The common method in the prior art is to copolymerize grease and polyurethane to make the grease have active groups so as to react with isocyanate, but the reaction temperature of ester exchange is between 240 ℃ and 260 ℃, and the energy consumption is high. Under such high temperature conditions, even if the nitrogen is used for protection, the color and luster of the product cannot be guaranteed, and the appearance of the product is influenced.
The existing fertilizer coating material utilizes modified vegetable oil of different methods as a part of reaction, the modification method is mainly an epoxidation method, and the main defects of the epoxidation method are as follows: in the epoxidation method, the separation of epoxide and non-double bond vegetable oil molecules is difficult, and the performance of the product is greatly influenced.
Chinese patent with publication number CN103304772A discloses a vegetable oil-based polyurethane coated controlled release fertilizer and a preparation method thereof, wherein the fertilizer is prepared by mixing vegetable oil polyol and isocyanate, and the prepared fertilizer has good controlled release effect. The technical scheme disclosed by the patent application has the following defects: there is no disclosure of a method for preparing polyol using vegetable oil, but the conventional method in the art is an epoxidation method. The main drawbacks of the epoxidation process are: the separation of the epoxide and the non-double bond vegetable oil molecules is difficult, the performance of the product is greatly influenced, the vegetable oil has large difference in quality batches, and the uncertainty of the quality can cause adverse effect on industrial production.
On the other hand, in the prior art, the fertilizer granules are coated with coating materials directly. In practice, it has been found that since fertilizer granules usually have edges and surface crystals, the edges and surface crystals are difficult to form into films during coating or are easy to break after film forming, resulting in the weakening of the sustained and controlled release effect of the finished product. The current major solution to this problem is to increase the amount of film-forming material, which in turn leads to increased production costs.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for preparing a degradable coating material by modifying vegetable oil through an ammonolysis method and application thereof, wherein the prepared coating material has better micropore air permeability and better degradable function; meanwhile, the surface of the fertilizer particles is modified before coating, so that the surface crystallization and edges and corners of the fertilizer particles are eliminated, the surface is smoother, and the coating effect is further improved.
The technical scheme for solving the technical problems of the invention is as follows:
the method for preparing the degradable coating material by modifying the vegetable oil by the ammonolysis method is characterized by comprising the following steps of:
preparing modified vegetable oil: under the protection of nitrogen, adding diethanolamine into vegetable oil, reacting for 20-40 min in a water bath at 40-60 ℃ under stirring to obtain modified vegetable oil, and cooling for later use; wherein the mass ratio of the vegetable oil to the diethanolamine is 100 (5-30);
(II) preparing a degradable coating material: respectively adding isocyanate and polyoxypropylene glycol into modified vegetable oil, reacting for 60-150 min under the condition of water bath at the temperature of 70-90 ℃, and cooling to 30-50 ℃; then adding diethylene glycol serving as a chain extender and stannous octoate serving as a catalyst, and reacting for 30-60 min under the condition of a water bath at 70-90 ℃; cooling to 30-50 ℃, adding N-methyldiethanolamine, and reacting for 40-90 min under the water bath condition of 70-90 ℃ to obtain the degradable coating material;
wherein the mass ratio of the modified vegetable oil to the isocyanate to the polyoxypropylene glycol to the diethylene glycol to the stannous octoate to the N-methyldiethanolamine is as follows: 100: (10-40): (70-110): (0.1-2): (0.1-3): (5-30).
The isocyanate is selected from one of PM200, PM400 and isophorone diisocyanate.
The vegetable oil comprises soybean oil, palm oil and castor oil.
The prepared degradable coating material is applied to fertilizer coating and is characterized in that:
(1) fertilizer particles are arranged in a roller, the temperature of the fertilizer particles is gradually heated to 40-50 ℃ from normal temperature under the rotation of the roller, urea-formaldehyde solution with the mass of 0.3-0.8% of the mass of the fertilizer particles is uniformly sprayed on the surfaces of the fertilizer particles in the gradual heating process, and the mass fraction of the solute of the urea-formaldehyde solution is 5-10%;
(2) and spraying and coating by using the prepared coating material, wherein the mass ratio of the fertilizer particles to the coating material is 100 (1-5).
Compared with the prior similar products or methods, the technical scheme of the invention has the following technical advantages:
the modified vegetable oil adopts ammonolysis reaction, and the hardness and the heat resistance of the generated product are both higher. The invention adopts ammonolysis reaction, is exothermic reaction, can recycle heat, and utilizes the waste heat in the process of preheating the fertilizer, thereby achieving the purpose of saving energy of the process.
The coating material prepared by the invention not only has the characteristics of preventing fertilizer from being instant after film forming and realizing slow controlled application, but also has the property of easy degradation.
According to the invention, a surface modification means of fertilizer particles is added, edges and surface crystals on the surfaces of the fertilizer particles are eliminated after treatment, so that the surfaces of the particles are smoother, the continuity and toughness of the coated film are better, the coating is more complete, the using amount of the film is reduced, and the production cost is reduced.
Detailed Description
The invention is further illustrated below with reference to examples and experimental data
Coating Material preparation example one
Preparing modified vegetable oil: under the protection of nitrogen, 20 g of diethanolamine is added into 100 g of soybean oil, the mixture is heated to 60 ℃ in a water bath, the reaction process is continuously stirred, the reaction is carried out for 20min, and the mixture is cooled for standby.
Preparing a coating material: adding 20 g of isophorone diisocyanate and 70 g of polyoxypropylene glycol into 100 g of modified vegetable oil, keeping the temperature to 70 ℃ in a water bath, reacting for 60min, and cooling to 30 ℃. Adding 0.2 g of chain extender diethylene glycol, then adding 0.15 g of stannous octoate catalyst, reacting for 30min in a water bath at 70 ℃, and cooling to 30 ℃. 10 g of N-methyldiethanolamine was added, and the reaction was carried out at 60 ℃ for 60 minutes.
Coating a film: firstly, urea particles are arranged in a roller, the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller, urea-formaldehyde solution with the mass of 0.4 percent of the mass of the fertilizer particles is uniformly sprayed on the surfaces of the urea particles in the gradual heating process, and the mass fraction of the solute of the urea-formaldehyde solution is 10 percent; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. The coated urea A1 is obtained.
Firstly, urea particles are arranged in a roller, and the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. To obtain coated urea B1.
Coated Material preparation example two
Preparing modified vegetable oil: under the protection of nitrogen, 20 g of diethanolamine is added into 100 g of soybean oil, the mixture is heated in a water bath to ensure that the temperature is 60 ℃, the reaction process is continuously stirred, the reaction is carried out for 30min, and the mixture is stopped and cooled for standby.
Preparing a coating material: 30 g of isophorone diisocyanate and 100 g of polyoxypropylene glycol are added into 100 g of modified vegetable oil, the temperature is kept to 80 ℃ in a water bath, the reaction is carried out for 90min, and the temperature is cooled to 50 ℃. Adding 0.2 g of chain extender diethylene glycol, then adding 0.15 g of stannous octoate catalyst, reacting for 40min in a water bath at 70 ℃, and cooling to 40 ℃.15 g of N-methyldiethanolamine were added and the reaction was carried out at 50 ℃ for 60 minutes.
Coating a film: firstly, urea particles are arranged in a roller, the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller, urea-formaldehyde solution with the mass of 0.4 percent of the mass of the fertilizer particles is uniformly sprayed on the surfaces of the urea particles in the gradual heating process, and the mass fraction of the solute of the urea-formaldehyde solution is 10 percent; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. The coated urea A2 is obtained.
Firstly, urea particles are arranged in a roller, and the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. To obtain coated urea B2.
Coating Material preparation example III
Preparing modified vegetable oil: under the protection of nitrogen, 10 g of diethanolamine amine is added into 100 g of soybean oil, water bath heating is carried out to ensure that the temperature is 40 ℃, the reaction process is continuously stirred, the reaction is carried out for 20min, and the mixture is stopped and cooled for standby.
Preparing a coating material: 20 g of isophorone diisocyanate and 80 g of polyoxypropylene glycol are added into 100 g of modified vegetable oil, the temperature is kept to 90 ℃ in a water bath, the reaction is carried out for 150min, and the temperature is cooled to 50 ℃. Adding 0.2 g of chain extender diethylene glycol, then adding 0.15 g of stannous octoate catalyst, reacting for 60min in a water bath at 70 ℃, and cooling to 50 ℃. 20 g of N-methyldiethanolamine were added and the reaction was carried out at 70 ℃ for 60 minutes.
Coating a film: firstly, urea particles are arranged in a roller, the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller, urea-formaldehyde solution with the mass of 0.4 percent of the mass of the fertilizer particles is uniformly sprayed on the surfaces of the urea particles in the gradual heating process, and the mass fraction of the solute of the urea-formaldehyde solution is 10 percent; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. The coated urea A3 is obtained.
Firstly, urea particles are arranged in a roller, and the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. To obtain coated urea B3.
Coating Material preparation example four
Preparing modified vegetable oil: under the protection of nitrogen, 10 g of diethanolamine is added into 100 g of soybean oil, water bath heating is carried out to ensure that the temperature is 40 ℃, the reaction process is continuously stirred, the reaction is carried out for 20min, and the mixture is stopped and cooled for standby.
Preparing a coating material: adding 25 g of isophorone diisocyanate and 100 g of polyoxypropylene glycol into 100 g of modified vegetable oil, keeping the temperature to 70 ℃ in a water bath, reacting for 60min, and cooling to 50 ℃. Adding 0.2 g of chain extender diethylene glycol, then adding 0.15 g of stannous octoate catalyst, reacting for 40min in a water bath at 70 ℃, and cooling to 30 ℃. Adding 25 g of N-methyldiethanolamine, and reacting at 30-70 ℃ for 60 minutes.
Coating a film: firstly, urea particles are arranged in a roller, the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller, urea-formaldehyde solution with the mass of 0.4 percent of the mass of the fertilizer particles is uniformly sprayed on the surfaces of the urea particles in the gradual heating process, and the mass fraction of the solute of the urea-formaldehyde solution is 10 percent; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. The coated urea A4 is obtained.
Firstly, urea particles are arranged in a roller, and the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. To obtain coated urea B4.
Coated Material preparation example five
The modified vegetable oil is obtained by an epoxidation method, benzene is used as a solvent, sulfuric acid is used as a catalyst, benzene, sulfuric acid, soybean oil and formic acid are mixed into a solution, hydrogen peroxide is dropwise added in the process of continuous stirring, after the completion, wastewater is refined and separated, the obtained modified vegetable oil is adjusted to be neutral by using a dilute alkali solution, an oil layer is distilled, benzene and water are removed, and the benzene is continuously condensed and separated for recycling. The mass ratio of soybean oil, formic acid, benzene and sulfuric acid is 100: 15:60:3.
Coating a film: firstly, urea particles are arranged in a roller, the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller, urea-formaldehyde solution with the mass of 0.4 percent of the mass of the fertilizer particles is uniformly sprayed on the surfaces of the urea particles in the gradual heating process, and the mass fraction of the solute of the urea-formaldehyde solution is 10 percent; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. The coated urea A5 is obtained.
Firstly, urea particles are arranged in a roller, and the temperature of the urea particles is gradually heated to 45 ℃ from normal temperature under the rotation of the roller; and then, spraying and coating are carried out by utilizing the prepared coating material, wherein the mass ratio of urea to the coating material is 100: 3. To obtain coated urea B5.
The obtained five parts of coated urea A1-A5 are respectively put into 500mL conical flasks and cultured in a constant-temperature water bath kettle, and the 24-hour nutrient release rate, the 28-day nutrient release rate and the 90-day nutrient release rate are detected and recorded by using a water dissolution method commonly used internationally. Meanwhile, the 28-day accumulated degradation rate of the film material is measured and calculated for the embodiment. The results are shown in Table 1.
Table 1: the nutrient release rate and the 28-day cumulative degradation rate of the coated urea A1-A5 are compared in a table.
When the above examples are compared comprehensively, the release rate of example 5 in 28 days exceeds 75%, and the release rate of the urea in a specified time can not reach the standard. In addition, the process flow of the embodiment 5 is complex, has great pollution to the environment, has poor product quality and is difficult to degrade. The other embodiments can ensure the release rate in different time periods, and simultaneously can regulate and control the dissolution time of the fertilizer in the membrane required by a customer by regulating and controlling the reaction time, the reaction temperature and the mass ratio of materials, wherein the membrane obtained under the reaction parameters in the embodiment 3 and the embodiment 4 has better effect.
Meanwhile, five parts of the coated urea A1-A5 and the coated urea B1-B5 are respectively put into 500mL conical flasks and cultured in a constant-temperature water bath kettle, and the nutrient release rate in 28 days is detected and recorded by using a water-soluble method commonly used internationally, and the results are shown in Table 2.
Table 2: a comparison of release rates for coated urea a and coated urea B28d is shown.
In examples 1 to 5, the release rate of the urea-formaldehyde solution 28d sprayed in the preheating stage is lower than that of the urea-formaldehyde solution sprayed directly on the coating material, which indicates that the coating material is more complete and better in coating performance after the urea-formaldehyde solution is sprayed, and the release rate of the fertilizer is effectively controlled, so that the coating effect is further improved by the method provided by the invention.