Coating material, preparation method thereof and application of coating material to coating agent for potassium chloride particles

Abstract

The invention belongs to the technical field of fertilizer manufacturing, and particularly relates to a coating material, a preparation method thereof and application of the coating material to a coating agent for potassium chloride particles. The preparation method of the coating material comprises the following steps: reacting liquid nitrile rubber with ethanol to prepare a nitrile rubber esterification intermediate; reacting the nitrile rubber esterification intermediate with hydrazine hydrate to prepare a nitrile rubber hydrazide product; reacting the nitrile rubber hydrazide product with the acylating chlorination polylactic acid to prepare modified polylactic acid; the modified polylactic acid reacts with tetrasodium iminodisuccinate and then is chelated with an inorganic metal trace element fertilizer to prepare the polylactic acid chelated metal trace element fertilizer, and a solution containing the polylactic acid chelated metal trace element fertilizer is used as a coating material, so that the release speed of the fertilizer can be effectively controlled, the impact resistance of a film is good, and meanwhile, the film can be applied to the field of organic fertilizers. Trace element fertilizer can be slowly released into the soil environment, and growth and development of plants are promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of fertilizer manufacturing, and specifically relates to a coating material, a preparation method thereof, and an application thereof as a coating agent for potassium chloride particles. Background Art

[0002] In the modern field of agriculture and forestry planting, the use of chemical fertilizers such as nitrogen fertilizers, phosphorus fertilizers, and potassium fertilizers has made great contributions to increasing the yield of crops. However, chemical fertilizers such as potassium chloride are easily lost with irrigation, rainwater, etc. due to their good water solubility, which not only causes waste of resources but also pollutes the water environment.

[0003] Chinese Patent CN102690142B discloses a production method of a slow-release granular potassium chloride fertilizer. The coating agent is prepared from linseed oil, glycerol, polyether, toluene diisocyanate, calcium naphthenate, xylene, methanol, cobalt naphthenate, lead naphthenate, and butanone oxime, that is, a polyurethane-based coating agent is formed. The polyurethane has poor degradation performance and is easy to pollute the environment. Poly(lactic acid) is made from starch extracted from renewable plant resources and is a new type of biodegradable material. Used as a coating agent for slow-release fertilizers, it has good biodegradability. However, poly(lactic acid) has problems of high brittleness and poor toughness. As a coating material for slow-release fertilizers, the film is easy to break, affecting the slow-release effect. "Study on the Preparation of Blended Modified Poly(lactic acid)-Based Films and Their Slow-Release Performance of Coated Fertilizers" published by Wang Congying et al. (Biochemical Engineering, Vol. 10, No. 2, April 2024) uses poly(lactic acid) as a raw material to prepare a biodegradable polymer film by blending and modifying with polyethylene glycol and poly(butylene succinate). The biomass ash residue and urea are mixed and prepared into spherical fertilizer cores, and the coated fertilizer particles are prepared by high-pressure spray coating the polymer film. The introduction of polyethylene glycol and poly(butylene succinate) can improve the elongation at break and impact strength of poly(lactic acid). However, polyethylene glycol, poly(butylene succinate) and poly(lactic acid) are physically blended, with poor compatibility and dispersion uniformity, and the toughening effect on poly(lactic acid) needs to be improved. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a coating material to solve the problem of poor slow-release effect caused by the high brittleness of the biodegradable coating material poly(lactic acid) in the prior art.

[0005] In order to achieve the above object, the technical scheme adopted by the present invention is as follows:

[0006] A preparation method of a coating material, comprising the following steps:

[0007] Step 1: Add liquid nitrile rubber and anhydrous ferric chloride to ethanol, ultrasonically mix, then heat to a set temperature, react, and after the reaction is completed, perform rotary evaporation and purification to obtain a nitrile rubber esterification intermediate;

[0008] Step 2: Add the nitrile rubber esterification intermediate into ethanol. After stirring and mixing, add the aqueous hydrazine hydrate solution and react. After the reaction is completed, perform rotary evaporation and purification to obtain the nitrile rubber hydrazide product;

[0009] Step 3: Dissolve polylactic acid in chloroform. Under nitrogen protection, add phosphorus trichloride dropwise. After the dropwise addition is completed, react. After the reaction is completed, precipitate, filter, wash, and dry to obtain acyl chloride-modified polylactic acid;

[0010] Dissolve the acyl chloride-modified polylactic acid in chloroform, add triethylamine and the nitrile rubber hydrazide product, react. After the reaction is completed, precipitate, filter, wash, and dry to obtain the modified polylactic acid;

[0011] Step 4: Disperse 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and tetrasodium iminodisuccinate (IDS) in a morpholineethanesulfonic acid (MES) buffer solution, stir, add N-hydroxysuccinimide (NHS), and continue stirring to obtain the graft modification solution;

[0012] Dissolve the modified polylactic acid in chloroform, add the graft modification solution, react. After the reaction is completed, obtain the grafted polylactic acid solution;

[0013] Step 5: Add an inorganic metal trace element fertilizer to the grafted polylactic acid solution, react. After the reaction is completed, obtain the coating material;

[0014] The coating material is a solution containing a polylactic acid chelated metal trace element fertilizer.

[0015] Preferably, in Step 1, the molar ratio of liquid nitrile rubber, anhydrous ferric chloride, and ethanol is 1:(1.5 - 2.5):(60 - 80), and the reaction conditions are to react in a closed reaction vessel at a set temperature for 4.5 - 5.5 h;

[0016] The reaction temperature is 115 - 125 °C.

[0017] Preferably, in Step 2, the molar ratio of the nitrile rubber esterification intermediate, hydrazine hydrate in the aqueous hydrazine hydrate solution, and ethanol is 1:(55 - 60):(50 - 70), and the reaction conditions are to reflux and react at a temperature of 85 - 95 °C for 3.5 - 4.5 h;

[0018] The aqueous hydrazine hydrate solution includes a 50 wt% aqueous hydrazine hydrate solution.

[0019] Preferably, in Step 3, when preparing the acyl chloride-modified polylactic acid, the mass ratio of polylactic acid, chloroform, and phosphorus trichloride is (50 - 60):(800 - 1200):(5 - 10), and the reaction conditions are to reflux and react at a temperature of 55 - 65 °C for 2.5 - 3.5 h.

[0020] Preferably, in the third step, when preparing the modified polylactic acid, the mass ratio of the acyl chloride polylactic acid, the hydrazide product of nitrile rubber, triethylamine, and chloroform is 60:(10.5 - 11):(1 - 2):(600 - 800), and the reaction conditions are to react at room temperature for 4 - 6 h.

[0021] Preferably, in the fourth step, the mass ratio of the modified polylactic acid, sodium iminodisuccinate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, chloroform, and morpholineethanesulfonic acid buffer solution is 70:(0.37 - 0.51):(7.8 - 9.3):(5.2 - 6.3):(800 - 1000):(300 - 450); the stirring conditions are to stir at a speed of 100 - 200 r / min at room temperature for 10 - 20 min, and the conditions for continuous stirring are to stir at a speed of 100 - 200 r / min at room temperature for 10 - 15 h, and the reaction conditions are to stir and react at room temperature for 1 - 2 h.

[0022] Preferably, in the fifth step, the mass ratio of the grafted polylactic acid solution to the inorganic metal trace element fertilizer is 100:(0.5 - 1), and the reaction conditions are to stir and react at room temperature for 10 - 15 h.

[0023] Preferably, the inorganic metal trace element fertilizer includes at least one of inorganic iron fertilizer, inorganic copper fertilizer, inorganic manganese fertilizer, and inorganic zinc fertilizer;

[0024] The inorganic iron fertilizer includes ferric chloride hexahydrate;

[0025] The inorganic copper fertilizer includes copper sulfate pentahydrate;

[0026] The inorganic manganese fertilizer includes manganese chloride tetrahydrate;

[0027] The inorganic zinc fertilizer includes zinc chloride monohydrate.

[0028] The present invention also discloses a coating material prepared by the preparation method of the coating material as described above.

[0029] An application of a coating material as described above as a coating agent for potassium chloride particles.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] In the present invention, using polylactic acid as the base material of the coating material can not only effectively extend the release time and rate of the fertilizer, but also has good biodegradability; by introducing nitrile rubber, the toughness of the polylactic acid material is improved, thereby improving the impact resistance of the film. By introducing the biodegradable chelating agent iminodisuccinic acid, inorganic metal trace element fertilizers can be chelated, improving the efficacy of the fertilizer and promoting the growth and development of plants.

[0032] In the present invention, liquid nitrile rubber reacts with ethanol under the catalysis of Lewis acid ferric chloride to convert the cyano group into a carboxylic acid ester group, obtaining a nitrile rubber esterification intermediate; then, through the hydrazinolysis reaction of the carboxylic acid ester group with hydrazine hydrate, the carboxylic acid ester group is converted into an acylhydrazide group, introducing a large number of amino groups onto the nitrile rubber molecule to obtain a nitrile rubber acylhydrazide product; the nitrile rubber acylhydrazide product reacts with the acyl chloride group at the end of the poly(lactic acid) chloride through the amino group, connecting the nitrile rubber molecule to the poly(lactic acid) molecule by a stable chemical bond (amide bond), realizing the toughening effect of nitrile rubber on poly(lactic acid) and obtaining modified poly(lactic acid).

[0033] Under the activation of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide, the carboxyl group on the sodium iminodisuccinate molecule can undergo a grafting reaction with the amino group on the modified poly(lactic acid) molecule to form an amide bond, bonding the chelating agent sodium iminodisuccinate to the poly(lactic acid) molecule. Further, through the chelating effect of iminodisuccinic acid on inorganic metal elements, a poly(lactic acid) chelated metal micronutrient fertilizer is prepared. Using the solution containing the poly(lactic acid) chelated metal micronutrient fertilizer as a coated fertilizer can not only effectively extend the release time and rate of the fertilizer, but also slowly release the micronutrient fertilizer into the soil environment for plant growth, promoting the growth and development of plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a process flow chart of the preparation of the poly(lactic acid) chelated metal micronutrient fertilizer in the present invention;

[0035] Figure 2 It is a bar chart of the toughness test results of the coating materials prepared in Examples 1-5 and Comparative Examples 1-2 of the present invention;

[0036] Figure 3 It is a bar chart of the potassium cumulative release rate test results of the coated potassium chloride prepared using the coating materials prepared in Example 1 and Comparative Examples 1-2 of the present invention as coating agents;

[0037] Figure 4 It is a bar chart of the copper ion cumulative release rate test results of the coated potassium chloride prepared using the coating materials prepared in Example 1 and Comparative Examples 1-2 of the present invention as coating agents. DETAILED DESCRIPTION OF THE INVENTION

[0038] Example 1

[0039] This example discloses a preparation method of a coating material, including the following steps:

[0040] Step 1. Liquid nitrile rubber and anhydrous ferric chloride are added to ethanol. The molar ratio of liquid nitrile rubber, anhydrous ferric chloride, and ethanol is 1:1.5:60. After ultrasonic mixing at a frequency of 50 kHz for 30 min, it is placed in a closed reaction vessel and heated to 115 °C at a heating rate of 5 °C / min, and the temperature of 115 °C is maintained for 5.5 h. After the reaction is completed, the unreacted ethanol is removed by rotary evaporation at 50 °C to obtain a reaction mixture. Ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 4 times that of ethanol are successively added to the reaction mixture for extraction to remove the inorganic phase. The extraction is repeated 2 times, and the organic phases are combined. Anhydrous magnesium sulfate is added to the organic phase for drying, and after filtration, the filtrate is rotary evaporated at 60 °C to remove ethyl acetate. The product is separated by silica gel column chromatography using V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber esterification intermediate;

[0041] Step 2. The nitrile rubber esterification intermediate is added to ethanol. After stirring and mixing at a speed of 300 r / min for 30 min, 50 wt% hydrazine hydrate aqueous solution is added. The molar ratio of the nitrile rubber esterification intermediate, hydrazine hydrate in the 50 wt% hydrazine hydrate aqueous solution, and ethanol is 1:55:50. The reaction is refluxed at 85 °C for 4.5 h. After the reaction is completed, ethanol is removed by rotary evaporation at 50 °C to obtain a reaction mixture. Ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 3.5 times that of ethanol are successively added to the reaction mixture, shaken, and after standing and separating layers, the upper organic phase is taken. Anhydrous magnesium sulfate is added to the organic phase for drying, and after filtration, the filtrate is rotary evaporated at 60 °C to remove ethyl acetate. The product is separated by silica gel column chromatography using V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber hydrazide product;

[0042] Step 3. Polylactic acid is dissolved in chloroform. Under nitrogen protection, phosphorus trichloride is added dropwise over a period of 40 min. The mass ratio of polylactic acid, chloroform, and phosphorus trichloride is 50:800:5. After the dropwise addition is completed, the reaction is refluxed at 55 °C for 3.5 h. After the reaction is completed, ethanol 5 times the mass of chloroform is added for precipitation, filtered, washed 3 times with ethanol, and dried in a vacuum drying oven at 60 °C for 24 h to obtain acyl chloride polylactic acid;

[0043] The acyl chloride polylactic acid is dissolved in chloroform, and triethylamine and the nitrile rubber hydrazide product are added. The mass ratio of acyl chloride polylactic acid, nitrile rubber hydrazide product, triethylamine, and chloroform is 60:10.5:1:600. The reaction is carried out at room temperature for 4 h. After the reaction is completed, ethanol 5 times the mass of chloroform is added for precipitation, filtered, washed 3 times with ethanol, and dried in a vacuum drying oven at 60 °C for 24 h to obtain modified polylactic acid;

[0044] Step 4: Disperse 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and sodium iminodisuccinate in morpholineethanesulfonic acid buffer solution, stir at a speed of 100 r / min at room temperature for 20 min to activate the carboxyl groups in sodium iminodisuccinate, add N-hydroxysuccinimide, and continue to stir at a speed of 100 r / min at room temperature for 15 h to fully activate the carboxyl groups, obtaining a graft-modified solution;

[0045] Dissolve the modified polylactic acid in chloroform, add the graft-modified solution, stir and react at a speed of 150 r / min at room temperature for 1 h to obtain a grafted polylactic acid solution;

[0046] Among them, the mass ratio of the modified polylactic acid, sodium iminodisuccinate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, chloroform, and morpholineethanesulfonic acid buffer solution is 70:0.37:7.8:5.2:800:300;

[0047] Step 5: Add copper sulfate pentahydrate to the grafted polylactic acid solution, and the mass ratio of the grafted polylactic acid solution to copper sulfate pentahydrate is 100:0.5. Stir and react at a speed of 150 r / min at room temperature for 10 h. After the reaction is completed, a coating material is obtained;

[0048] The coating material is a solution containing a polylactic acid chelated metal microelement fertilizer.

[0049] Example 2

[0050] This example discloses a preparation method of a coating material, including the following steps:

[0051] Step 1: Add liquid nitrile rubber and anhydrous ferric chloride to ethanol. The molar ratio of liquid nitrile rubber, anhydrous ferric chloride, and ethanol is 1:2.5:80. After ultrasonic mixing at a frequency of 50 kHz for 30 min, place it in a closed reaction vessel, heat it up to 125 °C at a heating rate of 5 °C / min, maintain the temperature of 125 °C for reaction for 4.5 h. After the reaction is completed, rotary evaporate the unreacted ethanol at a temperature of 50 °C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 4 times that of ethanol to the reaction mixture for extraction, remove the inorganic phase, repeat the extraction 2 times, combine the organic phases, add anhydrous magnesium sulfate to the organic phase for drying, filter, rotary evaporate the ethyl acetate from the filtrate at a temperature of 60 °C, and separate the product by silica gel column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber esterification intermediate;

[0052] Step 2: Add the nitrile rubber esterification intermediate into ethanol, stir and mix at a speed of 300 r / min for 30 min, then add 50 wt% hydrazine hydrate aqueous solution. The molar ratio of the nitrile rubber esterification intermediate, hydrazine hydrate in the 50 wt% hydrazine hydrate aqueous solution, and ethanol is 1:60:70. Carry out reflux reaction at 95 °C for 3.5 h. After the reaction is completed, rotary evaporate to remove ethanol at 50 °C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 3.5 times that of ethanol to the reaction mixture in sequence, shake, and after standing and separating layers, take the upper organic phase. Add anhydrous magnesium sulfate to the organic phase for drying, filter, and rotary evaporate the filtrate to remove ethyl acetate at 60 °C. The product is separated by silica gel column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain the nitrile rubber hydrazide product;

[0053] Step 3: Dissolve polylactic acid in chloroform, under nitrogen protection, dropwise add phosphorus trichloride, and the dropping time is 60 min. The mass ratio of polylactic acid, chloroform, and phosphorus trichloride is 60:1200:10. After the dropping is completed, carry out reflux reaction at 65 °C for 2.5 h. After the reaction is completed, add ethanol with a mass 5 times that of chloroform for precipitation, filter, wash with ethanol 3 times, and place in a vacuum drying oven at 60 °C for drying for 24 h to obtain acyl chloride polylactic acid;

[0054] Dissolve acyl chloride polylactic acid in chloroform, add triethylamine and the nitrile rubber hydrazide product. The mass ratio of acyl chloride polylactic acid, the nitrile rubber hydrazide product, triethylamine, and chloroform is 60:11:2:800. React at room temperature for 6 h. After the reaction is completed, add ethanol with a mass 5 times that of chloroform for precipitation, filter, wash with ethanol 3 times, and place in a vacuum drying oven at 60 °C for drying for 24 h to obtain modified polylactic acid;

[0055] Step 4: Disperse 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and sodium iminodisuccinate in morpholineethanesulfonic acid buffer solution, stir at a speed of 200 r / min at room temperature for 10 min to activate the carboxyl group in sodium iminodisuccinate, add N-hydroxysuccinimide, and continue to stir at a speed of 200 r / min at room temperature for 10 h to fully activate the carboxyl group to obtain a graft modification solution;

[0056] Dissolve modified polylactic acid in chloroform, add the graft modification solution, and stir and react at a speed of 100 r / min at room temperature for 2 h to obtain a grafted polylactic acid solution;

[0057] Among them, the mass ratio of modified polylactic acid, sodium iminodisuccinate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, chloroform, and morpholineethanesulfonic acid buffer solution is 70:0.51:9.3:6.3:1000:450;

[0058] Step 5: Add copper sulfate pentahydrate to the grafted polylactic acid solution. The mass ratio of the grafted polylactic acid solution to copper sulfate pentahydrate is 100:1. Stir and react at room temperature at a speed of 150 r / min for 15 h. After the reaction, a coating material is obtained.

[0059] The coating material is a solution containing a polylactic acid chelated metal micronutrient fertilizer.

[0060] Example 3

[0061] This example discloses a preparation method of a coating material, including the following steps:

[0062] Step 1: Add liquid nitrile rubber and anhydrous ferric chloride to ethanol. The molar ratio of liquid nitrile rubber, anhydrous ferric chloride, and ethanol is 1:1.8:65. After ultrasonic mixing at a frequency of 50 kHz for 30 min, place it in a sealed reaction vessel and heat it to 120 °C at a heating rate of 5 °C / min. Maintain the temperature of 120 °C for 5 h. After the reaction, rotate and evaporate the unreacted ethanol at a temperature of 50 °C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 4 times that of ethanol to the reaction mixture in sequence for extraction to remove the inorganic phase. Repeat the extraction 2 times, combine the organic phases, add anhydrous magnesium sulfate to the organic phases for drying, filter, and rotate and evaporate the ethyl acetate from the filtrate at a temperature of 60 °C. The product is separated by silica gel column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber esterification intermediate.

[0063] Step 2: Add the nitrile rubber esterification intermediate to ethanol. After stirring and mixing at a speed of 300 r / min for 30 min, add a 50 wt% hydrazine hydrate aqueous solution. The molar ratio of the nitrile rubber esterification intermediate, hydrazine hydrate in the 50 wt% hydrazine hydrate aqueous solution, and ethanol is 1:56:55. Reflux and react at a temperature of 90 °C for 4 h. After the reaction, rotate and evaporate the ethanol at a temperature of 50 °C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 3.5 times that of ethanol to the reaction mixture in sequence, shake, and take the upper organic phase after standing and separating layers. Add anhydrous magnesium sulfate to the organic phase for drying, filter, and rotate and evaporate the ethyl acetate from the filtrate at a temperature of 60 °C. The product is separated by silica gel column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber acylhydrazide product.

[0064] Step 3: Dissolve polylactic acid in chloroform. Under nitrogen protection, add phosphorus trichloride dropwise for 45 minutes. The mass ratio of polylactic acid, chloroform, and phosphorus trichloride is 52:900:6. After the dropwise addition, reflux and react at 60 °C for 3 hours. After the reaction is completed, add ethanol five times the mass of chloroform for precipitation, filter, wash with ethanol three times, and dry in a vacuum drying oven at 60 °C for 24 hours to obtain acyl-chlorinated polylactic acid;

[0065] Dissolve acyl-chlorinated polylactic acid in chloroform, add triethylamine and the hydrazide product of nitrile rubber. The mass ratio of acyl-chlorinated polylactic acid, the hydrazide product of nitrile rubber, triethylamine, and chloroform is 60:10.6:1.2:650. React at room temperature for 5 hours. After the reaction is completed, add ethanol five times the mass of chloroform for precipitation, filter, wash with ethanol three times, and dry in a vacuum drying oven at 60 °C for 24 hours to obtain modified polylactic acid;

[0066] Step 4: Disperse 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and tetrasodium iminodisuccinate in a morpholineethanesulfonic acid buffer solution. Stir at a speed of 150 r / min at room temperature for 15 minutes to activate the carboxyl group in tetrasodium iminodisuccinate. Add N-hydroxysuccinimide and continue to stir at a speed of 150 r / min at room temperature for 12 hours to fully activate the carboxyl group to obtain a graft-modified solution;

[0067] Dissolve modified polylactic acid in chloroform, add the graft-modified solution, and stir and react at a speed of 120 r / min at room temperature for 1.5 hours to obtain a grafted polylactic acid solution;

[0068] Among them, the mass ratio of modified polylactic acid, tetrasodium iminodisuccinate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, chloroform, and morpholineethanesulfonic acid buffer solution is 70:0.41:8:5.4:850:340;

[0069] Step 5: Add copper sulfate pentahydrate to the grafted polylactic acid solution. The mass ratio of the grafted polylactic acid solution to copper sulfate pentahydrate is 100:0.6. Stir and react at a speed of 150 r / min at room temperature for 12 hours. After the reaction is completed, obtain a coating material;

[0070] The coating material is a solution containing a polylactic acid chelated metal micronutrient fertilizer.

[0071] Example 4

[0072] This example discloses a preparation method of a coating material, including the following steps:

[0073] Step 1: Add liquid nitrile rubber and anhydrous ferric chloride into ethanol. The molar ratio of liquid nitrile rubber, anhydrous ferric chloride, and ethanol is 1:2:70. After ultrasonic mixing at a frequency of 50 kHz for 30 min, place it in a sealed reaction vessel and heat it to 120 °C at a heating rate of 5 °C / min. Maintain the temperature of 120 °C for 5 h. After the reaction is completed, rotary evaporate the unreacted ethanol at 50 °C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 4 times that of ethanol to the reaction mixture for extraction to remove the inorganic phase. Repeat the extraction 2 times, combine the organic phases, add anhydrous magnesium sulfate to the organic phase for drying, filter, and rotary evaporate the ethyl acetate from the filtrate at 60 °C. The product is separated by silica gel column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber esterification intermediate;

[0074] Step 2: Add the nitrile rubber esterification intermediate into ethanol. After stirring and mixing at a speed of 300 r / min for 30 min, add 50 wt% hydrazine hydrate aqueous solution. The molar ratio of the nitrile rubber esterification intermediate, hydrazine hydrate in the 50 wt% hydrazine hydrate aqueous solution, and ethanol is 1:57.5:60. Reflux and react at 90 °C for 4 h. After the reaction is completed, rotary evaporate the ethanol at 50 °C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 3.5 times that of ethanol to the reaction mixture, shake it, and take the upper organic phase after standing and separating. Add anhydrous magnesium sulfate to the organic phase for drying, filter, and rotary evaporate the ethyl acetate from the filtrate at 60 °C. The product is separated by silica gel column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber hydrazide product;

[0075] Step 3: Dissolve polylactic acid in chloroform. Under nitrogen protection, dropwise add phosphorus trichloride over a period of 45 min. The mass ratio of polylactic acid, chloroform, and phosphorus trichloride is 55:1000:7.5. After the addition is completed, reflux and react at 60 °C for 3 h. After the reaction is completed, add ethanol with a volume 5 times that of chloroform for precipitation, filter, wash it 3 times with ethanol, and dry it in a 60 °C vacuum drying oven for 24 h to obtain acyl chloride polylactic acid;

[0076] Dissolve the acyl chloride polylactic acid in chloroform, add triethylamine and the nitrile rubber hydrazide product. The mass ratio of the acyl chloride polylactic acid, the nitrile rubber hydrazide product, triethylamine, and chloroform is 60:10.8:1.5:700. React at room temperature for 5 h. After the reaction is completed, add ethanol with a volume 5 times that of chloroform for precipitation, filter, wash it 3 times with ethanol, and dry it in a 60 °C vacuum drying oven for 24 h to obtain modified polylactic acid;

[0077] Step 4: Disperse 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and tetrasodium iminodisuccinate in morpholineethanesulfonic acid buffer solution. Stir at a speed of 150 r / min at room temperature for 15 min to activate the carboxyl groups in tetrasodium iminodisuccinate. Add N-hydroxysuccinimide and continue to stir at a speed of 150 r / min at room temperature for 12.5 h to fully activate the carboxyl groups, obtaining a graft-modified solution;

[0078] Dissolve the modified polylactic acid in chloroform, add the graft-modified solution, and stir and react at a speed of 120 r / min at room temperature for 1.5 h to obtain a grafted polylactic acid solution;

[0079] Among them, the mass ratio of the modified polylactic acid, tetrasodium iminodisuccinate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, chloroform, and morpholineethanesulfonic acid buffer solution is 70:0.44:8.3:5.7:900:370;

[0080] Step 5: Add copper sulfate pentahydrate to the grafted polylactic acid solution. The mass ratio of the grafted polylactic acid solution to copper sulfate pentahydrate is 100:0.75. Stir and react at a speed of 150 r / min at room temperature for 12 h. After the reaction ends, obtain a coating material;

[0081] The coating material is a solution containing a polylactic acid chelated metal micronutrient fertilizer.

[0082] Example 5

[0083] This example discloses a preparation method of a coating material, including the following steps:

[0084] Step 1: Add liquid nitrile rubber and anhydrous ferric chloride to ethanol. The molar ratio of liquid nitrile rubber, anhydrous ferric chloride, and ethanol is 1:2.3:75. After ultrasonic mixing at a frequency of 50 kHz for 30 min, place it in a closed reaction vessel and heat it to 120 °C at a heating rate of 5 °C / min, and maintain the temperature of 120 °C for 5 h. After the reaction ends, rotary evaporate the unreacted ethanol at a temperature of 50 °C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 4 times that of ethanol to the reaction mixture for extraction to remove the inorganic phase. Repeat the extraction 2 times, combine the organic phases, add anhydrous magnesium sulfate to the organic phase for drying, filter, rotary evaporate the ethyl acetate from the filtrate at a temperature of 60 °C, and separate the product by silica column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber esterification intermediate;

[0085] Step 2: Add the nitrile rubber esterification intermediate into ethanol, stir and mix at a speed of 300 r / min for 30 min, then add 50 wt% hydrazine hydrate aqueous solution. The molar ratio of the nitrile rubber esterification intermediate, hydrazine hydrate in the 50 wt% hydrazine hydrate aqueous solution, and ethanol is 1:59:65. Carry out reflux reaction at 90 °C for 4 h. After the reaction is completed, rotary evaporate to remove ethanol at 50 °C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 3.5 times that of ethanol to the reaction mixture in sequence, shake, and take the upper organic phase after standing and separating layers. Add anhydrous magnesium sulfate to the organic phase for drying, filter, and rotary evaporate the filtrate to remove ethyl acetate at 60 °C. The product is separated by silica gel column chromatography using V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain the nitrile rubber hydrazide product;

[0086] Step 3: Dissolve polylactic acid in chloroform, under nitrogen protection, dropwise add phosphorus trichloride, and the dropping time is 45 min. The mass ratio of polylactic acid, chloroform, and phosphorus trichloride is 58:1100:9. After dropping is completed, carry out reflux reaction at 60 °C for 3 h. After the reaction is completed, add ethanol with a mass 5 times that of chloroform for precipitation, filter, wash with ethanol 3 times, and dry in a vacuum drying oven at 60 °C for 24 h to obtain acyl chloride polylactic acid;

[0087] Dissolve the acyl chloride polylactic acid in chloroform, add triethylamine and the nitrile rubber hydrazide product. The mass ratio of the acyl chloride polylactic acid, the nitrile rubber hydrazide product, triethylamine, and chloroform is 60:10.9:1.8:750. React at room temperature for 5 h. After the reaction is completed, add ethanol with a mass 5 times that of chloroform for precipitation, filter, wash with ethanol 3 times, and dry in a vacuum drying oven at 60 °C for 24 h to obtain modified polylactic acid;

[0088] Step 4: Disperse 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and sodium iminodisuccinate in morpholineethanesulfonic acid buffer solution, stir at a speed of 150 r / min at room temperature for 15 min to activate the carboxyl group in sodium iminodisuccinate, add N-hydroxysuccinimide, and continue to stir at a speed of 150 r / min at room temperature for 13 h to fully activate the carboxyl group to obtain a graft modification solution;

[0089] Dissolve the modified polylactic acid in chloroform, add the graft modification solution, and stir and react at a speed of 120 r / min at room temperature for 1.5 h to obtain a grafted polylactic acid solution;

[0090] Among them, the mass ratio of the modified polylactic acid, sodium iminodisuccinate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, chloroform, and morpholineethanesulfonic acid buffer solution is 70:0.48:0.91:0.61:950:420;

[0091] Step Five: Add copper sulfate pentahydrate to the grafted polylactic acid solution. The mass ratio of the grafted polylactic acid solution to copper sulfate pentahydrate is 100:0.9. Stir and react at room temperature at a speed of 150 r / min for 12 h. After the reaction ends, a coating material is obtained.

[0092] The coating material is a solution containing polylactic acid chelated metal micronutrient fertilizer.

[0093] Comparative Example 1

[0094] This comparative example discloses a preparation method of a coating material, which includes the following steps:

[0095] Step One: Add liquid nitrile rubber and anhydrous ferric chloride to ethanol. The molar ratio of liquid nitrile rubber, anhydrous ferric chloride, and ethanol is 1:1.5:60. After ultrasonic mixing at a frequency of 50 kHz for 30 min, place it in a closed reaction vessel and heat it to 115°C at a heating rate of 5°C / min, and maintain the temperature of 115°C for reaction for 5.5 h. After the reaction ends, rotate and evaporate the unreacted ethanol at a temperature of 50°C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 4 times that of ethanol to the reaction mixture in sequence for extraction to remove the inorganic phase. Repeat the extraction 2 times, combine the organic phases, add anhydrous magnesium sulfate to the organic phase for drying, filter, and rotate and evaporate the ethyl acetate from the filtrate at a temperature of 60°C. The product is separated by silica gel column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber esterification intermediate.

[0096] Step Two: Add the nitrile rubber esterification intermediate to ethanol. After stirring and mixing at a speed of 300 r / min for 30 min, add a 50 wt% hydrazine hydrate aqueous solution. The molar ratio of the nitrile rubber esterification intermediate, hydrazine hydrate in the 50 wt% hydrazine hydrate aqueous solution, and ethanol is 1:55:50. Reflux and react at a temperature of 85°C for 4.5 h. After the reaction ends, rotate and evaporate the ethanol at a temperature of 50°C to obtain a reaction mixture. Add ethyl acetate with a volume 1.5 times that of ethanol and deionized water with a volume 3.5 times that of ethanol to the reaction mixture in sequence, shake, and take the upper organic phase after standing and separating layers. Add anhydrous magnesium sulfate to the organic phase for drying, filter, and rotate and evaporate the ethyl acetate from the filtrate at a temperature of 60°C. The product is separated by silica gel column chromatography with V ethyl acetate / V petroleum ether = 1:4 as the eluent to obtain a nitrile rubber hydrazide product.

[0097] Step 3: Dissolve polylactic acid in chloroform. Under nitrogen protection, add phosphorus trichloride dropwise for 40 min. The mass ratio of polylactic acid, chloroform, and phosphorus trichloride is 50:800:5. After the dropwise addition, reflux and react at 55 °C for 3.5 h. After the reaction, add ethanol five times the mass of chloroform for precipitation, filter, wash with ethanol three times, and dry in a vacuum drying oven at 60 °C for 24 h to obtain acyl chloride-modified polylactic acid;

[0098] Dissolve acyl chloride-modified polylactic acid in chloroform, add triethylamine and the hydrazide product of butadiene acrylonitrile rubber. The mass ratio of acyl chloride-modified polylactic acid, the hydrazide product of butadiene acrylonitrile rubber, triethylamine, and chloroform is 60:10.5:1:600. React at room temperature for 4 h. After the reaction, add ethanol five times the mass of chloroform for precipitation, filter, wash with ethanol three times, and dry in a vacuum drying oven at 60 °C for 24 h to obtain modified polylactic acid;

[0099] Step 4: Disperse sodium iminodisuccinate in morpholineethanesulfonic acid buffer solution and stir at room temperature at a speed of 100 r / min for 20 min to obtain a sodium iminodisuccinate solution;

[0100] Dissolve modified polylactic acid in chloroform, add the sodium iminodisuccinate solution, and stir at room temperature at a speed of 150 r / min for 1 h to obtain a mixed solution;

[0101] Among them, the mass ratio of modified polylactic acid, sodium iminodisuccinate, chloroform, and morpholineethanesulfonic acid buffer solution is 70:0.37:800:300;

[0102] Step 5: Add copper sulfate pentahydrate to the mixed solution. The mass ratio of the mixed solution to copper sulfate pentahydrate is 100:0.5. Stir at room temperature at a speed of 150 r / min for 10 h to obtain a coating material;

[0103] The coating material is a mixed solution of modified polylactic acid-sodium iminodisuccinate containing inorganic metal trace element fertilizer.

[0104] Comparative Example 2

[0105] This comparative example discloses a preparation method of a coating material, including the following steps:

[0106] Step 1: Dissolve polylactic acid and liquid butadiene acrylonitrile rubber in chloroform. The mass ratio of modified polylactic acid, sodium iminodisuccinate, and chloroform is 70:0.37:1100; to obtain a mixed solution;

[0107] Step 2: Add copper sulfate pentahydrate to the mixed solution. The mass ratio of the mixed solution to copper sulfate pentahydrate is 100:0.5. Stir at room temperature at a speed of 150 r / min for 10 h to obtain a coating material;

[0108] The coating material is a mixed solution of polylactic acid - liquid nitrile rubber containing inorganic metal trace element fertilizers.

[0109] In the above examples and comparative examples: The liquid nitrile rubber was purchased from Shenzhen Masni Elastomer Co., Ltd., product number: LNBR - 26, with an acrylonitrile content of 26% and a molecular weight of 10,000; the polylactic acid was L - polylactic acid, purchased from Shanghai Kanglang Biotechnology Co., Ltd., with a molecular weight of 60,000; the morpholineethanesulfonic acid buffer solution was purchased from Tianjin Bailuns Biotechnology Co., Ltd., model: 2×MES buffer solution, concentration: 0.1 mol / L, pH value: 6.0 ± 0.2.

[0110] Test Example

[0111] (1) Toughness test: The coating materials prepared in Examples 1 - 5 and Comparative Examples 1 - 2 were cast into films on a glass plate. After being placed at room temperature for 36 h, they were dried in a vacuum drying oven at 60 °C for 8 h to obtain films with a thickness of 0.06 mm. The elongation at break of the films was measured by referring to the method in Standard GB / T 1040.3 - 2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets". The test results are shown in Table 1:

[0112] Table 1

[0113]

[0114] As can be seen from Table 1, the coating materials prepared in the present invention have good toughness. By introducing nitrile rubber, the toughness of the polylactic acid material can be effectively improved. Compared with Example 1, in Comparative Example 2, since the nitrile rubber is not connected to the polylactic acid molecule by a stable chemical bond, the compatibility and dispersion uniformity with polylactic acid decrease, and the toughening effect on the polylactic acid film is reduced.

[0115] (2) Sustained - release performance: Granular potassium chloride (potassium content (calculated as K2O) ≥ 60%) was poured into a coating machine rotating at 10 r / min. The coating materials prepared in Example 1 and Comparative Examples 1 - 2 were evenly sprayed on the surface of the granular potassium chloride through a high - pressure spray gun, with a coating rate of 10%, to obtain coated potassium chloride. 10 g of the coated potassium chloride was weighed and placed in a dialysis bag, which was then immersed in 250 mL of deionized water and placed in a constant - temperature environment at 25 °C for extraction. At regular intervals (1 d, 3 d, 7 d, 14 d, 21 d, 28 d, 35 d, 42 d, 49 d, 56 d), the extraction solution was taken to measure the potassium oxide content and copper ion content therein. At the same time, the dialysis bag containing the coated potassium chloride was immersed in the next 250 mL of deionized water for continued extraction. The cumulative release rates of potassium (calculated as K2O) and copper ions (Cu 2+ ) are shown in Table 2:

[0116] Table 2

[0117]

[0118] As can be seen from Table 2, when the coating material prepared by the present invention is used as a coating agent to prepare coated potassium chloride, it has good slow-release performance, which can not only effectively extend the release time and rate of potassium, but also slowly release trace element fertilizers. Compared with Example 1, in Comparative Example 1, the release rate of potassium did not change significantly. However, since the iminodisuccinic acid chelated copper ions were not grafted onto the polylactic acid molecules, as the small molecule iminodisuccinic acid migrated in the polylactic acid, the release rate of copper ions increased. In Comparative Example 2, no grafting reaction occurred between nitrile rubber and polylactic acid, the toughening effect on polylactic acid was weakened, the brittleness of the film was enhanced, and it was prone to breakage. The release rate of potassium increased. At the same time, no chelation treatment was carried out on copper ions, and the release rate of copper ions increased significantly.

[0119] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a coating material, characterized in that: The following steps are involved: Step 1: adding liquid nitrile rubber and anhydrous ferric chloride into ethanol, mixing by ultrasonication, heating to a set temperature, reacting, and after the reaction is completed, rotary evaporation and purification are performed to obtain an esterified nitrile rubber intermediate; Step 2: adding the esterified nitrile rubber intermediate into ethanol, stirring and mixing, adding a hydrazine hydrate aqueous solution, reacting, and after the reaction is completed, rotary evaporation and purification to obtain a nitrile rubber hydrazide product; Step 3, dissolving polylactic acid in chloroform, adding phosphorus trichloride dropwise under nitrogen protection, reacting after the addition is complete, precipitating after the reaction is complete, filtering, washing, and drying to obtain chlorinated polylactic acid; The chlorinated polylactic acid is dissolved in chloroform, triethylamine and acyl hydrazide product of nitrile rubber are added, reacted, precipitated, filtered, washed and dried after the reaction is completed, and modified polylactic acid is obtained; Step 4: Disperse 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and tetrasodium iminodisuccinate in a morpholineethanesulfonic acid buffer solution, stir, add N-hydroxysuccinimide, continue stirring, and obtain a grafting modification solution; Dissolving the modified polylactic acid in chloroform, adding the grafting modification liquid, reacting, and obtaining a grafted polylactic acid solution after the reaction is completed; Step 5, adding inorganic metal trace element fertilizer to the grafted polylactic acid solution to react, and after the reaction is completed, obtaining a coating material; The coating material is a solution containing polylactic acid chelated metal trace element fertilizer.

2. The method for preparing a coating material according to claim 1, characterized in that: In the step 1, the molar ratio of liquid nitrile rubber, anhydrous ferric chloride and ethanol is 1:(1.5-2.5):(60-80), and the reaction conditions are in a closed reaction vessel at a set temperature for 4.5-5.5 hours; The reaction temperature is 115-125°C.

3. The method for preparing a coating material according to claim 1, characterized in that: In the step 2, the molar ratio of the nitrile rubber esterification intermediate, the hydrazine hydrate in the hydrazine hydrate aqueous solution, and the ethanol is 1:(55-60):(50-70), and the reaction conditions are reflux reaction at a temperature of 85-95° C. for 3.5-4.5 hours; The hydrazine hydrate aqueous solution includes a 50 wt % hydrazine hydrate aqueous solution.

4. The method for preparing a coating material according to claim 3, characterized in that: In the step 3, when preparing polylactic acid chlorination, the mass ratio of polylactic acid, chloroform and phosphorus trichloride is (50-60):(800-1200):(5-10), and the reaction conditions are reflux reaction at a temperature of 55-65°C for 2.5-3.5h.

5. The method for preparing a coating material according to claim 1, characterized in that: In the step 2 and the step 3, when preparing the modified polylactic acid, the mass ratio of the chlorinated polylactic acid, the hydrazide product of nitrile rubber, triethylamine and chloroform is 60:(10.5-11):(1-2):(600-800), and the reaction conditions are to react at room temperature for 4-6 hours.

6. The method for preparing a coating material according to claim 1, characterized in that: In the step 4, the mass ratio of modified polylactic acid, tetrasodium iminodisuccinate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, chloroform, and morpholineethanesulfonic acid buffer solution is 70:(0.37-0.51):(7.8-9.3):(5.2-6.3):(800-1000):(300-450); the stirring condition is stirring at room temperature at a speed of 100-200r / min for 10-20min, the condition for continuing stirring is stirring at room temperature at a speed of 100-200r / min for 10-15h, and the reaction condition is stirring the reaction at room temperature for 1-2h.

7. The method for preparing a coating material according to claim 1, characterized in that: In the step 5, the mass ratio of the grafted polylactic acid solution to the inorganic metal trace element fertilizer is 100:(0.5-1), and the reaction conditions are stirring the reaction at room temperature for 10-15 hours.

8. The method for preparing a coating material according to claim 7, characterized in that: The inorganic metal trace element fertilizer includes at least one of inorganic iron fertilizer, inorganic copper fertilizer, inorganic manganese fertilizer and inorganic zinc fertilizer; The inorganic iron fertilizer includes ferric chloride hexahydrate; The inorganic copper fertilizer includes copper sulfate pentahydrate; The inorganic manganese fertilizer includes manganous chloride tetrahydrate; The inorganic zinc fertilizer includes zinc chloride monohydrate.

9. A coating material prepared by the method for preparing a coating material according to any one of claims 1 to 8.

10. Use of the coating material as claimed in claim 9 in a coating agent for potassium chloride particles.

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