CN114957803B - Modified kraft lignin reinforced composite film and preparation method thereof - Google Patents

Modified kraft lignin reinforced composite film and preparation method thereof Download PDF

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CN114957803B
CN114957803B CN202210621110.4A CN202210621110A CN114957803B CN 114957803 B CN114957803 B CN 114957803B CN 202210621110 A CN202210621110 A CN 202210621110A CN 114957803 B CN114957803 B CN 114957803B
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CN114957803A (en
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岳凤霞
欧金芬
胡松楠
祁海松
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South China University of Technology SCUT
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Abstract

The invention discloses a modified kraft lignin reinforced composite film and a preparation method thereof; the method comprises the steps of purifying kraft lignin by taking black liquor generated in a pulping process of a kraft method as a raw material, carrying out phenolization modification on the kraft lignin by adopting a phenol/sulfuric acid mixed system, carrying out anti-solvent self-assembly on the modified phenolized lignin to obtain lignin nano particles, respectively mixing the lignin nano particles with nano cellulose suspension or PVA as a reinforcing agent, carrying out ultrasonic dispersion uniformly, and carrying out vacuum suction filtration to obtain the phenolized lignin-cellulose or lignin-PVA composite film. The composite of the phenolized lignin can obviously improve the mechanical property, ultraviolet radiation resistance and water stability of the film, and can be used as a substitute material of petroleum-based non-biodegradable plastics.

Description

Modified kraft lignin reinforced composite film and preparation method thereof
Technical Field
The invention relates to the technical field of biological-based nano materials, in particular to a modified kraft lignin reinforced composite film and a preparation method thereof.
Background
Petroleum-based polymer plastics are used in various fields because of their various properties. However, the problem of pollution caused by the excessive use of non-biodegradable plastics is jeopardizing the ecological environment and the health of humans.
Therefore, there is an urgent need for biodegradable, low-cost, multifunctional and non-toxic renewable resources and materials to replace plastics, and improving the eco-friendly polymer ratio and developing sustainable alternative materials can effectively alleviate the problem of global plastic waste.
The film materials such as cellulose, polyvinyl alcohol (PVA) and the like have great potential in replacing non-degradable petroleum-based plastics due to the advantages of green degradability and the like. However, cellulose and PVA films often suffer from low strength and poor water stability, limiting their further development and functionalization applications. The lignin polymer has high biocompatibility and biodegradability due to the abundant content, low cost and environmental friendliness, and can be used as an excellent filler or reinforcing component for preparing various biodegradable film materials. Lignin itself contains polar groups such as phenolic hydroxyl groups, alcoholic hydroxyl groups and the like, can form hydrogen bonds and chemical bonds with cellulose and PVA, and acts as an adhesive and a filler in a composite membrane structure network. Meanwhile, the rich functional groups and the complex three-dimensional network structure in the lignin can also endow the composite film with certain hydrophobicity and ultraviolet shielding performance. Only a small amount of lignin is added while the transparency of the film is maintained, the performance of the composite film can be effectively improved, and the green degradability of cellulose and PVA can not be influenced. Thanks to the unique structure and nanoscale self-assembly of lignin polymers, composite membranes exhibit multiple functions (e.g. uv resistance, oxidation resistance, hydrophobicity and thermal stability) and excellent mechanical properties due to their cross-linked network structure, intermolecular interactions and biocompatibility. Lignin can therefore act as a bio-enhancer in many of the current film materials.
However, lignin structures recovered from the traditional separation method are damaged to different degrees, and the lignin has the advantages of low hydroxyl content, low activity, easy aggregation and the like, so that the compatibility between lignin and polymer is poor. The phenolic hydroxyl is used as an important functional group of lignin, has small volume and higher reactivity.
Therefore, the construction of an excellent lignin-cellulose or PVA composite interface by improving the phenolic hydroxyl content of lignin through modification is a key problem in preparing lignin reinforced composite materials.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention provides a modified kraft lignin reinforced composite film and a preparation method thereof by adopting a lignin phenolization modification and nanocrystallization treatment process.
The invention is realized by the following technical scheme:
the preparation method of the modified kraft lignin reinforced composite film comprises the following steps:
(1) Mixing kraft lignin and phenol, dissolving, adding H 2 SO 4 Stirring uniformly and then placing the mixture in a hydrothermal reaction kettle for reaction;
(2) Dissolving the phenolized product obtained in the step (1) in an acetone solution, dropwise adding the obtained solution into deionized water to precipitate lignin, filtering lignin precipitate, and freeze-drying to obtain phenolized lignin;
(3) Dissolving the phenolated lignin dried in the step (2) in an aqueous solution of acetone, quickly adding deionized water after complete dissolution, self-assembling into nano particles, and evaporating acetone to obtain a nano suspension of the phenolated lignin;
(4) Adding the phenolized lignin nano suspension prepared in the step (3) into a nano cellulose dispersion liquid, uniformly dispersing by ultrasonic, carrying out suction filtration to obtain a wet film, and drying to obtain a phenolized lignin-nano cellulose composite film;
or, adding the nano suspension of the phenolized lignin prepared in the step (3) into the PVA dispersion, uniformly dispersing by ultrasonic, pouring into a polytetrafluoroethylene mould, and naturally air-drying to obtain the phenolized lignin-PVA composite film.
Mixing kraft lignin and phenol in the step (1), dissolving, and adding H 2 SO 4 After being stirred uniformly, the mixture is placed in a hydrothermal reaction kettle for reaction, specifically: mixing kraft lignin and phenol, dissolving at 50deg.C, adding H 2 SO 4 Stirring uniformly, and then placing the mixture into a hydrothermal reaction kettle to react at 105 ℃.
In the step (3), the ratio of the phenolated lignin to the acetone aqueous solution is 5-30mg/mL; the volume ratio of the acetone solution to the deionized water is as follows: 1:10-30.
In the step (3), the mass fraction of the nano suspension of the phenolized lignin is 0.5-1%.
The phenolated lignin in the step (4) accounts for 5-30% of the total mass of the absolute dry compound.
The uniform ultrasonic dispersion in the step (4) means that the ultrasonic wave is carried out for 5 to 10 minutes at the power of 300 to 400W.
The drying in the step (4) means that the mixed solution is pumped and filtered under the vacuum pressure of 0.05-0.1MPa by a vacuum pump, the wet film formed by pumping and filtering is naturally dried for 4-10 hours at room temperature, and then hot-pressed for 5-8 minutes under the pressure of 0-0.1MPa at the temperature of 80-100 ℃.
The phenolated lignin-PVA film is prepared according to the ratio of phenolated lignin nano particles to PVA mixture of 40-60g/m 2 Quantitative downcasting of (2)And (5) air-drying to form a film.
The preparation method can obtain the phenolated lignin-nanocellulose or PVA composite film.
The thickness of the phenolized lignin-nanocellulose composite film prepared by the invention is 20-40 mu m, the tensile strength is 130-200MPa, and the elongation at break is 6-20%.
According to the invention, phenolized lignin is prepared by taking sulfate lignin as a raw material, and phenolized lignin nano particles obtained after nanocrystallization are used as a reinforcing agent to be mixed with nano cellulose/PVA aqueous dispersion, and the biomass-based composite film material with better mechanical properties, ultraviolet resistance and high light transmittance is prepared by respectively adopting a suction filtration molding method and a pouring molding method. After a proper amount of phenolized lignin is added for reinforcement, the tensile strength and the elongation at break of the composite film are improved, and the higher light transmittance is maintained.
In the invention, besides the entanglement of the compound networks through hydrogen bonds, the spherical phenolized lignin nano particles with small particle size and easy dispersion can further enhance the mechanical properties of the compound materials. The phenolic hydroxyl groups in the phenolated lignin and the hydroxyl groups in cellulose and PVA are promoted to generate a strong physical crosslinking network through intermolecular hydrogen bonding after phenolated modification and nanocrystallization treatment. Therefore, the phenolized lignin-nanocellulose composite film has higher mechanical strength and various excellent properties.
Compared with the prior art, the invention has the following advantages and effects:
the preparation process is simple, wherein the preparation process of the phenolized lignin is simple, the requirement on equipment is low, and the preparation of the nanocellulose has a certain industrial basis; the preparation method of the film can be used for industrial production.
The phenolized lignin can be dissolved in an aqueous solution of acetone, and uniformly dispersed nano particles can be precipitated by taking water as an antisolvent in one step.
The lignin, cellulose and PVA adopted by the invention are all green degradable materials, and are environment-friendly.
The phenolated lignin-nanocellulose/PVA composite film has good mechanical properties; compared with a pure nano cellulose film, the tensile strength and the elongation at break of the film are improved simultaneously, and the toughness reaches more than 3 times of the original toughness; along with the addition of the phenolized lignin, the composite film maintains higher visible light transmittance, and simultaneously has good ultraviolet absorption performance and hydrophobicity, and is expected to partially replace the petroleum-based polymer film.
Drawings
Fig. 1a is an SEM image of the phenolized lignin-nanocellulose composite film prepared in example 1.
FIG. 1b is a graph of UV-visible light transmittance at 200-800nm for the phenolized lignin-nanocellulose composite film prepared in example 1.
Fig. 2a is an SEM image of the phenolized lignin-nanocellulose composite film prepared in example 2.
FIG. 2b is a graph of UV-visible light transmittance at 200-800nm for the phenolized lignin-nanocellulose composite film prepared in example 2.
Fig. 3a is an SEM image of the phenolized lignin-nanocellulose composite film prepared in example 3.
FIG. 3b is a graph of UV-visible light transmittance at 200-800nm for the phenolized lignin-nanocellulose composite film prepared in example 3.
Fig. 4a is an SEM image of the phenolized lignin-nanocellulose composite film prepared in example 4.
FIG. 4b is a graph of UV-visible light transmittance at 200-800nm for the phenolized lignin-nanocellulose composite film prepared in example 4.
Fig. 5a is an SEM image of the lignin-nanocellulose composite film prepared in example 5.
FIG. 5b is a graph showing the UV-visible transmittance at 200-800nm of the lignin-nanocellulose composite film prepared in example 5.
FIG. 6a is a drawing of the lignin-PVA composite film prepared in example 6.
FIG. 6b is a graph showing the UV-visible transmittance at 200-800nm of the lignin-PVA composite film prepared in example 6.
FIG. 6c is a graph showing the water contact angle of the lignin-PVA composite film prepared in example 6.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
The specific conditions are not noted in the examples of the present invention, and are carried out according to conventional conditions or conditions suggested by the manufacturer. The raw materials, reagents, etc. used, which are not noted to the manufacturer, are conventional products commercially available.
The mechanical properties of the phenolized lignin-nanocellulose/PVA composite film and the pure nanocellulose/PVA film are obtained through a stretching experiment of a universal material tester, the sample size is 40mm multiplied by 5mm, the stretching rate is 2mm/min, the testing environment temperature is 25 ℃, and the relative humidity is 50%. The thickness of the sample was measured using a thickness gauge. The film transmittance was measured using an ultraviolet-visible spectrophotometer. The water contact angle was measured using a surface tensiometer.
Example 1:
(1) 100mg of kraft lignin was dissolved in 300mg of phenol and 2.73. Mu.L of H was added 2 SO 4 After stirring well, the mixture was placed in a hydrothermal reaction vessel and reacted at 105℃for 2 hours, the reaction mixture was cooled and dissolved with 5mL of an acetone/water (9:1, v/v) mixture. The resulting solution was added dropwise to 100mL of deionized water. The precipitate was filtered off, washed to neutrality with water and freeze-dried to yield phenolized lignin.
(2) 100mg of phenolized lignin was dissolved in 10mL of an acetone/water (3:1, v/v) mixture. The resulting solution was quickly poured into 100mL of vigorously stirred deionized water. Acetone was removed by rotary evaporation at 40 ℃ under reduced pressure to obtain phenolated lignin nanosuspension (mass fraction 0.5%).
(3) The 0.5wt% phenolated lignin nanosuspension was mixed with the 0.5wt% nanocellulose dispersion in a ratio (mass ratio of phenolated lignin to nanocellulose 5:95), and the resulting homogeneous mixture was sonicated for 5 minutes at a power of 300W. According to the mixture 40g/m 2 Is true for quantitative use of (2)The air filtration pump filters and forms under the vacuum pressure of 0.1MPa, the obtained wet film is naturally air-dried for 10 hours at room temperature, and then hot-pressed for 5 minutes under the pressure of 0.1MPa at 85 ℃.
The phenolated lignin-nanocellulose composite film prepared by the steps has the transmittance of 67.5% at the light wavelength of 550nm, the tensile strength of 136MPa, the elongation at break of 10.6% and the toughness of 10.59MJ/m 3 Compared with the pure nano cellulose film, the strength is improved by 4.6 percent, and the toughness is improved by 93.9 percent. The morphology image and the transmittance curve in the ultraviolet-visible region are shown in fig. 1.
Example 2:
(1) 100mg of kraft lignin was dissolved in 300mg of phenol and 2.73. Mu.L of H was added 2 SO 4 After stirring well, the mixture was placed in a hydrothermal reaction vessel and reacted at 105℃for 2 hours, the reaction mixture was cooled and dissolved with 5mL of an acetone/water (9:1, v/v) mixture. The resulting solution was added dropwise to 100mL of deionized water. The precipitate was filtered off, washed to neutrality with water and freeze-dried to yield phenolized lignin.
(2) 100mg of phenolized lignin was dissolved in 10mL of an acetone/water (3:1, v/v) mixture. The resulting solution was quickly poured into 100mL of vigorously stirred deionized water. Acetone was removed by rotary evaporation at 40 ℃ under reduced pressure to obtain phenolated lignin nanosuspension (mass fraction 0.5%).
(3) The 0.5wt% phenolated lignin nanosuspension was mixed with the 0.5wt% nanocellulose dispersion in a ratio (mass ratio of phenolated lignin to nanocellulose 10:90), and the resulting homogeneous mixture was sonicated for 5 minutes at a power of 300W. According to the mixture 40g/m 2 And (3) quantitatively filtering and forming the film by adopting a vacuum filtering pump under the vacuum pressure of 0.1MPa, naturally air-drying the obtained wet film at room temperature for 10 hours, and then hot-pressing the wet film at the temperature of 85 ℃ for 5 minutes under the pressure of 0.1 MPa.
The phenolated lignin-nanocellulose composite film prepared by the steps has the transmittance of 45.0% at the position of 550nm of light wavelength, the tensile strength of 171MPa, the elongation at break of 19.2% and the toughness of 20.07MJ/m 3 Improved strength compared to pure nanocellulose film31.5% and 267.6% improvement in toughness. The morphology image and the transmittance curve in the ultraviolet-visible region are shown in fig. 2.
Example 3:
(1) 100mg of kraft lignin was dissolved in 300mg of phenol and 2.73. Mu.L of H was added 2 SO 4 After stirring well, the mixture was placed in a hydrothermal reaction vessel and reacted at 105℃for 2 hours, the reaction mixture was cooled and dissolved with 5mL of an acetone/water (9:1, v/v) mixture. The resulting solution was added dropwise to 100mL of deionized water. The precipitate was filtered off, washed to neutrality with water and freeze-dried to yield phenolized lignin.
(2) 100mg of phenolized lignin was dissolved in 10mL of an acetone/water (3:1, v/v) mixture. The resulting solution was quickly poured into 100mL of vigorously stirred deionized water. Acetone was removed by rotary evaporation at 40 ℃ under reduced pressure to obtain phenolated lignin nanosuspension (mass fraction 0.5%).
(3) The 0.5wt% phenolated lignin nanosuspension was mixed with the 0.5wt% nanocellulose dispersion in a ratio (mass ratio of phenolated lignin to nanocellulose 20:80), and the resulting homogeneous mixture was sonicated for 5 minutes at a power of 300W. According to the mixture 40g/m 2 And (3) quantitatively filtering and forming the film by adopting a vacuum filtering pump under the vacuum pressure of 0.1MPa, naturally air-drying the obtained wet film at room temperature for 10 hours, and then hot-pressing the wet film at the temperature of 85 ℃ for 5 minutes under the pressure of 0.1 MPa.
The phenolated lignin-nanocellulose composite film prepared by the steps has the transmittance of 32.7% at the light wavelength of 550nm, the tensile strength of 153MPa, the elongation at break of 12.9% and the toughness of 13.2MJ/m 3 Compared with the pure nano cellulose film, the strength is improved by 17.7%, and the toughness is improved by 141.7%. The morphology image and the transmittance curve in the ultraviolet-visible region are shown in fig. 3.
Example 4:
(1) 100mg of kraft lignin was dissolved in 300mg of phenol and 2.73. Mu.L of H was added 2 SO 4 After stirring uniformly, putting into a hydrothermal reaction kettle, reacting for 2 hours at 105 ℃, cooling the reaction mixture, and using 5mL of acetone/water (9:1, v/v) mixed solutionDissolving. The resulting solution was added dropwise to 100mL of deionized water. The precipitate was filtered off, washed to neutrality with water and freeze-dried to yield phenolized lignin.
(2) 100mg of phenolized lignin was dissolved in 10mL of an acetone/water (3:1, v/v) mixture. The resulting solution was quickly poured into 100mL of vigorously stirred deionized water. Acetone was removed by rotary evaporation at 40 ℃ under reduced pressure to obtain phenolated lignin nanosuspension (mass fraction 0.5%).
(3) The 0.5wt% phenolated lignin nanosuspension was mixed with the 0.5wt% nanocellulose dispersion in a ratio (mass ratio of phenolated lignin to nanocellulose: 30:70), and the resulting homogeneous mixture was sonicated for 5 minutes at a power of 300W. According to the mixture 40g/m 2 And (3) quantitatively filtering and forming the film by adopting a vacuum filtering pump under the vacuum pressure of 0.1MPa, naturally air-drying the obtained wet film at room temperature for 10 hours, and then hot-pressing the wet film at the temperature of 85 ℃ for 5 minutes under the pressure of 0.1 MPa.
The phenolated lignin-nanocellulose composite film prepared by the steps has the transmittance of 13.5% at the light wavelength of 550nm, the tensile strength of 122MPa, the elongation at break of 11.7% and the toughness of 9.85MJ/m 3 Compared with the pure nano cellulose film, the strength is reduced by 8MPa, and the toughness is improved by 80.4 percent. The morphology image and the transmittance curve in the ultraviolet-visible region are shown in fig. 4. From this, it can be seen that the addition of phenolated lignin exceeding 20wt% easily causes aggregation, hinders interaction between lignin and cellulose, reduces hydrogen bond with nanocellulose, and is unfavorable for improvement of mechanical strength. Therefore, when the phenolated lignin nano-particles are used as the nano-cellulose film reinforcing agent, the addition amount of the phenolated lignin nano-particles is controlled to be 10-20%.
Example 5:
(1) 100mg of kraft lignin was dissolved in 10mL of an acetone/water (3:1, v/v) mixture. The resulting solution was quickly poured into 100mL of vigorously stirred deionized water. Acetone was removed by rotary evaporation at 40 ℃ under reduced pressure to obtain lignin nanosuspension (mass fraction 0.5%).
(2) Proportioning 0.5wt% lignin nano-suspension with 0.5wt% nano-cellulose dispersion(the mass ratio of lignin to nanocellulose is 10:90) and the uniform mixed solution is obtained by ultrasonic treatment for 5 minutes under the power of 300W. According to the mixture 40g/m 2 And (3) quantitatively filtering and forming the film by adopting a vacuum filtering pump under the vacuum pressure of 0.1MPa, naturally air-drying the obtained wet film at room temperature for 10 hours, and then hot-pressing the wet film at the temperature of 85 ℃ for 5 minutes under the pressure of 0.1 MPa.
The lignin-nanocellulose composite film prepared by the steps has the transmittance of 65.8% at the light wavelength of 550nm, the tensile strength of 138MPa, the elongation at break of 5.9% and the toughness of 5.1MJ/m 3 Compared with the pure nano cellulose film, the strength is improved by 8MPa, and the toughness is not obviously improved. The morphology image and the transmittance curve in the ultraviolet-visible region are shown in fig. 5. It follows that the non-phenolated kraft lignin nanoparticles have less pronounced enhancement effect on the mechanical properties of nanocellulose films, especially toughness, compared to phenolated lignin. The reason for this is that kraft lignin does not have enough phenolic hydroxyl groups to form hydrogen bonding with the hydroxyl groups of cellulose, which is disadvantageous for the improvement of mechanical strength.
Example 6:
(1) 100mg of kraft lignin was dissolved in 300mg of phenol and 2.73. Mu.L of H was added 2 SO 4 After stirring well, the mixture was placed in a hydrothermal reaction vessel and reacted at 105℃for 2 hours, the reaction mixture was cooled and dissolved with 5mL of an acetone/water (9:1, v/v) mixture. The resulting solution was added dropwise to 100mL of deionized water. The precipitate was filtered off, washed to neutrality with water and freeze-dried to yield phenolized lignin.
(2) 100mg of kraft lignin was dissolved in 10mL of an acetone/water (3:1, v/v) mixture. The resulting solution was quickly poured into 100mL of vigorously stirred deionized water. Acetone was removed by rotary evaporation at 40 ℃ under reduced pressure to obtain lignin nanosuspension (mass fraction 0.5%).
(3) 0.5wt% lignin nanosuspension was mixed with 5wt% PVA solution (lignin to PVA mass ratio 10:90) and sonicated at 300W power for 5 min to obtain a homogeneous mixture. According to the mixture 40g/m 2 Is poured into polytetrafluoroethylene quantitativelyIs dried in an oven at 50 c to remove excess moisture.
The lignin-PVA composite film prepared by the steps has the tensile strength of 24MPa, the elongation at break of 16 percent and the toughness of 3.2MJ/m 3 Compared with the pure PVA film, the strength is improved by 85 percent, almost 100 percent of ultraviolet light can be shielded, but the toughness is slightly reduced. The tensile curve and transmittance curve in the ultraviolet-visible region are shown in fig. 6. Therefore, the phenolized nano lignin not only can strengthen the cellulose film, but also has the strengthening effect on the PVA film. The increased phenolic hydroxyl groups in the phenolized lignin can also enhance the hydrogen bonding between lignin and PVA to enhance the mechanical properties of the composite film. In addition, the lignin has hydrophobicity and ultraviolet shielding property, so that the waterproof capability and the ultraviolet resistance of the PVA composite film are obviously improved, the water contact angle value can reach more than 90 degrees, and 99 percent of ultraviolet can be basically isolated. The invention improves the compatibility of lignin in other high polymer materials, endows the composite materials with excellent mechanical properties, ultraviolet resistance, water stability and the like, widens the application field of the composite materials, and can be used as a substitute material of petroleum-based non-biodegradable plastics.
As described above, the present invention can be preferably realized. The invention uses black liquor generated in the pulping process of the sulfate method as raw materials to purify the sulfate lignin, adopts a phenol/sulfuric acid mixed system to carry out phenolization modification on the sulfate lignin, and carries out anti-solvent self-assembly on the modified phenolized lignin to obtain lignin nano particles, and respectively mixes the lignin nano particles with nano cellulose suspension or PVA as a reinforcing agent for uniform ultrasonic dispersion, and then carries out vacuum suction filtration to obtain the phenolized lignin-cellulose or lignin-PVA composite film. The composite of the phenolized lignin can obviously improve the mechanical property, ultraviolet radiation resistance and water stability of the film, and can be used as a substitute material of petroleum-based non-biodegradable plastics.
The embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principles of the invention should be made and equivalents should be construed as falling within the scope of the invention.

Claims (4)

1. The preparation method of the modified kraft lignin reinforced composite film is characterized by comprising the following steps:
(1) Mixing kraft lignin and phenol, dissolving, adding H 2 SO 4 Stirring uniformly and then placing the mixture in a hydrothermal reaction kettle for reaction;
(2) Dissolving the phenolized product obtained in the step (1) in an acetone solution, dropwise adding the obtained solution into deionized water to precipitate lignin, filtering lignin precipitate, and freeze-drying to obtain phenolized lignin;
(3) Dissolving the phenolated lignin dried in the step (2) in an aqueous solution of acetone, quickly adding deionized water after complete dissolution, self-assembling into nano particles, and evaporating acetone to obtain a nano suspension of the phenolated lignin;
(4) Adding the phenolized lignin nano suspension prepared in the step (3) into a nano cellulose dispersion liquid, uniformly dispersing by ultrasonic, carrying out suction filtration to obtain a wet film, and drying to obtain a phenolized lignin-nano cellulose composite film;
or, adding the nano suspension of the phenolized lignin prepared in the step (3) into the PVA dispersion, uniformly dispersing by ultrasonic, pouring into a polytetrafluoroethylene mould, and naturally air-drying to obtain the phenolized lignin-PVA composite film;
mixing kraft lignin and phenol in the step (1), dissolving, and adding H 2 SO 4 Stirring uniformly, placing into a hydrothermal reaction kettle for reaction, specifically mixing kraft lignin and phenol, dissolving at 50deg.C, adding H 2 SO 4 Uniformly stirring, and then placing the mixture in a hydrothermal reaction kettle to react at 105 ℃;
in the step (3), the ratio of the phenolated lignin to the acetone aqueous solution is 5-30mg/mL;
in the step (3), the mass fraction of the nano suspension of the phenolized lignin is 0.5-1%;
the phenolated lignin in the step (4) accounts for 5-30% of the total mass of the absolute dry compound.
2. The method for preparing the modified kraft lignin reinforced composite film according to claim 1, wherein the method comprises the following steps: the uniform ultrasonic dispersion in the step (4) means that the ultrasonic wave is carried out for 5 to 10 minutes with the power of 300 to 400 and W.
3. The method for preparing the modified kraft lignin reinforced composite film according to claim 2, wherein the method comprises the following steps: the drying in the step (4) means that the mixed solution is pumped and filtered under the vacuum pressure of 0.05-0.1MPa by a vacuum pump, the formed wet film is naturally dried at room temperature for 4-10h, and then hot pressed at the temperature of 80-100 ℃ for 5-8 minutes under the pressure of 0-0.1 MPa.
4. A phenolated lignin-nanocellulose or PVA composite film obtained by the method of any of claims 1-3.
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