Isothiazole composite bactericide as well as preparation method and application thereof

Abstract

The invention relates to the technical field of circulating cooling water treatment, in particular to an isothiazole composite bactericide as well as a preparation method and application thereof, and the isothiazole composite bactericide comprises the following components in parts by mass: 10-20 parts of an isothiazole bactericide and 5-15 parts of isothiazolyl modified chitosan. The isothiazole composite bactericide disclosed by the invention can be used for efficiently inhibiting scaling of biological slime and metal impurities, and meanwhile, the dosage can be reduced, and secondary pollution to the environment is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of circulating cooling water treatment, and in particular to an isothiazole composite fungicide and a preparation method and application thereof. Background Art

[0002] Circulating cooling water systems play a vital role in industrial production. They reduce the temperature in the process by continuously circulating water. However, these systems often encounter problems such as scaling and biosludge during operation, which seriously affects the normal operation of the cooling water system.

[0003] Bioslime is a complex mixture of microbial communities and their secretions, including bacteria, fungi, algae, etc. In the circulating cooling water system, due to suitable conditions such as water temperature, pH value, dissolved oxygen, etc., microorganisms can easily reproduce and grow to form biofilms. These biofilms not only provide protection for microorganisms, but also capture and retain suspended matter and sediments in the system, leading to the accumulation of bioslime.

[0004] The accumulation of biological slime will have many impacts on the circulating cooling water system. First, it will adhere to the surface of the heat exchanger, reduce the heat exchange efficiency and increase energy consumption. Secondly, biological slime may also react with calcium and magnesium ions in the water to form insoluble salts, further aggravating the scaling phenomenon. Scaling not only affects the heat exchange efficiency, but also may cause pipe blockage, seriously affecting the normal operation of the system. In addition, biological slime may also cause corrosion problems. The acidic substances produced during microbial metabolism will lower the local pH value and promote metal corrosion. At the same time, biological slime covers the metal surface to form differential corrosion cells, accelerating the corrosion process.

[0005] Therefore, in order to control the biological slime and scaling problems in circulating cooling water, a series of measures are usually required, including the use of bactericides to control the growth of microorganisms, the use of scale inhibitors to prevent salt deposition, and regular system cleaning and maintenance. Through these methods, the impact of biological slime and scaling on the circulating cooling water system can be effectively reduced, ensuring the stability and efficient operation of the system.

[0006] Among them, fungicides are a class of chemicals widely used in various industrial production fields. They can effectively kill or inhibit the growth of microorganisms, ensure the smooth progress of industrial processes and the safety and quality of products. Among many fungicides, isothiazolinone has attracted much attention due to its broad-spectrum, high efficiency and low toxicity.

[0007] The main components of isothiazolinone include 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one. These components can destroy the cell membrane of microorganisms, rapidly and irreversibly inhibit their growth, leading to cell death, and thus have a significant killing effect on bacteria, fungi, algae, etc. This fungicide has high killing efficiency, good biodegradability, no residue, safe operation, good compatibility, strong stability, low use cost, and can be miscible with chlorine and most anionic, cationic and non-ionic surfactants. Therefore, it is widely used in oil fields, papermaking, pesticides, cutting oils, leather, inks, dyes, leather making and other industries.

[0008] For example, CN104663710A discloses "oxidative sterilization and algae removal agent for industrial circulating water system" composed of chlorine dioxide, tetradecyl dimethyl benzyl ammonium chloride, isothiazolinone, copper sulfate, polymaleic anhydride, penetrant T and deionized water. The oxidative sterilization and algae removal agent has no secondary pollution, low production cost, and is suitable for industrial production. For another example, CN103112935A discloses "a composite cooling circulating water sterilizer and its preparation method and use method" is prepared by sodium hypochlorite, isothiazolinone, hydroxyethylphosphonic acid and water. The sterilizer has a high killing rate of bacteria and algae and a long inhibition time. For another example, CN110999913A discloses "a sterilization and algae removal agent for circulating water and its preparation method" is prepared by glutaraldehyde, dodecyl dimethyl benzyl ammonium chloride and isothiazolinone as the main raw materials. The sterilization and algae removal agent has a slime stripping effect and has the characteristics of high efficiency, broad spectrum, rapidity, low toxicity and low price.

[0009] However, the above-mentioned patent disclosure does not mention or solve the problem of how to reduce the dosage while effectively inhibiting the generation of biological slime.

[0010] Therefore, it is urgent to develop an isothiazole composite fungicide that can effectively inhibit biological slime, reduce the dosage, and cause no secondary pollution to the environment. Summary of the invention

[0011] The main purpose of the present invention is to provide an isothiazole composite fungicide and a preparation method thereof, wherein the isothiazole composite fungicide can effectively inhibit the formation of biological slime and metal impurity scaling, and can reduce the dosage at the same time without secondary pollution to the environment.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0013] On one hand, the present invention provides an isothiazole composite fungicide, comprising the following components in parts by weight: 10 to 20 parts of isothiazole fungicide and 5 to 15 parts of isothiazole-modified chitosan.

[0014] In some embodiments, the isothiazole fungicide is one or more of 5-chloro-2-methyl-4-isothiazoline-3-one, 2-methyl-4-isothiazoline-3-one, 1,2-benzisothiazolinone, 2-butyl-1,2-benzisothiazolin-3-one and 2-methyl-1,2-benzisothiazolin-3-one.

[0015] In some embodiments, the method for preparing the isothiazole-modified chitosan comprises the following steps:

[0016] S1. Mix cyanuric chloride and an acid binding agent and add them to N,N-dimethylformamide, and dropwise add a diluted solution of benzisothiazolinone in N,N-dimethylformamide. After the dropwise addition is complete, heat the mixture to 75-85° C. and stir at a constant temperature for 4-6 hours. After the reaction is completed, cool the mixture to room temperature, extract, combine the organic phases, and concentrate and dry under reduced pressure to obtain compound A.

[0017] S2, compound A and sodium bicarbonate in step S1 are mixed and added with methanol, and a methanol dilution of diallylamine is added dropwise, and after the addition is complete, the temperature is raised to 50-60° C. and stirred at a constant temperature for 20-24 hours. After the reaction is completed, the temperature is lowered to room temperature, extracted, concentrated and dried under reduced pressure, and subjected to column chromatography to obtain a compound of formula I

[0018]

[0019] S3, adding chitosan to an acetic acid solution to dissolve and cooling to 0-5°C, then adding methacrylic anhydride thereto, continuing constant temperature stirring for 25-26 hours, and after the reaction is completed, adding ethanol thereto until no precipitation is produced, filtering, washing with ethanol, and drying to obtain pretreated chitosan;

[0020] S4. Under an inert protective gas atmosphere, mix the compound represented by formula I in step S2 and the pretreated chitosan in step S3, add deionized water to disperse, heat to 80-90° C., add an initiator, continue stirring for 1-2 hours, centrifuge after the reaction, filter, and dry to obtain isothiazole-modified chitosan.

[0021] Isothiazolinone can destroy the cell membrane of microorganisms, quickly and irreversibly inhibit their growth, leading to cell death, and thus has a significant killing effect on bacteria, fungi, algae, etc. However, the content of isothiazolinone will decrease with the discharge of circulating cooling water, and the sterilization and algaecide effects will decrease, resulting in large dosages and the inability to achieve sustained and efficient sterilization and algaecide.

[0022] The isothiazole-modified chitosan of the present application can be compounded with conventional isothiazole fungicides to achieve synergistic effects, thereby improving the sterilization efficiency and achieving long-term sterilization and algaecide effects, reducing the dosage and further reducing costs, and also improving the corrosion resistance of circulating cooling water equipment. The reasons may be: first, the isothiazole-modified chitosan of the present application can be compounded with conventional isothiazole fungicides to work synergistically. Conventional isothiazole fungicides can effectively disperse and kill most bacteria in the circulating water, while the isothiazole-modified chitosan can adhere to the inner wall of the cooling circulating water equipment to form an antibacterial and anti-algae film layer, effectively preventing the deposition and growth of algae. When the cooling circulating water system is drained, the conventional isothiazole fungicides are discharged with the water flow, while the isothiazole-modified chitosan can stably adsorb on the surface of the equipment, thereby achieving a continuous and long-term sterilization and algaecide effect, and can further reduce the dosage; second, the isothiazole-modified chitosan is rich in a large number of isothiazolinone structures, which can play a role in sterilization and inhibition of algae growth. At the same time, its cross-linked structure can increase the viscosity of the isothiazole-modified chitosan, improve the ability to adhere to the cooling circulating water equipment, and prevent equipment corrosion.

[0023] In some embodiments, in step S1, the acid binding agent is any one of sodium bicarbonate, potassium bicarbonate, sodium carbonate and potassium carbonate.

[0024] In some embodiments, in step S1, the molar ratio of the benzisothiazolinone to the acid binding agent is 1:(1.2-1.4).

[0025] In some embodiments, in step S1, the molar ratio of cyanuric chloride to benzisothiazolinone is 1:(1.9-2).

[0026] Preferably, in step S1, the molar ratio of cyanuric chloride to benzisothiazolinone is 1:1.95.

[0027] The present invention can adjust the molar ratio of cyanuric chloride and benzisothiazolinone so that two halogenated groups therein can be added to benzisothiazolinone, thereby improving the sterilization and algaecidal performance of isothiazole-modified chitosan.

[0028] In some embodiments, in step S2, the molar ratio of compound A to diallylamine is 1:(1-1.2).

[0029] Preferably, in step S2, the molar ratio of compound A to diallylamine is 1:1.1.

[0030] The present application can prevent the waste of raw materials and make the reaction more complete by regulating the molar ratio of compound A and diallylamine.

[0031] In some embodiments, in step S3, the mass ratio of chitosan to methacrylic anhydride is 1:(1-2).

[0032] Preferably, in step S3, the mass ratio of chitosan to methacrylic anhydride is 1:1.5.

[0033] The present application can endow chitosan with a certain cross-linking ability by regulating the mass ratio of chitosan and methacrylic anhydride, thereby improving its viscosity and increasing its ability to adhere to equipment. At the same time, it can also prevent excessive unsaturated double bonds from causing uneven cross-linking, resulting in a decrease in its stability and thus a decrease in the long-term corrosion inhibition ability of the equipment, as well as a decrease in the long-term sterilization and algaecide performance.

[0034] In some embodiments, in step S4, the mass ratio of the compound represented by formula I to the pretreated chitosan is 1:(0.4-0.6).

[0035] Preferably, in step S4, the mass ratio of the compound represented by formula I to the pretreated chitosan is 1:0.5.

[0036] The present application can prevent the cross-linking density of isothiazole-modified chitosan from being too low, thereby reducing its viscosity and making it difficult to improve the corrosion resistance of the equipment, by regulating the mass ratio of the compound shown in formula I and the pretreated chitosan. It can also prevent the swelling properties of isothiazole-modified chitosan from being reduced due to the increase in cross-linking density, thereby limiting the coordination effect between the hydrophilic groups therein and the metal ions on the surface of the equipment.

[0037] Another aspect of the present invention provides a method for preparing an isothiazole composite fungicide, comprising the following steps: mixing the isothiazole composite fungicide and isothiazole-modified chitosan to obtain the isothiazole composite fungicide.

[0038] In another aspect, the present invention provides an application of an isothiazole composite fungicide in circulating cooling water.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention adopts isothiazole fungicides and isothiazole-modified chitosan for synergistic compounding, which improves the sterilization efficiency and can also achieve long-term sterilization and algaecide effects, reduces the dosage and further reduces the cost, and can also improve the corrosion resistance of circulating cooling water equipment, which can not only effectively inhibit the generation of biological slime but also inhibit the generation of metal impurities scaling.

[0041] (2) The isothiazole-modified chitosan of the present invention can adhere to the inner wall of the cooling circulating water equipment to form an antibacterial and anti-algae film layer, which effectively prevents the deposition and growth of algae. When the cooling circulating water system is drained, the conventional isothiazole fungicide is discharged with the water flow, while the isothiazole-modified chitosan can stably adsorb on the surface of the equipment, thereby achieving a continuous and long-term sterilization and algae killing effect, and can further reduce the dosage; in addition, the isothiazole-modified chitosan is rich in a large number of isothiazolinone structures, which can play a role in sterilization and inhibition of algae growth. At the same time, its cross-linked structure can increase the viscosity of the isothiazole-modified chitosan, improve the ability to adhere to the cooling circulating water equipment, and play an effect of preventing equipment corrosion. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Preparation Example 1

[0044] The preparation method of isothiazole-modified chitosan comprises the following steps:

[0045] S1. 0.5 mol of cyanuric chloride and 0.75 mol of potassium bicarbonate were mixed and added to 1 L of N,N-dimethylformamide, into which 1.5 L of N,N-dimethylformamide dilution containing 0.98 mol of benzisothiazolinone was dripped, and after the dripping was completed, the temperature was raised to 80° C. and stirred at constant temperature for 5 h. After the reaction was completed, the temperature was cooled to 27° C., and the organic phases were extracted, combined, and concentrated and dried under reduced pressure to obtain compound A;

[0046] S2, 0.5 mol of compound A in step S1 and 0.65 mol of sodium bicarbonate were mixed and added to 2 L of methanol, and 500 mL of methanol dilution containing 0.55 mol of diallylamine was dripped into it. After the dripping was completed, the temperature was raised to 55°C and stirred at a constant temperature for 22 hours. After the reaction was completed, the temperature was lowered to 27°C, extracted, concentrated and dried under reduced pressure, and subjected to column chromatography to obtain the compound shown in Formula I

[0047]

[0048] The NMR analysis of the compound shown in Formula I is as follows: 1 H NMR (500 MHz, DMSO-d 6)δ8.05 (dd, J=5.0,1.6Hz,2H,H on benzene ring),7.59 (dd, J=5.0,1.8Hz,2H,H on benzene ring),7.49 (td, J=5.0,1.6Hz,2H,H on benzene ring),7.35 (td, J=5.0,1.7Hz,2H,H on benzene ring),5.97 (tt, J=10.0,7.3Hz,1H,H on double bond),5.18 (dddt, J=25.0,10.0,5.0Hz,2H,H on double bond),4.21 (dt, J=5.0,1.0Hz,2H,H of methylene),3.24 (s,3H,H of methyl);

[0049] S3, adding 50g chitosan to 1.5L 2wt% acetic acid solution to dissolve and cooling to 2°C, then adding 75g methacrylic anhydride thereto, continuing constant temperature stirring for 26h, after the reaction is completed, adding ethanol thereto until no precipitation is produced, filtering, washing with ethanol, and drying to obtain pretreated chitosan;

[0050] S4, in N 2 Under the atmosphere, 100 g of the compound represented by formula I in step S2 and 50 g of the pretreated chitosan in step S3 were mixed and dispersed in 5 L of deionized water, the temperature was raised to 85 ° C, 5 g of potassium persulfate was added thereto, and stirring was continued for 1.5 h. After the reaction was completed, centrifugation, filtration, and drying were performed to obtain isothiazole-modified chitosan.

[0051] Preparation Example 2

[0052] The preparation method of isothiazole-modified chitosan is the same as that of Preparation Example 1, except that the amount of benzisothiazolinone is 0.5 mol.

[0053] Preparation Example 3

[0054] The preparation method of isothiazole-modified chitosan is the same as that of Preparation Example 1, except that the amount of methacrylic anhydride is 85 g.

[0055] Preparation Example 4

[0056] The preparation method of isothiazole-modified chitosan is the same as that of Preparation Example 1, except that the amount of methacrylic anhydride is 65 g.

[0057] Preparation Example 5

[0058] The preparation method of isothiazole-modified chitosan is the same as that of Preparation Example 1, except that the amount of pretreated chitosan in step S4 is 40 g.

[0059] Preparation Example 6

[0060] The preparation method of isothiazole-modified chitosan is the same as that of Preparation Example 1, except that the amount of pretreated chitosan in step S4 is 60 g.

[0061] Example 1

[0062] An isothiazole composite fungicide comprises the following components in parts by weight: 15 parts of 5-chloro-2-methyl-4-isothiazoline-3-one and 10 parts of isothiazole-modified chitosan.

[0063] Wherein, the isothiazole-modified chitosan is prepared by Preparation Example 1.

[0064] The preparation method of isothiazole composite fungicide comprises the following steps: 5-chloro-2-methyl-4-isothiazoline-3-one and isothiazole-modified chitosan are mixed to obtain the isothiazole composite fungicide.

[0065] Example 2

[0066] An isothiazole composite fungicide comprises the following components in parts by weight: 10 parts of 5-chloro-2-methyl-4-isothiazoline-3-one and 5 parts of isothiazole-modified chitosan.

[0067] Wherein, the isothiazole-modified chitosan is prepared by Preparation Example 1.

[0068] The preparation method of isothiazole composite fungicide comprises the following steps: 5-chloro-2-methyl-4-isothiazoline-3-one and isothiazole-modified chitosan are mixed to obtain the isothiazole composite fungicide.

[0069] Example 3

[0070] An isothiazole composite fungicide comprises the following components in parts by weight: 20 parts of 5-chloro-2-methyl-4-isothiazoline-3-one and 15 parts of isothiazole-modified chitosan.

[0071] Wherein, the isothiazole-modified chitosan is prepared by Preparation Example 1.

[0072] The preparation method of isothiazole composite fungicide comprises the following steps: 5-chloro-2-methyl-4-isothiazoline-3-one and isothiazole-modified chitosan are mixed to obtain the isothiazole composite fungicide.

[0073] Example 4

[0074] An isothiazole composite fungicide and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the isothiazole-modified chitosan is prepared by Preparation Example 2.

[0075] Example 5

[0076] An isothiazole composite fungicide and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the isothiazole-modified chitosan is prepared by Preparation Example 3.

[0077] Example 6

[0078] An isothiazole composite fungicide and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the isothiazole-modified chitosan is prepared by Preparation Example 4.

[0079] Example 7

[0080] An isothiazole composite fungicide and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the isothiazole-modified chitosan is prepared by Preparation Example 5.

[0081] Example 8

[0082] An isothiazole composite fungicide and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the isothiazole-modified chitosan is prepared by Preparation Example 6.

[0083] Comparative Example 1

[0084] An isothiazole composite fungicide and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal mass portion of carboxymethyl chitosan is used instead of isothiazole-modified chitosan.

[0085] Performance Test:

[0086] (1) Bactericidal performance: Tested with reference to the "Bactericide Performance Evaluation Method" SY / T5890-1993 and the "Determination Method of Bacteria and Algae in Industrial Circulating Cooling Water" GB-T14643.1-2009. Ca in circulating water 2+ :260mg / L,Mg 2+ :28mg / L,Cl – :760mg / L, HCO 3 - :210mg / L, SO4 2-- :220mg / L,Na + :265mg / L, sterilization time is 2h, temperature is 50℃, and dosage concentration is 20mg / L;

[0087] (2) Scale inhibition rate: Tested according to GB / T16632-2019 "Determination of scale inhibition performance of water treatment agents - Calcium carbonate deposition method", Ca 2+The mass concentration is 6800mg / L, SO4 2- The mass concentration is 7100 mg / L, the solution pH is 7, the experimental temperature is 50°C, the temperature is kept constant for 6 hours, and the scale inhibition rate is calculated according to the formula disclosed in the standard;

[0088] The isothiazole composite fungicides of the embodiments and comparative examples were tested according to the above test method, and the results are shown in Table 1.

[0089] Table 1

[0090]

[0091]

[0092] According to the above results, it is found that the isothiazole composite fungicide of Examples 1 to 3 has good corrosion inhibition and scale inhibition efficiency and sterilization efficiency; in Example 4, due to the change in the molar ratio of cyanuric chloride and benzisothiazolinone, the scale inhibition efficiency of the isothiazole composite fungicide is reduced. The reason may be that the content of the antibacterial structure in the isothiazole-modified chitosan is reduced, and the microbial sterilization ability on the surface of the equipment is slightly worse, resulting in a small amount of microbial mud. In Example 5, due to the change in the mass ratio of chitosan and methacrylic anhydride, the cross-linking density of the isothiazole-modified chitosan is too increased, and the stability is poor, resulting in a decrease in the scale inhibition rate of the fungicide; in Example 6, due to the change in the mass ratio of chitosan and methacrylic anhydride, the Due to the change in the mass ratio of the compound shown in Formula I and the pretreated chitosan, the cross-linking density of the isothiazole-modified chitosan is reduced, and the adhesion ability is weakened, resulting in a decrease in the scale inhibition rate of the bactericide; in Example 7, due to the change in the mass ratio of the compound shown in Formula I and the pretreated chitosan, the cross-linking density of the isothiazole-modified chitosan is reduced, and the adhesion ability is weakened, resulting in a decrease in the scale inhibition rate of the bactericide; in Comparative Example 1, due to the use of equal mass parts of carboxymethyl chitosan instead of isothiazole-modified chitosan, the sterilization performance and scale inhibition performance of the isothiazole composite bactericide are reduced.

[0093] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. An isothiazole composite fungicide, characterized in that: The invention comprises the following components by weight: 10 to 20 parts of isothiazole fungicides and 5 to 15 parts of isothiazole-modified chitosan.

2. The isothiazole composite fungicide according to claim 1, characterized in that: The isothiazole fungicide is one or more of 5-chloro-2-methyl-4-isothiazoline-3-one, 2-methyl-4-isothiazoline-3-one, 1,2-benzisothiazolinone, 2-butyl-1,2-benzisothiazolin-3-one and 2-methyl-1,2-benzisothiazolin-3-one.

3. The isothiazole composite fungicide according to claim 1, characterized in that: The preparation method of the isothiazole-modified chitosan comprises the following steps: S1. Mix cyanuric chloride and an acid binding agent and add them to N,N-dimethylformamide, and dropwise add a diluted solution of benzisothiazolinone in N,N-dimethylformamide. After the dropwise addition is complete, heat the mixture to 75-85° C. and stir at a constant temperature for 4-6 hours. After the reaction is completed, cool the mixture to room temperature, extract, combine the organic phases, and concentrate and dry under reduced pressure to obtain compound A. S2, compound A and sodium bicarbonate in step S1 are mixed and added with methanol, and a methanol dilution of diallylamine is added dropwise, and after the addition is complete, the temperature is raised to 50-60° C. and stirred at a constant temperature for 20-24 hours. After the reaction is completed, the temperature is lowered to room temperature, extracted, concentrated and dried under reduced pressure, and subjected to column chromatography to obtain a compound of formula I S3, adding chitosan to an acetic acid solution to dissolve and cooling to 0-5°C, then adding methacrylic anhydride thereto, continuing constant temperature stirring for 25-26 hours, and after the reaction is completed, adding ethanol thereto until no precipitation is produced, filtering, washing with ethanol, and drying to obtain pretreated chitosan; S4. Under an inert protective gas atmosphere, mix the compound represented by formula I in step S2 and the pretreated chitosan in step S3, add deionized water to disperse, heat to 80-90° C., add an initiator, continue stirring for 1-2 hours, centrifuge after the reaction, filter, and dry to obtain isothiazole-modified chitosan.

4. The isothiazole composite fungicide according to claim 3, characterized in that: In step S1, the acid binding agent is any one of sodium bicarbonate, potassium bicarbonate, sodium carbonate and potassium carbonate.

5. The isothiazole composite fungicide according to claim 3, characterized in that: In step S1, the molar ratio of cyanuric chloride to benzisothiazolinone is 1:(1.9-2).

6. The isothiazole composite fungicide according to claim 3, characterized in that: In step S2, the molar ratio of compound A to diallylamine is 1:(1-1.2).

7. The isothiazole composite fungicide according to claim 3, characterized in that: In step S3, the mass ratio of chitosan to methacrylic anhydride is 1:(1-2).

8. The isothiazole composite fungicide according to claim 3, characterized in that: In step S4, the mass ratio of the compound represented by formula I to the pretreated chitosan is 1:(0.4-0.6).

9. A method for preparing the isothiazole composite fungicide according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: mixing an isothiazole fungicide and isothiazole-modified chitosan to obtain an isothiazole composite fungicide.

10. Use of the isothiazole composite fungicide according to any one of claims 1 to 8 in circulating cooling water.

Images