1. A preparation method of an alkaline seed coating agent film-forming agent is characterized in that: sodium carbonate is used as a catalyst, water is used as a medium, and water-soluble maleylation chitosan sodium, namely the alkaline seed coating agent film-forming agent, is prepared at normal temperature.

2. The method of claim 1, wherein: the preparation method comprises the following steps:

(1) adding water and glacial acetic acid into a reaction kettle, slowly adding chitosan into the kettle under low-speed stirring, and stirring to dissolve the chitosan;

(2) uniformly and alternately adding sodium carbonate and maleic anhydride into a high-speed stirring reaction kettle in sequence, and stopping the high-speed stirring reaction after a certain time;

(3) transferring the reaction mixed solution into a dissolving tank, adding hydrochloric acid while stirring, precipitating and separating out the maleoyl chitosan, and performing first centrifugal separation after curing; washing the precipitate with dilute hydrochloric acid, dewatering with centrifuge, transferring into dissolving tank, adding dilute sodium hydroxide under stirring to dissolve the precipitate into sodium salt, adding acetone to separate out white flocculent precipitate, centrifuging for the second time, and sun drying or air drying the obtained precipitate to obtain the target product.

3. The method of claim 2, wherein: and (3) at intervals of 20 minutes in the step (2), uniformly and alternately adding the weighed sodium carbonate and maleic anhydride which are divided into 6 parts into a high-speed stirring reaction kettle in sequence, and stopping the high-speed stirring reaction after a certain time.

4. The method of claim 2, wherein: during the first centrifugal separation, hydrochloric acid with the volume mass concentration of 1% is added while stirring, the pH value of the solution is adjusted to 1-2, the maleyl chitosan is precipitated and separated out, and centrifugal separation is carried out after curing for 1 hour.

5. The method of claim 2, wherein: and during the second centrifugal separation, washing the precipitate for 3 times by using dilute hydrochloric acid with the pH value of 2-3, and then dehydrating by using a centrifugal machine.

6. The application of the alkaline seed coating film-forming agent of claim 1, which is characterized in that: the multi-effect composite seed coating agent is prepared by taking sodium maleylation chitosan as a film forming agent, compounding a low-toxicity high-efficiency bactericide, adding an antifreeze agent and other auxiliary agents.

7. A method for preparing the seed coating agent of claim 6, which is characterized by comprising the following steps: dissolving the prepared film forming agent in 1-5 wt% water, and adding different proportions of sterilizing and antifreezing agents, and a certain proportion of emulsifier, dispersant and warning color according to the requirement; and fully mixing the mixed solution, stirring for 10-15 min by using a magnetic stirrer with the rotating speed of 100-200 r/min, finally supplementing water to 100%, and uniformly stirring by using a vacuum homogenizer to obtain the suspension seed coating agent with different effects.

Background art:

seed coating agents, as an environmentally friendly pesticide formulation, are increasingly being used for seed treatment of various crops. The film agent is an important component in the seed coating agent, and can effectively fix the seed coating agent on the seeds, so that air and a proper amount of moisture can pass through the film agent, the life function of the seeds is maintained, and the normal germination and seedling growth of the seeds are ensured; and the slow release of active ingredients such as pesticides or seed fertilizers can be realized, the lasting period of the pesticides and fertilizers is prolonged, and the growth of seedlings is promoted. Therefore, screening the film forming agent with excellent performance is a key factor for successfully developing the seed coating agent.

Film-forming agents commonly used in seed coating agents are: various polysaccharides and derivatives thereof such as sodium alginate, pectin, chitosan, gum arabic, gelatin, xanthan gum, starch, methyl cellulose, etc., and high molecular synthetic polymers such as polyvinyl acetate, polyvinyl alcohol, polyethylene glycol, polyacrylic acids, urea resin, polyvinylidene chloride, etc. The natural polymer film forming agent is non-toxic, stable, environment-friendly, safe, good in biocompatibility, cheap and easy to obtain, but poor in water solubility; the synthesized macromolecular film-forming agent has excellent stability, film-forming property and cohesiveness, but the preparation process has higher difficulty.

Chitin is widely distributed in nature, exists in shells of crustaceans such as shrimps and crabs, epidermis of insects such as mantis and silkworms (pupas), and cell walls of fungi such as mushrooms, is second only to cellulose in storage amount, and is the second largest renewable resource on the earth. Chitosan can be obtained by deacetylating chitin, and is increasingly used as a film-forming agent in seed coating agents due to abundant sources. However, chitosan applied in the seed coating agent at present is insoluble in water, so acetic acid, hydrochloric acid and the like are adopted for dissolving in the preparation process, but the dissolving operation steps are complicated; and the obtained chitosan solution is acidic, and has acidification influence on the microenvironment of seeds and germinated soil after coating.

The invention content is as follows:

the invention aims to solve the technical problem that chitosan serving as a film-forming agent in a seed coating agent needs to be dissolved by acetic acid or hydrochloric acid, the solution is acidic, and the acidification effect on soil is easily caused after the application.

In order to solve the problems, the invention provides a novel chitosan film forming agent with good water solubility, namely sodium maleylation chitosan (figure 1). The film forming agent is a modified chitosan derivative, is easy to dissolve in water, has good film forming performance, is easy to prepare, has a structure different from other chitosan (figure 2) used in seed coating agents at present, and has the corresponding effect of chitosan. And the sodium maleylation chitosan solution is alkalescent, which is beneficial to reducing the soil acidification phenomenon caused by excessive use of nitrogen fertilizer.

In order to achieve the purpose, the invention is realized by the following technical scheme that the preparation method of the alkaline seed coating film-forming agent takes sodium carbonate as a catalyst and water as a medium to prepare water-soluble maleylation chitosan sodium at normal temperature, namely the alkaline seed coating film-forming agent.

Further, the preparation method comprises the following steps:

(1) adding water and glacial acetic acid into a 100L enamel reaction kettle according to a certain mass ratio, slowly adding chitosan into the kettle under low-speed stirring, and stirring for about 2h to dissolve the chitosan; wherein glacial acetic acid is used as acid regulator to promote chitosan dissolution.

(2) At room temperature, at 20-minute intervals, uniformly and alternately adding weighed sodium carbonate and maleic anhydride which are divided into 6 parts into a high-speed stirring reaction kettle in sequence, and stopping after the high-speed stirring reaction is carried out for a certain time; wherein, sodium carbonate is used as an alkali regulator, and maleic anhydride is used as an acylating agent to participate in the reaction.

(3) Transferring the reaction mixed solution into a 300L dissolving tank, adding 1% (volume/weight percentage) hydrochloric acid while stirring, adjusting the pH value of the solution to 1-2, precipitating and separating out the maleoyl chitosan, curing for 1h, performing centrifugal separation, washing the precipitate for 3 times by using dilute hydrochloric acid with the pH value of 2-3, transferring the precipitate into the dissolving tank after dehydrating by using a centrifugal machine, adding dilute sodium hydroxide while stirring to dissolve the precipitate into sodium salt, adding acetone to separate out a white flocculent precipitate, performing centrifugal separation, and drying or airing the obtained precipitate to obtain the target product.

The application of the alkaline seed coating agent film-forming agent is to prepare the multi-effect type composite seed coating agent by taking sodium maleylation chitosan as the film-forming agent, compounding a low-toxicity high-efficiency bactericide, adding an antifreeze agent and other auxiliary agents.

Further, the seed coating agent is prepared by the following steps: 1-5 percent (weight/weight percentage) of the prepared film forming agent is dissolved in a proper amount of water, and then the sterilizing and antifreezing agents with different proportions, the emulsifying agent, the dispersing agent and the warning color with a certain proportion are added according to the requirement; and fully mixing the mixed solution, stirring for 10-15 min by using a magnetic stirrer with the rotating speed of 100-200 r/min, finally supplementing water to 100%, and uniformly stirring by using a vacuum homogenizer to obtain the suspension seed coating agent with different effects.

The invention has the beneficial effects that:

(1) provides a natural film forming agent with good water solubility and film forming performance, and then compounds a bactericide and an antifreeze to prepare the multi-effect seed coating agent.

(2) The film forming agent has high water solubility, is easy to prepare and is beneficial to the production of seed coating agents.

(3) The film forming agent is alkalescent, which is beneficial to improving the soil acidification degree caused by excessive use of nitrogen fertilizer and improving the germination and growth environment of seeds.

Drawings

FIG. 1 is a structural diagram of sodium maleyl chitosan;

FIG. 2 is a schematic view of chitosan structure;

FIG. 3 is a technical process flow diagram for the preparation of sodium maleyl chitosan;

FIG. 4 is an infrared spectrum of Chitosan (CH) and maleoyl Chitosan (CHM);

FIG. 5 shows the basal rot of wheat stems treated with control;

FIG. 6 shows the wheat stem base rot treated by the seed coating agent of the present invention.

The specific implementation mode is as follows:

in order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example (b): preparation of film-forming agent-sodium maleylation chitosan and field test for preventing and treating wheat stem basal rot

1. Preparation of film-forming agent-sodium maleochitosan:

weighing 20g of chitosan, putting the chitosan into a 1000ml three-neck flask provided with a stirrer, adding a proper amount of water and glacial acetic acid, and stirring for about 2 hours to dissolve the chitosan. Weighing the sodium carbonate and the acylating agent maleic anhydride with the experimental amount, evenly dividing into six parts, alternately adding the two parts at room temperature, quickly stirring after the addition, and continuously reacting for 1 hour. After the reaction is stopped, pouring the reactant into a 1000ml beaker, adding 1% hydrochloric acid while stirring, adjusting the pH value of the solution to 1-2, precipitating the maleoyl chitosan, curing for 1h, performing centrifugal separation, washing the precipitate for 3 times by using dilute hydrochloric acid with the pH value of 2-3, transferring the precipitate into a dissolving tank after the precipitate is dehydrated by a centrifugal machine, adding dilute sodium hydroxide while stirring to dissolve the precipitate into sodium salt, then adding acetone to separate out a white flocculent precipitate, performing centrifugal separation, and drying or airing the obtained precipitate to obtain the film-forming agent, namely the maleoyl chitosan sodium.

1.1 Structure and characterization of sodium maleoyl chitosan:

comparing the infrared spectra of Chitosan (CH) and maleic Chitosan (CHM) (FIG. 4), the occurrence of primary amine bending vibration peak delta NH at 1650cm-1 in chitosan, amide stretching vibration peak uNH at 3100cm-1 in maleyl chitosan, amide stretching vibration peak uC ═ O at 1620cm-1 and amide bending vibration peak delta NH at 1550cm-1 in chitosan indicates that N-acylation is carried out on amino group at C2; the stretching vibration peak upsilon C-O of ester appears at 1720cm-1 position in the maleoyl chitosan, which indicates that the hydroxyl at C3 and C6 position is subjected to O-acylation.

1.2 Water solubility:

the sodium maleylated chitosan prepared by the present invention and chitosan purchased from the market, each 2g, were taken and added with 50ml of water respectively, stirred for 5 minutes, and the results show: the sodium maleylation chitosan is completely dissolved, and the common chitosan is insoluble in water. Another published patent CN109809865A shows: the acylated chitosan used as the film agent is insoluble in water and needs to be dissolved by acetic acid; in other disclosed seed coating patents, chitosan used as a film-forming agent is insoluble in water and needs to be dissolved by acetic acid or hydrochloric acid for use, which is not described herein.

1.3 determination of pH value of the film-forming agent:

the pH value of the film-forming agent is measured according to the method of GB/T1601-93, the pH value is 7.5-8.5, and the film-forming agent is alkalescent.

1.4 measurement of film formation time:

coating seeds of corn, wheat, mung bean and Chinese cabbage with the seed coating agent compounded by the maleyl chitosan, pouring the uniformly coated seeds on a clean paper surface, observing the surface of the paper surface, and recording the film forming time until the solidified film is not sticky. After 3 times of repeated tests, the measured film forming time is between 4.5 and 7.0min (see table 1), and the film forming time is far lower than 20min specified in the related standards of the seed coating agent, which indicates that the maleyl chitosan has good film forming property.

TABLE 1 film Forming time for seed coating with sodium maleoyl Chitosan Complex seed coating

Repetition of	Corn seed	Wheat seed	Mung bean seeds	Chinese cabbage seeds
					1	5.5	6.5	5.5	4.5
2	6.0	6.5	6.0	4.5
					3	5.5	7.0	6.0	5.0

1.5 film formation uniformity measurement:

the method comprises the steps of dripping sodium maleochitosan on a glass slide, carrying out tape casting, drying and film forming, and then soaking in water for 0.5h to completely scrape off a film from the glass slide. This indicates that the uniformity and integrity of the film formation are good.

1.6 determination of influence of film-forming agent on seed germination:

according to GB/T3543.4-1995, the germination test is carried out by using the coated corn, wheat and Chinese cabbage seeds, and the effect of the seed coating agent on seed germination is tested. As can be seen from table 2: no matter the content of the film forming agent is 1.0 percent or 5.0 percent, the germination rates and the germination potentials of the coated wheat, corn and Chinese cabbage seeds are equivalent to those of the control seeds, which shows that the film forming agent has no influence on the germination of the seeds.

TABLE 2 influence of the coating on the seed germination vigor and germination rate

2. Seed coating preparation:

weighing 2g of prepared sodium maleochitosan, adding 20ml of water, stirring and dissolving for later use; measuring 2ml of pentanol, 3ml of prothioconazole, 16ml of prochloraz, 8ml of azoxystrobin and 2ml of 1, 2-propylene glycol, mixing, and stirring for 10-15 min by using a magnetic stirrer with the rotating speed of 100-200 r/min for later use; then 0.5ml of sorbitan fatty acid ester, 0.5ml of PEG2000 (polyethylene glycol 2000) and 0.3ml of alkaline rose essence are respectively measured, after mixing, the mixture is stirred for 10min to 15min by a magnetic stirrer with the rotating speed of 100r/min to 200r/min, then the prepared components are mixed, finally the water is supplemented to 100ml, and the mixture is stirred uniformly by a vacuum homogenizer to obtain 100ml of suspension seed coating agent.

3. Seed coating:

diluting the seed coating agent prepared in the step 2 by using 100ml of the seed coating agent, coating 50kg of wheat seeds, and airing (drying) for later use.

4. And (3) field test design:

4.1 test treatment: the test was carried out with reference to GB/T17980.108-2004. There are 4 treatments in total: firstly, the seed coated by the seed coating agent of the invention, secondly, the seed coated by the commercial 3 percent difenoconazole suspension seed coating agent, thirdly, the seed coated by the commercial 50 percent thiophanate-methyl suspension seed coating agent and fourthly, the seed which is not coated are used as a contrast. Each treatment was repeated 3 times for 12 cells, 20m per cell²The seeding rate is 10kg/667m2, and seeding is carried out according to the local normal seeding time.

4.2 disease investigation: in the wheat filling period, randomly taking 5 points in each cell, taking 20 plants in each point, digging out the plants with roots, keeping the root system complete, taking back samples, and carrying out stem base rot grading investigation indoors according to the grading standard: level 0: the whole plant has no browning symptoms; level 1: root deformation; and 3, level: the first stem node of the overground part has the phenomenon of browning and rotting; and 5, stage: the second stem node of the overground part has browning and rotting phenomena; and 7, stage: the lesion spots exceed the second stem node but have no white spike; and 9, stage: the lesion spots are beyond the second stalk node and have white spikes.

4.3 investigation of effects: the results show (table 3): the control effects of 3 percent of difenoconazole and 50 percent of thiophanate-methyl are 23.9 percent and 29.5 percent respectively, the white spike rate is 9.7 percent and 8.6 percent respectively, the disease indexes are 38.9 and 36.3 respectively, and both the disease index and the white spike rate are remarkably lower than those of a control; the seed coating agent of the invention has the control effect of 46.3 percent, the white spike rate of 5.2 percent and the disease index of 24.3, and the disease index and the white spike rate are obviously lower than those of the two seed coating agents. Therefore, the seed coating agent of the invention has the best effect.

Table 3: control effect of different seed coating agents on wheat stem basal rot

Treatment of	Index of disease condition	Control effect (%)	Percentage of white spike (%)
				1. The seed coating agent coating of the invention	24.3aA	46.3	5.2aA
2. 3% Difenoconazole coating	38.9bA	23.9	9.7bA
				3. 50% thiophanate-methyl coating	36.3bA	29.5	8.6bA
4. Control (without coating)	56.1cB	—	17.6cB