Composite filler, fluoride-free oil-proof paper based on physical plugging and preparation method of fluoride-free oil-proof paper

Abstract

The invention discloses a composite filler, fluoride-free oil-proof paper based on physical plugging and a preparation method of the fluoride-free oil-proof paper, and belongs to the technical field of fluoride-free oil-proof paper. Montmorillonite is subjected to chitosan modification to enhance the dispersity and stability of montmorillonite in a paper pulp system, so that the montmorillonite forms a continuous layered barrier structure in a paper sheet, and then alkyl-containing amidated nano-cellulose is introduced as a flexible connection component, so that the composite filler can form a synergistic chimeric structure with a paper-based fiber network; the fluorine-free oil-proof paper can realize excellent oil-proof performance without depending on a surface coating, keeps stable oil-proof effect under actual use conditions of friction, folding and the like, and is suitable for application scenes such as food packaging and the like with higher requirements on environmental protection property and use reliability.

Description

Technical Field

[0001] This invention belongs to the field of fluorine-free oil-proof paper technology, specifically a composite filler, a fluorine-free oil-proof paper based on physical sealing, and its preparation method. Background Technology

[0002] Fried food packaging comes into direct contact with high-fat foods for extended periods during actual use. Fat can easily seep into the packaging material during storage and transport, affecting food hygiene and the user experience. Traditional greaseproof paper often relies on fluorinated compounds for its oil-repellent effect. However, fluorinated materials have raised concerns about their environmental durability and potential health risks. With increasingly stringent food safety regulations and the continuous promotion of green and sustainable packaging concepts, fluorine-free greaseproof paper that is safe for food contact is gradually becoming an important development direction in the field of fried food packaging bags.

[0003] Currently, the main methods for preparing fluorine-free oil-resistant paper focus on introducing fluorine-free oil-resistant agents onto the surface of the paper base material. A continuous coating is then formed on the paper surface through coating, sizing, or other methods to prevent grease from penetrating into the paper. However, this type of coated fluorine-free oil-resistant paper often suffers from the problem that the coating is easily damaged during folding, friction, or pressure, leading to micro-cracks, localized wear, or structural damage. This weakens the continuity of the coating, allowing grease to penetrate along the damaged areas, and the oil-resistant performance decreases significantly with use.

[0004] Therefore, how to construct a stable and durable oil-resistant structure inside the paper-based material without relying on surface coatings, so as to maintain good oil-resistant performance under repeated friction and folding conditions, has become a core technical problem that urgently needs to be solved in the field of fluorine-free oil-resistant paper. Summary of the Invention

[0005] The purpose of this invention is to provide a composite filler, a fluorine-free oil-proof paper based on physical blocking, and a method for preparing the same. By synergistically designing montmorillonite and nanocellulose, they cooperate with each other in the pores of the paper base to effectively block the migration process of oil in the paper base, achieving an oil-proof effect dominated by structural barrier, so as to meet the packaging application requirements with high requirements for safety, environmental protection and reliability.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] This invention provides a composite filler, prepared through the following steps:

[0008] Chitosan-modified montmorillonite, alkyl-amiditized nanocellulose, and deionized water were placed in a reactor and reacted at 50-60℃ for 4-6 hours. The lower solid layer was collected by centrifugation, washed, and vacuum dried to constant weight to obtain the composite filler.

[0009] Furthermore, the ratio of chitosan-modified montmorillonite, alkyl-containing amidated nanocellulose, and deionized water is 40-60:20-30:600-800.

[0010] Furthermore, the preparation process of chitosan-modified montmorillonite is as follows:

[0011] Montmorillonite and deionized water were placed in a reaction vessel and ultrasonically dispersed at 25-35℃ for 1-2 hours. A mixed solution prepared with chitosan and 2wt% glacial acetic acid was added, and the mixture was reacted at 50-60℃ for 20-24 hours. The mixture was filtered, and the filter cake was washed with deionized water until the pH of the deionized water was 7. The mixture was then vacuum dried to constant weight to obtain chitosan-modified montmorillonite.

[0012] Furthermore, the ratio of montmorillonite, chitosan, glacial acetic acid, and deionized water is 60-80g: 10-15g: 600-800mL: 1-1.5L.

[0013] Furthermore, the preparation process of alkyl-containing amidated cellulose nanoparticles is as follows:

[0014] Dodecylamine and anhydrous ethanol were placed in a reaction vessel and stirred at 25-35℃ for 10-20 min. A suspension of carboxyl-rich nanocellulose was added, and the mixture was reacted at 60-80℃ with the same stirring rate for 4-6 h. After centrifugation, the lower solid layer was collected, washed, and freeze-dried to constant weight to obtain alkyl-containing amidated nanocellulose.

[0015] Furthermore, the ratio of dodecylamine, carboxyl-rich nanocellulose suspension, and anhydrous ethanol is 10-20g: 2-3L: 100-200mL.

[0016] Furthermore, the preparation process of the carboxyl-rich nanocellulose suspension is as follows:

[0017] TEMPO nanocellulose, a 1 mol / L citric acid solution, and deionized water were placed in a reaction vessel and reacted at 60-80℃ for 1-3 h. After centrifugation, washing, and dialysis, a carboxyl-rich nanocellulose suspension was obtained.

[0018] Furthermore, the ratio of TEMPO nanocellulose, citric acid solution, and deionized water is 60-80g: 120-160mL: 2-3L.

[0019] This invention also provides a fluorine-free oil-resistant paper based on physical sealing, comprising the following raw materials by weight:

[0020] 200-400 parts of fiber-reinforced slurry, 30-50 parts of composite filler, and 4-8 parts of cationic starch.

[0021] This invention also provides a method for preparing a fluorine-free oil-resistant paper based on physical sealing, comprising the following steps:

[0022] Fiberized pulp, composite filler and cationic starch are placed in a high-speed mixer and mixed at a mixing rate of 800-1200 r / min for 1-2 hours. The mixture is then formed and pressed in a multi-functional press for 1-3 minutes. Finally, it is dried in a forced-air drying oven to constant weight to obtain fluorine-free oil-resistant paper based on physical sealing.

[0023] Furthermore, the pressure of the multi-functional press is 0.2-0.4 MPa.

[0024] This step uses fiber-fiberized pulp as a continuous skeletal phase, composite fillers as functional reinforcing phases, and cationic starch as an interface regulating and bonding promoting component to jointly construct the paper system. Under high-speed stirring conditions in the aqueous phase, the fiber-fiberized pulp is fully dispersed to form a stable network structure. The composite filler is uniformly spread and distributed in the fiber gaps within the system. Simultaneously, the cationic starch swells in water, and the positively charged quaternary ammonium salt groups on its molecular chains can combine with carboxyl and hydroxyl groups on the surface of fibers and composite fillers through electrostatic adsorption and hydrogen bonding, enhancing the interfacial compatibility and structural stability between components. During papermaking, pressing, and drying, the fibers interweave and rearrange through hydrogen bonding to form a dense skeleton. Under the bridging effect of cationic starch, the composite filler is stably embedded in the fiber network, significantly reducing the paper pore size, thereby achieving physical sealing of oils through structural densification.

[0025] Furthermore, the preparation method of the fiber-reinforced pulp is as follows:

[0026] Place 300-500g of bleached softwood chemical pulp in a pulper for pulping. Stop pulping when the freeness reaches 40-50°SR to obtain fiberized pulp.

[0027] This step involves pulping, which gradually separates the fiber bundles in the bleached softwood chemical pulp, resulting in better pulp dispersion, a significantly increased fiber surface area, and exposure of more hydroxyl active sites on the cellulose molecular chains. This facilitates the embedding and fixation of composite fillers.

[0028] The beneficial effects of this invention are:

[0029] 1. The fluorine-free oil-resistant paper based on physical sealing prepared in this invention introduces alkyl-amylated nanocellulose and chitosan-modified montmorillonite into the paper-based system to construct a multifunctional composite filler structure. By introducing higher density and uniformly distributed carboxyl functional groups onto the nanocellulose, more alkyl chains can be grafted onto the nanocellulose to form an alkylamide structure. While maintaining the good binding properties of the cellulose skeleton, it obtains a certain oleophobic tendency, reducing the wetting and penetration driving force of grease on the hydrophilic paper-based structure. It can participate in the construction of the fiber network and form an interface environment unfavorable to grease inside the paper-based pores. At the same time, the modification of montmorillonite by chitosan improves the dispersion stability of montmorillonite in the paper-based pulp system and its interfacial compatibility with the fiber network. Its layered structure can be stably embedded in the paper sheet and form physical barrier units, thereby avoiding agglomeration, migration or local collapse under friction and pressure conditions. The composite filler as a whole has oleophobicity, binding capacity and structural stability, providing a functional basis for the subsequent construction of physical sealing fluorine-free oil-resistant paper that does not rely on surface coatings.

[0030] 2. The fluorine-free oil-resistant paper prepared by this invention, based on physical sealing, contains chitosan-modified montmorillonite in a stable, layered structure within the paper sheet, which significantly extends the penetration path of grease in the paper base material. Alkylamide-containing nanocellulose fills the spaces between the montmorillonite layers and the fiber pores in the form of flexible nanofibers, jointly constructing a synergistic barrier structure. The alkylamide-containing nanocellulose forms a stable bond with the inorganic layers and the paper base fiber network through its surface functional groups such as carboxyl and amide groups, thereby ensuring the continuity and integrity of the barrier structure within the paper sheet. At the same time, the alkylamide segments introduced on its surface can undergo coordinated deformation with the fiber network under external force without easily causing brittle damage, and continuously reduce the affinity of the paper base pore interface for grease. This allows the composite filler to form multi-level, continuous, and stable barrier units within the paper sheet, enabling the fluorine-free oil-resistant paper to maintain good oil-resistant performance even under repeated friction and folding conditions.

[0031] 3. The fluorine-free oil-resistant paper prepared by this invention, based on physical sealing, integrates the composite filler with the paper-based fiber network, making the oil-resistant structure an integral part of the overall paper structure. Chitosan-modified montmorillonite serves as a stable, embedded layered structure as the barrier framework, while alkylamide-containing nanocellulose acts as a flexible connecting unit. This ensures stable support for the oil-resistant performance from the overall paper structure. Both cellulose and chitosan are derived from renewable biomass resources, belonging to renewable natural polymer materials. Montmorillonite is a natural inorganic layered mineral filler with widely available and environmentally friendly raw materials, avoiding potential environmental hazards. The oil-resistant function is achieved through a physical sealing mechanism, ensuring a lower environmental burden during use and recycling, meeting green environmental protection requirements. Furthermore, it effectively overcomes the problem of oil-resistant performance degradation under friction and folding conditions in traditional fluorine-free oil-resistant paper during actual use. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: This example provides a composite filler, prepared through the following steps:

[0034] S1: Place 60g TEMPO nanocellulose, 120mL citric acid solution with a concentration of 1mol / L and 2L deionized water in a reaction vessel, stir at 200r / min at 60℃ for 1h. After the reaction is completed, cool to room temperature, centrifuge, remove the supernatant, add deionized water to the lower precipitate and wash twice, dialyze with an 8-14kDa dialysis bag to obtain a carboxyl-rich nanocellulose suspension.

[0035] S2: Place 10g dodecylamine and 100mL anhydrous ethanol in a reaction vessel, stir at 200r / min for 10min at 25℃, add 2L of carboxyl-rich nanocellulose suspension, and react at the same stirring rate at 60℃ for 4h. After the reaction is completed, cool to room temperature, centrifuge, collect the lower solid, wash twice with deionized water and anhydrous ethanol, freeze dry to constant weight to obtain alkyl amidated nanocellulose.

[0036] S3: Place 60g of montmorillonite and 1L of deionized water in a reaction vessel and ultrasonically disperse at 25℃ for 1h. Add 10g of chitosan and 600mL of a mixed solution prepared with 2wt% glacial acetic acid. Stir at 300r / min at 50℃ for 20h. After the reaction is completed, cool to room temperature, filter, wash the filter cake with deionized water until the pH of the deionized water is 7, and vacuum dry the filter cake at 60℃ to constant weight to obtain chitosan-modified montmorillonite.

[0037] S4: 40g of chitosan-modified montmorillonite, 20g of alkyl-containing amidated nanocellulose and 600mL of deionized water were placed in a reaction vessel and stirred at 200r / min at 50℃ for 4h. After the reaction was completed, the mixture was cooled to room temperature, and the lower solid was collected by centrifugation. The solid was washed twice with ethanol and deionized water and dried under vacuum at 60℃ to constant weight to obtain the composite filler.

[0038] Example 2: This example provides a composite filler, prepared through the following steps:

[0039] S1: Place 70g of TEMPO nanocellulose, 140mL of 1mol / L citric acid solution and 2.5L of deionized water in a reaction vessel, stir at 250r / min at 70℃ for 2h. After the reaction is completed, cool to room temperature, centrifuge, remove the supernatant, add deionized water to the lower precipitate and wash 3 times, dialyze with an 8-14kDa dialysis bag to obtain a carboxyl-rich nanocellulose suspension.

[0040] S2: Place 15g dodecylamine and 150mL anhydrous ethanol in a reaction vessel, stir at 250r / min for 15min at 30℃, add 2.5L of carboxyl-rich nanocellulose suspension, react at 70℃ with the same stirring rate for 5h, cool to room temperature after the reaction is completed, centrifuge, collect the lower solid, wash 3 times with deionized water and anhydrous ethanol, freeze dry to constant weight to obtain alkyl amidated nanocellulose.

[0041] S3: Place 70g of montmorillonite and 1.2L of deionized water in a reactor and ultrasonically disperse at 30℃ for 1.5h. Add 12g of chitosan and 700mL of a 2wt% glacial acetic acid solution and stir at 55℃ for 400r / min for 22h. After the reaction is complete, cool to room temperature, filter, wash the filter cake with deionized water until the pH of the deionized water is 7, and vacuum dry the filter cake at 70℃ to constant weight to obtain chitosan-modified montmorillonite.

[0042] S4: 50g of chitosan-modified montmorillonite, 25g of alkyl-containing amidated nanocellulose and 700mL of deionized water were placed in a reaction vessel and stirred at 250r / min at 55℃ for 5h. After the reaction was completed, the mixture was cooled to room temperature, and the lower solid was collected by centrifugation. The solid was washed three times with ethanol and deionized water and dried under vacuum at 70℃ to constant weight to obtain the composite filler.

[0043] Example 3: This example provides a composite filler, prepared through the following steps:

[0044] S1: Place 80g TEMPO nanocellulose, 160mL citric acid solution with a concentration of 1mol / L and 3L deionized water in a reaction vessel, stir at 300r / min at 80℃ for 3h. After the reaction is completed, cool to room temperature, centrifuge, remove the supernatant, add deionized water to the lower precipitate and wash 4 times, dialyze with an 8-14kDa dialysis bag to obtain a carboxyl-rich nanocellulose suspension.

[0045] S2: Place 20g dodecylamine and 200mL anhydrous ethanol in a reaction vessel, stir at 300r / min for 20min at 35℃, add 3L of carboxyl-rich nanocellulose suspension, and react at the same stirring rate at 80℃ for 6h. After the reaction is completed, cool to room temperature, centrifuge, collect the lower solid, wash 4 times with deionized water and anhydrous ethanol, freeze dry to constant weight to obtain alkyl amidated nanocellulose.

[0046] S3: Place 80g of montmorillonite and 1.5L of deionized water in a reactor and ultrasonically disperse at 35℃ for 2h. Add 15g of chitosan and 800mL of a mixed solution prepared with 2wt% glacial acetic acid. Stir at 500r / min at 60℃ for 24h. After the reaction is complete, cool to room temperature, filter, wash the filter cake with deionized water until the pH of the deionized water is 7, and vacuum dry the filter cake at 80℃ to constant weight to obtain chitosan-modified montmorillonite.

[0047] S4: 60g of chitosan-modified montmorillonite, 30g of alkyl-containing amidated nanocellulose and 800mL of deionized water were placed in a reaction vessel and stirred at 300r / min at 60℃ for 6h. After the reaction was completed, the mixture was cooled to room temperature, and the lower solid was collected by centrifugation. The solid was washed 4 times with ethanol and deionized water and dried under vacuum at 80℃ to constant weight to obtain the composite filler.

[0048] The composite fillers prepared in Examples 1-3 above are first processed by treating TEMPO nanocellulose in a citric acid system. Under acidic conditions, the hydroxyl groups on the surface of the nanocellulose undergo esterification activation and carboxyl enrichment, resulting in a high density of carboxyl active sites on the nanocellulose surface, thus obtaining a carboxyl-rich nanocellulose suspension. Subsequently, the introduced dodecylamine molecules, containing primary amine groups, can undergo a condensation-type amidation reaction with the carboxyl groups on the surface of the carboxyl-rich nanocellulose under heating conditions, forming alkyl-containing amidated nanocellulose. Simultaneously, the montmorillonite surface carries a negative charge, and after chitosan dissolves in an acetic acid system, its amino groups are protonated to form -NH3. + Chitosan binds to montmorillonite sheets through electrostatic adsorption. Simultaneously, the hydroxyl and amino groups on the chitosan molecular chain form hydrogen bonds with the hydroxyl groups on the montmorillonite surface, resulting in intercalation adsorption to a certain extent, thus obtaining chitosan-modified montmorillonite. Finally, when chitosan-modified montmorillonite is compounded with alkyl-amiditized nanocellulose in an aqueous system, the -NH3 groups on the chitosan molecular chain... + and -OH with -COO on the surface of nanocellulose - Stable hydrogen bonds and electrostatic interactions are formed between -OH groups, and composite fillers are ultimately obtained through multiple non-covalent interactions.

[0049] Example 4: This example provides a fluorine-free oil-resistant paper based on physical sealing, which is prepared through the following steps:

[0050] Step 1: Place 300g of bleached softwood chemical pulp in a pulper for pulping. Stop pulping when the freeness reaches 40°SR to obtain fiber-reinforced pulp.

[0051] Step 2: Place 200g of fiber-reinforced pulp, 30g of the composite filler prepared in Example 1, and 4g of cationic starch in a high-speed mixer and mix at a stirring rate of 800r / min for 1h. After mixing, pour the mixed pulp into a paper forming machine for papermaking to form wet paper. Place the wet paper in a multi-functional press and press it at a pressure of 0.2MPa for 1min. Transfer the pressed wet paper to a forced-air drying oven and dry it at 90℃ to constant weight. After cooling, obtain fluorine-free oil-resistant paper based on physical sealing.

[0052] Example 5: This example provides a fluorine-free oil-resistant paper based on physical sealing, which is prepared through the following steps:

[0053] Step 1: Place 400g of bleached softwood chemical pulp in a pulper for pulping. Stop pulping when the freeness reaches 45°SR to obtain fiber-reinforced pulp.

[0054] Step 2: Place 300g of fiber-reinforced pulp, 40g of the composite filler prepared in Example 2, and 6g of cationic starch in a high-speed mixer and mix at a stirring rate of 1000r / min for 1.5h. After mixing, pour the mixed pulp into a paper forming machine to form wet paper. Place the wet paper in a multi-functional press and press it at a pressure of 0.3MPa for 2min. Transfer the pressed wet paper to a forced-air drying oven and dry it at 100℃ to constant weight. After cooling, obtain fluorine-free oil-resistant paper based on physical sealing.

[0055] Example 6: This example provides a fluorine-free oil-resistant paper based on physical sealing, which is prepared through the following steps:

[0056] Step 1: Place 500g of bleached softwood chemical pulp in a pulper for pulping. Stop pulping when the freeness reaches 50°SR to obtain fiberized pulp.

[0057] Step 2: Place 400g of fiber-reinforced pulp, 50g of the composite filler prepared in Example 3 and 8g of cationic starch in a high-speed mixer and mix at a stirring rate of 1200r / min for 2 hours. After mixing, pour the mixed pulp into a paper forming machine to form wet paper. Place the wet paper in a multi-functional press and press it at a pressure of 0.4MPa for 3 minutes. Transfer the pressed wet paper to a forced-air drying oven and dry it at 110℃ to constant weight. After cooling, obtain fluorine-free oil-resistant paper based on physical sealing.

[0058] The fluorine-free oil-resistant paper based on physical sealing prepared in Examples 4-6 above was tested for total migration, specific migration, heavy metals, volatile organic compounds, and prohibited and restricted substances in accordance with standard GB / T36392-2025. All indicators met the requirements of GB / T 36392-2025 and can be used for food contact applications.

[0059] Comparative Example 1: Based on Example 5, commercially available TEMPO nanocellulose was used instead of the alkyl-containing amidated nanocellulose prepared in S2 of Example 2, while the other steps remained unchanged.

[0060] Comparative Example 2: Based on Example 5, commercially available montmorillonite was used instead of the chitosan-modified montmorillonite prepared in S3 of Example 2, while the other steps remained unchanged.

[0061] Comparative Example 3: Based on Example 5, the alkyl-containing amidated nanocellulose prepared in S2 of Example 2 was used to replace the composite filler used in step 2, while the other steps remained unchanged.

[0062] Comparative Example 4: Based on Example 5, the chitosan-modified montmorillonite prepared in S3 of Example 2 was used to replace the composite filler used in step 2, while the other steps remained unchanged.

[0063] The TEMPO nanocellulose purchased in the above examples and comparative examples was produced by Tianjin Wood Elf Co., Ltd., with a carboxyl content of 1.2 mmol / g; the montmorillonite was produced by Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., and was a layered natural sodium-based montmorillonite; the chitosan was produced by Shanghai Kanglang Biotechnology Co., Ltd., with a degree of deacetylation ≥90% and an average viscosity of 100 mPa•s; the bleached softwood chemical pulp was produced by Huanggang Chenming Pulp & Paper Co., Ltd.; and the cationic starch was produced by Guangdong Huimei Starch Technology Co., Ltd., model HM-633.

[0064] The fluorine-free oil-resistant paper based on physical sealing prepared in Examples 4-6 and Comparative Examples 1-4 was subjected to performance testing, and the test results are shown in Table 1.

[0065] Sample preparation: In accordance with standard GB / T 450-2008, the fluorine-free oil-proof paper based on physical sealing of the above examples and comparative examples was conditioned for 24 hours at 25°C and 50% relative humidity before being cut.

[0066] Mechanical properties: Referring to standard GB / T 12914-2018, paper was cut into strips with a width of 15mm and a length of 200mm in both the transverse and longitudinal directions. Tensile strength was tested. A tensile strength tester was used to apply tension to the sample at a constant tensile speed until the sample broke. The maximum tensile force at the time of breakage was recorded, and the tensile strength of the paper was calculated. The higher the tensile strength, the better the mechanical properties of the paper.

[0067] Oil resistance performance: Referring to standard GB / T 22805.2-2008, the paper is cut into 100mm×100mm rectangular samples, the samples are placed flat on a horizontal test platform, a specified amount of oily medium is applied to the surface of the sample, and the sample is observed for a specified time to see if there is any oil penetration, wetting or back seepage. The oil resistance grade is used as the evaluation index. The higher the oil resistance grade, the better the oil resistance performance.

[0068] Following the method TAPPI T 476, the paper sample is fixed on the rotating platform of the abrasion tester and subjected to 100 revolutions of friction treatment. After the abrasion treatment is completed, the abrasion area is selected as the test area, and the oil resistance performance is tested again to determine the oil resistance level. The higher the oil resistance level, the better the oil resistance performance.

[0069] Table 1 Performance Test Table of Fluorine-Free Oil-Resistant Paper

[0070] As shown in Table 1, the fluorine-free oil-resistant paper prepared in Examples 4-6 based on physical sealing exhibits significantly better longitudinal and transverse tensile strength and oil-resistant performance than Comparative Examples 1-4. This indicates that the alkyl-amidated nanocellulose and chitosan-modified montmorillonite composite filler introduced in this invention not only does not weaken the mechanical properties of the paper, but also enhances the overall structural strength of the paper through synergistic effects with the paper fiber network. Furthermore, after friction treatment, the oil-resistant grade of the example samples only slightly decreased and remained at a high level, while the oil-resistant grade of the comparative sample decreased significantly. This demonstrates that the oil-resistant performance of the fluorine-free oil-resistant paper of this invention mainly originates from the stable physical sealing structure constructed within the paper sheet. By constructing a multi-level, continuous barrier system formed by the composite filler and the paper matrix synergistically within the paper sheet, the oil-resistant structure remains stable under actual use conditions such as friction, thereby achieving a balance between good mechanical properties and durable oil-resistant performance.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A composite filler, characterized in that, It is obtained by wet mixing of chitosan-modified montmorillonite and alkyl-containing amidated nanocellulose, and comprises, by weight: 40-60 parts of chitosan-modified montmorillonite and 20-30 parts of alkyl-amiditized nanocellulose; The alkyl-containing amidated cellulose nanoparticles are prepared by the following steps: Dodecylamine and anhydrous ethanol were placed in a reaction vessel and stirred at 25-35℃ for 10-20 min. A suspension of carboxyl-rich nanocellulose was added, and the mixture was reacted at 60-80℃ with the same stirring rate for 4-6 h. After centrifugation, the lower solid layer was collected, washed, and freeze-dried to constant weight to obtain alkyl-containing amidated nanocellulose.

2. The composite filler according to claim 1, characterized in that, The ratio of dodecylamine, carboxyl-rich nanocellulose suspension, and anhydrous ethanol is 10-20g: 2-3L: 100-200mL.

3. The composite filler according to claim 2, characterized in that, The carboxyl-rich nanocellulose suspension was prepared by the following steps: TEMPO nanocellulose, a 1 mol / L citric acid solution, and deionized water were placed in a reaction vessel and reacted at 60-80℃ for 1-3 h. After centrifugation, washing, and dialysis, a carboxyl-rich nanocellulose suspension was obtained.

4. The composite filler according to claim 3, characterized in that, The ratio of TEMPO nanocellulose, citric acid solution, and deionized water is 60-80g: 120-160mL: 2-3L.

5. The composite filler according to claim 1, characterized in that, The chitosan-modified montmorillonite was prepared through the following steps: Montmorillonite and deionized water were placed in a reaction vessel and ultrasonically dispersed at 25-35℃ for 1-2 hours. A mixed solution prepared with chitosan and 2wt% glacial acetic acid was added, and the mixture was reacted at 50-60℃ for 20-24 hours. The mixture was filtered, and the filter cake was washed with deionized water until the pH of the deionized water was 7. The mixture was then vacuum dried to constant weight to obtain chitosan-modified montmorillonite.

6. A composite filler according to claim 5, characterized in that, The ratio of montmorillonite, chitosan, glacial acetic acid, and deionized water is 60-80g: 10-15g: 600-800mL: 1-1.5L.

7. A fluorine-free oil-resistant paper based on physical sealing, characterized in that, By weight, it includes the following raw materials: 200-400 parts of fiber-reinforced pulp, 30-50 parts of composite filler, and 4-8 parts of cationic starch; The composite filler is the composite filler described in any one of claims 1-6.

8. The method for preparing a fluorine-free oil-resistant paper based on physical sealing according to claim 7, characterized in that, Includes the following steps: Fiberized pulp, composite filler and cationic starch are placed in a high-speed mixer and mixed at a mixing rate of 800-1200 r / min for 1-2 hours. The mixed pulp is then formed and pressed in a multi-functional press for 1-3 minutes. After drying with forced air to constant weight, fluorine-free oil-resistant paper based on physical sealing is obtained.

9. The method for preparing a fluorine-free oil-resistant paper based on physical sealing according to claim 8, characterized in that, The pressing pressure of the multi-functional press is 0.2-0.4 MPa.

10. The method for preparing a fluorine-free oil-resistant paper based on physical sealing according to claim 8, characterized in that, The fiber-reinforced pulp is obtained by beating bleached softwood chemical pulp, and the freeness of the fiber-reinforced pulp is 40-50°SR.

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