CN114808543B - Preparation method of high-performance food oil-proof paper-based material containing nano-fibril cellulose composite coating - Google Patents

Abstract

The invention discloses a preparation method of a high-performance food oil-proof paper base material containing nanofibril cellulose composite coating, which comprises the following steps: (1) nanofibril cellulose suspension prepared by Tempo oxidation homogenization method; (2) propylene glycol alginate is added to water, mix uniformly, obtain the propylene glycol alginate solution that the mass volume percentage concentration is 1-2%; (3) the nanocellulose that the mass volume percentage concentration is 1-3% The suspension is mixed with the propylene glycol alginate solution with a mass percent concentration of 1-2% according to the mass ratio of nanofibrillar cellulose to propylene glycol alginate of 1:1-3, stirred evenly, dispersed under ultrasonic waves for 10-20min, and removed (4) Evenly coat the coating solution on the surface of the food packaging base paper; (5) Fully dry the coated paper at room temperature to obtain food oil-resistant packaging paper. The invention can simultaneously improve the oil resistance, mechanical properties and barrier properties of paper.

Description

A high-performance food grease-proof paper-based material containing nanofibril cellulose composite coating preparation method

(1) Technical field

The invention belongs to the technical field of wrapping paper, and in particular relates to a preparation method of a food greaseproof paper base material.

(2) Technical background

Grease-proof paper is oil-proof paper used for food packaging. With the development of the economy, the problem of food safety is urgent, so solving the safety problem of packaging paper closely related to food has also been put on the agenda. Ordinary paper is made of plant cellulose fibers, and cellulose itself is lipophilic. The surface tension of cellulose is much greater than that of oil, so that oil can infiltrate cellulose, and there are a lot of pores between fibers. , Grease can penetrate paper through capillary action, so ordinary paper does not have oil-proof properties. Grease-proof paper can be simply understood as a type of paper obtained by applying a layer of oil-proof coating on ordinary paper. It can be used for food packaging paper that resists oil penetration, such as cake paper, McDonald's KFC hamburger packaging paper, etc.

Patent CN106368047A discloses a biopolymer oil-proof paper prepared from sodium alginate and soybean protein isolate, which has good oil-proof performance. However, these biopolymers are highly hydrophilic, which limits the application of greaseproof paper. Patent CN112982028A has invented a method for preparing biodegradable hydrophobic and oil-proof paper, slowly adding nano-microfibrils and micro-nano bamboo powder into polyvinyl alcohol solution, dispersing and ultrasonically obtaining polyvinyl alcohol/nano-microfibrils/ The micro-nano bamboo powder coating is coated on the surface of base paper to obtain hydrophobic and oil-proof paper. However, poor mechanical properties and barrier properties limit the application of this biodegradable hydrophobic and oil-resistant paper.

CN 110195373 A discloses a preparation method of food oil-proof paper, which is to apply the sodium alginate solution on the base paper, and obtain coated paper after drying, then spray the propylene glycol alginate solution on the coated paper, and dry Get food greaseproof paper. The oil-proof paper prepared by the method is green and environment-friendly, and the hydrophobicity of the oil-proof paper is enhanced on the basis of ensuring the oil-proof performance of the paper. However, the coating of sodium alginate solution has strong polarity and low density. After being coated on the base paper and dried, the paper fibers will become loose and the mechanical properties will be poor.

In the present invention, the mechanical properties of base paper can be enhanced by coating and sizing the coating mixed with nanofibril cellulose; Applied to dry paper after sizing to improve the grease resistance and barrier properties of the paper. The preparation technology is green and environmentally friendly, and can expand the application of greaseproof paper in food packaging.

(3) Contents of the invention

In view of the above problems, the object of the present invention is to provide a method for preparing green and high-efficiency food oil-resistant packaging paper. Use cycle.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

The present invention provides a kind of preparation method of food oil-proof paper base material containing nano-fibril cellulose composite coating, comprising the following steps:

(1) Nano-fibril cellulose suspension prepared by Tempo oxidation homogeneous method: get coniferous wood pulp and dilute it with deionized water in a beaker to obtain a mass volume percent concentration of 1-3% (w/v, its unit is g/mL) slurry, after stirring at a speed of 300-700r/min for 0.5-1.5h, add TEMPO, NaBr and NaClO in sequence, and continue to stir for 1.5-2.5h, then dropwise add NaOH aqueous solution (preferably its concentration is 0.8- 1mol/L) to adjust the pH of the slurry to 10-10.5, when the pH is maintained at 10-10.5, add absolute ethanol to terminate the reaction, use a vacuum filter to filter the reacted slurry, and filter the residue fully with deionized water Wash to obtain a clean slurry, add water to adjust the mass volume percent concentration of the slurry to 1-3% (w/v), then pour it into a high-pressure homogenizer and treat it with a pressure of 80-100bar for 4-6 times to obtain a mass volume percent concentration 1-3% (w/v) nanofibril cellulose suspension; wherein the mass ratio of softwood pulp, TEMPO, NaBr, and NaClO is 6-10g: 0.10-0.14g: 0.6-1.0g: 6- 10g;

(2) adding propylene glycol alginate to water, and mixing uniformly to obtain a propylene glycol alginate solution with a concentration of 1-2% by mass volume;

(3) the propylene glycol alginate solution that the mass percent concentration is 1-3% of the nanocellulose suspension and the mass percent concentration is 1-2% according to the mass ratio of the nanofibril cellulose and the propylene glycol alginate is 1: 1-3 mixing, stirring evenly, dispersing under ultrasonic wave for 10-20 minutes, removing air bubbles, and obtaining a coating with good dispersibility;

(4) the coating liquid is evenly coated on the surface of the food packaging base paper, and the coating amount (in terms of the quality of the coating liquid coated on the food packaging base paper per unit area) is controlled to be 1-5g/m ² ;

(5) Fully drying the coated paper at room temperature (preferably 23±2° C.) to obtain a food grease-proof paper base material containing nanofibril cellulose composite coating.

As a preference, in step (1), the mass ratio of softwood pulp, TEMPO, NaBr, and NaClO is 8g: 0.12g: 0.8g: 8g.

As a further preference, step (1) is implemented as follows: take coniferous wood pulp and dilute it with deionized water in a beaker to obtain a 1-3% (w/v) slurry, after stirring for 1 h at a rotating speed of 500r/min, Add TEMPO, NaBr and NaClO in sequence, and continue to stir for 2 hours. Add NaOH aqueous solution dropwise to adjust the pH of the slurry to 10-10.5. When the pH is maintained at 10-10.5, add absolute ethanol to terminate the reaction. The slurry is suction filtered, and the filter residue is fully washed with deionized water to obtain a clean slurry, and the mass volume percentage concentration of the slurry is adjusted to 1-3% (w/v) by adding water, and then poured into a high-pressure homogenizer for 90bar pressure treatment 5 times to obtain a nanofibril cellulose suspension with a mass volume percentage concentration of 1-3% (w/v); wherein, the mass ratio of softwood pulp, TEMPO, NaBr, and NaClO is 8g: 0.12g : 0.8g: 8g.

As preferably, in step (3), the nanofibril cellulose and the alginic acid propylene glycol ester solution that the mass percentage concentration is 1-3% nano-cellulose suspension and the mass percentage concentration are 1-2% The mass ratio of propylene glycol ester is 1:1.

In the step (4) of the present invention, there is no special requirement for the coating method, as long as "uniform coating" can be achieved, generally the following operations can be performed: the food packaging base paper is installed on the coating machine, fixed with a coating rod, taken Put a certain volume of coating liquid on one end of the paper, start the coating machine, and coat the coating liquid evenly on the paper.

As preferably, the mass percent concentration of the nanocellulose suspension is 1%, the mass percent concentration of the propylene glycol alginate solution is 1%, and the nanocellulose suspension and the propylene glycol alginate solution are mixed according to the nanofibril cellulose and seaweed The mass ratio of propylene glycol ester was 1:1 to prepare the coating, and the coating amount in step (4) was controlled to be 2g/m ² .

By adopting above-mentioned technology, compared with prior art, the beneficial effect of the present invention is as follows:

1. The present invention uses propylene glycol alginate and nanocellulose as the oil-resistant functional components, and prepares an oil-resistant coating with strong oil-resistant performance and good air permeability through the mutual compounding of the two components. Using this coating can greatly improve the coating performance. The oil-proof performance of the cloth paper improves the application value of the paper.

Specifically, nanocellulose can form hydrogen bonds between molecules or interact with water molecules, so that the nanocellulose suspension has excellent rheological properties of shear thinning. Therefore, the nanocellulose suspension can be coated on paper to prepare food grease-proof paper with the effect of blocking grease and solvent penetration. However, nanocellulose has a large surface energy, which will make the air permeability of the paper poor, and the polar part of the surface energy is low, which will lead to a decrease in its oil resistance. As a low surface energy oleophobic substance, propylene glycol alginate itself is oil repellent, and the overall surface energy of the compound decreases after being compounded with nanocellulose, which improves the oil resistance and air permeability of the paper.

2. Coating with the mixed solution of propylene glycol alginate and nanocellulose can improve the mechanical strength and barrier properties of the paper base, thereby expanding the application range of oil-resistant paper and prolonging the service life.

Specifically, the molecular chain arrangement of propylene glycol alginate is compact, the crystallinity is high, and the anti-oil performance is good, which is very suitable for food oil-resistant packaging. However, the molecular weight of propylene glycol alginate is small. When it is used directly, its mechanical properties are far from those of traditional paper-plastic materials, which greatly limits the scope of use. After propylene glycol alginate is compounded with nanocellulose, intermolecular hydrogen bonds will be formed, making the molecular chains in the system staggered and extended, which can improve the mechanical properties of paper-based materials. In addition, the nanofibrillar cellulose in biomass has a large specific surface area due to its small size effect, and has a higher level of tensile strength and Young's modulus than ordinary cellulose. After coating and using Paper-based materials with good barrier properties and high strength can be prepared.

(4) Description of drawings

Fig. 1 is a scanning electron microscope image of the surface and cross-section of the oil-proof barrier paper prepared in Example 1-3.

Fig. 2 is the surface diiodomethane and the water contact angle of the oil-proof barrier paper prepared by embodiment and comparative example;

Fig. 3 is a transmission electron micrograph of nanofibril cellulose prepared in Example and Comparative Example 3.

(5) Specific implementation methods

The embodiments of the present invention will be described in detail below, so that the content and features of the present invention can be easily understood by researchers in the field, so as to define the protection scope of the present invention in more detail. However, the present invention is not limited by the following examples.

Experimental materials: coniferous wood pulp and food packaging base paper are provided by Zhejiang Hengda New Material Co., Ltd.; TEMPO, NaBr, NaClO, NaOH, absolute ethanol, propylene glycol alginate and other reagents are all analytically pure, provided by Shanghai Macklin Biochemical Technology Co., Ltd. provided by the company.

Example 1

(1) Nanofibril cellulose suspension prepared by Tempo oxidation homogenization method: get 8g softwood pulp in a 1500mL beaker and dilute to 1% (w/v) slurry with deionized water, after stirring at 500r/min for 1h, Add 0.12g TEMPO, 0.8gNaBr, 80mL 10% NaClO solution in turn, and continue to stir for 2h, add dropwise 0.5mol/L NaOH to adjust the pH of the slurry to 10-10.5, when the pH is maintained at 10-10.5, add 5mL of absolute ethanol to stop Reaction, filter the slurry after the reaction with a vacuum filter device and wash the filter residue with deionized water, repeat 3 times to obtain a clean slurry, add water to adjust the mass volume concentration of the slurry to 1% (w/v) Pour it into a high-pressure homogenizer and treat it with a pressure of 90 bar for 5 times to obtain a nanofibril cellulose suspension with a concentration of 1% by mass and volume.

(2) 1.5g propylene glycol alginate was added into 100mL water, and mixed uniformly to obtain a propylene glycol alginate solution with a concentration of 1.5% by mass volume;

(3) Mix 1% nanocellulose suspension and 1.5% propylene glycol alginate solution at a volume ratio of 1:1, stir evenly, disperse under ultrasonic waves for 15 minutes, remove air bubbles, and obtain a coating with good dispersibility.

(4) Coating liquid is evenly coated on the surface of food packaging base paper, and coating amount is controlled at ^2g /m ;

(5) Fully dry the coated paper at room temperature (23±2°C) to obtain oil-resistant wrapping paper.

Example 2

(1) Nanofibril cellulose suspension prepared by Tempo oxidation homogeneous method: get 8g softwood pulp in a 1500mL beaker and dilute to 2% (w/v) slurry with deionized water, after stirring at 500r/min for 1h, Add 0.14g TEMPO, 1.0gNaBr, 100mL 10% NaClO solution in sequence, and continue to stir for 2h, add 0.5mol/L NaOH dropwise to adjust the pH of the slurry to 10-10.5, when the pH is maintained at 10-10.5, add 5mL absolute ethanol Terminate the reaction, use a vacuum filter to filter the reacted slurry and wash the filter residue with deionized water, repeat 3 times to obtain a clean slurry, add water to adjust the mass volume concentration of the slurry to 2% (w/v) Pour it into a high-pressure homogenizer and treat it with a pressure of 90 bar for 5 times to obtain a nanofibril cellulose suspension with a concentration of 2% by mass and volume.

(2) 1g propylene glycol alginate is added in 100g water, mix uniformly, obtain the propylene glycol alginate solution that the mass volume percent concentration is 1%;

(3) Mix 2% nanocellulose suspension and 1% propylene glycol alginate solution at a volume ratio of 1:3, stir evenly, disperse under ultrasonic waves for 15 minutes, remove air bubbles, and obtain a coating with good dispersibility.

(4) Coating liquid is evenly coated on the surface of food packaging base paper, and coating amount is controlled at ^2g /m ;

(5) Fully dry the coated paper at room temperature (23±2°C) to obtain oil-resistant wrapping paper.

Example 3

(1) Nanofibril cellulose suspension prepared by Tempo oxidation homogenization method: get 8g softwood pulp in a 1500mL beaker and dilute to 1% (w/v) slurry with deionized water, after stirring at 500r/min for 1h, Add 0.12g TEMPO, 0.8gNaBr, 80mL 10% NaClO solution in turn, and continue to stir for 2h, add dropwise 0.5mol/L NaOH to adjust the pH of the slurry to 10-10.5, when the pH is maintained at 10-10.5, add 5mL of absolute ethanol to stop Reaction, filter the slurry after the reaction with a vacuum filtration device, wash the filter residue with deionized water, repeat 3 times to obtain a clean slurry, add water to adjust the mass volume concentration of the slurry to 1% (w/v) and pour Put it into a high-pressure homogenizer and process it 5 times with a pressure of 90 bar to obtain a nanofibril cellulose suspension with a concentration of 1% by mass volume.

(2) 1.5g propylene glycol alginate was added into 100g water, and mixed uniformly to obtain a propylene glycol alginate solution with a mass volume percent concentration of 1.5%;

(3) Mix 1% nanocellulose suspension and 1.5% propylene glycol alginate solution at a volume ratio of 1:1, stir evenly, disperse under ultrasonic waves for 15 minutes, remove air bubbles, and obtain a coating with good dispersibility.

(4) Coating liquid is evenly coated on the surface of food packaging base paper, and coating amount is controlled at 4g/m ^;

(5) Fully dry the coated paper at room temperature (23±2°C) to obtain oil-resistant wrapping paper.

Comparative example 1:

(1) Nanofibril cellulose suspension prepared by Tempo oxidation homogenization method: get 8g softwood pulp in a 1500mL beaker and dilute to 1% (w/v) slurry with deionized water, after stirring at 500r/min for 1h, Add 0.12g TEMPO, 0.8gNaBr, 80mL 10% NaClO solution in turn, and continue to stir for 2h, add dropwise 0.5mol/L NaOH to adjust the pH of the slurry to 10-10.5, when the pH is maintained at 10-10.5, add 5mL of absolute ethanol to stop Reaction, the slurry after the reaction is suction-filtered with a vacuum filtration device, and the filter residue is washed with deionized water. After repeating 3 times, a clean slurry is obtained. Add water to adjust the slurry to 1% (w/v) and pour it into a high-pressure homogenizer 5 times in 90 bar pressure to obtain a nanofibril cellulose suspension with a concentration of 1% by mass volume.

(2) Mix 1% nanocellulose suspension and deionized water at a volume ratio of 1:1, stir evenly, disperse under ultrasonic waves for 15 minutes, remove air bubbles, and obtain a coating with good dispersibility.

(3) Coating liquid is evenly coated on the surface of food packaging base paper, and coating amount is controlled at ^2g /m ;

(4) Fully dry the coated paper at room temperature (23±2°C) to obtain oil-resistant wrapping paper.

Comparative example 2:

(1) 1.5g propylene glycol alginate was added into 100mL water, and mixed uniformly to obtain a propylene glycol alginate solution with a concentration of 1.5% by mass volume;

(2) Mix 1.5% propylene glycol alginate solution and deionized water at a volume ratio of 1:1, stir evenly, disperse under ultrasonic waves for 15 minutes, remove air bubbles, and obtain a coating with good dispersibility.

(3) Coating liquid is evenly coated on the surface of food packaging base paper, and coating amount is controlled at ^2g /m ;

(4) Fully dry the coated paper at room temperature (preferably 23±2° C.) to obtain oil-resistant wrapping paper.

Comparative example 3:

(1) Nanofibril cellulose suspension prepared by Tempo oxidation homogenization method: get 5g softwood pulp in a 1500mL beaker and dilute to 1% (w/v) slurry with deionized water, after stirring at 500r/min for 1h, Add 0.16g TEMPO, 1.2gNaBr, 40mL 10% NaClO solution in sequence, add dropwise 0.5mol/L NaOH to adjust the pH of the slurry to 11-12, continue stirring for 2h, adjust the pH of the slurry to 10, when the pH is maintained at 10, Add 5mL of absolute ethanol to terminate the reaction, use a vacuum filter to filter the reacted slurry and wash the filter residue with deionized water, repeat 3 times to obtain a clean slurry, add water to adjust the mass volume concentration of the slurry to 1% ( w/v) and then poured into a high-pressure homogenizer and treated 5 times with a pressure of 90 bar to obtain a nanofibril cellulose suspension with a concentration of 1% by mass volume.

(2) 1g of propylene glycol alginate was added to 100mL of water, and mixed uniformly to obtain a propylene glycol alginate solution with a concentration of 1.5% by mass volume;

(3) Mix 1% nanocellulose suspension and 1.5% propylene glycol alginate solution at a volume ratio of 1:1, stir evenly, disperse under ultrasonic waves for 15 minutes, remove air bubbles, and obtain a coating with good dispersibility.

(4) Coating liquid is evenly coated on the surface of food packaging base paper, and coating amount is controlled at ^2g /m ;

(5) Fully dry the coated paper at room temperature (23±2°C) to obtain oil-resistant wrapping paper.

The oil-resistant wrapping paper that embodiment and comparative example prepare are tested, and method is as follows:

1. Mechanical performance test:

According to GB/T 450-2008, the paper to be tested shall be sampled, and the sample shall be balanced at 25°C and 50%RH for at least 24h.

Ring crush strength: refer to GB/T 2679.8-1995, use the ring crush compressometer to measure the ring crush strength of the paper, expressed by the ring crush index, make three groups for each sample, and take the average value.

Ring compressive strength index Rd=1000R/W, where, Rd represents the ring compressive index (N m/g); R represents the ring compressive strength (kN/m); W represents the quantitative value of the sample (g/m ² )

Bursting strength: With reference to GB/T 454-2002, use an electronic bursting strength testing machine to measure the bursting strength of paper, make three groups for each sample, take the average value, and express it in kPa.

2. Smoothness test:

Referring to GB/T 456-2002, use a smoothness tester to measure the smoothness of paper, make three groups for each sample, take the average value, and express it in s.

3. Air permeability test:

According to the standard GB/T458-2008, the Bendtsen air permeability of the paper is measured using an L&W air permeability meter, and the measurement area is 10 cm ² .

4. Oil resistance test:

According to the latest standard TAPPI 559cm-02, the oil repellency grade of coated paper is determined, and the oil repellency grade is used to represent the oil repellency of paper.

5. Contact angle measurement:

Contact angles were measured using a contact angle surface analyzer, and other contact angle measurements were performed by adding 3 µL of water droplets and diiodomethane. Result analysis:

The oil-proof wrapping paper prepared in Examples 1-3 was tested by a scanning electron microscope, and the results are shown in FIG. 1 . It is observed from the image that the coating is evenly coated on the paper, the fibers of the coated paper are criss-crossed, and there are many fluffy fillers. The coating can fill a large number of gaps between paper fibers, thereby preventing oil from penetrating into paper through the capillary action of fiber gaps, which is the reason for its oil-repelling effect. The surface of the oil-proof paper prepared in Example 1 is almost completely covered without gaps and the cross-section is relatively dense, and such a microstructure can enhance its oil-proof performance. The outlines of several large fibers can be seen on the surface of Example 2, and the surface of the fibers is almost completely covered, but there are large pores in the cross section, which is due to the large size of the prepared nanofibril cellulose, which makes the coating itself compact. Sex is poor. In Example 3, obvious flocculent fillers and gaps can be seen on the surface, and there are many holes in the cross section. This is due to the fact that excessive coating application will damage the coated paper fibers during the drying stage, and the coating will also aggregate and agglomerate.

The oil contact angles and water contact angles of the oil-resistant papers prepared in Examples and Comparative Examples are shown in FIG. 2 . Among them, the oil contact angle and water contact angle of Example 1 are the largest, indicating that it has the best oil and water resistance, while the oil contact angle and water contact angle of Comparative Example 2 are relatively small. This shows that the small-sized nanofibrillar cellulose and propylene glycol alginate can improve the oil and hydrophobic properties of paper.

The transmission electron micrographs of the nanofibrillar cellulose prepared in Examples 1-3 and Comparative Example 3 are shown in FIG. 3 . The nanofibrillar cellulose in Examples 1 and 3 are similar in shape and size, and the nanofibrillar cellulose in Example 2 is slightly larger in size and in the shape of crossed long rods. The size of the nanofibrillar cellulose in Comparative Example 3 was significantly increased and was in the form of flakes. This shows that the ratio of TEMPO, NaBr, and NaClO and the reaction pH have a great influence on the size and morphology of nanofibrillar cellulose when using the Tempo oxidation homogeneous method to prepare nanofibrillar cellulose.

Table 1 shows the mechanical properties, smoothness, air permeability and oil-repellent grades of the prepared examples and comparative examples of oil-resistant paper. The ring crush strength index reflects the overall compressive strength of the paper, while the burst strength reflects the single-point compressive strength of the paper. The mechanical properties of the oil-resistant papers of the examples are higher than those of the comparative examples and far better than those of the paper-based materials, among which example 1 has the best performance. Appropriate ratio of coating and smaller size of nanofibrillar cellulose can increase the smoothness of paper, the results showed that 1% nanocellulose suspension and 1.5% propylene glycol alginate solution were mixed 1:1 for coating. The oil-resistant paper prepared in Example 1 had the highest smoothness and oil-resistant rating. The air permeability is related to the surface and internal cellulose gaps of the paper, and the air permeability of Example 1 is the best, which is consistent with the results observed in Figure 1.

Table 1

Claims (5)

1. a preparation method of a food oil-proof paper-based material containing nanofibril cellulose composite coating, comprising the steps: (1) Take coniferous wood pulp and dilute it with deionized water in a beaker to obtain a slurry with a concentration of 1-3% by mass volume. After stirring for 0.5-1.5h at a rotating speed of 300-700r/min, add TEMPO, NaBr and NaClO, and continue to stir for 1.5-2.5h, dropwise add NaOH aqueous solution to adjust the pH of the slurry to 10-10.5, when the pH is maintained at 10-10.5, add absolute ethanol to terminate the reaction, and use a vacuum filter to filter the pH of the slurry after the reaction Suction filter the slurry, wash the filter residue fully with deionized water to obtain a clean slurry, add water to adjust the mass volume percentage concentration of the slurry to 1-3%, pour it into a high-pressure homogenizer and treat it with 80-100bar pressure for 4-6 times , to obtain the nanofibril cellulose suspension that the mass volume percentage concentration is 1-3%; wherein the mass ratio of coniferous wood pulp, TEMPO, NaBr, NaClO is 6-10g: 0.10-0.14g: 0.6-1.0g: 6-10g; (2) adding propylene glycol alginate to water, and mixing uniformly to obtain a propylene glycol alginate solution with a concentration of 1-2% by mass volume; (3) the propylene glycol alginate solution that the mass percent concentration is 1-3% of the nanocellulose suspension and the mass percent concentration is 1-2% according to the mass ratio of the nanofibril cellulose and the propylene glycol alginate is 1: 1-3 mixing, stirring evenly, dispersing under ultrasonic wave for 10-20 minutes, removing air bubbles, and obtaining a coating with good dispersibility; (4) Coating liquid is evenly coated on the surface of food packaging base paper, and coating amount is controlled as 1-5g/m ² ; (5) Fully drying the coated paper at room temperature to obtain a food grease-proof paper base material containing nanofibril cellulose composite coating. 2. The preparation method according to claim 1, characterized in that: in step (1), the mass ratio of softwood pulp, TEMPO, NaBr, and NaClO is 8g: 0.12g: 0.8g: 8g. 3. the preparation method as claimed in claim 1, is characterized in that: step (1) is implemented as follows: get coniferous wood pulp and dilute with deionized water in beaker, obtain the slurry that mass volume percent concentration is 1-3% , after stirring at a speed of 500r/min for 1h, add TEMPO, NaBr and NaClO in turn, and continue to stir for 2h, add NaOH aqueous solution dropwise to adjust the pH of the slurry to 10-10.5, when the pH is maintained at 10-10.5, add anhydrous Ethanol terminates the reaction, and the slurry after the reaction is suction-filtered with a vacuum filter device, and the filter residue is fully washed with deionized water to obtain a clean slurry. Process 5 times with 90bar pressure in the quality machine, obtain the nanofibril cellulose suspension that mass volume percent concentration is 1-3%; Wherein, the feeding mass ratio of described coniferous wood pulp, TEMPO, NaBr, NaClO is 8g: 0.12g: 0.8g: 8g. 4. the preparation method as described in any one in claim 1-3, it is characterized in that: in step (3), be that the nanocellulose suspension of 1-3% by mass volume percent concentration and mass percent concentration are The 1-2% propylene glycol alginate solution is mixed according to the mass ratio of nanofibril cellulose and propylene glycol alginate at 1:1. 5. the preparation method as described in any one in claim 1-3 is characterized in that: the mass percent concentration of nanocellulose suspension is 1%, and the mass percent concentration of propylene glycol alginate solution is 1%, Nano-cellulose suspension and propylene glycol alginate solution were mixed according to the mass ratio of nano-fibril cellulose and propylene glycol alginate as 1:1 to prepare coating, and the coating amount in step (4) was controlled to be 2g/m ² .

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