparation process is the same as in Embodiment 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0086] Example 17

[0087] The difference between this embodiment and Embodiment 1 is that the content of Glu is adjusted to 25wt%, while the rest of the preparation process is the same as in Embodiment 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0088] Example 18

[0089] The difference between this embodiment and Embodiment 1 is that the content of Glu is adjusted to 35wt%, while the rest of the preparation process is the same as in Embodiment 1, to obtain a CNC / PEGDA / PHEA-Glu liquid crystal composite film.

[0090] Comparative Example 1

[0091] The difference between this comparative example and Example 1 is that the Glu content was adjusted to 0, while the rest of the preparation process was the same as in Example 1, and a CNC / PEGDA / PHEA liquid crystal film was obtained.

[0092] The materials prepared in the above embodiments and comparative examples were subjected to performance tests, and the comparison results with those of Example 1 are shown in Table 3.

[0093] Table 3. Effects of Glu content on film absorbance and mechanical properties

[0094]

[0095]

[0096] The tensile test results of the CNC / PEGDA / PHEA-Glu liquid crystal composite film are shown in Table 3. As can be seen from the figure, without the addition of Glu, the elongation at break of the film was 51.1±2.6%, and the tensile strength was 8.8±1.3 MPa. After the addition of Glu, with the increase of Glu content, the elongation at break continuously increased while the tensile strength continuously decreased. When the Glu content was 35%, the elongation at break reached its maximum value of 140.68±4.34%, which is 2.7 times that of the CNC / PEGDA / PHE composite film, while the tensile strength decreased to its minimum value of 5.66±0.92 MPa. This indicates that the small molecule Glu acts as a plasticizer, effectively improving the tensile strain of the CNC / PEGDA / PHEA-Glu liquid crystal composite film and providing a basis for its stretchable color-changing ability.

[0097] Comparative Example 2

[0098] (1) A CNC suspension (solid content of 2.5%) was prepared using the method of Example 1.

[0099] (2) Pour 16 mL of CNC suspension into a polystyrene petri dish (60 mm in diameter) and perform evaporation self-assembly treatment for 4.5 days (25 °C, 50 RH) to obtain pure CNC liquid crystal film.

[0100] Comparative Example 3

[0101] (1) A CNC suspension (solid content of 2.5%) was prepared using the method of Example 1.

[0102] (2) First, polyethylene glycol (PEG) particles were added to deionized water and stirred at room temperature to obtain a polyethylene glycol solution (5% solids content). Then, the CNC suspension (16 mL) and PEG solution (4.8 mL) were mixed and stirred for 12 h. The mixture was then poured into a polystyrene petri dish (60 mm in diameter) and subjected to evaporative self-assembly treatment for 4.5 days (25 °C, 50% RH) to obtain a CNC / PEG composite membrane.

[0103] Comparative Example 4

[0104] (1) A CNC suspension (solid content of 2.5%) was prepared using the method of Example 1.

[0105] (2) First, polyvinyl alcohol (PVA) particles were added to deionized water and stirred at room temperature to obtain a PVA solution (5% solid content). Then, CNC suspension (16 mL), PVA solution (4.8 mL), and Glu (0.06 g) were mixed and stirred for 12 h. The mixture was then poured into a polystyrene petri dish (60 mm in diameter) and subjected to evaporative self-assembly treatment for 4.5 days (25 °C, 50% RH) to obtain a CNC / (PVA:Glu) composite membrane.

[0106] Comparative Example 5

[0107] (1) A CNC suspension (solid content of 2.5%) was prepared using the method of Example 1.

[0108] (2) Add waterborne polyurethane (WPU) solution (4.8g, solid content 5%) to CNC suspension (16mL), stir vigorously at room temperature for 12h, and then pour it into polystyrene petri dish (diameter 60mm) for 4.5 days of evaporation self-assembly treatment (25℃, 50%RH) to obtain CNC / WPU composite film.

[0109] The performance of the materials prepared in the above comparative example was tested, and the results compared with those of Example 1 are shown in Table 4.

[0110] Table 4. Effects of Glu content on film absorbance and mechanical properties

[0111]

[0112] As shown in the table above, compared to conventional CNC liquid crystal composite films, this invention significantly improves the flexibility and stretchability of the CNC liquid crystal film by constructing a dual-network structure of PEGDA and PHEA within the film and adding Glu plasticizer. Furthermore, this film exhibits excellent stretch-induced color-changing properties, with the color-changing range covering the entire visible light spectrum, making it promising for applications in deformation detection, damage monitoring, and other fields.

[0113] In summary, the stretchable color-changing flexible cellulose liquid crystal composite film of this invention uses nanocrystalline cellulose as a matrix, polyethylene glycol diacrylate and hydroxyethyl polyacrylate as fillers, and glucose as a plasticizer, and is obtained through self-assembly. The stretchable color-changing flexible cellulose liquid crystal composite film prepared by this invention has good flexibility, can be bent or folded arbitrarily, and its elongation at break is greatly improved. At the same time, the composite film also has a distinct cholesteric structure, exhibits strong structural color, and produces a significant color change when subjected to tensile deformation. Furthermore, the CNC matrix, as a natural polymer, has excellent renewability and is environmentally friendly, conforming to the concepts of sustainable development and green chemistry.

[0114] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a stretch-color-changing flexible cellulose liquid crystal composite film, characterized in that: include, A nanocrystalline cellulose suspension, a polyethylene glycol diacrylate solution, glucose and a photoinitiator were mixed and stirred in the dark. The mixture was then kept at a constant temperature and humidity to allow it to evaporate and self-assemble, generating a CNC composite film. After ultraviolet light treatment, a CNC / PEGDA-Glu liquid crystal film was obtained. The CNC / PEGDA-Glu liquid crystal film is immersed in a 2-hydroxyethyl acrylate solution containing a photoinitiator and a crosslinking agent, and then subjected to ultraviolet light treatment; finally, it is dried to prepare the cellulose liquid crystal composite film. The mass fraction of polyethylene glycol diacrylate relative to the nanocrystalline cellulose matrix is ​​10-55%; the volume ratio of hydroxyethyl 2-acrylate to water in the hydroxyethyl 2-acrylate solution is 1:0.25-4.

2. The method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film as described in claim 1, characterized in that: The glucose content is 2 to 35 wt% of nanocrystalline cellulose.

3. The method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film as described in claim 1, characterized in that: The photoinitiator includes one or more of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone, 2-hydroxy-2-methyl-1-phenylacetone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 1-hydroxycyclohexylphenyl ketone, and the amount of the photoinitiator used is 0.5~2.0 wt% of polyethylene glycol diacrylate and hydroxyethyl 2-acrylate.

4. The method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film as described in claim 1, characterized in that: The self-assembly process takes place at a temperature of 20-30°C, a humidity of 40-60%RH, and a time of 3-5 days.

5. The method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film as described in claim 1, characterized in that: The film is immersed in hydroxyethyl 2-acrylate solution for 18 to 24 hours at a temperature of 35 to 45°C.

6. The method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film as described in claim 1, characterized in that: The crosslinking agent includes one or more of N,N-methylenebisacrylamide, divinylbenzene, or diisocyanate compounds, and the content of the crosslinking agent is 0.5 to 1.5 wt% of 2-hydroxyethyl acrylate.

7. The method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film as described in claim 1, characterized in that: The ultraviolet light irradiation treatment includes an irradiation intensity of 50 W, an ultraviolet wavelength of 365 nm, a distance of 10–15 cm between the light source and the thin film, and an irradiation time of 15–30 min.

8. The method for preparing the stretch-color-changing flexible cellulose liquid crystal composite film as described in claim 1, characterized in that: The method for preparing the nanocrystalline cellulose includes: mixing microcrystalline cellulose with sulfuric acid solution for acid hydrolysis; adding deionized water to terminate the acid hydrolysis reaction; allowing the solution to stand; taking the lower layer; centrifuging to collect the solid; dispersing the solid in water to form a nanocrystalline cellulose suspension; then placing the suspension in a dialysis bag for dialysis to bring the pH of the suspension to neutral; and ultrasonically dispersing the suspension to obtain a nanocrystalline cellulose suspension. The concentration of the sulfuric acid solution is 64 wt%; the mass ratio of microcrystalline cellulose to sulfuric acid solution is 1:8~10; the acid hydrolysis reaction temperature is 45~50 ℃; and the acid hydrolysis time is 60~75 min.

9. The stretch-color-changing flexible cellulose liquid crystal composite film prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of the cellulose liquid crystal composite film as described in claim 9 in the fields of deformation sensing, deformation detection, damage monitoring and optics.

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