Apple bagging-free film agent and preparation method thereof

Abstract

The invention discloses an apple bagging-free film agent and a preparation method thereof, and relates to the technical field of agricultural application. The invention relates to a preparation method of a bagging-free film agent for apples. The preparation method comprises the following steps: preparing porous chitosan by adopting a gas foaming method; the preparation method comprises the following steps: dissolving porous chitosan in isopropanol, adding salicylic acid, heating for reaction, and evaporating to obtain a porous chitosan-salicylic acid graft; adding graphite-phase carbon nitride into water, mixing, adding the porous chitosan-salicylic acid graft, and uniformly stirring to obtain a compound; the preparation method comprises the following steps: activating humic acid, and grafting and modifying to obtain modified humic acid; dissolving the modified humic acid in a potassium hydroxide solution to obtain a modified potassium humate solution; and mixing the compound with the modified potassium humate solution, then adding glycosaminoglycan, and adding glycerol while stirring to obtain the apple bagging-free film agent. After the bagging-free film agent is applied to the surfaces of fruits, a layer of uniform and continuous ultrathin biological film can be formed, and the bagging-free film agent is good in bacteriostasis and disease and pest prevention capacity and has high air permeability and ductility.

Description

Technical Field

[0001] The present application relates to the field of agricultural application technology, and in particular to an apple bag-free film and a preparation method thereof. Background Art

[0002] After apples are bagged, a relatively closed microenvironment can be formed, which can protect against sun, moisturize, waterproof, keep warm, prevent pollution and pests, and significantly improve the quality of the fruit. The commonly used apple bags are generally composite paper plus black plastic film fruit bags, but in recent years, the disadvantages of this kind of fruit bags have also continued to emerge. Not only does it consume wood when making bags, but it also scatters in the fields after removing the bags, causing serious damage to the soil. In addition, bagging is labor-intensive and time-consuming, and the investment accounts for a large proportion. Paper plus black plastic film fruit bags are also prone to cause serious shading of fruits, uneven coloring, and affect the taste and quality of fruits. Apple bag-free cultivation has the advantages of being environmentally friendly, reducing labor costs, and improving fruit quality. It is mainly to apply the bag-free film to the surface of the fruit by spraying to form a uniform, continuous ultra-thin biofilm to replace the traditional fruit bagging. However, the existing apple bag-free film has a relatively single function, poor antibacterial and pest-resistant capabilities, and its air permeability and ductility need to be improved, which has a certain impact on fruit quality and yield. Summary of the invention

[0003] The main purpose of this application is to provide an apple bag-free film and a preparation method thereof, aiming to solve the technical problems that the existing apple bag-free film has a single function and its performance needs to be improved.

[0004] To achieve the above purpose, the present application proposes a method for preparing an apple bag-free film, comprising the following steps:

[0005] The porous chitosan is prepared by a gas foaming method; the porous chitosan is dissolved in isopropanol, salicylic acid is added, heated to react, and then evaporated to obtain a porous chitosan-salicylic acid graft;

[0006] After adding graphite phase carbon nitride into water and mixing, adding the porous chitosan-salicylic acid grafted material, stirring and mixing, to obtain a composite;

[0007] The humic acid is activated and then grafted to obtain modified humic acid; the modified humic acid is dissolved in a potassium hydroxide solution to obtain a modified potassium humate solution;

[0008] The complex is mixed with the modified potassium humate solution, glycosaminoglycan is added, and glycerol is added while stirring to obtain an apple bag-free film.

[0009] Optionally, the step of preparing porous chitosan by gas foaming method comprises:

[0010] Prepare chitosan acetic acid solution, add Tween-20 and Span-20, then add sodium bicarbonate, mix well, adjust the pH to 4.5-5, react at 25°C-50°C for 1h-3h, adjust the pH to 7, filter, wash with anhydrous ethanol, and then perform low-temperature vacuum drying at 40°C-50°C to obtain porous chitosan.

[0011] Optionally, the step of dissolving the porous chitosan in isopropanol, adding salicylic acid, heating to react, and evaporating to obtain a porous chitosan-salicylic acid graft comprises:

[0012] The porous chitosan is added to isopropanol and stirred until completely dissolved, then salicylic acid is added, and the reaction is condensed and refluxed at 75° C.-85° C. for 5 h-6 h, and then the reaction product is rotary evaporated at 48° C.-52° C. to obtain a porous chitosan-salicylic acid graft.

[0013] Optionally, the step of adding graphite phase carbon nitride into water and mixing, then adding the porous chitosan-salicylic acid grafted product, stirring and mixing, and obtaining the composite comprises:

[0014] Graphite phase carbon nitride is added into water and ultrasonically dispersed, the ultrasonic frequency is 40kHz-80kHz, the ultrasonic time is 10min-25min, and then the porous chitosan-salicylic acid graft is added and stirred, the stirring speed is 120r / min-140r / min, and the stirring time is 5min-12min to obtain a composite.

[0015] Optionally, the step of activating humic acid comprises:

[0016] The humic acid is ultrasonically dispersed in a hydrogen peroxide solution at an ultrasonic frequency of 30kHz-50kHz and an ultrasonic time of 3h-5h. After standing for 16h-24h, the supernatant is taken and dried to obtain activated humic acid.

[0017] Optionally, the grafting modification step comprises:

[0018] The grafting agent is prepared using sodium sulfite and pyruvic acid as raw materials;

[0019] Add the grafting agent and water to the activated humic acid, stir, adjust the pH value to 9-12, heat to 95-100° C., react for 4-5 hours, and dry at 65-70° C. for 2-3 hours after the reaction is completed;

[0020] Wherein, the mass ratio of the activated humic acid to the grafting agent is 1:(2-5).

[0021] Optionally, the step of preparing the grafting agent using sodium sulfite and pyruvic acid as raw materials comprises:

[0022] After dissolving sodium sulfite in water, pyruvic acid is added dropwise, heated to 50°C-60°C and kept warm for 1.5h-2.5h, then continued to heat to 60°C-70°C, and then formaldehyde solution is added dropwise. After the formaldehyde solution is added dropwise, it is continued to heat to 85°C-95°C and kept warm for 4.5h-5.5h, and then extracted with ethanol, separated, and dried to obtain a grafting agent;

[0023] Wherein, the mass ratio of the sodium sulfite to the pyruvic acid is 1:(1-2).

[0024] Optionally, in the step of mixing the complex with the modified potassium humate solution, adding glycosaminoglycan, and adding glycerol while stirring to obtain an apple bag-free film, the complex and the modified potassium humate solution are mixed in a mass ratio of (5-12): (2-4); the concentration of glycosaminoglycan in the apple bag-free film is 8g / L-15g / L.

[0025] The present application also proposes an apple bagging-free film preparation, which is obtained by using the preparation method of the apple bagging-free film preparation mentioned above.

[0026] When the apple bag-free film is used, it is diluted with water by 200 to 800 times and then sprayed on the surface of apple fruits at the young fruit stage. After the film is formed, it is sprayed on the surface of apple fruits once every 15 to 25 days.

[0027] This application at least includes the following beneficial effects:

[0028] The present application first prepares porous chitosan. Since chitosan has good film-forming and moisturizing functions, it can prevent fruits and vegetables from losing water. Chitosan also has good antibacterial properties and killing effects on crop pests. The present application uses porous chitosan with a porous structure as the main membrane component, which not only increases the specific surface area and porosity of chitosan, but also facilitates the subsequent grafting of chitosan and salicylic acid. At the same time, when the porous chitosan forms a protective film, its porous structure is conducive to increasing the porosity and permeability of the membrane, thereby increasing the air permeability of the apple bag-free film, which is conducive to controlling the exchange of gases (such as oxygen, carbon dioxide, ethylene, etc.) and promoting the growth of apple fruits. Salicylic acid can induce a variety of plants to develop resistance to a variety of pathogens and diseases, promote plant defense responses, and salicylic acid can also be used as a plant growth regulator to regulate plant growth metabolism. The present application adopts Grafting salicylic acid, which has antibacterial function, onto the amino group of porous chitosan can play a synergistic role in antibacterial effect and further increase the antibacterial ability. Then, through the composite cross-linking of graphite phase carbon nitride and porous chitosan, the graphite phase carbon nitride is evenly distributed in the three-dimensional network cross-linking structure of chitosan, so that the bag-free film has higher ductility and flexibility. In addition, the graphite phase carbon nitride can produce superoxide free radicals under light excitation. It has strong redox properties and can oxidize the unsaturated phospholipid molecular layer in the bacterial cell membrane, causing cell leakage and ultimately killing bacteria, thereby having strong antibacterial properties. After the graphite phase carbon nitride is composited with the porous chitosan-salicylic acid graft, the antibacterial performance and insect repellent ability of the film can be further enhanced, so that the apple bag-free film of the present application can play a role in long-term inhibition of pathogens and long-term repellent of pests without the use of pesticides.

[0029] Humic acid can improve the stress resistance of plants and has the function of complexing metal ions. It is easy to carry the medium and trace elements required by plants into the plant body, improve the utilization rate of various nutrients by apple fruits, and then promote the nutritional growth of apple fruits. Therefore, the present application activates and grafts humic acid to increase the active coordination groups on the humic acid molecules, further promote the complexation reaction with metal ions, and at the same time, the grafted modified humic acid has higher complexation stability and can form a more stable metal humic acid complex, which is beneficial to promote the absorption of nutrients by apple fruits.

[0030] Glycosaminoglycan has strong viscosity, which can enhance the adhesion of apple bag-free film on apple fruit, and play a better protective role on apple fruit. Glycosaminoglycan is composed of carbohydrate units with amino or carboxyl groups, which can absorb water for hydration, which is beneficial to increase air permeability. At the same time, glycosaminoglycan is a polyvalent anion with a great affinity for a variety of metal ions. It can regulate the distribution of these ions in tissues and promote the absorption of nutrients by apple fruit.

[0031] This application uses chitosan-salicylic acid-graphite phase carbon nitride composite, modified potassium humate and glycosaminoglycan as the main components of apple bag-free film. After being sprayed on the surface of the fruit, a uniform and continuous ultra-thin biofilm can be formed. It has good antibacterial and disease and pest prevention capabilities, and has high air permeability and ductility. Compared with conventional bagging treatment, it can also improve the quality and yield of apple fruit. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0033] Figure 1 This is a flow chart of the preparation method of the apple bag-free film described in the embodiments of the present application.

[0034] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0036] In view of the technical problems existing in the above-mentioned prior art, the embodiment of the present application provides a method for preparing an apple bag-free film, comprising the following steps:

[0037] S10. Preparing porous chitosan by gas foaming method.

[0038] The step of preparing porous chitosan by gas foaming method comprises:

[0039] Prepare chitosan acetic acid solution, add Tween-20 and Span-20, then add sodium bicarbonate, mix well, adjust the pH to 4.5-5, react at 25°C-50°C for 1h-3h, adjust the pH to 7, filter, wash with anhydrous ethanol, and then perform low-temperature vacuum drying at 40°C-50°C to obtain porous chitosan.

[0040] The present application uses chitosan as the main membrane component. Chitosan has good film-forming and antibacterial properties. It can form a dense film on the surface of bacteria through electrostatic adsorption with the surface of bacteria, preventing bacteria from absorbing nutrients, thereby inhibiting bacterial growth, and it also has a killing effect on certain crop pests. In order to further enhance the air permeability of the membrane, the present application adopts a gas foaming method. By introducing gas foam into the chitosan solution, porous chitosan with a pore structure is generated during the curing process. Since sodium bicarbonate can produce CO2 gas when it meets acid, a pore structure is formed on the surface of chitosan. After adjusting the pH and washing to remove sodium bicarbonate, chitosan with a porous surface can be obtained. This not only increases the specific surface area and porosity of chitosan, but also facilitates the subsequent grafting of chitosan and salicylic acid. At the same time, when the porous chitosan forms a protective film, its porous structure is conducive to increasing the porosity and permeability of the membrane, thereby increasing the air permeability of the apple bag-free membrane, thereby improving the gas exchange capacity and promoting the growth of apple fruits.

[0041] S20, dissolving the porous chitosan in isopropanol, adding salicylic acid, heating to react, and then evaporating to obtain a porous chitosan-salicylic acid graft.

[0042] Specifically, the porous chitosan is added to isopropanol, stirred until completely dissolved, and then salicylic acid is added. The reaction is condensed and refluxed at 75° C.-85° C. for 5 h-6 h, and then the reaction product is rotary evaporated at 48° C.-52° C. to obtain a porous chitosan-salicylic acid graft.

[0043] Salicylic acid can be used as a plant growth regulator to regulate plant growth and metabolism. At the same time, salicylic acid can induce resistance in a variety of plants to a variety of pathogens and diseases and promote plant defense responses. The present application can play a synergistic role in antibacterial effects by grafting salicylic acid, which has antibacterial function, onto the amino group of porous chitosan, further increasing the antibacterial ability. At the same time, it can promote the growth and metabolism of apples, which is beneficial to improving the quality of apple fruits.

[0044] S30, adding graphite phase carbon nitride into water and mixing, then adding the porous chitosan-salicylic acid grafted material, stirring and mixing, to obtain a composite.

[0045] Graphite phase carbon nitride is added into water and ultrasonically dispersed, the ultrasonic frequency is 40kHz-80kHz, the ultrasonic time is 10min-25min, and then the porous chitosan-salicylic acid graft is added and stirred, the stirring speed is 120r / min-140r / min, and the stirring time is 5min-12min to obtain a composite.

[0046] Graphite phase carbon nitride has a planar two-dimensional sheet structure similar to graphene. By composite cross-linking graphite phase carbon nitride and porous chitosan, the graphite phase carbon nitride is evenly distributed in the three-dimensional network cross-linking structure of chitosan, which can make the bag-free film have higher ductility and flexibility. Graphite phase carbon nitride has good biocompatibility, low toxicity and high stability. The superoxide free radicals generated under light excitation have strong redox properties, which can oxidize the unsaturated phospholipid molecular layer in the bacterial cell membrane, causing cell leakage and ultimately killing bacteria, thereby having strong antibacterial properties. After composite graphite phase carbon nitride with porous chitosan-salicylic acid grafts, the antibacterial and insect repellent properties of the film can be further enhanced, so that the apple bag-free film of the present application can play a long-term role in inhibiting pathogens and repelling pests without the use of pesticides.

[0047] S40, activating the humic acid, and then grafting and modifying it to obtain modified humic acid; dissolving the modified humic acid in a potassium hydroxide solution to obtain a modified potassium humate solution.

[0048] Specifically, the step of activating humic acid comprises:

[0049] The humic acid is ultrasonically dispersed in a hydrogen peroxide solution at an ultrasonic frequency of 30kHz-50kHz and an ultrasonic time of 3h-5h. After standing for 16h-24h, the supernatant is taken and dried to obtain activated humic acid.

[0050] The mass concentration of the hydrogen peroxide solution is 10%; the humic acid can be mineral source humic acid such as weathered coal humic acid, peat humic acid and lignite humic acid.

[0051] Humic acid has good physiological activity and absorption, complexation, exchange and other functions, and can improve the stress resistance of plants. At the same time, because it has the function of complexing metal ions, it is easy to carry the medium and trace elements required by plants into the plant body, improve the utilization rate of various nutrients by apple fruits, and thus promote the nutritional growth of apple fruits. However, the soluble humic acid content in untreated mineral humic acid is low, and it is difficult to be directly utilized by apple fruits. Therefore, the present application activates the humic acid by adding hydrogen peroxide, so that the macromolecular chains in the humic acid are broken into small molecular chains under the oxidation action of hydrogen peroxide, and the total acidic group and active group content of the humic acid are increased, which is beneficial to the subsequent grafting reaction. In addition, the present application uses ultrasonic wave for activation treatment. The aqueous solution will induce cavitation effect under the action of ultrasonic wave, and "internal collapse" will occur in the compression phase of the sound field, thereby generating a large number of oxygen free radicals such as ·OH and ·HO to oxidize and degrade the humic acid, thereby increasing the oxygen-carbon ratio (O / C) and hydrogen-carbon ratio (H / C) of the humic acid, and obtaining more free humic acid.

[0052] Furthermore, the activated humic acid is grafted and modified, specifically including:

[0053] After dissolving sodium sulfite in water, pyruvic acid is added dropwise, heated to 50°C-60°C and kept warm for 1.5h-2.5h, then continued to heat to 60°C-70°C, and then formaldehyde solution is added dropwise. After the formaldehyde solution is added dropwise, it is continued to heat to 85°C-95°C and kept warm for 4.5h-5.5h, and then extracted with ethanol, separated, and dried to obtain a grafting agent;

[0054] Wherein, the mass ratio of the sodium sulfite to the pyruvic acid is 1:(1-2);

[0055] Add the grafting agent and water to the activated humic acid, stir, adjust the pH value to 9-12, heat to 95-100° C., react for 4-5 hours, and dry at 65-70° C. for 2-3 hours after the reaction is completed;

[0056] Wherein, the mass ratio of the activated humic acid to the grafting agent is 1:(2-5).

[0057] In order to further promote the complexation of humic acid with metal ions, the present invention uses sodium sulfite and pyruvic acid to form a grafting agent, which reacts with the functional groups on the humic acid molecules through a grafting reaction to increase new coordination groups (such as -SO3 - , -COOH, etc.), these groups can provide more electron density in structure, which is beneficial to the complexation with metal ions, and after grafting, the activity of humic acid will also increase, which can further promote the complexation reaction with metal ions. At the same time, the grafted modified humic acid has higher complexation stability and can form more stable metal humic acid complexes, which is beneficial to carry the middle and trace elements required for apple growth into the plant body and promote the absorption of nutrients by apple fruit.

[0058] S50, mixing the complex with the modified potassium humate solution, adding glycosaminoglycan, and adding glycerol while stirring to obtain an apple bag-free film.

[0059] The complex and the modified potassium humate solution are mixed in a mass ratio of (5-12):(2-4); the concentration of the glycosaminoglycan in the apple bag-free film is 8g / L-15g / L.

[0060] In order to further enhance the adhesion and air permeability of the apple bag-free film, the present application adds glycosaminoglycan after mixing the composite with the modified potassium humate solution. Due to the strong viscosity of glycosaminoglycan, the adhesion of the apple bag-free film on the apple fruit can be enhanced, so that the apple bag-free film is not easy to fall off even under the scouring of heavy rain, which plays a good protective role for the apple fruit. Glycosaminoglycan is composed of carbohydrate units with amino or carboxyl groups, which can absorb water for hydration, which is beneficial to increase the air permeability. At the same time, glycosaminoglycan is a multivalent anion, which is sensitive to K + 、Na + , Ca 2+ Mg 2+ It has a greater affinity with ions such as pyrimidines, cytokines, and oligosaccharides, and can therefore regulate the distribution of these ions in tissues and promote the absorption of nutrients by apple fruits.

[0061] Specifically, hyaluronic acid can be used as the glycosaminoglycan.

[0062] The embodiments of the present application also provide an apple bagging-free film preparation, which is obtained by the preparation method of the apple bagging-free film preparation described above.

[0063] When the apple bag-free film is used, it is diluted with water by 200 to 800 times and then sprayed on the surface of apple fruits at the young fruit stage. After the film is formed, it is sprayed on the surface of apple fruits once every 15 to 25 days.

[0064] The above technical solution of the present application is described in detail below in conjunction with specific embodiments.

[0065] Example 1

[0066] An apple bag-free film is prepared by the following steps:

[0067] 0.2 g of chitosan was added to 100 mL of 2% acetic acid solution, and then 0.05 g of Tween-20 and 0.05 g of Span-20 were added, and then sodium bicarbonate was added to control the final concentration of sodium bicarbonate to be 6% (w / v). After mixing evenly, hydrochloric acid was added to adjust the pH to 5. After reacting at 37° C. for 2 h, ammonia water was added to adjust the pH to 7 to form a white flocculent precipitate. After suction filtration, the precipitate was washed with anhydrous ethanol and then low-temperature vacuum dried at 45° C. to obtain porous chitosan;

[0068] 3.5 g of the porous chitosan was added to a small amount of isopropanol (the amount added was sufficient to allow stirring), and after stirring until completely dissolved, 1.5 g of salicylic acid was added, and the mixture was condensed and refluxed at 80° C. for 5.5 h, and the reaction product was rotary evaporated at 50° C. to obtain a porous chitosan-salicylic acid grafted product;

[0069] 0.2 g of graphite carbon nitride was added to 200 mL of water and ultrasonically dispersed at an ultrasonic frequency of 60 kHz and an ultrasonic time of 17 min, and then 10 g of porous chitosan-salicylic acid graft was added and stirred at a stirring speed of 130 r / min and a stirring time of 9 min to obtain a composite;

[0070] 500 g of humic acid was ultrasonically dispersed in 3 kg of 10% hydrogen peroxide solution at an ultrasonic frequency of 40 kHz for 4 h. After standing for 20 h, the supernatant was taken and dried to obtain activated humic acid.

[0071] After dissolving 10 g of sodium sulfite in 120 mL of water, 150 g of pyruvic acid was added dropwise, heated to 55° C. and kept warm for 2.0 h, then continued to heat to 65° C., and then 100 mL of a formaldehyde solution with a mass concentration of 8% was added dropwise. After the formaldehyde solution was added dropwise, it was continued to heat to 90° C. and kept warm for 5.0 h, and then extracted with ethanol, separated, and dried to obtain a grafting agent;

[0072] Take 100g of activated humic acid, add 250g of grafting agent and 200mL of water, stir, adjust the pH value to 11, heat to 98°C, react for 4.5h, and then dry at 68°C for 2.5h to obtain modified humic acid;

[0073] Take 300 g of modified humic acid and 300 g of potassium hydroxide and dissolve them in 500 mL of water to obtain a modified potassium humate solution;

[0074] 800 g of the complex was mixed with 200 g of modified potassium humate solution, and 12 g of glycosaminoglycan was added, and 40 g of glycerol was added while stirring to obtain an apple bag-free film.

[0075] Example 2

[0076] An apple bag-free film is prepared by the following steps:

[0077] 0.2 g of chitosan was added to 100 mL of 2% acetic acid solution, and then 0.05 g of Tween-20 and 0.05 g of Span-20 were added, and then sodium bicarbonate was added and the concentration of sodium bicarbonate was controlled to be 6% (w / v). After mixing evenly, hydrochloric acid was added to adjust the pH to 4.5. After reacting at 25°C for 3 hours, ammonia water was added to adjust the pH to 7 to form a white flocculent precipitate. After suction filtration, the precipitate was washed with anhydrous ethanol and then low-temperature vacuum dried at 40°C to obtain porous chitosan.

[0078] 3.5 g of the porous chitosan was added to a small amount of isopropanol, and after stirring until completely dissolved, 1.5 g of salicylic acid was added, and the mixture was condensed and refluxed at 75° C. for 6 h, and the reaction product was rotary evaporated at 48° C. to obtain a porous chitosan-salicylic acid graft;

[0079] 0.2 g of graphite carbon nitride was added into 200 mL of water and ultrasonically dispersed at an ultrasonic frequency of 40 kHz for 25 min, and then 10 g of porous chitosan-salicylic acid graft was added and stirred at a stirring speed of 120 r / min for 12 min to obtain a composite;

[0080] 500 g of humic acid was ultrasonically dispersed in 3 kg of 10% hydrogen peroxide solution at an ultrasonic frequency of 30 kHz for 5 h. After standing for 16 h, the supernatant was taken and dried to obtain activated humic acid.

[0081] After dissolving 10 g of sodium sulfite in 110 mL of water, 100 g of pyruvic acid was added dropwise, heated to 50° C. and kept warm for 1.5 h, then continued to heat to 60° C., and then 100 mL of 8% formaldehyde solution was added dropwise. After the formaldehyde solution was added dropwise, it was continued to heat to 85° C. and kept warm for 4.5 h, then extracted with ethanol, separated, and dried to obtain a grafting agent;

[0082] Take 100g of activated humic acid, add 200g of grafting agent and 200mL of water, stir, adjust the pH value to 9, heat to 95℃, react for 5h, and then dry at 65℃ for 3h to obtain modified humic acid;

[0083] Take 300 g of modified humic acid and 300 g of potassium hydroxide and dissolve them in 500 mL of water to obtain a modified potassium humate solution;

[0084] 600 g of the complex was mixed with 400 g of modified potassium humate solution, and 10 g of glycosaminoglycan was added, and 35 g of glycerol was added while stirring to obtain an apple bag-free film.

[0085] Example 3

[0086] An apple bag-free film is prepared by the following steps:

[0087] 0.2 g of chitosan was added to 100 mL of 2% acetic acid solution, and then 0.05 g of Tween-20 and 0.05 g of Span-20 were added, and then sodium bicarbonate was added and the concentration of sodium bicarbonate was controlled to be 6% (w / v). After mixing evenly, hydrochloric acid was added to adjust the pH to 5. After reacting at 50° C. for 1 h, ammonia water was added to adjust the pH to 7 to form a white flocculent precipitate. After suction filtration, the precipitate was washed with anhydrous ethanol and then low-temperature vacuum dried at 50° C. to obtain porous chitosan.

[0088] 3.5 g of the porous chitosan was added to a small amount of isopropanol, and after stirring until completely dissolved, 1.5 g of salicylic acid was added, and the mixture was condensed and refluxed at 85° C. for 5 h, and the reaction product was rotary evaporated at 48° C. to obtain a porous chitosan-salicylic acid graft;

[0089] 0.2 g of graphite carbon nitride was added to 200 mL of water and ultrasonically dispersed at an ultrasonic frequency of 80 kHz for 10 min, and then 10 g of porous chitosan-salicylic acid graft was added and stirred at a stirring speed of 140 r / min for 5 min to obtain a composite;

[0090] 500 g of humic acid was ultrasonically dispersed in 3 kg of 10% hydrogen peroxide solution at an ultrasonic frequency of 50 kHz for 3 h. After standing for 24 h, the supernatant was taken and dried to obtain activated humic acid.

[0091] After dissolving 10 g of sodium sulfite in 150 mL of water, 200 g of pyruvic acid was added dropwise, heated to 60° C. and kept warm for 2.5 h, then continued to heat to 70° C., and then 100 mL of a formaldehyde solution with a mass concentration of 8% was added dropwise. After the formaldehyde solution was added dropwise, it was continued to heat to 95° C. and kept warm for 5.5 h, and then extracted with ethanol, separated, and dried to obtain a grafting agent;

[0092] Take 100g of activated humic acid, add 500g of grafting agent and 200mL of water, stir, adjust the pH value to 12, heat to 100℃, react for 4h, and then dry at 70℃ for 2h to obtain modified humic acid;

[0093] Take 300 g of modified humic acid and 300 g of potassium hydroxide and dissolve them in 500 mL of water to obtain a modified potassium humate solution;

[0094] 700 g of the complex was mixed with 300 g of modified potassium humate solution, and 15 g of glycosaminoglycan was added, and 45 g of glycerol was added while stirring to obtain an apple bag-free film.

[0095] Comparative Example 1

[0096] Compared with Example 1, the composite was replaced with porous chitosan-salicylic acid grafted material, and the other steps remained unchanged.

[0097] Comparative Example 2

[0098] Compared with Example 1, the humic acid was not activated and modified, and the other steps remained unchanged.

[0099] Test example

[0100] 1.1 Test time and location:

[0101] This experiment was conducted from March to October 2023 in Xipo Village, Dianzhang Street, Xingping City, Xianyang City, Shaanxi Province.

[0102] 1.2 Overview of the test site:

[0103] The experimental field has flat terrain, uniform soil fertility, medium soil fertility and is slightly alkaline. Before the experiment, soil samples at a depth of 0 cm to 40 cm were collected from the experimental field, and the basic soil nutrient conditions were measured as shown in Table 1 below.

[0104] Table 1 Soil nutrient indexes

[0105]

[0106] 1.3 Experimental design:

[0107] The apple variety used for the test was Fuji apple, 5 years old, with a spacing of 1.2m between plants and 3.5m between rows. The trees were strong and of uniform age. The experimental plot area was 50m 2 The experiment set up five treatments, repeated 3 times, randomly arranged, and the experimental treatments were: CK1 (no bagging treatment), CK2 (conventional fruit bagging treatment), A1 (apple bagging-free film treatment in Example 1 of the present application), A2 (apple bagging-free film treatment in Comparative Example 1 of the present application), and A3 (apple bagging-free film treatment in Comparative Example 2 of the present application). The usage of the apple bagging-free film of the present application is: dilute the apple bagging-free film agent with water 200 times, and spray it on the surface of apple fruit from the young fruit stage. After the film is formed, spray it on the surface of apple fruit once every 20 days, spray it 7 times during the whole growth period, and measure various indicators at the harvest period in October.

[0108] 1.4 Test results:

[0109] The effects of different treatments on apple indicators and yield are shown in Tables 2 and 3.

[0110] Table 2 Apple growth and development indicators

[0111]

[0112] Table 3 Effects of different treatments on yield

[0113]

[0114] It can be seen from Tables 2 and 3 that the nutritional growth and yield of apples in the plots treated differently are different. Under the bag-free film treatment of the embodiment of the present application, the fresh weight of the louver, louver thickness, fruit shape index, fruit hardness, fruit sugar content and single fruit weight of the apple tree are greatly improved compared with the conventional bagging treatment, and the yield per mu is increased by 13.1% compared with the conventional bagging treatment; in Comparative Example 1, no graphite phase carbon nitride is compounded, and graphite phase carbon nitride can significantly improve the antibacterial and disease and pest prevention capabilities of the bag-free film for apples, resulting in a decrease in the growth condition and yield of apples in Comparative Example 1 compared with Example 1; and in Comparative Example 2, humic acid is not treated. After activation and modification, humic acid can significantly improve its role in complexing metal ions, thereby carrying the secondary elements and trace elements required for apple growth into the plant body, improving the utilization rate of nutrients by apple fruits, and promoting apple growth. Therefore, Comparative Example 2 has a certain impact on the nutritional growth and yield of apples. In summary, the apple bag-free film of the embodiment of the present application is used for treatment, which has a significant promoting effect on the vegetative growth and reproductive growth of apples.

[0115] The above description is only an optional embodiment of the present application, and does not limit the patent scope of the present application. All equivalent structural transformations made by using the contents of the present application specification and drawings under the inventive concept of the present application, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A method for preparing an apple bag-free film, characterized in that: The following steps are involved: The porous chitosan is prepared by a gas foaming method; the porous chitosan is dissolved in isopropanol, salicylic acid is added, heated to react, and then evaporated to obtain a porous chitosan-salicylic acid graft; After adding graphite phase carbon nitride into water and mixing, adding the porous chitosan-salicylic acid grafted material, stirring and mixing, to obtain a composite; The humic acid is activated and then grafted to obtain modified humic acid; dissolving the modified humic acid in a potassium hydroxide solution to obtain a modified potassium humate solution; The complex is mixed with the modified potassium humate solution, glycosaminoglycan is added, and glycerol is added while stirring to obtain an apple bag-free film.

2. The method for preparing the apple bag-free film according to claim 1, characterized in that: The step of preparing porous chitosan by gas foaming method comprises: Prepare chitosan acetic acid solution, add Tween-20 and Span-20, then add sodium bicarbonate, mix well, adjust the pH to 4.5-5, react at 25°C-50°C for 1h-3h, adjust the pH to 7, filter, wash with anhydrous ethanol, and then perform low-temperature vacuum drying at 40°C-50°C to obtain porous chitosan.

3. The method for preparing the apple bag-free film according to claim 1, characterized in that: The step of dissolving the porous chitosan in isopropanol, adding salicylic acid, heating to react, and evaporating to obtain a porous chitosan-salicylic acid graft comprises: The porous chitosan is added to isopropanol and stirred until completely dissolved, then salicylic acid is added, and the reaction is condensed and refluxed at 75° C.-85° C. for 5 h-6 h, and then the reaction product is rotary evaporated at 48° C.-52° C. to obtain a porous chitosan-salicylic acid graft.

4. The method for preparing the apple bag-free film according to claim 1, characterized in that: The step of adding graphite phase carbon nitride into water and mixing, adding the porous chitosan-salicylic acid grafted material, stirring and mixing, and obtaining the composite comprises: Graphite phase carbon nitride is added into water and ultrasonically dispersed, the ultrasonic frequency is 40kHz-80kHz, the ultrasonic time is 10min-25min, and then the porous chitosan-salicylic acid graft is added and stirred, the stirring speed is 120r / min-140r / min, and the stirring time is 5min-12min to obtain a composite.

5. The method for preparing the apple bag-free film according to claim 1, characterized in that: The step of activating humic acid comprises: The humic acid is ultrasonically dispersed in a hydrogen peroxide solution at an ultrasonic frequency of 30kHz-50kHz and an ultrasonic time of 3h-5h. After standing for 16h-24h, the supernatant is taken and dried to obtain activated humic acid.

6. The method for preparing the apple bag-free film according to claim 5, characterized in that: The graft modification step comprises: The grafting agent is prepared using sodium sulfite and pyruvic acid as raw materials; Add the grafting agent and water to the activated humic acid, stir, adjust the pH value to 9-12, heat to 95-100° C., react for 4-5 hours, and dry at 65-70° C. for 2-3 hours after the reaction is completed; Wherein, the mass ratio of the activated humic acid to the grafting agent is 1:(2-5).

7. The method for preparing the apple bag-free film according to claim 6, characterized in that: The step of preparing the grafting agent using sodium sulfite and pyruvic acid as raw materials comprises: After dissolving sodium sulfite in water, pyruvic acid is added dropwise, heated to 50°C-60°C and kept warm for 1.5h-2.5h, then continued to heat to 60°C-70°C, and then formaldehyde solution is added dropwise. After the formaldehyde solution is added dropwise, it is continued to heat to 85°C-95°C and kept warm for 4.5h-5.5h, and then extracted with ethanol, separated, and dried to obtain a grafting agent; Wherein, the mass ratio of the sodium sulfite to the pyruvic acid is 1:(1-2).

8. The method for preparing the apple bag-free film according to claim 1, characterized in that: In the step of mixing the complex with the modified potassium humate solution, adding glycosaminoglycan, and adding glycerol while stirring to obtain an apple bag-free film, the complex and the modified potassium humate solution are mixed in a mass ratio of (5-12): (2-4); the concentration of the glycosaminoglycan in the apple bag-free film is 8g / L-15g / L.

9. An apple bag-free film, characterized in that: Obtained by the preparation method of the apple bag-free film according to any one of claims 1 to 8.

10. The apple bag-free film according to claim 9, characterized in that: When the apple bag-free film is used, it is diluted with water by 200 to 800 times and then sprayed on the surface of apple fruits at the young fruit stage. After the film is formed, it is sprayed on the surface of apple fruits once every 15 to 25 days.

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