CN110551302B - Flexible liquid crystal film and preparation method thereof - Google Patents
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Abstract
The invention provides a flexible cellulose liquid crystal film and a preparation method thereof. The method comprises the following steps: mixing wood pulp and a concentrated sulfuric acid solution, heating while stirring, adding water after heating, and uniformly mixing to obtain a mixed solution; centrifuging the mixed solution, and taking the upper suspension; dialyzing the upper suspension until the suspension is neutral, and concentrating the suspension to obtain CNC suspension; uniformly mixing the CNC suspension with a trimethylolethane solution, and then carrying out ultrasonic treatment to obtain a CNC/TME mixed solution; and drying the CNC/TME mixed solution to obtain the flexible cellulose liquid crystal film. The flexible cellulose liquid crystal film obtained by the method has good cholesteric liquid crystal characteristics. The method can effectively increase the flexibility and toughness of the film. The preparation method is simple to operate, controllable in process, low in cost, easy for mass production, and applicable to product anti-counterfeiting, encryption of important files and the like.
Description
Technical Field
The invention belongs to the field of preparation of functional film materials, and particularly relates to a flexible liquid crystal film and a preparation method thereof.
Background
Cellulose is the most abundant natural macromolecule in nature and widely exists in plant cell walls and marine animals. The cellulose has the characteristics of low price, no toxicity, reproducibility, good biocompatibility, biodegradability and the like, and the characteristics make the cellulose become a good functional material.
Cellulose is treated by sulfuric acid to obtain a Cellulose Nanocrystalline (CNC) with a rod-shaped rigid morphology, and when a certain critical concentration is reached, the chiral nematic liquid crystal film is obtained through self-assembly. The regular arrangement of the nano-cellulose crystals can be kept in the film, so that the film has special optical properties, such as selective reflection of circularly polarized light, birefringence, circular dichroism and the like, and can be used for the aspects of product anti-counterfeiting, encryption of important documents and the like.
Pure cellulose liquid crystal films are very fragile and difficult to completely uncover, which seriously affects the application range and value of the films. In the patent "a bacterial cellulose liquid crystal phase iridescent film and its preparation method and application" (patent application No. CN 201710338909.1), hydroxypropyl guar gum is added to improve the brittleness of the film, but the flexibility of the film is not improved well.
Disclosure of Invention
In order to overcome the above-mentioned disadvantages of the prior art, the present invention aims to provide a flexible liquid crystal film and a method for preparing the same. The invention utilizes the viscosity of the polyalcohol solution to introduce the Trimethylolethane (TME) into a liquid crystal film system, thereby improving the flexibility and toughness without influencing the optical performance of the liquid crystal film.
The invention aims to provide a preparation method of a high-flexibility liquid crystal film.
Another object of the present invention is to provide a flexible liquid crystal film (flexible cellulose cholesteric liquid crystal film) prepared by the above preparation method.
The purpose of the invention is realized by at least one of the following technical solutions.
The invention provides a preparation method of a flexible cellulose liquid crystal film, which comprises the following steps:
(1) mixing wood pulp and concentrated sulfuric acid solution, performing heating treatment (acidolysis) under a stirring state, adding deionized water (terminating reaction), and uniformly mixing to obtain a mixed solution (white emulsion);
(2) centrifuging the mixed solution obtained in the step (1) for 3-4 times, and collecting an upper suspension;
(3) pouring the suspension liquid obtained in the step (2) into a dialysis bag, carrying out dialysis treatment, dialyzing with deionized water until the suspension liquid is neutral, and then soaking the dialysis bag into a polyethylene glycol solution (preferably polyethylene glycol with the molecular weight of 20000) to concentrate the suspension liquid to obtain a CNC suspension liquid;
(4) uniformly mixing the CNC suspension liquid obtained in the step (3) with a trimethylolethane solution (TME solution), and then carrying out ultrasonic treatment to obtain a CNC/TME mixed solution;
(5) and (4) drying the CNC/TME mixed solution obtained in the step (4) to obtain the flexible cellulose liquid crystal membrane (CNC/TME membrane).
Further, the wood pulp in the step (1) is softwood pulp or hardwood pulp; the concentration of the wood pulp is 95-100 wt%; the mass percentage concentration of the concentrated sulfuric acid solution is 60-70 wt%; the mass-volume ratio of the oven dry mass of the wood pulp to the volume of the concentrated sulfuric acid solution is 1:8-14 g/mL.
Further, the stirring speed in the stirring state in the step (1) is 300-400rpm, the temperature of the heating treatment is 45-60 ℃, and the time of the heating treatment is 45-60 min.
Further, the volume ratio of the concentrated sulfuric acid solution to water in the step (1) is 1: 9-12.
Further, the centrifugation treatment time in the step (2) is 3-4 times, the centrifugation treatment speed is 8000-10000rpm, the centrifugation treatment time is 10-12min, and the centrifugation treatment temperature is 0-10 ℃.
Further, the molecular weight cut-off of the dialysis bag in the step (3) is 14000.
Further, the concentration of the polyethylene glycol solution in the step (4) is 15-20wt%, preferably 10-15wt%, the molecular weight of the polyethylene glycol is 16000-.
Further, the concentration of the trimethylolethane solution in the step (4) is 10wt% -20 wt%; the volume ratio of the CNC suspension to the trimethylolethane solution is (9-6): 1;
preferably, the volume ratio of the CNC suspension to TME solution is 9:1, 8:1, 7:1 or 6: 1.
Further, the temperature of ultrasonic treatment is 0-5 ℃, the time of ultrasonic treatment is 10-15min, and the ultrasonic frequency of ultrasonic treatment is 20-40 KHz.
Preferably, the power of the ultrasonic treatment is 200-300W
Further, the temperature of the drying treatment in the step (5) is 30-35 ℃, the humidity of the drying environment is 60-80%, and the time of the drying treatment is 72-96 h.
Preferably, the drying process is drying in a polystyrene petri dish.
The invention provides a flexible cellulose liquid crystal film prepared by the preparation method.
The invention utilizes the viscosity of the polyalcohol solution to increase the flexibility of the film, and the polyalcohol solution does not influence the formation of fingerprint texture in the cholesteric phase.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) according to the preparation method provided by the invention, the selected raw material softwood is a renewable resource, and has the advantages of low cost, wide source, degradability, environmental friendliness and the like;
(2) according to the preparation method provided by the invention, hydroxyl on the surface of the cellulose nanocrystal prepared by a sulfuric acid method is oxidized into sulfonic groups, so that the nanorod is negatively charged, and a stable crystalline nano cellulose suspension can be formed under the electrostatic action among crystalline nano celluloses, so that the aggregation of fibers cannot be caused in the self-evaporation process;
(3) according to the preparation method provided by the invention, the adopted raw material, namely trimethylolethane, is a good plasticizer, is tasteless, has good stability and has good glossiness; the solution is mixed with the cellulose nanocrystals, so that the flexibility of the liquid crystal film can be effectively improved;
(4) the preparation method provided by the invention selects an evaporation-induced self-assembly method to prepare the liquid crystal film, and has the advantages of convenient operation, simple condition control and good controllability.
Drawings
FIG. 1 is a view of the flexible cellulose liquid crystal film obtained in example 1 observed under an optical microscope.
Detailed Description
The following description of the embodiments of the present invention is provided in connection with the accompanying drawings and examples, but the invention is not limited thereto. It is noted that the processes described below, if not specifically described in detail, are all realizable or understandable by those skilled in the art with reference to the prior art. The reagents or apparatus used are not indicated to the manufacturer, and are considered to be conventional products available by commercial purchase.
Example 1
A preparation method of a flexible cellulose liquid crystal film comprises the following steps:
(1) weighing 10 g of absolutely dry softwood pulp, adding the absolutely dry softwood pulp into a three-neck flask, adding 100 ml of concentrated sulfuric acid solution with the mass percentage concentration of 60wt%, stirring at the temperature of 50 ℃ and the rotating speed of 400 r/min for 1 hour, pouring the mixture into the beaker after the acid hydrolysis is finished, adding deionized water with the volume 8 times that of the concentrated sulfuric acid solution to terminate the reaction, and obtaining white emulsion;
(2) centrifuging the white emulsion obtained in the step (1) at 10 ℃ at 10000 r/min for 10min, taking the upper suspension, repeatedly centrifuging for 3 times, and combining the suspensions;
(3) pouring the suspension liquid obtained in the step (2) into a dialysis bag with the molecular weight of 14000, and dialyzing with deionized water for 10 days until the suspension liquid is neutral;
(4) soaking the dialysis bag containing the suspension in the step (3) in a polyethylene glycol (molecular weight of 16000) solution with the mass percentage concentration of 15wt% for concentrating for 8h until the mass percentage concentration of the suspension is 3 wt%, so as to obtain a CNC suspension;
(5) preparing a trimethylolethane solution (TME solution) with the mass percentage concentration of 10 wt%;
(6) uniformly mixing the CNC suspension liquid with the weight percentage of 3 obtained in the step (4) and the TME solution with the weight percentage of 10 obtained in the step (5) according to the volume ratio of 9:1, then carrying out ultrasonic treatment for 10min at the ultrasonic frequency of 40KHz, and controlling the temperature at 0 ℃ to obtain a CNC/TME mixed solution;
(7) weighing 5 mL of the CNC/TME mixed solution obtained in the step (6), putting the mixture into a polystyrene culture dish with the diameter of 35 mm, and naturally drying the mixture for 72 h at the temperature of 30 ℃ (the ambient humidity is 60%) to obtain a CNC/TME membrane, namely the flexible cellulose liquid crystal membrane.
Fig. 1 is a view showing the effect of the flexible cellulose liquid crystal film obtained in example 1 observed under a polarization microscope. As can be seen from fig. 1, the internal structure of the flexible cellulose liquid crystal film is cholesteric liquid crystal, and the formation of fingerprint texture is not affected after trimethylolethane is added. The flexible film prepared in example 1 is folded in half, the bending angle can reach 70 degrees, the flexible film automatically returns to the original state 3min after folding, and the folding can be repeated three times.
Example 2
A preparation method of a flexible cellulose liquid crystal film comprises the following steps:
(1) weighing 10 g of absolutely dry softwood pulp, adding the absolutely dry softwood pulp into a three-neck flask, adding 100 ml of concentrated sulfuric acid solution with the mass percentage concentration of 60wt%, stirring at the temperature of 60 ℃ at the rotating speed of 350 r/min for 45min, pouring the mixture into the beaker after the acidolysis is finished, adding deionized water with the volume 8 times that of the concentrated sulfuric acid solution to terminate the reaction, and obtaining white emulsion;
(2) centrifuging the white emulsion obtained in the step (1) at 10 ℃ at 10000 r/min for 10min, taking the upper suspension, repeatedly centrifuging for 3 times, and combining the suspensions;
(3) pouring the suspension liquid obtained in the step (2) into a dialysis bag with the molecular weight of 14000, and dialyzing with deionized water for 10 days until the suspension liquid is neutral;
(4) soaking the dialysis bag containing the suspension in the step (3) in a polyethylene glycol (with molecular weight of 18000) solution with the mass percentage concentration of 16 wt% for concentrating for 6h until the mass percentage concentration of the suspension is 3 wt%, so as to obtain CNC suspension;
(5) preparing a trimethylolethane solution (TME solution) with the mass percentage concentration of 10 wt%;
(6) uniformly mixing the CNC suspension liquid with the weight percentage of 3 obtained in the step (4) and the TME solution with the weight percentage of 10 obtained in the step (5) according to the volume ratio of 8:1, then carrying out ultrasonic treatment for 10min at the ultrasonic frequency of 40KHz, and controlling the temperature at 0 ℃ to obtain a CNC/TME mixed solution;
(7) and (3) putting 5 mL of the CNC/TME mixed solution obtained in the step (6) into a polystyrene culture dish with the diameter of 35 mm, and naturally drying for 72 h at the temperature of 30 ℃ (the ambient humidity is 70%) to obtain a CNC/TME membrane, namely the flexible cellulose liquid crystal membrane.
The effect of the flexible cellulose liquid crystal film obtained in example 2 observed under a polarization microscope was similar to that of example 1, and the internal structure thereof was cholesteric liquid crystal, as shown in fig. 1. The flexible film prepared in example 2 is folded in half, the bending angle can reach 80 degrees, the flexible film automatically returns to the original state 3min after folding, and the folding can be repeated three times.
Example 3
A preparation method of a flexible cellulose liquid crystal film comprises the following steps:
(1) weighing 10 g of absolutely dry softwood pulp, adding the absolutely dry softwood pulp into a three-neck flask, adding 100 ml of concentrated sulfuric acid solution with the mass percentage concentration of 64 wt%, stirring at the temperature of 50 ℃ and the rotating speed of 350 r/min for 1 hour, pouring the mixture into the beaker after the acid hydrolysis is finished, adding deionized water with the volume 10 times that of the concentrated sulfuric acid solution to terminate the reaction, and obtaining white emulsion;
(2) centrifuging the white emulsion obtained in the step (1) at 10 ℃ at 10000 r/min for 10min, taking the upper suspension, repeatedly centrifuging for 4 times, and combining the suspensions;
(3) pouring the suspension liquid obtained in the step (2) into a dialysis bag with the molecular weight of 14000, and dialyzing with deionized water for 10 days until the suspension liquid is neutral;
(4) soaking the dialysis bag containing the suspension in the step (3) in a polyethylene glycol (molecular weight 20000) solution with the mass percentage concentration of 20wt% for concentration for 5h until the mass percentage concentration of the suspension is 3 wt%, so as to obtain a CNC suspension;
(5) preparing a trimethylolethane solution (TME solution) with the mass percentage concentration of 10 wt%;
(6) uniformly mixing the 3 wt% of CNC suspension obtained in the step (4) with the 10wt% of TME solution obtained in the step (5) according to the volume ratio of 7:1, then performing ultrasonic treatment for 12min at the ultrasonic frequency of 30KHz, and controlling the temperature at 0 ℃ to obtain CNC/TME mixed solution;
(7) and (3) weighing 5 ml of the CNC/TME mixed solution obtained in the step (6), putting the mixture into a polystyrene culture dish with the diameter of 35 mm, and naturally drying the mixture for 72 h at the temperature of 30 ℃ (the ambient humidity is 75%) to obtain a CNC/TME membrane, namely the flexible cellulose liquid crystal membrane.
The effect of the flexible cellulose liquid crystal film obtained in example 3 observed under a polarization microscope was similar to that of example 1, and the internal structure thereof was cholesteric liquid crystal, as shown in fig. 1. The flexible film prepared in example 3 was folded in half, the bending angle of which could reach 100 °, and after 4min after folding, it automatically returned to the original state and could be repeated four times.
Example 4
A preparation method of a flexible cellulose liquid crystal film comprises the following steps:
(1) weighing 10 g of absolutely dry softwood pulp, adding the absolutely dry softwood pulp into a three-neck flask, adding 100 ml of concentrated sulfuric acid solution with the mass percentage concentration of 64 wt%, stirring at the temperature of 50 ℃ and the rotating speed of 350 r/min for 50min, pouring the mixture into the beaker after the acid hydrolysis is finished, adding deionized water with the volume 10 times that of the concentrated sulfuric acid solution to terminate the reaction, and obtaining white emulsion;
(2) centrifuging the white emulsion obtained in the step (1) at 10 ℃ at 10000 r/min for 10min, taking the upper suspension, repeatedly centrifuging for 3 times, and combining the suspensions;
(3) pouring the suspension liquid obtained in the step (2) into a dialysis bag with the molecular weight of 14000, and dialyzing with deionized water for 10 days until the suspension liquid is neutral;
(4) soaking the dialysis bag containing the suspension in the step (3) in a polyethylene glycol (molecular weight 20000) solution with the mass percentage concentration of 15wt% for concentrating for 8h until the mass percentage concentration of the suspension is 3 wt%, so as to obtain a CNC suspension;
(5) preparing a trimethylolethane solution (TME solution) with the mass percentage concentration of 10 wt%;
(6) uniformly mixing the 3 wt% of CNC suspension obtained in the step (4) with the 10wt% of TME solution obtained in the step (5) according to the volume ratio of 6:1, then carrying out ultrasonic treatment for 12min at the ultrasonic frequency of 30KHz, and controlling the temperature at 2 ℃ to obtain CNC/TME mixed solution;
(7) and (3) weighing 5 ml of the CNC/TME mixed solution obtained in the step (6), putting the mixture into a polystyrene culture dish with the diameter of 35 mm, and naturally drying the mixture for 72 h at the temperature of 30 ℃ (the ambient humidity is 80%) to obtain a CNC/TME membrane, namely the flexible cellulose liquid crystal membrane.
The effect of the flexible cellulose liquid crystal film obtained in example 4 observed under a polarization microscope was similar to that of example 1, and the internal structure thereof was cholesteric liquid crystal, as shown in fig. 1. The flexible film prepared in example 4 is folded in half, the bending angle can reach 120 degrees, the flexible film automatically returns to the original state after 5min after folding, and the folding can be repeated for five times.
Example 5
A preparation method of a flexible cellulose liquid crystal film comprises the following steps:
(1) weighing 10 g of absolutely dry hardwood pulp, adding the absolutely dry hardwood pulp into a three-neck flask, adding 100 ml of concentrated sulfuric acid solution with the mass percentage concentration of 65 wt%, stirring the mixture at the temperature of 50 ℃ for 1 hour at the rotating speed of 300 r/min, pouring the mixture into a beaker after the acid hydrolysis is finished, adding deionized water with the volume being 12 times that of the concentrated sulfuric acid solution to terminate the reaction, and obtaining white emulsion;
(2) centrifuging the white emulsion obtained in the step (1) at 10 ℃ at 10000 r/min for 10min, taking the upper suspension, repeatedly centrifuging for 3 times, and combining the suspensions;
(3) pouring the suspension liquid obtained in the step (2) into a dialysis bag with the molecular weight of 14000, and dialyzing with deionized water for 10 days until the suspension liquid is neutral;
(4) soaking the dialysis bag containing the suspension in the step (3) in a polyethylene glycol (molecular weight 20000) solution with the mass percentage concentration of 15wt% for concentration until the mass percentage concentration of the suspension is 3 wt%, so as to obtain a CNC suspension;
(5) preparing a trimethylolethane solution (TME solution) with the mass percentage concentration of 10 wt%;
(6) uniformly mixing the 3 wt% of CNC suspension obtained in the step (4) with the 10wt% of TME solution obtained in the step (5) according to the volume ratio of 8:1, then carrying out ultrasonic treatment for 15min at the ultrasonic frequency of 20KHz, and controlling the temperature at 5 ℃ to obtain CNC/TME mixed solution;
(7) and (3) taking 5 ml of the CNC/TME mixed solution obtained in the step (6), putting the mixture into a polystyrene culture dish with the diameter of 35 mm, and naturally drying the mixture for 96h at the temperature of 30 ℃ (the ambient humidity is 60%) to obtain a CNC/TME membrane, namely the flexible cellulose liquid crystal membrane.
The effect of the flexible cellulose liquid crystal film obtained in example 5 observed under a polarization microscope was similar to that of example 1, and the internal structure thereof was cholesteric liquid crystal, as shown in fig. 1. The flexible film prepared in example 5 is folded in half, the bending angle can reach 80 degrees, the flexible film automatically returns to the original state 3min after folding, and the folding can be repeated three times.
Example 6
A preparation method of a flexible cellulose liquid crystal film comprises the following steps:
(1) weighing hardwood pulp (with the oven-dry mass of 10 g and the hardwood pulp concentration of 95 wt%) and adding the hardwood pulp into a three-neck flask, adding 95 ml of concentrated sulfuric acid solution with the mass percentage concentration of 68 wt%, stirring at the temperature of 50 ℃ at the rotating speed of 350 r/min for 45min, pouring the mixture into the flask after the acid hydrolysis is finished, adding deionized water with the volume being 12 times that of the concentrated sulfuric acid solution to terminate the reaction, and obtaining white emulsion;
(2) centrifuging the white emulsion obtained in the step (1) at 10 ℃ at 10000 r/min for 10min, taking the upper suspension, repeatedly centrifuging for 3 times, and combining the suspensions;
(3) pouring the suspension liquid obtained in the step (2) into a dialysis bag with the molecular weight of 14000, and dialyzing with deionized water for 10 days until the suspension liquid is neutral;
(4) soaking the dialysis bag containing the suspension in the step (3) in a polyethylene glycol (molecular weight 20000) solution with the mass percentage concentration of 20wt% for concentration for 5h until the mass percentage concentration of the suspension is 3 wt%, so as to obtain a CNC suspension;
(5) preparing a trimethylolethane solution (TME solution) with the mass percentage concentration of 10 wt%;
(6) uniformly mixing the 3 wt% of CNC suspension obtained in the step (4) with the 10wt% of TME solution obtained in the step (5) according to the volume ratio of 6:1, then carrying out ultrasonic treatment for 15min at the ultrasonic frequency of 40KHz, and controlling the temperature at 0 ℃ to obtain CNC/TME mixed solution;
(7) and (3) weighing 5 ml of the CNC/TME mixed solution obtained in the step (6), putting the mixture into a polystyrene culture dish with the diameter of 35 mm, and naturally drying the mixture for 80 h at the temperature of 35 ℃ (the ambient humidity is 60%) to obtain a CNC/TME membrane, namely the flexible cellulose liquid crystal membrane.
The effect of the flexible cellulose liquid crystal film obtained in example 6 observed under a polarization microscope was similar to that of example 1, and the internal structure thereof was cholesteric liquid crystal, as shown in fig. 1. The flexible film prepared in example 6 is folded in half, the bending angle can reach 120 degrees, the flexible film automatically returns to the original state after 5min after folding, and the folding can be repeated for five times.
The above examples are only preferred embodiments of the present invention, which are intended to be illustrative and not limiting, and those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention.
Claims (2)
1. A preparation method of a flexible cellulose liquid crystal film is characterized by comprising the following steps:
(1) mixing wood pulp with a concentrated sulfuric acid solution, heating while stirring, adding water, and uniformly mixing to obtain a mixed solution;
(2) centrifuging the mixed solution obtained in the step (1) to obtain an upper suspension;
(3) pouring the suspension liquid obtained in the step (2) into a dialysis bag, carrying out dialysis treatment until the suspension liquid is neutral, and then soaking the dialysis bag into a polyethylene glycol solution to concentrate the suspension liquid to obtain a CNC suspension liquid;
(4) uniformly mixing the CNC suspension liquid obtained in the step (3) with a trimethylolethane solution, and then carrying out ultrasonic treatment to obtain a CNC/TME mixed liquid;
(5) drying the CNC/TME mixed solution obtained in the step (4) to obtain the flexible cellulose liquid crystal film;
the wood pulp in the step (1) is softwood pulp or hardwood pulp; the concentration of the wood pulp is 95-100 wt%; the mass percentage concentration of the concentrated sulfuric acid solution is 60-70 wt%; the mass-volume ratio of the oven dry mass of the wood pulp to the volume of the concentrated sulfuric acid solution is 1:8-14 g/mL;
the stirring speed in the stirring state in the step (1) is 300-400rpm, the heating treatment temperature is 45-60 ℃, and the heating treatment time is 45-60 min;
the volume ratio of the concentrated sulfuric acid solution to water in the step (1) is 1: 9-12;
the centrifugation treatment frequency of the step (2) is 3-4 times, the centrifugation treatment speed is 8000-10000rpm, the centrifugation treatment time is 10-12min, and the centrifugation treatment temperature is 0-10 ℃;
the molecular weight cut-off of the dialysis bag in the step (3) is 14000;
the mass percentage concentration of the polyethylene glycol solution in the step (3) is 15-20wt%, the molecular weight of the polyethylene glycol is 16000-;
the mass percentage concentration of the trimethylolethane solution in the step (4) is 10-20 wt%; the volume ratio of the CNC suspension to the trimethylolethane solution is (6-9) to 1; the temperature of the ultrasonic treatment is 0-5 ℃, the time of the ultrasonic treatment is 10-15min, and the ultrasonic frequency of the ultrasonic treatment is 20-40 KHz;
and (5) drying at 30-35 ℃, at 60-80% for 72-96 h.
2. A flexible cellulose liquid crystal film produced by the production method according to claim 1.
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