Environment-friendly fluoride-free oil-proof agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of fluorine-free oil-proofing agent preparation, in particular to an environment-friendly fluorine-free oil-proofing agent and a preparation method and application thereof.The environment-friendly fluorine-free oil-proofing agent is prepared from, by weight, 11-16 parts of cellulose nanowhiskers subjected to permeation crosslinking treatment, 9-13 parts of polyether modified polydimethylsiloxane, 6-8 parts of nanometer titania and 4-6 parts of octadecyl methacrylate. 3 to 5 parts of chitosan, 58 to 68 parts of deionized water and 1.2 to 2.2 parts of sodium dodecyl benzene sulfonate. Cellulose nanowhiskers, nano titanium dioxide and other key components are innovatively modified, supercritical permeation, plasma cross-linking and biomimetic mineralization technologies are adopted, the performance of all the components and the binding force between the components and a paper pulp molding base material are remarkably improved, the compactness of an oil-proof film formed by the environment-friendly fluoride-free oil-proof agent is enhanced, and the oil-proof effect is improved. The oil-proof agent has significantly improved barrier ability to a plurality of greases, has improved oil-proof grade, and effectively solves the problem of poor oil-proof effect of a traditional fluoride-free oil-proof agent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fluorine-free oil-proof agent preparation, in particular to an environmentally friendly fluorine-free oil-proof agent and its preparation method and application. BACKGROUND

[0002] Paper pulp molded products, as a degradable green packaging material, have a continuously expanding application range. However, the hydrophilicity and porous structure of the paper pulp molded products make them prone to penetration when in contact with oil, and thus require oil-proof treatment to improve their performance.

[0003] Currently, fluorine-free oil-proof agents for paper pulp molding mainly have the following problems: First, most of the fluorine-free oil-proof agents in the prior art use acrylate, paraffin, starch, chitosan, etc. as the main raw materials.

[0004] For example, in the patent with the patent application number CN202310353525.2, 2-ethylhexyl acrylate, modified starch, emulsified paraffin, and inorganic fillers are used, which can achieve certain oil-proof effect, but rely on filling the fiber voids and forming a simple film layer, and the oil-proof durability is poor. The oil-proof performance is prone to degradation after long-term use or contact with high-temperature oil.

[0005] Second, some existing technologies also introduce silicone components, but most of them are conventional polysiloxanes or polysilazanes.

[0006] For example, in the patent with the patent application number CN202510674432.9, modified polysilazane is used, but it mainly improves the oil-repellent performance by introducing hydrophobic groups, and lacks high-temperature stability and bonding force with paper pulp fibers.

[0007] In summary, it is of great significance to develop an environmentally friendly fluorine-free oil-proof agent with strong oil-proof performance, durability, and adaptability to paper pulp molding, as well as its preparation method and application. SUMMARY

[0008] To solve one of the above technical problems, the technical solution adopted is: an environmentally friendly fluorine-free oil-proof agent, comprising the following components in parts by weight: 11-16 parts of cellulose nanowhiskers treated by permeation crosslinking, 9-13 parts of polyether-modified polydimethylsiloxane, 6-8 parts of nano-titanium dioxide, 4-6 parts of methacrylic acid octadecyl ester, 3-5 parts of chitosan, 58-68 parts of deionized water, and 1.2-2.2 parts of sodium dodecylbenzenesulfonate.

[0009] On the basis of any of the above technical solutions, the cellulose nanowhiskers are further optimized by the following method: Supercritical infiltration treatment: the cellulose nanowhisker is placed in a supercritical carbon dioxide device, the pressure is set to 10 MPa, the temperature is 45 DEG C, the concentration of 5% gamma-aminopropyl triethoxysilane vapor is introduced, and the silane reagent is infiltrated into the internal pores of the nanowhisker under the condition of keeping the temperature and pressure for 2 hours; On the basis of any one of the technical solutions above, further optimization is: plasma crosslinking treatment: the cellulose nanowhisker treated by supercritical infiltration is transferred to a plasma surface treatment instrument, the vacuum degree is set to 3 Pa, the oxygen flow is 15 sccm, the power is 100 W, and the treatment time is 5 minutes. The silane and the nanowhisker are covalently crosslinked by high-energy particle bombardment, and then the uniformity of the silicon element distribution (coefficient of variation ≤5%) is determined by X-ray photoelectron spectroscopy.

[0010] On the basis of any one of the technical solutions above, further optimization is: the specific method for modifying the nanometer titanium dioxide by biomimetic mineralization-hydrophobic coating is: (1) Biomimetic mineralization treatment: The nanometer titanium dioxide with an initial particle size of 20-30 nm is dispersed in a Tris-HCl buffer simulation body fluid (pH=7.4) with a solid-liquid ratio of 1:50 (the simulation body fluid contains CaCl210 mmol / L, Na2HPO46 mmol / L, NaCl 137 mmol / L, and KCl 2.7 mmol / L), and the obtained dispersion liquid is transferred to a sealed reaction kettle and placed in a 37 DEG C constant temperature water bath for 12 hours. During this period, the dispersion liquid is gently stirred for 10 minutes every 3 hours (stirring rate 50 rpm). After the reaction is completed, centrifugal separation is performed (rotation speed 8000 rpm, time 15 min), and the nanometer titanium dioxide coated with a biomimetic layer of hydroxyapatite is obtained.

[0011] (2) Hydrophobic coating treatment: The obtained nanometer titanium dioxide is dispersed in anhydrous ethanol with a solid-liquid ratio of 1:40, and pure perfluorodecyl triethoxysilane (with a purity of ≥98%, the amount is 5% of the mass of the nanometer titanium dioxide) is added. The mixture is placed in an ultrasonic reaction instrument with a frequency of 40 kHz and a power of 300 W, and ultrasonic reaction is carried out at 60 DEG C constant temperature water bath for 3 hours (ultrasonic mode is continuous ultrasonic, and the reaction container is a three-necked flask with reflux device). After the reaction is completed, centrifugal separation is performed (rotation speed 10000 rpm, time 20 min), and the obtained nanometer titanium dioxide is washed with anhydrous ethanol for 3 times and dried at 80 DEG C under vacuum for 4 hours.

[0012] On the basis of any of the preceding technical solutions, further optimization is that the polyether-modified polydimethylsiloxane is an end group restructured polyether-modified polydimethylsiloxane, and a preparation method thereof is as follows: polyether-modified polydimethylsiloxane and methyl triethoxysilane are mixed at a molar ratio of 1:1.3, 0.6% of dibutyltin dilaurate in the mixed system is added as a catalyst, and the mixture is reacted in a microwave device (power 400W, frequency 2450MHz) at 85℃ for 2h, and then ultraviolet light (wavelength 254nm, power 120W) is irradiated for 1h.

[0013] The microwave-assisted end group exchange reaction: the ester exchange reaction of the hydroxyl group at the end of the polyether-modified polydimethylsiloxane molecular chain and the ethoxyl group of methyl triethoxysilane is catalyzed by dibutyltin dilaurate, and the reaction rate is promoted by the thermal effect and non-thermal effect (molecular vibration acceleration) of the microwave, so that the ethoxysilane group is introduced into the end of the siloxane chain to form an intermediate product.

[0014] On the basis of any of the preceding technical solutions, further optimization is that the chitosan is modified chitosan, and a preparation method thereof comprises: (1) Enzymatic treatment: chitosan is dispersed in an acetic acid aqueous solution with pH=5.0, 0.5% of cellulase in the chitosan is added, and the enzymatic hydrolysis is stirred in a 45℃ constant-temperature water bath for 2h; (2) Quaternary ammonium treatment: glycidyltrimethylammonium chloride is added to the chitosan solution after enzymatic hydrolysis, the molar ratio of the glycidyltrimethylammonium chloride and the chitosan glucose unit is 1:1.8, the temperature is raised to 60℃ and stirred for 6h, 10% of sodium hydroxide aqueous solution is added to adjust the pH to 7.0, and the solid product is obtained by centrifugal separation, washed with deionized water for 3 times and then vacuum dried at 80℃ for 4h.

[0015] The application also provides a preparation method of the environment-friendly fluorine-free oil-proof agent, which comprises the following steps: (S1) Pre-dispersion of modified components: according to the weight parts described above, the cellulose nanocrystalline after the penetration crosslinking treatment and deionized water are added into a double-screw mixing kettle with temperature control, magnetic field assisted double-frequency ultrasonic treatment is started for 25min, and the particle size distribution is monitored by an online particle size analyzer during the treatment to obtain a uniform dispersion liquid I; (S2) Silicone-biomass synergistic compounding: end group restructured polyether-modified polydimethylsiloxane and modified chitosan are added to the dispersion liquid I, the temperature is raised to 70℃, supercritical carbon dioxide is introduced and microwave is applied at the same time, and stirring is performed for 1.5h to obtain a mixed liquid II; (S3) Plasma assisted emulsion polymerization: composite modified nanometer titanium dioxide, octadecyl methacrylate and initiator ammonium persulfate are added to the mixed liquid II, the amount of the ammonium persulfate is 0.8% of the mass of the octadecyl methacrylate, nitrogen is introduced to remove oxygen for 30min, and then the mixture is transferred to a plasma polymerization reactor for polymerization at 75℃ for 3h to obtain an emulsion III. (S4) Gradient post-processing shaping: the emulsion III is first subjected to freeze-thaw cycles, frozen at -75℃ for 10h→thawed at 30℃ for 1.5h, repeated for 3 times, to promote molecular chain rearrangement, then removed unreacted impurities by multi-stage membrane filtration, and finally aged at 25℃ for 48h under inert gas protection to obtain the environmentally friendly fluorine-free oil repellent.

[0016] On the basis of any one of the technical solutions above, further optimization is that in the step S1 modification component pre-dispersion, when the magnetic field assisted double frequency ultrasonic treatment is selected, a neodymium iron boron superconducting magnet is used to generate a uniform magnetic field, the magnetic field direction is parallel to the axial direction of the double screw mixing kettle, and the magnetic field strength is controlled at 0.4T; The absolute value of the zeta potential of the dispersion liquid I is greater than or equal to 35mV, which ensures that the cellulose nanowhiskers are in a monodisperse state in water, and avoids uneven performance of the oil repellent due to particle agglomeration in the subsequent compounding process.

[0017] On the basis of any one of the technical solutions above, further optimization is that in the step S1 double frequency ultrasonic treatment, low frequency 20kHz, power 320W is used to treat for 10min first, which is used to destroy the initial agglomerates of cellulose nanowhiskers; then switch to high frequency 60kHz, power 420W for 15min, to achieve fine dispersion of nanowhiskers.

[0018] On the basis of any one of the technical solutions above, further optimization is that in the step S2, when the microwave is applied synchronously, pulse microwave radiation is used, working for 15s, pausing for 5s, the microwave power is set to 380W, and the frequency is 2450MHz; the stirring process is driven by a variable frequency motor, and the stirring rate is gradually increased from 300rpm at the beginning to 550rpm, and the viscosity and temperature changes of the mixed liquid II are recorded every 15min during the 1.5h reaction process.

[0019] On the basis of any one of the technical solutions above, further optimization is that in the step S3 polymerization process, ultrasonic assistance of 40kHz, power 280W is started at the same time, and the ultrasonic is used in an intermittent manner, working for 8s, pausing for 2s; during the reaction process, the reaction temperature is monitored in real time by a temperature sensor, when the temperature exceeds 75℃, a circulating cooling water system is started to control the temperature, so that the temperature fluctuation range is controlled within ±1℃; after 3h of reaction, the residual monomer content in the emulsion III is detected by a gas chromatograph, when the residual content of octadecyl methacrylate is less than 0.5%, the reaction is stopped.

[0020] The environmentally friendly fluorine-free oil repellent prepared according to the above preparation method is applied in food packaging paper, paper lunch box, baking paper, food grade paper tray and disposable paper cup, and the use method thereof when applied is as follows: (1) Dip coating treatment: dilute the environment-friendly fluorine-free oil-proof agent to 8-12% solid content, immerse the paper product in the diluted oil-proof agent solution, and impregnate for 5-8 min under a vacuum degree of -0.08 MPa, so that the oil-proof agent fully penetrates into the fiber inside the paper product; then take out the paper product, spin dry for 3-5 min at a centrifugal speed of 800-1000 r / min to remove the excess oil-proof agent on the surface; (2) Drying and curing: send the dip-coated paper product into a hot air circulating drying box, pre-dry at 60 DEG C for 10-15 min, and then heat to 120 DEG C for drying for 20-25 min, so that the oil-proof agent forms a dense oil-proof film on the surface of the paper product; (3) The paper product treated above is subjected to subsequent oil-proof performance test.

[0021] Compared with the prior art, the present application has the following advantages: 1. The present application significantly improves the performance of each component and its bonding force with the pulp molding base material by innovatively modifying key components such as cellulose nanowhiskers and nano-titanium dioxide, using supercritical infiltration, plasma crosslinking, and biomimetic mineralization technology, which enhances the denseness of the oil-proof film formed by the environment-friendly fluorine-free oil-proof agent and significantly improves the barrier ability to various oils, thereby improving the oil-proof grade and effectively solving the problem of poor oil-proof effect of traditional fluorine-free oil-proof agents.

[0022] 2. In the preparation process of the oil-proof agent, the present application uses the innovative process of magnetic field assisted double-frequency ultrasonic, supercritical carbon dioxide and microwave co-action, and plasma assisted emulsion polymerization to realize uniform dispersion and efficient compounding of each component, accurately control the polymer structure and reaction process, and greatly improve the batch stability of the product, thereby effectively reducing the product quality difference caused by unstable process and improving the production efficiency and product qualification rate.

[0023] 3. The present application selects biomass materials such as cellulose nanowhiskers and chitosan, and environment-friendly chemical reagents, and the entire preparation process is free of harmful solvent residues, so that the prepared environment-friendly fluorine-free oil-proof agent meets the safety standards of food contact materials and can be widely applied in the field of food packaging, realizes efficient oil-proof performance, guarantees food safety and environmental friendliness, and meets the demand for sustainable development.

[0024] 4. The present application reconstructs the end group of polyether modified polydimethylsiloxane, introduces a more stable triethoxysilane end group, and forms a three-dimensional network structure through ultraviolet light induced crosslinking, which significantly improves the hydrolysis resistance and oxidation resistance of the oil-proof film, and the oil-proof film still maintains good mechanical properties and oil-proof effect in a wide temperature range from -40 DEG C to 180 DEG C, effectively avoiding the cracking and peeling of the oil-proof layer in special environments, and widening the application range of the product.

[0025] 5. The application method of the environment-friendly fluorine-free oil-proof agent of the present application adopts the innovative process of vacuum impregnation, centrifugal drying, and gradient drying, realizes uniform adhesion and precise film formation control of the oil-proof agent on paper products, increases the penetration depth of the oil-proof agent in the paper fibers, forms an oil-proof film that is firmly combined with the substrate, and is not easily damaged in the folding, extrusion and other processing processes of the paper products, significantly improves the oil-proof performance and durability of the paper products, and reduces the waste of the oil-proof agent and the production cost. DETAILED DESCRIPTION

[0026] The embodiments of the technical scheme of the present application will be described in detail below. The following embodiments are only used to more clearly illustrate the technical scheme of the present application.

[0027] Example 1: An environment-friendly fluorine-free oil-proof agent, comprising the following components in parts by weight: cellulose nanowhiskers treated by penetration and cross-linking 11-16 parts, polyether modified polydimethylsiloxane 9-13 parts, nano titanium dioxide 6-8 parts, methacrylic acid octadecyl ester 4-6 parts, chitosan 3-5 parts, deionized water 58-68 parts, and sodium dodecyl benzene sulfonate 1.2-2.2 parts.

[0028] The present application uses cellulose nanowhiskers treated by penetration and cross-linking to provide skeleton support and binding sites; polyether modified polydimethylsiloxane as the main film-forming material to impart oil-proof properties; nano titanium dioxide is modified to enhance the oil-proof and adhesion properties; methacrylic acid octadecyl ester is involved in polymerization to improve the compactness of the film; chitosan improves compatibility and adhesion; deionized water is used as a solvent; and sodium dodecyl benzene sulfonate is used as an emulsifier to promote dispersion. The physical and chemical properties of each component interact, allowing the oil-proof agent to form a stable system with oil-proof function.

[0029] The use of cellulose nanowhiskers treated by penetration and cross-linking, compared to conventional cellulose derivatives, allows silane reagents to penetrate deeply and covalently bond through supercritical penetration and plasma cross-linking technology, not only enhancing the adhesion of the oil-proof agent to the substrate, but also providing anchoring space for other components with its porous structure; polyether modified polydimethylsiloxane is reconstructed by end groups, converting easily degradable hydroxyl end groups into stable triethoxysilane end groups, and forming a three-dimensional network through ultraviolet light cross-linking, significantly improving the durability of the oil-proof film in extreme environments and solving the problem of poor weather resistance of traditional organic silicon materials.

[0030] The present application uses fluorine-free materials as the basis, selects environmentally friendly raw materials such as cellulose nanowhiskers and chitosan, and the preparation process does not leave harmful solvent residues. While achieving high-efficiency oil-proof performance, it meets the safety standards for food contact materials, and balances high performance and environmental protection.

[0031] On the basis of any of the preceding technical solutions, further optimization is that: the specific method for the penetration cross-linking treatment of the cellulose nanowhiskers is: supercritical penetration treatment, the cellulose nanowhiskers are placed in a supercritical carbon dioxide device, a pressure of 10 MPa and a temperature of 45 DEG C are set, and 5% gamma-aminopropyl triethoxysilane vapor is introduced, and the silane reagent is allowed to penetrate into the internal pores of the nanowhiskers under the condition of keeping the temperature and pressure for 2 hours.

[0032] The high diffusivity and low surface tension characteristics of supercritical carbon dioxide enable the gamma-aminopropyl triethoxysilane vapor to break through the pore barriers of the cellulose nanowhiskers, and realize the deep penetration of silane molecules into the internal pores of the nanowhiskers in a supercritical fluid environment, thereby forming a pre-modified state with uniform distribution inside and outside.

[0033] The limitation that conventional silane soaking can only modify the surface of the nanowhiskers is solved, and the silane reagent is uniformly distributed in the micropores of the nanowhiskers through forced penetration in a supercritical environment, thereby providing sufficient reaction sites for subsequent cross-linking.

[0034] Supercritical carbon dioxide has the dual functions of solvent and swelling agent, and simultaneously pre-expands the porosity of the nanowhiskers during the penetration process, thereby providing more reaction space for subsequent plasma cross-linking.

[0035] Plasma cross-linking treatment: the cellulose nanowhiskers treated by supercritical penetration are transferred to a plasma surface treatment instrument, a vacuum degree of 3 Pa, an oxygen flow of 15 sccm, and a power of 100 W are set, and the treatment is performed for 5 min, thereby realizing the covalent cross-linking of silane and nanowhiskers through high-energy particle bombardment, and then the uniformity of the distribution of silicon elements is determined by X-ray photoelectron spectroscopy.

[0036] In a high-vacuum (3 Pa) oxygen plasma environment, high-energy electrons and ions generated by a power of 100 W bombard the silane molecules on the surface and inside of the nanowhiskers, activate the chemical reaction between the ethoxyl groups of the silane and the hydroxyl groups on the surface of the nanowhiskers, form Si-O-C covalent bonds, and fix the physically penetrated silane molecules in the structure of the nanowhiskers.

[0037] The high-energy effect of the plasma strengthens the bonding strength between the silane and the nanowhiskers, avoids the silane overflow problem caused by conventional thermal cross-linking, and further expands the pore structure by using the etching effect of the oxygen plasma.

[0038] On the basis of any of the preceding technical solutions, further optimization is that: the specific method for the biomimetic mineralization-hydrophobic coating composite modification of the nanometer titanium dioxide is: (1) biomimetic mineralization treatment: The anatase nano-titanium dioxide with an initial particle size of 20-30 nm is dispersed in a Tris-HCl buffer solution with a pH of 7.4 at a solid-liquid ratio of 1:50 (the simulated body fluid contains CaCl2 10 mmol / L, Na2HPO4 6 mmol / L, NaCl 137 mmol / L, and KCl 2.7 mmol / L), and the obtained dispersion is transferred to a sealed reaction kettle, and then is placed in a 37°C constant-temperature water bath for 12 hours, during which the dispersion is gently stirred every 3 hours for 10 minutes (at a stirring speed of 50 rpm), and then is centrifuged (at a speed of 8000 rpm for 15 minutes), to obtain nano-titanium dioxide coated with a hydroxylapatite biomimetic layer.

[0039] By generating a hydroxylapatite biomimetic layer on the surface of the anatase nano-titanium dioxide, the hydroxyl and phosphate polar groups of the hydroxylapatite are utilized to enhance the hydrogen bonding and electrostatic adsorption capacity of the nano-particles to the pulp molding substrate, so as to solve the problems of easy agglomeration of unmodified nano-titanium dioxide in the pulp and weak binding force (easy to fall off) of the nano-titanium dioxide to the fibers, and to ensure long-term adhesion of a subsequent oil-proof layer to the surface of the substrate.

[0040] The hydroxylapatite biomimetic layer has a nano-scale porous structure, which can improve the surface roughness of the nano-titanium dioxide, provide a substrate for subsequent hydrophobic coating to form a micro-nano composite rough structure, and further improve the final oil-proof effect.

[0041] (2) Hydrophobic coating treatment: The nano-titanium dioxide obtained above is dispersed in anhydrous ethanol at a solid-liquid ratio of 1:40, and then pure perfluorodecyltriethoxysilane (with a purity of ≥98%) is added (the amount of the perfluorodecyltriethoxysilane is 5% of the mass of the nano-titanium dioxide), and then the mixture is placed in an ultrasonic reactor with a frequency of 40 kHz and a power of 300 W, and is subjected to ultrasonic reaction at a constant temperature of 60°C for 3 hours (the ultrasonic mode is continuous ultrasonic, and the reaction container is a three-necked flask with a reflux device); after the reaction, the mixture is centrifuged (at a speed of 10000 rpm for 20 minutes), washed with anhydrous ethanol for 3 times, and vacuum dried at 80°C for 4 hours, to obtain the composite modified nano-titanium dioxide.

[0042] By directional arrangement of the hydrophobic long chain of the perfluorodecyltriethoxysilane on the surface of the nano-particles, a gradient wetting structure of a hydrophilic inner layer (hydroxylapatite)-hydrophobic outer layer (perfluorinated chain) is formed, which can effectively block the penetration of oil molecules.

[0043] The perfluorodecyltriethoxysilane is covalently bonded to the hydroxyl groups of the hydroxylapatite through Si-O-P covalent bonding, and compared with physical adsorption type hydrophobic modification, the covalent bonding can prevent the hydrophobic layer from falling off, and solves the problem of poor weather resistance of traditional hydrophobic modification.

[0044] The anhydrous ethanol dispersion system is compatible with the components such as silicone, oil-repellent monomers and the like of the subsequent oil-proof agent, the ultrasonic assistance can promote uniform coating of the perfluorosilane and avoid the oil-proof defects caused by local hydrophobicity deficiency; the residual solvent can be completely removed through vacuum drying, and the odor or safety hazard caused by solvent volatilization on the paper pulp molded product can be prevented.

[0045] On the basis of any one of the technical solutions above, further optimization is that the polyether-modified polydimethylsiloxane is an end group restructured polyether-modified polydimethylsiloxane, and a preparation method thereof is as follows: polyether-modified polydimethylsiloxane is mixed with methyl triethoxysilane at a molar ratio of 1:1.3, 0.6% of dibutyltin dilaurate in the mixed system is added as a catalyst, and then the mixture is reacted at 85°C in a microwave device (power 400W, frequency 2450MHz) for 2h, followed by ultraviolet light irradiation (wavelength 254nm, power 120W) for 1h.

[0046] Microwave-assisted end group exchange reaction: the ester exchange reaction of the hydroxyl group at the end of the polyether-modified polydimethylsiloxane molecular chain and the ethoxyl group of methyl triethoxysilane occurs under the catalysis of dibutyltin dilaurate, and the reaction rate is promoted by the thermal effect and non-thermal effect (molecular vibration acceleration) of the microwave, so that the ethoxysilane group is introduced into the end of the siloxane chain to form an intermediate product.

[0047] Ultraviolet light-induced cross-linking reinforcement: the ultraviolet light with a wavelength of 254nm activates the ethoxysilane group in the intermediate product to cause partial hydrolysis and condensation, forming a-Si-O-Si- covalent cross-linking point, and the end group restructured structure is stabilized by photochemical action to avoid the end group rollback after the microwave reaction.

[0048] The end group of the conventional polyether-modified polydimethylsiloxane is a hydroxyl group, which is prone to chain scission and degradation under high temperature (≥120°C) or high humidity environment, and the introduction of the triethoxysilane end group with higher stability through end group restructuring can improve the hydrolysis resistance and oxidation resistance of the molecular chain.

[0049] The mild cross-linking induced by ultraviolet light enables the siloxane molecules to form a three-dimensional network structure, the tensile strength of the oil-proof film is improved, and the oil-proof layer is prevented from cracking when the paper pulp molded substrate is bent.

[0050] On the basis of any one of the technical solutions above, further optimization is that the chitosan is modified chitosan, and a preparation method thereof comprises: (1) Enzymatic treatment: chitosan is dispersed in an acetic acid aqueous solution with a pH of 5.0, 0.5% of cellulase in the mass of the chitosan is added, and the enzyme is hydrolyzed at 45°C in a constant-temperature water bath for 2h; (2) Quaternary ammonium treatment: glycidyltrimethylammonium chloride is added to the chitosan solution after enzymatic hydrolysis, the molar ratio of which to chitosan glucose unit is 1:1.8, the temperature is raised to 60 DEG C and stirred for 6 hours, 10% sodium hydroxide aqueous solution is added to adjust the pH to 7.0, and the solid product is obtained by centrifugal separation, washed with deionized water for 3 times and dried at 80 DEG C under vacuum for 4 hours.

[0051] The unmodified chitosan can only be dissolved in an acidic solution due to its strong molecular chain rigidity and dense hydrogen bonding, and is prone to aggregation and precipitation in a neutral or alkaline pulp slurry system. By enzymatic hydrolysis to cut long chains and quaternary ammonium to introduce polar groups, the chitosan can be quickly dissolved in a neutral water environment, adapt to the water-based system of oil-proof agent, and solve the poor solubility problem of conventional chitosan.

[0052] The unmodified chitosan has poor film-forming compactness, and the oil-proof performance is limited when used alone. By modifying and controlling the molecular chain length and surface activity, it can not only act as a binder to promote the uniform distribution of oil-proof components on the fiber surface, but also form a dense oil-proof film with silicone and hydrophobic particles to strengthen the oil-proof barrier effect.

[0053] The polarity of the quaternary ammonium cation can neutralize the weak negative electricity on the surface of modified nano titanium dioxide, silicone and other hydrophobic components, reduce the interfacial repulsion, prolong the dispersion stability of the hydrophobic components in the chitosan solution, and greatly reduce the delamination probability during the storage of the oil-proof agent.

[0054] Embodiment 2: Compared with embodiment 1, the difference lies in that it further comprises the following technical features: The application also provides an environmentally friendly fluorine-free oil-proof agent preparation method, comprising the following steps: (S1) Pre-dispersion of modified components: according to the above weight fraction, the cellulose nanowhisker treated by penetration and crosslinking is added to a twin-screw mixing kettle with temperature control, and magnetic field assisted double-frequency ultrasonic treatment is started for 25 minutes, during which the particle size distribution is monitored by an online particle size analyzer to obtain a uniform dispersion liquid I.

[0055] In this step, the cellulose nanocrystals after crosslinking treatment are added into a double screw mixing kettle with temperature control with deionized water, and a neodymium iron boron superconducting magnet generates a uniform magnetic field with a strength of 0.4T and a direction parallel to the axis of the double screw mixing kettle. In this magnetic field environment, the cellulose nanocrystals are subjected to magnetic field force and will be oriented along the magnetic force line. At the same time, the double-frequency ultrasound plays a synergistic role. Low-frequency ultrasound (20 kHz, 320 W) is used for 10 min first, which can effectively destroy the initial agglomerates of cellulose nanocrystals and break down larger agglomerates by using its strong mechanical force. Then, high-frequency ultrasound (60 kHz, 420 W) is switched on for 15 min, and the high-frequency vibration and cavitation effect generated by high-frequency ultrasound can realize fine dispersion of nanocrystals at the molecular level. The particle size distribution is monitored in real time by an online particle size analyzer, and feedback control is used to ensure that the dispersion process achieves the expected effect, and finally a uniform dispersion liquid I with uniform particle size is obtained.

[0056] The magnetic field assists the directional arrangement of cellulose nanocrystals, reducing the disorderly entanglement and agglomeration tendency between particles; the step-by-step treatment of double-frequency ultrasound first breaks the agglomeration and then finely disperses, which effectively improves the dispersion efficiency compared to single-frequency ultrasound, and enables the nanocrystals to achieve a highly uniform dispersion state in water.

[0057] (S2) Organic silicon-biomass synergistic composite: add end group restructured polyether modified polydimethylsiloxane and modified chitosan to dispersion liquid I, heat to 70°C, introduce supercritical carbon dioxide and apply microwave at the same time, stir for 1.5 h to obtain mixture II.

[0058] In this step, the dispersion liquid I is first heated to 70°C to provide a suitable temperature environment for the subsequent reaction. Then supercritical carbon dioxide is introduced. When carbon dioxide is in a supercritical state with a pressure of 9 MPa and a temperature of 42°C, it has high diffusivity as a gas and strong solubility as a liquid, which can reduce the surface tension of the end group restructured polyether modified polydimethylsiloxane, make the organic silicon molecular chain fully stretch, and also reduce the surface energy of the biomass material such as modified chitosan, promoting the interaction between molecules.

[0059] Supercritical carbon dioxide as a special medium improves the diffusion and solubility of molecules, and the rapid heating and non-thermal effect of microwave play a dual role.

[0060] Pulse microwave radiation and variable frequency stirring are used to accurately control the reaction process. Pulse microwave avoids local overheating and side reactions that may occur due to continuous heating, and by controlling the microwave working and pause time, the reaction rate and degree can be accurately controlled. Variable frequency stirring gradually increases the stirring speed according to the reaction progress, which avoids damaging the molecular structure at a low speed in the early stage of the reaction, and increases the speed to promote full reaction in the later stage.

[0061] (S3) Plasma-assisted emulsion polymerization: Add composite modified nano-titanium dioxide, octadecyl methacrylate and initiator ammonium persulfate to the mixed solution II, the amount of which is 0.8% of the mass of octadecyl methacrylate, and then introduce nitrogen to remove oxygen for 30 minutes. Then, transfer the mixed system to a plasma polymerization reactor and perform polymerization at 75°C for 3 hours to obtain emulsion III.

[0062] Introduce nitrogen to remove oxygen for 30 minutes, which is to remove oxygen in the system because oxygen can inhibit free radical polymerization and affect the polymerization effect. After the oxygen removal is completed, the mixed system is transferred to a plasma polymerization reactor, and polymerization is carried out at 75°C under the conditions of a vacuum degree of 4 Pa, an argon flow rate of 25 sccm, and a power of 100 W. In the plasma environment, high-energy electrons, ions and other particles bombard monomer molecules (octadecyl methacrylate) and free radicals generated by initiator decomposition, activate the double bonds of monomers, and initiate polymerization to continuously connect monomer molecules to form polymer chains.

[0063] (S4) Gradient post-processing shaping: Freeze-emulsion III at -75°C for 10 hours, then thaw at 30°C for 1.5 hours, repeat 3 times to promote molecular chain rearrangement, then remove unreacted impurities through multi-stage membrane filtration, and finally age at 25°C under inert gas protection for 48 hours to obtain an environmentally friendly fluorine-free oil repellent.

[0064] When emulsion III is frozen at -75°C for 10 hours, water molecules in the system rapidly crystallize into fine ice crystals. The growth of these ice crystals can exert a squeezing effect on the polymer particles and molecular chains in the emulsion, breaking the original disordered entanglement state of the molecular chains and promoting the rearrangement of the molecular chains. Inert gas can isolate oxygen and prevent the oxidation and degradation of polymer molecular chains during the aging process.

[0065] Multi-stage membrane filtration uses ceramic membranes with different pore sizes for step-by-step filtration, which can accurately remove impurities of different sizes and improve the impurity removal rate. Compared with single filtration, multi-stage membrane filtration can more thoroughly remove unreacted impurities, avoiding the negative effects of impurities on the performance of the oil repellent, such as preventing impurities from causing oil-repellent film holes and reducing oil-repellent effect, and ensuring the quality stability and uniformity of the oil repellent.

[0066] On the basis of any one of the above technical solutions, further optimization is that in the step S1 modification component pre-dispersion, during the magnetic field assisted double frequency ultrasonic treatment, a neodymium-iron-boron superconducting magnet is selected to generate a uniform magnetic field, the magnetic field direction is parallel to the axial direction of the double screw mixing kettle, and the magnetic field strength is controlled at 0.4T.

[0067] Due to the axial parallelism of the magnetic field direction and the twin-screw mixing kettle, the cellulose nanowhiskers will be orderly arranged along the magnetic force line direction under the action of the magnetic field force. This directional arrangement effectively reduces the agglomeration phenomenon caused by disordered collision and interaction between nanowhiskers.

[0068] The ordered structure formed by the cellulose nanowhiskers in the dispersion liquid I can better form an interwoven network with paper fibers during the subsequent oil-proof agent coating process, thereby improving the adhesion of the oil-proof agent on the surface of the paper fibers. It is especially suitable for application scenarios where the food box is used to contain food containing a large amount of oil.

[0069] The absolute value of the zeta potential of the dispersion liquid I is ≥ 35 mV, which ensures that the cellulose nanowhiskers are in a monodispersed state in water, thereby avoiding uneven performance of the oil-proof agent due to particle agglomeration during the subsequent compounding process.

[0070] On the basis of any one of the above technical solutions, further optimization is that in step S1, the low-frequency 20 kHz, power 320 W is used for 10 min to destroy the initial agglomerates of the cellulose nanowhiskers, and then the high-frequency 60 kHz, power 420 W is switched to for 15 min to achieve fine dispersion of the nanowhiskers.

[0071] On the basis of any one of the above technical solutions, further optimization is that in step S2, pulsed microwave radiation is used, working for 15 s and pausing for 5 s, the microwave power is set to 380 W, and the frequency is 2450 MHz; the stirring process is driven by a variable frequency motor, and the stirring rate is gradually increased from 300 rpm at the beginning to 550 rpm, and the viscosity and temperature changes of the mixed liquid II are recorded every 15 min during the 1.5 h reaction process.

[0072] The intermittent action of the microwave ensures that the reaction is sufficient and stable, and avoids local overheating; the variable frequency stirring ensures uniform mixing of the materials and promotes effective collision and reaction between molecules.

[0073] On the basis of any one of the above technical solutions, further optimization is that in step S3, ultrasonic assistance of 40 kHz, power 280 W is started simultaneously during the polymerization process, and the ultrasonic works intermittently, working for 8 s and pausing for 2 s; during the reaction process, the reaction temperature is monitored in real time by a temperature sensor, and when the temperature exceeds 75℃, a circulating cooling water system is started to control the temperature, so that the temperature fluctuation range is controlled within ± 1℃; after 3 h of reaction, the residual monomer content in the emulsion III is detected by a gas chromatograph, and when the residual content of methacrylic acid octadecyl ester is less than 0.5%, the reaction is stopped.

[0074] The cavitation effect of ultrasonic generation forms a local high-temperature and high-pressure microenvironment in the working stage, promotes the decomposition of initiator ammonium persulfate to generate free radicals, and accelerates the polymerization reaction of octadecyl methacrylate monomer; at the same time, mechanical stirring can effectively disperse the modified nano-titanium dioxide particles and prevent them from agglomerating in the polymerization process.

[0075] Embodiment 3: Compared with Embodiment 2, the difference lies in that it further comprises the following technical features: The environmentally friendly fluorine-free oil-proof agent prepared according to the above preparation method is applied in food packaging paper, paper lunch box, baking paper, food-grade paper tray and disposable paper cup. The use method thereof is as follows: (1) Dip coating treatment: dilute the environmentally friendly fluorine-free oil-proof agent to a solid content of 8-12%, immerse the above paper product in the diluted oil-proof agent solution, and immerse for 5-8 min under a vacuum degree of-0.08 MPa, so that the oil-proof agent fully penetrates into the fiber inside the paper product; then take out the paper product, and spin dry for 3-5 min at a centrifugal speed of 800-1000 r / min to remove the excess oil-proof agent on the surface.

[0076] The environmentally friendly fluorine-free oil-proof agent is diluted to a solid content of 8-12% in order to have appropriate viscosity and fluidity, facilitating uniform coating and penetration on the surface of the paper product. Immerse for 5-8 min under a vacuum degree of-0.08 MPa, and use the negative pressure principle to eliminate the air resistance in the fiber pores of the paper product, so that the oil-proof agent solution quickly and fully penetrates into the fiber pores under the action of pressure difference.

[0077] Then spin dry for 3-5 min at a centrifugal speed of 800-1000 r / min to remove the excess oil-proof agent on the surface of the paper product by centrifugal force, avoid the accumulation of oil-proof agent on the surface, and ensure the uniform adhesion of the oil-proof agent on the surface and inside of the paper product, while controlling the adhesion amount of the oil-proof agent.

[0078] Dip coating treatment realizes uniform adhesion and precise dosage control of the oil-proof agent on the paper product; the drying and curing process promotes the formation of a dense, stable and firmly combined oil-proof film of the oil-proof agent on the paper product; performance testing is used to evaluate whether the paper product treated by the oil-proof agent meets the actual application requirements and ensures product quality.

[0079] (2) Drying and curing: send the dip-coated paper product into a hot air circulating drying oven, pre-dry at 60℃ for 10-15 min, then heat up to 120℃ for drying for 20-25 min, so that the oil-proof agent forms a dense oil-proof film on the surface of the paper product.

[0080] First, pre-drying at 60℃ for 10-15min, this stage slowly removes most of the water in the paper product, to avoid the rapid evaporation of water resulting in the rapid solidification of oil repellent on the surface of the paper product and form uneven film or crack. Then heated to 120℃ for 20-25min, at higher temperatures, the polymer molecules in the oil repellent chain accelerate movement and cross-linking with each other, forming a dense three-dimensional network structure of oil-proof film, while the binding force between the oil repellent and the paper fiber is further enhanced.

[0081] (3) The paper product after the above treatment, the subsequent oil-proof performance test.

[0082] It can be seen that the application process of vacuum impregnation - centrifugal drying - gradient drying is systematically optimized from the penetration, adhesion amount control to the film forming process of the oil repellent. Compared with the traditional soaking coating and single temperature drying, this process can better adapt to the characteristics of the environment-friendly fluorine-free oil repellent, improve the quality and uniformity of the oil-proof film, reduce the waste of the oil repellent, reduce the production cost, and improve the production efficiency.

[0083] The treated paper product is tested for oil-proof performance, and the barrier ability of the oil-proof film formed on the surface of the paper product to different oils, the durability of the oil-proof film and other performance indicators are detected by standard test methods (such as TAPPI T559cm-02 standard), to verify the actual application effect of the oil repellent.

[0084] The above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application; any alternative improvement or change made by those skilled in the art to the embodiments of the present application falls within the protection scope of the present application.

[0085] The details of the present application not described are well known to those skilled in the art.

Claims

1. An environmentally friendly fluorine-free oil repellent, characterized by comprising: The components include the following weight parts: 11-16 parts of cellulose nanowhiskers after penetration crosslinking treatment, 9-13 parts of polyether modified polydimethylsiloxane, 6-8 parts of nano titanium dioxide, 4-6 parts of methacrylic acid octadecyl ester, 3-5 parts of chitosan, 58-68 parts of deionized water, and 1.2-2.2 parts of sodium dodecyl benzene sulfonate.

2. The environmentally friendly fluorine-free oil repellent agent according to claim 1, characterized by, The polyether modified polydimethylsiloxane is an end group restructured polyether modified polydimethylsiloxane, and the preparation method is as follows: polyether modified polydimethylsiloxane and methyl triethoxysilane are mixed at a molar ratio of 1:1.3, 0.6% of dibutyl tin dilaurate is added as a catalyst, and the mixture is reacted at 85°C in a microwave device for 2 hours, and then irradiated with ultraviolet light for 1 hour.

3. The environmentally friendly fluorine-free oil repellent agent according to claim 1, characterized by, The chitosan is modified chitosan, and the preparation method comprises: (1) enzymatic treatment: disperse chitosan in an acetic acid aqueous solution with pH=5.0, add 0.5% of cellulase based on the mass of chitosan, and stir for enzymatic hydrolysis in a 45°C constant temperature water bath for 2 hours; (2) quaternization treatment: add glycidyltrimethylammonium chloride to the chitosan solution after enzymatic hydrolysis, with a molar ratio of 1:1.8 between glycidyltrimethylammonium chloride and chitosan glucose units, stir at 60°C for 6 hours, add 10% sodium hydroxide aqueous solution to adjust the pH to 7.0, centrifuge to obtain a solid product, wash with deionized water for 3 times, and then vacuum dry at 80°C for 4 hours.

4. A method for preparing an environmentally friendly fluorine-free oil repellent agent, characterized by, The method comprises the following steps: (S1) pre-dispersion of modified components: according to the above weight parts, cellulose nanowhiskers after penetration crosslinking treatment and deionized water are added to a double screw mixing kettle with temperature control, and magnetic field assisted double frequency ultrasonic treatment is started for 25 minutes, during which the particle size distribution is monitored by an online particle size analyzer to obtain a uniform dispersion liquid I; (S2) organic silicon-biomass synergistic composite: end group restructured polyether modified polydimethylsiloxane and modified chitosan are added to the dispersion liquid I, heated to 70°C, supercritical carbon dioxide is introduced, and microwave is applied at the same time, and stirred for 1.5 hours to obtain a mixed liquid II; (S3) plasma assisted emulsion polymerization: composite modified nano titanium dioxide, methacrylic acid octadecyl ester and initiator ammonium persulfate are added to the mixed liquid II, the amount of ammonium persulfate is 0.8% of the mass of methacrylic acid octadecyl ester, oxygen is removed by introducing nitrogen for 30 minutes, then transferred to a plasma polymerization reactor, and polymerized at 75°C for 3 hours to obtain an emulsion III; (S4) gradient post-treatment shaping: the emulsion III is first subjected to freeze-thaw cycles, frozen at -75°C for 10 hours, then thawed at 30°C for 1.5 hours, repeated for 3 times to promote molecular chain rearrangement, then removed unreacted impurities by multi-stage membrane filtration, and finally aged at 25°C for 48 hours under inert gas protection to obtain an environmentally friendly fluorine-free oil repellent.

5. The method of claim 4, wherein: In the step S1 of pre-dispersion of modified components, a neodymium-iron-boron superconducting magnet is used to generate a uniform magnetic field, the magnetic field direction is parallel to the axial direction of the double screw mixing kettle, and the magnetic field strength is controlled at 0.4T. The absolute value of zeta potential of the dispersion liquid I is ≥35mV, which ensures that the cellulose nanowhiskers are in a monodispersed state in water, and avoids uneven oil repellent performance caused by particle agglomeration in the subsequent composite process.

6. The method of claim 5, wherein: The double-frequency ultrasonic treatment in step S1 is performed by first treating for 10 min at a low frequency of 20 kHz and a power of 320 W to break the initial agglomerates of cellulose nanowhiskers, and then switching to a high frequency of 60 kHz and a power of 420 W for 15 min to finely disperse the nanowhiskers.

7. The method of claim 6, wherein: In step S2, the microwave is applied synchronously by pulse microwave radiation, with a working time of 15 s and a pause time of 5 s, a microwave power of 380 W, and a frequency of 2450 MHz; the stirring process is driven by a variable frequency motor, and the stirring rate is gradually increased from 300 rpm at the beginning to 550 rpm; the viscosity and temperature of the mixed solution II are recorded every 15 min during the 1.5 h reaction process.

8. The method of claim 7, wherein: In step S3, ultrasonic assistance is simultaneously started at a frequency of 40 kHz and a power of 280 W, and the ultrasonic is intermittently operated with a working time of 8 s and a pause time of 2 s; during the reaction process, the reaction temperature is monitored in real time by a temperature sensor, and when the temperature exceeds 75℃, a circulating cooling water system is started to control the temperature, so that the temperature fluctuation range is controlled within ±1℃; after 3 h of reaction, the residual monomer content in the emulsion III is detected by a gas chromatograph, and when the residual content of octadecyl methacrylate is less than 0.5%, the reaction is stopped.

9. The environmentally friendly fluorine-free oil repellent prepared by the preparation method of claim 8 is applied in food packaging paper, paper lunch boxes, baking paper, food-grade paper holders, and disposable paper cups, and the use method thereof is as follows: (1) Dip coating treatment: dilute the environment-friendly fluorine-free oil-proof agent to a solid content of 8-12%, immerse the paper product in the diluted oil-proof agent solution, and impregnate for 5-8 min under a vacuum degree of -0.08 MPa, so that the oil-proof agent fully penetrates into the fiber inside the paper product; Then, the paper product is taken out and spun dry at a centrifugal speed of 800-1000 r / min for 3-5 min to remove excess oil repellent on the surface; (2) Drying and curing: the paper product after immersion coating is sent into a hot air circulating drying oven, pre-dried at 60℃ for 10-15 min, and then dried at 120℃ for 20-25 min to form a dense oil-repellent film on the surface of the paper product; (3) The paper product after the above treatment is subjected to subsequent oil-repellent performance test.