Sodium alginate covering film and preparation method thereof

Abstract

The invention discloses a sodium alginate coating film and a preparation method thereof in the technical field of coating film materials. The sodium alginate coating film is formed by crosslinking sodium alginate derived from seaweed or seaweed and soluble calcium. The preparation method comprises the following two steps: sodium alginate extraction and coating preparation: firstly, extracting sodium alginate powder from seaweed or sea grass through raw material pretreatment, alkali liquor extraction and purification treatment; and dissolving the powder in cold water to prepare a coating liquid, coating the coating liquid on the surface of paper, drying, immersing into a calcium solution, cross-linking, and drying again to obtain the sodium alginate coated paper product. The covering film is prepared from food-grade natural raw materials, has no chemical substance migration risk, can be completely degraded, has toughness equivalent to that of a traditional plastic covering film and good water resistance, oil resistance and high temperature resistance, is wide in raw material source and simple in preparation process, is suitable for various paper products such as paper boxes for food, and has wide application prospects. The problems that a traditional plastic film pollutes the environment, harms human health and is difficult to recycle are solved.

Description

Technical Field

[0001] This invention relates to the field of coating materials technology, specifically to a sodium alginate coating and its preparation method. Background Technology

[0002] Plastic products have become widely used in various fields due to their convenience, especially in the food service industry where cardboard boxes are often lined with plastics such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polylactic acid (PLA), and polyvinyl chloride (PVC). However, the hazards posed by plastic products are becoming increasingly serious, forming a complete chain of hazards from production, use, to disposal.

[0003] From a human health perspective, when plastic products come into contact with oils or high temperatures, plasticizers and plastic particles can migrate into food. Long-term ingestion may lead to problems such as reproductive system and endocrine disorders, acute and chronic toxicity, carcinogenic risks, and organ damage. From an environmental perspective, plastics have a degradation cycle of hundreds of years, causing serious pollution to water bodies and soil, and destroying biodiversity. Furthermore, coated cardboard boxes are paper-plastic composites, requiring paper-plastic separation during recycling, a complex process. Even biodegradable materials like PLA require specific industrial composting conditions to degrade, making true environmental protection difficult. Therefore, developing a material that is harmless to humans, has excellent environmental performance, and can replace traditional plastic coatings has become an urgent technical problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a sodium alginate coating and its preparation method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a sodium alginate coating, comprising:

[0006] It is formed by cross-linking sodium alginate and soluble calcium. The sodium alginate is derived from seaweed or seagrass. The seaweed includes all genera of brown algae, red algae, green algae, and blue algae. The seagrass includes common seagrasses of Hydrocharitaceae, Posidoniaceae, Hymenaceae, and Lysimachiae. The soluble calcium includes at least one of calcium lactate, calcium chloride, and calcium carbonate.

[0007] Preferably, the seaweed specifically includes at least one of kelp, wakame, giant kelp, Sargassum, laver, agaric, Euphorbia lathyris, Ulva, sea lettuce, Chlorella, Spirulina, and Microcystis.

[0008] A method for preparing a sodium alginate coating, comprising the following steps:

[0009] S1: Sodium alginate extract:

[0010] 1.1. Raw material pretreatment: Select the seaweed or seagrass mentioned above, wash it with seawater to remove impurities, crush it into 1-2cm particles, and soak it in 0.1-0.2% dilute hydrochloric acid for 30 minutes to remove iodine, mannitol and pigments;

[0011] 1.2. Alkali extraction: Add the pretreated raw materials to a 3-5% sodium carbonate or sodium hydroxide solution and stir at a constant temperature of 60-70℃ for 2-3 hours until completely dissolved into a viscous gel.

[0012] 1.3. Purification treatment: The solution is filtered through a 100-200 mesh sieve and centrifuged at 3000-4000 r / min for 10 minutes to remove impurities. 5-10% calcium chloride solution is added to the filtrate and stirred until flocculent precipitate is formed. The precipitate is soaked in 5-10% dilute hydrochloric acid to replace calcium ions. The solution is washed with pure water until the pH is neutral. A mixture of gel and sodium ethanol carbonate is added and stirred to neutralize the solution. Then, 3 times the volume of 95% ethanol is added to cause the solid to flocculate and precipitate. The solution is dried with hot air at 60-70℃ until the moisture content is <15%. After pulverization, the solution is passed through an 80-100 mesh sieve to obtain sodium alginate powder.

[0013] S2: Coating preparation:

[0014] 2.1. Dissolve sodium alginate powder in cold water, stir thoroughly and let stand to remove air bubbles, then coat the liquid evenly on the paper surface and dry it.

[0015] 2.2. The coated paper is immersed in calcium solution for full cross-linking, and then dried again to obtain sodium alginate coated paper products.

[0016] Preferably, the paper mentioned in step S2 includes white cardboard, kraft paper and other existing papers, and more preferably paper for food packaging.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] This invention optimizes an existing sodium alginate coating and its preparation method. Sodium alginate is extracted from natural raw materials such as seaweed and seagrass, all of which are food-grade. The coating poses no risk of chemical migration and is even edible, ensuring high safety and complete harmlessness to the human body. The coating is fully biodegradable, and the degradation process does not pollute water, soil, or biodiversity. Furthermore, the coated paper products do not require complex paper-plastic separation processes for recycling, reducing recycling difficulty and demonstrating excellent environmental performance, meeting environmental requirements. The membrane structure formed by the cross-linking of sodium alginate and calcium ions is stable and has consistent performance, possessing toughness comparable to traditional plastic coatings, while also exhibiting good water resistance, oil resistance, and high-temperature resistance, meeting the needs of paper products used in the catering industry and other sectors. The seaweed used covers all genera and phyla of brown algae, red algae, green algae, and cyanobacteria, and the seagrass includes various common varieties. The raw materials are widely available and easily accessible, and the preparation process is simple and easy to scale up. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1

[0021] A method for preparing a sodium alginate coating includes the following steps:

[0022] S1: Sodium alginate extract:

[0023] 1.1. Raw material pretreatment: Select kelp (brown algae) as raw material, rinse with seawater to remove impurities such as mud and shells, crush the kelp into 1-2cm particles, soak in 0.1% dilute hydrochloric acid for 30 minutes to remove iodine, mannitol and pigments.

[0024] 1.2. Alkali extraction: Prepare a 3% sodium carbonate solution, add the pretreated kelp particles to the sodium carbonate solution, and stir at a constant temperature of 60°C for 2 hours until the kelp is completely dissolved to form a viscous gel.

[0025] 1.3. Purification: The gel solution was filtered through a 100-mesh sieve to remove kelp residue, yielding a dark brown crude liquid. The crude liquid was centrifuged at 3000 r / min for 10 minutes to remove minor impurities. A 5% calcium chloride solution was slowly added to the filtrate, and the mixture was stirred until the flocculent precipitate was completely formed. The precipitate was soaked in 5% dilute hydrochloric acid for 30 minutes to replace calcium ions. The precipitate was repeatedly rinsed with pure water until pH=7 to remove residual acid and salt. The gel was neutralized by stirring with a mixture of ethanol and sodium carbonate, and three times the volume of 95% ethanol was added to cause the solid to flocculate and precipitate. The solid was dried with hot air at 60℃ until the moisture content was 12%, pulverized, and passed through an 80-mesh sieve to obtain white sodium alginate powder.

[0026] S2: Coating preparation:

[0027] 2.1. Dissolve sodium alginate powder in cold water, stir thoroughly, let stand for 30 minutes to remove air bubbles, coat the liquid evenly on the surface of white cardboard, and dry at 80℃ for 1 hour.

[0028] 2.2. Immerse the dried white cardboard in a calcium chloride solution for 30 minutes to allow sodium alginate to fully crosslink with calcium ions, and then dry it again at 80°C for 1 hour to obtain sodium alginate-coated white cardboard.

[0029] Example 2

[0030] A method for preparing a sodium alginate coating includes the following steps:

[0031] S1: Sodium alginate extract:

[0032] 1.1. Raw material pretreatment: Select laver (red algae) and hydrocharitoid seaweed as mixed raw materials, rinse with seawater to remove impurities, crush into 1-2cm particles, soak in 0.2% dilute hydrochloric acid for 30 minutes to remove iodine, mannitol and pigments.

[0033] 1.2. Alkali extraction: Prepare a 5% sodium hydroxide solution, add the pretreated mixed raw materials to the sodium hydroxide solution, and stir at a constant temperature of 70°C for 3 hours until the raw materials are completely dissolved to form a viscous gel.

[0034] 1.3. Purification: Filter the gel solution through a 200-mesh sieve to remove residue, obtaining a dark brown crude liquid; centrifuge the crude liquid at 4000 r / min for 10 minutes to remove minor impurities; slowly add 10% calcium chloride solution to the filtrate and stir until the flocculent precipitate is completely precipitated; soak the precipitate in 10% dilute hydrochloric acid for 30 minutes to replace calcium ions; repeatedly wash the precipitate with pure water until pH=7 to remove residual acid and salt; neutralize the gel with a mixture of ethanol and sodium carbonate, add 3 times the volume of 95% ethanol to cause the solid to flocculate and precipitate; dry the solid with hot air at 70℃ until the moisture content is 10%, pulverize and pass through a 100-mesh sieve to obtain a light yellow sodium alginate powder.

[0035] S2: Coating preparation:

[0036] 2.1. Dissolve sodium alginate powder in cold water, stir thoroughly, let stand for 20 minutes to remove air bubbles, coat the liquid evenly on the surface of kraft paper, and dry at 90℃ for 40 minutes.

[0037] 2.2. Immerse the dried kraft paper in a calcium lactate solution for 40 minutes to allow sodium alginate to fully crosslink with calcium ions, and then dry it again at 90°C for 40 minutes to obtain sodium alginate-coated kraft paper.

[0038] Performance tests were conducted on the sodium alginate-coated paper products prepared in Examples 1 and 2 above. The results showed that the coating adhered tightly to the paper without peeling; after soaking at room temperature for 24 hours, the paper showed no damage or leakage, demonstrating good water resistance; after contact with edible oil, the coating showed no swelling or oil penetration, exhibiting excellent oil resistance; after being placed in a high-temperature environment of 100℃ for 30 minutes, the coating structure remained stable, without deformation or odor, and its high-temperature resistance met the usage requirements. Furthermore, the coating can be completely degraded in the natural environment within 3 months, leaving no pollutant residue after degradation, demonstrating outstanding environmental performance.

[0039] Although the present invention has been described above with reference to embodiments, various modifications can be made thereto without departing from the scope of the invention. In particular, the exhaustive description of these combinations is not provided in this specification merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium alginate coating, characterized in that, include: It is formed by cross-linking sodium alginate and soluble calcium. The sodium alginate is derived from seaweed or seagrass. The seaweed includes all genera of brown algae, red algae, green algae, and blue algae. The seagrass includes common seagrasses of Hydrocharitaceae, Posidoniaceae, Hymenaceae, and Lysimachiae. The soluble calcium includes at least one of calcium lactate, calcium chloride, and calcium carbonate.

2. The sodium alginate coating according to claim 1, characterized in that, The seaweed specifically includes at least one of the following: kelp, wakame, giant kelp, sargassum, laver, agaric, Euphorbia lathyris, sea lettuce, sea lettuce, reef algae, chlorella, spirulina, and microcystis.

3. A method for preparing a sodium alginate coating, characterized in that, Includes the following steps: S1: Sodium alginate extract: (1.1). Raw material pretreatment: Select the seaweed or seagrass described in claim 1 or 2, wash it with seawater to remove impurities, crush it into 1-2cm particles, and soak it in 0.1-0.2% dilute hydrochloric acid for 30 minutes to remove iodine, mannitol and pigments; (1.2). Alkali extraction: Add the pretreated raw materials to a 3-5% sodium carbonate or sodium hydroxide solution and stir at a constant temperature of 60-70℃ for 2-3 hours until completely dissolved into a viscous gel. (1.3). Purification treatment: filter through a 100-200 mesh sieve, centrifuge at 3000-4000 r / min for 10 minutes to remove impurities, add 5-10% calcium chloride solution to the filtrate and stir until flocculent precipitate is formed, soak the precipitate with 5-10% dilute hydrochloric acid to replace calcium ions, wash with pure water until pH neutral, add a mixture of gel and sodium carbonate ethanol and stir to neutralize, then add 3 times the volume of 95% ethanol to flocculate and precipitate the solid, dry with hot air at 60-70℃ until the moisture content is <15%, pulverize and pass through an 80-100 mesh sieve to obtain sodium alginate powder; S2: Coating preparation: (2.1). Dissolve sodium alginate powder in cold water, stir thoroughly and let stand to remove air bubbles, then coat the liquid evenly on the paper surface and dry it. (2.2). The coated paper is immersed in calcium solution for full cross-linking and then dried again to obtain sodium alginate coated paper products.

4. The method for preparing a sodium alginate coating according to claim 3, characterized in that, The paper mentioned in step S2 includes white cardboard, kraft paper and other existing papers, preferably paper for food packaging.

5. An application of sodium alginate coating as described in claim 1 or 2 in the coating of paper products, characterized in that, The paper products include food-grade paper boxes.