CN113461986B - Preparation method of hydrophobic degradable starch nano composite film and obtained product - Google Patents

Abstract

The invention discloses a preparation method of a hydrophobic degradable starch nano composite film and an obtained product, wherein starch is firstly dissolved in water, a turbid uniform hydrothermal starch carbon nano microsphere solution is obtained through hydrothermal reaction in a high-pressure reaction kettle, then the hydrothermal starch carbon nano microsphere solution or a mixture of the hydrothermal starch carbon nano microsphere solution and nano calcium carbonate is added into a mixed system consisting of starch, glycerol and water according to a certain dosage, and after starch is gelatinized for a certain time, the composite film product is prepared through a casting method or a tape casting method. The method disclosed by the invention is simple to operate, strong in feasibility, and capable of preparing the degradable bio-based composite starch film under the condition of not undergoing chemical modification, wherein various substances are abundant in source and low in cost, and the prepared composite film is strong in hydrophobicity, good in mechanical property, high in cost performance and environment-friendly.

Description

A kind of preparation method and obtained product of hydrophobic degradable starch nanocomposite film

technical field

The invention relates to a method for preparing a hydrophobic and degradable starch nanocomposite film and a product thereof, belonging to the technical field of new functional materials.

Background technique

With the further advancement of smart cities, the Internet of Things, big data, artificial intelligence, etc. have promoted the vigorous development of the catering industry, which has spawned more and more plastic products. However, plastic products cause serious environmental pollution because they are difficult to be biodegraded in the environment. At the same time, their raw materials are mainly petroleum. The increasing use of plastic products will inevitably further aggravate the "oil crisis" and lead to an increase in plastic prices. In response to this problem, in January 2020, the National Development and Reform Commission and the Ministry of Ecology and Environment issued the "Opinions on Further Strengthening Plastic Pollution Control", stipulating that by the end of 2020, the use of non-degradable disposable plastic straws will be prohibited in the catering industry nationwide. Therefore, finding alternative degradable materials for plastics has attracted more and more attention from scholars and research groups. At present, among many film-forming base materials, starch has become the most widely studied biodegradable material at home and abroad because of its wide source, low price, renewable and biodegradable properties. However, there are many hydroxyl groups and hydrogen bonds in the structure of pure starch films, which have strong affinity for water molecules, making the finished film easy to absorb water and dissolve, and its poor hydrophobicity severely limits the further expansion and application of starch films. At present, in order to improve the hydrophobic properties of starch films, most researches tend to introduce other non-polar groups through chemical modification methods such as crosslinking and esterification to neutralize the polar groups in starch films. The hydrophilicity of the starch film has been greatly improved, but the chemical groups introduced are more or less toxic, the process is complicated, and to a certain extent affects the degradable characteristics of the starch film, which may cause secondary environmental pollution. Pollution, so its finished film has not been well popularized and applied.

In addition, the pure starch film also has the problem of poor mechanical properties and low practicability, which limits its application in the packaging industry.

Contents of the invention

Aiming at the disadvantages of poor hydrophobicity and poor mechanical properties of existing starch films, the present invention provides a method for preparing a hydrophobic and degradable starch nanocomposite film and the resulting product. The preparation method has easy-to-obtain raw materials, low cost, and can be implemented Introduce starch carbon nanospheres or starch carbon nanospheres and nano-calcium carbonate into the starch film. These introduced substances do not change the structure of the film-forming starch, and at the same time greatly improve the hydrophobicity and mechanical properties of the starch film. performance, has excellent application prospects.

Studies have shown that the strong hydrophobicity of lotus leaves is due to the "lotus effect" on the surface of lotus leaves. There are complex multiple nano- and micron-scale ultrastructures on the surface of lotus leaves, which can form micron-scale surface concave-convex structures. The grooves between the structures can be occupied by air, so that an extremely thin layer of air is formed on the surface of the lotus leaf. Water droplets cannot fill the grooves and can roll on the surface of the lotus leaf. Therefore, the lotus leaf has super-hydrophobic properties. Inspired by the hydrophobic effect on the surface of lotus leaves, the present invention uses starch after high-pressure hydrothermal carbonization reaction to prepare nano-scale hydrothermal starch carbon nano-microsphere solution, which is used alone or in combination with nano-calcium carbonate to uniformly fill the starch film Among them, increasing the microscopic roughness of the starch film surface makes it form an air isolation layer with water molecules, effectively improving its hydrophobicity. In addition, the content of oxygen-containing functional groups in starch decreases after high-pressure hydrothermal carbonization, starch reacts with water under high temperature and high pressure conditions, and continuously hydrolyzes to produce glucose; glucose molecules are dehydrated under hydrothermal conditions, carbon atoms covalently interact with each other and form aromatic rings , finally obtained starch carbon nanospheres, presenting a hydrophobic aromatic ring region, and these characteristics also improved the hydrophobicity of the starch film to a large extent.

Concrete technical scheme of the present invention is as follows:

A method for preparing a hydrophobic degradable starch nanocomposite film, the method comprising the following steps:

(1) Mix starch and water evenly, and the resulting mixture is subjected to a hydrothermal reaction in a high-pressure reactor to obtain a starch carbon nanosphere solution, which can also be called a pretreatment solution;

(2) Mix the starch carbon nanosphere solution in step (1) with nano-calcium carbonate, and perform ultrasonic treatment to uniformly disperse the nano-calcium carbonate;

(3) Mix glycerin, water and starch in a container, cover the container with a cover with a through hole, heat and stir to obtain a mixed solution;

(4) Pour the starch carbon nanosphere solution of step (1) or the mixture of step (2) into the mixed solution of step (3), and continue heating and stirring;

(5) The mixture in step (4) is formed into a film and dried to obtain a hydrophobic and degradable starch nanocomposite film.

Further, the starch used in the present invention can be various types of starch, such as corn starch, potato starch, tapioca starch, etc., all of which can be used, and the performance of various types of starch is equivalent.

Further, in step (1), the dosage relationship between starch and water is 1g:30-40ml. In order to make the starch and water mix quickly, they can be mixed under heating and stirring conditions, for example, they can be heated and stirred in a magnetic stirrer at about 60°C to form a uniform turbid liquid.

Further, in step (1), the temperature of the hydrothermal reaction is 170-190°C, and the time of the hydrothermal reaction is 8-10 h.

Further, in step (2), the nano-calcium carbonate particles are nano-calcium carbonate infiltrated with ethanol. After infiltrated with ethanol, the nano-calcium carbonate particles are more likely to be uniformly dispersed in the starch carbon nanosphere solution. The so-called infiltration refers to immersing the nano-calcium carbonate particles in absolute ethanol so that the surface is fully covered with ethanol. In a specific embodiment of the present invention, 0.05-0.5 g of nano-calcium carbonate particles are infiltrated with 1-2 ml of absolute ethanol.

Further, in step (3), the mass ratio of glycerin, starch and water is 1.5-2.5:5:75-85, preferably 2:5:80. The present invention optimizes the dosage of glycerin, which can improve the hydrophobicity and mechanical properties of the starch film.

Furthermore, in step (3), when heating and stirring, it is necessary to cover the container with a cover with several through holes, the purpose of which is to prevent excessive evaporation of water and cause the liquid to be too viscous. The lid with the through hole can also be realized by means of a plastic wrap, the container is sealed with a plastic wrap, and then some small holes are inserted on the plastic wrap to get final product.

Further, in step (3), stir glycerin, water and starch at 85-100°C for 1-2 h.

Further, in step (4), only the starch carbon nanosphere solution is added to the mixed solution of step (3), or the mixed solution of starch carbon nanosphere solution and nano-calcium carbonate particles is added, preferably both are added. . By adjusting the amount of starch carbon nanospheres and nano-calcium carbonate, the hydrophobicity and mechanical properties of the starch film can be well improved.

Further, in step (4), the dosage relationship between starch and starch carbon nanosphere solution is: 5 g: 10-75 ml, preferably 5 g: 50-55 ml. The dosage relationship between the starch carbon nanosphere solution and the nano-calcium carbonate infiltrated by ethanol is: 50-55 ml: 0.05-0.5 g, preferably 50-55 ml: 0.2 g.

Further, in step (4), after pouring the starch carbon nanosphere solution in step (1) or the mixture in step (2), stir at 85-100°C for 1-2 h.

Further, in step (5), the film-forming method of the mixture may be casting method or casting method.

Further, in step (5), the drying is blast drying, the drying temperature is 30-40°C, and the drying time is 8-10 h.

The invention draws on the hydrophobic principle of lotus leaves to form microscopic roughness on the surface of the starch film, effectively improving the hydrophobicity of the starch film and increasing the contact angle. In addition, through the introduction of glycerin, nano-calcium carbonate, starch carbon nano-microspheres and the adjustment of reaction conditions, the hydrophobicity, tensile strength and elongation of the composite film were further improved, and the contact angle can reach up to 103°. These excellent The performance makes it have a good advantage as a packaging material, and will not change the starch structure, will not introduce toxic chemical groups, simple preparation, low cost, and effectively solve the shortcomings of poor hydrophobicity and poor mechanical properties of the current starch film , has a great application prospect in the catering industry. Therefore, the hydrophobic degradable starch nanocomposite film prepared according to the above method is also within the protection scope of the present invention.

The beneficial effects of the present invention are as follows:

1. Starch itself has many hydrophilic polar groups, and hydrogen bonds are often formed between and within its molecules, which have strong affinity for water molecules, resulting in poor hydrophobicity of starch films. In the present invention, starch carbon nanometer microsphere solution and nano calcium carbonate are added to shape the microstructure of the surface of the starch film to form an air isolation layer with water molecules, thereby improving the hydrophobicity of the starch film.

2. The existing starchy packaging film has poor mechanical properties and low practicability, which limits its application in the packaging industry. The present invention increases the tensile strength of the starch film by adding the hydrothermally formed starch carbon nano-microsphere solution and nano-calcium carbonate, improves the mechanical properties, and expands its application prospect.

3. PTFE is an existing hydrophobic material in my country, and the PTFE industry needs to invest a relatively large amount of land and raw materials for production, especially the high cost of raw materials, which is likely to cause product price fluctuations. At the same time, according to the list of carcinogens of the International Agency for Research on Cancer of the World Health Organization, polytetrafluoroethylene is a Class 3 carcinogen, which is harmful to the human body and the environment. Among many film-forming base materials, starch, especially corn starch, is cheap, which reduces the research and development cost of the present invention. At the same time, according to the "China Corn Starch Industry Market Demand and Investment Planning Analysis Report", my country's corn starch production is generally increasing year by year, with a high concentration of production capacity, easy access to raw materials and abundant supply.

4. The sources of the starch carbon nanospheres and film materials formed by the hydrothermal method of the present invention are all starch, and the film-forming starch is made into a degradable starch nanocomposite film without chemical modification by the method of filling, The obtained composite film has higher safety and does not destroy the original structure of the starch.

5. The process flow of the present invention is simple, the feasibility is strong, the operation is easy to understand, and the molding time is relatively short. The sources of various substances are abundant and the price is low, and the prepared starch nanocomposite film has strong hydrophobicity, high cost performance, and is green and environmentally friendly.

Description of drawings

Figure 1 is a trend diagram of the contact angle of the composite film with the amount of pretreatment solution (ml).

Fig. 2 is the trend diagram of the contact angle of the composite film with the addition amount (g) of nano-calcium carbonate under the optimal pretreatment liquid amount (ml).

Fig. 3 is a trend diagram of the tensile strength (N) and elongation at break of the composite film with the amount of pretreatment solution (ml).

Fig. 4 is the trend diagram of the tensile strength (N) and elongation at break of the composite film with the addition amount (g) of nano-calcium carbonate under the optimal pretreatment liquid amount (ml).

Figure 5 is the trend diagram of the water permeability coefficient [e ^-12 g·cm/(cm ² ·s·Pa)] of the composite film with the amount of pretreatment solution (ml).

Figure 6 shows the trend of the water permeability coefficient [e ^-12 g·cm/(cm ² ·s·Pa)] of the composite film with the amount of nano calcium carbonate added (g) under the optimum pretreatment liquid amount (ml).

Detailed ways

The present invention will be further described through specific examples below, and the following descriptions are only exemplary and not intended to limit the content thereof.

In the following examples, the contact angle is determined by the method in the international standard GB/T 30693-2014 "Measurement of Contact Angle of Plastic Film and Water".

In the following examples, the tensile strength and elongation were measured using the method in the international standard ISO 1184-1983 "Determination of Tensile Properties of Plastic Films".

In the following examples, the water vapor transmission rate and water vapor transmission coefficient are in accordance with GB/T 1037-1988 "Test Method for Water Vapor Permeability of Plastic Films and Sheets---Cup Method" (corresponding to ASTM E96 -1980) to determine the method defined in.

Example 1

(1) Dissolve 2 g of cornstarch in 70 ml of ultrapure water, heat and stir in a magnetic stirrer at about 60°C for 30 minutes to obtain a uniform turbid liquid, transfer the turbid liquid to a high-pressure reactor, and heat it at 180°C The lower seal was hydrothermally reacted for 8 h to obtain a turbid hydrothermal starch carbon nanosphere solution (hereinafter referred to as the pretreatment solution), which was cooled for later use.

(2) Dissolve 5g of cornstarch and 2.0g of glycerin in 80g of ultrapure water, pour the resulting mixture into a beaker, seal the mouth of the beaker with a film and insert it (the aperture should not be too large or too small), and heat it at about 97°C After stirring for 1 hour in a magnetic stirrer, add 0 ml, 10 ml, 35 ml, 40 ml, 45 ml, 50 ml, 55 ml, 60 ml, 65 ml, 70 ml, 75 ml of cooled pretreatment solution, Stirring was continued for 1 h in a magnetic stirrer at around 97 °C.

(3) Pour the mixed solution in (2) onto the template through gauze, and dry it in a blast drying oven at 35 °C for 8 hours to prepare a starch nanocomposite film with a thickness of 0.13-0.18 mm.

Figure 1 is the trend diagram of the contact angle of the starch nanocomposite film with the addition amount (ml) of the pretreatment solution. It can be seen from the figure that the addition of the pretreatment solution has the effect of improving the contact angle of the starch nanocomposite film. With the increase of the pretreatment solution, the contact angle first increased and then decreased. Among them, when the pretreatment solution was added at 50-55 ml, the hydrophobic performance was the best, and the contact angle was the best, which was above 89°.

Fig. 3 is a trend diagram of the tensile strength (N) and elongation at break of the starch nanocomposite film with the addition amount (ml) of the pretreatment solution. When no pretreatment solution was added, the elongation at break was high but the tensile strength was low. When adding a small amount of pretreatment liquid, the tensile strength increased but the elongation at break decreased slightly, and the tensile strength reached the maximum value at 55 ml; after adding the pretreatment liquid, the tensile strength and elongation at break both showed downward trend. Among them, when the amount of pretreatment solution was 55 ml, the tensile strength of the original starch film was improved and the elongation at break was considerable.

Figure 5 is the trend diagram of the water permeability coefficient [e ^-12 g·cm/(cm ² ·s·Pa)] of the composite film with the amount of pretreatment solution (ml). It can be concluded from the figure that when no pretreatment liquid is added, the water permeability coefficient is low. When 10ml of pretreatment liquid is added, the water permeability coefficient increases. When more than 10ml of pretreatment liquid is added, the water permeability coefficient tends to decrease, and when 55ml The water permeability coefficient reaches the lowest value; when more than 55ml of pretreatment liquid is added, the water permeability coefficient begins to rise, and the most preferred value is 55 ml.

In conclusion, when the pretreatment liquid was added in an amount of 50-55 ml, especially when the added amount was 55 ml, the hydrophobic properties, tensile strength, elongation at break and air permeability of the obtained starch nanocomposite films were the best.

Example 2

(1) According to the method of Example 1, a hydrothermal starch carbon nanosphere solution (hereinafter referred to as the pretreatment solution) was prepared.

(2) Dissolve 5 g of cornstarch and 2.0 g of glycerin in 80 g of ultrapure water, pour the resulting mixture into a beaker, seal the mouth of the beaker with film and insert the hole (the aperture should not be too large or too small), and put it at 97 °C Stir for 1 h on a left and right magnetic stirrer.

(3) Mix 55 ml of the cooled pretreatment solution in step (1) with 0.05 g, 0.1 g, 0.2 g, and 0.5 g of nano-calcium carbonate soaked in anhydrous ethanol, and 30 minutes of ultrasonic dispersion to make the nano-calcium carbonate Evenly dispersed in the pretreatment solution.

(4) Pour the mixed liquid that has been sonicated in step (3) into the beaker in step (2), and continue to stir in a magnetic stirrer at about 97 °C for 1 h.

(5) Pour the mixed solution in (4) through gauze on the template, and dry it in a blast drying oven at 35 °C for 8 h to prepare a starch nanocomposite film with a thickness of 0.13-0.18 mm.

Fig. 2 is the trend diagram of the contact angle of the composite film with the addition amount (g) of nano-calcium carbonate under the optimal pretreatment liquid amount (ml). Compared with Figure 1, it can be seen that under the premise of adding the optimal amount of pretreatment solution, the addition of nano-calcium carbonate has the effect of increasing the contact angle of the starch nanocomposite film, and with the increase of nano-calcium carbonate, the contact angle increases first Afterwards, the decreasing trend, among them, when the addition amount of nano-calcium carbonate is 0.2 g, the hydrophobic performance is better, and the contact angle can reach 103°.

Fig. 4 is the trend diagram of the tensile strength (N) and elongation at break of the composite film with the addition amount (g) of nano-calcium carbonate under the optimal pretreatment liquid amount (ml). Because the addition of nano-calcium carbonate improves its hydrophobicity, its mechanical properties are changed. With the addition of nano-calcium carbonate particles, the compactness of the film is affected to a certain extent. Under the premise of adding the optimal amount of pretreatment solution, the addition of nano-calcium carbonate reduced the tensile strength and elongation at break of the original starch film. When the addition of nano-calcium carbonate was 0.2g, the tensile strength and elongation at break The amount that elongation decreases is the lowest, therefore, the add-on of nano-calcium carbonate is preferably 0.2g.

Figure 6 shows the trend of the water permeability coefficient [e ^-12 g·cm/(cm ² ·s·Pa)] of the composite film with the amount of nano calcium carbonate added (g) under the optimal pretreatment liquid amount (ml). When no nano calcium carbonate is added, the water permeability coefficient is 3.562e ^-12 g cm/(cm ² s Pa). After adding 0.05g nano calcium carbonate, the water permeability coefficient increases. When more than 0.05g nano calcium carbonate is added, The water permeability coefficient tends to decrease, and the water permeability coefficient reaches the lowest value at 0.2g; when more than 0.2g of nano-calcium carbonate is added, the water permeability coefficient begins to show an upward trend, and the most preferred value is 0.2g.

In summary, when the addition amount of nano-calcium carbonate is 0.1-0.5 g, especially when the addition amount is 0.2 g, the hydrophobic properties, tensile strength, elongation at break and air permeability of the obtained starch nanocomposite films are the best.

Example 3

(1) Prepare a hydrothermal carbon nanosphere solution (hereinafter referred to as pretreatment solution) according to the method in Example 1.

(2) Dissolve 5g of cornstarch in 80g of ultrapure water, then add 1.5g, 1.8g, 2.0g, and 2.5g of glycerin respectively, pour the resulting mixture into beakers, seal the mouth of the beaker with film too large or too small), after stirring for 1 hour in a magnetic stirrer at a temperature of about 97°C, add 55ml of the solution in step (1) to take out the cooled pretreatment solution in the autoclave. Stirring was continued for 1 h in a magnetic stirrer at around °C.

(3) Pour the mixed solution in (2) over the gauze and pour it on the template, and dry it in a blast drying oven at 35°C for 8 hours to prepare a starch nanocomposite film starch film with a thickness of 0.13-0.18 mm.

The contact angle, tensile strength, elongation at break and water permeability coefficient of the composite films obtained under different glycerin dosages are shown in Table 1 below.

As can be seen from the results in the above table, when the optimum amount of glycerin is 2.0g, the overall performance is the best.

The present invention enhances its hydrophobicity by adding starch carbon nanometer microsphere solution. Based on the contact angle data tracked in real time, starch nanocomposite films with different hydrophobic properties were prepared according to different dosages of starch carbon nanosphere solutions. For optimal hydrophobic performance, its hydrophobic angle is increased from 38.12° to 89.50°; by changing the amount of glycerin to improve the tensile strength and elongation of starch film, this standard refers to the international standard ISO 1184-1983 "Plastic Film Tensile Properties Determination", the test shows that when the amount of starch is 5 g and the amount of glycerol is 2 g, the mechanical properties of the prepared starch nanocomposite film are better, the tensile strength is 8.769 N, and the elongation at break is 68.20%. By adding nano-calcium carbonate particles, the contact angle of the starch film was further improved. When the nano-calcium carbonate particles were 0.2g, the contact angle increased from 89.50° to 103°.

Claims (10)

1. a method for preparing a hydrophobic degradable starch nanocomposite film, characterized in that it may further comprise the steps: (1) Uniformly mix starch and water, and the resulting mixture is hydrothermally reacted in a high-pressure reactor to obtain a starch carbon nanosphere solution; (2) Mix the starch carbon nanosphere solution in step (1) with nano-calcium carbonate, and perform ultrasonic treatment to uniformly disperse the nano-calcium carbonate; (3) Mix glycerin, water and starch in a container, cover the container with a cover with a through hole, heat and stir to obtain a mixed solution; (4) Pour the mixture of step (2) into the mixture of step (3), and continue heating and stirring; (5) Forming the mixture in step (4) into a film and drying to obtain a hydrophobic and degradable starch nanocomposite film; In step (2), the nano-calcium carbonate is nano-calcium carbonate infiltrated by ethanol; In step (4), the dosage relationship between starch and starch carbon nanosphere solution is: 5 g: 10-75 ml, and the dosage relationship between starch carbon nanosphere solution and ethanol-infiltrated nano-calcium carbonate is: 50-55 ml : 0.05-0.5 g. 2. The preparation method according to claim 1, characterized in that: in steps (1) and (3), the starch includes corn starch, potato starch or tapioca starch. 3. The preparation method according to claim 1, characterized in that: in step (1), the ratio of starch to water is 1g:30-40ml. 4. The preparation method according to claim 1, characterized in that: in step (1), the temperature of the hydrothermal reaction is 170-190°C, and the time of the hydrothermal reaction is 8-10h. 5. The preparation method according to claim 1, characterized in that: in step (3), the mass ratio of glycerin, starch and water is 1.5-2.5:5:75-85. 6. The preparation method according to claim 1, characterized in that: in step (3), the mass ratio of glycerin, starch and water is 2:5:80. 7. The preparation method according to claim 1, characterized in that: in step (3), stir glycerin, water and starch at 85-100°C for 1-2 h; in step (4), pour into step (2 ) mixture, stirred at 85-100 °C for 1-2 h. 8. The preparation method according to claim 1, characterized in that: in step (4), the dosage relationship between starch and starch carbon nanosphere solution is: 5 g: 50-55 ml, starch carbon nanosphere solution and The dosage relationship of nano-calcium carbonate after ethanol infiltration is: 50-55 ml: 0.2 g. 9. The preparation method according to claim 1, characterized in that: in step (5), the drying temperature is 30-40 °C, and the drying time is 8-10 h. 10. The hydrophobic degradable starch nanocomposite film prepared according to the preparation method of the hydrophobic degradable starch nanocomposite film according to claim 1.

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