A method for rapidly evaluating the nutrient release rate of bio-based coated urea

Abstract

The present invention discloses a method for rapidly evaluating the nutrient release rate of bio-based coated urea, which relates to the technical field of controlled-release fertilizer coating materials. This method is achieved by preparing a series of biodegradable film materials based on different combinations of different bio-based materials and measuring their water absorption rates. A series of different bio-based polyester polyols are mixed and crosslinked with isocyanates and cured into films on glass plates to obtain a series of coating materials with different nutrient release characteristics and a certain thickness. A certain mass of the film materials is taken for water absorption rate measurement, and based on the relationship between the water absorption rate and the nutrient release of the coated fertilizer, the rapid evaluation of the nutrient release of the film materials is realized. The method of the present invention requires a shorter experimental time, has a simpler process, low cost, and can evaluate the nutrient release of the coated urea without making the coated urea again, providing a simple method for screening and identifying film materials for the specialization of coated fertilizers and the precise control of nutrient release.

Description

Technical Field

[0001] The present invention relates to the technical field of controlled-release fertilizer coating materials, and particularly relates to a method for rapidly evaluating the characteristics of bio-based thin film materials and the nutrient release rate of the corresponding coated urea. Background Art

[0002] Polymers, especially polyurethane film materials, have become the main film materials for preparing coated urea due to their easy film formation and excellent controlled-release effect. Bio-based materials have gradually become a research hotspot for film material preparation due to their low price, wide source, renewable, and biodegradable advantages. In recent years, due to factors such as the environmental friendliness and low cost of bio-based materials, the research and development of technologies and product innovations related to bio-based polyurethanes have gradually increased, such as castor oil-based polyurethanes, soybean oil-based polyurethanes, linseed oil-based polyurethanes, palm oil-based polyurethanes, rapeseed oil-based polyurethanes, etc. Among many vegetable oils, castor oil-based polyurethanes and soybean oil-based polyurethanes are the most widely used. Currently, they have become the main bio-based degradable materials for preparing coated slow-release fertilizers. The formulation, property evaluation of bio-oil-based slow-release film materials, and research on the corresponding coated urea have become hotspots.

[0003] Due to different plant species and the differences in soil and hydrothermal conditions in different regions, it is difficult to precisely match the nutrient release of coated urea with the nutrient requirements of plants, resulting in fluctuations in the effects of slow-release fertilizers in different crops and different regions. Therefore, using different formulations of bio-based degradable materials to achieve the synchronization of slow-release fertilizer nutrient release and crop nutrient requirements has always been a concern in the industry. Different sources of coating materials, differences in molecular structure functional groups, and the influence of different coating processes after different formulations on the nutrient permeability of the formed film are obvious. Therefore, using different types of bio-based polyester polyols and isocyanates for different formulations and composites to construct a series of film materials with different nutrient release modes and realizing the specialization of coated urea and the matching of nitrogen supply in fertilizers with crop requirements are important technical paths.

[0004] Common methods for detecting and evaluating the nutrient release rate of slow-release fertilizers include the water leaching rate method, soil culture method, diffusion and permeability method, electro-ultrafiltration method, isotope method, etc. Among them, the water leaching rate method is the most commonly used method at present and is also the evaluation method for nutrient release in the national slow-release fertilizer standard (GB / T 23348). This method needs to be implemented on the basis of processing and preparing a series of membrane materials and coated urea products by combining bio-based materials from different sources, which has the disadvantages of long experimental cycle, complex process, high time and labor costs. The test results can only roughly evaluate its nutrient release characteristics, greatly limiting the evaluation efficiency of new slow-release membrane materials and also being the bottleneck restricting the research and development and production of special slow-release fertilizers for precise nutrient release. At present, there are few reports on the rapid determination method for the nutrient release rate of coated controlled-release fertilizers. Some of the membrane material parameters of the determination methods are not universal, and some even deviate from the characteristics of the membrane materials. Therefore, the technical supervision department and the slow-release fertilizer research and development and production enterprises urgently need a rapid detection method to quickly detect the characteristic parameters of different membrane materials within a short time and estimate the nutrient release law of slow-release fertilizers (urea), so as to realize the rapid combination and precise identification of slow-release coating materials, providing a method for precise combination of membrane materials and rapid evaluation of nutrient release for the development of special slow-release urea. Summary of the Invention

[0005] In view of the problems in the prior art, the present invention provides a method for rapidly evaluating the speed of nutrient release based on measuring the water absorption rate of bio-based membrane materials.

[0006] A method for rapidly evaluating the speed of nutrient release of bio-based coated urea, the method comprising:

[0007] S1: Measuring the water absorption rate of the membrane material: Wet the membrane material with water, and measure the weights of the membrane material before and after wetting, denoted as M 1 and M 2 , and calculate the water absorption rate W through the formula

[0008]

[0009] ; a ;

[0010] S2: The time when the saturated water absorption rate of the coating material is reached is highly correlated with the nitrogen release period. The estimation formula for predicting the release period and the time of saturated water absorption rate is:

[0011] y = kx;

[0012] where y is the predicted release period of the coated urea, x is the time when the membrane material reaches the saturated water absorption rate, and k is the correlation coefficient between the time when the saturated water absorption rate of the coating material is reached and the nitrogen release period, obtained by linear fitting;

[0013] The k value is used as a characteristic parameter for the nutrient release rate at the same time. The larger the k value, the slower the nutrient release rate of the coated urea, and the smaller the k value, the faster the nutrient release rate of the coated urea.

[0014] Preferably, the membrane material is a polymer formed by combining a bio-based polyester polyol and an isocyanate.

[0015] Preferably, k = 1.94.

[0016] Preferably, the error between y and the actual release period of the corresponding bio-based coated urea does not exceed 14 days.

[0017] Preferably, the membrane material is prepared in the following manner:

[0018] (1) Mix the bio-based polyester polyol and the isocyanate, and mix them on a high-speed disperser for 20 to 50 seconds to obtain a homogeneous mixture;

[0019] (2) Pour the mixture onto a clean and dry glass plate, and use a coating rod with a thickness of 80 microns to evenly coat the mixture on the glass plate to form a coated film layer;

[0020] (3) Place the coated glass plate on an infrared drying oven at 40 to 60 °C for curing. Wait until the surface of the coated film layer is cured and does not stick to the hand, then raise the temperature of the infrared drying oven to 70 to 80 °C for aging. After 20 to 40 minutes, take it out, transfer it to an oven at 50 to 60 °C for further aging until the coated film layer is completely cured to form a film with stable strength. Remove the film from the glass plate to obtain it.

[0021] Furthermore, put the coating material into an oven and dry it at 50 °C for 24 hours.

[0022] Furthermore, put the dried coating material on a balance and weigh it. Take 0.5 g of the membrane material, and record the mass of the membrane material weighed at this time as M 1 , less than 0.5 g will easily cause errors, and too much will increase the test cost.

[0023] Furthermore, put the weighed membrane material into a beaker filled with deionized water and soak it completely.

[0024] Furthermore, put the beaker containing the membrane material and deionized water into a constant temperature incubator set at 25 °C.

[0025] Furthermore, after 1, 3, 7, 10, and 14 days of soaking time, take out the membrane material every 7 days and use filter paper to absorb the residual water on the surface of the membrane. Weigh the membrane at this time and record it as M 2 .

[0026] Further, after weighing the infiltrated membrane material, put the membrane material back into the beaker filled with deionized water and continue infiltration until the weight of the membrane material no longer changes, and record the infiltration time when the water absorption rate reaches saturation.

[0027] The time for the membrane material to reach the saturated water absorption rate is the time from when the membrane material starts to be infiltrated by water until the mass of the infiltrated membrane material no longer changes.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] In the present invention, the water absorption rate of the membrane material can be measured after the membrane material is synthesized, rather than after the coated urea is separated. Compared with the traditional nutrient measurement, it provides a faster and simpler evaluation method for the nutrient release of coated urea, that is, the rate of nutrient release can be determined according to the water absorption rate before the urea is coated, and its release period can be preliminarily determined. Moreover, in the follow-up, coated urea meeting the expected release period can be produced by designing the water absorption rate of the membrane material with different ratios or different membrane thicknesses;

[0030] The present invention provides technical support for the design of the nutrient mode of the special membrane material combination and the coated urea that meets the crop requirements, realizes the relatively precise design of the membrane material and the nutrient release of the coated urea, and shortens the R & D cycle of new special slow-release fertilizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings:

[0032] Figure 1 Graph of the change of water absorption rate of different membrane materials with infiltration time;

[0033] Figure 2 Graph of the nitrogen cumulative release rate of coated urea with different membrane materials;

[0034] Figure 3 7-day nitrogen release rate of coated urea with different membrane materials;

[0035] Figure 4 Fitting curve graph of the water absorption rate of different membrane materials and the nitrogen cumulative release rate of coated urea;

[0036] Figure 5 Fitting curve graph of the water absorption rate of different membrane materials and the 7-day nitrogen release rate of coated urea. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. To better reveal the variation law of water absorption rate, the selected film materials are all film materials with a specific thickness prepared by coating rods with controllable thickness.

[0038] Example 1

[0039] A method for quickly evaluating the nutrient release rate of bio-based coated urea is as follows:

[0040] (1) Determination of the water absorption rate of the film material: Take 0.5 g of the film material (coded as A1) prepared from bio-based raw materials (small molecule castor oil polyester polyol: macromolecule castor oil polyester polyol: isocyanate = 5.5:0.5:4) after drying, and place them in beakers filled with deionized water for complete infiltration. Place them in a constant temperature oven at 25 °C. After 1, 3, 7, 10, and 14 days of infiltration, use filter paper to absorb the residual water on the film every 7 days. At this time, weigh the film and calculate its water absorption performance, and record the time to reach the saturated water absorption rate. The formula for calculating the water absorption rate is as follows:

[0041]

[0042] In the formula: Wa is the water absorption rate; M 2 The weight of the film after infiltration; M 1 Is the weight of the dry film.

[0043] (2) Controlled release performance test: For the film material formula in the above selected examples, through the drum granulation and spraying processes, prepare polyurethane-coated urea samples with a coating thickness of 3.0%. Determination of the nutrient release of coated urea: Weigh 10.00 g of the controlled release fertilizer and put it into a small bag made of 100-mesh nylon screen. After sealing, put the small bag into a 250 mL plastic bottle, add 200 mL of distilled water, seal it with a lid, and place it in a 25 °C incubator. Sampling is carried out every 7 days after 1, 7, 14, and 21 days. When the nutrient dissolution rate reaches more than 80%, it is considered that the release is complete. When sampling, invert the glass bottle 3 times to make the liquid concentration in the bottle uniform, and then take out about 40 ml of the liquid from the bottle and put it into a small glass bottle for nitrogen determination. Then, pour out all the remaining liquid in the bottle, add 200 mL of distilled water again, seal it, and put it back into the incubator for continued cultivation. Nitrogen dissolution rate: Determine nitrogen by the Kjeldahl method.

[0044] The water absorption rate of the film material in Example 1, the cumulative nitrogen release rate of the coated urea in static water extraction, and the nitrogen release rate in 7 days are recorded as follows, as shown in Table 1 below.

[0045] Table 1: Data on the water absorption rate of the film material in Example 1 and the nutrient release of the coated urea

[0046] Time / day Water absorption rate (%) Cumulative release rate (%) 7-day release rate (%) 1 0.72 0.05 0.05 3 1.30 0.32 / 7 1.70 0.41 0.36 10 1.48 1.02 / 14 2.03 1.68 1.27 21 2.25 3.69 2.01 28 2.54 6.82 3.13 35 2.64 11.77 4.95 42 2.94 17.85 6.08 49 3.15 26.58 8.73 56 3.14 35.26 8.68 63 3.55 41.60 6.34 70 3.52 48.08 6.48 77 3.25 53.82 5.74 84 58.57 4.75 91 62.82 4.25 98 66.26 3.44 105 69.87 3.61 112 73.10 3.23 119 75.82 2.72 126 77.93 2.11 133 80.19 2.26

[0047] Example 2

[0048] A method for rapidly evaluating the nutrient release rate of bio-based coated urea is as follows:

[0049] (1) Determination of the water absorption rate of the membrane material: Take 0.5 g of the membrane material (coded as A2) made from different bio-based raw materials after drying (small molecule castor oil polyester polyol, castor oil polyester polyol: isocyanate = 3:3:4), and place them separately in beakers filled with deionized water for complete immersion. Place them in a constant temperature oven at 25 °C. After immersion times of 1, 3, 7, 10, and 14 days, use filter paper to absorb the residual water on the membrane every 7 days. At this time, weigh the membrane and calculate its water absorption performance, and record the time to reach the saturated water absorption rate. The water absorption rate calculation formula is as follows:

[0050]

[0051] Where: Wa is the water absorption rate; M 2 The weight of the membrane after immersion; M 1 Is the weight of the dry membrane.

[0052] (2) The same as Example 1.

[0053] The recorded water absorption rate of the membrane material in Example 2, the cumulative nitrogen release rate of the coated urea in static water extraction, and the nitrogen release rate in 7 days are as follows, as shown in Table 2 below.

[0054] Table 2: Data on the water absorption rate of the membrane material in Example 2 and the nutrient release of the coated urea

[0055]

[0056]

[0057] Example 3

[0058] A method for rapidly evaluating the nutrient release rate of bio-based coated urea is as follows:

[0059] (1) Determination of the water absorption rate of the membrane material: Take 0.5 g of the membrane material (coded as A3) made from another bio-based raw material after drying (epoxidized soybean oil polyester polyol: isocyanate = 6.5:3.5), and place them separately in beakers filled with deionized water for complete immersion. Place them in a constant temperature oven at 25 °C. After immersion times of 1, 3, 7, 10, and 14 days, use filter paper to absorb the residual water on the membrane every 7 days. At this time, weigh the membrane and calculate its water absorption performance, and record the time to reach the saturated water absorption rate. The water absorption rate calculation formula is as follows:

[0060]

[0061] Where: Wa is the water absorption rate; M 2 is the weight of the film after infiltration; M 1 is the weight of the dry film.

[0062] (2) The same as Example 1.

[0063] The water absorption rate of the film material, the cumulative release rate of nitrogen leached from the coated urea in static water, and the nitrogen release rate in 7 days of Example 3 are recorded as follows, as specifically shown in Table 3 below.

[0064] Table 3: Determination data of water absorption rate of film material and nutrient release of coated urea in Example 3

[0065]

[0066]

[0067] The relevant curves of the water absorption performance of Examples 1-3 are as Figure 1 shown, and the relevant release curve data are respectively as Figure 2 and Figure 3 shown. The water absorption saturation time and the release period data of the coated urea of Examples 1-3 are specifically shown in Table 4 below. To further illustrate the relationship between the water absorption rate and the nutrient release, the measured data of the water absorption rate and the nutrient release are fitted, and the relevant curves are as Figure 4 , Figure 5 and Table 5 shown.

[0068] Table 4 Determination data of water absorption rate and release period of Examples 1-3

[0069] Membrane material Time to reach water absorption saturation / day Release period / day Example 1 63 133 Example 2 56 105 Example 3 35 56

[0070] Table 5 Fitting relationship between the time (x) to reach the saturated water absorption rate and the release period (y) of Examples 1-3

[0071] Relationship formula Correlation coefficient y = 1.94x 0.987

[0072] The results show that: under the condition of a certain film thickness, the nutrient release law of the coated urea of the three different bio-based film materials is highly consistent with the change law of the water absorption rate of the three film materials. The order of fast and slow water absorption rate and nutrient release is: Film A3 > Film A2 > Film A1. The water absorption rate of the film material increases with the prolongation of the soaking time. When the water absorption rate approaches saturation, the nutrient release rate of the coated urea also reaches the maximum, indicating that the water absorption rate of the film material can be used as an index for the fast and slow nutrient release of bio-based coated urea. The results also show that the nutrient release period of the bio-based coated urea is close to 2 times the time for the film material to reach the saturated water absorption rate, and the relationship between the two shows a highly significant correlation. Among them, the maximum difference between 2 times the time for the coating material to reach the saturated water absorption rate and the release period of the coated urea is only 14 days.

[0073] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for rapidly evaluating the nutrient release rate of bio-based coated urea, characterized in that: The method comprises: S1: Determine the water absorption rate of the coating material: soak the coating material with water, measure the weight of the coating material before and after soaking, record it as M1 and M2, and use the formula Calculate the water absorption W a ; S2: The time when the coating material reaches saturated water absorption is highly correlated with the nitrogen release period. The estimated formula for the release period and saturated water absorption time is: y = kx; Among them, y is the predicted release period of coated urea, x is the time when the coating material reaches saturated water absorption, and k is the correlation coefficient between the time when the coating material reaches saturated water absorption and the nitrogen release period, which is obtained by linear fitting; The k value is also used as a characteristic parameter of the nutrient release rate. The larger the k value, the slower the nutrient release rate of the coated urea, and the smaller the k value, the faster the nutrient release rate of the coated urea.

2. A method for rapidly evaluating the nutrient release rate of bio-based coated urea according to claim 1, characterized in that: The coating material is a polymer formed by combining bio-based polyester polyol and isocyanate.

3. A method for rapidly evaluating the nutrient release rate of bio-based coated urea according to claim 2, characterized in that: The k=1.

94.

4. The method for rapidly evaluating the nutrient release rate of bio-based coated urea according to claim 1, characterized in that: The coating material is prepared in the following manner: (1) mixing the bio-based polyester polyol and the isocyanate, and mixing them on a high-speed disperser for 20 to 50 seconds to obtain a homogeneous mixed liquid; (2) Pour the mixed solution onto a clean and dry glass plate, and evenly spread the mixed solution on the glass plate using a coating rod with a thickness of 80 μm to form a coating film layer; (3) Place the coated glass plate in an infrared drying oven at 40-60°C for curing. When the surface of the coating film is cured and no longer sticky, increase the temperature of the infrared drying oven to 70-80°C for curing. Take it out after 20-40 minutes and transfer it to an oven at 50-60°C for further curing until the coating film is completely cured to form a film with stable strength. Remove the film from the glass plate.

5. The method for rapidly evaluating the nutrient release rate of bio-based coated urea according to claim 1, characterized in that: The M1 is 0.5g.

6. The method for rapidly evaluating the nutrient release rate of bio-based coated urea according to claim 1, characterized in that: During infiltration, the water covers the encapsulating material.

7. A method for rapidly evaluating the nutrient release rate of bio-based coated urea according to claim 1, characterized in that: The soaking temperature was 25°C.

8. A method for rapidly evaluating the nutrient release rate of bio-based coated urea according to claim 1, characterized in that: The time for the coating material to reach the saturated water absorption rate is the time from when the coating material begins to be infiltrated by water to when the mass of the infiltrated coating material no longer changes.

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