Starch-based oil-proof coating as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of oil-proof coatings, and discloses a starch-based oil-proof coating as well as a preparation method and application thereof. The method comprises the following steps: 1) reacting cassava starch with sodium periodate under the condition that the pH is 2-4, centrifugally washing to be neutral, and drying to obtain dialdehyde starch; 2) dispersing dialdehyde starch in water, and then performing gelatinization treatment to obtain a dialdehyde starch solution; dissolving chitosan in an acetic acid solution to obtain a chitosan solution; and 3) mixing the chitosan solution with the dialdehyde starch solution, adjusting the pH value to be acidic, and reacting to obtain the starch-based oil-proof coating. The method is simple, green and environment-friendly; the prepared coating is safe and biodegradable, has excellent oil-proof performance, and improves the tensile strength and tear strength of the paper.

Description

Technical Field

[0001] This invention belongs to the technical field of oil-resistant coatings, specifically relating to a starch-based oil-resistant coating, its preparation method, and its application. Background Technology

[0002] Starch is a natural polysaccharide, mainly synthesized by plants, and serves as a form of energy storage for them. It consists of two main components: amylose and amylopectin. Amylose is formed by α-D-glucose units linked by α-1,4 glycosidic bonds; amylopectin is formed by further branching through α-1,6 glycosidic bonds. In cassava starch, amylopectin accounts for approximately 80%, while amylose accounts for approximately 20%.

[0003] An oil-resistant coating is a special surface coating designed to prevent the adhesion of grease and dirt. It typically forms a protective film on the material surface through physical or chemical methods, thereby reducing oil penetration and adhesion. Oil-resistant coatings are used in many fields, such as food packaging: to prevent grease penetration and keep food fresh; the textile industry: to create functional fabrics that resist oil stains; electronics: to protect the surfaces of electronic devices from oil contamination; and building materials: for surface treatment to extend the lifespan of materials.

[0004] Currently, most oil-resistant coatings on the market are petroleum-based or other fluoropolymers. While they offer excellent oil resistance, their long degradation cycles cause serious environmental pollution, and the microplastics produced during decomposition pose significant health risks. Therefore, developing readily available, environmentally friendly, harmless, and biodegradable oil-resistant coating alternatives is becoming increasingly important.

[0005] The starch-based oil-resistant coating provided by this invention not only has excellent oil-resistant properties, but also is non-toxic, harmless, and biodegradable. It is an excellent alternative to petroleum-based products and fluoropolymers, and has great development value. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and deficiencies of existing technologies and provide a starch-based oil-repellent coating and its preparation method. This invention modifies cassava starch with sodium periodate through a double aldehyde process, oxidizing the hydroxyl groups on the C2 and C3 of the original starch to aldehyde groups and opening the starch ring. The resulting starch has a high aldehyde content and high reactivity. Subsequently, the double-aldehyde starch is gelatinized and reacted with chitosan solution at different pH levels to crosslink, forming a dense oil-repellent coating with excellent oil-repellent properties. The solvents used in this invention are only water and a very small amount of acetic acid. Compared with traditional petroleum-based oil-repellent coatings, the process is green and safe, with no toxic byproducts, and the product is biodegradable, making it an environmentally friendly product.

[0007] Another object of the present invention is to provide an application of the above-mentioned starch-based oil-resistant coating. The starch-based oil-resistant coating is used as an oil-resistant coating for paper, applied to the surface of the paper.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a starch-based oil-resistant coating includes the following steps:

[0010] (1) Cassava starch is reacted with sodium periodate at a pH of 2-4, centrifuged and washed until neutral, and dried to obtain dialdehyde starch; the specific preparation steps of the dialdehyde starch are as follows: cassava starch is dispersed in water to obtain a starch suspension; the starch suspension is mixed with sodium periodate, and the pH is adjusted to 2-4.

[0011] The reaction was carried out under heat, followed by centrifugation and washing until neutral, and then drying to obtain dialdehyde starch.

[0012] (2) Disperse dialdehyde starch in water and then gelatinize it to obtain a dialdehyde starch solution; dissolve chitosan in acetic acid solution to obtain a chitosan solution; the concentration of the acetic acid solution is 0.5wt% to 1.5wt%; the concentration of chitosan in the chitosan solution is 0.5wt% to 1.5wt%;

[0013] (3) Mix chitosan solution with dialdehyde starch solution, adjust pH to acidic, react to obtain starch-based oil-resistant coating.

[0014] The concentration of the starch suspension in step (1) is 8-12 wt%.

[0015] The mass ratio of sodium periodate to cassava starch is 0.8-1.3:1, preferably 1.2:1.

[0016] The reaction temperature is 30-40℃; the reaction time is 4-6 hours.

[0017] In step (2), the ratio of dialdehyde starch to water is such that the concentration of dialdehyde starch in water and dialdehyde starch is 8-12 wt%. The gelatinization temperature is 92-98℃, and the gelatinization time is 35-45 min.

[0018] The amount of chitosan used in step (3) is 2-8% of the mass of dialdehyde starch, preferably 4-6%. The reaction time is 1.5-2.5 h. After mixing in step (3), the pH is adjusted to 2-5, preferably 4.

[0019] When the starch-based oil-resistant coating is applied to paper, the coating amount is 2-5 g / m². 2 .

[0020] The starch-based oil-resistant coating is prepared by the above method.

[0021] The starch-based oil-resistant coating is used for oil-resistant coating of paper, and the paper used is coated base paper.

[0022] The oils used in the oil-proofing process include peanut oil, castor oil, etc.

[0023] The present invention has the following advantages and effects compared with the prior art:

[0024] (1) The method of the present invention does not use organic solvents that are harmful to the human body, but only water and a small amount of acetic acid, and the process is green and safe.

[0025] (2) The oil-resistant coating prepared by the present invention has the advantages of being environmentally friendly, biodegradable, and harmless to the human body, and also has excellent oil-resistant effect.

[0026] (3) The oil-resistant coating prepared by the present invention can adhere firmly to the paper surface without other adhesives, forming a uniform and stable coating. Attached Figure Description

[0027] Figure 1 Optical images showing the oil resistance of Examples 1-4, Comparative Examples 1-2, and the base paper; 0h, 1h, 2h, and 3h corresponding to Comparative Example 2 represent the time it takes for edible oil to drop onto the paper coated with the coating prepared in Comparative Example 2.

[0028] Figure 2 The images shown are SEM images of Examples 2-3, Comparative Examples 1-2, and the original paper. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, all materials and reagents used are commercially available.

[0030] Example 1

[0031] A method for preparing a starch-based oil-resistant coating includes the following steps:

[0032] (1) Disperse 10g of cassava starch in 90g of water to prepare a 10wt% starch suspension;

[0033] (2) Add 12g of sodium periodate to the starch suspension, adjust the pH to 2, react at 35℃ for 5h, wash with water and centrifuge until neutral, freeze dry for 72h to obtain dialdehyde starch (aldehyde content is 11.82±0.19mmol / g);

[0034] (3) Disperse 10g of dialdehyde starch in 90g of water and gelatinize it in a 95℃ water bath for 45min to obtain a dialdehyde starch solution.

[0035] (4) Dissolve 0.5g of chitosan in 49.5g of 1wt% acetic acid solution to prepare a 1% chitosan solution;

[0036] (5) Add chitosan solution to dialdehyde starch solution, adjust pH=2, stir for 2h to obtain oil-resistant coating.

[0037] The oil-resistant coating was applied to the surface of the base paper using a wire rod and dried in an oven at 40°C for 20 minutes. The coating basis weight was 4 g / m². 2 .

[0038] Example 2

[0039] A method for preparing a starch-based oil-resistant coating includes the following steps:

[0040] The difference from Example 1 is that in step (5), adjusting pH=2 is changed to adjusting pH=3.

[0041] Example 3

[0042] A method for preparing a starch-based oil-resistant coating includes the following steps:

[0043] The difference from Example 1 is that in step (5), adjusting pH=2 is changed to adjusting pH=4.

[0044] Example 4

[0045] A method for preparing a starch-based oil-resistant coating includes the following steps:

[0046] The difference from Example 1 is that in step (5), adjusting pH=2 is changed to adjusting pH=5.

[0047] Example 5

[0048] A method for preparing a starch-based oil-resistant coating includes the following steps:

[0049] The difference from Example 3 is that the coating amount is 4 g / m³. 2 Change to 3g / m 2 .

[0050] Example 6

[0051] A method for preparing a starch-based oil-resistant coating includes the following steps:

[0052] The difference from Example 3 is that the coating amount is 4 g / m³. 2 Change to 2g / m 2 .

[0053] Comparative Example 1

[0054] A method for preparing a cassava starch coating includes the following steps:

[0055] (1) Disperse 10g of cassava starch in 90g of deionized water to form a starch suspension.

[0056] (2) Place the above suspension in a 95°C water bath and keep it warm and stir for 40 minutes to form a uniform and transparent colloidal solution.

[0057] (3) After cooling to room temperature, the coating is applied to the surface of the base paper using a wire brush, and then dried in an oven at 40℃ for 20 minutes to obtain cassava starch coated paper. The coating basis weight is 4 g / m². 2 .

[0058] Comparative Example 2

[0059] A method for preparing a dialdehyde starch coating includes the following steps:

[0060] (1) Disperse 10g of starch in 90g of deionized water to prepare a 10% starch suspension.

[0061] (2) Add 12g of sodium periodate, adjust the pH to 2, and react at 35℃ for 5h.

[0062] (3) After the reaction, the product was washed with deionized water, centrifuged until neutral, and freeze-dried for 72 h to obtain dialdehyde starch.

[0063] (4) Disperse 10g of dialdehyde starch in 90g of deionized water and gelatinize it in a 95℃ water bath for 40min to obtain a dialdehyde starch solution.

[0064] The dialdehyde starch solution was coated onto the surface of the base paper using a wire rod and dried in an oven at 40°C for 20 minutes. The coating basis weight was 4 g / m². 2 .

[0065] Performance testing

[0066] Kit Oil Repellency Rating Test: This experiment determines the oil repellency rating of oil-resistant paper according to the test method specified in TAPPI T 559cm-12, using the oil repellency rating to represent the paper's oil resistance. This method uses castor oil, toluene, and n-heptane to prepare 12 liquids with different surface tensions. Specific preparation data are shown in Table 1. A higher rating indicates better oil resistance (solution 1 has the weakest oil resistance, and solution 12 has the strongest penetration). This method can quickly and effectively test the oil resistance of paper (the 12 solutions have 12 different penetration capabilities; if the paper does not penetrate within 15 seconds, it means the paper has reached the rating corresponding to that solution).

[0067] Table 1. Kit Oil Resistance Rating Test Reagents

[0068]

[0069] The oil resistance rating of the coated papers prepared in Examples 1-6 and Comparative Examples 1-2 was tested, and the test results are shown in Tables 2 and 3.

[0070] Oil resistance test of greaseproof paper: Use a dropper to drop edible oil (peanut oil) onto the surface of the test paper, observe at regular intervals whether the oil droplets penetrate the paper, and record the amount of oil that passes through the paper (40g / m²). 2 The time taken was measured. The oil resistance of the coated papers prepared in Examples 1-4 and Comparative Examples 1-2 was tested, and the test results are shown in Table 4.

[0071] Physical performance testing: The tensile strength of the greaseproof paper was determined according to GB / T453-2002, the tear strength was determined according to GB / T455-2002, and the air permeability was determined using an L&W 166 air permeability meter. The test results are shown in Table 5.

[0072] Table 2. Oil resistance rating test results of the oil-resistant paper kits prepared in different embodiments.

[0073] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Kit oil resistance rating 10 11 12 10 3 8

[0074] Table 3. Oil resistance rating test results of the oil-resistant paper kits prepared in different embodiments.

[0075] Example 3 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Kit oil resistance rating 12 11 10 3 8

[0076] Table 4. Oil resistance time test results of oil-proof paper prepared in different embodiments.

[0077] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Oil resistance time 3h 5h 6h 2h 3min 2h

[0078] Table 5. Test results of physical properties of the base paper for different embodiments and comparative examples.

[0079]

[0080] Table 2 shows that when the coating amount is 4 g / m², 2 Initially, the original starch coating Kit had an oil resistance rating of only level 3. However, after oxidation, the oil resistance rating of the dialdehyde starch coating Kit improved to level 8. This is because during the drying process of the dialdehyde starch coating, the aldehyde groups undergo a condensation reaction with intramolecular or intermolecular hydroxyl groups, forming a denser film that significantly improves oil barrier properties. The oil resistance rating test results of Kits in Examples 1-4 show that chitosan and dialdehyde starch crosslink through a Schiff base reaction to generate a large number of C=N connections, making the dried film denser and further enhancing its oil resistance. The oil resistance performance was best at a reaction pH of 4. At pH 2 and 5, the oil resistance rating decreased significantly. This may be because excessively high and low pH values ​​inhibited the Schiff base reaction, leading to a decrease in crosslinking density and thus a decrease in coating density, resulting in a lower oil resistance rating.

[0081] Table 3 shows that when the reaction pH is 4, the coating amount is 3 g / m³. 2 The paper has a Kit oil resistance rating of 11; even with a coating weight of 2g / m². 2 At that time, its Kit oil resistance rating was still slightly higher than 4g / m 2 Simple dialdehyde starch coating.

[0082] Table 4 shows that the prepared oleophobic paper exhibits the best oil resistance at a reaction pH of 4, which is superior to Comparative Example 1 and Comparative Example 2, consistent with its Kit oil resistance rating test results. This further verifies its excellent oil resistance performance.

[0083] Table 5 shows the physical performance test results, when the coating amount is 4 g / m² 2 Around the same time, the air permeability of all coated papers decreased compared to the base paper, while the tensile strength and tear strength increased. Example 3 exhibited the lowest air permeability, decreasing from 0.6330 μm / Pa·s to 0.0030 μm / Pa·s. The tensile strength of Example 3 increased from 3.98 kN / m to 4.80 kN / m, an increase of 20.6%, and its tear strength increased from 249 mN to 380.5 mN, an increase of 52.81%. This indicates that Example 3 not only possesses the best oil resistance but also the best physical properties.

[0084] Figure 1 The images show optical graphs for testing the oil resistance of Examples 1-4, Comparative Examples 1-2, and the base paper. The 0h, 1h, 2h, and 3h values ​​corresponding to Comparative Example 2 represent the time it takes for edible oil droplets to fall onto the paper coated with the coating prepared in Comparative Example 2.

[0085] Figure 2 The images shown are SEM images of Examples 2-3, Comparative Examples 1-2, and the original paper.

[0086] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a starch-based oil-resistant coating, characterized in that: Includes the following steps: (1) Cassava starch was reacted with sodium periodate at pH 2 to 4, centrifuged and washed until neutral, and dried to obtain dialdehyde starch. (2) Disperse dialdehyde starch in water and then gelatinize it to obtain a dialdehyde starch solution; dissolve chitosan in acetic acid solution to obtain a chitosan solution; the concentration of the acetic acid solution is 0.5wt% to 1.5wt%; the concentration of chitosan in the chitosan solution is 0.5wt% to 1.5wt%; (3) Mix chitosan solution with dialdehyde starch solution, adjust pH to acidic, react to obtain starch-based oil-resistant coating; The mass ratio of sodium periodate to cassava starch is 0.8-1.3:1; The amount of chitosan used in step (3) is 2-8% of the mass of dialdehyde starch; After mixing in step (3), adjust the pH to 2-5.

2. The method for preparing the starch-based oil-resistant coating according to claim 1, characterized in that: The mass ratio of sodium periodate to cassava starch in step (1) is 1.2:1; the reaction temperature is 30-40℃; and the reaction time is 4-6 hours. In step (3), the starch-based oil-resistant coating is applied to paper at a rate of 2-5 g / m². 2 .

3. The method for preparing the starch-based oil-resistant coating according to claim 1, characterized in that: The amount of chitosan used in step (3) is 4-6% of the mass of dialdehyde starch; the reaction time is 1.5-2.5 h.

4. The method for preparing the starch-based oil-resistant coating according to claim 1, characterized in that: The specific preparation steps of the dialdehyde starch in step (1) are as follows: cassava starch is dispersed in water to obtain a starch suspension; the starch suspension is mixed with sodium periodate, the pH is adjusted to 2-4, the reaction is carried out at a constant temperature, the mixture is centrifuged and washed until neutral, and then dried to obtain dialdehyde starch.

5. The method for preparing the starch-based oil-resistant coating according to claim 4, characterized in that: The concentration of the starch suspension in step (1) is 8–12 wt%.

6. The method for preparing the starch-based oil-resistant coating according to claim 1, characterized in that: In step (2), the ratio of the amount of dialdehyde starch to water is 8-12 wt% in both the water and the starch; the gelatinization temperature is 92-98℃ and the gelatinization time is 35-45 min.

7. A starch-based oil-resistant coating obtained by the preparation method according to any one of claims 1 to 6.

8. The application of the starch-based oil-resistant coating according to claim 7, characterized in that: The starch-based oil-resistant coating is used for oil-resistant coating of paper.

9. The application according to claim 8, characterized in that: The paper used is coated base paper; The oils used for oil protection include peanut oil and castor oil.

Images