Preparation method and application of a non-fluorine oil-proof coating film for food

Abstract

The present application relates to the technical field of oil-proof materials, and particularly relates to a preparation method and application of a fluorine-free oil-proof coating for food. The method comprises the following steps: under an oxygen-free condition, a fluorine-free acrylic ester combination solution, an initiator, an emulsifier and a polyvinyl alcohol aqueous solution are uniformly mixed to make the acrylic ester combination solution undergo emulsion polymerization to obtain a fluorine-free oil-proof agent; the fluorine-free oil-proof agent is coated on the surface of tableware, and is dried to obtain a fluorine-free oil-proof coating. The fluorine-free oil-proof coating for food prepared by the method has the advantages of fluorine-free oil resistance, good film forming performance, thermal stability, good acid resistance and the like, and the paper pulp tableware coated with the coating has the advantages of environmental protection, degradability, oil resistance, acid resistance and heat resistance, and has a good application prospect in the field of disposable food tableware.

Description

Technical Field

[0001] The present invention relates to the technical field of oil-proof materials, and in particular to a preparation method and application of a fluorine-free oil-proof coating for food. Background Art

[0002] Pulp molding uses herbaceous plants such as sugarcane bagasse, corn stalks, wheat straw, reeds, and rice straw as raw materials. This utilizes agricultural waste, fully maximizing plant resource utilization. The production process is simple, and the finished product possesses a certain degree of mechanical strength, making it a promising material for environmentally friendly tableware. However, paper materials have a high porosity and inherent hydroxyl groups in their fibers, making them non-oil and water-resistant. This makes them unsatisfactory for food tableware packaging.

[0003] To improve this characteristic, functional additives such as waterproofing agents, oil-repellent agents, and other adhesives, brighteners, plasticizers, and antioxidants are added to the pulp during the pulping process of pulp molded products in order to achieve good results. However, these additives can migrate into food during contact between tableware and food, and then be ingested by the human body, posing a certain risk to human health. This requires effective modification of pulp molded tableware. This involves surface treatment of the pulp molded tableware and application of an oil-repellent agent to form a surface coating, giving it excellent properties such as water and oil resistance, suitable for direct contact with food. Furthermore, since tableware inevitably comes into contact with acidic substances, the coating also needs to have a certain acid resistance.

[0004] Oil repellents have numerous industrial applications, such as patent 201911177507.3, which discloses a fluoropolymer and a protective coating containing the same. This fluoropolymer protective coating exhibits strong adhesion and high hardness, as well as excellent water and oil resistance and acid and alkali resistance. However, the use of fluorinated materials in tableware can pose food safety risks. Therefore, a food-contactable, fluorine-free oil repellent coating with excellent oil and acid resistance is urgently needed. Summary of the Invention

[0005] The present invention aims to overcome the defects in the prior art that fluorine-containing oil-proof coatings cannot be used in the food field and the production cost of bio-based fluorine-free oil-proof agents is high. A preparation method and application of fluorine-free oil-proof coatings for food are proposed to overcome the above defects.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A method for preparing a fluorine-free oil-proof coating for food, comprising the following steps:

[0008] S1. Under anaerobic conditions, uniformly mixing a fluorine-free acrylate composition liquid, an initiator, an emulsifier, and a polyvinyl alcohol (PVA) aqueous solution, so that the acrylate composition liquid undergoes emulsion polymerization to obtain a fluorine-free oil repellent;

[0009] S2. Applying a fluorine-free oil-proof agent on the surface of the tableware and drying it to obtain a fluorine-free oil-proof coating.

[0010] Whether an oil repellent contains fluorine affects its performance. Fluorine-containing oil repellents refer to fluorinated surfactants, typically perfluorinated compounds, which are fully fluorinated anionic polymers with hydrophobic and oleophobic properties. The stability of the fluorine-carbon bond allows fluorinated compounds to maintain their properties, including chemical and heat resistance, in a variety of environments. However, due to the presence of the fluoride layer, non-polar substances such as water and oil are repelled by the surface fluoride molecules when they come into contact with the coating surface. This repulsive force prevents the water and oil droplets from maintaining stable contact with the coating surface, instead forming spherical water or oil droplets that easily roll off the surface.

[0011] Fluorine-free bio-based oil repellents, however, have high raw material and production costs, typically requiring compounding with other oil repellents to achieve excellent water and oil resistance. This also requires the purchase of additional production equipment and the establishment of production lines, increasing both process and labor costs. Silicone-based oil repellents, like these, are also difficult to commercialize on a large scale. Therefore, the present invention optimizes the process flow and demonstrates, through experiments, that the resulting oil-repellent coating exhibits excellent heat, oil, and acid resistance.

[0012] Preferably, the fluorine-free acrylic ester composition liquid in step S1 consists of butyl acrylate (BA), hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA).

[0013] As a further preference, the oil-to-water ratio of the fluorine-free oil repellent obtained by emulsion polymerization in step S1 is ≥1:2.

[0014] Preferably, the initiator in step S1 is water-soluble azobisisobutylamidine hydrochloride (V-50).

[0015] Preferably, the emulsifier in step S1 is a combination of one or more of polysorbate 80 (Tween 80) and sodium oleate.

[0016] Preferably, the fluorine-free oil repellent obtained in step S1 has a solid content of 35% to 45%.

[0017] Preferably, in step S2, the fluorine-free oil repellent is applied by spin coating, and a drying operation is performed while coating.

[0018] As a further preference, the drying operation temperature is 70-100° C. and the drying time is 2-3 hours.

[0019] On the other hand, the present invention discloses a fluorine-free oil-proof coating prepared based on the above method, and its application in coating the surface of pulp molded tableware.

[0020] Therefore, the present invention has the following beneficial effects:

[0021] (1) The present invention conducts emulsion polymerization of acrylic ester monomers BA, HEMA, and EMA in an oxygen-free environment to synthesize a fluorine-free oil repellent having good stability and being safe and non-toxic.

[0022] (2) The present invention directly applies the fluorine-free oil-proof agent on the surface of tableware, and forms an oil-proof film through a drying operation, which has good oil resistance, temperature resistance and acid resistance.

[0023] (3) The fluorine-free oil-proof coating for food prepared by the present invention has a simple preparation process, low cost, safety and non-toxicity, and good stability, and has good application prospects in the field of disposable food tableware. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM size morphology of the fluorine-free oil repellent in Example 1 of the present invention.

[0025] Figure 2 This is a comparison chart of the oil and high temperature resistance of coated tableware and uncoated tableware.

[0026] Figure 3 This is a comparison chart of the acid resistance of coated tableware and uncoated tableware. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be further clearly and completely described below through specific examples and in conjunction with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are given, but they are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods used in the following examples are conventional methods unless otherwise specified, and the materials, reagents, etc. used in the examples, unless otherwise specified, can be obtained from commercial channels.

[0028] The present invention provides a method for preparing a food-contactable fluorine-free oil-proofing agent coating, comprising the following steps:

[0029] (1) Preparation of dispersant: 1.0-3.0 parts of polyvinyl alcohol are added to 100 ml of aqueous solution and stirred with a magnetic stirrer to fully dissolve and mix the solution to obtain a PVA aqueous solution with a concentration of 1.0-3.0%.

[0030] (2) System construction and deoxygenation: 0.3-0.4 parts of V-50 initiator were added to a three-necked flask, fixed on a mechanical stirring device, and the three-necked flask was immersed in a water bath. The reaction system was vacuumed and nitrogen was circulated to ensure that the reaction system was in an oxygen-free environment;

[0031] (3) Oil phase pretreatment: Use a balance to accurately weigh 30-40 parts of BA, HEMA, and EMA monomers into a monomer tube to obtain an oil phase solution, which is then purged with nitrogen for more than 20 minutes to remove oxygen from the solution.

[0032] (3) Pretreatment of the aqueous phase: Use a balance to accurately weigh 2.0-4.0 parts of emulsifier and 50-70 parts of PVA aqueous solution in a conical flask, shake thoroughly to completely dissolve the emulsifier to obtain an aqueous solution, and then flow nitrogen through the solution for more than 20 minutes to remove oxygen from the solution.

[0033] (4) Addition reaction: Under nitrogen protection, use a syringe to extract the oil phase and the water phase respectively into a three-necked flask, and seal the injection port with wax to prevent oxygen from entering the reaction process;

[0034] (5) Reaction: Set the reaction temperature to 25-40°C, the reaction time to 5-8h, and the reaction speed to 100-400r to start the emulsion polymerization reaction;

[0035] (6) Stopping the reaction: When the polymerization reaction reaches the desired state, stop stirring, remove the three-necked flask, cool to room temperature, transfer the emulsion to a clean sample bottle, and obtain a fluorine-free oil repellent emulsion. Determine its solid content and conversion rate.

[0036] (7) Coating: Fix the sugarcane bagasse pulp molded tableware on a rotating device and spray the prepared fluorine-free oil repellent agent. Adjust the rotation speed so that the oil repellent agent is evenly coated on the tableware surface. Dry at 70-100°C for 2-3 hours to obtain a food-contactable fluorine-free oil repellent coating. The coating is then subjected to an oil repellency test.

[0037] The characterization test method in the embodiment of the present invention is as follows:

[0038] Determination of reaction conversion rate (Conv.%): Conv.% = (S2 / S1) * 100%. In the above formula, S1 is the solid content of the solution before the reaction, and S2 is the solid content of the emulsion after the polymerization reaction.

[0039] SEM determination of fluorine-free oil repellent:

[0040] Take 5 μL of the above-mentioned fluorine-free oil repellent emulsion and dilute it to 1 mL with deionized water. Take a drop of the diluted emulsion on a clean silicon wafer of 0.5 cm × 0.5 cm in size, dry it naturally at room temperature, spray gold coating it, and after cooling, use SEM to characterize it.

[0041] Oil-proof and heat-resistant test: Spin-coat the fluorine-free oil-proof agent on the surface of pulp tableware and dry it. Then add a certain amount of hot oil at 95±5 ℃ at room temperature. Let it stand at room temperature for 6 hours to observe whether there is wrinkling or leakage. The oil-proof property can reach 6 hours without penetration.

[0042] Example 1

[0043] The raw material composition of the fluorine-free oil repellent reaction is as follows: monomer BA: HEMA: EMA = 13mL: 2mL: 20mL, Tween 80: sodium oleate: 2.5% PVA solution = 2.0g: 0.5g: 50mL, V-50: 0.35g, and the oil-water ratio is 35:50.

[0044] Take 0.35g of initiator V-50 into a clean three-necked flask, seal the bottle mouth with a rubber stopper, fix it on a stirring device, and perform vacuum + nitrogen bubbling cycles 6 times to ensure that the system is in an oxygen-free state. During the cycle, weigh BA:HEMA:EMA = 13mL: 2mL: 20mL respectively in a monomer tube to obtain the oil phase, accurately weigh Tween 80: sodium oleate: 2.5% PVA aqueous solution = 2.0g: 0.5g: 50mL in a conical flask to obtain the water phase, and bubble nitrogen into the water phase and oil phase for more than 20min respectively to deoxygenate. After the cycle is completed, under nitrogen protection, use a syringe to pump the water phase and oil phase into the three-necked reaction bottle respectively, seal the sample inlet with wax, turn on the agitator, set the stirring speed to 300r, the reaction temperature to 30℃, and react for 6h. After the reaction is completed, the three-necked flask is removed, air is introduced, and the mixture is cooled to room temperature. The emulsion is transferred to the sample to obtain a fluorine-free oil repellent. The obtained fluorine-free oil repellent is spin-coated onto the surface of pulp molded tableware and dried at 80°C for 2 hours to obtain a food-contactable fluorine-free oil repellent coating.

[0045] Take a small amount of emulsion for SEM characterization to obtain the emulsion size morphology, such as Figure 1 The test results show that the solid content of the emulsion is 40.5%, the conversion rate of the polymerization reaction is 98.7%, and the average particle size of the obtained fluorine-free oil repellent is 118 nm.

[0046] Example 2

[0047] The oil-water ratio was 33:60, and the raw materials for the fluorine-free oil repellent agent were as follows: monomers BA:HEMA:EMA = 12.2 mL:1.9 mL:18.8 mL, Tween 80:sodium oleate:2.5% PVA solution = 2.4 g:0.6 g:60 mL, and V-50:0.35 g. The reaction temperature was 30°C, the reaction time was 6 h, and the reaction speed was 300 rpm. The specific preparation steps were the same as in Example 1. Test results showed that the solid content of the emulsion was 35.3%, the conversion rate of the polymerization reaction was 99.0%, and the average particle size of the resulting fluorine-free oil repellent agent was 120 nm.

[0048] Comparative Example 1

[0049] The oil-water ratio was 30:65, and the raw materials for the fluorine-free oil repellent agent were as follows: monomers BA:HEMA:EMA = 11.1 mL:1.7 mL:17.1 mL, Tween 80:sodium oleate:2.5% PVA solution = 2.4 g:0.65 g:65 mL. The reaction temperature was 30°C, the reaction time was 6 h, and the reaction speed was 300 rpm. The specific preparation steps were the same as in Example 1. Test results showed that the solid content of the emulsion was 31.3%, the conversion rate of the polymerization reaction was 95.7%, and the average particle size of the resulting fluorine-free oil repellent agent was 147 nm.

[0050] Comparative Example 2

[0051] The oil-water ratio was 25:70, and the raw materials for the fluorine-free oil repellent agent were as follows: monomers BA:HEMA:EMA = 9.3 mL:1.4 mL:14.3 mL, Tween 80:sodium oleate:2.5% PVA solution = 2.8 g:0.7 g:70 mL. The reaction temperature was 30°C, the reaction time was 6 h, and the reaction speed was 300 rpm. The specific preparation steps were the same as in Example 1. Test results showed that the solid content of the emulsion was 24.57%, the conversion rate of the polymerization reaction was 95.3%, and the average particle size of the resulting fluorine-free oil repellent agent was 143 nm.

[0052] Comparative Example 3

[0053] The oil-water ratio was 20:80, and the raw materials for the fluorine-free oil repellent agent were as follows: monomers BA:HEMA:EMA = 7.4 mL:1.1 mL:11.4 mL, Tween 80:sodium oleate:2.5% PVA solution = 3.2 g:0.8 g:80 mL. The reaction temperature was 30°C, the reaction time was 6 h, and the reaction speed was 300 rpm. The specific preparation steps were the same as in Example 1. Test results showed that the solid content of the emulsion was 21.9%, the conversion rate of the polymerization reaction was 91.3%, and the average particle size of the resulting fluorine-free oil repellent agent was 189 nm.

[0054] The above tableware was tested by adding 95±5℃ hot oil and leaving it at room temperature for 6 hours to observe whether the surface of the tableware was wrinkled or deformed, whether there were stains on the back of the tableware, and whether there was liquid leakage. Figure 2 As shown, the uncoated tableware was completely soaked in oil, while the tableware coated with the oil-repellent coatings of Examples 1 and 2 showed virtually no oil stains. By comparison with Comparative Examples 1-3, emulsions synthesized with an oil-to-water ratio greater than 1:2 and a solids content of 35% or more showed excellent oil repellency, with this effect lasting for more than 6 hours.

[0055] Then conduct acid resistance test:

[0056] The polyacrylate oil repellent was evenly spin-coated on the inner surface of pulp molded tableware. The tableware was dried and acid resistance was tested by adding 95±5℃ hot acetic acid to the tableware coated with the oil repellent at room temperature (20℃). The tableware was left to stand at room temperature for 6 hours. Figure 3 As shown, a is tableware with the fluorine-free oil-proof coating of the present invention, and b is tableware not coated with the fluorine-free oil-proof coating.

[0057] Results showed that tableware coated with the present invention's fluorine-free, oil-resistant coating remained intact after exposure to hot acetic acid, exhibiting no deformation, peeling, wrinkling, or leakage. However, tableware without the present invention's fluorine-free, oil-resistant coating exhibited greater penetration and noticeable discoloration on the bottom. These results demonstrate the acid resistance of pulp-molded tableware coated with a polyacrylate oil-resistant agent.

[0058] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modification, equivalent replacement and improvement made by any technician familiar with the profession to the above embodiment without departing from the scope of the technical solution of the present invention and based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a fluorine-free oil-proof coating for food, characterized in that: The steps include: S1. Under anaerobic conditions, a fluorine-free acrylate combination liquid, an initiator, an emulsifier and a 2.5% polyvinyl alcohol aqueous solution are uniformly mixed to emulsion polymerize the acrylate combination liquid to obtain a fluorine-free oil-proofing agent; the fluorine-free acrylate combination liquid is composed of butyl acrylate, hydroxyethyl methacrylate and ethyl methacrylate, and the volume ratio of butyl acrylate: hydroxyethyl methacrylate: ethyl methacrylate is 13mL: 2mL: 20mL; the initiator is water-soluble azobisisobutylamidine hydrochloride; the emulsifier is a combination of polysorbate 80 and sodium oleate; wherein the ratio of polysorbate 80: sodium oleate: 2.5% polyvinyl alcohol aqueous solution is 2.0g: 0.5g: 50mL, and the amount of water-soluble azobisisobutylamidine hydrochloride is 0.35g; the oil-water ratio during the preparation process is 35:50, wherein the oil phase is the fluorine-free acrylate combination liquid, and the aqueous phase is a mixture of the emulsifier and the 2.5% polyvinyl alcohol aqueous solution; S2. Applying a fluorine-free oil-proof agent on the surface of the pulp molded tableware, and drying the mixture to obtain a fluorine-free oil-proof coating.

2. A method for preparing a fluorine-free oil-proof coating for food, characterized in that: The steps include: S1. Under anaerobic conditions, a fluorine-free acrylate combination liquid, an initiator, an emulsifier and a 2.5% polyvinyl alcohol aqueous solution are uniformly mixed to emulsion polymerize the acrylate combination liquid to obtain a fluorine-free oil-proofing agent; the fluorine-free acrylate combination liquid is composed of butyl acrylate, hydroxyethyl methacrylate and ethyl methacrylate, and the volume ratio of butyl acrylate: hydroxyethyl methacrylate: ethyl methacrylate is 12.2 mL: 1.9 mL: 18.8 mL; the initiator is water-soluble azobisisobutylamidine hydrochloride; the emulsifier is a combination of polysorbate 80 and sodium oleate; wherein the ratio of polysorbate 80: sodium oleate: 2.5% polyvinyl alcohol aqueous solution is 2.4 g: 0.6 g: 60 mL, and the amount of water-soluble azobisisobutylamidine hydrochloride is 0.35 g; the oil-water ratio during the preparation process is 33:60, wherein the oil phase is the fluorine-free acrylate combination liquid, and the aqueous phase is a mixture of the emulsifier and the 2.5% polyvinyl alcohol aqueous solution; S2. Applying a fluorine-free oil-proof agent on the surface of the pulp molded tableware, and drying the mixture to obtain a fluorine-free oil-proof coating.

3. The method for preparing a fluorine-free oil-proof coating for food according to claim 1 or 2, characterized in that: In step S2, the fluorine-free oil repellent is applied by spin coating, and a drying operation is performed while coating.

4. The method for preparing a fluorine-free oil-proof coating for food according to claim 3, characterized in that: The drying operation temperature is 70-100° C. and the drying time is 2-3 hours.

5. Use of a fluorine-free oil-proof coating prepared by the method according to claim 1 or 2 in coating the surface of pulp molded tableware.

Images