CN111749043B

CN111749043B - Preparation method of safe, nontoxic and anti-sticking coating for liquid food

Info

Publication number: CN111749043B
Application number: CN202010045854.7A
Authority: CN
Inventors: 周晓
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-01-16
Filing date: 2020-01-16
Publication date: 2022-04-29
Anticipated expiration: 2040-01-16
Also published as: CN111749043A

Abstract

The invention discloses a preparation method of a safe and nontoxic coating for preventing liquid food from being adhered, which relates to the related field of coating preparation. Comprises the following materials: solution A, 15g of polyvinyl alcohol, 85ml of deionized water, 12.5ml of citric acid monohydrate and 1.25g of hydrophobic nano silicon dioxide; liquid B, 4g of palm wax, 100ml of ethyl acetate and 2g of hydrophobic nano silicon dioxide; coating the food-grade coated paper; dissolving polyvinyl alcohol in deionized water; adding a citric acid monohydrate solution, heating, stirring and esterifying; adding hydrophobic nano silicon dioxide, stirring and dispersing to obtain solution A; adding the palm wax into ethyl acetate, stirring until the wax is dissolved, and standing to room temperature; adding hydrophobic nano silicon dioxide, and carrying out ultrasonic treatment to obtain a solution B; and mixing the solution A and the solution B, stirring and ultrasonically dispersing to obtain a coating solution.

Description

Preparation method of safe, nontoxic and anti-sticking coating for liquid food

Technical Field

The invention relates to the field related to coating preparation, in particular to a preparation method of a safe, nontoxic and anti-sticking coating for liquid food.

Background

The preparation of the coating for preventing the liquid food from being adhered is based on the surface infiltration theory. The surface wetting theory is modified from the initial Young equation to a Wenzel complete wetting model, and finally developed into a Cassie-Baxter model as a theory for judging the surface hydrophobic property of the material. The surface is hydrophobic when the static contact angle of the surface and water is more than 90 degrees, and is super-hydrophobic when the static contact angle of the surface and water is more than 150 degrees and the rolling angle is less than 10 degrees. At present, two main methods for constructing a hydrophobic surface are to construct a rough surface structure and to modify a low surface energy substance on the surface; the method for preparing the super-hydrophobic surface comprises a sol-gel method, an etching method, a vapor deposition method, a template method, an electrostatic spinning method and the like. The liquid food contains complex substances, and the coating is not adhered to other substances in the liquid food to achieve the anti-adhesion effect. Such complex material compositions are similar to seawater containing diverse organisms. At present, antifouling paints on the surfaces of marine ships are mainly low-surface-energy antifouling paints, including but not limited to antifouling paints of organic silicon modified different organic resins, organic silicon antifouling paints modified by nano materials and organic silicon bionic composite antifouling systems.

Zhenggulin and the like are prepared into a palm wax emulsion with good stability by using an emulsification method, a sol-gel method is adopted to prepare modified silica sol by using octyl triethoxysilane as a precursor, and cotton fabrics are subjected to hydrophobic modification by using the palm wax emulsion and the silica sol.

Chinese patent No. CN106115072A, silica, polytetrafluoroethylene emulsion and beeswax prepared by sol-gel method are added into the mixture of polyvinyl alcohol and citric acid esterification reaction to prepare the coating which can not be stuck with yoghourt.

Due to the restriction of safety, in the aspect of food packaging, long-chain fluorocarbon materials and various toxic organic substances cannot be used in the preparation process, and even if toxic organic solvents do not participate in the formation of a coating, the preparation process cannot be guaranteed to have no residue absolutely, so that potential threat is caused to the safety of a human body; in addition, the cracking phenomenon and the stability problem of the solid coating with limited adhesiveness after long-time air drying also limit the wide application of the coating; the traditional hydrophobic surface preparation method has the problems of long forming period, inconvenient large-area use, complex method, high precision requirement on a reagent purity instrument and the like, so that the method is difficult to be practically applied in industrial production; therefore, the market urgently needs to develop a preparation method of a coating which is safe, non-toxic and anti-adhesive to liquid food to help people to solve the existing problems.

Disclosure of Invention

The invention aims to provide a preparation method of a coating which is safe, non-toxic and anti-sticking to liquid food, the coating is safe, non-toxic, suitable and effective in anti-sticking material and more stable by improving the used materials, and in the preparation process, instruments are common, the operation is simple and convenient, and the time consumption of the preparation process is short.

In order to achieve the purpose, the invention provides the following technical scheme: a preparation method of a safe, nontoxic and anti-sticking liquid food coating comprises the following materials: solution A, 15g of polyvinyl alcohol, 85ml of deionized water, 12.5ml of citric acid monohydrate and 1.25g of hydrophobic nano silicon dioxide;

liquid B, 4g of palm wax, 100ml of ethyl acetate and 2g of hydrophobic nano silicon dioxide;

and (5) food-grade laminating paper.

Preferably, the method comprises the following steps:

s1: weighing 15g of polyvinyl alcohol and dissolving in 85ml of deionized water;

s2: adding 12.5ml of citric acid monohydrate solution into the dissolved solution prepared in the S1, heating to 95 ℃, and stirring in a round-bottom flask for esterification reaction for 4 hours;

s3: adding 1.25g of hydrophobic nano silicon dioxide into the round-bottom flask of S2, and continuously stirring and dispersing for 1h to obtain solution A;

s4: adding 4g of palm wax into 100ml of ethyl acetate, magnetically stirring at 75 ℃ until the wax is dissolved, and standing to room temperature;

s5: adding 2g of hydrophobic nano silicon dioxide into the solution which is S4 and is kept stand to room temperature, and carrying out ultrasonic treatment for 1h to prepare uniform suspension liquid B;

s6: mixing the solution A prepared in the step S3 with the solution B prepared in the step S5, stirring and ultrasonically dispersing to obtain a final coating solution;

s7: and (3) coating the coating solution prepared by the S6 on food-grade coated paper by using a dipping and pulling method, and naturally drying to obtain a finished product.

Preferably, the ethyl acetate is analytically pure AR 99%.

Preferably, the citric acid monohydrate is analytically pure.

Preferably, in the S2, the citric acid monohydrate solution has a mass concentration of 10%.

Preferably, in S6, the volume ratio of the liquid a to the liquid B is 1: and 5, mixing.

Preferably, in S7, the food-grade coated paper is used for checking the applicability of the coating film.

Preferably, the stirring process adopts a constant temperature heating heat collection type magnetic stirrer.

Compared with the prior art, the invention has the beneficial effects that:

1. the reagents in the coating are safe and nontoxic, a substance with long-chain fluorocarbon is not used, and low-toxicity ethyl acetate is used as a solvent and is volatilized from the coating substance after being dried in the air;

2. the esterification reaction of citric acid modified polyvinyl alcohol is applied to the preparation of the coating liquid with the hydrophobic nanoparticles, so that the stability of the coating is effectively improved, and the problem of cracking and falling of the coating prepared by the existing method after long-term storage is solved;

3. the method is characterized in that the esterification reaction of citric acid modified polyvinyl alcohol is eliminated, other complex chemical reactions are not involved, the final coating liquid is prepared by full physical dispersion, and the used laminating paper and the prepared coating which is not adhered with yoghourt can be biodegraded, so that the environmental pollution is avoided;

4. the invention mainly relies on a simpler dipping method for coating, a rough coating structure is constructed on the surface of the coated paper, the wetting theory is fastened, the preparation method of the super-hydrophobic material and the application of the antifouling organic silicon in the aspect of ocean ships are developed, the safety and the non-toxicity required by food packaging are achieved, and the non-adhesion to various liquid foods is realized;

5. the preparation process has lower requirements on instruments, is simple to operate, and is quicker to prepare compared with other coatings which are not adhered to the surface.

Drawings

FIG. 1 is an overview of a fully automated microscopic droplet wettability meter of the present invention with a first 3 microliter droplet of water on the surface of the coating;

FIG. 2 is an overview of a fully automated microscopic droplet wettability meter of the present invention with a second 3 microliter droplet of water on the surface of the coating;

FIG. 3 is a full-automatic microscopic droplet wettability measuring instrument perspective view of a third 3. mu.L droplet of the present invention on the coating surface;

FIG. 4 is a view of a fully automated microscopic droplet wettability meter of 3 microliters of yogurt (a food liquid with a relatively high viscosity) of the present invention dropped on the surface of a coating;

FIG. 5 is an enlarged view of a cold field emission scanning electron microscope 50.0k according to the present invention;

FIG. 6 is a 10.0k enlarged view of a cold field emission scanning electron microscope in accordance with the present invention;

FIG. 7 is an enlarged view of a cold field emission scanning electron microscope 5.0k according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

1. The main materials are as follows:

hydrophobic nano silicon dioxide with the average grain diameter of 7-40 nm; in the technology, the hydrophobic nano silicon dioxide plays a role in preventing adhesion.

Ethyl acetate, AR 99%; the coating is a relatively safe organic solvent, and the volatile property ensures that the coating can be quickly dried.

Palm wax, which is a complex mixture mainly composed of esters of acids and hydroxy acids, the complex composition of which ensures that the palm wax is difficult to be compatible with liquid food, but has good adhesion, moisture resistance and oxidation and deterioration resistance, and is widely applied to coating films in the field of food and medicine;

the invention uses the palm wax to construct the rough structure of the anti-adhesion surface, and simultaneously improves the stability of the hydrophobic nano silicon dioxide particles on the surface of the coating by virtue of the adhesion property of the palm wax.

Polyvinyl alcohol with the polymerization degree of 1700 plus or minus 50, the solubility of 87.0-89.0mol and the viscosity of 20.0-26.0; citric acid monohydrate, analytically pure;

the polyvinyl alcohol has film forming property but also has water absorption property, so that the polyvinyl alcohol is not suitable for being directly applied to coating preparation, and the water absorption property can be weakened on the basis of not damaging the film forming property by modifying the polyvinyl alcohol through citric acid monohydrate.

Deionized water.

The food-grade laminating paper is safe and nontoxic and is a suitable base material; testing the film coating effect on food-grade coated paper is beneficial to testing the applicability of the film coating (as shown in figure 1, figure 2, figure 3 and figure 4 applied to test the film coating).

The specific weight grams or milliliters of each material are as follows:

solution A, 15g of polyvinyl alcohol, 85ml of deionized water, 12.5ml of citric acid monohydrate and 1.25g of hydrophobic nano silicon dioxide;

and (5) food-grade laminating paper.

2. The main equipment is as follows:

an electronic analytical balance; a constant temperature heating heat collection type magnetic stirrer; a full-automatic micro-droplet wettability measuring instrument; and (5) transmitting a scanning electron microscope in a cold field.

3. The implementation method comprises the following steps:

s2: adding 12.5ml of citric acid monohydrate solution with the mass concentration of 10% into the dissolved solution prepared in the S1, heating to 95 ℃, and stirring in a round-bottom flask for esterification reaction for 4 hours;

s5: adding 2g of hydrophobic nano-silica into the solution which is S4 and is kept stand to room temperature, and carrying out ultrasonic treatment for 1h to fully disperse the hydrophobic nano-silica to prepare uniform suspension liquid B;

s6: mixing the solution A prepared in the step S3 with the solution B prepared in the step S5 in a volume ratio of 1: 5, mixing, stirring and ultrasonically dispersing to obtain a final coating liquid;

The liquid food which can be prevented from being adhered by the coating prepared by the invention comprises water, pure milk, coffee and yoghourt.

Table 1 table of contact angle data for fig. 1, 2, 3 and 4

The Cassie-Baxter model is used as a theory for judging the surface hydrophobicity of the material, and is a hydrophobic surface when the static contact angle of the surface and water is more than 90 degrees, and is a super-hydrophobic surface when the static contact angle of the surface and water is more than 150 degrees and the rolling angle is less than 10 degrees.

The practical application observation of the invention can show that the contact angle of the food liquid is larger than 110 degrees no matter the food liquid is clear water or has larger viscosity, the contact angle of the food liquid is larger than 120 degrees in three groups of tests of the clear water, and the condition that the static contact angle of the surface and the water required by the hydrophobic surface is obviously larger than 90 degrees shows that the invention can achieve obvious hydrophobic effect.

4. Application prospect:

4.1 technical description of adaptability Range and popularization prospect

The coating better realizes the anti-adhesion performance and can enable various liquid foods to slide off the surface of the coating. The invention can provide a sample reference for the industrial production and application of the anti-sticking liquid food.

The anti-adhesion performance can be used in food packaging, and can be applied to other fields requiring self-cleaning by means of more precise and large-scale production equipment.

4.2 market analysis and economic prediction

At present, materials not stained with liquid food comprise glass and some special ceramics, but the food packaging bottle used for one-off use under most conditions has expensive price and is difficult to popularize among consumers. The new coating prepared by using the low-cost reagent reduces the price and is easier to popularize and put into the market.

The non-sticking coating is applied to the liquid food packaging industry, can provide convenience for consumers and optimizes the consumption experience.

The product or enterprise which is not adhered with the coating can be used as a propaganda highlight of the product, thereby promoting sales, increasing profits, driving material updating and promoting economic development.

The application field of the non-adhesive surface is expanded, and the low surface energy material has wider application space.

Although the technology is based on liquid food packaging, it can be improved and widely used in the long term, and applied to other containers requiring anti-adhesion performance.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Claims

1. A preparation method of a safe, nontoxic and anti-sticking liquid food coating is characterized by comprising the following materials: solution A, 15g of polyvinyl alcohol, 85ml of deionized water, 12.5ml of citric acid monohydrate and 1.25g of hydrophobic nano silicon dioxide;

coating the food-grade coated paper;

the preparation method of the coating comprises the following steps:

2. The method of claim 1, wherein the coating is selected from the group consisting of: the ethyl acetate was analytically pure AR 99%.

3. The method of claim 1, wherein the coating is selected from the group consisting of: the citric acid monohydrate was analytically pure.

4. The method of claim 1, wherein the coating is selected from the group consisting of: in the S2, the mass concentration of the citric acid monohydrate solution is 10%.

5. The method of claim 1, wherein the coating is selected from the group consisting of: in the S6, the volume ratio of the solution A to the solution B is 1: and 5, mixing.

6. The method of claim 1, wherein the coating is selected from the group consisting of: in the S7, the food-grade laminating paper is used for checking the applicability of the coating film.

7. The method of claim 1, wherein the coating is selected from the group consisting of: the stirring process adopts a constant temperature heating heat collection type magnetic stirrer.