CN115353568B - Carboxylated cellulose nanocrystalline, intelligent film, preparation method and application - Google Patents
Carboxylated cellulose nanocrystalline, intelligent film, preparation method and application Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
- C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
- C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
- C08B15/04—Carboxycellulose, e.g. prepared by oxidation with nitrogen dioxide
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
- C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
- C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
- G01N21/783—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour for analysing gases
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
- C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
- C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2401/00—Characterised by the use of cellulose, modified cellulose or cellulose derivatives
- C08J2401/02—Cellulose; Modified cellulose
- C08J2401/04—Oxycellulose; Hydrocellulose
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Abstract
The invention belongs to the technical field of cellulose materials and packaging films, and particularly relates to carboxylated cellulose nanocrystals, a preparation method and application thereof, and an intelligent film prepared from the carboxylated cellulose nanocrystals and a preparation method thereof. The carboxylated cellulose nanocrystalline provided by the invention has larger specific surface area and higher carboxyl content, and the carboxyl on the surface can adsorb alkaline gas through chemical force, so that after the carboxylated cellulose nanocrystalline is added into a film material containing an acid-base indicator to prepare a packaging film, the surface structure of the film material is coarser, the diffusion path of ammonia gas penetrating into an intelligent film is increased, and the intermolecular hydrogen bond is stronger, so that the response sensitivity of the packaging film to the ammonia gas can be obviously improved under the condition of lower addition amount of the carboxylated cellulose nanocrystalline, and meanwhile, the water vapor barrier property, the mechanical property and the thermal stability are also stronger.
Description
Technical Field
The invention belongs to the technical field of cellulose materials and packaging films, and particularly relates to carboxylated cellulose nanocrystals, a preparation method and application thereof, and an intelligent film prepared from the carboxylated cellulose nanocrystals and a preparation method thereof.
Background
With the development of science and technology, packaging film materials are not limited to simple packaging, but can also control certain characteristics of food ingredients and provide information to producers, retailers and consumers during food storage and transfer. Such packaging materials are known as smart film materials. While fast reaction has been the main goal of smart film fabrication.
In the prior art, a method for improving ammonia response performance of an intelligent film by using cellulose nanocrystals is available, but the introduction of the cellulose nanocrystals can affect mechanical performance and waterproof performance of the intelligent film, the dosage needs to be controlled, and the effect of the cellulose nanocrystals on improving ammonia response performance can be reduced if the dosage is too low, so that color response is not obvious.
Disclosure of Invention
Aiming at the technical problems, the invention provides a carboxylated cellulose nanocrystal, an intelligent film, a preparation method and application. The carboxylated cellulose nanocrystalline has larger specific surface area and more carboxyl number, can obviously improve the response sensitivity to ammonia gas when being applied to intelligent film materials, and has stronger water vapor barrier property, mechanical property and thermal stability.
In order to solve the technical problems, the embodiment of the invention adopts the following technical scheme:
in a first aspect, an embodiment of the present invention provides a method for preparing carboxylated cellulose nanocrystals, including the following operations:
dispersing a cellulose raw material in an aqueous solution containing citric acid and hydrochloric acid, reacting for 3-4 hours at 70-90 ℃, washing the obtained suspension with deionized water until the pH is neutral, carrying out ultrasonic treatment on the washed suspension for 20-40 min, and drying to obtain carboxylated cellulose nanocrystalline;
the concentration of the citric acid in the aqueous solution is 2.5-3.5M, the concentration of the hydrochloric acid is 15-25% v/v, and the mass of the citric acid is 19-29 times of the mass of the cellulose.
The invention adopts the concentration of the citric acid and the mass ratio of the citric acid to the cellulose to fully hydrolyze the cellulose raw material, and then the cellulose raw material and the citric acid are subjected to esterification reaction to generate Cellulose Nanocrystals (CNCs) with more carboxyl groups on the surface, namely carboxylated cellulose nanocrystals (CNCa). In the preparation method, if the concentration of the citric acid is too high or the mass ratio is too high, the esterified product is hydrolyzed to reduce the number of carboxyl groups in the product; otherwise, the cellulose is insufficiently hydrolyzed.
The amorphous region of cellulose has disordered molecular chain arrangement, is more relaxed, and has larger intermolecular distance. The temperature condition in the preparation method can lead the citric acid to enter the amorphous region for reaction first, thereby leading the carboxyl content on the CNCs to be obviously increased, and the cellulose raw material can be hydrolyzed into glucose, so that the long-chain glucose part of the easily accessible amorphous region is broken, and the carboxyl content in the CNCs can not be reduced due to higher reaction temperature.
The contact time of the cellulose raw material and the citric acid is directly related to the contact sufficiency of the cellulose raw material and the citric acid, and the contact sufficiency of the cellulose raw material and the citric acid can be ensured by the reaction time of 3-4 hours, so that the hydrolysis reaction of the cellulose raw material is more complete, more carboxyl groups are formed in the CNCs through the esterification reaction, and the excessive degradation of the cellulose raw material into sugar substances such as glucose and the like can be caused by the overlong reaction time, so that the carboxyl content of the CNCs is reduced.
Because acidolysis is insufficient to enable acidolysis products of cellulose to reach nano-size, the cellulose nano-crystal particles with nano-size are obtained through ultrasonic treatment after cleaning.
The carboxylated cellulose nanocrystalline prepared by the method reaches a nano state, so that the carboxylated cellulose nanocrystalline has larger specific surface area, and the surface carboxyl of the carboxylated cellulose nanocrystalline can adsorb alkaline gas through chemical force. Therefore, after the acid-base indicator is added into the film material containing the acid-base indicator to prepare the packaging film, the surface structure of the film material can be coarser, the diffusion path of ammonia gas penetrating into the intelligent film is increased, and the intermolecular hydrogen bond is stronger, so that the response sensitivity of the packaging film to the ammonia gas can be remarkably improved, and the acid-base indicator can be used for monitoring the food quality in real time through the color change of the acid-base indicator. At the same time, the water vapor barrier properties, mechanical properties and thermal stability (TGA) of the film are also stronger.
In actual operation, the cellulose raw material can be dispersed in the aqueous solution of citric acid, and then the aqueous solution of hydrochloric acid is added, or the aqueous solution of citric acid and hydrochloric acid can be prepared first and then the cellulose raw material is added, and the two modes do not influence the reaction result, so the patent is not limited.
Preferably, the cellulose raw material is microcrystalline cellulose.
Preferably, the concentration of citric acid in the aqueous solution is 3.0M and the concentration of the hydrochloric acid solution is 20% v/v.
Preferably, the molar ratio of the citric acid to the hydrochloric acid is 2-3:1.
Preferably, the mass of the citric acid is 24 times the mass of the cellulose.
Preferably, the reaction temperature is 80 ℃.
Preferably, the reaction time is 4 hours.
In a second aspect, the embodiment of the invention also provides a carboxylated cellulose nanocrystal, which is prepared by the preparation method.
In a third aspect, the embodiment of the invention also provides an application of the carboxylated cellulose nanocrystals in preparing intelligent films. The carboxylated cellulose nanocrystal has rich specific surface area and more carboxyl functional groups, can improve the ammonia response performance of the membrane material, and can be used for preparing intelligent membrane materials with high sensitivity to ammonia.
In a fourth aspect, the embodiment of the invention also provides an intelligent film, which comprises the carboxylated cellulose nanocrystalline, an acid-base indicator and a film forming material.
In a fifth aspect, an embodiment of the present invention further provides a method for preparing an intelligent film, specifically including the following steps:
s1, dissolving polyvinyl alcohol (PVA) in a glycerol water solution, adding an acid-base indicator and dissolving, and then adding the carboxylated cellulose nanocrystalline and dissolving to obtain a film forming solution; the mass of glycerin in the glycerin aqueous solution is 25-35% of the mass of the polyvinyl alcohol, the mass of the acid-base indicator is 3.5-4.5% of the mass of the polyvinyl alcohol, and the mass of the carboxylated cellulose nanocrystalline is 5.5-6.5% of the mass of the polyvinyl alcohol;
and S2, degassing the film forming solution, pouring the film forming solution on an organic glass plate, and drying the film forming solution to obtain the intelligent film.
Experiments prove that the intelligent film prepared by the method by using the polyvinyl alcohol, the glycerol, the carboxylated cellulose nanocrystalline and the acid-base indicator has high response sensitivity to ammonia gas, and can show remarkable colorimetric response in a short time in a low ammonia concentration, so that the fresh or deterioration condition of food packaged by the intelligent film can be indicated by ammonia gas generated by food, and the quality of the food is reflected in real time; meanwhile, the intelligent film has ideal hydrophobic property and mechanical property, and the main film forming substance polyvinyl alcohol is nontoxic, good in thermoplasticity and biodegradable. Therefore, the intelligent film has practical application value and good application prospect in the food industry.
Preferably, the mass-volume ratio of the polyvinyl alcohol to the glycerol aqueous solution is 4.5-5.5:100 (g: mL).
Preferably, the acid-base indicator is Anthocyanin (AH).
Preferably, the mass of the acid-base indicator is 4% of the mass of the polyvinyl alcohol.
Optionally, the preparation method of the acid-base indicator comprises the following steps: extracting purple potato powder with 75-85% v/v ethanol water solution under dark condition, removing solvent, purifying with macroporous adsorbent resin, and drying. The extraction method preferably adopts ultrasonic extraction and cold soaking, and optionally, the ultrasonic extraction time is 35-45 min; cold soaking at 4 deg.c for 18-30 hr; the drying method is preferably freeze drying.
Optionally, the macroporous adsorbent resin is selected from HP-20, AB-8, DM130, HPD-100, NKA-9, D101 macroporous adsorbent resins.
The invention has the beneficial effects that: the carboxylated cellulose nanocrystalline obtained by the preparation method disclosed by the invention has rich specific surface area and carboxyl content, the rich specific surface area of the carboxylated cellulose nanocrystalline is used for an intelligent film, the contact area between gas and the intelligent film is increased, and the surface carboxyl has adsorption capacity to alkaline gas through chemical force, so that the response sensitivity of the intelligent film to ammonia gas is improved, the problem that the color response of a film material is not obvious is solved, meanwhile, the hydrophobicity and mechanical property required by the intelligent film as packaging are taken into consideration, and the carboxylated cellulose nanocrystalline is expected to be applied to the food industry, and the quality of foods is monitored in real time.
Drawings
FIG. 1 is a transmission electron microscope image of carboxylated cellulose nanocrystals prepared in example 1;
FIG. 2 is a graph showing the particle size of carboxylated cellulose nanocrystals prepared in example 1;
FIG. 3 is a Zeta potential diagram of carboxylated cellulose nanocrystals prepared in example 1;
FIG. 4 is an infrared spectrum of microcrystalline cellulose and carboxylated cellulose nanocrystals prepared as used in example 1;
FIG. 5 is an X-ray diffraction pattern of microcrystalline cellulose and carboxylated cellulose nanocrystals prepared as used in example 1;
FIG. 6 is a nuclear magnetic resonance image of microcrystalline cellulose and the carboxylated cellulose nanocrystals produced as used in example 1;
FIG. 7 is an infrared spectrum and an X-ray diffraction pattern of PVA/AH-CNCA, PVA/AH and PVA of example 7;
FIG. 8 is a graph showing mechanical property test of PVA/AH-CNCA film and PVA/AH film of example 7;
FIG. 9 is a graph showing the sensitivity of PVA/AH-CNCA films and PVA/AH films to ammonia vapor in example 7;
FIG. 10 is a graph showing the thermal stability test of PVA/AH-CNCA films and PVA/AH films of example 7;
FIG. 11 is the effect of the mass ratio of citric acid to cellulose on the carboxyl content of CNCs in test example 1;
FIG. 12 is a graph showing the effect of reaction temperature on the carboxyl group content of CNCs in test example 2;
FIG. 13 shows the effect of reaction time on the carboxyl content of CNCs in test example 3.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
The embodiment provides a carboxylated cellulose nanocrystal, which is prepared by the following steps:
3.0g of microcrystalline cellulose (MCC) was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL (6M) hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Performing transmission electron microscope observation on the obtained CNCA powder, wherein the prepared CNCA is in a short rod structure as shown in figure 1; the particle size distribution is shown in fig. 2: the particles are uniformly dispersed, the diameter is about 10-30 nm, the length is about 80-200 nm, the granularity is mainly concentrated at 350-400 nm, and the small amount of particles are distributed in the range of 20-30 nm; the Zeta potential diagram is shown in figure 3, and the Zeta potential is-39.8 mV, which shows that the obtained CNCA suspension has better stability.
The microcrystalline cellulose used in this example and the CNCA prepared were subjected to infrared, X-ray and nuclear magnetic detection, and the results are shown in fig. 4 to 6. As can be seen from the infrared spectrogram, the CNCA prepared in the embodiment has a new peak at 1735cm < -1 >, which indicates the existence of carboxyl. And the carboxyl group content was determined to be about 1.19mmol/g by titration experiments. As can be seen from the XRD spectrum, microcrystalline cellulose and CNCA cellulose type I prepared in this example did not change, indicating that the reaction process did not occur in the crystalline region. In addition, the crystallinity of the cellulose increased from 69.07% to 74.06%. From the nuclear magnetic resonance spectrum, it can be seen that microcrystalline cellulose corresponds to methylene (C8, C11), carboxylic acid carbonyl (C10, C12) and ester group (C7) of citric acid at 105.8ppm (C1), 89.5ppm (C4), 66.1ppm (C6), 70 to 80ppm (C2, C3 and C5), and CNCA at a characteristic signal peak around chemical shift delta of 43.7ppm and 173.2 ppm. Indicating that the reaction site of CNCA obtained by acidolysis of microcrystalline cellulose by citric acid is mainly at the C6 position.
Example 2
The embodiment provides a carboxylated cellulose nanocrystal, which is prepared by the following steps:
3.0g of microcrystalline cellulose was dispersed in 100mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 20mL (6M) hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Example 3
The embodiment provides a carboxylated cellulose nanocrystal, which is prepared by the following steps:
3.0g of microcrystalline cellulose was dispersed in 150mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 30mL (6M) hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Example 4
The embodiment provides a carboxylated cellulose nanocrystal, which is prepared by the following steps:
3.0g of microcrystalline cellulose was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL (6M) hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 70℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Example 5
The embodiment provides a carboxylated cellulose nanocrystal, which is prepared by the following steps:
3.0g of microcrystalline cellulose was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL (6M) hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 90℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Example 6
The embodiment provides a carboxylated cellulose nanocrystal, which is prepared by the following steps:
3.0g of microcrystalline cellulose was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL (6M) hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 3 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Example 7
The embodiment provides an intelligent film, which is prepared by the following steps:
1. extraction and purification of Anthocyanin (AH)
The purple potato is washed, peeled and sliced, and then is frozen, dried and crushed into powder. Mixing the purple potato powder with 80% v/v ethanol at a ratio of 1:8, ultrasonically extracting for 40min, soaking in a refrigerator at 4deg.C for 24 hr, and evaporating at 37deg.C to remove ethanol. Then, purification is carried out by using HP-20 macroporous resin, and substances such as saccharides and the like are removed. The experimental operations are all protected from light by tinfoil paper. Finally, the purified anthocyanin powder is obtained by adopting a vacuum freeze drying method and is preserved in a refrigerator at the temperature of 4 ℃ far away from illumination.
2. Preparation of smart films
5g of PVA was weighed out and dissolved in 100mL of an aqueous glycerin solution having a concentration of 0.15g/L, followed by stirring with an electric stirrer at 90℃for 3 hours to prepare a PVA solution. A PVA/AH solution was prepared by adding 0.2g of purple potato anthocyanin powder to the cooled PVA solution. Then, 0.3g of the carboxylated cellulose nanocrystals prepared in example 1 were added to the PVA/AH solution. After degassing with an ultrasonic breaker at room temperature for 30min, the solution was poured onto a plexiglass plate (25X 4 cm) and dried in a vacuum oven at 40℃for 36h. The sample is expressed as PVA/AH-CNCA.
The infrared spectra and X-ray diffraction patterns of PVA/AH-CNCA, PVA/AH and PVA are shown in FIG. 7 (a pattern is an infrared spectrum and b pattern is an X-ray diffraction pattern).
As shown in FIG. 7, it can be seen from the infrared spectrum that after AH is added, the film material is at 1041cm -1 The peak at which disappeared due to molecular interactions between PVA matrix and AH. However, after adding CNCA at 1041cm -1 The peak at which occurs again. Indicating that the addition of CNCA disrupts the original hydrogen bonding between molecules. At the same time, it can be found that 1089cm compared with PVA/AH -1 The peaks where the CNCA film material was added were weaker, indicating that the amorphous regions of PVA were destroyed. Wherein the peak value of the added CNCA film material is 2908cm -1 Offset, which is a signal of a strong specific molecular interaction caused by a change in chemical groups.
The PVA/AH solution prepared in this example was poured onto a plexiglass plate (25X 4 cm) and dried in a vacuum oven at 40℃for 36h to give a PVA/AH film as a control. The resulting PVA/AH-CNCA and PVA/AH films were subjected to mechanical, ammonia response and thermal stability testing after 24 hours of exposure to ambient temperature having a relative humidity of 57%.
The mechanical properties test results are shown in fig. 8: compared with PVA/AH film, the PVA/AH-CNCA film has raised tensile strength and lowered breaking elongation, and the PVA/AH-CNCA film with the carboxylated cellulose nanocrystal has excellent mechanical performance.
The results of the ammonia response performance test are shown in FIG. 9 (a is 0.008mol/L ammonia solution; b is 0.2mol/L ammonia solution; c is 2mol/L ammonia solution), and the PVA/AH film has the lowest color change to ammonia gas and obvious color difference change to ammonia gas and identifiable color change at the same concentration and at different times and at different concentrations and at the same time. In addition, the PVA/AH-CNCA film exhibits a significant change in color from blue to yellow, both under low and high concentration conditions, and exhibits a rapid response effect compared to the PVA/AH film. This is due to the abundance of specific surface area and carboxyl functionality of nanocellulose.
The hydrophobic properties of PVA/AH-CNCA and PVA/AH films are shown in Table 1.
TABLE 1 hydrophobic Properties of PVA/AH-CNCA and PVA/AH films
As shown in table 1, the reduced moisture content of the CNCA added film materials, probably due to hydrogen bonding, prevented their interaction with water. And, the WVP of the membrane material (their ability to allow water to pass) is related to its water content: the lower the moisture content, the lower the WVP. Clearly, the addition of CNCA reduced the WVP. It can also be seen that the water solubility decreases upon addition of CNCA, as the presence of CNCA can reduce its water solubility by increasing the attractive forces between polymer molecules or by inhibiting water diffusion into the sample. In addition, the addition of CNCA makes the membrane material have better hydrophobicity, and the water vapor blocking capability is enhanced.
The results of the thermal stability test are shown in FIG. 10 (graph a is the TGA curve; graph b is the DTG curve), and the TGA and DTG curves of the samples exhibit four stages of weight loss. The first weight loss occurs at 30-120 deg.c due to evaporation of the adsorbed water in the film. Weight loss in the second stage is in the range of 150-250 ℃ due to glycerolysis. Notably, the third stage of weight loss of PVA/AH film was observed to be between 280℃and 350℃while PVA/AH-CNCA film was observed to be between 280℃and 380 ℃. The higher temperature stability of CNCA is the reason behind these two different temperature ranges. The fourth stage is between 350-500 ℃ and 380-500 ℃ respectively. It can be concluded that the presence of CNCA enhances the thermal stability of the smart film relative to PVA/AH. This is mainly because the strong hydrogen bond between CNCA and PVA/AH increases the cross-linking between macromolecules in the film, thus inhibiting thermal degradation of PVA/AH complex and enhancing the heat resistance of the smart film.
Comparative example 1
The comparative example provides a carboxylated cellulose nanocrystal, the preparation method of which is as follows:
3.0g of microcrystalline cellulose was dispersed in 50mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 10mL of hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Comparative example 2
The comparative example provides a carboxylated cellulose nanocrystal, the preparation method of which is as follows:
3.0g of microcrystalline cellulose was dispersed in 200mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 40mL of hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Comparative example 3
The comparative example provides a carboxylated cellulose nanocrystal, the preparation method of which is as follows:
3.0g of microcrystalline cellulose was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL of hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 50℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Comparative example 4
The comparative example provides a carboxylated cellulose nanocrystal, the preparation method of which is as follows:
3.0g of microcrystalline cellulose was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL of hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 60℃for 4 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Comparative example 5
The comparative example provides a carboxylated cellulose nanocrystal, the preparation method of which is as follows:
3.0g of microcrystalline cellulose was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL of hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 2 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Comparative example 6
The comparative example provides a carboxylated cellulose nanocrystal, the preparation method of which is as follows:
3.0g of microcrystalline cellulose was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL of hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 5 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Comparative example 7
The comparative example provides a carboxylated cellulose nanocrystal, the preparation method of which is as follows:
3.0g of microcrystalline cellulose was dispersed in 125mL of aqueous citric acid (3M), and hydrolyzed by mechanical stirring in a 250mL flask with 25mL of hydrochloric acid (20%, v/v) as a catalyst, and the resulting suspension was repeatedly centrifuged with deionized water until neutral, with stirring at 80℃for 7 hours. Then, the suspension was treated in an ultrasonic cell disruptor (1400W) for 30min to obtain an aqueous CNCA solution. Finally, the suspension was freeze-dried in vacuo for 24h to give CNCA powder.
Comparative example 8
The comparative example provides an intelligent film, which is prepared by the following steps:
1. extraction and purification of anthocyanins
Same as in example 7
2. Preparation of smart films
5g of PVA was weighed out and dissolved in 100mL of an aqueous glycerin solution having a concentration of 0.15g/L, followed by stirring with an electric stirrer at 90℃for 3 hours to prepare a PVA solution. A PVA/AH solution was prepared by adding 0.1g of purple potato anthocyanin powder to the cooled PVA solution. Thereafter, the solution was poured onto a plexiglass plate (25X 4 cm) and dried in a vacuum oven at 40℃for 36h. The sample is expressed as PVA/AH.
Comparative example 9
The comparative example provides an intelligent film, which is prepared by the following steps:
1. extraction and purification of anthocyanins
Same as in example 7
2. Preparation of smart films
5g of PVA was weighed out and dissolved in 100mL of an aqueous glycerin solution having a concentration of 0.15g/L, followed by stirring with an electric stirrer at 90℃for 3 hours to prepare a PVA solution. A PVA/AH solution was prepared by adding 0.3g of purple potato anthocyanin powder to the cooled PVA solution. Thereafter, the solution was poured onto a plexiglass plate (25X 4 cm) and dried in a vacuum oven at 40℃for 36h. The sample is expressed as PVA/AH.
Comparative example 10
The comparative example provides an intelligent film, which is prepared by the following steps:
1. extraction and purification of anthocyanins
Same as in example 7
2. Preparation of smart films
5g of PVA was weighed out and dissolved in 100mL of an aqueous glycerin solution having a concentration of 0.15g/L, followed by stirring with an electric stirrer at 90℃for 3 hours to prepare a PVA solution. A PVA/AH solution was prepared by adding 0.4g of purple potato anthocyanin powder to the cooled PVA solution. Thereafter, the solution was poured onto a plexiglass plate (25X 4 cm) and dried in a vacuum oven at 40℃for 36h. The sample is expressed as PVA/AH.
Test example 1
The carboxyl content of the carboxylated cellulose nanocrystals obtained in examples 1 to 3, comparative example 1 and comparative example 2 was measured by titration method, and the results are shown in fig. 11: the carboxyl group content of the carboxylated cellulose nanocrystals obtained in examples 1 to 3 was significantly higher than that of comparative examples 1 and 2 (P < 0.05), wherein the carboxyl group content of the carboxylated cellulose nanocrystals obtained in example 1 could reach 1.19mmol/g.
Test example 2
The carboxyl content of the carboxylated cellulose nanocrystals obtained in example 1, example 4, example 5, comparative example 3, comparative example 4 was measured by titration method, and the results are shown in fig. 12: the carboxyl content of the carboxylated cellulose nanocrystals obtained in example 1, example 4, example 5 was significantly higher than that of comparative examples 3 and 4 (P < 0.05).
Test example 3
The carboxyl group content of the carboxylated cellulose nanocrystals obtained in example 1, example 6, and comparative examples 5 to 7 was measured by titration, and the results are shown in fig. 13: the carboxyl content of the carboxylated cellulose nanocrystals obtained in example 1 and example 6 is significantly higher than that of comparative examples 5-7 (P < 0.05).
Test example 4
The PVA/AH film of example 7 and the PVA/AH films produced in comparative examples 8 to 10 were subjected to the hydrophobic property test and the mechanical property test after being left at an ambient temperature of 57% relative humidity for 24 hours, as shown in tables 2 and 3.
TABLE 2 results of hydrophobic Property test
Note that: different lower case letters indicate significant differences between the same columns (P < 0.05).
The PVA and AH molecular structures are rich in hydroxyl groups, so that the PVA and AH molecular structures have good hydrophilicity. From the above table, it can be seen that the PVA/AH film of example 7 had the lowest moisture content, water solubility and water vapor permeability.
TABLE 3 mechanical test results
Note that: different lower case letters indicate significant differences between the same columns (P < 0.05).
As can be seen from Table 3, the PVA/AH film of example 7 has the best tensile strength. The elongation at break is not too high or too low, and the mechanical properties of the PVA/AH film of example 7 are best overall.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, or alternatives falling within the spirit and principles of the invention.
Claims (6)
1. An intelligent membrane, characterized by comprising: carboxylated cellulose nanocrystals, acid-base indicators, polyvinyl alcohol and glycerol; wherein the polyvinyl alcohol is a film-forming material; the mass of the glycerol is 25% -35% of the mass of the polyvinyl alcohol, the mass of the acid-base indicator is 3.5% -4.5% of the mass of the polyvinyl alcohol, and the mass of the carboxylated cellulose nanocrystalline is 5.5% -6.5% of the mass of the polyvinyl alcohol;
the preparation method of the carboxylated cellulose nanocrystalline specifically comprises the following operations:
dispersing a cellulose raw material in an aqueous solution containing citric acid and hydrochloric acid, reacting for 3-4 hours at 70-90 ℃, washing the obtained suspension with deionized water until the pH is neutral, carrying out ultrasonic treatment on the washed suspension for 20-40 min, and drying to obtain carboxylated cellulose nanocrystalline;
the concentration of the citric acid in the aqueous solution is 2.5-3.5M, and the concentration of the hydrochloric acid is 15-25% v/v; the carboxyl content of the carboxylated cellulose nanocrystal is 1.19mmol/g.
2. The smart film of claim 1, wherein the cellulosic feedstock is microcrystalline cellulose; and/or
The concentration of the citric acid in the aqueous solution is 3.0M, and the concentration of the hydrochloric acid solution is 20% v/v; and/or
The molar ratio of the citric acid to the hydrochloric acid is 2-3:1.
3. The smart film of claim 1, wherein the reaction temperature is 80 ℃.
4. A smart film according to claim 3, wherein the reaction time is 4 hours.
5. The method for preparing an intelligent film according to any one of claims 1 to 4, comprising the steps of:
s1, dissolving polyvinyl alcohol in a glycerol water solution, adding an acid-base indicator and dissolving, and then adding carboxylated cellulose nanocrystals and dissolving to obtain a film forming solution;
and S2, degassing the film forming solution, pouring the film forming solution on an organic glass plate, and drying the film forming solution to obtain the intelligent film.
6. The method for preparing an intelligent film according to claim 5, wherein the mass-volume ratio of the polyvinyl alcohol to the glycerol aqueous solution is 4.5-5.5 g/100 ml; and/or
The acid-base indicator is anthocyanin; and/or
The mass of the acid-base indicator is 4% of the mass of the polyvinyl alcohol.
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