Lignin-based slow-release manganese fertilizer microcapsules, and preparation method and application thereof

Abstract

The application discloses a lignin-based slow-release manganese fertilizer microcapsule and a preparation method and application thereof. Lignin nanoparticles are prepared by taking sodium lignosulfonate as raw material, and a water-in-oil-in-water (W / O / W) Pickering double emulsion is prepared by adopting a one-step emulsification strategy. The double emulsion is used as a template for interfacial polymerization of the lignin nanoparticles and epichlorohydrin to form a microcapsule wall material, and manganese fertilizer (MnSO4) is successfully encapsulated in the microcapsule. Long-acting release of Mn(II) is realized, and the application realizes high-value utilization of lignin while effectively repairing cadmium pollution of rice. The preparation method of the slow-release manganese fertilizer has the advantages of low cost, green and harmless, environmental friendliness and the like.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer microcapsule preparation technology, specifically relating to a lignin-based slow-release manganese fertilizer microcapsule, its preparation method, and its application. Background Technology

[0002] Soil is a vital natural resource for human survival and development; however, in recent decades, heavy metal pollution has severely exacerbated soil pollution problems. On the one hand, heavy metals in the soil accumulate and enter the human body, impacting human health; on the other hand, heavy metal pollution in soil also has long-term effects on crop growth, yield, and soil fertility. This has adversely affected agricultural production and daily life worldwide. The most common toxic heavy metals are lead (Pb), cadmium (Cd), copper (Cu), chromium (Cr), mercury (Hg), zinc (Zn), and aluminum (Al). Due to their mutagenic and carcinogenic properties, these heavy metals are considered "priority pollutants" by the U.S. Environmental Protection Agency (USEPA, 1996). Cadmium, as a carcinogen, can cause functional disorders in many organs, such as the liver and kidneys, due to excessive accumulation in the body. Since rice is the staple food crop for nearly half the world's population, cadmium-contaminated rice becomes a major route of direct human exposure to cadmium. Cadmium pollution poses a threat to human life and health worldwide and has become a serious global problem. Therefore, remediating these heavy metal pollutants is a crucial step in maintaining environmental stability.

[0003] Studies have found that rice exhibits antagonistic effects in its absorption of manganese and cadmium, with manganese potentially reducing cadmium absorption by rice roots. Providing crops with essential nutrients, such as divalent cations, and mitigating antagonistic interactions between these nutrients and cadmium to reduce cadmium absorption is considered an effective strategy for reducing cadmium accumulation in rice. Manganese is one of the most important micronutrients in soil, participating in photosynthesis, regulating enzyme activity, and influencing protein, carbohydrate, and lipid metabolism. It is an essential micronutrient for plant growth and development. Manganese deficiency may inhibit plant growth and development; therefore, applying manganese fertilizer may be an important solution for remediating cadmium pollution in rice. Slow-release fertilizers, characterized by labor and cost savings, long-lasting effects, and synchronous absorption with crops, are widely recognized as a new type of fertilizer for improving crop fertilizer utilization, reducing agricultural non-point source pollution, and decreasing labor input, and are already widely used in horticulture. Therefore, encapsulating conventional manganese fertilizer in membranes or capsules to form slow-release manganese fertilizer can ensure the long-term release of manganese fertilizer, which provides a new approach for remediating cadmium pollution in crops and enabling crops to efficiently absorb nutrients.

[0004] Microcapsules are miniature containers with polymer wall materials. Their size generally ranges from 5-200 μm, and they come in various shapes, with spherical and elliptical shapes being the most common. Microencapsulation technology is a technique for encapsulating trace amounts of substances within a polymer film, serving as a micro-packaging technology for storing solids, liquids, and gases. The core material is encapsulated within the wall material using physical or chemical methods, forming a single-shell or multi-shell structure. This gives microcapsules the functions of protecting the core material, controlling its release, and enhancing its stability. Lignin, as a natural high-molecular-weight biomass-based material, is non-toxic, harmless, biodegradable under natural conditions, widely available, and inexpensive. However, most lignin byproducts are directly incinerated as industrial waste, with only 2% of industrial lignin used to manufacture high-value-added products such as additives, dispersants, adhesives, and surfactants. Increasingly, experts and scholars are conducting extensive research on the high-value applications of lignin, such as in the slow / controlled release applications of pharmaceuticals, fertilizers, pesticides, dyes, and cosmetics. There are three main methods for preparing lignin-based slow-release fertilizers: chemical modification, chelation modification, and coating modification. These methods are typically costly and can cause environmental pollution during preparation and application. Using lignin as a raw material to prepare microcapsules for encapsulating fertilizers is an effective strategy to address these issues.

[0005] Therefore, there is a need to develop a method for preparing slow-release fertilizer microcapsules that is simple in process and has excellent encapsulation effect. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a lignin-based slow-release manganese fertilizer microcapsule. The microcapsule provided by the present invention encapsulates a manganese solution as the internal aqueous phase, effectively slowing down the release rate of Mn fertilizer.

[0007] The second objective of this invention is to provide an environmentally friendly, low-cost, and simple method for preparing lignin-based slow-release manganese fertilizer microcapsules.

[0008] The third objective of this invention is to provide an application of lignin-based slow-release manganese fertilizer microcapsules.

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

[0010] The present invention discloses a lignin-based slow-release manganese fertilizer microcapsule, wherein the microcapsule is composed of an inner aqueous phase, an oil phase encapsulating the inner aqueous phase, and a lignin-based wall material encapsulating the oil phase, wherein the inner aqueous phase is a manganese source solution.

[0011] The lignin-based slow-release manganese fertilizer microcapsules provided by this invention encapsulate a manganese source solution as an inner aqueous phase within an oil phase, and are then encapsulated by a lignin-based wall material. This effectively slows down the release rate of Mn fertilizer. When applied as fertilizer for rice growth, it not only meets the growth needs of rice at different growth stages and improves the utilization rate of fertilizer nutrients, but also effectively remediates cadmium pollution in rice.

[0012] In a preferred embodiment, the manganese source is selected from at least one of manganese sulfate, manganese carbonate, and manganese chloride, preferably manganese sulfate monohydrate. The manganese source used is a water-soluble manganese fertilizer.

[0013] In a preferred embodiment, the oil phase is liquid paraffin. The inventors have discovered that the choice of oil phase is crucial; an unsuitable oil phase can prevent the preparation of a W / O / W type Pickering emulsion, i.e., it can prevent the encapsulation of the manganese source into microcapsules.

[0014] This invention also provides a method for preparing lignin-based slow-release manganese fertilizer microcapsules. A manganese source is added to a dispersion containing lignin nanoparticles, and then Tween 80 is added to obtain an aqueous phase. Epichlorohydrin and liquid paraffin are mixed to obtain an oil phase. The aqueous and oil phases are mixed and homogenized to obtain a W / O / W type Pickering emulsion. The W / O / W type Pickering emulsion is subjected to a crosslinking reaction to obtain lignin-based slow-release manganese fertilizer microcapsules.

[0015] The preparation method of this invention uses lignin nanoparticles as a Pickering emulsion stabilizer. The lignin nanoparticles can be simultaneously wetted by both the oil and aqueous phases. During the preparation of the Pickering emulsion, the lignin nanoparticles adsorb around the emulsion droplets, separating the aqueous and oil phases to form droplets. Because the lignin nanoparticles are charged, there is electrostatic repulsion between the droplets, thereby reducing droplet collision and aggregation. Furthermore, during the homogenization process, the lignin nanoparticles and Tween 80 act as stabilizers to stabilize the oil-water interface and the water-oil interface. This allows the manganese source, as the inner aqueous phase, to be successfully encapsulated into microcapsules and stably exist within them. Finally, the lignin nanoparticles and epichlorohydrin in the Pickering emulsion undergo a cross-linking reaction to generate the microcapsule wall material, which enables the microcapsules to protect the internal manganese source and release it slowly.

[0016] In this invention, lignin nanoparticles and Tween 80 are used together as stabilizers to stabilize the oil-water interface and the water-oil interface. This is the basis for the stable distribution of the manganese source within the microcapsules as the internal aqueous phase. With the combined action of lignin nanoparticles and Tween 80, the encapsulation efficiency of the internal aqueous phase is quite considerable. If lignin nanoparticles are used alone, or if other surfactants are used instead of Tween 80, the manganese source cannot be encapsulated into the microcapsules.

[0017] In a preferred embodiment, the lignin-containing nanoparticle dispersion contains lignin nanoparticles with a mass fraction of 0.5–3.0 wt%.

[0018] In a preferred embodiment, the method for obtaining the dispersion containing lignin nanoparticles is as follows: dissolving sodium lignin sulfonate in ethylene glycol to obtain a lignin solution, then adding HCl solution to the lignin solution to obtain a mixture, and dialysis to obtain the dispersion containing lignin nanoparticles. In this invention, lignin nanoparticles are prepared using an acid precipitation method.

[0019] In actual operation, sodium lignosulfonate is added to ethylene glycol and stirred to fully dissolve the sodium lignosulfonate particles. Then, it is filtered through a 0.45μm microfilter to remove insoluble impurities in the sodium lignosulfonate and obtain a lignin solution.

[0020] In a further preferred embodiment, the solid-liquid mass-volume ratio of sodium lignosulfonate to ethylene glycol is 0.25–1.5 g: 50.0 mL.

[0021] Further preferably, the concentration of the HCl solution is 0.01–0.1 mol / L, more preferably 0.025 mol / L.

[0022] A further preferred embodiment is that the HCl solution is added to the lignin solution at a rate of 0.1–1 mL / min. -1 Preferably 0.4 mL / min -1 .

[0023] In a further preferred embodiment, the volume ratio of the HCl solution to the lignin solution is 5 to 10:45.

[0024] In a further preferred embodiment, the dialysis bag for dialysis has a MWCO of 300 Da.

[0025] In practice, 15 mL of the solution was placed in a dialysis bag (MWCO = 300 Da) and dialyzed in a 2 L beaker for five days, with the water changed three times a day. After completion, a dispersion containing lignin nanoparticles was obtained.

[0026] In a preferred embodiment, the pH of the dispersion containing lignin nanoparticles is adjusted to alkaline before the manganese source containing lignin nanoparticles is added to the dispersion.

[0027] Further optimization involves using a 5% (w / w) NaOH solution and a 0.1 mol / L HCl solution to adjust the pH of the dispersion containing lignin nanoparticles to 8.

[0028] In a preferred embodiment, the solid-liquid mass ratio of the manganese source to the dispersion containing lignin nanoparticles is 0.01–0.1 g: 24 mL.

[0029] In a preferred embodiment, the volume ratio of Tween 80 to the dispersion containing lignin nanoparticles is 0.1–0.6:24, more preferably 0.1–0.3:24, and even more preferably 0.2:24. The optimal encapsulation effect is achieved when the amount of Tween 80 added is controlled within the above range; too much or too little will prevent the manganese source from effectively encapsulating into the microcapsules.

[0030] In a preferred embodiment, the volume ratio of epichlorohydrin to liquid paraffin is 0.1–0.4:16, more preferably 0.2–0.4:16, and even more preferably 0.27:16.

[0031] In a preferred embodiment, the volume ratio of the dispersion containing lignin nanoparticles to liquid paraffin is 4 to 6:4, preferably 6:4.

[0032] The inventors discovered that when the proportions of raw materials in each oil phase and water phase are controlled within the above-mentioned range, the encapsulation efficiency of the inner water phase is ultimately optimal.

[0033] In a preferred embodiment, the homogenization speed is 15,000–20,000 rpm, preferably 18,000 rpm, and the homogenization time is 1–5 min, preferably 2 min. In this invention, the homogenization parameters are controlled within the above ranges; otherwise, the encapsulation effect is poor. If the homogenization parameters are outside the range of this invention, a W / O / W type Pickering emulsion cannot be prepared, meaning the manganese source cannot be encapsulated into the microcapsules, resulting in insufficient sustained release.

[0034] In actual operation, W / O / W type Pickering emulsions were obtained by homogenization in a high-shear homogenizing emulsifier HR-500D.

[0035] In a preferred embodiment, the temperature of the crosslinking reaction is 60–100°C, preferably 65°C, and the reaction time is 4–6 hours, preferably 5 hours.

[0036] Further preferably, the crosslinking reaction is carried out under stirring, and the stirring speed is 200-400 rpm, preferably 300 rpm.

[0037] The present invention also provides an application of lignin-based slow-release manganese fertilizer microcapsules, which are used as fertilizer for rice growth.

[0038] The beneficial effects of this invention are:

[0039] 1. The slow-release manganese fertilizer microcapsules prepared by this invention have a simple process and good slow-release performance. Omnibus (OM) and CLSM characterization of the microcapsules show that manganese sulfate solution is encapsulated inside the microcapsules as the internal aqueous phase, with a good encapsulation efficiency. Slow-release experiments show that the release rate of the microcapsules increases with increasing temperature. After 85 hours, the cumulative release rates at 35℃, 25℃, and 15℃ are 72.2%, 66.9%, and 68.5%, respectively. Within the first 13 hours, Mn... 2+ The cumulative release rates at 35℃, 25℃, and 15℃ were 60.5%, 56.7%, and 53.4%, respectively. The results indicate that by controlling the release of Mn... 2+ Encapsulation within microcapsules can slow down the release rate of Mn fertilizer to some extent. This means that the release of slow-release manganese fertilizer microcapsules can meet the growth needs of rice at different growth stages and improve the utilization rate of fertilizer nutrients.

[0040] 2. The slow-release manganese fertilizer microcapsules prepared in this invention have demonstrated their ability to remediate cadmium pollution in rice through rice experiments. Compared with rice without manganese fertilizer, the cadmium content in the roots of rice treated with slow-release manganese fertilizer was reduced by 34.7%, and the cadmium content in the branches and leaves was reduced by 16.5%.

[0041] 3. The preparation method provided by the present invention is simple and easy to implement, requires no expensive equipment, and the raw materials are widely available and inexpensive. Attached Figure Description

[0042] Figure 1 This is a SEM image of the lignin nanoparticles in Example 1.

[0043] Figure 2 The images are Cryo-SEM (a-b), OM (c-d), and CLSM (e-f) images of the sustained-release manganese fertilizer microcapsules Mn@LNS-EL in Example 1.

[0044] Figure 3 The slow-release curves of the slow-release manganese fertilizer microcapsule Mn@LNS-EL in Example 1 at 15℃, 25℃, and 35℃ are shown in (a). The manganese deficiency symptoms of rice seedlings without manganese treatment are shown in (b). The control group, water treatment, MnSO4 treatment, and rice seedlings treated with Mn@LNS-EL grown in an environment of 0.45 mg / L Cd are also shown. Detailed Implementation

[0045] The following examples are intended to further illustrate the present invention, but not to limit it.

[0046] Example 1

[0047] (1) Preparation of lignin nanoparticle dispersion: Sodium lignin sulfonate was used as the raw material. 0.3 g of sodium lignin sulfonate was dissolved in 50.0 mL of ethylene glycol. The solution was stirred for 3 hours to fully dissolve the sodium lignin sulfonate particles. The solution was then filtered through a 0.45 μm microfilter to remove insoluble impurities from the sodium lignin sulfonate. 10 mL of 0.025 mol / L HCl was added at a concentration of 0.4 mL / min. -1 The solution was added at a rate of 100 mg / L to 45 mL of filtered lignin solution. Then, 15 mL of the solution was placed in a dialysis bag (MWCO = 300 Da) and dialyzed in a 2 L beaker for five days, changing the water three times a day. After completion, a dispersion containing lignin nanoparticles was obtained.

[0048] (2) Preparation of (W / O / W) water-in-oil-in-water double emulsion:

[0049] Aqueous phase: The pH of the dispersion containing lignin nanoparticles was adjusted to 8 with NaOH and HCl. 0.1g of MnSO4·H2O powder was added to 24mL of 1.5wt% dispersion containing lignin nanoparticles, and then 0.2mL of Tween 80 was added and stirred until fully dissolved to form the aqueous phase.

[0050] Oil phase: 0.3 mL of crosslinking agent epichlorohydrin and 16 mL of liquid paraffin were mixed as the oil phase.

[0051] The aqueous and oil phases were mixed and homogenized for 2 minutes at 16,000 rpm using a high-shear homogenizer HR-500D to obtain a W / O / W type Pickering emulsion.

[0052] (3) Preparation of sustained-release manganese fertilizer microcapsules

[0053] The W / O / W type Pickering emulsion prepared above was poured into a 100 mL round-bottom flask and reacted at 60 °C and 200 rpm for 4 h to obtain lignin wall material microcapsules.

[0054] Figure 1 This is a scanning electron microscope (SEM) image of lignin nanoparticles prepared by acid precipitation. Measurements using a Malvern nanoparticle size analyzer showed that the average particle size of the lignin nanoparticles was 88.78 nm, with a polydispersity index of 0.209. The lignin particles exhibited a relatively uniform particle size distribution and good dispersibility, with no observed aggregation. This lays the foundation for using lignin particles to stabilize Pickering emulsions.

[0055] Figure 2(a-b) Cryo-Scanning Electron Microscopy (CSE) images of the sustained-release manganese fertilizer microcapsules Mn@LNS-EL; (c-d) Optical Microscopy images of the sustained-release manganese fertilizer microcapsules Mn@LNS-EL; (e-f) Laser Confocal Microscopy (LCM) images of the sustained-release manganese fertilizer microcapsules Mn@LNS-EL. As shown in the figures, the sustained-release manganese fertilizer microcapsules exhibit regular shapes and smooth surfaces, with a size of 20 μm. Figure b shows that interfacial polymerization has resulted in a 0.7 μm capsule wall. Figures c-d show that the microcapsules are uniformly distributed and of similar size, encapsulating numerous small droplets. It is speculated that the encapsulated droplets are an aqueous phase, i.e., a manganese sulfate solution. To verify this hypothesis, we took LCM images of the microcapsules, as shown in Figures e-f. In the preparation of the water-in-oil-in-water emulsion, we stained the oil phase liquid paraffin with Nile Red fluorescent dye. The results showed that the oil phase was stained green, while the manganese sulfate solution, as the inner aqueous phase, was encapsulated within the microcapsules. This indicates the successful preparation of microcapsules encapsulating Mn fertilizer. This provides a basis for the effective sustained release of Mn from the microcapsules. 2+ This provides a solid foundation for the remediation of cadmium pollution in rice.

[0056] Figure 3 (a) Slow-release curves of the manganese fertilizer microcapsule Mn@LNS-EL at 15℃, 25℃, and 35℃; (b) Manganese deficiency symptoms in rice seedlings without manganese application; (c) Control group, water treatment, MnSO4 treatment, and Mn@LNS-EL treatment rice seedlings grown in an environment with 0.45 mg / L Cd. As shown in Figure a, the release rate of the microcapsules increased with increasing temperature. After 85 h, the cumulative release rates at 35℃, 25℃, and 15℃ were 72.2%, 66.9%, and 68.5%, respectively. Within the first 13 hours, Mn... 2+ The cumulative release rates at 35℃, 25℃, and 15℃ were 60.5%, 56.7%, and 53.4%, respectively. The results indicate that by controlling the release of Mn... 2+ Encapsulation within microcapsules can slow down the release rate of Mn fertilizer to some extent. This means that the release of Mn@LNS-EL fertilizer can meet the growth needs of rice at different growth stages and improve the utilization rate of fertilizer nutrients.

[0057] Table 1 shows the effects of different treatments on cadmium content in the roots and branches of rice seedlings; Table 2 shows the effects of different treatments on Mn content in the roots and branches of rice seedlings. Compared with rice without manganese fertilizer, the cadmium content in the roots of rice treated with slow-release manganese fertilizer decreased by 34.7%, and the cadmium content in the branches and leaves of rice decreased by 16.5%.

[0058] Table 1

[0059]

[0060] Table 2

[0061]

[0062] Figure 3 The testing method for a is as follows:

[0063] (1) Determination of Mn by ultraviolet spectrophotometry 2+ Content: Pipette 5 mL of Mn@LNS-EL suspension into a 25 mL graduated colorimetric tube, add 1.6 mL of sulfuric acid (1+1), 0.8 mL of phosphoric acid, and 8 mL of pure water, then add 0.1 g of potassium periodate. Place the graduated colorimetric tube in a water bath and maintain it at above 90℃ for 30 min, until the purple-red color is fully developed. After cooling, immediately dilute with water to the mark and shake well. Then, measure the absorbance at 540 nm using a 1 cm absorption dish on a UV-Vis spectrophotometer, and find the corresponding Mn content from the working curve.

[0064] (2) Sustained-release volume: Mn@LNS-EL (10 mL, 1160 mg / L) was transferred to a dialysis bag (MWCO = 300 Da), using ultrapure water as the release medium. The dialysis bag was placed in a beaker containing 100 mL of ultrapure water, and the dialysis apparatus was placed in a constant-temperature shaker for the sustained-release experiment. The temperature of the shaker was set to 15℃, 25℃, and 35℃, and the rotation speed was 200 rpm. Every so often, 5 mL of release medium was drawn from outside the dialysis bag, and 5 mL of ultrapure water was added to the beaker to ensure that the volume of the release medium remained constant. The absorbance of the diluted solution at 540 nm was measured by ultraviolet-spectrum spectrophotometry.

[0065] Example 2:

[0066] (1) Preparation of lignin nanoparticle dispersion: Sodium lignin sulfonate was used as the raw material. 0.3 g of sodium lignin sulfonate was dissolved in 50.0 mL of ethylene glycol. The solution was stirred for 3 hours to fully dissolve the sodium lignin sulfonate particles. The solution was then filtered through a 0.45 μm microfilter to remove insoluble impurities from the sodium lignin sulfonate. 10 mL of 0.05 mol / L HCl was added at a concentration of 0.7 mL / min. -1 The solution was added at a rate of 100 mg / L to 45 mL of filtered lignin solution. Then, 15 mL of the solution was placed in a dialysis bag (MWCO = 300 Da) and dialyzed in a 2 L beaker for five days, changing the water three times a day. After completion, a dispersion containing lignin nanoparticles was obtained.

[0067] (2) Preparation of (W / O / W) water-in-oil-in-water double emulsion:

[0068] Aqueous phase: The pH of the dispersion containing lignin nanoparticles was adjusted to 9 using NaOH and HCl. 0.1 g of MnSO4·H2O powder was added to 24 mL of 1.5 wt% dispersion containing lignin nanoparticles, and then 0.4 mL of Tween 80 was added and stirred until fully dissolved to form the aqueous phase.

[0069] Oil phase: 0.35 mL of crosslinking agent epichlorohydrin and 16 mL of liquid paraffin were mixed as the oil phase.

[0070] The aqueous and oil phases were mixed and homogenized for 3 minutes at 16,500 rpm using a high-shear homogenizer HR-500D to obtain a W / O / W type Pickering emulsion.

[0071] (3) Preparation of sustained-release manganese fertilizer microcapsules

[0072] The W / O / W type Pickering emulsion prepared above was poured into a 100mL round-bottom flask and reacted at 70℃ and 300rpm for 5h to obtain lignin wall material microcapsules.

[0073] Example 3:

[0074] (1) Preparation of lignin nanoparticle dispersion: Sodium lignin sulfonate was used as the raw material. 0.3 g of sodium lignin sulfonate was dissolved in 50.0 mL of ethylene glycol. The solution was stirred for 3 hours to fully dissolve the sodium lignin sulfonate particles. The solution was then filtered through a 0.45 μm microfilter to remove insoluble impurities from the sodium lignin sulfonate. 10 mL of 0.1 mol / L HCl was added at a concentration of 1 mL / min. -1 The solution was added at a rate of 100 mg / L to 45 mL of filtered lignin solution. Then, 15 mL of the solution was placed in a dialysis bag (MWCO = 300 Da) and dialyzed in a 2 L beaker for five days, changing the water three times a day. After completion, a dispersion containing lignin nanoparticles was obtained.

[0075] (2) Preparation of (W / O / W) water-in-oil-in-water double emulsion:

[0076] Aqueous phase: The pH of the dispersion containing lignin nanoparticles was adjusted to 10 with NaOH and HCl. 0.1g of MnSO4·H2O powder was added to 24mL of 1.5wt% dispersion containing lignin nanoparticles, and then 0.6mL of Tween 80 was added and stirred until fully dissolved to form the aqueous phase.

[0077] Oil phase: 0.4 mL of crosslinking agent epichlorohydrin and 16 mL of liquid paraffin were mixed as the oil phase.

[0078] The aqueous and oil phases were mixed and homogenized for 4 minutes at 18,000 rpm using a high-shear homogenizer HR-500D to obtain a W / O / W type Pickering emulsion.

[0079] (3) Preparation of sustained-release manganese fertilizer microcapsules

[0080] The W / O / W type Pickering emulsion prepared above was poured into a 100mL round-bottom flask and reacted at 80℃ and 400rpm for 6h to obtain lignin wall material microcapsules.

[0081] Comparative Example 1

[0082] The other conditions were the same as in Example 1, except that hexadecane was chosen as the oil phase, and the manganese source could not be encapsulated into the microcapsules as in Example 1.

[0083] Comparative Example 2

[0084] The other conditions were the same as in Example 1, except that lignin nanoparticles were used alone as a stabilizer, and the manganese source could not be encapsulated into the microcapsules as in Example 1.

[0085] Comparative Example 3

[0086] The other conditions were the same as in Example 1, except that the microcapsules were prepared at 100°C during the interfacial polymerization process, and the manganese source could not be encapsulated into the microcapsules as in Example 1.

[0087] Comparative Example 4

[0088] The other conditions were the same as in Example 1, except that the water-to-oil ratio was 8:2, and the manganese source could not be encapsulated into the microcapsules as in Example 1.

Claims

1. A method for preparing lignin-based slow-release manganese fertilizer microcapsules, characterized in that: A manganese source was added to a dispersion containing lignin nanoparticles, and then Tween 80 was added to obtain an aqueous phase. Epichlorohydrin was mixed with liquid paraffin to obtain an oil phase. The aqueous and oil phases were mixed and homogenized to obtain a W / O / W type Pickering emulsion. The W / O / W type Pickering emulsion was subjected to a cross-linking reaction to obtain lignin-based slow-release manganese fertilizer microcapsules. The lignin-based slow-release manganese fertilizer microcapsule consists of an inner aqueous phase, an oil phase encapsulating the inner aqueous phase, and a lignin-based wall material encapsulating the oil phase. The inner aqueous phase is a manganese source solution. The solid-liquid mass ratio of the manganese source to the dispersion containing lignin nanoparticles is 0.1 g: 24 mL. The volume ratio of Tween 80 to the dispersion containing lignin nanoparticles is 0.2 mL: 24 mL; The volume ratio of epichlorohydrin to liquid paraffin is 0.3 mL: 16 mL; The volume ratio of the dispersion containing lignin nanoparticles to liquid paraffin is 24 mL: 16 mL. The cross-linking reaction was carried out at a temperature of 60°C.

2. The method for preparing a lignin-based slow-release manganese fertilizer microcapsule according to claim 1, characterized in that: In the dispersion containing lignin nanoparticles, the mass fraction of lignin nanoparticles is 0.5~3.0wt%.

3. The method for preparing a lignin-based slow-release manganese fertilizer microcapsule according to claim 1 or 2, characterized in that: The method for obtaining the dispersion containing lignin nanoparticles is as follows: dissolve sodium lignin sulfonate in ethylene glycol to obtain a lignin solution, then add HCl solution to the lignin solution to obtain a mixed solution, and then dialyze to obtain a dispersion containing lignin nanoparticles. The solid-liquid mass-volume ratio of sodium lignosulfonate to ethylene glycol is 0.25~1.5g:50.0mL; The concentration of the HCl solution is 0.01~0.1 mol / L; The HCl solution was added to the lignin solution at a rate of 0.1~1 mL / min. -1 , The volume ratio of the HCl solution to the lignin solution is 5~10:45; The dialysis bag used for dialysis has a MWCO of 300 Da.

4. The method for preparing a lignin-based slow-release manganese fertilizer microcapsule according to claim 1 or 2, characterized in that: The pH of the dispersion containing lignin nanoparticles was adjusted to alkaline, and then the manganese source was added to the dispersion containing lignin nanoparticles. The pH of the dispersion containing lignin nanoparticles was adjusted to 8 using a 5% NaOH solution and a 0.1 mol / L HCl solution.

5. The method for preparing a lignin-based slow-release manganese fertilizer microcapsule according to claim 1 or 2, characterized in that; The homogenization speed is 15,000 to 20,000 rpm, and the homogenization time is 1 to 5 minutes.

6. The method for preparing a lignin-based slow-release manganese fertilizer microcapsule according to claim 1 or 2, characterized in that; The cross-linking reaction takes 4-6 hours. The crosslinking reaction is carried out under stirring at a speed of 200-400 rpm.

7. The method for preparing a lignin-based slow-release manganese fertilizer microcapsule according to claim 1 or 2, characterized in that: The manganese source is selected from at least one of manganese sulfate, manganese carbonate, and manganese chloride.

8. The application of a lignin-based slow-release manganese fertilizer microcapsule prepared by the preparation method according to any one of claims 1-7, characterized in that: The lignin-based slow-release manganese fertilizer microcapsules are used as fertilizer for rice growth.

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