CN116375531A - Temperature-sensitive polyurethane coated controlled-release fertilizer and preparation method thereof - Google Patents
Temperature-sensitive polyurethane coated controlled-release fertilizer and preparation method thereof Download PDFInfo
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05C—NITROGENOUS FERTILISERS
- C05C9/00—Fertilisers containing urea or urea compounds
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05C—NITROGENOUS FERTILISERS
- C05C9/00—Fertilisers containing urea or urea compounds
- C05C9/005—Post-treatment
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
- C05G3/00—Mixtures of one or more fertilisers with additives not having a specially fertilising activity
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
- C05G3/00—Mixtures of one or more fertilisers with additives not having a specially fertilising activity
- C05G3/40—Mixtures of one or more fertilisers with additives not having a specially fertilising activity for affecting fertiliser dosage or release rate; for affecting solubility
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
- C05G5/00—Fertilisers characterised by their form
- C05G5/10—Solid or semi-solid fertilisers, e.g. powders
- C05G5/12—Granules or flakes
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
- C05G5/00—Fertilisers characterised by their form
- C05G5/30—Layered or coated, e.g. dust-preventing coatings
- C05G5/37—Layered or coated, e.g. dust-preventing coatings layered or coated with a polymer
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
- C05G5/00—Fertilisers characterised by their form
- C05G5/30—Layered or coated, e.g. dust-preventing coatings
- C05G5/38—Layered or coated, e.g. dust-preventing coatings layered or coated with wax or resins
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P60/00—Technologies relating to agriculture, livestock or agroalimentary industries
- Y02P60/20—Reduction of greenhouse gas [GHG] emissions in agriculture, e.g. CO2
- Y02P60/21—Dinitrogen oxide [N2O], e.g. using aquaponics, hydroponics or efficiency measures
Abstract
The invention discloses a temperature-sensitive polyurethane coated controlled release fertilizer which comprises the following components in percentage by mass: 94-97 parts of large-particle urea; 0.38-0.96 part of polycaprolactone diol; 0.76-1.92 parts of polyether polyol; 0.84-2.11 parts of curing agent; 0.5-1 part of liquid paraffin, and also discloses a preparation method of the temperature-sensitive polyurethane coated controlled release fertilizer, which is suitable for the technical field of fertilizer controlled release, and has the advantages of simple production process, low production cost, long controlled release period, temperature change response performance and good degradability.
Description
Technical Field
The invention belongs to the technical field of fertilizer controlled release, and particularly relates to a temperature-sensitive polyurethane coated controlled release fertilizer and a preparation method thereof.
Background
The contribution rate of the fertilizer to the grain yield is about 40-60%, and plays a very important role in guaranteeing the grain safety. However, with the development of the fertilizer industry and the blind pursuit of crop yield by farmers, the production of fertilizers consumes a large amount of resources, and excessive fertilization also causes serious environmental problems. The controlled release fertilizer is developed and used, so that the fertilizer utilization efficiency can be improved, the resource consumption and carbon emission can be reduced, and the ecological environment can be improved. In particular in asian countries where the population is 60% of the world population, controlled release technology is considered to be the best means of optimizing fertilizer use. Through half century development, the controlled release fertilizer with excellent release performance has been developed, and is applied in farmland in a large scale, under the condition of fertilizer decrement, the grain yield can still be ensured, even the yield is increased, the fertilizer utilization rate is improved, and good agronomic, environmental and economic benefits are shown.
The Chinese is pushing a new green fertilizer research and development plan, and the accurate and intelligent release of fertilizer is a new hot spot for the research and development of controlled release fertilizer. Because the crop growth is influenced by environmental factors such as soil, temperature, microorganisms and the like, the environment-responsive intelligent controlled-release fertilizer is developed, and the nutrient release of the controlled-release fertilizer can be changed in response to the environmental factors. The root system, biomass and nitrogen absorption amount of crops are known to be positively correlated with the surface temperature, and if the release rate of the controlled release fertilizer nutrient can respond to the ground temperature of the crop nutrient in the rapid absorption period, the intelligent release is realized, and the release rate can be more accurately matched with the crop nutrient absorption rate.
Polydopamine is taken as a coating layer material, poly (N-isopropyl acrylamide) or poly (N, N-dimethylamino ethyl methacrylate) and other materials are grafted on the surface of the coating layer to form a double-layer coating, and the multi-element compound fertilizer is taken as a fertilizer core to prepare the temperature-sensitive coated controlled release fertilizer. The defects are that: (1) the fertilizer synthesis process is complex and the synthesis period is long; (2) the fertilizer core used by the fertilizer has limited selection and the application range is reduced; and polymer residues used in the synthesis process may also affect soil; (3) temperature sensitive fertilizers based on polydopamine are represented by that the response range of the polydopamine to the temperature cannot completely coincide with the actual environmental temperature change at present.
In the Chinese patent 'a temperature-responsive coated controlled release fertilizer and a preparation method thereof (application publication number: CN 113135793A)', biomass polyurethane is adopted as an inner layer, and biomass temperature-sensitive hydrogel is adopted as an outer layer membrane material, so that the double-layer coated temperature-responsive coated controlled release fertilizer is prepared, however, the preparation process of the fertilizer is complex, the raw materials and chemical additives are more, the energy consumption and the cost are higher, the outer layer temperature-sensitive acrylamide hydrogel belongs to a matrix type, the use amount is larger, and the large-area popularization on field crops is not facilitated.
In the preparation method of the degradable temperature-responsive sustained-release fertilizer coating material and the coating method thereof (publication No. CN 106589258B), temperature-responsive polyphosphate is adopted as the coating material, the raw material needs to be prepared for many times, the fertilizer process is complex, the coating material needs to be heated to a molten state and sprayed on the surface of fertilizer particles in a coating machine, the release mechanism is that release is carried out at low temperature, release is reduced at high temperature, and the release is not matched with the temperature (25-30 ℃) at which most crop nutrients are absorbed, so that the method is difficult to be practically applied.
In the Chinese patent application, polypropylene oxide and polyphenyl ether are adopted as temperature-sensitive coating materials to prepare the temperature-sensitive type slow-release coated fertilizer, wherein the temperature-sensitive type slow-release coated fertilizer is in a hydrophobic state at high temperature (more than 5 ℃), so that the nutrient release amount is reduced; the nutrient release amount is large because the nutrient is in a hydrophilic state at low temperature (5 ℃); contrary to the law that most crops have increased nutrient absorption when the temperature is increased, the method is only suitable for winter crops and vegetables, and has limited action range.
The temperature-sensitive polyurethane is a temperature-sensitive material widely adopted at present, and the polyurethane coated controlled release fertilizer is a current mainstream product, but the preparation of the temperature-sensitive coated controlled release fertilizer by taking the temperature-sensitive polyurethane polymer as a coating material is not reported at present.
In summary, the existing slow-release fertilizer has the following disadvantages:
(1) Most of the controlled release fertilizer nutrients are released with the rise of temperature, but the release is not controllable and cannot be accurately released according to the soil temperature.
(2) The existing polyethylene and other organic polymer membrane shells are slow to degrade in soil, and environmental pollution is easy to cause.
(3) The existing temperature-sensitive coated controlled release fertilizer has the defects that the core selection of the fertilizer used by the fertilizer is limited, the application range is small, the preparation process is complex, and the response range of most temperature-sensitive fertilizers to temperature cannot completely coincide with the actual environmental temperature change.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a temperature-sensitive polyurethane coated controlled release fertilizer and a preparation method thereof.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the temperature-sensitive polyurethane coated controlled release fertilizer comprises the following components in percentage by mass:
94-97 parts of large-particle urea;
0.38-0.96 part of polycaprolactone diol;
0.76-1.92 parts of polyether polyol;
0.84-2.11 parts of curing agent;
0.5 to 1 part of liquid paraffin.
Preferably, the particle size of the large-particle urea particles is 2-6 mm.
Preferably, the polycaprolactone diol has a molecular weight of 2000-3000 and a hydroxyl value of 56-37 KOH/g.
Preferably, the polyether polyol has a functionality of from 2 to 4.
Preferably, the polyether polyol comprises any one or a combination of at least two of polyethylene oxide polyol, polypropylene oxide polyol, polymer polyol or polytetrahydrofuran.
Preferably, the curing agent is liquefied MDI.
In a second aspect, a preparation method of the temperature-sensitive polyurethane coated controlled release fertilizer comprises the following steps:
s1, starting a Roots blower, wherein after air flow is buffered and balanced by a buffer tank, the air flow enters a fluidized bed after being heated by an electric heater, so that the temperature in the fluidized bed is ensured to be 85 ℃, and the fluidized bed is in a working state;
s2, adding the formula amount of large-particle urea into a fluidized bed through an inlet, preheating for 2 minutes, and then spraying the formula amount of liquid paraffin placed in a storage tank into the fluidized bed to pretreat the surface of the large-particle urea for 2 minutes;
s3, adding the formula amount of polycaprolactone diol, the formula amount of polyether polyol, the catalyst and the foaming agent into a fluidized bed, uniformly mixing, conveying the mixture to a nozzle to atomize the mixture to the surface of large-particle urea by using a peristaltic pump B, simultaneously adding the formula amount of curing agent, conveying the mixture to the nozzle by using the peristaltic pump B, and rapidly mixing the mixture with the reaction material of a storage tank A in the nozzle to atomize the mixture;
s4, atomizing the reaction material at the speed of 3g/min, operating for 15 minutes, stopping adding the reaction material, coating, and taking out the temperature-sensitive polyurethane coated controlled release fertilizer from an outlet, wherein the temperature-sensitive polyurethane coated controlled release fertilizer is preferably selected from the temperature-sensitive polyurethane coated controlled release fertilizer, wherein the mass ratio of the temperature-sensitive polyurethane to the liquid paraffin is 3-6%, the particle size of the fertilizer particles is 2-6 mm, and the mass-volume ratio of the fertilizer to the liquid paraffin is (450-500) (1-5) g/mL.
In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:
(1) In the invention, a layer of polycaprolactone diol (PCL) modified polyurethane material with temperature sensitivity is wrapped on the surface of the fertilizer particles, when the temperature is lower than the critical temperature, the modified polyurethane has no obvious change, and the fertilizer nutrient release is less; when the temperature is higher than the critical temperature, the modified polyurethane shows a bursting phenomenon, and fertilizer nutrients are dissolved and released outwards. Forming the modified polyurethane coated controlled release fertilizer with temperature responsiveness.
(2) According to the invention, the modified polyurethane prepared by selecting the polycaprolactone diol and the polyether polyol mixed in a specific molar ratio can adjust the temperature response performance of the modified polyurethane coated fertilizer according to the temperature of different crop nutrient absorption peaks, and can realize rapid release of nutrients at the temperature required by different crop nutrient release peaks.
(3) In the invention, the controlled release performance of the modified polyurethane coated controlled release fertilizer is regulated by regulating the difference of the molecular weight of polycaprolactone diol, and the release period range is wide and can be up to 1-6 months.
(4) The polycaprolactone diol modified polyurethane coated controlled release fertilizer with the temperature response characteristic has the advantages of simple production process, low production cost, long controlled release period, temperature change response performance and good degradability.
Drawings
FIG. 1 is a flow chart of a preparation method of a temperature-sensitive polyurethane coated controlled release fertilizer.
Reference numerals: 1. roots blower; 2. a buffer tank; 3. an electric heater; 4. a fluidized bed; 5. an empty inlet; 6. an outlet; 7. a melting furnace; 8. temperature-sensitive polyurethane coated controlled release fertilizer.
Detailed Description
The specific embodiment of the temperature-sensitive polyurethane coated controlled release fertilizer and the preparation method thereof are further described below with reference to fig. 1. The temperature-sensitive polyurethane coated controlled release fertilizer and the preparation method thereof are not limited to the descriptions of the following examples.
Example 1:
the embodiment of the temperature-sensitive polyurethane coated controlled release fertilizer comprises the following components in percentage by mass:
97 parts of large-particle urea;
0.96 parts of polycaprolactone diol;
1.92 parts of polyether polyol;
2.11 parts of liquefied MDI (curing agent);
1 part of liquid paraffin.
Wherein, the particle size of the large-particle urea particles is 6mm.
Wherein the polycaprolactone diol has a molecular weight of 3000 and a hydroxyl value of 37KOH/g.
Wherein the polyether polyol has a functionality of 4.
Wherein the polyether polyol is polytetrahydrofuran.
Example 2:
the embodiment of the temperature-sensitive polyurethane coated controlled release fertilizer comprises the following components in percentage by mass:
94 parts of large-particle urea;
0.38 parts of polycaprolactone diol;
0.76 parts of polyether polyol;
0.84 parts of liquefied MDI (curing agent);
0.5 part of liquid paraffin.
Wherein, the particle size of the large-particle urea particles is 2mm.
Wherein the polycaprolactone diol has a molecular weight of 2000 and a hydroxyl number of 56KOH/g.
Wherein the polyether polyol has a functionality of 2.
Wherein the polyether polyol is polyoxyethylene polyol.
Example 3:
the embodiment of the temperature-sensitive polyurethane coated controlled release fertilizer comprises the following components in percentage by mass:
95 parts of large-particle urea;
0.68 parts of polycaprolactone diol;
1.47 parts of polyether polyol;
1.45 parts of liquefied MDI (curing agent);
0.75 part of liquid paraffin.
Wherein, the particle size of the large-particle urea particles is 4mm.
Wherein the polycaprolactone diol has a molecular weight of 2500 and a hydroxyl value of 45KOH/g.
Wherein the polyether polyol has a functionality of 3.
Wherein the polyether polyol is polyoxypropylene polyol.
Example 4:
the embodiment of the preparation method of the temperature-sensitive polyurethane coated controlled release fertilizer is shown in fig. 1, and comprises the following steps:
s1, starting a Roots blower 1, enabling air flow to enter a fluidized bed 4 after being heated by an electric heater 3 after being buffered and balanced by a buffer tank 2, ensuring the temperature in the fluidized bed to be 85 ℃, and enabling the fluidized bed to be in a working state;
s2, adding the formula amount of large-particle urea into a fluidized bed through an inlet 5 to preheat for 2 minutes, and then spraying the formula amount of liquid paraffin placed in a storage tank 7 into the fluidized bed 4 to pretreat the surface of the large-particle urea for 2 minutes;
s3, adding the formula amount of polycaprolactone diol, the formula amount of polyether polyol, the catalyst and the foaming agent into the fluidized bed 4, uniformly mixing, conveying the mixture to a nozzle to atomize the mixture to the surface of the large-particle urea by using a peristaltic pump B, simultaneously adding the formula amount of curing agent, conveying the mixture to the nozzle by using the peristaltic pump B, and rapidly mixing the mixture with the reaction material of the storage tank A in the nozzle to atomize the mixture;
s4, atomizing the reaction material at the speed of 3g/min, operating for 15 minutes, stopping adding the reaction material, coating, and taking out the temperature-sensitive polyurethane coated controlled release fertilizer 8 from the outlet 6.
Wherein, in the temperature-sensitive polyurethane coated controlled release fertilizer, the mass ratio of the temperature-sensitive polyurethane is 3-6%, the particle size of the fertilizer particles is 2-6 mm, and the mass volume ratio of the fertilizer to the liquid paraffin is (450-500) (1-5) g/mL.
Example 5
The embodiment provides polyurethane coated urea with temperature sensitivity, and the preparation method comprises the following steps:
the temperature of the coating fluidized bed is controlled to be 80-85 ℃, and 1000g of large-particle urea is added according to the dosage of 7.11g of polycaprolactone diol with the molecular weight of 2000, 15.97g of polyether polyol and 17.12g of MDI, so that the large-particle urea is in a stable fluidized state. Then 8g of liquid paraffin is added, evenly mixed, and after 2 minutes, polycaprolactone diol/polyether polyol mixture and MDI are slowly dripped to prepare the polyurethane coated controlled release urea. The coating rate is 4%, the reaction time is about 20min, and the temperature-responsive modified polyurethane coated urea (PCRU 1) is prepared after the urea particles are completely coated.
Comparative example 1
The embodiment provides a modified polyurethane coated controlled release urea, which is prepared by the following steps:
the temperature of the coated fluidized bed is controlled to be 80-85 ℃, and 1000g of large-particle urea is added according to the dosage of 35.52g of polycaprolactone diol with the molecular weight of 2000 and 4.68g of MDI, so that the large-particle urea is in a stable fluidized state. Then adding 8g of liquid paraffin, uniformly mixing, and slowly dripping polycaprolactone diol and MDI after 2 minutes to prepare the polyurethane coated controlled release urea. The coating rate is 4%, the reaction time is about 20min, and the modified polyurethane coated urea (PCRU 2) is prepared after the urea particles are completely coated.
Comparative example 2
The embodiment provides a modified polyurethane coated controlled release urea, which is prepared by the following steps:
the temperature of the coated fluidized bed is controlled to be 80-85 ℃, and 1000g of large-particle urea is added according to the dosage of 36.98g of polycaprolactone diol with the molecular weight of 3000 and 3.22g of MDI, so that the large-particle urea is in a stable fluidized state. Then adding 8g of liquid paraffin, uniformly mixing, and slowly dripping polycaprolactone diol and MDI after 2 minutes to prepare the polyurethane coated controlled release urea. The coating rate is 4%, the reaction time is about 20min, and the modified polyurethane coated urea (PCRU 3) is prepared after the urea particles are completely coated.
Comparative example 3
The comparative example provides a polyurethane coated controlled release urea, the preparation method is as follows:
the temperature of the coated fluidized bed is controlled to be 80-85 ℃, and 1000g of large-particle urea is added according to the dosage of 19.96g of mono-polyether polyol and 20.24g of MDI, so that the mixture is in a stable fluidized state. Then adding 8g of liquid paraffin, uniformly mixing, and slowly dripping polyether polyol curing agent after 2 minutes to prepare the polyurethane coated controlled release urea. The coating rate is 4%, the reaction time is about 20min, and the comparative polyurethane coated urea (CRU) is prepared after the urea particles are completely coated.
Test one determination of Nitrogen Release Rate of Fertilizer
Weighing 10.00g of coated fertilizer, placing in a nylon mesh bag, placing into a plastic bottle with a cover, adding 200ml of deionized water, covering a bottle cap, placing into a constant temperature box at 25 ℃, standing, and soaking. Each sample was replicated 2 times. Sampling assay times were days 1, 4, 7, 10, 14, 21 and 28, taking 7 total samples. During each sampling, the leaching solution in the plastic bottle is completely poured out for measuring the release amount of the N element of the coated fertilizer, and 200ml of deionized water is added to continuously soak the coated fertilizer. And measuring the release rate of nitrogen in the leaching solution by adopting a p-dimethylaminobenzaldehyde-spectrophotometry method, and calculating the cumulative release rate of nitrogen.
TABLE 1 cumulative dissolution rates of various polyurethane coated controlled release fertilizers
The cumulative release rate of N nutrients of the 4 fertilizers is shown in Table 1, the initial N release rate of PCRU1 is 2.1%, the cumulative N release rate on the 28 th day is 81.8%, the controlled release period can reach more than 30 days, and the difference from the common polyurethane fertilizer (CRU) is small. The initial release rate of CRU was 1.2%, and the cumulative N release rate on day 28 was 73.5%. In contrast, the initial N release rates of PCRU2 and PCRU3 were 88.5% and 85.5%, with poor controllability. The controlled release performance of the PCL coated fertilizer can be greatly improved by blending the PPG and the PCL 2000.
Test of degradation Rate of two Membrane Shell
The coated controlled release fertilizers of example 5 and comparative examples 1-3 were soaked with clear water and rinsed multiple times to completely remove the fertilizer on the membrane shell, the residual membrane was filtered off, dried and sieved, leaving a portion of the membrane shell greater than 2mm for use. And (3) putting a certain amount of the membrane shell into the net bag, embedding the net bag into soil, taking out the net bag after 3 months, and measuring the degradation rate. The degradation rate of the film shell after three months in example 5 was 7%, the degradation rates of the film shells after three months in comparative example 1 and comparative example 2 were 30% and 35%, respectively, and the degradation rate of the film shell of the general polyurethane urea in comparative example 3 was 0.5%.
Test three temperature variation test
The nutrient release rates of example 5 (PCRU 1) and comparative example 3 (CRU) were measured at different temperatures by the variable temperature water soak method (as shown in Table 2). 10.00g of coated fertilizer is weighed, each sample is repeated for 3 times, and the coated fertilizer is placed in a constant temperature box at a specific temperature for standing and soaking. The initial temperature was 22℃and after 24 hours the temperature was raised to 36℃every 4 hours for 84 hours. Samples were taken every 4 hours for a total of 21 samples. When sampling is carried out each time, 1ml of leaching liquid is sucked by a liquid-transferring gun, 1ml of deionized water is added, and the sucked leaching liquid is used for measuring the nitrogen nutrient release performance of the coated fertilizer. At a constant temperature of 22 ℃, the nitrogen release of the example 5 is slow, the nitrogen release rate is slightly increased after 48 hours, the accumulated nitrogen release rate is gradually increased to 6.79% after 82 hours, and the nitrogen dissolution rate per hour is 0.08%. Under the temperature changing condition, the nutrient release rate of the example 5 is gradually increased in the temperature rising process of 0-66 h (22-32 ℃), and the nitrogen accumulation release rate is consistent with the constant temperature treatment without obvious increase although the temperature is increased by 10 ℃. In the period of 66-68 h, when the temperature is raised from 32 ℃ to 33 ℃, the accumulated release rate of nitrogen is raised from 3.97% to 9.59%, and the increase is 1.4 times; the release rate per unit hour is suddenly increased from 0.06% to 1.40% before 66 hours, and is increased by 22.3 times, which shows that example 5 shows obvious temperature sensitivity at 32-33 ℃. In the heating process of 68-82 h (33-36 ℃), the nutrient release rate is consistent with the previous period. After 82h, when the temperature was restored to 22 ℃, the release rate was again slowed, and the slope of the fitted line was close to the constant temperature release at 22 ℃, indicating that when the ambient temperature was below 33 ℃, the release was again restored to the previous level. The change process of the nitrogen accumulation release rate under the variable temperature condition shows that the nutrient accelerated release of the embodiment is obvious along with the increase of the ambient temperature to about 33 ℃, and the embodiment has the temperature response characteristic.
As a control, comparative example 3 was similar to the example release profile at constant temperature. Under the temperature changing condition, the comparative example 3 is consistent with the constant temperature process of 22 ℃ in 46h, and the release rate is increased uniformly along with the temperature rise in the temperature rising process of 46-82 h (27-36 ℃), but no obvious mutation exists. Such changes, although affected by temperature, do not have a sensitive temperature.
TABLE 2 cumulative dissolution rates of various polyurethane coated controlled release fertilizers
The principle is as follows:
the temperature sensitivity and the controlled release performance of the temperature-sensitive polyurethane reaction product are different in the molecular weight of the polycaprolactone diol, the ratio of the polycaprolactone diol to the polyether polyol, the auxiliary agent and the processing method thereof. The temperature sensitive polyurethane is generally formed by reacting a curing agent with a polyol (C, N double bonds in n=c=o of polyisocyanate are broken, active hydrogen of the polyol is connected, and a polymer is formed), and has a typical block structure, and a main chain is generally formed by a soft segment (soft segment) and a rigid segment (hard segment) block. The temperature sensitive polyurethane hard segment is a carbamate group formed by a small molecular chain extender and a curing agent (diisocyanate), and a microphase crystal region is easy to form and microphase separation is generated between the temperature sensitive polyurethane hard segment and the soft segment. The mixture of polycaprolactone diol and polyether polyol as the soft segment in the molecular chain of the polymer has flexibility, phase transition temperature of 0-60 deg.c, crystallization melting temperature Tm of polycaprolactone diol, flexibility and elasticity, and rigidity. The diisocyanate has relatively fixed molecular weight, and the hardness is not strong, and the difference of the molecular weight of polycaprolactone diol can reach several times (500-3000) and the mixing proportion of the polycaprolactone diol and polyether polyol, so that the polyurethane is an important point for adjusting the performance of temperature-sensitive polyurethane. The temperature-sensitive polyurethane hard segment-soft segment structure is regulated by regulating and controlling the molecular weight of polycaprolactone diol and the mixing proportion of the polycaprolactone diol and polyether polyol, so that the release performance of the coated fertilizer is regulated and controlled.
The temperature-sensitive polyurethane material is different from the polyurethane material in that: (1) The temperature-sensitive polyurethane can be subjected to abrupt change before and after the phase transition temperature of the soft segment, and has a switching effect. Below the switching temperature, the temperature-sensitive polyurethane has complete crystal morphology, flexibility and controlled release performance; and above the switching temperature, the soft segment crystals of the temperature-sensitive polyurethane are completely melted and disappear, so that the temperature-sensitive polyurethane shows temperature-sensitive property. The phase state transition of the temperature-sensitive polyurethane soft segment determines the intelligent response characteristic of the material. (2) In the preparation process of the temperature-sensitive polyurethane coated controlled release fertilizer, film forming reaction is carried out on the surface of the fertilizer particles by the temperature-sensitive polyurethane, and in addition, after film forming, certain flexibility of the film layer is also expected to be realized in order to ensure good controlled release performance.
The invention adopts polycaprolactone glycol with the molecular weight of 2000-3000 and polyether polyol to be mixed according to a certain proportion as special materials for preparing the coated controlled release fertilizer, and the special materials react with a curing agent in situ to prepare the polyurethane coated fertilizer, and the temperature-sensitive polyurethane molecular design thought is as follows:
firstly, in order to ensure that the coated controlled release fertilizer film layer has temperature sensitivity, the invention selects polycaprolactone diol with the molecular weight of 2000-3000 and the hydroxyl value of 56-37 KOH/g to prepare the film material. Polycaprolactone diols having a molecular weight of 2000 and a hydroxyl number of 56KOH/g are preferred.
Second, in order to secure a certain toughness and strength of the film layer, the functionality of the polyether polyol should be between 2 and 4, and the polyether polyol includes any one or a combination of at least two of polyoxyethylene polyol, polyoxypropylene polyol, polymer polyol and polytetrahydrofuran, for example, a combination of polyoxyethylene polyol and polyoxypropylene polyol, a combination of polyoxypropylene polyol and polytetrahydrofuran or a combination of polyoxyethylene polyol and polytetrahydrofuran, etc., but not limited to the above-listed combinations, and other combinations not listed in the above-listed combination range are equally applicable.
Thirdly, mixing polycaprolactone diol and polyether polyol in a molar ratio of 1-2:8-9; the preferred molar ratio is 2:8.
Fourth, the hard segment of polyurethane is formed by selecting a curing agent as the hard segment, preferably liquefied MDI as a reactant. The ratio of polyether polyol to MDI was 1:1.1.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (8)
1. The temperature-sensitive polyurethane coated controlled release fertilizer is characterized by comprising the following components in percentage by mass:
94-97 parts of large-particle urea;
0.38-0.96 part of polycaprolactone diol;
0.76-1.92 parts of polyether polyol;
0.84-2.11 parts of curing agent;
0.5 to 1 part of liquid paraffin.
2. The temperature-sensitive polyurethane coated controlled release fertilizer of claim 1, wherein: the particle size of the large-particle urea particles is 2-6 mm.
3. The temperature-sensitive polyurethane coated controlled release fertilizer of claim 1, wherein: the molecular weight of polycaprolactone diol is 2000-3000, and the hydroxyl value is 56-37 KOH/g.
4. The temperature-sensitive polyurethane coated controlled release fertilizer of claim 1, wherein: the polyether polyol has a functionality of 2 to 4.
5. The temperature-sensitive polyurethane coated controlled release fertilizer of claim 1, wherein: the polyether polyol comprises any one or a combination of at least two of polyoxyethylene polyol, polyoxypropylene polyol and polytetrahydrofuran.
6. The temperature-sensitive polyurethane coated controlled release fertilizer of claim 1, wherein: the curing agent is liquefied MDI.
7. A preparation method of a temperature-sensitive polyurethane coated controlled release fertilizer comprises the following steps:
s1, starting a Roots blower (1), enabling air flow to enter a fluidized bed (4) after being buffered and balanced by a buffer tank (2) and heated by an electric heater (3), ensuring the temperature in the fluidized bed to be 85 ℃, and enabling the fluidized bed to be in a working state;
s2, adding the formula amount of large-particle urea into a fluidized bed through an inlet (5) to preheat for 2 minutes, and then spraying the formula amount of liquid paraffin placed in a storage tank (7) into the fluidized bed (4), so as to pretreat the surface of the large-particle urea for 2 minutes;
s3, adding the formula amount of polycaprolactone diol, the formula amount of polyether polyol, the catalyst and the foaming agent into a fluidized bed (4), uniformly mixing, conveying to a nozzle by using a peristaltic pump B to atomize the mixture to the surface of the large-particle urea, simultaneously adding the formula amount of curing agent, conveying to the nozzle by using the peristaltic pump B, and rapidly mixing the mixture with the reaction material of a storage tank A in the nozzle to atomize;
s4, atomizing the reaction material at the speed of 3g/min, operating for 15 minutes, stopping adding the reaction material, coating, and taking out the temperature-sensitive polyurethane coated controlled release fertilizer (8) from the outlet (6).
8. The method for preparing the temperature-sensitive polyurethane coated controlled release fertilizer according to claim 7, which is characterized in that: in the temperature-sensitive polyurethane coated controlled release fertilizer, the mass ratio of the temperature-sensitive polyurethane is 3-6%, the particle size of fertilizer particles is 2-6 mm, and the mass volume ratio of the fertilizer to the liquid paraffin is (450-500) (1-5) g/mL.
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