Attapulgite modified lignin / epoxy resin-based double-layer controlled-release fertilizer and preparation method thereof

Abstract

The application provides a palygorskite modified lignin / epoxy resin-based double-layer controlled-release fertilizer and a preparation method thereof, and belongs to the technical field of fertilizer manufacturing. The preparation method comprises the following steps: mixing and dissolving a liquefying agent and a polyol, adding lignin and an acid catalyst to perform a reaction, then adding palygorskite modification to obtain a palygorskite modified lignin-based polyol, and spraying the palygorskite modified lignin-based polyol, an isocyanate compound and a catalyst to the surface of a fertilizer to perform an in-situ polymerization reaction, so as to obtain an inner-layer coated fertilizer; mixing and dissolving epoxy resin and a wax water-blocking agent to obtain an outer-layer coating solution, and spraying the outer-layer coating solution to the outer surface of the inner-layer coated fertilizer, then spraying an amine compound, so that the double-layer controlled-release fertilizer is obtained. The double-layer controlled-release fertilizer breaks through the dependence of traditional fertilizers on non-degradable petroleum-based materials, not only realizes the easy degradability of the film material, effectively avoids secondary pollution, but also significantly reduces the production cost, and has extremely high economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer manufacturing, specifically relating to an attapulgite-modified lignin / epoxy resin-based bilayer slow-release fertilizer and its preparation method. Background Technology

[0002] Modern agriculture has an ever-increasing demand for chemical fertilizers to support the food needs of a growing global population. However, traditional fertilizer application methods suffer from low utilization rates and significant nutrient loss, leading not only to economic waste but also to a series of environmental problems such as water eutrophication, soil acidification, and greenhouse gas emissions. To address these challenges, controlled-release fertilizer technology has emerged. By controlling the rate of nutrient release, it enables plants to better absorb and utilize nutrients, thereby improving fertilizer utilization, reducing environmental pollution, and ultimately promoting sustainable agricultural development.

[0003] Currently, the coating materials for controlled-release fertilizers mainly rely on synthetic polymers, such as polyurethane, polyethylene, and polypropylene. While these materials exhibit excellent controlled-release performance, their non-degradable nature leads to environmental problems such as soil residue and plastic pollution, contradicting the principles of sustainable agriculture. Therefore, finding biodegradable and environmentally friendly coating materials has become a key challenge in the field of controlled-release fertilizer research.

[0004] Lignin, an abundant renewable resource derived from plant cell walls, is one of the most abundant natural aromatic polymers on Earth. Its excellent biodegradability, low cost, rich active functional groups, and good film-forming properties make it an ideal candidate for preparing coating materials for controlled-release fertilizers. However, the mechanical and water-blocking properties of lignin alone are relatively poor, making it difficult to meet the performance requirements of controlled-release fertilizer coating materials. To overcome these limitations, researchers have begun exploring the composite modification of lignin with other materials to improve its coating performance, hoping to develop a novel, efficient, environmentally friendly, and low-cost controlled-release fertilizer, providing a feasible solution to address the environmental problems caused by traditional fertilizers and promote sustainable agricultural development. Summary of the Invention

[0005] The purpose of this invention is to provide a novel slow-release fertilizer that is efficient, environmentally friendly, and low-cost.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing an attapulgite-modified lignin / epoxy resin-based bilayer controlled-release fertilizer, comprising the following steps:

[0008] S1: Mix and dissolve the liquefying agent and polyol to obtain a mixed solution. Then, add lignin and an acid catalyst to the mixed solution to react and obtain liquefied lignin-based polyol.

[0009] S2: Attapulgite is dispersed in the liquefied lignin-based polyol described in S1 to obtain attapulgite-modified lignin-based polyol;

[0010] S3: The attapulgite-modified lignin-based polyol, isocyanate compound and catalyst described in S2 are sprayed onto the fertilizer surface in sequence to carry out in-situ polymerization reaction to obtain inner-coated fertilizer.

[0011] S4: Mix and dissolve epoxy resin and wax water-blocking agent to obtain an outer coating solution;

[0012] S5: Spray the outer coating solution described in S4 onto the outer surface of the inner coating fertilizer described in S3, and then spray an amine compound. After the reaction is completed, the attapulgite-modified lignin / epoxy resin-based double-layer slow-release fertilizer is obtained.

[0013] Preferably, the mass ratio of the liquefying agent to the polyol in S1 is 12-14:1-2;

[0014] The liquefying agent is a mixture of polyethylene glycol and polycaprolactone diol in a mass ratio of 8:4 to 6.

[0015] The dissolution process involves a rotation speed of 300–400 rpm, a temperature of 120–180°C, and a time of 40–80 min.

[0016] Preferably, the polyethylene glycol is one or more of polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, and polyethylene glycol 800;

[0017] The polycaprolactone diol is one or more of polycaprolactone diol 530, polycaprolactone diol 830, and polycaprolactone diol 2000;

[0018] The polyol is one or both of ethylene glycol and glycerol.

[0019] Preferably, the amount of lignin and acid catalyst used in S1 is 50-200g of lignin and 0.1-2g of acid catalyst per 100g of mixed solution;

[0020] The lignin is one or more of alkali lignin, sulfate lignin and lignin sulfonate, and the lignin particle size is 60-120 mesh.

[0021] The acid catalyst is one or more of sulfuric acid and hydrochloric acid;

[0022] The reaction is carried out at a temperature of 120–180°C for a time of 0.5–1.5 h.

[0023] Preferably, the attapulgite in S2 accounts for 1 to 10 wt% of the total amount of the liquefied lignin-based polyol system;

[0024] The attapulgite is selected from one or more of high-quality attapulgite, opal attapulgite, dolomite attapulgite and montmorillonite attapulgite.

[0025] The temperature for dispersing the attapulgite in S2 is 120–180°C, and the time is 30–60 min.

[0026] Preferably, the mass ratio of the modified lignin-based polyol and the isocyanate compound in S3 is 1-2:1-1.25;

[0027] The catalyst accounts for 0.1% of the total mass of the modified lignin-based polyols and isocyanate compounds.

[0028] Preferably, the isocyanate compound is selected from one or more of toluene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, methylcyclohexyl diisocyanate, or tetramethylphenyl diisocyanate;

[0029] The catalyst is selected from one or more of the following: dibutyltin dilaurate, stannous octanoate, zinc naphthenate, zinc isooctanoate, bismuth carboxylate, bismuth isooctanoate, phenylmercuric propionate, or phenylmercuric acetate.

[0030] The fertilizer is selected from one or more of urea, ammonium nitrate, ammonium sulfate, monoammonium phosphate, diammonium phosphate, and potassium chloride.

[0031] Preferably, in step S3, the fertilizer needs to be preheated to 75-85°C before coating the inner layer fertilizer.

[0032] Preferably, the mass ratio of epoxy resin to wax water-blocking agent in S4 is (3-10):1;

[0033] The mass ratio of the outer coating solution to the amine compound is (1-4):1;

[0034] The epoxy resin is selected from one or more of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, E44 type epoxy resin, acrylic resin or brominated epoxy resin.

[0035] The wax water-blocking agent is selected from one or more of paraffin wax, microcrystalline wax, sulfonated paraffin wax, chlorinated paraffin wax or polyethylene wax;

[0036] The amine compound is selected from one or more of triethylenetetramine, diethylenetriamine, m-phenylenediamine, or polyamide.

[0037] The present invention also provides an attapulgite-modified lignin / epoxy resin-based bilayer slow-release fertilizer.

[0038] Beneficial effects

[0039] (1) The raw material lignin of the present invention has the characteristics of low cost, renewable and wide availability, while the coating material is easy to degrade in the natural environment and is environmentally friendly.

[0040] (2) The present invention uses attapulgite-modified lignin and epoxy resin as double-layer coating materials, which can more precisely control the release rate of nutrients, further improve the utilization efficiency of fertilizers, and extend the effective action time of fertilizers, which can make up for the shortcomings of single-layer coated fertilizers that have short slow release time and are not easy to control.

[0041] (3) This invention utilizes attapulgite to increase the roughness of the membrane material, improve the surface energy, and enhance the hydrophobicity of the membrane material. Attapulgite is a natural nano clay mineral with a unique rod-shaped structure, a large specific surface area, excellent adsorption and ion exchange properties. Combining attapulgite with lignin can effectively improve the mechanical strength, water resistance, and nutrient adsorption capacity of lignin-based coating materials, thereby improving the performance of controlled-release fertilizers.

[0042] (4) The preparation process of this invention is simple, easy to operate, and low in cost. By adjusting the coating thickness, it can meet the nutrient requirements of different crops at different growth stages. The prepared double-layer slow-release fertilizer has a good controlled release effect, with an initial nutrient release rate of ≤2% and a cumulative release period of ≥28 days.

[0043] This invention utilizes lignin, a renewable resource, to develop a novel environmentally friendly controlled-release fertilizer. It breaks away from the reliance of traditional fertilizers on non-degradable petroleum-based materials, achieving not only easily degradable membrane materials and effectively avoiding secondary pollution, but also significantly reducing production costs, resulting in extremely high economic benefits. This fertilizer, combining excellent controlled-release performance, low cost, and environmental friendliness, aligns with the trend of sustainable development and provides a strong guarantee for the sustainable development of future agriculture. Attached Figure Description

[0044] Figure 1 The cumulative nitrogen release of the double-layer slow-release fertilizers prepared in Examples 1-5 is shown. Detailed Implementation

[0045] Unless otherwise specified, all methods described herein are conventional methods. Unless otherwise specified, all materials described herein are available from publicly available commercial sources.

[0046] In this invention, high-quality attapulgite has an attapulgite content of more than 85%, and the main impurities are micron-sized detrital quartz and feldspar, as well as a small amount of authigenic opal and dolomite.

[0047] The lignin used in the various embodiments and comparative examples of this invention was obtained from Shandong Xinglong Paper Industry (Group) Co., Ltd., the urea was purchased from Shaanxi Shanhua Coal Chemical Group Co., Ltd., and the polyphenylmethyl polyisocyanate was purchased from Guangzhou Baichuan Chemical Co., Ltd.

[0048] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0049] Example 1

[0050] S1: Polyethylene glycol 400, polycaprolactone diol 530 and glycerol were mixed in a mass ratio of 8:4:1 and placed in a three-necked flask equipped with a stirrer and a condenser. The mixture was heated to 160°C in an oil bath and stirred at 350 rpm for 40 min to obtain a mixed solution. Then, 70 g of alkali lignin that had passed through a 100-mesh sieve and 2 g of concentrated sulfuric acid with a mass fraction of 98% were added to 100 g of the mixed solution. The mixture was mixed evenly and the reaction was continued at 160°C and atmospheric pressure (101.325 kPa) for 1 h to obtain liquefied lignin-based polyol.

[0051] S2: Add 3 wt% of high-quality attapulgite to the liquefied lignin-based polyol described in S1, and continue the reaction at 160°C for 50 min until the mixture is homogeneous to obtain attapulgite-modified lignin-based polyol.

[0052] S3: Weigh 1000g of large granular urea with an average particle size of 3-5mm, place it in a rotary drum coating machine and preheat it at 80℃ for 15min to obtain preheated fertilizer;

[0053] Weigh 9.62g of the attapulgite-modified lignin-based polyol, 12.03g of hexamethylene diisocyanate, and stannous octoate (0.1% of the total mass of the attapulgite-modified lignin-based polyol and hexamethylene diisocyanate) as described in S2, and spray them sequentially onto the preheated fertilizer surface. Perform an in-situ polymerization reaction at 80℃ for 30 minutes. After the reaction is completed, allow the fertilizer to cool naturally to obtain the inner coating fertilizer.

[0054] S4: Mix E44 type epoxy resin and paraffin wax at a mass ratio of 9:1 and heat to 90°C to completely dissolve them to obtain an outer coating solution.

[0055] S5: Weigh 7.42g of the outer coating solution and spray it evenly onto the surface of the inner coating fertilizer described in S3. Then, carry out an in-situ polymerization reaction with 1.86g of triethylenetetramine at 80℃ for 20min to obtain an attapulgite-modified lignin / epoxy resin-based double-layer slow-release fertilizer.

[0056] Example 2

[0057] S1: Polyethylene glycol 400, polycaprolactone diol 830 and glycerol were mixed in a mass ratio of 8:6:1 and placed in a three-necked flask equipped with a stirrer and a condenser. The mixture was heated to 180°C in an oil bath and stirred at 350 rpm for 50 min to obtain a mixed solution. Then, 70 g of alkali lignin that had passed through a 100-mesh sieve and 2 g of concentrated sulfuric acid with a mass fraction of 98% were added to 100 g of the mixed solution. The mixture was mixed evenly and the reaction was continued at 180°C and atmospheric pressure (101.325 kPa) for 1 h to obtain liquefied lignin-based polyol.

[0058] S2: Add 5 wt% of high-quality attapulgite to the liquefied lignin-based polyol described in S1, and continue the reaction at 160°C for 50 min until the mixture is homogeneous to obtain attapulgite-modified lignin-based polyol.

[0059] S3: Weigh 1000g of large granular urea with an average particle size of 3-5mm, place it in a rotary drum coating machine and preheat it at 80℃ for 15min to obtain preheated fertilizer;

[0060] Weigh 14.81g of the attapulgite-modified lignin-based polyol, 18.52g of hexamethylene diisocyanate, and stannous octoate (0.1% of the total mass of the attapulgite-modified lignin-based polyol and hexamethylene diisocyanate) as described in S2, and spray them sequentially onto the preheated fertilizer surface. Perform an in-situ polymerization reaction at 80℃ for 30 minutes. After the reaction is completed, allow the fertilizer to cool naturally to obtain the inner coating fertilizer.

[0061] S4: Mix E44 type epoxy resin and paraffin wax at a mass ratio of 9:1 and heat to 90°C to completely dissolve them to obtain an outer coating solution.

[0062] S5: Weigh 6.67g of the outer coating solution and spray it evenly onto the surface of the inner coating fertilizer described in step S3. Then, carry out an in-situ polymerization reaction with 1.67g of triethylenetetramine at 80°C for 20 minutes to obtain attapulgite-modified lignin / epoxy resin-based double-layer slow-release fertilizer.

[0063] Example 3

[0064] S1: Polyethylene glycol 200, polycaprolactone diol 530 and glycerol were mixed in a mass ratio of 8:4:2 and placed in a three-necked flask equipped with a stirrer and a condenser. The mixture was heated to 160°C in an oil bath and stirred at 350 rpm for 60 min to obtain a mixed solution. Then, 65 g of alkali lignin that had passed through a 100-mesh sieve and 1.5 g of concentrated sulfuric acid with a mass fraction of 98% were added to 100 g of the mixed solution. The mixture was mixed evenly and the reaction was continued at 160°C and atmospheric pressure (101.325 kPa) for 1 h to obtain liquefied lignin-based polyol.

[0065] S2: Add 5 wt% of high-quality attapulgite to the liquefied lignin-based polyol described in S1, and continue the reaction at 160°C for 50 min until the mixture is homogeneous to obtain attapulgite-modified lignin-based polyol.

[0066] S3: Weigh 1000g of large granular urea with an average particle size of 3-5mm, place it in a rotary drum coating machine and preheat it at 80℃ for 15min to obtain preheated fertilizer;

[0067] Weigh 14.81g of the attapulgite-modified lignin-based polyol, 18.52g of hexamethylene diisocyanate, and stannous octoate (0.1% of the total mass of the attapulgite-modified lignin-based polyol and hexamethylene diisocyanate) as described in S2, and spray them sequentially onto the preheated fertilizer surface. Perform an in-situ polymerization reaction at 80℃ for 30min. After the reaction is completed, allow the fertilizer to cool naturally to obtain the inner coating fertilizer.

[0068] S4: Mix E44 type epoxy resin and paraffin wax at a mass ratio of 9:1 and heat to 90°C to completely dissolve them to obtain an outer coating solution.

[0069] S5: Weigh 6.67g of the outer coating solution and spray it evenly onto the surface of the inner coating fertilizer described in step S3. Then, carry out an in-situ polymerization reaction with 1.67g of triethylenetetramine at 80°C for 20 minutes to obtain attapulgite-modified lignin / epoxy resin-based double-layer slow-release fertilizer.

[0070] Example 4

[0071] S1: Polyethylene glycol 600, polycaprolactone diol 830 and glycerol were mixed in a mass ratio of 8:4:1 and placed in a three-necked flask equipped with a stirrer and a condenser. The mixture was heated to 160°C in an oil bath and stirred at 350 rpm for 70 min to obtain a mixed solution. Then, 65 g of alkali lignin that had passed through a 100-mesh sieve and 2 g of concentrated sulfuric acid with a mass fraction of 98% were added to 100 g of the mixed solution. The mixture was mixed evenly and the reaction was continued at 160°C and atmospheric pressure (101.325 kPa) for 1 h to obtain liquefied lignin-based polyol.

[0072] S2: Add 3 wt% of high-quality attapulgite to the liquefied lignin-based polyol described in S1, and continue the reaction at 160°C for 50 min until the mixture is homogeneous to obtain attapulgite-modified lignin-based polyol.

[0073] S3: Weigh 1000g of large granular urea with an average particle size of 3-5mm, place it in a rotary drum coating machine and preheat it at 80℃ for 15min to obtain preheated fertilizer;

[0074] Weigh 18.71g of the attapulgite-modified lignin-based polyol, 23.39g of hexamethylene diisocyanate, and stannous octoate (0.1% of the total mass of the attapulgite-modified lignin-based polyol and hexamethylene diisocyanate) as described in S2, and spray them sequentially onto the preheated fertilizer surface. Perform an in-situ polymerization reaction at 80℃ for 30min. After the reaction is completed, allow the fertilizer to cool naturally to obtain the inner coating fertilizer.

[0075] S4: Mix E44 type epoxy resin and paraffin wax at a mass ratio of 9:1 and heat to 90°C to completely dissolve them to obtain an outer coating solution.

[0076] S5: Weigh 8.42g of the outer coating solution and spray it evenly onto the surface of the inner coating fertilizer described in S3. Then, carry out an in-situ polymerization reaction with 2.11g of triethylenetetramine at 80℃ for 20min to obtain the attapulgite-modified lignin / epoxy resin-based double-layer slow-release fertilizer.

[0077] Example 5

[0078] S1: Polyethylene glycol 400, polycaprolactone diol 2000 and glycerol were mixed in a mass ratio of 8:6:2 and placed in a three-necked flask equipped with a stirrer and a condenser. The mixture was heated in an oil bath to 180°C and stirred at 350 rpm for 80 min to obtain a mixed solution. Then, 70 g of alkali lignin that had passed through a 100-mesh sieve and 1.5 g of concentrated sulfuric acid with a mass fraction of 98% were added to 100 g of the mixed solution. The mixture was mixed evenly and reacted at 180°C and atmospheric pressure (101.325 kPa) for 1 h to obtain liquefied lignin-based polyol.

[0079] S2: Add 5 wt% of high-quality attapulgite to the liquefied lignin-based polyol described in S1, and continue the reaction at 160°C for 50 min until the mixture is homogeneous to obtain attapulgite-modified lignin-based polyol.

[0080] S3: Weigh 1000g of large granular urea with an average particle size of 3-5mm, place it in a rotary drum coating machine and preheat it at 80℃ for 15min to obtain preheated fertilizer;

[0081] Weigh 18.71g of the attapulgite-modified lignin-based polyol, 23.39g of hexamethylene diisocyanate, and stannous octoate (0.1% of the total mass of the attapulgite-modified lignin-based polyol and hexamethylene diisocyanate) as described in S2, and spray them sequentially onto the preheated fertilizer surface. Perform an in-situ polymerization reaction at 80℃ for 30min. After the reaction is completed, allow the fertilizer to cool naturally to obtain the inner coating fertilizer.

[0082] S4: Mix E44 type epoxy resin and paraffin wax at a mass ratio of 9:1 and heat to 90°C to completely dissolve them to obtain an outer coating solution.

[0083] S5: Weigh 8.42g of the outer coating solution and spray it evenly onto the surface of the inner coating fertilizer described in step S3. Then, carry out an in-situ polymerization reaction with 2.11g of triethylenetetramine at 80°C for 20 minutes to obtain the attapulgite-modified lignin / epoxy resin-based double-layer slow-release fertilizer.

[0084] Test case

[0085] The controlled-release performance of the obtained double-layer controlled-release fertilizer was tested according to the national standard GB / T 23348~2009. The steps are as follows: Weigh 10g of the double-layer controlled-release fertilizer and place it in a 100-mesh nylon mesh bag. After sealing, place the mesh bag containing the double-layer controlled-release fertilizer into a 300mL plastic bottle, add 250mL of deionized water, seal the bottle, and incubate it in a biochemical incubator at 25℃. Samples were taken at regular intervals (sampling times were 24h, 3d, 5d, 7d, 10d, 13d, 16d, 19d, 22d, 25d, 28d, 35d, 42d, 49d, 56d, 63d…). During sampling, the plastic bottle was inverted three times to ensure that the liquid concentration in the bottle was consistent. Take 50 mL of the extract, cool it, and then determine the total nitrogen content. The coating thickness and controlled-release performance of different fertilizers are shown in Table 1. The coating thickness is expressed as the percentage of coating material in the core fertilizer. The date corresponding to 80% cumulative nutrient release is defined as the cumulative nutrient release period of the fertilizer. Results Figure 1 As shown.

[0086] Table 1. Coating thickness and controlled-release performance of different fertilizers

[0087] Encapsulation thickness Initial dissolution rate of nitrogen Controlled release period Example 1 3％ 1.55％ 42d Example 2 4％ 1.01％ 49d Example 3 4％ 0.98％ 56d Example 4 5％ 0.79％ 56d Example 5 5％ 0.75％ 63d

[0088] Depend on Figure 1 As shown in Table 1, the prepared double-layer slow-release fertilizer has a good controlled-release effect, with an initial nutrient dissolution rate of ≤2% and a cumulative release period of ≥28 days.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an attapulgite-modified lignin / epoxy resin-based bilayer slow-release fertilizer, characterized in that, Includes the following steps: S1: Mix and dissolve the liquefying agent and polyol to obtain a mixed solution. Then, add lignin and an acid catalyst to the mixed solution to react and obtain liquefied lignin-based polyol. S2: Attapulgite is dispersed in the liquefied lignin-based polyol described in S1 to obtain attapulgite-modified lignin-based polyol; S3: The attapulgite-modified lignin-based polyol, isocyanate compound and catalyst described in S2 are sprayed onto the fertilizer surface in sequence to carry out in-situ polymerization reaction to obtain an inner-coated fertilizer. S4: Mix and dissolve epoxy resin and wax water-blocking agent to obtain an outer coating solution; S5: Spray the outer coating solution described in S4 onto the outer surface of the inner coating fertilizer described in S3, and then spray an amine compound. After the reaction is complete, the attapulgite-modified lignin / epoxy resin-based double-layer slow-release fertilizer is obtained. The liquefying agent in S1 is a mixture of polyethylene glycol and polycaprolactone diol, the polyol is glycerol, and the mass ratio of polyethylene glycol, polycaprolactone diol and glycerol is 8:6:

2. The amount of lignin and acid catalyst used is 65-70g of lignin and 1.5-2g of acid catalyst per 100g of mixed solution; The attapulgite mentioned in S2 accounts for 3-5 wt% of the total amount of the liquefied lignin-based polyol system; The attapulgite is selected from one or more of high-quality attapulgite, opal attapulgite, dolomite attapulgite and montmorillonite attapulgite. The temperature for dispersing the attapulgite in step S2 is 160~180℃, and the time is 30~60 min.

2. The preparation method according to claim 1, characterized in that, The dissolution process involves a rotation speed of 300-400 rpm, a temperature of 120-180℃, and a time of 40-80 min.

3. The preparation method according to claim 2, characterized in that, The polyethylene glycol is one or more of polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600 and polyethylene glycol 800; The polycaprolactone diol is one or more of polycaprolactone diol 530, polycaprolactone diol 830, and polycaprolactone diol 2000.

4. The preparation method according to claim 3, characterized in that, The lignin in S1 is one or more of alkali lignin, sulfate lignin and lignin sulfonate, and the lignin particle size is 60~120 mesh. The acid catalyst is one or more of sulfuric acid and hydrochloric acid; The reaction is carried out at a temperature of 120~180℃ for a time of 0.5~1.5h.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the modified lignin-based polyol and isocyanate compound in S3 is 1~2:1~1.25; The catalyst accounts for 0.1% of the total mass of the modified lignin-based polyols and isocyanate compounds.

6. The preparation method according to claim 5, characterized in that, The isocyanate compound is selected from one or more of toluene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, methylcyclohexyl diisocyanate, or tetramethylphenyldimethyl diisocyanate; The catalyst is selected from one or more of the following: dibutyltin dilaurate, stannous octanoate, zinc naphthenate, zinc isooctanoate, bismuth carboxylate, bismuth isooctanoate, phenylmercuric propionate, or phenylmercuric acetate. The fertilizer is selected from one or more of urea, ammonium nitrate, ammonium sulfate, monoammonium phosphate, diammonium phosphate, and potassium chloride.

7. The preparation method according to claim 6, characterized in that, In S3, the fertilizer needs to be preheated to 75~85℃ before coating the inner layer of the fertilizer.

8. The preparation method according to claim 7, characterized in that, The mass ratio of epoxy resin to wax water-blocking agent in S4 is (3~10):1; The mass ratio of the outer coating solution to the amine compound is (1~4):1; The epoxy resin is selected from one or more of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, E44 type epoxy resin, acrylic resin or brominated epoxy resin. The wax water-blocking agent is selected from one or more of paraffin wax, microcrystalline wax, sulfonated paraffin wax, chlorinated paraffin wax or polyethylene wax; The amine compound is selected from one or more of triethylenetetramine, diethylenetriamine, m-phenylenediamine, or polyamide.

9. An attapulgite-modified lignin / epoxy resin-based bilayer controlled-release fertilizer prepared by the preparation method according to any one of claims 1 to 8.

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