Hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and preparation method thereof

Abstract

The invention provides a hydroxymethylated lignin-based urea formaldehyde slow release fertilizer and a preparation method thereof, and the preparation method comprises the following steps: carrying out hydroxymethylation modification on lignin nanofiber (LCNF) to obtain hydroxymethylated lignin nanofiber (HLCNF), and then mixing urea, a formaldehyde solution and the HLCNF to prepare the hydroxymethylated lignin-based urea formaldehyde (HLCNF-UF). HLCNF is introduced into a urea formaldehyde molecular chain, so that hydroxymethylated lignin-based urea formaldehyde also has a long-acting slow-release effect, the effective utilization rate of nitrogen elements in urea formaldehyde by crops is improved, and the excessive loss of nutrients is reduced. The mechanical strength of the modified hydroxymethylated lignin-based urea formaldehyde is remarkably enhanced, so that the integrity of the fertilizer can be ensured in the processing, transportation and storage processes, and the method is a key factor for reducing loss and improving efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of urea formaldehyde slow-release fertilizers, in particular to a hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof. Background Art

[0002] In order to meet the nutrient needs of plants in different growth cycles, reduce the loss of fertilizers in the soil and avoid the pollution of the environment caused by excessive nitrogen fertilizer application, modifying fertilizers and developing new slow-release fertilizers has become an effective solution strategy. Urea formaldehyde slow-release fertilizer (UF), as one of the representatives of slow-release fertilizers, is the first variety to be applied on a large scale and commercialized. This urea formaldehyde slow-release fertilizer forms a long-chain polymer with low solubility through a hydroxymethylation addition reaction of formaldehyde and urea under alkaline conditions, followed by a methylene condensation reaction under acidic conditions. This polymer can be decomposed by soil microorganisms, thereby achieving the slow release of nitrogen for plant absorption. By compounding other nitrogen, phosphorus, potassium, trace elements and organic matter, urea formaldehyde compound fertilizers that meet the needs of different crop growth cycles can be prepared, reducing the number of fertilization times and reducing production costs.

[0003] However, with the continuous development of urea-formaldehyde slow-release fertilizers, the urea-formaldehyde slow-release fertilizers produced by the prior art are difficult to be destroyed and decomposed by microorganisms due to the strong hydrogen bonding between molecular chains and the regular molecular chain arrangement, which makes the utilization rate of nitrogen element low and the release rate difficult to match with the crop growth demand. Therefore, regulating the structure of urea-formaldehyde molecular chain and crystallization region is a key issue to expand its application field. In addition, the mechanical properties of existing urea-formaldehyde slow-release fertilizers are not good, which is not conducive to transportation. Improving its mechanical properties and ensuring the integrity of fertilizers during processing, transportation and storage are important factors to reduce losses and improve efficiency. Summary of the invention

[0004] In view of the above background research, the present invention provides a urea formaldehyde slow-release fertilizer modified by hydroxymethylated lignin nanofibers, which can slowly release nutrients during soil degradation, and also has good mechanical properties, is easy to transport and store, and is particularly simple in preparation process.

[0005] The present invention aims to use formaldehyde to hydroxymethylate lignin nanofibers (LCNF) under alkaline conditions to obtain hydroxymethylated lignin nanofibers (HLCNF), and then add them into hydroxymethylurea solution in different mass ratios for polymerization reaction to prepare urea-formaldehyde polymers with high mechanical strength and excellent sustained-release performance.

[0006] The specific implementation is in accordance with the following technical solutions:

[0007] A method for modifying hydroxymethylated lignin-based urea formaldehyde comprises the following steps:

[0008] (1) A 37-40% formaldehyde solution is fully mixed with LCNF under mechanical stirring, wherein the LCNF accounts for 5-20% of the total mass of formaldehyde, and potassium hydroxide is used to adjust the pH of the mixture to about 11. Subsequently, the mixture is reacted at a water bath temperature of 60°C for 80 minutes to obtain hydroxymethylated lignin nanofibers (HLCNF).

[0009] (2) Urea and 37 wt% formaldehyde solution were fully mixed in a molar ratio of 1.1-1.8:1, and potassium hydroxide was used to adjust the pH value to 8-9, the temperature was raised to 50°C, and mechanical stirring was carried out for 30 minutes. Then a fixed mass of HLCNF was added, and mechanical stirring was continued for 30 minutes. After the hydroxylation reaction was completed, phosphoric acid was used to adjust the pH value to 5.0, and the temperature was raised to 70°C to allow a methylene polymerization reaction to occur. After the polymerization reaction was completed, potassium hydroxide was used to adjust the pH value of the system to neutral to terminate the reaction, and then the mixture was filtered, dried, and crushed to obtain hydroxymethylated lignin-based urea formaldehyde (HLCNF-UF).

[0010] Preferably, the formaldehyde solution has a mass concentration of 37-40%, which can effectively improve the reaction rate and prevent explosion caused by excessive reaction.

[0011] Preferably, the potassium hydroxide can be replaced by sodium hydroxide, ammonia water or one or more thereof.

[0012] Preferably, the phosphoric acid can be replaced by one or more of lactic acid, superphosphate, and ammonium polyphosphate (oligomeric).

[0013] Preferably, the mass of the hydroxymethylated lignin nanofibers is 5-20% of the total mass of formaldehyde.

[0014] The present invention has the advantages as described below:

[0015] (1) Solution polymerization is used to prevent explosion during the methylenization reaction, which causes the product to be over-polymerized and stick to the reactor, thereby increasing the cleaning cost.

[0016] (2) The molecular structure of urea formaldehyde contains a large number of hydrogen bonds, which makes the molecular structure of urea formaldehyde stable and difficult to decompose. The addition of hydroxymethylated lignin nanofibers destroys the hydrogen bonding of urea formaldehyde molecules, reduces the crystallinity, and is conducive to the degradation of fertilizers in the environment, thereby increasing the release rate of nutrients.

[0017] (3) The compressive strength of the prepared hydroxymethylated lignin nanofiber urea formaldehyde is much higher than that of pure urea formaldehyde. Therefore, when it is actually used as a granular fertilizer, the prepared hydroxymethylated lignin nanofiber urea formaldehyde is easier to handle than pure urea formaldehyde, and can reduce the loss during transportation and thus reduce the breakage loss.

[0018] (4) The prepared HLCNF-UF urea formaldehyde slow-release fertilizer contains nitrogen, an essential nutrient element for plant growth, and can slowly release nutrients during the degradation process, thus being more conducive to plant absorption during growth.

[0019] (5) The prepared HLCNF-UF urea formaldehyde slow-release fertilizer can be directly used as a biodegradable slow-release nitrogen fertilizer, or it can be compounded with other organic matter, NPK and other nutrient elements to prepare a slow-release compound fertilizer. It can also be used to prepare a single species slow-release fertilizer suitable for the growth of different plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] These drawings are only used to assist in understanding the technical solution of the present invention and do not limit the scope of protection of the present invention. Each drawing is closely related to the corresponding embodiment or technical solution. By analyzing the drawings, the structure, function and relationship of the prepared materials can be more intuitively understood. It should be pointed out that although specific drawings are provided herein, the present invention is not limited to the implementation methods shown in these schematic diagrams, and any equivalent changes and alternatives within the spirit and scope of the present invention belong to the scope of protection of the present invention. Therefore, the drawings only provide a way to clearly explain the invention, and the specific implementation forms and details can be adjusted and optimized according to actual needs.

[0021] Figure 1 The preparation flow chart of HLCNF-UF.

[0022] Figure 2 FTIR spectrum of synthesized hydroxymethylated lignin nanofibers (HLCNF).

[0023] Figure 3 FTIR spectra of directly synthesized UF and HLCNF-UF.

[0024] Figure 4 are TG(A) and DTG(B) of the material.

[0025] Figure 5 XRD spectra of UF and HLCNF-UF.

[0026] Figure 6 The compression performance diagram and average compression strength diagram of UF and HLCNF-UF.

[0027] Figure 7 Comparative release curves of nitrogen in still water of UF and HLCNF-UF.

[0028] Figure 8 Cumulative release curve of nitrogen in still water of UF and HLCNF-UF.

[0029] Figure 1In the figure, the synthetic routes of UF and HLCNF-UF are shown.

[0030] Figure 2 In the figure, LCNF before and after hydroxymethylation are shown to study the effect of hydroxymethylation modification on the change of LCNF functional groups. -1 The stretching vibration peaks of -OH are at 1450, 1500, and 1590 cm -1 The absorption peak at 1040 cm is attributed to the C=C skeleton vibration of the benzene ring. -1 The absorption peak at belongs to the CO stretching vibration absorption peak of phenolic substances in LCNF. The infrared spectrum of HLCNF has similar absorption peaks to LCNF. It can be seen from the figure that the -OH stretching vibration peak of HLCNF is enhanced, which indicates that the hydroxyl content of HLCNF after hydroxymethylation modification is increased, making HLCNF more reactive in the hydroxymethylation reaction of formaldehyde and urea.

[0031] Figure 3 In the case of UF and HLCNF-UF, the -1 There are characteristic absorption peaks at 1650cm -1 The absorption peak at 1600cm is the bending vibration peak of -NH2-. -1 The absorption peak at is attributed to the bending vibration peak of -NH-. Compared with UF, the bending vibration peak of -NH- of HLCNF-UF is significantly weakened, which indicates that the addition of HLCNF reduces the amide groups in the system in a polymerized form and reduces the degree of polymerization of urea formaldehyde slow-release fertilizer, which will help promote the degradation of microorganisms and thus accelerate the nutrient release rate of fertilizers in the middle and late stages.

[0032] Figure 4Among them, the thermal stability of HLCNF-UF is higher than that of UF. This is because there are a large number of phenylpropane structural units in LCNF, which have good thermal stability. After reacting with hydroxymethyl urea, the overall thermal stability of slow-release fertilizer can be improved. The pyrolysis temperature of UT in the figure has three stages, namely 190-276℃, 276-290℃, and 290-315℃, and the corresponding thermal weight losses are 15.61%, 53.15%, and 87.87%. The thermal weight loss of UF mainly comes from the thermal decomposition process of amide groups. At lower temperatures, the primary amide groups at the ends of the molecular chains will break, while the secondary amide groups on the main chain of the molecules will break at higher temperatures. The pyrolysis of HLCNF-UF is also divided into three stages, namely 130-269℃, 269-287℃, and 287-506℃, and the corresponding thermal weight losses are 9.56%, 45.24%, and 78.62%. It can be seen that the pyrolysis temperature of HLCNF-UF in the first two stages is significantly lower than that of UF. This is because the addition of HLCNF hinders the condensation reaction of hydroxymethyl urea, resulting in more primary amide groups in HLCNF-UF, which can significantly increase the release rate of urea formaldehyde slow-release fertilizer in the later stage, thereby shortening the release cycle.

[0033] Figure 5 By comparing the XRD spectra of UF, HLCNF+UF, and HLCNF-UF, it can be concluded that UF has characteristic absorption peaks at 2θ=22.5°, 24.9°, and 31.3°, which indicates that there are certain crystalline regions in UF. This is because UF molecules contain a large number of amide groups, in which C=O and -NH- act as hydrogen bond acceptors and donors, respectively, and a large number of hydrogen bonds are formed in the UF molecular structure. This effect makes the UF molecular chain arrangement more regular and the molecular structure more stable, and finally forms a crystalline region that is difficult to degrade. The characteristic crystallization peaks of UF (2θ=22.5°, 24.9°, and 31.3°) also appear in HLCNF-UF, and the crystallinity of HLCNF-UF is 31.73%, which is lower than 44.69% of HLCNF+UF, indicating that the addition of HLCNF can destroy the hydrogen bonding effect of urea formaldehyde molecular chains to a certain extent and reduce the crystallinity, which will be beneficial to the degradation of fertilizers by microorganisms in the soil and increase the fertilizer release rate.

[0034] Figure 6 Overall, the maximum compressive strength of HLCNF-UF is 3.67MPa, which is 4 times the maximum compressive strength of UF 0.91MPa. This is because HLCNF-UF contains a large number of phenylpropane structural units. These rigid groups can significantly improve the mechanical properties of fertilizers, thereby reducing transportation losses and loss costs.

[0035] Figure 7In the first day of release in water, UF released 9.22% while HLCNF-UF released 4.05%. It can be seen that the addition of HLCNF reduced the initial release rate and reduced the nutrient loss of slow-release fertilizer in the early stage. After the seventh day, the average daily release rate of HLCNF-UF gradually exceeded the release rate of UF, indicating that the addition of HLCNF increased the release rate of slow-release fertilizer in the later stage. And the nitrogen nutrient release rate of UF gradually decreased after 25 days, while the nutrient release rate of HLCNF-UF remained at a high level in 20-50 days.

[0036] Figure 8In the figure, the static water cumulative release curves of UF and HLCNF-UF are shown. The nutrient release cycle of UF can be divided into three stages: from the 1st to the 5th day, the nutrient release rate reaches 27.75% rapidly; from the 6th to the 40th day, the nutrient release rate gradually slows down and reaches 50.65% on the 40th day; from the 41st to the 90th day, the nutrient release rate slows down further and reaches 59.55% on the 90th day, which is only 8.9% higher than the previous stage. Since each urea molecule can react with two formaldehyde molecules, and in the urea-formaldehyde (UF) system, the molar ratio of urea to formaldehyde is 1.1-1.8:1, which means that the amount of urea added is excessive. Therefore, after the reaction is completed, a large amount of urea that has not participated in the reaction still remains in the system. As a fast-acting nutrient, urea can dissolve quickly in water, so the nutrient release rate is high on the first day after the reaction. Similar to other polymers, the molecular weight of UF is polydisperse. Small molecule UF is easier to release into water, while large molecule UF dissolves slowly in water due to the entanglement between molecular chains. Therefore, the cumulative release rate of static water nutrients of UF gradually slows down over time. The cumulative release curve of nitrogen nutrients of HLCNF-UF is similar to that of UF. From the 1st to the 5th day, the nutrient release is rapid, and the cumulative release rate reaches 16.33%; from the 6th to the 40th day, the nutrient release rate is slightly accelerated, and the cumulative release rate reaches 57.23%, and the total release rate exceeds that of UF on the 30th day; from the 41st to the 90th day, the nutrient release rate gradually slows down, and finally reaches a release rate of 75.28%, which is 15.73% higher than the total release rate of UF. This is because hydroxymethylated lignin contains abundant functional groups such as phenolic hydroxyl groups and ether bonds, which give lignin slow release, chelation and adhesion functions, thereby inhibiting the release of unreacted urea to a certain extent. Therefore, the nitrogen release rate of HLCNF-UF on the 1st to 5th day was lower than that of UF. In HLCNF-UF, because it contains more small molecule UF and the hydroxymethyl groups in HLCNF help to improve the solubility of fertilizer, the nitrogen release rate of the system is relatively fast. The addition of HLCNF changed the nitrogen release pattern of urea formaldehyde slow-release fertilizer. In the later stage of the static water release experiment, HLCNF-UF was able to continuously release more nutrients, showing a fertilization pattern that was more in line with the growth needs of plants. DETAILED DESCRIPTION

[0037] In order to more clearly illustrate the purpose, technical solutions and advantages of the present invention, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments only represent some examples of the present invention, not all embodiments. Based on the embodiments of the present invention, other implementation methods that can be derived by ordinary technicians in this field without creative work all belong to the protection scope of the present invention.

[0038] The experimental determination standards in the present invention are:

[0039] Compression strength test: The compression strength of the sample is measured using a universal testing machine. The product after the reaction is pressed into a special mold and placed in an oven to dry to constant weight, obtaining cylindrical particles of uniform size (radius 7mm, height 7mm). The particles are placed individually on the universal testing machine and compressed at a rate of 5mm / min. The compression is stopped when the deformation reaches 50% of the maximum value. All treatments must be repeated more than five times.

[0040] Determination of nutrient release performance in static water: 0.5 g of sample was placed in a transparent plastic bottle containing 100 mL of distilled water, and then the bottle was placed in a dark environment and incubated at room temperature. At each incubation stage (1, 3, 5, 7, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 and 90 days), 5 mL of solution was taken out of the bottle, and the cumulative nutrient release rate of the material was determined by the p-dimethylaminobenzaldehyde colorimetric method.

[0041] Preferably, the reaction is carried out at a urea:formaldehyde molar ratio of 1.5:1, and the preparation of HLCNF-UF is carried out according to the following steps according to the combination of the examples in Table 1.

[0042] Table 1 Combination of component ratios for HLCNF-UF preparation

[0043]

[0044] Example 1

[0045] A hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof, comprising the following steps:

[0046] (1) 17 g of LCNF was added to a 100 mL beaker, and then 20 mL of deionized water was added to the beaker to disperse it evenly under mechanical stirring. Subsequently, 3 g of formaldehyde solution was added, and the pH of the system was adjusted to about 11 with potassium hydroxide solution. Finally, the mixture was reacted at 60 °C in a water bath for 80 min, and then centrifuged and washed until neutral to obtain hydroxymethylated modified lignin nanofibers (HLCNF).

[0047] (2) 30 g of urea and 27 g of formaldehyde solution were added to a 250 mL three-necked flask, and the pH of the system was adjusted to 8-9 with a 5% potassium hydroxide solution, and the temperature was raised to 50° C. and mechanically stirred for 30 min. Then, hydroxymethylated lignin nanofibers were added and the reaction was continued with mechanical stirring for 30 min. Then, the pH was adjusted to 5.0 with 5% phosphoric acid, and the temperature was raised to 70° C. and mechanical stirring was continued for 30 min to allow polymerization to occur. After the reaction was completed, the pH of the system was adjusted to neutral with potassium hydroxide to terminate the reaction, and then the mixture was filtered, dried in an oven at 60° C., and granulated to obtain hydroxymethylated lignin-based urea formaldehyde.

[0048] Example 2

[0049] A hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof, comprising the following steps:

[0050] (1) 34 g of LCNF was added to a 100 mL beaker, and then 20 mL of deionized water was added to the beaker to disperse it evenly under mechanical stirring. Subsequently, 6 g of formaldehyde solution was added, and the pH of the system was adjusted to about 11 with potassium hydroxide solution. Finally, the mixture was reacted at 60 °C water bath temperature for 80 min, and then centrifuged and washed until neutral to obtain hydroxymethylated modified lignin nanofibers (HLCNF).

[0051] (2) 30 g of urea and 27 g of formaldehyde solution were added to a 250 mL three-necked flask, and the pH of the system was adjusted to 8-9 with a 5% potassium hydroxide solution, and the temperature was raised to 50° C. and mechanically stirred for 30 min. Then, hydroxymethylated lignin nanofibers were added and the reaction was continued with mechanical stirring for 30 min. Then, the pH was adjusted to 5.0 with 5% phosphoric acid, and the temperature was raised to 70° C. and mechanical stirring was continued for 30 min to allow polymerization to occur. After the reaction was completed, the pH of the system was adjusted to neutral with potassium hydroxide to terminate the reaction, and then the mixture was filtered, dried in an oven at 60° C., and granulated to obtain hydroxymethylated lignin-based urea formaldehyde.

[0052] Example 3

[0053] A hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof, comprising the following steps:

[0054] (1) 51 g of LCNF was added to a 100 mL beaker, and then 20 mL of deionized water was added to the beaker to disperse it evenly under mechanical stirring. Then 9 g of formaldehyde solution was added, and the pH of the system was adjusted to about 11 with potassium hydroxide solution. Finally, the mixture was reacted at 60 °C in a water bath for 80 min, and then centrifuged and washed until neutral to obtain hydroxymethylated modified lignin nanofibers (HLCNF).

[0055] (2) 30 g of urea and 27 g of formaldehyde solution were added to a 250 mL three-necked flask, and the pH of the system was adjusted to 8-9 with a 5% potassium hydroxide solution, and the temperature was raised to 50° C. and mechanically stirred for 30 min. Then, hydroxymethylated lignin nanofibers were added and the reaction was continued with mechanical stirring for 30 min. Then, the pH was adjusted to 5.0 with 5% phosphoric acid, and the temperature was raised to 70° C. and mechanical stirring was continued for 30 min to allow polymerization to occur. After the reaction was completed, the pH of the system was adjusted to neutral with potassium hydroxide to terminate the reaction, and then the mixture was filtered, dried in an oven at 60° C., and granulated to obtain hydroxymethylated lignin-based urea formaldehyde.

[0056] Example 4

[0057] A hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof, comprising the following steps:

[0058] (1) 68 g of LCNF was added to a 100 mL beaker, and then 20 mL of deionized water was added to the beaker to disperse it evenly under mechanical stirring. Subsequently, 12 g of formaldehyde solution was added, and the pH of the system was adjusted to about 11 with potassium hydroxide solution. Finally, the mixture was reacted at 60 °C in a water bath for 80 min, and then centrifuged and washed until neutral to obtain hydroxymethylated modified lignin nanofibers (HLCNF).

[0059] (2) 30 g of urea and 27 g of formaldehyde solution were added to a 250 mL three-necked flask, and the pH of the system was adjusted to 8-9 with a 5% potassium hydroxide solution, and the temperature was raised to 50° C. and mechanically stirred for 30 min. Then, hydroxymethylated lignin nanofibers were added and the reaction was continued with mechanical stirring for 30 min. Then, the pH was adjusted to 5.0 with 5% phosphoric acid, and the temperature was raised to 70° C. and mechanical stirring was continued for 30 min to allow polymerization to occur. After the reaction was completed, the pH of the system was adjusted to neutral with potassium hydroxide to terminate the reaction, and then the mixture was filtered, dried in an oven at 60° C., and granulated to obtain hydroxymethylated lignin-based urea formaldehyde.

Claims

1. A hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof, characterized in that: The preparation method comprises the following steps: The urea and formaldehyde solution were mixed in a molar ratio of 1.1-1.8:1, and potassium hydroxide was used to adjust the pH value to 8-9, the temperature was raised to 50°C, and mechanical stirring was performed for 30 minutes. Then, hydroxymethylated lignin nanofibers were added, and mechanical stirring was performed for 30 minutes. Phosphoric acid was used to adjust the pH to 5.0, and the temperature was raised to 70°C. Mechanical stirring was continued for 30 minutes to allow polymerization to occur. After the reaction, potassium hydroxide was used to adjust the pH of the system to neutral to terminate the reaction. Then, the mixture was filtered, dried, and granulated to obtain hydroxymethylated lignin nanofiber urea formaldehyde.

2. The hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and preparation method thereof as claimed in claim 1, characterized in that: The formaldehyde aqueous solution has a mass concentration of 37-40%.

3. A hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof as claimed in claim 1, characterized in that: The potassium hydroxide can be replaced by sodium hydroxide, ammonia water or one or more of them.

4. The hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and preparation method thereof as claimed in claim 1, characterized in that: The phosphoric acid can be replaced by one or more of lactic acid, superphosphate, and ammonium polyphosphate (oligomeric).

5. The hydroxymethylated lignin nanofiber according to claim 1, characterized in that: The hydroxymethylated lignin nanofibers are prepared by mixing the lignin nanofibers and formaldehyde solution uniformly with mechanical stirring, adjusting the pH to 11, and reacting at 60° C. for 80 minutes to obtain the hydroxymethylated lignin nanofibers.

6. The hydroxymethylated lignin nanofiber according to claim 5, characterized in that The mass of the hydroxymethylated lignin nanofibers is 5-20% of the total mass of formaldehyde.

7. A hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof as claimed in claim 1, characterized in that: The drying temperature is 60°C.

8. The urea formaldehyde prepared by using the hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and the preparation method thereof as claimed in any one of claims 1 to 7 is used in the preparation of slow-release nitrogen fertilizer.

9. A hydroxymethylated lignin-based urea formaldehyde slow-release fertilizer and a preparation method thereof according to claim 1, characterized in that: The prepared hydroxymethylated lignin-based urea formaldehyde is a polymer slow-release nitrogen fertilizer with high mechanical strength and excellent slow-release performance.

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