CN106700110A - Preparation method of graphene oxide/nano cellulose/polyvinyl alcohol composite film - Google Patents

Abstract

The preparation method of graphene oxide/nanometer cellulose/polyvinyl alcohol composite film aims to solve the problem of poor mechanical properties and barrier properties of existing degradable polyvinyl alcohol packaging films. Methods: 1. Preparation of nanocellulose; 2. Preparation of graphene oxide; 3. Preparation of nanocellulose/polyvinyl alcohol mixed solution; 4. Preparation of graphene oxide solution; 5. Preparation of composite film. The mechanical properties of the composite film prepared by the present invention can reach 101.49MPa in tensile strength, which is 42.4% higher than that of PVA film, the oxygen barrier property is 2.08 times higher than that of pure PVA film, and the thermal decomposition temperature is increased by 10-20°C. High light transmission. The invention belongs to the field of preparation of composite packaging films.

Description

Preparation method of graphene oxide/nanocellulose/polyvinyl alcohol composite film

technical field

The invention relates to a preparation method of a composite packaging film.

Background technique

Polyvinyl alcohol (PVA) has good biodegradability, film-forming property, printability, environmental friendliness and solubility. It is one of the packaging materials with great application potential and is widely used in packaging, biomedical and other industries. However, the molecular chain of polyvinyl alcohol contains a large number of hydroxyl groups, and there are a large number of hydrogen bonds in the molecule. The mechanical properties and barrier properties of biodegradable materials prepared from it often cannot meet higher requirements for use. Therefore, improving the mechanical properties of polyvinyl alcohol and improving its barrier properties have become the main problems to be solved urgently.

The size of nanocellulose (NCC) reaches the nanoscale, light weight and high strength. Therefore, when it is combined with some polymer materials, it can form a highly entangled nanofiber network structure. This series of excellent properties of nanocellulose makes it a performance Excellent filler material, widely used in high-performance composite materials. Significant progress has been made in the use of nanocellulose to reinforce polymers such as polylactic acid, chitosan, epoxy resin, and polyvinyl alcohol. The addition of nanocellulose has improved the strength, mechanical properties, and thermal stability of the polymer. Significant improvements have been made and the application fields of polymers have been broadened.

Graphene oxide has a two-dimensional nanosheet structure, which makes graphene oxide have good barrier properties. Graphene oxide contains a large number of oxygen-containing groups (-OH, C=O, C= O and other oxygen-containing groups), -OH, C=O are distributed on the edge of the graphene oxide sheet, and C=O and other oxygen-containing groups are distributed between the graphene oxide sheets. The existence of these functional groups increases the The distance between the graphene oxide sheets is increased, so that the solvent can better enter the inside of the sheet, and the dispersion of graphene oxide is improved.

However, the mechanical properties and barrier properties of NCC/PVA composite films and GO/PVA composite films prepared by existing methods are poor.

Contents of the invention

The invention aims to solve the problem of poor mechanical properties and barrier properties of the existing degradable polyvinyl alcohol packaging film, and provides a preparation method of a graphene oxide/nanocellulose/polyvinyl alcohol composite film.

The preparation method of graphene oxide/nanocellulose/polyvinyl alcohol composite film is carried out according to the following steps:

1. Preparation of nanocellulose;

Two, prepare graphene oxide;

3. Preparation of nanocellulose/polyvinyl alcohol mixed solution:

Mix 13.56ml of nanocellulose suspension with a concentration of 5.9g/L, 3.919g of polyvinyl alcohol and 86.44ml of distilled water in a 90°C water bath at a high speed of 500r/min for 2h to obtain a nanocellulose/polyvinyl alcohol mixed solution ;

4. Graphene oxide solution equipment:

Prepare a graphene oxide solution with a weight percentage of 0.1wt%-0.3wt%, and ultrasonically treat it for 30 minutes to obtain a graphene oxide solution;

5. Preparation of composite film: Pour the graphene oxide solution into the nanocellulose/polyvinyl alcohol mixed solution, stir and mix evenly, and then ultrasonically remove air bubbles for 30 minutes to obtain a film-forming liquid, which is placed on a flat glass plate Spread the film and dry it at room temperature to obtain a graphene oxide/nanocellulose/polyvinyl alcohol composite film.

The preparation method of nanocellulose in step 1 is as follows:

Weigh 7g of microcrystalline cellulose, add it to 100mL of sulfuric acid solution with a mass fraction of 64%, stir it with a magnetic stirrer to make it evenly mixed, then put it in a water bath at 40°C and stir at a speed of 500r/min for 2h, and then sonicate for 15min , dilute with 1000ml deionized water, end the reaction, let it stand for 24 hours, pour off the supernatant, collect the lower layer solution and put it in a centrifuge washing at a speed of 8000r/min, until it is in the form of a non-layered hydrosol colloid, collect the colloid and put it in a dialysis bag , using deionized water as the dialysate, dialyzed until the pH value of the suspension colloid is 7, to obtain nanocellulose.

The preparation method of graphene oxide in step 2 is as follows:

(1) 1.0 g of natural flake graphite, 1.0 g of NaNO ₃ and 46 mL of concentrated sulfuric acid with a mass fraction of 98% were mixed and placed in an ice bath at 5° C., stirred for 1 h, and mixed uniformly to obtain a mixed solution;

(2) Add 6g of KMnO ₄ to the mixture, stir for 1h, then move the solution to a water bath at 50°C, and stir at a speed of 500r/min for 4h, the solution turns from black to beige;

(3) Raise the temperature in the water bath to 85°C, and stir at a speed of 500r/min for 1h to obtain a soil brown suspension solution;

(4) Pour the obtained earth brown suspension solution into 200mL H ₂ O ₂ deionized aqueous solution, treat it in an ice bath, the suspension turns brownish yellow, and let the suspension stand at room temperature for 24 hours;

Wherein _200mL of H2O2 deionized aqueous solution contains _6mL of H2O2 with a mass concentration of 30 _{% ;}

(5) Pour out the upper layer acid solution, repeatedly centrifuge and wash with deionized water, and the centrifuge speed is 8000r/min, until the pH value of the suspension is neutral, and obtain the graphite oxide colloid;

(6) Put the graphene oxide colloid into a table-top forced air constant temperature drying oven and dry it for 24 hours at a temperature of 75° C. to obtain graphene oxide.

The mechanical properties of the composite film prepared by the present invention can reach 101.49MPa in tensile strength, which is 42.4% higher than that of PVA film, the oxygen barrier property is 2.08 times higher than that of pure PVA film, and the thermal decomposition temperature is increased by 10-20°C. High light transmission.

Description of drawings

Fig. 1 is the SEM photo of the surface of PVA composite film in experiment one; Fig. 2 is the SEM photo of the surface of PVA-N1 composite film in experiment one; Fig. 3 is the SEM photo of the surface of PVA-N6 composite film in experiment one; Fig. 4 is the PVA in experiment one Composite film section SEM photo; Fig. 5 is the SEM photo of PVA-N1 composite film section in experiment one; Fig. 6 is the SEM photo of PVA-N6 composite film section in experiment one; Fig. 7 is the infrared spectrogram of composite film in experiment one; Fig. 8 is the X-ray diffraction spectrogram of composite film in experiment one; Fig. 9 is the TG curve of composite film in experiment one; Fig. 10 is the TG curve of composite film in experiment one; Fig. 11 is the tensile strength of composite film in experiment one Curve; Fig. 12 is the elongation at break curve of composite film in experiment one; Fig. 13 is the oxygen transmission coefficient curve of composite film in experiment one; Fig. 14 is the transmittance curve of composite film in experiment one; Fig. 15 is experiment The haze curve of the composite film in the first; Figure 16 is the water absorption curve of the composite film in the experiment one; Figure 17 is the surface SEM figure of PVA in the experiment two; Figure 18 is the surface SEM figure of the composite film PVA-G3 in the experiment two; Figure 19 is a surface SEM image of the composite film PVA-G5 in experiment two; Figure 20 is a cross-sectional SEM image of PVA in experiment two; Figure 21 is a cross-sectional SEM image of composite film PVA-G3 in experiment two; Figure 22 is an experiment in two The cross-sectional SEM figure of the composite film PVA-G5; Figure 23 is the infrared spectrum of the composite film in experiment two; Figure 24 is the XRD figure of the composite film in experiment two; Figure 25 is the TG curve of the composite film in experiment two; Figure 26 It is the DTG curve figure of the composite film in the experiment two; Fig. 27 is the tensile strength curve figure of the composite film in the experiment two; Fig. 28 is the elongation at break curve figure of the composite film in the experiment two; Fig. 29 is the composite film in the experiment two Figure 30 is the light transmittance curve of the composite film in experiment two; Figure 31 is the haze curve of the composite film in experiment two; Figure 32 is the water absorption curve of the composite film in experiment two; Figure 33 is The SEM image of the PVA film surface in experiment three; Figure 34 is the SEM image of the composite film PN-G1 in the experiment three; Figure 35 is the SEM image of the composite film PN-G3 in the experiment three; Figure 36 is the cross-sectional shape of the PVA film in the experiment three Fig. 37 is the cross-sectional topography of composite film PN-G1 in experiment three; Fig. 38 is the cross-section topography of composite film PN-G3 in experiment three; Fig. 39 is NCC/GO/PVA in experiment three The infrared spectrogram of the composite film; Figure 40 is the X-ray diffraction comparison figure of the NCC/GO/PVA composite film in the experiment three; Figure 41 is the TG curve of the NCC/GO/PVA composite film in the experiment three; Figure 42 is the experiment three The DTG curve of NCC/GO/PVA composite film; Figure 43 is the tensile strength curve of NCC/GO/PVA composite film in experiment three; Figure 44 is the breaking elongation curve of NCC/GO/PVA composite film in experiment three; Figure 45 is the NCC/ The oxygen transmission coefficient curve of GO/PVA composite film; Fig. 46 is the transmittance curve of NCC/GO/PVA composite film in experiment three; Fig. 47 is the haze curve of NCC/GO/PVA composite film in experiment three; Fig. 48 is the water absorption curve of the NCC/GO/PVA composite film in experiment three.

detailed description

The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

Specific embodiment one: the preparation method of graphene oxide/nanocellulose/polyvinyl alcohol composite film in this embodiment is carried out according to the following steps:

1. Preparation of nanocellulose;

Two, prepare graphene oxide;

3. Preparation of nanocellulose/polyvinyl alcohol mixed solution:

Mix 13.56ml of nanocellulose suspension with a concentration of 5.9g/L, 3.919g of polyvinyl alcohol and 86.44ml of distilled water in a 90°C water bath at a high speed of 500r/min for 2h to obtain a nanocellulose/polyvinyl alcohol mixed solution ;

4. Graphene oxide solution equipment:

Prepare a graphene oxide solution with a weight percentage of 0.1wt%-0.3wt%, and ultrasonically treat it for 30 minutes to obtain a graphene oxide solution;

5. Preparation of composite film: Pour the graphene oxide solution into the nanocellulose/polyvinyl alcohol mixed solution, stir and mix evenly, and then ultrasonically remove air bubbles for 30 minutes to obtain a film-forming liquid, which is placed on a flat glass plate Spread the film and dry it at room temperature to obtain a graphene oxide/nanocellulose/polyvinyl alcohol composite film.

The raw materials used in this embodiment are shown in Table 1:

Table 1

Experimental raw materials and names Specification Manufacturer microcrystalline cellulose column chromatography Sinopharm Chemical Reagent Co., Ltd. Concentrated sulfuric acid (98%) Analytical pure Sinopharm Chemical Reagent Co., Ltd. Phosphotungstic acid Analytical pure Tianjin Kemiou Chemical Reagent Co., Ltd. Polyvinyl alcohol (alcoholysis degree 99.8% ~ 100%) chemically pure Tianjin Kemiou Chemical Reagent Co., Ltd. Dialysis bag Molecular weight cut off 8000 Beijing Solaibao Technology Co., Ltd.

Instruments and equipment used in this embodiment are shown in Table 2:

Table 2

equipment name model Manufacturer Digital temperature control magnetic stirrer 90-4 Shanghai Zhenre Experimental Equipment Co., Ltd. Electronic balance JA5003 Shanghai Sunny Hengping Scientific Instrument Co., Ltd. Electric constant temperature water bath DK-98-ⅡA Tianjin Test Instrument Co., Ltd. centrifuge TGL-20B Shanghai Anting Scientific Instrument Factory

Specific embodiment two: the difference between this embodiment and specific embodiment one is that the preparation method of nanocellulose in step one is as follows:

Weigh 7g of microcrystalline cellulose, add it to 100mL of sulfuric acid solution with a mass fraction of 64%, stir it with a magnetic stirrer to make it evenly mixed, then put it in a water bath at 40°C and stir at a speed of 500r/min for 2h, and then sonicate for 15min , dilute with 1000ml deionized water, end the reaction, let it stand for 24 hours, pour off the supernatant, collect the lower layer solution and put it in a centrifuge washing at a speed of 8000r/min, until it is in the form of a non-layered hydrosol colloid, collect the colloid and put it in a dialysis bag , using deionized water as the dialysate, dialyzed until the pH value of the suspension colloid is 7, to obtain nanocellulose. Others are the same as in the first embodiment.

Specific embodiment three: the difference between this embodiment and specific embodiment one or two is that the preparation method of graphene oxide in step 2 is as follows:

(1) 1.0 g of natural flake graphite, 1.0 g of NaNO ₃ and 46 mL of concentrated sulfuric acid with a mass fraction of 98% were mixed and placed in an ice bath at 5° C., stirred for 1 h, and mixed uniformly to obtain a mixed solution;

(2) Add 6g of KMnO ₄ to the mixture, stir for 1h, then move the solution to a water bath at 50°C, and stir at a speed of 500r/min for 4h, the solution turns from black to beige;

(3) Raise the temperature in the water bath to 85°C, and stir at a speed of 500r/min for 1h to obtain a soil brown suspension solution;

(4) Pour the obtained earth brown suspension solution into 200mL H ₂ O ₂ deionized aqueous solution, treat it in an ice bath, the suspension turns brownish yellow, and let the suspension stand at room temperature for 24 hours;

Wherein _200mL of H2O2 deionized aqueous solution contains _6mL of H2O2 with a mass concentration of 30 _{% ;}

(5) Pour out the upper layer acid solution, repeatedly centrifuge and wash with deionized water, and the centrifuge speed is 8000r/min, until the pH value of the suspension is neutral, and obtain the graphite oxide colloid;

(6) Put the graphene oxide colloid into a table-top forced air constant temperature drying oven and dry it for 24 hours at a temperature of 75° C. to obtain graphene oxide. Others are the same as those in the first or second embodiment.

Embodiment 4: This embodiment differs from Embodiment 1 to Embodiment 3 in that in step 4, a graphene oxide solution with a weight percentage of 0.2 wt % is prepared. Others are the same as those in the first to third specific embodiments.

Adopt following experiment verification effect of the present invention:

experiment one:

Preparation method of composite film:

1. The preparation method of nanocellulose (NCC) is as follows:

Weigh 7g of microcrystalline cellulose, add it to 100mL of sulfuric acid solution with a mass fraction of 64%, stir it with a magnetic stirrer to make it evenly mixed, then put it in a water bath at 40°C and stir at a speed of 500r/min for 2h, and then sonicate for 15min , dilute with 1000ml deionized water, end the reaction, let it stand for 24 hours, pour off the supernatant, collect the lower layer solution and put it in a centrifuge washing at a speed of 8000r/min, until it is in the form of a non-layered hydrosol colloid, collect the colloid and put it in a dialysis bag , using deionized water as the dialysate, dialyzed until the pH value of the suspension colloid is 7, to obtain nanocellulose.

2. Preparation of nanocellulose/polyvinyl alcohol mixed solution:

The nanocellulose suspension and polyvinyl alcohol (PVA) distilled water were stirred at a high speed of 500 r/min in a water bath at 90°C for 2 hours to obtain a nanocellulose/polyvinyl alcohol mixed solution;

3. Ultrasonicate the nanocellulose/polyvinyl alcohol mixed solution for 30 minutes to remove the air bubbles in the solution, pour an appropriate amount of the solution on a flat glass plate to lay a film, and dry it at room temperature to obtain a composite film.

The raw materials are shown in Table 3:

table 3

The experimental results are expressed as the arithmetic mean of the three results of the same component obtained under the same exposure conditions.

It can be seen from Figures 1 to 3 that the surface uniformity of the pure PVA film and the composite film is good, smooth and flat, without obvious cracks, indicating that the compatibility between PVA and NCC is good, and there is no phase separation phenomenon. The particle size of NCC is small, and when the addition amount is 0.5wt%, it can be evenly distributed in the PVA matrix; but when the addition amount is 6wt%, NCC appears to be partially agglomerated, appearing as white large particles, and the surface smoothness decreases.

Figures 3-6 show the cross-sectional SEM images of pure PVA film and 0.5wt% and 6wt% PVA/NCC composite films. The cross-section of pure PVA film has delamination phenomenon, and the distribution of fracture marks is uneven, indicating the molecular binding force of pure PVA Weak, uneven force. While the NCC addition amount is 0.5wt% the fracture distribution of the composite film is relatively uniform, indicating that an appropriate amount of NCC can be uniformly dispersed in the PVA matrix, and the composite film is stressed through the uniform dispersion of NCC and the binding force of the hydrogen bond with the matrix. more uniform. When the addition of NCC is 6wt%, the cross-section of the composite film has many cracks and is irregular. This may be due to the agglomeration of excessive NCC, which deteriorates the compatibility between it and PVA, resulting in uneven stress on the film and affecting the mechanical properties of the composite film.

Figure 7 shows the infrared spectra of the PVA film and the NCC/PVA composite film. It can be seen from the figure that the characteristic peak at the wavenumber at 3346cm ^-1 is the characteristic peak of the -OH group, and a strong absorption occurs at 2939cm ^-1 The peak is the CH bond stretching vibration absorption peak of methylene in PVA. With the increase of NCC content, the characteristic peak at about 1050cm ^-1 of the composite film becomes more and more obvious, which is caused by the CO(C-3) stretching vibration of alcohol in NCC. The composite film after adding NCC has no new characteristic peaks, indicating that the association between NCC and PVA only occurs in physical reactions, not changes in chemical properties ^[21] .

Figure 8 is the XRD spectrum of pure PVA film and NCC/PVA composite film, PVA has a strong diffraction peak at 2θ=19.6°, and the XRD pattern of the composite film also has a strong diffraction peak at 2θ=19.6°, and the position does not occur Change, indicating that the addition of NCC did not change the PVA crystal structure, but the strength increased slightly, indicating that the crystallinity of PVA increased, and NCC played the role of a nucleating agent.

Figure 9 and Figure 10 are curves of the influence of different contents of NCC on the thermal stability of the PVA composite film. Combining with the DTG curve of the film in Figure 2-10, it can be seen that the thermal weight loss of pure PVA film and NCC/PVA composite film is divided into three stages. , the weight loss rate of the composite film at this stage is slightly smaller than that of the PVA film, which shows that the ability of the composite film to absorb water is weakened; the second stage 193 ° C ~ 332 ° C is the dehydration reaction on the PVA side chain, and the initial decomposition temperature of the PVA film is 193 ° C. Afterwards, as the temperature increases, the decomposition rate accelerates. According to the DTG diagram, it can be seen that the decomposition rate is the fastest at 235°C, and the weight loss rate in this area is 56.44%. The weight loss in the third stage is above 390°C. The reaction in this stage is mainly After the burning of the carbon skeleton, after the second stage of thermal decomposition, the residual macromolecular polyolefins will further undergo a chain scission reaction in the third stage of thermal weight loss to form small molecular polyolefins. Comparing the thermal weight loss results of pure PVA film and composite film, it can be seen that the addition of NCC increases the initial decomposition temperature of the second stage of PVA composite film, and the initial decomposition temperature of PVA-N6 is slightly higher than that of PVA-N4, because NCC The thermal initial decomposition temperature of NCC is relatively high (begins to decompose at 330°C), and there is a strong force between NCC and PVA molecules, which increases the thermal stability of the composite film. The addition of NCC can increase the initial degradation temperature of the main degradation process of the prepared composite film. It can be seen that the addition of NCC can enhance the thermal stability of the film to a certain extent.

Mechanical properties mainly include the plasticity, flexibility, elasticity and hardness of materials, which are the basic indicators that packaging materials need to possess. Packaging materials with different scopes of application and uses have different requirements for mechanical properties. The effect of different mass fractions of NCC on the tensile strength of PVA composite films is shown in Figure 11. The tensile strength of the composite film showed an upward trend with the increase of NCC content. When the mass fraction of NCC was 2wt%, the tensile strength of the composite film showed a maximum value of 88.48MPa, which was 24.17% higher than that of the pure PVA film. However, as the content of NCC continued to increase, the tensile strength decreased gradually. When the NCC content was 6wt%, the tensile strength decreased to 75.71MPa. This is mainly because the hydroxyl groups in the NCC structure are associated with the hydroxyl groups on the PVA molecular chain, and there is a strong adhesion between the two molecules under the action of hydrogen bonds, which leads to stress during stretching by both PVA and NCC. Share, and NCC itself has a high mechanical strength, so that the nanocomposite film exhibits good mechanical properties. When the NCC content is higher than 2wt%, the mechanical properties of the composite membranes tend to decline again, which may be related to the agglomeration of NCC in the composite membranes. Elongation at break is an index parameter that characterizes the tensile elongation and toughness of materials. Figure 12 shows the results of the elongation at break of the composite film. With the increase of NCC content, the elongation at break of the composite film shows a downward trend. The first reason is that the compatibility with the matrix becomes worse with the increase of NCC content. , and NCC whiskers will restrict the movement of PVA molecular chains, resulting in a decrease in flexibility and an increase in brittleness of the composite film; in addition, when the NCC content increases to a certain extent, agglomeration will occur, resulting in stress concentration and brittle fracture.

Table 4 is the oxygen transmission rate of the composite film. The oxygen transmission rate of pure PVA film is 2141.17cm ³ /m ² ·24h·0.1Mpa, which is a low barrier film. After adding a small amount of NCC, the oxygen transmission rate of the composite film decreases, and the barrier property of the film becomes better and better. Due to the difference in the thickness of the samples, the oxygen transmission rate was converted into the oxygen transmission coefficient to characterize the oxygen barrier property of the film to remove the difference caused by the thickness. Figure 13 is the oxygen transmission coefficient of the composite film. The oxygen transmission coefficient of pure PVA film is 85.65cm ³ ·cm/m ² ·24h·0.1Mpa. With the increase of NCC content, the oxygen transmission coefficient of the film decreases gradually. When the NCC content is 0.5wt%, 1wt%, 1.5wt%, 2wt%, 4wt%, 6wt%, the oxygen transmission coefficient of pure PVA film is respectively The oxygen permeability coefficient is 60.22%, 55.67%, 57.25%, 51.25%, 39.67% and 51.21%, and the oxygen barrier performance is significantly improved. The reason may be that the NCC molecule is very small. After mixing with PVA, the gaps between PVA molecules are reduced. That is, the free volume decreases, when the gas passes through the film, the number of obstacles increases, and the distance through the film increases. At the same time, the cross-linking effect and the addition of small molecule NCC reduce the mobility of the polymer molecular segment, and the increase in the packing density causes the transmission coefficient. reduce. However, when the NCC content exceeds 4wt%, only increasing the NCC content cannot effectively improve the oxygen barrier properties of the composite film.

Table 4

serial number Film thickness (μm) Air permeability (cm ³ /m ² ·24h·0.1Mpa) PVA 40 2141.165 PVA-N1 31 1663.776 PVA-N2 29 1644.341 PVA-N3 38 1290.400 PVA-N4 37 1186.414 PVA-N5 28 1213.368 PVA-N6 twenty two 1993.494

Light transmittance is the ability of a material to transmit light, which is related to the light absorption and reflection properties of the material, and is generally characterized by light transmittance and haze ^[45] . The light transmittance of the composite film depends largely on the dispersion of NCC in PVA. Figure 14 and Figure 15 show the variation of light transmittance and haze of the composite film with NCC content, respectively. Although with the increase of NCC content, the light transmittance of NCC/PVA composite film decreased gradually, and the haze increased gradually. The results show that even when the NCC content reaches a maximum of 6wt%, the light transmittance of the composite film is still above 90%, and the haze is below 2.5%. It can be seen that the addition of NCC within this range does not cause a significant decrease in the light transmittance of the composite film , the addition of NCC has little effect on the light transmittance and haze of the film.

Water absorption is an important index to measure the water resistance of materials. Table 5 shows the weight change with time of different film materials in a humidity environment of 50% RH. It can be seen from Table 5 that the quality of the film has been increasing. Based on the difference in initial weight and quantified water absorption, the water absorption curve of the film over time was calculated, as shown in Figure 16. From Figure 16, it can be seen very intuitively that PVA is very easy to absorb water. The water absorption of pure PVA film has been increasing linearly. The water absorption of NCC/PVA composite film is significantly lower than that of pure PVA. About 10h, the water absorption rate of the composite film with NCC content greater than 1wt% decreased, while the increase of water absorption rate of pure PVA and PVA-N1 composite film did not change significantly.

table 5

From the above experimental results, it can be seen that:

(1) There is no chemical reaction between NCC and PVA, and the addition of NCC improves the crystallinity of PVA. The surface of PVA film and NCC/PVA composite film is smooth, the cross-section is uniform, no obvious phase separation occurs, and the compatibility of NCC and PVA is good.

(2) Thermogravimetric analysis shows that the addition of NCC can make the thermal decomposition temperature of the composite film higher than that of the PVA film, which can enhance the thermal stability of the film to a certain extent.

(3) Adding NCC will increase the tensile strength of PVA film, but at the same time it will reduce the elongation at break of the film. When the mass fraction of NCC is 2wt%, the tensile property of the composite film is the best, and the tensile strength can reach 88.48MPa.

(4) Adding NCC can improve the oxygen barrier performance of the composite film. When the NCC content is 4wt%, the oxygen transmission coefficient of the composite film is 39.67% of that of the pure PVA film.

(5) With the increase of NCC content, the light transmittance of the composite film decreases gradually, and the haze increases gradually, but the addition of NCC has little influence on the light transmittance and haze of the film in the range of 6wt%, and the light transmittance of the composite film The light transmittance did not decrease significantly.

(6) The water resistance of NCC/PVA composite film is slightly higher than that of PVA film, and with the increase of NCC content, the water absorption of composite film is lower than that of pure PVA film.

Experiment 2:

Preparation method of composite film:

One, the preparation method of graphene oxide is as follows:

(1) 1.0 g of natural flake graphite, 1.0 g of NaNO ₃ and 46 mL of concentrated sulfuric acid with a mass fraction of 98% were mixed and placed in an ice bath at 5° C., stirred for 1 h, and mixed uniformly to obtain a mixed solution;

(2) Add 6g of KMnO ₄ to the mixture, stir for 1h, then move the solution to a water bath at 50°C, and stir at a speed of 500r/min for 4h, the solution turns from black to beige;

(3) Raise the temperature in the water bath to 85°C, and stir at a speed of 500r/min for 1h to obtain a soil brown suspension solution;

(4) Pour the obtained earth brown suspension solution into 200mL H ₂ O ₂ deionized aqueous solution, treat it in an ice bath, the suspension turns brownish yellow, and let the suspension stand at room temperature for 24 hours;

Wherein _200mL of H2O2 deionized aqueous solution contains _6mL of H2O2 with a mass concentration of 30 _{% ;}

(5) Pour out the upper layer acid solution, repeatedly centrifuge and wash with deionized water, and the centrifuge speed is 8000r/min, until the pH value of the suspension is neutral, and obtain the graphite oxide colloid;

(6) The graphene oxide colloid was put into a table-top forced air constant temperature drying oven and dried at a temperature of 75° C. for 24 hours to obtain graphene oxide (GO).

2. Put the PVA in a conical flask filled with 60mL of distilled water, and stir for 2 hours at a high speed with a power-intensive electric stirrer at a temperature of 500r/min in a water bath at 90°C to completely dissolve the PVA to obtain a PVA aqueous solution;

Three, configuration concentration is 0.05wt% (the composite film obtained under this concentration is PVA-G1), 0.1wt% (the composite film obtained under this concentration is PVA-G2), 0.15wt% (the composite film obtained under this concentration PVA-G3), 0.2wt% (the composite film obtained under this concentration is PVA-G4), 0.3wt% (the composite film obtained under this concentration is PVA-G5) GO solution and ultrasonic treatment for 30min to make it uniform Disperse in distilled water, then pour the GO solution into the PVA aqueous solution, stir vigorously with a booster stirrer for 1 hour, and then ultrasonically remove the air bubbles for 30 minutes after mixing evenly, then pour the mixed solution on a flat glass plate to lay a film, and store it at room temperature Dry to obtain a composite film.

Figure 17-Figure 22 are SEM photos of the surface and cross-section of the composite film of PVA-G3 and PVA-G5. The surface of the composite film is smooth and wrinkle-free, indicating that GO is uniformly dispersed in the PVA matrix. The cross-section of the film is relatively regular. Compared with the cross-sectional images of the pure PVA film, it can be seen that the flatness of the cross-section gradually decreases with the increase of the GO content.

Figure 23 shows the infrared spectrum of PVA and the composite film. A strong absorption peak appears at the wave number of 2939 cm ^-1 which is the CH bond stretching vibration absorption peak of the methylene group in PVA. The C=O bond stretching vibration peak corresponding to the carboxyl group at the wavenumber of 1731 cm ^-1 in the original graphite oxide disappeared, indicating that there was no chemical reaction between GO and PVA, which was a physical combination.

Figure 24 is an X-ray diffraction pattern, from which it can be seen that the composite thin film has a diffraction peak around 2θ=19.6°. Compared with the pure PVA film, the diffraction peak did not shift in position, so the addition of GO did not change the PVA crystal structure, and the intensity of the diffraction peak increased, which may be affected by the hydrogen bond of the hydroxyl groups in PVA and GO. There is no characteristic peak of GO near 2θ of 26°, indicating that GO is well dispersed in PVA without agglomeration.

The influence curves of different contents of GO on the thermal stability of the composite film are shown in Figure 25 and Figure 26. The weight loss rates of PVA, PVA-G2, and PVA-G5 in the first stage are 6.84%, 5.26%, and 5.01%, respectively, and the water adsorption capacity of the composite film at room temperature is slightly smaller than that of PVA film; -G2, PVA-G5 weight loss is about 54.41%, 54.38%, 53.88%. Compared with PVA, the initial decomposition temperature of PVA/GO film at this stage is 10°C higher than that of PVA; the weight loss in the third stage is above 396°C. The stage reaction is mainly the burning of the carbon skeleton. After the second stage of thermal decomposition, the residual macromolecular polyolefins will further undergo a chain scission reaction in the third stage of thermal weight loss to form small molecular polyolefins, and the compound continues Decomposition, the carbon residue rate of the sample is about 15.74%.

Figure 27 and Figure 28 are graphs showing the influence of different mass fractions of GO on the tensile strength and elongation at break of the composite film, respectively. The tensile strength of the composite film first increased and then decreased with the increase of GO content. When the mass fraction of GO was 0.1wt%, the tensile strength of the composite film showed a maximum value of 90.96MPa, which was 27.66% higher than that of the pure PVA film. But with the increase of GO content, the tensile strength decreased obviously, and when the addition amount was 0.3wt%, the tensile strength dropped to 49.95MPa. This is mainly due to the intermolecular force formed between the oxygen-containing groups of GO and the hydroxyl groups on the PVA molecular chain, which makes the composite film exhibit good tensile properties. The PVA matrix has good compatibility and increases the mechanical properties of the composite material. When the content of GO was higher, the tensile properties of the composite membrane showed a downward trend again, which may be related to the agglomeration of GO.

Figure 28 The elongation at break of the composite film shows that the elongation at break of the composite film gradually decreases with the increase of the GO content, because the GO sheet will restrict the movement of the PVA molecular chain, resulting in a decrease in the flexibility of the composite film and an increase in brittleness; in addition , when the GO content increases to a certain extent, agglomeration and uneven dispersion will occur, resulting in stress concentration and brittle fracture.

Table 6 shows the oxygen transmission rate of composite membranes with different GO contents. After adding GO, the oxygen transmission rate of the composite film tends to decrease, and the oxygen barrier property of the composite film becomes better with the increase of GO content. Convert the oxygen transmission rate to the oxygen transmission coefficient to characterize the oxygen barrier property of the film to remove the difference caused by the thickness.

Fig. 29 shows the oxygen transmission coefficient of the converted composite film. When the GO content is 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.3wt%, the oxygen transmission coefficient is 94.97%, 78.03%, 61.77%, 60.41% and 54.77% of the oxygen transmission coefficient of the PVA film, respectively. %, the oxygen barrier performance of PVA film can be enhanced with a small amount of GO, which may be due to the good dispersion of ultrasonically stripped GO sheets and easy intercalation in the PVA matrix. This intercalation structure provides bending for the diffusion of oxygen molecules. Small molecules must diffuse around GO and cannot directly pass through the film surface vertically, resulting in an increase in the permeation path of oxygen molecules in the PVA film containing GO, thereby improving the barrier property of the composite film to oxygen.

Table 6

serial number Film thickness (μm) Air permeability (cm ³ /m ² ·24h·0.1Mpa) PVA 40 2141.165 PVA-G1 36 2259.520 PVA-G2 48 1392.352 PVA-G3 39 1356.667 PVA-G4 40 1293.450 PVA-G5 31 1513.201

Figure 30 and Figure 31 show the light transmittance and haze of the composite film as a function of GO content. Although the light transmittance of GO/PVA composite film decreased gradually and the haze gradually increased with the increase of GO content, but when the GO content was lower than 0.15wt%, the light transmittance of the composite film was still above 85.26%, and the haze Below 3%, the addition of GO has little effect on the light transmittance and haze of the film in this range. When the GO content exceeds 0.20wt%, the light transmittance of the composite film decreases further and the haze increases further. This is because the amount of material in the film increases, which hinders and reflects the transmitted light, and reduces the light transmittance. The GO content of 0.3wt% is the lowest light transmittance of the composite film, because GO is dispersed in the film, which further weakens the transmittance. Light has a greater effect on its obstruction and reflection.

Table 7 shows the weight change over time of PVA and composite films with different GO contents in a humidity environment of 50% RH. It can be seen from Table 7 that the quality of the film has been increasing, eliminating the difference in the initial weight of the film, and quantifying Water absorption, calculate the water absorption change curve of the film over time, as shown in Figure 32. It can be seen from the figure that with the increase of GO content, the water absorption of GO/PVA composite film is slightly lower than that of pure PVA, but after 10 hours, the water absorption of pure PVA film and composite film has no saturation tendency, indicating that the blending with GO Finally, the water absorption of the composite membrane decreased and the water resistance increased, which may be due to the low content of GO blended with PVA and the limited content of oxygen-containing functional groups that can combine with hydroxyl groups in PVA molecules.

Table 7

serial number dry weight 2 hours 4h 6 hours 8 hours 10h PVA 0.621 0.6499 0.6643 0.6759 0.6905 0.7011 PVA-G1 0.5103 0.5382 0.5507 0.5614 0.5758 0.5848 PVA-G2 0.4662 0.4892 0.5025 0.5116 0.5241 0.5292 PVA-G3 0.5259 0.5535 0.5562 0.5607 0.5738 0.582 PVA-G4 0.63 0.6515 0.6562 0.6678 0.6731 0.6808 PVA-G5 0.4335 0.454 0.4591 0.4668 0.4766 0.4816

The above experimental results draw the following conclusions:

(1) GO obtained after graphite oxidation has oxygen-containing functional groups, and the number of GO layers after ultrasonic treatment is small. After adding GO, PVA and GO are combined by intermolecular forces without chemical changes; PVA/GO film In the second stage, the initial decomposition temperature is 10°C higher than that of PVA.

(2) The tensile strength of the composite film first increased and then decreased with the increase of GO content. When the mass fraction of GO was 0.1wt%, the tensile strength of the composite film showed a maximum value of 90.96MPa, which was 27.66% higher than that of the pure PVA film. But with the increase of GO content, the tensile strength decreased obviously, and when the addition amount was 0.3wt%, the tensile strength dropped to 49.95MPa. The elongation at break of the composite film decreased gradually with the increase of GO content.

(3) Adding a small amount of GO can enhance the oxygen barrier performance of PVA film, and the oxygen transmission rate decreases with the increase of GO content.

(4) With the increase of GO content, the light transmittance of the composite film decreased gradually, and the haze gradually increased. When the GO content was 0.30wt%, the light transmittance of the GO/PVA composite film dropped to 77.68%, and the haze increased. As high as 5.36, the light transmittance decreases.

(5) The addition of GO slightly reduces the water absorption of the PVA composite film.

Experiment three:

The preparation method of graphene oxide/nanocellulose/polyvinyl alcohol composite film is carried out according to the following steps:

1. Preparation of nanocellulose:

Weigh 7g of microcrystalline cellulose, add it to 100mL of sulfuric acid solution with a mass fraction of 64%, stir it with a magnetic stirrer to make it evenly mixed, then put it in a water bath at 40°C and stir at a speed of 500r/min for 2h, and then sonicate for 15min , dilute with 1000ml deionized water, end the reaction, let it stand for 24 hours, pour off the supernatant, collect the lower layer solution and put it in a centrifuge washing at a speed of 8000r/min, until it is in the form of a non-layered hydrosol colloid, collect the colloid and put it in a dialysis bag , using deionized water as the dialysate, dialyzed until the pH value of the suspension colloid is 7, to obtain nanocellulose.

2. Preparation of graphene oxide:

(1) 1.0 g of natural flake graphite, 1.0 g of NaNO ₃ and 46 mL of concentrated sulfuric acid with a mass fraction of 98% were mixed and placed in an ice bath at 5° C., stirred for 1 h, and mixed uniformly to obtain a mixed solution;

(2) Add 6g of KMnO ₄ to the mixture, stir for 1h, then move the solution to a water bath at 50°C, and stir at a speed of 500r/min for 4h, the solution turns from black to beige;

(3) Raise the temperature in the water bath to 85°C, and stir at a speed of 500r/min for 1h to obtain a soil brown suspension solution;

(4) Pour the obtained earth brown suspension solution into 200mL H ₂ O ₂ deionized aqueous solution, treat it in an ice bath, the suspension turns brownish yellow, and let the suspension stand at room temperature for 24 hours;

Wherein _200mL of H2O2 deionized aqueous solution contains _6mL of H2O2 with a mass concentration of 30 _{% ;}

(5) Pour out the upper layer acid solution, repeatedly centrifuge and wash with deionized water, and the centrifuge speed is 8000r/min, until the pH value of the suspension is neutral, and obtain the graphite oxide colloid;

(6) Put the graphene oxide colloid into a table-top forced air constant temperature drying oven and dry it for 24 hours at a temperature of 75° C. to obtain graphene oxide.

3. Preparation of nanocellulose/polyvinyl alcohol mixed solution:

Mix 13.56ml of nanocellulose suspension with a concentration of 5.9g/L, 3.919g of polyvinyl alcohol and 86.44ml of distilled water in a 90°C water bath at a high speed of 500r/min for 2h to obtain a nanocellulose/polyvinyl alcohol mixed solution ;

4. Graphene oxide solution equipment:

The preparation weight percent is 0.1wt% (the composite film obtained under this concentration is PN-G1), 0.2wt% (the composite film obtained under this concentration is PN-G2), 0.3wt% (the composite film obtained under this concentration is PN-G1), 0.3wt% (the composite film obtained under this concentration is PN-G3) graphene oxide solution, and ultrasonic treatment 30min, obtain graphene oxide solution;

5. Preparation of composite film: Pour the graphene oxide solution into the nanocellulose/polyvinyl alcohol mixed solution, stir and mix evenly, and then ultrasonically remove air bubbles for 30 minutes to obtain a film-forming liquid, which is placed on a flat glass plate Spread the film and dry it at room temperature to obtain a graphene oxide/nanocellulose/polyvinyl alcohol composite film (NCC/GO/PVA composite film).

The surface morphology of the composite film is shown in Figure 33-35. The surface of the composite film is flat and smooth without cracks and other defects, indicating that the three components of GO, NCC and PVA have good compatibility. The number of broken marks on the cross-section of PN-G3 composite membrane increased, which may be due to the agglomeration of excess GO, which made the compatibility between it and PVA worse, resulting in uneven stress on the film and reducing the mechanical properties of the composite membrane.

It can be seen from Figure 40 that the NCC/PVA nanocomposite film with GO added has a strong diffraction peak around 2θ=19.6°, indicating that the addition of GO within the experimental range did not change the PVA crystal structure, and the intensity of the diffraction peak increased, which may be due to The hydrogen bond of hydroxyl groups in GO, PVA and NCC increases the crystallinity of PVA.

Figures 41 and 42 are the thermogravimetric curves of the composite film. The thermal decomposition of the composite film is divided into three stages. The initial decomposition temperature of the film in the second stage is 5-10°C higher than that of the PVA-N4 film. This is because the blend structure formed by GO and NCC and the interaction between the PVA molecular chains are stronger, which makes the composite film thermally decompose. It is necessary to consume more energy to destroy this part of the intermolecular force, so as to increase the thermal stability of the composite film; the addition of GO has little effect on the third stage of thermal decomposition, and the amount of carbon residue in the film tends to be stable after 600 °C.

It can be seen from Figure 43 that the tensile strength of the NCC/PVA composite film added with GO first increases and then decreases. A small amount of GO helps to improve the tensile properties of the NCC/PVA composite film. It reaches 101.49MPa, which is 12.39% higher than the tensile strength of PVA-N4 film, and the elongation at break decreases gradually with the increase of GO content.

Table 8 shows the changes in the oxygen transmission rate of the composite film after adding GO. The addition of GO can increase the oxygen barrier property of the composite film.

Table 8

GO content wt% Film thickness (μm) Air permeability (cm ³ /m ² ·24h·0.1Mpa) 0 37 1186.414 0.1 29 1518.043 0.2 25 1306.358 0.3 37 1510.229

Fig. 45 is the oxygen transmission coefficient of the converted composite film. When the GO content is 0.1wt%, 0.2wt%, 0.3wt%, the oxygen transmission coefficient is 93.68%, 74.40%, 127.30% of the oxygen transmission coefficient of the PVA-N4 film, the oxygen barrier property first increases and then decreases, and the barrier property The oxygen performance has been improved, which is because the three-dimensional structure formed after the hybridization of GO and NCC has a more obvious shielding effect on small molecules.

Figures 46 and 47 show the light transmittance and haze of the composite films prepared in this experiment as a function of GO content. Although the light transmittance of GO/NCC/PVA composite films gradually decreased and the haze increased gradually with the increase of GO content. But when the content of GO is 0.3wt%, the light transmittance of the composite film drops to 76.88%, and the haze rises to 5.54. It can be seen that the addition of GO will weaken the light transmittance of the composite film, but the effect is limited.

Table 9 shows the weight change with time of NCC/PVA composite films modified with different mass fractions of GO in a humidity environment of 50% RH. It can be seen from Table 9 that the mass change of the film can be calculated by eliminating the initial weight of the film. The change curve of water absorption rate with time is shown in Figure 48. It can be seen from Figure 48 that the addition of GO content can significantly reduce the water absorption rate of NCC/PVA composite film. After 2 hours of experiment, the water absorption rate of GO/NCC/PVA composite film is much lower than that of pure PVA film and NCC/PVA composite film. , the water absorption tends to be saturated, and the water resistance is enhanced to a certain extent. The main reason may be that although the content of GO is small, it can form a three-dimensional structure with NCC after being mixed with NCC. When the PVA molecular chain is intercalated, the PVA molecular chain is affected. The intermolecular force of the molecule is stronger than that of a single two-dimensional structure, making it unable to combine with water molecules.

Table 9

serial number dry weight 2 hours 4h 6 hours 8 hours 10h PVA-N4 0.4878 0.5085 0.51277 0.5227 0.5294 0.5367 PN-G1 0.3882 0.4077 0.407 0.4112 0.4165 0.4161 PN-G2 0.5061 0.5225 0.5242 0.5269 0.5298 0.5323 PN-G3 0.396 0.4112 0.4139 0.4168 0.4196 0.4213

From the above experimental results, it can be seen that:

(1) The three components in the NCC, GO and PVA films are well dispersed, the surface is smooth, and there is no obvious separation. With the increase of GO content, the flatness of the cross section decreases;

(2) The mixing of the three did not produce new absorption peaks, and NCC, GO and PVA were bound together by intermolecular forces;

(3) GO can increase the initial decomposition temperature of the NCC/PVA composite film; adding 0.1wt% GO to the tensile strength of the composite film is 12.39% higher than that of the PVA-N4 film, but the addition of GO leads to the elongation at break The synergistic effect of GO and NCC can significantly improve the water resistance of PVA film; a small amount of GO can enhance the oxygen barrier performance of PVA-N4 film; the addition of GO will weaken the light transmittance of PVA-N4 film and increase the haze of the film , so that the light transmittance of the film decreases.

(4) In the GO, NCC, PVA blend system, the component with the best comprehensive performance within the experimental range is the composite film of 4wt% NCC and 0.1wt% GO synergistically reinforced PVA, and the composite film obtained by this component has the best mechanical properties Well, the tensile strength can reach 101.49MPa, which is 42.4% higher than that of PVA film, the oxygen barrier property is 2.08 times higher than that of pure PVA film, the thermal decomposition temperature is increased by 10-20°C, and it has high light transmittance.

The main conclusions obtained are as follows:

(1) The length of NCC prepared by acid hydrolysis supplemented by ultrasound is between 137-258nm, the diameter is 9-20nm, and the aspect ratio is 13; the GO prepared by the improved Hummers method is in the shape of transparent flakes, with a small number of layers There are wrinkles in the area.

(2) Composite films of NCC and PVA with different mass ratios were prepared by casting method. The compatibility of NCC and PVA is good, the surface of the composite film is smooth, the cross-section is uniform, and no obvious phase separation occurs. The addition of NCC can improve the mechanical properties, thermal stability and water resistance of the composite film. In the experimental range, the addition of NCC can make the thermal decomposition temperature of the composite film higher than that of the PVA film. The addition of NCC has an effect on the light transmittance and haze of the film. The NCC/PVA composite film with 2wt% NCC has the best performance. The tensile strength of the composite film is 88.48MPa, which is 24% higher than that of PVA film; the oxygen permeability coefficient is 51.25cm ³ ·cm /cm ² ·s·Pa is 51.25% of the oxygen transmission coefficient of pure PVA film, the light transmittance is 91.42%, the haze is 1.60, and the light transmission is good.

(3) GO obtained after graphite oxidation treatment and ultrasonic dispersion has oxygen-containing functional groups, GO has good dispersion in water, and the surface of GO/PVA composite films with different mass fractions prepared by casting is smooth, and SEM shows that the two are compatible Good, the decomposition temperature of GO/PVA film is 10℃ higher than that of PVA; when the mass fraction of GO is 0.1wt%, the tensile strength of the composite film can reach 90.96MPa, which is 27.66% higher than that of pure PVA film. The oxygen barrier performance of PVA film can be enhanced with a small amount of GO, and the oxygen barrier property is up to 1.56 times higher than that of pure PVA film; the addition of GO will reduce the light transmittance of the composite film, but the effect is limited; the addition of GO makes the composite film The water absorption rate is lower than that of PVA film.

(4) The research on the NCC/GO/PVA ternary film shows that the three components in the composite film are well dispersed, have good compatibility, and have no obvious phase separation. The three components are combined by intermolecular forces, which is a physical nature combined. The addition of GO increases the initial decomposition temperature of PVA-N4 film by 5-10°C; adding a small amount of GO can improve the tensile strength, water resistance and oxygen barrier properties of the composite film.

(5) The component with the best comprehensive performance of GO/NCC/PVA ternary film within the experimental range is the composite film of 2wt% NCC and 0.1wt% GO synergistically reinforced PVA. The composite film obtained by this component has the best mechanical properties, tensile The tensile strength can reach 101.49MPa, which is 42.4% higher than that of PVA film. The oxygen barrier property is 2.08 times higher than that of pure PVA film, and the thermal decomposition temperature is increased by 10-20 ° C. At the same time, it has high light transmission.

Claims (4)

1. the preparation method of graphene oxide/nanocellulose/polyvinyl alcohol composite film is characterized in that the preparation method of graphene oxide/nanocellulose/polyvinyl alcohol composite film is carried out according to the following steps: 1. Preparation of nanocellulose; Two, prepare graphene oxide; 3. Preparation of nanocellulose/polyvinyl alcohol mixed solution: Mix 13.56ml of nanocellulose suspension with a concentration of 5.9g/L, 3.919g of polyvinyl alcohol and 86.44ml of distilled water in a 90°C water bath at a high speed of 500r/min for 2h to obtain a nanocellulose/polyvinyl alcohol mixed solution ; 4. Graphene oxide solution equipment: Prepare a graphene oxide solution with a weight percentage of 0.1wt%-0.3wt%, and ultrasonically treat it for 30 minutes to obtain a graphene oxide solution; 5. Preparation of composite film: Pour the graphene oxide solution into the nanocellulose/polyvinyl alcohol mixed solution, stir and mix evenly, and then ultrasonically remove air bubbles for 30 minutes to obtain a film-forming liquid, which is placed on a flat glass plate Spread the film and dry it at room temperature to obtain a graphene oxide/nanocellulose/polyvinyl alcohol composite film. 2. according to the preparation method of the described graphene oxide/nanocellulose/polyvinyl alcohol composite film of claim 1, it is characterized in that the preparation method of nanocellulose in step 1 is as follows: Weigh 7g of microcrystalline cellulose, add it to 100mL of sulfuric acid solution with a mass fraction of 64%, stir it with a magnetic stirrer to make it evenly mixed, then put it in a water bath at 40°C and stir at a speed of 500r/min for 2h, and then sonicate for 15min , dilute with 1000ml deionized water, end the reaction, let it stand for 24 hours, pour off the supernatant, collect the lower layer solution and put it in a centrifuge washing at a speed of 8000r/min, until it is in the form of a non-layered hydrosol colloid, collect the colloid and put it in a dialysis bag , using deionized water as the dialysate, dialyzed until the pH value of the suspension colloid is 7, to obtain nanocellulose. 3. according to the preparation method of the described graphene oxide/nanometer cellulose/polyvinyl alcohol composite membrane of claim 1, it is characterized in that the preparation method of graphene oxide in step 2 is as follows: (1) 1.0 g of natural flake graphite, 1.0 g of NaNO ₃ and 46 mL of concentrated sulfuric acid with a mass fraction of 98% were mixed and placed in an ice bath at 5° C., stirred for 1 h, and mixed uniformly to obtain a mixed solution; (2) Add 6g of KMnO ₄ to the mixture, stir for 1h, then move the solution to a water bath at 50°C, and stir at a speed of 500r/min for 4h, the solution turns from black to beige; (3) Raise the temperature in the water bath to 85°C, and stir at a speed of 500r/min for 1h to obtain a soil brown suspension solution; (4) Pour the obtained earth brown suspension solution into 200mL H ₂ O ₂ deionized aqueous solution, treat it in an ice bath, the suspension turns brownish yellow, and let the suspension stand at room temperature for 24 hours; Wherein _200mL of H2O2 deionized aqueous solution contains _6mL of H2O2 with a mass concentration of 30 _{% ;} (5) Pour out the upper layer acid solution, repeatedly centrifuge and wash with deionized water, and the centrifuge speed is 8000r/min, until the pH value of the suspension is neutral, and obtain the graphite oxide colloid; (6) Put the graphene oxide colloid into a table-top forced air constant temperature drying oven and dry it for 24 hours at a temperature of 75° C. to obtain graphene oxide. 4. according to the preparation method of the described graphene oxide/nanometer cellulose/polyvinyl alcohol composite film of claim 1, it is characterized in that the graphene oxide solution that the weight percentage is 0.2wt% is prepared in step 4.