A bio-based anti-floating polyurethane coating material, its preparation method and application

Abstract

This invention discloses an anti-floating, fully bio-based polyurethane coating material, its preparation method, and its application. The anti-floating, fully bio-based polyurethane coating material comprises a mixed biomass polyol and a bio-based polyisocyanate, wherein the isocyanate index R of the mixed biomass polyol and the bio-based polyisocyanate is 0.4–0.85. The mixed biomass polyol is composed of lignin-based polyol, vegetable oil polyol, and dispersant in a mass ratio of (55–125):(45–325):(0.5–4.5). The coated slow-release fertilizer prepared by this patented product has advantages such as easy degradation of the coating material and anti-floating properties. By controlling the proportion of lignin-based polyol in the entire composition, the controlled-release period can reach 1 to 5 months, enabling rapid nutrient release at a certain point in the mid-to-late stages of crop growth, improving fertilizer utilization and crop yield, and is particularly suitable for rice and semi-arid crop planting areas in southern China.

Description

Technical Field

[0001] This invention relates to the technical field of coated slow-release fertilizer production, specifically to an anti-floating, fully bio-based polyurethane coating material, its preparation method, and its application. Background Technology

[0002] Controlled-release fertilizer is a new type of fertilizer that slowly releases nutrients, providing them continuously and evenly throughout the crop's growth cycle. This reduces fertilizer loss, improves fertilizer utilization, saves production costs, and lowers the risk of environmental pollution. In recent years, with the continuous development of global agriculture and increased attention to environmental protection, its application has become increasingly widespread, making it an important part of modern agriculture.

[0003] Existing traditional controlled-release fertilizers are mainly petrochemical-derived polyurethane-coated controlled-release fertilizers. Although polyurethane itself has good stability, the polyurethane films currently popular on the market are mostly synthesized from petrochemical-derived polyols and isocyanates. Controlled-release fertilizers using a single petrochemical-derived polyol for coating often release nutrients into the soil too quickly, preventing crops from absorbing the necessary nutrients in a timely manner. This not only affects crop growth and yield but may also lead to waste and environmental pollution. In addition, petrochemical-derived isocyanates are highly toxic, and the production process of isocyanates often involves the use of toxic phosgene, which can cause irritation and damage to the human body, such as eye, skin, and respiratory irritation, and allergic reactions.

[0004] Existing coated controlled-release fertilizers have problems such as easy stratification of polyol components during production, high viscosity coefficient, need to be stirred at any time, high energy consumption, and unstable quality of the initial materials in the early stage of production.

[0005] The nutrient release principle of controlled-release fertilizers is to encapsulate the nutrients in the fertilizer using a coating material. Soil moisture enters through the membrane pores, dissolving some of the nutrients. Osmotic pressure is created inside and outside the membrane, causing the nutrients to be released through the pores. Nutrient release is mainly limited by conditions such as temperature and moisture. It is generally believed that when the relative soil moisture content is above 80%, the soil pores can reach water vapor saturation, and the nutrient release rate of controlled-release fertilizer reaches its maximum. However, in semi-arid crop growing areas, soil field water holding capacity is unstable. When the relative moisture content cannot be stabilized within this threshold range for a long period, especially when the relative moisture content is below 75%, soil water suction increases, and the rate of water infiltration of controlled-release fertilizer decreases. This can lead to insufficient nutrient supply during the critical growth stages of crops, and problems such as excessive vegetative growth and delayed maturity in later stages of growth.

[0006] In rice-growing areas of southern China, after the application of controlled-release fertilizers, a large number of particles float on the water surface and move with the wind, which can easily cause uneven fertilization. In traditional production, a layer of surfactant can be sprayed on the fertilizer surface to prevent floating during the fertilization process. However, as nutrients are released, the surfactant is diluted or degraded by water, and the membrane shell will eventually float to the water surface, which can be easily ingested by aquatic organisms and birds, posing a significant ecological risk.

[0007] In summary, different planting patterns and soil conditions limit the application of controlled-release fertilizers, which is not conducive to product promotion and restricts the development of the controlled-release fertilizer industry. Summary of the Invention

[0008] In view of the above-mentioned prior art, the purpose of this invention is to provide an anti-floating, fully bio-based polyurethane coating material, its preparation method, and its application.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides an anti-floating fully bio-based polyurethane coating material, the anti-floating fully bio-based polyurethane coating material comprising a mixed biomass polyol and a bio-based polyisocyanate, wherein the isocyanate index R of the mixed biomass polyol and the bio-based polyisocyanate is 0.4 to 0.85; the mixed biomass polyol is composed of lignin-based polyol, vegetable oil polyol and dispersant in a mass ratio of (55 to 125): (45 to 325): (0.5 to 4.5).

[0011] Preferably, the isocyanate index R = N NCO / N OH ;

[0012] The isocyanate index R is the ratio of bio-based polyisocyanate equivalents to mixed biomass polyol equivalents, i.e., the molar ratio of –NCO groups to –OH groups.

[0013] Preferably, the dispersing agent is selected from one or more of the following: dimercaptodiphenyldimethyltin (DMT), dimethyl stannous acid methyl ester, diethylenetriamine, triethylenediamine, triethanolamine, methyldiethanolamine, dimethylethanolamine, ethanolamine, n-butyl titanate, diisopropyl titanate, and tetraalkyl titanate.

[0014] Preferably, the bio-based polyisocyanate is selected from one or more of 1,5-pentanedimethyl diisocyanate and 1,6-hexanediisocyanate.

[0015] Preferably, the vegetable oil polyol is prepared by the following method:

[0016] (1) Add vegetable oil and alcohol to a reaction vessel, heat to 60-70℃ and add enzyme catalyst, react for 6-10 hours to obtain reaction solution;

[0017] (2) The enzyme catalyst was separated by vacuum distillation of the reaction solution, the alcohol was removed by rotary evaporation, and then washed with saturated sodium chloride solution and dried to obtain vegetable oil polyol.

[0018] Preferably, in step (1), the mass ratio of the vegetable oil, alcohol and enzyme catalyst is (50-250):(120-300):(0.1-10).

[0019] Preferably, the vegetable oil is selected from one or more of peanut oil, olive oil, rapeseed oil, corn oil, sesame oil, cottonseed oil, rice bran oil, sunflower seed oil, flaxseed oil, safflower seed oil, soybean oil, palm oil, and tea seed oil.

[0020] Preferably, the alcohol is selected from one or more of glycerol, ethylene glycol, propylene glycol, 1,3-propanediol, diethylene glycol, trimethylolpropane, triethanolamine, pentaerythritol, cyclohexanediol, sorbitol, low molecular weight polyether polyols, and PTMEG.

[0021] Preferably, in step (1), the enzyme catalyst is selected from one or more of Lipozyme 43, Novozyme 435, LipozymeRM IM, Lipozyme TL IM, Rhizopusarrbizus, Candida rugosa, Rhizopusoryzae, and Lipase PS.

[0022] Preferably, the lignin-based polyol is prepared by the following method:

[0023] Add the polyol and catalyst to a three-necked flask, heat to 100-140℃, add lignin powder, stir continuously, react for 60-120 minutes, and after the lignin powder is completely decomposed and turns black, cool to room temperature to obtain lignin-based polyol.

[0024] Preferably, the mass ratio of the polyol, catalyst and lignin powder is (300-400):(5-15):(30-150).

[0025] Preferably, the lignin is selected from one or more of the following: lignocellulose, wheat straw, sugarcane bagasse, rice straw, rice husk, corn cob, corn stalk, eucalyptus, pine, fir, camphor, birch, beech, and poplar.

[0026] Preferably, the polyol is selected from one or two of ethylene glycol, polyethylene glycol 400, diethylene glycol, glycerol, 1,3-propanediol, 1,4-butanediol, and ethylene glycol.

[0027] Preferably, the catalyst is selected from sulfuric acid, phosphoric acid, silicotungstic acid, phosphomolybdic acid, silicotonic acid, and NaBH4.

[0028] In a second aspect, the present invention provides the application of the above-mentioned anti-floating fully bio-based polyurethane coating material in the preparation of coated slow-release fertilizers.

[0029] A third aspect of the present invention provides an anti-floating, fully bio-based polyurethane-coated slow-release fertilizer, comprising a fertilizer core and the aforementioned anti-floating, fully bio-based polyurethane coating material, wherein the anti-floating, fully bio-based polyurethane coating material is sprayed onto the surface of the fertilizer core.

[0030] Preferably, the preparation method of the anti-floating, fully bio-based polyurethane-coated slow-release fertilizer includes the following steps:

[0031] The granular fertilizer, which serves as the core of the fertilizer, is heated to 50-70°C in a coating machine. The above-mentioned anti-floating fully bio-based polyurethane coating material is sprayed onto the surface of the granular fertilizer in batches. The amount of coating material input each time is 1-2% of the total mass of the granular fertilizer. The coating is cured for 3-6 minutes. The above steps are repeated until the coating material accounts for 3%-4.5% of the total mass of the core fertilizer.

[0032] The beneficial effects of this invention are:

[0033] 1. The anti-floating, fully bio-based polyurethane coating material of the present invention can achieve cross-linking and interpenetrating coating of two biomass polyol materials. The prepared coated slow-release fertilizer has the advantages of easy degradation of the membrane material and anti-floating properties. By controlling the proportion of lignin-based polyol in the whole composition, the controlled release period can reach 1 to 5 months. It can realize the rapid release of nutrients at a certain point in the middle and late stages of crop growth, improve fertilizer utilization and crop yield, and is particularly suitable for rice and semi-arid crop planting areas in the south.

[0034] 2. The plant oil polyol prepared by this invention using inexpensive and readily available plant oil has strong water resistance, and the cross-linked lignin-based polyol has good biocompatibility. The coating material prepared by reacting multifunctional groups with bio-based isocyanates has high strength and biodegradability, and is green and environmentally friendly.

[0035] 3. The preparation method of vegetable oil polyols of the present invention has many advantages over epoxy ring-opening method, etc.: the reaction conditions are mild, the reaction temperature is generally below 70°C, and the energy consumption is low; the product and catalyst are easy to separate, the catalyst can be reused, the reaction product is easy to process, and there is little environmental pollution and waste.

[0036] 4. The mixed polyols produced by this method are not prone to separation, have a uniform texture, low viscosity coefficient, high fluidity, are not easy to clog pipelines during production, have a wide range of applications, low production energy consumption, solve the problem of product particle formation caused by uneven mixing of coating solution, and improve the commercial attributes of the product.

[0037] 5. The anti-floating mechanism in this method utilizes the hydrophilicity of hydroxyl-terminated polyurethane to enable fertilizer to sink quickly in water and prevent the membrane from floating after nutrient release. This eliminates the need for additional anti-floating additives, reducing production costs and process complexity, and also lowers the soil moisture content threshold that limits the release of nutrients from controlled-release fertilizers. Attached Figure Description

[0038] Figure 1 : Anti-floating effect diagrams of different coated controlled-release fertilizers;

[0039] Figure 2 Nitrogen release rate curves of different coated controlled-release fertilizers in soils with different field water holding capacities;

[0040] Figure 3 : The layering of different polyols after mixing and actual images of mixed polyols with added dispersing agents;

[0041] Figure 4 The adhesion and reaction time of controlled-release fertilizers with different R values ​​during the coating process;

[0042] Figure 5 Nutrient release characteristics of different controlled-release fertilizers prepared in Example 4. Detailed Implementation

[0043] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0044] As described in the background section, different planting patterns and soil conditions limit the performance of controlled-release fertilizers. Based on this, the present invention uses lignin-based polyols prepared by lignin liquefaction and plant oil polyols prepared by transesterification of plant oils and alcohols under an enzyme catalyst as soft segments, and bio-based polyisocyanate curing agents as hard segments to synthesize a fully bio-based polyurethane film in situ on the fertilizer surface, thereby controlling the slow release of fertilizer nutrients.

[0045] The preparation of polyols from liquefied lignin utilizes an acid pyrolysis and hydrogenation method to convert lignin into polyester. Compared to traditional liquefaction processes, this method significantly increases the content of hydroxyl active functional groups through catalytic hydrogenation and reduction, reducing the generation of non-film-forming substances and effectively improving the quality of the coating on liquefied biomass materials. Soybean oil polyols are prepared by transesterification of small-molecule polyols with vegetable oils. This method requires less reagent, has a mild reaction temperature, eliminates the need for toxic organic solvents, and allows for catalyst reuse. The production process is safe, simple, convenient, and has low investment costs. Adding dispersing agents ensures uniform mixing and prevents stratification of the mixed polyols. The mixed polyols have a low viscosity coefficient, excellent flowability, and more uniform spraying, avoiding inconsistencies in the quality of controlled-release fertilizer products within the same batch caused by uneven polyol texture. Cross-linking and interpenetration modification of two biomass polyols is used to regulate the proportion of lignin-based polyols in the overall composition, enabling rapid nutrient release at a specific point in the mid-to-late stages of crop growth. This further extends the nutrient release period without increasing the coating thickness, meeting the nutrient requirements of the critical period for crop yield formation.

[0046] When drought occurs or field water holding capacity is low, the swelling property of lignin-based polyols absorbs the surrounding water, causing an increase in their weight and volume. This causes the coated urea to swell, releasing nutrients to the outside of the membrane for crop absorption, thus ensuring fertilization under drought conditions.

[0047] By adjusting the isocyanate index R of the mixed biomass polyol and bio-based polyisocyanate within a reasonable range, the hydrophilicity of the terminal hydroxyl polyurethane enables the fertilizer to sink rapidly in water, and the membrane shell is not prone to floating after nutrient release. Furthermore, it lowers the soil moisture content threshold that limits the release of nutrients from controlled-release fertilizers, thereby expanding the application range of controlled-release fertilizers. The controlled-release fertilizer of this invention has advantages such as easy production and processing, anti-floating properties, easily degradable membrane material, high utilization rate, and high crop yield. It is particularly suitable for rice-growing areas in southern China and semi-arid crop-growing areas where the promotion of traditional controlled-release fertilizers is not feasible, and has significant economic, social, and ecological benefits.

[0048] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0049] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0050] Dispersing agents: Dithiodiphenyl dimethyltin (Hubei Zhonglong Kang Sheng Fine Chemical Co., Ltd.), Methyl dimethylstannous acid (Xindian Chemical Materials (Shanghai) Co., Ltd.), Diethylenetriamine (Jinan Liyang Chemical Co., Ltd.), Triethylenediamine (Changzhou Hengda Chemical Co., Ltd.), Triethanolamine (Shanghai Aladdin Biochemical Technology Co., Ltd.), Methyldiethanolamine (Shanghai Aladdin Biochemical Technology Co., Ltd.), n-Butyl titanate (Jiangsu Pules Biotechnology Co., Ltd.), Diisopropyl titanate (Hubei Zhonglong Kang Sheng Fine Chemical Co., Ltd.), Tetraalkyl titanate (Nanjing Feiteng New Material Technology Co., Ltd.), Dimethylethanolamine (Shanghai Aladdin Biochemical Technology Co., Ltd.), Ethanolamine (Shanghai Aladdin Biochemical Technology Co., Ltd.).

[0051] Bio-based polyisocyanates: 1,5-pentanedimethyl diisocyanate (Gansu Yinguang Juyin Chemical Co., Ltd.), 1,6-hexanediisocyanate (Shanghai Aladdin Biochemical Technology Co., Ltd.).

[0052] Enzyme catalysts: Lipozyme 43 was purchased from Novozymes (China) Investment Co., Ltd.; Lipase PS was purchased from Hangzhou Chuangke Biotechnology Co., Ltd.

[0053] Novozym 435, Lipozyme RM IM, Lipozyme TL IM, Rhizopusarrbizus, Candidarugosa, and Rhizopusoryzae are described in the literature "Research Status of Ester Exchange in Synthetic Polyol Ester Base Oils (Lubricating Oils, Fang Lu, Liang Yuxiang. 2019)".

[0054] The conventional petrochemical source polyester polyol used in the examples was purchased from Wanhua Chemical Group Co., Ltd.; the lignocellulose used was purchased from Shandong Longli Biotechnology Co., Ltd.

[0055] Example 1: Preparation of Anti-floating, fully bio-based polyurethane-coated slow-release fertilizer

[0056] (1) Preparation of mixed polyols:

[0057] Preparation of lignin-based polyol: 220 g PEG-400, 90 g glycerol, and 12 g sulfuric acid were added to a three-necked flask. The flask was heated to approximately 120 °C in an oil bath. 140 g of lignocellulose powder was then added to the flask and mixed with the solvent while continuously stirring. After 90 min, the lignocellulose powder completely decomposed and turned black. The flask was immediately removed from the oil bath and cooled to room temperature to obtain a lignin-based polyol with a hydroxyl value of 140 mgKOH / g.

[0058] Preparation of soybean oil polyol: 150g of soybean oil and 250g of cyclohexanediol were added to a reaction vessel. The temperature was raised to 65℃ and 2g of Lipozyme TL IM was added. The reaction was carried out for 6.5 hours. After the reaction was completed, the reaction vessel was allowed to cool naturally to obtain the reaction solution. The enzyme catalyst was separated from the reaction solution by vacuum distillation, and excess alcohol was removed by rotary evaporation at 60℃. The remaining liquid was washed three times with saturated sodium chloride solution and dried with a desiccant to obtain soybean oil polyol with a hydroxyl value of 166mgKOH / g.

[0059] Preparation of mixed polyols: 150g soybean oil polyol, 150g lignin-based polyol and 0.8g dimercaptodiphenyl dimethyltin (DMT) were mixed and stirred in a reactor for 7.5 min to obtain lignin-soybean oil polyol with a hydroxyl value of 153 mgKOH / g.

[0060] Table 1. Viscosity comparison of different polyols

[0061]

[0062] (2) Preparation of anti-floating bio-based polyurethane coating material:

[0063] A mixture of lignin-soybean oil polyol and 1,5-pentanedimethyl diisocyanate at a mass ratio of 7:3 was used to obtain an anti-floating, fully bio-based polyurethane coating material. In this embodiment, the isocyanate index R of the mixed biomass polyol and 1,5-pentanedimethyl diisocyanate in the anti-floating, fully bio-based polyurethane coating material is 0.8.

[0064] (3) Preparation of anti-floating coated slow-release fertilizer

[0065] 10 kg of urea particles with a diameter of 3.0~3.6 mm were added to a high-efficiency coating machine and heated to about 65°C. A prepared anti-floating, fully bio-based polyurethane coating material was then high-pressure sprayed onto the surface of the urea particles. The amount of coating material added was 1% of the urea mass. The mixture was cured for 4 minutes, forming a dense coating on the fertilizer surface. This coating process was repeated three times until the coating material accounted for 3% of the total urea mass. After the reaction was complete, the mixture was cooled to 25°C to obtain the coated slow-release fertilizer, denoted as SBOPCU.

[0066] Example 2: Preparation of Anti-floating, fully bio-based polyurethane-coated slow-release fertilizer

[0067] (1) Preparation of mixed polyols

[0068] Preparation of wheat straw-based polyols: 150g of polyethylene glycol 400 and 50g of glycerol were mixed with 2.5g of sulfuric acid and placed in a three-necked flask equipped with a flow condenser, thermometer, and electric stirrer. After preheating to 140℃ and protecting with nitrogen, the reflux condenser was turned on, and the electric stirrer was set to 800 rpm / min. -1 The mixture was rotated at a certain speed. Then, 50g of straw powder was poured into the reactor, mixed with the solution, refluxed, and continuously stirred for 90 minutes to obtain a wheat straw-based polyol with a hydroxyl value of 144 mgKOH / g.

[0069] Preparation of peanut oil polyol: 100g of peanut oil, 100g of sorbitol, and 50g of cyclohexanediol were added to a reaction vessel. The temperature was raised to 65℃, and 2g of Rhizopus sarrbizus was added. The reaction was carried out for 6 hours. After the reaction was completed, the reaction vessel was allowed to cool naturally to obtain the reaction solution. The enzyme catalyst was separated from the reaction solution by vacuum distillation, and excess alcohol was removed by rotary evaporation at 60℃. The remaining liquid was washed three times with saturated sodium chloride solution and dried with a desiccant to obtain a peanut oil polyol with a hydroxyl value of 136mgKOH / g.

[0070] Preparation of mixed polyols: 150g peanut polyol, 100g wheat straw-based polyol and 0.8g triethanolamine were mixed and stirred in a reactor for 7.5min to obtain wheat straw-peanut oil polyol with a hydroxyl value of 139.2mgKOH / g.

[0071] (2) Preparation of anti-floating bio-based polyurethane coating material:

[0072] Wheat straw-peanut oil polyol and 1,5-pentanedimethyl diisocyanate were mixed at a mass ratio of 3:1 to obtain an anti-floating, fully bio-based polyurethane coating material. In this embodiment, the isocyanate index R of the mixed biomass polyol and the bio-based polyisocyanate in the anti-floating, fully bio-based polyurethane coating material is 0.7.

[0073] (3) Preparation of anti-floating coated slow-release fertilizer

[0074] 20 kg of large-particle urea with a diameter of 3.0~3.6 mm was loaded into a rotating drum and heated to 65°C. The prepared anti-floating fully bio-based polyurethane coating material was sprayed onto the urea surface at a rate of 1% of the urea mass each time, and this process was repeated three times until the coating amount accounted for 3.0% of the total urea mass. This yielded a wheat straw-peanut oil-based polyurethane-coated controlled-release fertilizer. Tests showed that the controlled-release period of this wheat straw-peanut oil-based polyurethane-coated controlled-release fertilizer was 2 months.

[0075] Example 3: Preparation of Anti-floating, fully bio-based polyurethane-coated slow-release fertilizers with different R values

[0076] (1) Preparation of corn-cotton straw-based polyols:

[0077] Corn stalks and cotton stalks were cut into sections at a 1:1 mass ratio, ground, and passed through a 200-mesh sieve. They were then dried at 60°C for later use. In a three-necked flask equipped with a stirrer, temperature measuring device, and nitrogen purging chamber, 150g of 1,4-butanediol, 200g of glycerol, and 9g of NaBH4 catalyst were added. The temperature was raised to 140°C, and 100g of corn and wheat stalk powder was added. The mixture was reacted at 190°C for approximately 120 minutes to prepare a corn-cotton based polyol with a basic value of 125 mgKOH / g. The mixture was then cooled before use.

[0078] (2) Preparation of bio-based isocyanate complexes:

[0079] A bio-based isocyanate compound was obtained by compounding 1,5-pentanedimethyl diisocyanate and 1,6-hexanediisocyanate in a mass ratio of 7:3.

[0080] (3) Preparation of anti-floating bio-based polyurethane coating materials with different R values:

[0081] According to the addition amounts of peanut oil polyol (prepared in Example 2), corn-cotton straw-based polyol, bio-based isocyanate compound, and 3.5g of titanate n-butyl ester in Table 2, anti-floating fully bio-based polyurethane coating materials with different R values ​​were obtained.

[0082] (4) Preparation of anti-floating coated controlled-release fertilizer

[0083] 20 kg of granular urea with a particle size of 3.0 mm-3.6 mm was weighed and added to a rotating drum and heated to 65 °C. The anti-floating fully bio-based polyurethane coating material prepared in step (3) was sprayed onto the urea surface in three high-pressure sprays, with the coating amount accounting for 3.0% of the total weight of the urea. After each spraying, the coating was cured for 3 minutes, and after the three sprayings, a film layer with a thickness of 3% was formed. After the coating material was cured on the urea surface into a dense and tough polyurethane coating, it was cooled to obtain fully bio-based polyurethane-coated urea with different R values ​​and nitrogen release days.

[0084] Table 2. Mass of polyol and isocyanate compound added for controlled-release fertilizers with different R values.

[0085]

[0086] Example 4: Preparation of bio-based polyurethane-coated slow-release fertilizers with different nutrient release days

[0087] (1) Preparation of mixed polyols

[0088] Using the soybean oil polyol and lignin-based polyol prepared in Example 1, the soybean oil polyol and liquefied lignin-based polyol were mixed evenly according to the addition amounts in Table 3. Based on the total mass of the two polyols obtained, 0.4% by mass of dimercaptodiphenyl dimethyltin (DMT) was added as a dispersant to obtain a mixed polyol.

[0089] (2) Preparation of isocyanate complexes:

[0090] A bio-based isocyanate compound was obtained by compounding 1,5-pentanedimethyl diisocyanate and 1,6-hexanediisocyanate in a mass ratio of 7:3.

[0091] (3) Preparation of anti-floating bio-based polyurethane coating material:

[0092] According to the amount of isocyanate compound added in Table 3, it was mixed with the prepared mixed polyol to obtain bio-based polyurethane coating materials with different nutrient release days.

[0093] (4) Preparation of anti-floating coated controlled-release fertilizer

[0094] Weigh 20 kg of granular urea with a particle size of 3.0 mm-3.6 mm and add it to the drum and heat it to 60 °C. The anti-floating bio-based polyurethane coating material prepared in step (3) is sprayed onto the urea surface in three high-pressure sprays. After each spraying, the coating material is cured for 3 minutes. After the three sprayings are completed, the coating material is cured on the urea surface into a dense and tough polyurethane coating, forming a controlled-release fertilizer with different nutrient release days.

[0095] Table 3. Mass of polyol and isocyanate compound added to coated fertilizers with different nutrient release days.

[0096]

[0097] Comparative Example 1

[0098] The difference between Comparative Example 1 and Example 1 is as follows:

[0099] A coated controlled-release fertilizer, denoted as PPCU, was prepared by using a mixture of traditional petrochemical-derived polyester polyol and 1,5-pentanedimethyl diisocyanate as coating materials. The mass ratio of polyester polyol to 1,5-pentanedimethyl diisocyanate was 7:3, and the coating thickness was 3%. The hydroxyl value of the polyester polyol was 124 mgKOH / g.

[0100] Comparative Example 2

[0101] The difference between Comparative Example 2 and Example 1 is as follows:

[0102] A coated controlled-release fertilizer, denoted as SBCU, was prepared by using a mixture of a single lignin-based polyol and 1,5-pentanedimethyl diisocyanate as the coating material. The mass ratio of lignin-based polyol to 1,5-pentanedimethyl diisocyanate was 7:3, and the coating thickness was 3%. The hydroxyl value of the lignin-based polyol was 140 mgKOH / g.

[0103] Comparative Example 3

[0104] The difference between Comparative Example 3 and Example 1 is as follows:

[0105] A coated controlled-release fertilizer, denoted as SOPCU, was prepared by using a mixture of soybean oil polyol and 1,5-pentanedimethyl diisocyanate as coating materials. The mass ratio of soybean oil polyol to 1,5-pentanedimethyl diisocyanate was 7:3, and the coating thickness was 3%. The hydroxyl value of the soybean oil polyol was 166 mg KOH / g.

[0106] Test Example 1: Anti-floating test

[0107] Three groups of anti-floating fully bio-based polyurethane-coated slow-release fertilizers with different R values ​​prepared in Example 3 (Table 2) were used to conduct anti-floating tests. The tests were divided into three treatments, and each treatment was repeated three times.

[0108] The specific experimental method was as follows: 100 coated controlled-release fertilizer pellets were used for each treatment. On day 1 of nutrient release, day 14 of nutrient release, and after complete nutrient release, the temperature was recorded at 200 rpm / min using a magnetic stirrer. -1 The number of particles floating on the water surface after stirring at a certain speed for 2 minutes. Floating rate = (Number of floating particles / Total number of particles) 100%.

[0109] pass Figure 1 It can be observed that in the initial stage of nutrient release, the fertilizer particles are relatively large and do not float because a large amount of urea is still encapsulated within the membrane. However, as nitrogen is released, the nutrient content within the membrane gradually decreases, and floating occurs. When the R value is greater than 1, the floating rate is 23% on the 14th day of nutrient release, and 44% of the membrane shell floats on the water surface after nutrient release is complete. With the increase of polyol addition, polyurethane-coated controlled-release fertilizer with terminal hydroxyl groups is formed. Furthermore, as the R value decreases and the hydroxyl group value increases, the number of floating particles gradually decreases on the 14th day of nutrient release and after nutrient release is complete. When the R value is 0.46, the floating rate is only 9% after nutrient release is complete.

[0110] Experimental Example 2: Soil Experiments with Different Water Holding Capacities

[0111] The experiment consisted of three treatments: treatments 1-3 used the liquefied lignin-soybean oil-based polyurethane-coated controlled-release fertilizer prepared in Example 1 and the controlled-release fertilizer prepared in Comparative Examples 1-3, respectively. Each treatment was repeated three times. The nutrient release rate of different coated controlled-release fertilizers was measured under the conditions of 25℃ still water, 70% field capacity, and 80% field capacity.

[0112] Test method: Take 5.00 g of controlled-release fertilizer and 250 g of soil (soil physicochemical properties: pH 7.35, available phosphorus 43.07 mg / kg, available potassium 107.64 mg / kg, organic matter 0.98%, electrical conductivity 157.30 μS / cm) and put them into a small plastic bag. Mix them and then add a certain amount of water to make the relative moisture content reach 70% and 80%. Then seal the bag and place it in an incubator in a constant temperature incubator at (25±0.5)℃ to measure the nutrient release rate.

[0113] The specific sampling method is as follows: All fertilizer is transferred to a 2 mm soil sieve. Carefully rinse off any remaining soil adhering to the fertilizer surface with tap water, then rinse three times with distilled water. Next, absorb the moisture from the fertilizer surface with absorbent paper and place it in a pre-weighed weighing bottle. Dry the bottle in a 60℃ oven, cool, weigh, and calculate the release rate. Figure 2 As shown.

[0114] from Figure 2 As we can see, when PPCU and SOPCU coated controlled-release fertilizers are at 70% field capacity, the reduced soil moisture content prevents the coated fertilizer from absorbing enough water to dissolve nitrogen, resulting in a slower nutrient release rate compared to 80% field capacity and still water conditions. However, SBCU coated with lignin showed no significant difference in nutrient release between 70% and 80% field capacity. Furthermore, when using lignin and soybean oil to prepare coated controlled-release fertilizers, no significant difference was observed in nutrient release between 70% and 80% field capacity and still water conditions, ensuring timely nutrient release for crop absorption during critical nutrient-demanding periods.

[0115] As shown in Figure 2, in a static water experiment at 25℃, the controlled-release period of the coated controlled-release fertilizer SBOPCU prepared in Example 1 of this application was 83 days; the controlled-release period of PPCU prepared in Comparative Example 1 was 50 days; the controlled-release period of SBCU prepared in Comparative Example 2 was 32 days; and the controlled-release period of SOPCU prepared in Comparative Example 3 was 39 days. Therefore, the cross-linking and interpenetration of the two materials can achieve long-term nutrient release. Under the same coating thickness, the interconnected modified SBOPCU can achieve 90 days of nutrient slow release, further extending the nutrient release days without increasing the coating thickness to meet the nutrient requirements of the critical period of crop yield formation.

[0116] Experimental Example 3: Layering Test After Mixing Different Polyols

[0117] The experiment consisted of four treatments: A: liquefied lignin-based polyol prepared in Example 1 + soybean oil polyol prepared in Example 1 + diethylenetriamine; B: liquefied lignin-based polyol prepared in Example 1 + soybean oil polyol prepared in Example 1; C: soybean oil polyol prepared in Example 1 + castor oil polyol + diethylenetriamine; D: soybean oil polyol prepared in Example 1 + castor oil.

[0118] Test method: Different polyols were mixed at a 1:1 mass ratio with 0.5% dispersant added. Following the treatment design, the mixture was stirred until homogeneous, then poured into plastic tubes and allowed to stand for 24 hours. The mixing and stratification effects of the liquid were then observed. Figure 3 As shown, no stratification occurred in treatments A and C with added dispersant, while obvious stratification occurred in treatments B and C.

[0119] Experimental Example 4: Adhesion and Reaction Time During the Coating Process of Example 3

[0120] In the preparation process of the coated fertilizer in Example 3, after the anti-floating, fully bio-based polyurethane coating material was added to the drum in three batches, the curing status inside the drum was recorded by taking a picture one minute after the third addition. If the fertilizer flows and disperses within the drum, it indicates a good reaction effect; if the fertilizer adheres heavily to the drum walls, it indicates a poor curing effect.

[0121] Table 4. Adhesion of Controlled-Release Fertilizers with Different R Values ​​to the Fertilizer Container Frame

[0122]

[0123] from Figure 4 As can be seen, when R > 1, excessive isocyanate addition leads to severe adhesion and fouling of the material on the drum walls during preparation. The fertilizer forms rings along the bottom of the drum and adheres firmly to the bottom, preventing complete reaction and reducing reaction time to 30 minutes. As R decreases, the coating process becomes smoother. When R is 0.57, the fertilizer inside the drum exhibits good dispersion, allowing for complete reaction of the membrane material. However, when R further decreases to 0.46, excessive polyol and insufficient isocyanate result in a large amount of hydroxyl groups remaining, leading to adhesion.

[0124] Experimental Example 5: Nutrient Release Rate Detection of Controlled-Release Fertilizers with Different Release Days

[0125] According to the People's Republic of China National Standard for Slow-Release Fertilizers GB / T 23348-2009, the nitrogen release rate of the coated controlled-release fertilizers prepared in Example 4 with different R values ​​and different coating thicknesses was determined. The time required for the cumulative nutrient release rate to reach 80% was recorded as the controlled-release period. The controlled-release periods of the different coated controlled-release fertilizers prepared in Example 4 were found to be 30d, 60d, 90d, 120d, and 150d, respectively.

[0126] Depend on Figure 5 It is known that by using cross-linking and interpenetration modification of two biomass polyols to regulate the proportion of lignin-based polyols in the entire composition, nutrients can be rapidly released at a certain point in the middle and late stages of crop growth. For 30-90 day coated controlled-release fertilizers, the nutrient release period can be controlled by adjusting the ratio of soybean oil polyols to liquefied lignin-based polyols without increasing the coating thickness. For coated controlled-release fertilizers with a release period of more than 90 days, long-term nutrient release can also be achieved by increasing the coating thickness.

[0127] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A fully bio-based anti-floating polyurethane coating material, characterized in that, The anti-floating bio-based polyurethane coating material comprises a mixture of biomass polyols and bio-based polyisocyanates, wherein the isocyanate index R of the mixture of biomass polyols and the bio-based polyisocyanates is 0.4 to 0.85; the mixture of biomass polyols is composed of lignin-based polyols, vegetable oil polyols, and dispersing agents mixed in a mass ratio of (55~125):(45~325):(0.5~4.5). The lignin-based polyol is prepared by the following method: Add the polyol and catalyst to a three-necked flask, heat to 100-140℃, add lignin powder, stir constantly, react for 60-120 minutes, and after the lignin powder is completely decomposed and turns black, cool to room temperature to obtain lignin-based polyol. The mass ratio of the polyol, catalyst, and lignin powder is (300-400):(5-15):(30-150). The lignin is selected from one or more of the following: lignocellulose, wheat straw, sugarcane bagasse, rice straw, rice husk, corn cob, corn stalk, eucalyptus, pine, fir, camphor, birch, beech, and poplar. The plant oil polyols are prepared by the following method: (1) Add vegetable oil and alcohol to a reaction vessel, heat to 60-70℃ and add enzyme catalyst, react for 6-10 hours to obtain reaction solution; (2) The enzyme catalyst was separated by vacuum distillation of the reaction solution, the alcohol was removed by rotary evaporation, and then the solution was washed with saturated sodium chloride solution and dried to obtain vegetable oil polyol. In step (1), the mass ratio of the vegetable oil, alcohol and enzyme catalyst is (50-250):(120-300):(0.1-10).

2. The anti-floating, fully bio-based polyurethane coating material according to claim 1, characterized in that, The dispersing agent is selected from one or more of the following: dimercaptodiphenyldimethyltin, dimethylstannous methyl ester, diethylenetriamine, triethylenediamine, triethanolamine, methyldiethanolamine, dimethylethanolamine, ethanolamine, n-butyl titanate, diisopropyl titanate, and tetraalkyl titanate.

3. The anti-floating, fully bio-based polyurethane coating material according to claim 1, characterized in that, The bio-based polyisocyanate is selected from 1,5-pentanedimethyl diisocyanate or a bio-based isocyanate compound obtained by compounding 1,5-pentanedimethyl diisocyanate and 1,6-hexanediisocyanate in a mass ratio of 7:

3.

4. The anti-floating, fully bio-based polyurethane coating material according to claim 1, characterized in that, The polyol is selected from one or two of ethylene glycol, polyethylene glycol 400, diethylene glycol, glycerol, 1,3-propanediol, and 1,4-butanediol; the catalyst is selected from one of sulfuric acid, phosphoric acid, silicotungstic acid, phosphomolybdic acid, silicotungstic acid, and NaBH4.

5. The anti-floating, fully bio-based polyurethane coating material according to claim 1, characterized in that, The enzyme catalyst is selected from one or more of Lipozyme 43, Novozyme 435, Lipozyme RM IM, Lipozyme TL IM, Rhizopusarrbizus, Candida rugosa, Rhizopusoryzae, and Lipase PS.

6. The application of the anti-floating, fully bio-based polyurethane coating material according to any one of claims 1-5 in the preparation of coated slow-release fertilizers.

7. The application according to claim 6, characterized in that, The coated slow-release fertilizer has at least one of the following properties (1)-(3): (1) Prevent fertilizer from floating; (2) Applicable to crop planting areas where the relative soil moisture content is less than 75%; (3) Applicable to rice-growing areas in the south.

8. A fully bio-based, anti-floating, slow-release fertilizer coated with polyurethane, characterized in that, The fertilizer core includes a bio-based anti-floating polyurethane coating material as described in any one of claims 1-5, wherein the bio-based anti-floating polyurethane coating material is sprayed onto the surface of the fertilizer core.

9. The method for preparing the anti-floating, fully bio-based polyurethane-coated slow-release fertilizer according to claim 8, characterized in that, Includes the following steps: The granular fertilizer, which serves as the core of the fertilizer, is heated to 50-70°C in a coating machine. The anti-floating fully bio-based polyurethane coating material according to any one of claims 1-5 is sprayed onto the surface of the granular fertilizer in batches. The amount of the anti-floating fully bio-based polyurethane coating material input each time is 1-2% of the total mass of the granular fertilizer. The coating is cured for 3-6 minutes. The above steps are repeated until the coating material accounts for 3%-4.5% of the total mass of the core fertilizer.

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