Description:FIELD OF THE INVENTION

The present invention relates to the field of nanotechnology, specifically relates to the synthesis, characterization, and application of polyphosphoric acid (PPA) nanoparticles having particle size less than 50 nm. These particles are useful in the synthesis of nano fertilizers, particularly nano P, nano NP and nano NPK fertilizers.

BACKGROUND OF THE INVENTION

Agriculture has evolved in parallel with human evolution. Conventional agriculture demands the regular use of fertilizers, along with traditional agricultural practices, which can tremendously boost crop growth, the yield, the productivity, and the nutritional value.

The widespread use of fertilizers is a result of the increased global demand for food. The commonly used chemical fertilizers may increase plant growth and output, but they have deleterious effects on the soil, the environment, and even human health. Therefore, nano fertilizers are one of the most promising solutions or substitutes for conventional fertilizers. These engineered materials are composed of nanoparticles containing macro- and micronutrients that are delivered to the plant through roots or leaves in a regulated manner.

Nanoparticles are defined as particles which have size of < 100 nm and can be spherical or one-dimensional, inorganic, polymeric, biological or surfactant-based particles. Because of their size and high surface area to volume ratio, these particles have a wide range of potential applications.

Nanoparticles possess higher surface to volume fractions and distinctive features that make them very appropriate for use as compared to their bulk counterparts. The joint venture of nanotechnologies with agricultural and food science is emerging as a potential approach to increase plant growth and yield. With the help of this technology, farmers can utilize nanoparticles effectively and precisely with other limited resources like water and costly synthetic fertilizers.

Nanoparticles in nano fertilizers are nanoscale particles that can be used to control the release of nutrients to plants. Nano fertilizers are designed to be more efficient and cost-effective than traditional fertilizers. They can also help improve crop yields and reduce environmental impact. Due to their small size, they can easily penetrate the stomatal openings on the leaf surface. Once inside, they can enter the plant cell and deliver the nutrients to different parts of the plant.

Nanoparticles in nano fertilizers can be made from organic or inorganic nanomaterials. Inorganic nanomaterials include metal oxides like MgO, ZnO, and TiO2, while organic nanomaterials include lipids, and polymers. Nano fertilizers can also be formulated in different ways, such as suspensions, emulsions, gels, granulation, compression, and extrusion.

Nanoparticles in nano fertilizers can be used to slowly release nutrients under controlled conditions, which can reduce the amount of fertilizer that needs to be applied and improve its efficiency. Studies have shown that nano fertilizers can provide a continual supply of nutrients to plants over time, which can help them grow more healthily.

Phosphoric acid is the starting material for most commercial phosphate fertilizers, but its acidity and chemical properties make it difficult to apply directly. About 90% of phosphoric acid produced is used to make fertilizers, mainly converted into three phosphate salts: triple superphosphate (TSP), diammonium phosphate (DAP), and monoammonium phosphate (MAP).

Polyphosphoric acid (PPA) is a colorless, viscous liquid that can be used in many applications. For fertilizer applications, typically, ammonia reacts with polyphosphoric acid to form ammonium polyphosphate. It's a liquid “P” fertilizer that can increase agricultural production typically given through drip irrigation.

Frontiers in Bioengineering and Biotechnology, volume 8, article 4, 2020 discloses stable chitosan nanoparticles using polyphosphoric acid. Here polyphosphoric acid acts as a cross-linker to produce chitosan nanoparticles. However, the said article does not mention the synthesis of polyphosphoric acid nanoparticles using chitosan.

The present invention provides preparation of polyphosphoric acid nanoparticles and its use in the preparation of stable nano P fertilizer, nano NP (nitrogen and phosphorus) fertilizer and nano NPK (nitrogen, phosphorus, and potassium) fertilizer having particle size less than 100 nm.
SUMMARY OF THE INVENTION

The present invention is to provide a stable polyphosphoric acid nanoparticle having particle size (D90) less than 50 nm, pH ranges from 2.0 to 6.0 and zeta potential ranges -5 mV to + 25 mV.

In an aspect of the present invention is to provide a novel method for synthesizing polyphosphoric acid nanoparticles wherein the process comprising of:
a) preparing an aqueous solution of polyphosphoric acid,
b) preparing an aqueous cationic solution, and
c) adding dropwise the aqueous solution of step (b) to the solution of step (a) under stirring at 500-700 rpm for 20-30 minutes at room temperature to form polyphosphoric acid (PPA) nanoparticles.

In another aspect of present invention, the cationic agent is selected from poly ethylenimine (PEI), poly (diallyl dimethylammonium chloride) (PDDA), ethylenediamine (EDA), and lysine (Lys).

In another aspect of the present invention is to provide polyphosphoric acid (PPA) nanoparticles having a particle size (D90) (as measured by dynamic light scattering (DLS), and high-resolution transmission electron microscopy (HR-TEM) to be less than 50 nanometres.

In another aspect of the present invention is to provide polyphosphoric acid nanoparticles having the pH range from 2.0 to 6.0.

In yet another aspect of the present invention is to provide a process for the preparation of nano NP formulation using polyphosphoric acid nanoparticles, wherein the process comprising of:
a) dissolving a natural polymer in acetic acid and ammonium hydroxide mixture,
b) dissolving Urea in water under stirring,
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to get nano Urea,
e) slowly adding polyphosphoric acid nano particle solution to nano Urea solution under stirring by maintaining the pH 4.0 to 6.0 to form nano NP formulation.

In yet another aspect of the present invention is to provide a process for the preparation of stable nano NP formulation, wherein the process comprising the steps of:
a) dissolving a natural polymer in acetic acid,
b) dissolving DAP and Urea in water under stirring,
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to form a mixture of nano DAP and nano Urea,
e) slowly adding polyphosphoric acid solution to step (d) solution under stirring.
f) adding cationic agent to step (e) by maintaining pH of 4.0 to 6.0 to form a stable nano NP formulation.

In yet another aspect of the present invention is to provides a process for the preparation of nano NPK formulation using polyphosphoric acid nanoparticles wherein the process comprising of:
a) dissolving a natural polymer and potassium acetate in acetic acid under stirring,
b) preparing Urea solution in water
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to get nano NK formulation,
e) slowly adding polyphosphoric acid nano particle solution to mixture obtained in (d) to obtain nano NPK formulation.

These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the disclosed subject matter, nor is it intended to be used to limit the scope of the disclosed subject matter.

BRIEF DESCRIPTION OF DRAWINGS:

Figure 1 depicts High resolution transmission electron microscope (HR-TEM) images recorded for polyphosphoric acid (PPA)- poly ethylenimine (PEI) nano particles (10-20 nm), in accordance with example 1. HR-TEM is carried out by using JEOL JEM 2100 plus.

Figure 2 depicts High resolution transmission electron microscope (HR-TEM) images recorded for polyphosphoric acid (PPA)- poly (diallyl dimethylammonium chloride) (PDDA) nano particles (20-40 nm) in accordance with example 2. HR-TEM is carried out by using JEOL JEM 2100 plus.

Figure 3 depicts High resolution transmission electron microscope (HR-TEM) images recorded for polyphosphoric acid (PPA)- ethylenediamine (EDA) nano particles (5-20 nm) in accordance with example 3(a). HR-TEM is carried out by using JEOL JEM 2100 plus.

Figure 4 depicts Fourier Transform Infrared Spectroscopy (FTIR) images of neat polyphosphoric acid and polyphosphoric acid nanoparticles. (a) neat polyphosphoric acid; (b) polyphosphoric acid with poly ethylenimine (PEI) nanoparticles; (c) polyphosphoric acid with Poly (diallyl dimethylammonium chloride) (PDDA) nanoparticles; (d) polyphosphoric acid with ethylenediamine (EDA) nanoparticles; and (e) polyphosphoric acid with Lysine (Lys) nanoparticles.

The bands centered at 1630–1633, 2980-3154 cm-1 correspond respectively to the bending vibration of the H–O–H bond and stretching vibration of –O–H bond from water molecules. The feature at 1120 cm-1 is assigned to P=O stretching vibration for polyphosphoric acid (curve a). This band shifts to higher wavenumbers upon nanoparticle formation as seen in curve (b) to (e). This is due to the hydrogen bonding interaction between hydrogens of amine groups associated with cationic molecules with lone pair of oxygen in polyphosphoric acid. Another feature in polyphosphoric acid (curve a) at 966 cm-1 is assigned to P-O stretching vibration. This band also shifts to above 1000 cm-1 upon nanoparticle formation. This shift is due to the strong ionic interaction between polyphosphoric acid and cationic molecules.

DESCRIPTION OF THE INVENTION

Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions, and compounds referred to or indicated in this specification, individually or collectively, and all combinations of any or more of such steps or features.

For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here.

These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.

The articles "a", "an" and "the" are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The terms "comprise" and "comprising" are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as "consists of only".

Throughout this specification, unless the context requires otherwise the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated element or step or group of elements or steps but not the exclusion of any other element or step or group of elements or steps.

The term "including" is used to mean "including but not limited to". "including" and "including but not limited to" are used interchangeably.

The term “nanoparticle” refers to any particle having an average diameter of less than 100 nanometres (nm). In some embodiments, nanoparticles have an average diameter of less than 50 nm, less than 25 nm, less than 10 nm or less than 5 nm. Smaller particle size gets more surface area, leading to improved solubility in soil and water.

The term “zeta potential” refers to the potential difference existing between the surface of a solid component dispersed in a dispersion medium and the bulk of the dispersion medium. The value of zeta potential implies to the stability of a formulation.

Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

In an embodiment of the present invention provides a stable polyphosphoric acid nanoparticle having a particle size (D90) is less than 50 nm, pH ranges from 2.0 to 6.0 and zeta potential ranges -5mV to + 25 mV.

In another embodiment of the present invention provides a novel method for synthesizing polyphosphoric acid nanoparticles wherein the process comprising of:
a) preparing an aqueous solution of polyphosphoric acid,
b) preparing an aqueous cationic solution, and
c) adding dropwise the aqueous solution of step (b) to the solution of step (a) under stirring at 500-700 rpm for 20-30 minutes at room temperature to form polyphosphoric acid (PPA) nanoparticles.

According to the present embodiment, the first step is to prepare aqueous solution of polyphosphoric acid by dissolving it in water. Second step involves preparation of aqueous solution of cationic molecule by dissolving it in water. This is followed by dropwise addition of aqueous cationic solution to the polyphosphoric acid solution under stirring at 500-700 rpm for 20-30 minutes under water bath (since the reaction is exothermic) to form polyphosphoric acid (PPA) nanoparticles.

According to the present embodiment, the cationic agent is selected from poly ethylenimine (PEI), poly (diallyl dimethylammonium chloride) (PDDA), ethylenediamine (EDA), and lysine (Lys).

According to the present embodiment, the polyphosphoric acid nanoparticles have particle size (D90) as measured by dynamic light scattering (DLS), and high-resolution transmission electron microscopy (HR-TEM) is less than 50 nm.

According to the present embodiment, the polyphosphoric acid nanoparticles have pH range from 2.0 to 6.0.

According to the present embodiment, the polyphosphoric acid nanoparticles are stable at 54 °C for 14 days and exhibits a zeta potential in a range of -5 mV to + 25 mV measured directly without dilution.

In yet another embodiment of the present invention, provides use of polyphosphoric acid nanoparticles for the synthesis of nano NP formulations.

In yet another embodiment of the present invention provides a process for the preparation of nano NP formulation using polyphosphoric acid nanoparticles, wherein the process comprising of:
a) dissolving a natural polymer in acetic acid and ammonium hydroxide mixture,
b) dissolving Urea in water under stirring,
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to get nano Urea,
e) slowly adding polyphosphoric acid nano particle solution to nano Urea solution under stirring by maintaining the pH 4.0 to 6.0 to form nano NP formulation.

According to the present embodiment, the natural polymer is dissolved in acetic acid and ammonium hydroxide mixture. A nano urea solution is prepared by dissolving urea in water under stirring and sprayed to natural polymer solution followed by the addition of cross-linking agent solution and spreading agent. To this mixture polyphosphoric acid nanoparticle solution is slowly added to nano urea solution under stirring by maintaining the pH 4.0 to 6.0 to obtain nano NP formulation.

In yet another embodiment of the present invention provides a process for the preparation of stable nano NP formulation, wherein the process comprising the steps of:
a) dissolving a natural polymer in acetic acid,
b) dissolving DAP and Urea in water under stirring,
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to form a mixture of nano DAP and nano Urea,
e) slowly adding polyphosphoric acid solution to step (d) solution under stirring.
f) Adding cationic agent to step (e) by maintaining pH of 4.0 to 6.0 to form a stable nano NP formulation.

According to the present embodiment, the stable nano NP formulation that contains nano urea, nano DAP and polyphosphoric acid nanoparticles to achieve varying N:P ratio of 1:1 to 1:5.

In yet another embodiment of the present invention provides a process for the preparation of nano NPK formulation using polyphosphoric acid nanoparticles, wherein the process comprising of:
a) dissolving a natural polymer and potassium acetate in acetic acid under stirring,
b) preparing Urea solution in water
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to get nano NK formulation,
e) slowly adding polyphosphoric acid nano particle solution to mixture obtained in (d) to obtain nano NPK formulation.

According to the present embodiment, the natural polymer is dissolved in acetic acid followed by potassium acetate under stirring. A nano urea solution is prepared by dissolving urea in water under stirring and sprayed to natural polymer solution followed by the addition of cross-linking agent solution and spreading agent. To this mixture polyphosphoric acid nanoparticle solution is slowly added to nano urea solution under stirring by maintaining the pH 4.0 to 6.0 to obtain nano NP formulation.

According to the embodiments herein, natural polymers refer to such as agar, starches, alginates, chitosan, and cellulose. Natural polymers are commercially viable in field-based agricultural applications as they are cheap, readily available and biodegradable. According, to the present invention the natural polymer is chitosan.

The term “cross-linking agent” refers to a compound added to a formulation to facilitate the cross-linking of one or more components of the formulation. According, to the present embodiment the cross-linking agent is selected from sodium tripolyphosphate (STPP), polyacrylic acid, copolymers of acrylic acid, or combinations thereof.

The term “spreading agent” refers to one or more compounds added to a formulation to enhance the dispersion of the components and to facilitate ease of handling. According, to the present embodiment the spreading agent is selected from trisiloxane ethoxylate (Silwet 408), or the like.

The present invention provides a stable liquid nano fertiliser formulations containing Nitrogen and Phosphorous (as P2O5) having N:P ratio of 1:1 to 1:5 wherein the hydrodynamic diameter of the particles is less than 100 nm. The product of the present invention is stable at least for 24 months.

According to an embodiment, the nano NP formulation composed of at least two principal ingredients, nitrogen and phosphorous, additionally can combine with other nano nutrients such as nano potassium to produce Nano NPK fertilizers. The product of the present invention is stable at least for 24 months.

EXAMPLES:

The disclosure will now be illustrated with the working examples, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one ordinary person skilled in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices, and materials are described herein. It is to be understood that this disclosure is not limited to methods, and experimental conditions described, as such methods and conditions may apply.

EXAMPLE 1: Preparation of polyphosphoric acid (PPA) nanoparticles (20% P2O5) with Poly ethylenimine (PEI):
Aqueous solution of polyphosphoric acid (PPA) was prepared by dissolving 24 grams of polyphosphoric acid (PPA) in 98 mL of distilled water under constant stirring (24 grams in 98 mL). Subsequently, 2 mL of 33% poly ethylenimine (PEI) in water (PEI: water) solution was added dropwise to the reaction mixture, which was then stirred at 500 rpm for 30 minutes.

EXAMPLE 2: Preparation of polyphosphoric acid (PPA) nanoparticles (20% P2O5) with Poly (diallyl dimethylammonium chloride) (PDDA):
Aqueous solutions of polyphosphoric acid (PPA) (24 grams in 90 mL) and poly (diallyl dimethylammonium chloride) (PDDA) (1 mL in 9 mL) were prepared by dissolving the respective components in distilled water under constant stirring. The poly (diallyl dimethylammonium chloride) (PDDA) solution (10 mL) was then slowly added dropwise to the polyphosphoric acid (PPA) solution (90 mL) under continuous stirring at 500 rpm for 30 minutes.

EXAMPLE 3: Preparation of nano P formulation with different amounts of P2O5 in the final nano P product.
(a) Preparation of polyphosphoric acid (PPA) nanoparticles (20% P2O5) with Ethylenediamine (EDA):
Aqueous polyphosphoric acid (PPA) solution was prepared by dissolving 24 grams of polyphosphoric acid (PPA) in 95 mL of distilled water under constant stirring (24 grams in 95 mL). Subsequently, 5 mL of ethylenediamine (EDA) was slowly added to the solution while maintaining the pH around 5.0. The reaction mixture was then stirred at 500 rpm for 30 minutes.
(b) Preparation of polyphosphoric acid (PPA) nanoparticles (40% P2O5) with Ethylenediamine (EDA):
The aqueous polyphosphoric acid (PPA) solution was prepared by dissolving 48 grams of polyphosphoric acid (PPA) in 75-80 mL of distilled water under constant stirring. Subsequently, 10-12 mL of ethylenediamine (EDA) was slowly added to the solution while maintaining the pH around 4.5- 5.5. The reaction mixture was then stirred at 500 rpm for 30 minutes.
(c) Preparation of polyphosphoric acid (PPA) nanoparticles (60% P2O5) with Ethylenediamine (EDA):
The aqueous polyphosphoric acid (PPA) solution was prepared by dissolving 72 grams of polyphosphoric acid (PPA) in 65-75 mL of distilled water under constant stirring. Subsequently, 15-17 mL of ethylenediamine (EDA) was slowly added to the solution while maintaining the pH around 4.5- 5.5. The reaction mixture was then stirred at 500 rpm for 30 minutes.

EXAMPLE 4: Preparation of polyphosphoric acid (PPA) nanoparticles (20% P2O5) with Lysine (Lys):
Aqueous solutions of polyphosphoric acid (PPA) (24 grams in 90 mL) and Lysine (2 grams in 10 mL) were prepared by dissolving the respective components in distilled water under constant stirring. The Lysine solution (10 mL) was then slowly added dropwise to the polyphosphoric acid (PPA) solution (90 mL) under continuous stirring at 500 rpm for 30 minutes.

Table 1: Comprehensive parameters of polyphosphoric acid (PPA) nanoparticles:
S. No Component Name pH Particle Size Zeta Potential
D50 D90
1 PPA-PEI 1.92 7 10 16.8
2 PPA-PDDA 1.71 24 34 2
4 PPA-EDA 4.85 4 6 0.3
5 PPA-Lys 1.86 2 8 -0.9

Table 2: Stability data of polyphosphoric acid (PPA) nanoparticles:
Stability study at
temperature (540C) Particle size (D90) using DLS method
Day 0 (recorded same day when product is prepared) 12 nm
Day 3 18 nm
Day 5 13 nm
Day 7 35 nm
Day 14 48 nm

Table 2 represents the polyphosphoric acid nanoparticles prepared according to the present invention are very stable and the particle size is well below 50 nm at elevated temperature.

Advantages of the polyphosphoric acid (PPA) nanoparticles:
The present disclosure provides a novel and economic process to obtain a stable and convenient-to-use polyphosphoric acid (PPA) nano particle for agricultural applications.

 Polyphosphoric acid (PPA) nano particles can be directly used as a nano P-fertilizer through drip irrigation or through foliar application where exclusive P fertilization is required.
 Additionally, polyphosphoric acid (PPA) nanoparticles can combine with other nano nutrients such as nano N, nano K etc. to prepare a formulation consisting of Nano NP or nano NPK fertilizers.
 This versatility provides multiple options for the use of polyphosphoric acid (PPA) nanoparticles as a fertilizer in combination with other ingredients (both nano or non-nano and traditional water-soluble fertilizers).

EXAMPLE 5: Preparation of Nano NP (8% N & 20% P2O5) formulation using polyphosphoric acid nano particles:

Step 1: Preparation of polyphosphoric acid nanoparticles (40% P2O5):
Dissolved 480 grams of polyphosphoric acid in 600 mL distilled water. To this solution 80-90 mL of ethylenediamine (EDA) was added to control the pH around 5.0. The solution was stirred for 30 min, and then adjust the final volume of reaction mixture to 1000 mL

Step-2: Preparation of nano Urea (16% N):
Dissolved 350 grams urea in 320 ml of distilled water with constant stirring for 30 min. 400 mL of chitosan 1.25 % solution (prepared by dissolving 12.5 grams of Chitosan in 100 mL acetic acid and 900 mL water mixture under stirring at room temperature) was added to 10 mL of glacial acetic acid and 15 mL of ammonium hydroxide (25-30%) mixture. Spray urea solution into chitosan solution and stir for 30 minutes. To this solution 20 mL of sodium tripolyphosphate (STPP) 10% solution, and 5 mL Silwet 408 were added under constant stirring for 30 minutes.

Step-3: Process of synthesis Nano NP formulation:
500 mL nano urea (16%) solution was slowly added to 500 mL of polyphosphoric acid (40% P2O5) nanoparticles with constant stirring at 500 rpm for 30 minutes.

Product specification: Nitrogen 8%; Phosphorous (as P2O5) 20%; pH – 5.0 (±0.5); Specific gravity (SPG) – 1.2-1.3; Particle size by dynamic light scattering (DLS) – 50 nm; and Viscosity, cPs – 10-35.

EXAMPLE 6: Preparation of nano NP formulation (8% N & 20% P2O5) using in-situ polyphosphoric acid nanoparticles:

Step 1: Preparation of Nano Urea and nano DAP:
Dissolved 150 grams of DAP in 350 ml of distilled water with constant stirring for 30 min. After complete dissolution add 130 grams of urea in the DAP solution above with constant stirring for 30 min. Take 300 mL of chitosan 1.25% solution (prepared by dissolving 12.5 grams of Chitosan in 100 mL acetic acid and 900 mL water mixture under stirring at room temperature). Spray DAP-Urea solution into chitosan solution and stir for 30 minutes. To this solution add 20 mL of sodium tripolyphosphate (STPP) 10% solution with constant stirring for 30 minutes.
Step 2: In situ preparation of nano NP formulation using polyphosphoric acid nanoparticles with ethylenediamine:
Prepare aqueous solution of polyphosphoric acid by dissolving 190 grams of polyphosphoric acid in 50 mL of distilled water in water bath. Add dropwise to step-1 solution with constant stirring for 30 min. After this, add 50-60 mL of ethylenediamine (EDA) to the reaction mixture. The pH of the reaction is monitored and maintained at 4.0 to 6.0 with continuous cold-water circulation in the reactor.
Product specification: Nitrogen 8%; Phosphorous (as P2O5) 20%; pH – 5.0 (±0.5); Specific gravity (SPG) – 1.2-1.3; Particle size by dynamic light scattering (DLS) – 50 nm; and Viscosity, cPs – 10-35.

EXAMPLE 7: Preparation of Nano NPK (10% N; 10% P2O5 & 10% K) formulation using in-situ polyphosphoric acid nanoparticles.

Step 1: Preparation Potassium acetate and Urea nanoparticles:
215 grams of potassium acetate was dissolved in 300 mL of chitosan 1.25% solution (prepared by dissolving 12.5 grams of Chitosan in 100 mL acetic acid and 900 mL water mixture under stirring at room temperature) with constant stirring for 30 min to form a potassium-chitosan solution. Dissolve 220 grams of Urea in 250 mL distilled water with constant stirring for 30 min to obtain a Urea solution. The Urea solution was sprayed into potassium-chitosan solution and stirred for 30 minutes. To this solution 20 mL of sodium tripolyphosphate (STPP) 10% solution was added with constant stirring for 30 minutes.

Step 2: Preparation of nano NPK formulation using in-situ polyphosphoric acid nanoparticles:
Prepared aqueous solution of polyphosphoric acid by dissolving 119 grams of polyphosphoric acid in 30 mL distilled water in water batch. Added dropwise 2 mL of ethylenediamine with constant stirring in water batch. Added polyphosphoric acid nanoparticle to step-1 reaction mixture drop wise with continuous cold-water circulation in the reactor.

Product specification: Nitrogen 10%; Phosphorous (as P2O5) 10%; Potassium (as K2O) 10%; pH – 6.5 (±0.5); Specific gravity (SPG) – 1.2-1.3; Particle size by dynamic light scattering (DLS) – 50 nm; and Viscosity, cPs – 10-35.
Claims:

1. A stable polyphosphoric acid (PPA) nano particles having a particle size (D90) less than 50 nm, pH ranges from 2.0 to 6.0 and zeta potential -5mV to + 25 mV.

2. A novel method for synthesizing polyphosphoric acid nano particles, wherein the process comprising of:
a) preparing an aqueous solution of polyphosphoric acid,
b) preparing an aqueous cationic solution, and,
c) adding dropwise the aqueous solution of step (b) to the solution of step (a) under stirring at 500-700 rpm for 20-30 minutes at room temperature to form polyphosphoric acid (PPA) nanoparticles.

3. The process as claimed in claim 2, wherein the cationic agent is selected from poly ethylenimine (PEI), poly (diallyl dimethylammonium chloride) (PDDA), ethylenediamine (EDA), and lysine (Lys).

4. A process for the preparation of nano NP formulation using polyphosphoric acid, wherein the process comprising the steps of:
a) dissolving a natural polymer in acetic acid and ammonium hydroxide mixture,
b) dissolving Urea in water under stirring,
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to get nano urea,
e) slowly adding polyphosphoric acid nano particle solution to nano urea solution under stirring by maintaining the pH of 4.0 to 6.0 to form nano NP formulations.

5. A process for the preparation of stable nano NP formulation, wherein the process comprising the steps of:
a) dissolving a natural polymer in acetic acid,
b) dissolving DAP and Urea in water under stirring,
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to form a mixture of nano DAP and nano urea,
e) slowly adding polyphosphoric acid solution to step (d) solution under stirring.
f) adding cationic agent to step (e) by maintaining pH of 4.0 to 6.0 to form a stable nano NP formulation.

6. A process for the preparation of nano NPK formulation using polyphosphoric acid nanoparticles obtained according to claim 2, wherein the process comprising the steps of:
a) dissolving a natural polymer and potassium acetate in acetic acid under stirring,
b) preparing Urea solution in water
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to get nano NK formulation,
e) slowly adding polyphosphoric acid nano particle solution to mixture obtained in (d) to obtain nano NPK formulation.

7. The process as claimed in claim 4 to claim 6, wherein the natural polymer is chitosan.

8. The process as claimed in claim 4 to claim 6, wherein the cross-linking agent is selected from sodium tripolyphosphate (STPP), polyacrylic acid, copolymers of acrylic acid, or combinations thereof.

9. The process as claimed in claim 4 to claim 6, wherein the spreading agent is trisiloxane ethoxylate (Silwet 408).

10. The process as claimed in claim 5, wherein the nano NP formulation contains nano Urea, nano DAP and polyphosphoric acid nanoparticles to achieve N:P ratio of 1:1 to 1:5.

Dated this 30th day of September 2024

Sahadev Katam
General Manager, Legal-IPR
Coromandel International Limited
Registered Indian Patent Agent (IN/PA/5560)
, Claims:Claims:

1. A stable polyphosphoric acid (PPA) nano particles having a particle size (D90) less than 50 nm, pH ranges from 2.0 to 6.0 and zeta potential -5mV to + 25 mV.

2. A novel method for synthesizing polyphosphoric acid nano particles, wherein the process comprising of:
a) preparing an aqueous solution of polyphosphoric acid,
b) preparing an aqueous cationic solution, and,
c) adding dropwise the aqueous solution of step (b) to the solution of step (a) under stirring at 500-700 rpm for 20-30 minutes at room temperature to form polyphosphoric acid (PPA) nanoparticles.

3. The process as claimed in claim 2, wherein the cationic agent is selected from poly ethylenimine (PEI), poly (diallyl dimethylammonium chloride) (PDDA), ethylenediamine (EDA), and lysine (Lys).

4. A process for the preparation of nano NP formulation using polyphosphoric acid, wherein the process comprising the steps of:
a) dissolving a natural polymer in acetic acid and ammonium hydroxide mixture,
b) dissolving Urea in water under stirring,
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to get nano urea,
e) slowly adding polyphosphoric acid nano particle solution to nano urea solution under stirring by maintaining the pH of 4.0 to 6.0 to form nano NP formulations.

5. A process for the preparation of stable nano NP formulation, wherein the process comprising the steps of:
a) dissolving a natural polymer in acetic acid,
b) dissolving DAP and Urea in water under stirring,
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to form a mixture of nano DAP and nano urea,
e) slowly adding polyphosphoric acid solution to step (d) solution under stirring.
f) adding cationic agent to step (e) by maintaining pH of 4.0 to 6.0 to form a stable nano NP formulation.

6. A process for the preparation of nano NPK formulation using polyphosphoric acid nanoparticles obtained according to claim 2, wherein the process comprising the steps of:
a) dissolving a natural polymer and potassium acetate in acetic acid under stirring,
b) preparing Urea solution in water
c) spraying aqueous solution of step (b) to the solution of step (a) under constant stirring,
d) adding a solution of cross-linking agent and spreading agent to step (c) solution under stirring to get nano NK formulation,
e) slowly adding polyphosphoric acid nano particle solution to mixture obtained in (d) to obtain nano NPK formulation.

7. The process as claimed in claim 4 to claim 6, wherein the natural polymer is chitosan.

8. The process as claimed in claim 4 to claim 6, wherein the cross-linking agent is selected from sodium tripolyphosphate (STPP), polyacrylic acid, copolymers of acrylic acid, or combinations thereof.

9. The process as claimed in claim 4 to claim 6, wherein the spreading agent is trisiloxane ethoxylate (Silwet 408).

10. The process as claimed in claim 5, wherein the nano NP formulation contains nano Urea, nano DAP and polyphosphoric acid nanoparticles to achieve N:P ratio of 1:1 to 1:5.

Dated this 30th day of September 2024

Sahadev Katam
General Manager, Legal-IPR
Coromandel International Limited
Registered Indian Patent Agent (IN/PA/5560)