DESC:
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]

“A PLANT NUTRIENT CARRYING ABSORBENT POLYMER AND A PROCESS OF PREPARATION THEREOF”

Hindustan Gum & Chemicals Ltd., an Indian Company at: Birla Colony, Bhiwani 127021, Haryana, India

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of the Invention:
The present invention provides a super absorbent polymer with plant nutrient additive which comprises a controlled blending of super absorbent polymer and hydroxyapatite and it’s hybrid based nutrients. The plant nutrient absorbent polymer can be mixed with soil so as to increase water retention capacity of the soil and provide nutrient which is essential for plant growth.

Background of the Invention:
Super absorbent polymer is an extremely hydrophilic polymer that is crosslinked into a three-dimensional network and has a unique ability to absorb at least a few hundred times of water as compared to its original dry weight. Super absorbent polymer based on acrylic acid or acrylate polymers have good absorption, retention and permeability properties.

However, the problem with the acrylic acid based polymers is that they are non-degradable and cause long term pollution to the environment. It takes many years for them to degrade under soil.

Additionally, the plant requires nutrients to grow and the traditional nutrient which are consumed by plants typically include between 40–70% nitrogen (N) and 80–90% phosphorus (P). However, the existing acrylic acid or acrylate based polymers do not full fill these requirements.

Thus, there exists a need to provide a polymer product which is easily degradable to the environment and also provide nutrients to the plants without drastically disturbing the water absorbing capacity of the polymer.

Summary of the invention:
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features.

Accordingly, the present invention provides a plant nutrient carrying absorbent polymer comprising a super absorbent polymer comprising polyglucosyl polymer chain linked to at least one acrylic acid or acrylate polymer chain and a hydroxyapatite. In an embodiment of the invention, hydroxyapatite comprises un-modified hydroxyapatite having a size in the range of 1 to 30 nm and modified hydroxyapatite having a size in the range of 1 to 60 nm. In another embodiment of the present invention, the modified hydroxyapatite comprises urea. In yet another embodiment of the invention, an aqueous solution containing 50% w/v of the polyglucosyl polymer chain has viscosity in the range of 5000-50000 cps at a room temperature.

In an embodiment of the invention, the acrylic acid or acrylate polymer chain comprises acrylic acid monomer neutralized to an extent of 60 % to 90% by the neutralizing agent. In another embodiment of the invention, the acrylic acid or acrylate polymer chain is present in an amount of about 10% to about 50 % by weight of the plant nutrient carrying absorbent polymer.

The polyglucosyl polymer chain is present in an amount in the range of about 18% to about 90% by weight of the plant nutrient carrying absorbent polymer. In an embodiment of the invention, hydroxyapatite is present in an amount of about 1% to 10% by weight of the plant nutrient carrying absorbent polymer. The super absorbent polymer comprises a cross-linking agent in an amount of about 0.1 to about 1% by weight. The cross-linkers are methylene bis- acrylamide (MBA) or Trimethylolpropane triacrylate (TMPTA).

The invention furthermore provides a process for preparing a plant nutrient carrying absorbent polymer, said process comprising mixing at least one acrylic acid or acrylate monomer, a polyglucosyl polymer, a cross-linking agent and hydroxyapatite under a polymerizing condition to obtain the plant nutrient carrying absorbent polymer.

To further clarify the advantages and features of the invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES:
In order that the invention may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying drawings. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention where:
Figure 1 illustrates a flow diagram for preparation of hydroxyapatite, in accordance with an embodiment of the invention;
Figure 2 illustrates a FTIR graph of a sample hydroxyapatite, in accordance with an embodiment of the invention;
Figure 3 illustrates a DLS graph if a sample hydroxyapatite, in accordance with an embodiment of the invention;
Figure 4 illustrates a flow diagram for preparation of MAP-Hydroxyapatite hybrid, in accordance with an embodiment of the invention;
Figure 5 illustrates a flow diagram for preparation of NPK-zeolite, in accordance with an embodiment of the invention;
Figure 6 illustrates a flow diagram for preparation of urea-hydroxyapatite hybrid, in accordance with an embodiment of the invention;
Figure 7 illustrates a FTIR graph of a sample hydroxyapatite-urea hybrid, in accordance with an embodiment of the invention;
Figure 8 illustrates a DLS graph of a sample hydroxyapatite-urea hybrid, in accordance with an embodiment of the invention;
Figure 9 illustrates a FTIR graph of the normal SAP prepared without NF, in accordance with an embodiment of the invention; and
Figure 10 illustrates a FTIR graph of the Urea-Hydroxyapatite hybrid incorporated super absorbent polymer, in accordance with an embodiment of the invention.

It may be noted that to the extent possible, like reference numerals have been used to represent like steps in the drawings. Further, skilled artisans will appreciate that the steps are illustrated for simplicity in the form of blocks, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

Detailed Description of the invention:
For the purpose of promoting an understanding of the principles of the invention, specific language will be used for describing the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications being contemplated as would normally occur to one skilled in the art to which the invention relates. It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.

A glycosyl group is a univalent free radical or substituent structure obtained by removing the hemiacetal hydroxyl group from the cyclic form of a monosaccharide and, by extension, of a lower oligosaccharide. The glycosyl group has the chemical structure - I as shown below:
… I

Two or more (preferably more) glycosyl groups can be linked to one another to form a poly glycosyl polymer chain.

In a preferred aspect of the invention, the poly glycosyl polymer chain substantially resembles the structure of at least one of an Amylose (having the chemical structure II), an Amylopectin (having the chemical structure III), pullulan (having well known chemical structure, which is not shown), glycogen (having well known chemical structure, which is not shown), dextran (having well known chemical structure, which is not shown), chrysolaminarin (having well known chemical structure, which is not shown), curdlan (having well known chemical structure, which is not shown), laminarin (having well known chemical structure, which is not shown), lentinan (having well known chemical structure, which is not shown), lichenin (having well known chemical structure, which is not shown), pleuran (having well known chemical structure, which is not shown), and zymosan (having well known chemical structure, which is not shown).

… II

…III

In a preferred embodiment of the invention, since predominantly comprises amylose and amylopectin, both of which contain glycosyl polymer chains, starch can be used as the source of the glycosyl polymer chains. The starch can be obtained from natural resources as well as can be from artificial resources (for example, can be synthesized in the laboratory). Starch can be categorized into native starches and modified starches.

Starch consists mainly of amylose and amylopectin. Amylose is a linear molecule of a-D- glucopyranosyl units linked by (1-4)-a-linkages. Amylopectin is a highly branched polymer of a-Dglucopyranosyl units linked by (1-4)-a-linkages and by(1-6)-a-linkages that constitute the branch points. Each glucose unit possesses a maximum of three hydroxyls that can undergo chemical substitution. Native starches can be physically (pre-gelatinized starches) and/or chemically modified for improved functionality.

The most common sources of native starch used in these modifications are various roots, tubers, cereals and legumes.

Modified starches are used in applications requiring special properties not attainable by native starches. Chemical modifications of native starches are often performed, in an aqueous suspension under controlled conditions of pH, time and temperature, unless otherwise indicated in the description of the respective annex. After sufficient reaction time, the modified starch is recovered by filtration or centrifugation, washed with water, dried and packaged.

The relevant modification reactions can be, separately or in combination, fragmentations (hydrolysis, oxidation, enzymatic), bleaching, oxidation, esterification, etherification or phosphorylation of one or more of the hydroxyl groups of the a-D-glucopyranosyl units or crosslinking using polyfunctional agents.

The term dextrinised starch or dextrin roasted starch comprises by way of non-limiting example, starches that are obtained by dry heating or roasting of native starch with hydrochloric acid or ortho-phosphoric acid in heated and/or agitated vessels. The final dextrin roasted starch is obtained by drying and include starches identified by International Numbering System (INS) number 1400.

The term acid treated starch comprises by way of non-limiting example, starches that are obtained by treating a slurry or a suspension of native food starch with dilute hydrochloric acid, ortho-phosphoric acid, or sulphuric acid and include starches identified by International Numbering System (INS) number 1401.The term alkali treated starch comprises by way of non-limiting example, starches that are obtained by treating a suspended solution of native food starches with sodium hydroxide or potassium hydroxide and include starches identified by International Numbering System (INS) number 1402.

The term bleached starch comprises by way of non-limiting example, starches that are obtained by treating a suspended solution of native food starches with Peracetic acid and/or hydrogen peroxide, or sodium hypochlorite, sodium chlorite, sulfur dioxide, alternative permitted forms of sulphites, potassium permanganate, or ammonium persulfate and include starches identified by International Numbering System (INS) number 1403.

The terms oxidized starch comprises by way of non-limiting example, starches that are obtained by treatment of food starch with sodium hypochlorite and include starches that are identified by International Numbering System (INS) number 1404.

The term enzymatically modified starch comprises by way of non-limiting example, starches that are obtained by treating a suspension of native food starch with one or more food-grade amyolytic-enzymes (e.g., a-amylase (E.C. 3.2.1.1), ß-amylase (3.2.1.2), glucoamylase (3.2.1.3), isoamylase (3.2.1.68), pullulanase (E.C. 3.2.1.41)) and include starches that are identified by International Numbering System (INS) number 1405.

The term mono-starch phosphate comprises by way of non-limiting example, starches that are obtained by esterification/crosslinking of unmodified food starch with ortho-phosphoric acid, or sodium or potassium orthophosphate, or sodium tripolyphosphate and include starches that are identified by International Numbering System (INS) number 1410.

The term di-starch phosphate comprises by way of non-limiting example, starches that are obtained by crosslinking of unmodified food starch with sodium trimetaphosphate or phosphorus oxychloride and include starches that are identified by International Numbering System (INS) number 1412.

The term phosphated di-starch phosphate comprises by way of non-limiting example, starches that are obtained by esterification/crosslinking of unmodified food starch with sodium trimetaphosphate or phosphorus oxychloride combined with esterification with orthophosphoric acid, or sodium or potassium orthophosphate, or sodium tripolyphosphate and include starches that are identified by International Numbering System (INS) number 1413.

The term acetylated distarch phosphate comprises by way of non-limiting example, starches that are obtained by esterification/crosslinking of unmodified food starch with sodium trimetaphosphate or phosphorus oxychloride combined with esterification with acetic anhydride or vinyl acetate and include starches that are identified by International Numbering System (INS) number 1414.

The term starch acetate comprises by way of non-limiting example, starches that are obtained by esterification of food starches with acetic anhydride or vinyl acetate and include starches that are identified by International Numbering System (INS) number 1420.

The term hydroxypropyl distarch phosphate by way of non-limiting example, starches that are obtained by esterification of unmodified food starch with sodium trimetaphosphate or phosphorus oxychloride combined with etherification by propylene oxide and include starches that are identified by International Numbering System (INS) number 1422.

The term hydroxypropyl starch comprises by way of non-limiting example, starches that are obtained by etherification of unmodified food starch with propylene oxide and include starches that are identified by International Numbering System (INS) number 1440.

The term hydroxypropyl distarch phosphate comprises by way of non-limiting example, starches that are obtained by esterification of unmodified food starch with sodium trimetaphosphate or phosphorus oxychloride combined with etherification by propylene oxide and include starches that are identified by International Numbering System (INS) number 1442.
The term starch sodium octenyl succinate comprises by way of non-limiting example, starches that are obtained by treatment of unmodified food starch with Octenylsuccinic anhydride and either sodium hydroxide or sodium carbonate as a pH buffer for neutralization and include starches that are identified by International Numbering System (INS) number 1450.

The term acetylated oxidized starch comprises by way of non-limiting example, starches that are obtained by treatment of food starch with sodium hypochlorite followed by esterification with acetic anhydride and include starches that are identified by International Numbering System (INS) number 1451.

The term Starch aluminum octenyl succinate comprises by way of non-limiting example, starches that are identified by International Numbering System (INS) number 1452.

Modified starches are used in applications requiring special properties not attainable by native starches. Chemical modifications of native starches are often performed, in an aqueous suspension under controlled conditions of pH, time and temperature, unless otherwise indicated in the description of the respective annex. After sufficient reaction time, the modified starch is recovered by filtration or centrifugation, washed with water, dried and packaged.

The relevant modification reactions can be, separately or in combination, fragmentations (hydrolysis, oxidation, enzymatic), bleaching, oxidation, esterification, etherification or phosphorylation of one or more of the hydroxyl groups of the a-D-glucopyranosyl units or crosslinking using poly functional agents.

Hydroxyapatite (HA) is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH) and a ceramic material which forms the mineral phase of bone. It is comprised primarily of calcium and phosphate at a respective ratio of 1:67.

Accordingly, the present invention provides a plant nutrient carrying absorbent polymer that comprises super absorbent polymer and a hydroxyapatite. In an embodiment of the invention, the hydroxyapatite is loaded on the super absorbent polymer. In another embodiment of the invention, the super absorbent polymer comprises polyglucosyl polymer chain which is further linked to at least one acrylic acid or acrylate polymer chain. In still another embodiment of the invention, the polyglucosyl polymer chain is present in an amount in the range of about 18 to about 50% by weight of the super absorbent polymer.

In an embodiment of the invention, polyglucosyl polymer chain comprises modified starch. Further, the modified starch is selected from a group comprising an enzymatically modified starch, dextrinised starch, an acid treated starch, an alkali treated starch, a bleached starch, an oxidized starch, mono-starch phosphate, di-starch phosphate, phosphated di-starch phosphate, acetylated distarch phosphate, starch acetate, hydroxypropyl starch, hydroxypropyl distarch phosphate, starch sodium octenyl succinate, and acetylated oxidized starch.

In an embodiment of the invention, the acrylic acid or acrylate polymer chain comprises acrylic acid monomer and a neutralizing agent. The neutralizing agent is having an alkali metal cation and potassium metal cation. The neutralizing agent is selected from the group of, but not limited to, sodium hydroxide, potassium hydroxide (KOH), and calcium hydroxide.

In an embodiment of the invention, the super absorbent polymer further comprises a cross-linker, which may be methylene bis- acrylamide (MBA) or Trimethylolpropane triacrylate (TMPTA). In an embodiment of the invention, the super absorbent polymer comprises a cross-linking agent in an amount of about 0.1 to about 1% by weight of the super absorbent polymer.

In an embodiment of the invention, hydroxyapatite comprises un-modified hydroxyapatite and modified hydroxyapatite. In an embodiment of the invention, the un-modified hydroxyapatite has a size in the range of 1 to 30 nm. In still another embodiment of the invention, the modified hydroxyapatite has a size in the range of 1 to 60 nm.

In an embodiment of the invention, the modified hydroxyapatite contains urea which is a source of nitrogen.

In an embodiment of the invention, an aqueous solution containing 50% w/v of the polyglucosyl polymer chain has viscosity in the range of 5000-50000 cps at a room temperature.

In an embodiment of the invention, the acrylic acid or acrylate polymer chain comprises acrylic acid monomer neutralized to an extent of 60 to 90% by the neutralizing agent.

In an embodiment of the invention, the acrylic acid or acrylate polymer chain is present in an amount of about 10 to about 50 % by weight.

In another embodiment of the invention, the polyglucosyl polymer chain is present in an amount in the range of about 18 to about 90% by weight of the water absorbent polymer.

In an embodiment of the invention, the hydroxyapatite is present in an amount of about 1 to 10% by weight of the plant nutrient carrying absorbent polymer.

Accordingly, the present invention provides a process for preparing a plant nutrient carrying absorbent polymer, said process comprising: mixing at least one acrylic acid or acrylate monomer, a polyglucosyl polymer, a cross-linking agent and hydroxyapatite under a polymerizing condition to obtain the plant nutrient carrying absorbent polymer. In an embodiment of the invention, the acrylic acid or acrylate polymer chain comprises acrylic acid monomer neutralized to an extent of 60 to 90% by the neutralizing agent.

In an embodiment of the invention, modified hydroxyapatite comprises hydroxyapatite hybrid linked with nitrogen nutrient.

In an embodiment of the invention, the modified hydroxyapatite/un-modified hypoxyapatite also delivers calcium (which is considered as a minor nutrient) to the soil.

In an embodiment of the invention, modified hydroxyapatite is urea-hydroxyapatite hybrid.

Example 1: Preparation of Hydroxyapatite
Referring to Figure 1, there is illustrated a flow chart of a process for preparation of hydroxyapatite by a wet chemical method by using calcium hydroxide and phosphoric acid having a weight ratio of 1:1 to 1:2 with a solid content of 40%. Firstly, the calcium hydroxide is dispersed in water (102). Then phosphoric acid is added drop by drop to the calcium hydroxide dispersion (104). After that the mixture is stirred vigorously (106) for about 2 hours under ambient condition to obtain a milky white dispersion which contains hydrpoxyaparite (108).

Characterization of Hydroxyapatite
The milky white dispersion thus obtained was subjected to FTIR analysis to cross check formation of Hydroxyapatite. The result of the FTIR analysis is shown in Figure 2, which confirms formation of Hydroxyapatite. The size of Hydroxyapatite was evaluated using dynamic light scattering (DLS) technique. The DLS graph as obtained for three samples Hydroxyapatite is shown in Figure 3. From the DLS graph it can be inferred that the sample Hydroxyapatite thus obtained has particle size in the range of 1 to 30 nm.

Example 2: Preparation of MAP-Hydroxyapatite hybrid
Referring to Figure 4, there is illustrated a flow chart for preparing MAP-Hydroxyapatite hybrid. Firstly ammonia (NH3) as a source of nitrogen is dispersed with calcium hydroxide at room temperature (202) and thereafter phosphoric acid is added to the above dispersion (204). After certain amount of stirring MAP-Hydroxyapatite hybrid is obtained (206). It was however observed that MAP-Hydroxyapatite hybrid merely contained 4 to 6 wt% of nitrogen.

Example 3: Preparation of NPK-zeolite hybrid
Referring to Figure 5, there is illustrated a process for preparation of NPK-zeolite hybrid. Firstly, sodium silicate is dispersed with ethyl alcohol (302). Thereafter, aluminium sulphate is added (304). The dispersion containing sodium silicate and aluminium sulphate in ethyl alcohol is heated, while continuously cooling the vapour produced and returning the liquid to the dispersion (306). The dispersed solution is then filtered out and dried (308) to obtain a solid material. The solid material is annealed at 650o C to obtain zeolite (310). The zeolite is treated with NPK (nitrogen, phosphorus and potassium) salts (312) to obtain NPK-zeolite hybrid. It was however observed that the process of loading salts of nitrogen, phosphorus and potassium on to a zeolite is a length process and the cost of the NPK-zeolite hybrid is substantially high.

Example 4: Preparation of urea-hydroxyapatite hybrid
Referring to Figure 6, there is illustrated a flow chart for preparing urea-hydroxyapatite hybrid. As per the process, urea and calcium hydroxide are dispersed in water at room temperature (402). Thereafter 0.6 moles of phosphoric acid is added with respect to calcium hydroxide (404) to obtain mother liquor. The mother liquor is agitated for about 2 hours to obtain urea-hydroxyapatite hybrid (406).

In the above process, the weight ratio between urea and hydroxyapatite weight could be varied from 1:1 to 5:1. Thus, the amount of nitrogen loading on hydroxyapatite was substantially high as compared to the MAP-Hydroxyapatite hybrid. Also, this process does not involve annealing at temperature of about 650o C. Thus, the process for preparing Urea-hydroxyapatite hybrid is faster and more economical as compared to the process for preparing NPK-zeolite hybrid.

Characterization of Urea-Hydroxyapatite hybrid fertilizer
The product as obtained at the end of the process as described above was subjected to FTIR analysis to cross-check formation of Urea-Hydroxyapatite hybrid. The result of the FTIR analysis is shown in Figure 7. The peak positions at 3428, 1677 and 1458 cm–1 are corresponding to the presence of N–HC=O, and N–C–N bond which are shifted from their position of 3441, 1682 and 1465 cm–1 respectively, confirms formation of Urea- Hydroxyapatite hybrid.

The size of Urea-Hydroxyapatite hybrid was evaluated using dynamic light scattering (DLS) technique. The DLS graph as obtained for three samples of Urea- Hydroxyapatite hybrid is shown in Figure 8. From the DLS graph it can be inferred that the sample Urea-Hydroxyapatite hybrid thus obtained has particle size in the range of 1 to 60 nm.

Experiment 1: Micro-Batch (Lab) Scale process for preparation of plant nutrient carrying absorbent polymer loading with hydroxyapatite:
The lab-scale process for preparing plant nutrient carrying absorbent polymer having hydroxyapatite loaded thereupon involved mixing the acrylic acid monomer, different types of starches (having different viscosities and in different weight percentage), a cross linker, a hydroxyapatite and a polymerization initiator in a kettle.

Lab scale process was performed using different types of polyglucosyl polymers, typically native starches or modified starches such as, Guar Gum, Carboxy methyl Guar Gum, Oxidized Guar Gum, Sesbania Gum, Carboxymethyl Cellulose, Carboxymethyl Tamarid, Cassia Tora Gum, Topica Starch, Carboxy Methyl Starch Oxidized Starch/ Thin Boiling Starch, Maize Starch and Dextrinized Starch.

The temperature was maintained at about 65°C to obtain plant nutrient carrying absorbent polymer. The plant nutrient carrying absorbent polymer is subsequently cooled to room temperature and cut into small pieces. Thereafter, the cut pieces were dried in a hot air oven. The dried plant nutrient carrying absorbent polymer is grinded having particle size of 1000 microns.

The acrylic acid monomer taken in these experiments was neutralized using sodium or potassium hydroxide to an extent of 90%. The cross-linker used in these examples was methylene bis- acrylamide (MBA) or Trimethylolpropane triacrylate (TMPTA). The amount of cross-linker used was 0.5 wt% of the weight of the plant nutrient carrying absorbent polymer. The amount of hydroxyapatite was 5% of the plant nutrient carrying absorbent polymer. The hydroxyapatite was prepared as per Example 1 described above. The polymerization initiator was Ammonium persulphate and an amount of initiator used was 0.5 wt%. The different types of starches used, the weight percentage of the starches in the plant nutrient carrying absorbent polymer, the viscosity of the starches which were used, and the water absorbency for the plant nutrient carrying absorbent polymer thus obtained is tabulated in Table 1 provided herein below:

Table 1: Results of Experiment 1
S. No Name / Type / Source of polyglucosyl polymer Viscosity Range Brookfield RVT SP #4, 20 RPM at 25 °C) w/w% of polyglucosyl polymer in the SAP Absorbency value
1 Guar Gum (1% w/v aq solution) 5000- 8000 cps 2% 276 g/g
2 Guar Gum (1% w/v aq solution) 5000- 8000 cps 5% 226 g/g
3 Carboxy methyl Guar Gum (1% w/v aq solution) 2000-4000 cps 2% 285 g/g
4 Carboxy methyl Guar Gum (1% w/v aq solution) 2000-4000 cps 5% 245 g/g
5 Oxidized Guar Gum (1% w/v aq solution) 50-100 cps 4% 297 g/g
6 Oxidized Guar Gum (1% w/v aq solution) 50-100 cps 8% 195 g/g
7 Sesbania Gum (1% w/v aq solution) 50 - 100 cps 2% 280 g/g
8 Sesbania Gum (1% w/v aq solution) 50 - 100 cps 5% 205 g/g
9 Carboxymethyl Cellulose (1% w/v aq solution)1000-2000 cps 5% 271 g/g
10 Carboxymethyl Tamarid (1% aq solution) 1000 - 2000 cps 5% 346/g
11 Carboxymethyl Tamarid (1% aq solution) 1000 - 2000 cps 10% 257 g/g
12 Carboxymethyl Tamarid (8%w/v aq solution) 20000-40000 Cps 5% 326 g/g
13 Carboxymethyl Tamarid (8%w/v aq solution) 20000-40000 Cps 10% 245 g/g
14 Cassia Tora Gum (1%w/v aq solution, Hot & cold). 1000 - 1500 cps 5% 334 g/g
15 Cassia Tora Gum (1%w/v aq solution, Hot & cold). 1000 - 1500 cps 10% 265 g/g
16 Cassia Tora Gum (2% w/v aq solution, Hot & cold). 2000-3000 cps 5% 306 g/g
17 Cassia Tora Gum (2% w/v aq solution, Hot & cold). 2000-3000 cps 10% 245 g/g
18 Topica Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 10% 495 g/g
19 Topica Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 20% 421 g/g
20 Topica Starch (5% w/v aq solution, Hot & cold). 5,000-10,000 cps 10% 443 g/g
21 Topica Starch (5% w/v aq solution, Hot & cold). 5,000-10,000 cps 20% 393 g/g
22 Carboxy Methyl Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 10% 445 g/g
23 Carboxy Methyl Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 20% 370 g/g
24 Carboxy Methyl Starch (8% w/v aq solution, Hot & cold). 5000 - 10000 cps 10% 397 g/g
25 Carboxy Methyl Starch (8% w/v aq solution, Hot & cold). 5000 - 10000 cps 20% 347 g/g
26 Oxidized Starch/ Thin Boiling Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 10% 496 g/g
27 Oxidized Starch/ Thin Boiling Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 30% 421 g/g
28 Oxidized Starch/ Thin Boiling Starch (10% w/v aq solution, Hot & cold). 5000 - 10000 cps 10% 470 g/g
29 Oxidized Starch/ Thin Boiling Starch (10% w/v aq solution, Hot & cold). 5000 - 10000 cps 30% 400 g/g
30 Maize Starch (1% aq solution, Hot & cold). 1000 - 1500 cps 10% 590 g/g
31 Maize Starch (1% aq solution, Hot & cold). 1000 - 1500 cps 25% 443 g/g
32 Maize Starch (5% aq solution, Hot & cold). 2000 - 10000 cps 10% 241 g/g
33 Maize Starch (5% aq solution, Hot & cold). 2000 - 10000 cps 25% 145 g/g
34 Dextrinized Starch (1% w/v aq solution, Hot & cold). 1000 - 15000 cps 18% 471 g/g
35 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 18% 398 g/g

Thus, it was observed that almost all types / sources of the polyglucosyl polymer and hydroxyapatite yielded Plant nutrient carrying absorbant polymer.

All of the “Sources of polyglucosyl polymer and hydroxyapatite” indicated in Table 1 were obtained from SHAANXI HAIBO BIOTECHNOLOGY CO., LTD. No.11 Tangyan South Road, Xian, Shaanxi, China.

Experiment 2: Micro-Batch (Lab) Scale process for preparation of plant nutrient carrying absorbent polymer loading with urea-hydroxyapatite hybrid :
The lab-scale process for preparing plant nutrient carrying absorbent polymer having urea-hydroxyapatite hybrid loaded thereupon involved mixing the acrylic acid monomer, different types of starches (having different viscosities and in different weight percentage), a cross linker, urea-hydroxyapatite hybrid and a polymerization initiator in a kettle. The temperature was maintained at about 65°C to obtain plant nutrient carrying absorbent polymer. The plant nutrient carrying absorbent polymer is subsequently cooled to room temperature and cut into small pieces. Thereafter, the cut pieces were dried in a hot air oven. The dried plant nutrient carrying absorbent polymer is grinded having particle size of 1000 microns.

The acrylic acid monomer taken in these experiments was neutralized using sodium or potassium hydroxide to an extent of 90%. The cross-linker used in these examples was methylene bis- acrylamide (MBA) or Trimethylolpropane triacrylate (TMPTA). The amount of cross-linker used was 0.5 wt% of the weight of the plant nutrient carrying absorbent polymer. The amount of urea-hydroxyapatite hybrid was 5% of the plant nutrient carrying absorbent polymer. The urea-hydroxyapatite hybrid was prepared as per Example 4 described above. The polymerization initiator was Ammonium persulphate and an amount of initiator used was 0.5 wt%. The different types of starches used, the weight percentage of the starches in the plant nutrient carrying absorbent polymer, the viscosity of the starches which were used, and the water absorbency for the plant nutrient carrying absorbent polymer thus obtained is tabulated in Table 2 provided herein below:

Table 2: Results of Experiment 2
S. No Name / Type / Source of polyglucosyl polymer Viscosity Range Brookfield RVT SP #4, 20 RPM at 25 °C) w/w% of polyglucosyl polymer in the SAP Absorbency value
36 Guar Gum (1% w/v aq solution) 5000- 8000 cps 2% 275 g/g
37 Guar Gum (1% w/v aq solution) 5000- 8000 cps 5% 226 g/g
38 Carboxy methyl Guar Gum (1% w/v aq solution) 2000-4000 cps 2% 284 g/g
39 Carboxy methyl Guar Gum (1% w/v aq solution) 2000-4000 cps 5% 247 g/g
40 Oxidized Guar Gum (1% w/v aq solution) 50-100 cps 4% 296 g/g
41 Oxidized Guar Gum (1% w/v aq solution) 50-100 cps 8% 196 g/g
42 Sesbania Gum (1% w/v aq solution) 50 - 100 cps 2% 281 g/g
43 Sesbania Gum (1% w/v aq solution) 50 - 100 cps 5% 204 g/g
44 Carboxymethyl Cellulose (1% w/v aq solution)1000-2000 cps 5% 270 g/g
45 Carboxymethyl Tamarid (1% aq solution) 1000 - 2000 cps 5% 345 g/g
46 Carboxymethyl Tamarid (1% aq solution) 1000 - 2000 cps 10% 257 g/g
47 Carboxymethyl Tamarid (8%w/v aq solution) 20000-40000 Cps 5% 327 g/g
48 Carboxymethyl Tamarid (8%w/v aq solution) 20000-40000 Cps 10% 245 g/g
49 Cassia Tora Gum (1%w/v aq solution, Hot & cold). 1000 - 1500 cps 5% 334 g/g
50 Cassia Tora Gum (1%w/v aq solution, Hot & cold). 1000 - 1500 cps 10% 266 g/g
51 Cassia Tora Gum (2% w/v aq solution, Hot & cold). 2000-3000 cps 5% 306 g/g
52 Cassia Tora Gum (2% w/v aq solution, Hot & cold). 2000-3000 cps 10% 246 g/g
53 Topica Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 10% 495 g/g
54 Topica Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 20% 422 g/g
55 Topica Starch (5% w/v aq solution, Hot & cold). 5,000-10,000 cps 10% 443 g/g
56 Topica Starch (5% w/v aq solution, Hot & cold). 5,000-10,000 cps 20% 392 g/g
57 Carboxy Methyl Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 10% 445 g/g
58 Carboxy Methyl Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 20% 370 g/g
59 Carboxy Methyl Starch (8% w/v aq solution, Hot & cold). 5000 - 10000 cps 10% 396 g/g
60 Carboxy Methyl Starch (8% w/v aq solution, Hot & cold). 5000 - 10000 cps 20% 347 g/g
61 Oxidized Starch/ Thin Boiling Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 10% 497 g/g
62 Oxidized Starch/ Thin Boiling Starch (1% w/v aq solution, Hot & cold). 1000 - 2000 cps 30% 421 g/g
63 Oxidized Starch/ Thin Boiling Starch (10% w/v aq solution, Hot & cold). 5000 - 10000 cps 10% 471 g/g
64 Oxidized Starch/ Thin Boiling Starch (10% w/v aq solution, Hot & cold). 5000 - 10000 cps 30% 400 g/g
65 Maize Starch (1% aq solution, Hot & cold). 1000 - 1500 cps 10% 591 g/g
66 Maize Starch (1% aq solution, Hot & cold). 1000 - 1500 cps 25% 443 g/g
67 Maize Starch (5% aq solution, Hot & cold). 2000 - 10000 cps 10% 240 g/g
68 Maize Starch (5% aq solution, Hot & cold). 2000 - 10000 cps 25% 145 g/g
69 Dextrinized Starch (1% w/v aq solution, Hot & cold). 1000 - 15000 cps 18% 470 g/g
70 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 18% 398 g/g

Thus, it was observed that almost all types / sources of the polyglucosyl polymer super absorbent polymer. Additionally, it was observed that the water absorption capacity of the plant nutrient carrying absorbent polymer having urea-hydroxyapatite hybrid loaded thereupon was almost at par with the plant nutrient carrying absorbent polymer having hydroxyapatite loaded thereupon (as obtained in Experiment 1).

All of the “Sources of polyglucosyl polymer and hydroxyapatite” indicated in Table 2 were obtained from SHAANXI HAIBO BIOTECHNOLOGY CO., LTD. No.11 Tangyan South Road, Xian, Shaanxi, China.

Experiment 3: Macro-Batch Scale process for preparation of plant nutrient carrying absorbent polymer loading with hydroxyapatite:
The same concept is applied for 7 kg batch process in CKR-10 reactor, with different starches/modified starches such as, Guar Gum, Carboxy methyl Guar Gum, Oxidized Guar Gum, Sesbania Gum, Carboxymethyl Cellulose, Carboxymethyl Tamarid, Cassia Tora Gum, Topica Starch, Carboxy Methyl Starch Oxidized Starch/ Thin Boiling Starch, Maize Starch and Modified Starch (Dextrinized Starch).

The process involved mixing the acrylic acid monomer, different types of starches (having different viscosities and in different weight percentage), a suitable crosslinker and a polymerization initiator inside the CKR batch reactor instead of kettle to obtain a super absorbent polymer.

The acrylic acid monomer taken in these experiments was neutralized using potassium hydroxide to an extent of 90%. The cross-linker used in these examples was methylene bis- acrylamide (MBA) or Trimethylolpropane triacrylate (TMPTA). The amount of cross-linker used was 0.5 wt% of the weight of the super absorbent polymer. The polymerization initiator was Ammonium persulphate and an amount of initiator used was 0.5 wt%. The different types of starches used, the weight percentage of the starches in the plant nutrient carrying absorbent polymer, the viscosity of the starches which were used, and the water absorbency for the plant nutrient carrying absorbent polymer, thus obtained is tabulated in Table 3 provided herein below:

Table 3: Results of Experiment 3:

S. No Name / Type / Source of polyglucosyl polymer Viscosity Range Brookfield RVT SP #4, 20 RPM at 25 °C) w/w% of polyglucosyl polymer in the SAP Absorbency value
1 Guar Gum (1% w/v aqsolution) 5000- 8000 cps 2% Uniform Polymer not formed
2 Guar Gum (1% w/v aqsolution).5000- 8000 cps 5% Uniform Polymer not formed
3 Carboxy methyl Guar Gum (1% w/v aq solution).2000-4000 cps 2% 270 g/g
4 Carboxy methyl Guar Gum (1% w/v aq solution).2000-4000 cps 5% 230 g/g
5 Oxidized Guar Gum (1% w/v aq solution).50-100 cps 4% 280 g/g
6 Oxidized Guar Gum (1% w/v aq solution).50-100 cps 8% 170 g/g
7 Sesbania Gum (1% w/v aq solution). 50 - 100 cps 2% Uniform Polymer not formed
8 Sesbania Gum (1% w/v aq solution). 50 - 100 cps 5% Uniform Polymer not formed
9 Carboxymethyl Cellulose (1% w/v aq solution).1000-2000 cps 5% 250 g/g
10 Carboxymethyl Tamarid (1% aq solution). 1000 - 2000 cps 5% 330 g/g
11 Carboxymethyl Tamarid (1% aq solution). 1000 - 2000 cps 10% 240 g/g
12 Carboxymethyl Tamarid (8%w/vaq solution). 20000-40000 Cps 5% 310 g/g
13 Carboxymethyl Tamarid (8%w/vaq solution). 20000-40000 Cps 10% 230 g/g
14 Cassia Tora Gum (1%w/vaq solution, Hot & cold). 1000 - 1500 cps 5% Uniform Polymer not formed
15 Cassia Tora Gum (1%w/vaq solution, Hot & cold). 1000 - 1500 cps 10% Uniform Polymer not formed
16 Cassia Tora Gum (2% w/vaq solution, Hot & cold). 2000-3000 cps 5% Uniform Polymer not formed
17 Cassia Tora Gum (2% w/vaq solution, Hot & cold). 2000-3000 cps 10% Uniform Polymer not formed
18 Topica Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 10% Uniform Polymer not formed
19 Topica Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 20% Uniform Polymer not formed
20 Topica Starch (5% w/vaq solution, Hot & cold). 5,000-10,000 cps 10% Uniform Polymer not formed
21 Topica Starch (5% w/vaq solution, Hot & cold). 5,000-10,000 cps 20% Uniform Polymer not formed
22 Carboxy Methyl Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 10% 380 g/g
23 Carboxy Methyl Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 20% 340 g/g
24 Carboxy Methyl Starch (8% w/vaq solution, Hot & cold). 5000 - 10000 cps 10% 370 g/g
25 Carboxy Methyl Starch (8% w/vaq solution, Hot & cold). 5000 - 10000 cps 20% 300 g/g
26 Oxidized Starch/ Thin Boiling Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 10% 480 g/g
27 Oxidized Starch/ Thin Boiling Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 30% 400 g/g
28 Oxidized Starch/ Thin Boiling Starch (10% w/vaq solution, Hot & cold). 5000 - 10000 cps 10% 400 g/g
29 Oxidized Starch/ Thin Boiling Starch (10% w/vaq solution, Hot & cold). 5000 - 10000 cps 30% 350 g/g
30 Maize Starch (1% aq solution, Hot & cold). 1000 - 1500 cps 10% Uniform Polymer not formed
31 Maize Starch (1% aq solution, Hot & cold). 1000 - 1500 cps 25% Uniform Polymer not formed
32 Maize Starch (5% aq solution, Hot & cold). 2000 - 10000 cps 10% Uniform Polymer not formed
33 Maize Starch (5% aq solution, Hot & cold). 2000 - 10000 cps 25% Uniform Polymer not formed
34 Dextrinized Starch (1% w/v aq solution, Hot & cold). 1000 - 15000 cps 18% 480 g/g
35 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 18% 400 g/g

In many instances, Uniform Polymer not formed. Specifically, when native starches such as Guar Gum, Sesbania Gum, Cassia Tora Gum, Topica Starch, and Maize Starch taken with hydroxyapatite displayed a tendency to generate distinct agglomerates, resulting in a lack of uniformity within the samples. Contrary to the above, use of the modified starches such as Carboxy methyl Guar Gum, Oxidized Guar Gum, Carboxymethyl Cellulose, Carboxymethyl Tamarid, Carboxy Methyl Starch, Oxidized Starch/ Thin Boiling Starch, and Dextrinized Starch resulted in formation of uniform super absorbent polymer.

The hydroxyapatite is loaded in the super absorbent polymer (which were formed as per the above table) to obtain a plant nutrient carrying absorbent polymer. To load the hydroxyapatite on to the super absorbent polymer, the super absorbent polymer was dipped and allowed to soak overnight in a dispersion of hydroxyapatite.

The plant nutrient carrying absorbent polymer thus obtained is dried in a tray dryer using up flow and down flow of hot air at a temperature range of 80 °C for 90 min, followed by subsequent grinding of the dried plant nutrient carrying absorbent polymer.

It was observed that hydroxyapatite was getting loaded on to all of the super absorbent polymers.

Experiment 4: Macro-Batch Scale process for preparation of plant nutrient carrying absorbent polymer loading with urea-hydroxyapatite hybrid:
Instead of loading hydroxyapatite onto the super absorbent polymers formed in Experiment 3, urea-hydroxyapatite hybrid as prepared in Example 4 was loaded on to the super absorbent polymers formed in Experiment 3. To load urea-hydroxyapatite hybrid on to the super absorbent polymer, the super absorbent polymer was dipped and allowed to soak overnight in a dispersion of urea-hydroxyapatite hybrid as obtained in Example 4. The plant nutrient carrying absorbent polymer thus obtained is dried in a tray dryer using up flow and down flow of hot air at a temperature range of 80 °C for 90 min, followed by subsequent grinding of the dried plant nutrient carrying absorbent polymer.

It was observed that urea-hydroxyapatite hybrid was also getting loaded on to all of the super absorbent polymers.

Experiment 5: Continuous process for preparation of a plant nutrient carrying absorbent polymer loading with hydroxyapatite:
In continuous process only modified starches such as Carboxy methyl Guar Gum, Oxidized Guar Gum, Carboxymethyl Cellulose, Carboxymethyl Tamarid, Carboxy Methyl Starch, Oxidized Starch/ Thin Boiling Starch, and Dextrinized Starch were taken for preparation of a superabsorbent polymer (as the remaining options failed in Experiment 3). The continuous process comprises the steps of:
a) neutralising an acrylic acid with an alkali hydroxide at a temperature of 15-30°C to a degree of neutralization in the range of 40-90%;
b) mixing a crosslinker to the neutralized acrylic acid to obtain a first reaction mass;
c) preparing an aqueous solution of modified starch having a concentration and viscosity as per Table 5;
d) mixing a crosslinker to the aqueous solution of modified starch to obtain a second reaction mass;
e) mixing the first reaction mass with the second reaction mass at 30-80°C and further adding a mixed initiator system comprising of 0.02-0.10 wt% of redox including the ammonium peroxydisulfate (APS)/ Potassium persulphate (KPS) solution (1-3 L/h) for preparing a super absorbent polymer; the quantity of the second reaction mass is such the wt/wt% of the starch is as per Table 5;
f) in case, uniform super absorbent polymer is formed, the same is passed through a dispersion containing 1-10% of hydroxyapatite to obtain a plant nutrient carrying absorbent polymer;
g) drying the plant nutrient carrying absorbent polymer obtained in the step f) under a tray dryer using up and down flow of hot air at a temperature range of 140 °C -170 °C for 30-60 minutes; and
h) grinding the dried plant nutrient carrying absorbent polymer obtained in the step f) to get the targeted plant nutrient carrying absorbent polymer having particle size of 800- 1200 microns.

Table 5 provided herein below describes the outcome of Experiment 5:

Table 5: Results of Experiment 5:

S.No Name / Type / Source of polyglucosyl polymer Viscosity Range Brookfield RVT SP #4, 20 RPM at 25 °C) w/w% of polyglucosyl polymer in the SAP Absorbency value
3 Carboxy methyl Guar Gum (1% w/v aq solution).2000-4000 cps 2% Uniform Polymer not formed
4 Carboxy methyl Guar Gum (1% w/v aq solution).2000-4000 cps 5% Uniform Polymer not formed
5 Oxidized Guar Gum (1% w/v aq solution).50-100 cps 4% Uniform Polymer not formed
6 Oxidized Guar Gum (1% w/v aq solution).50-100 cps 8% Uniform Polymer not formed
9 Carboxymethyl Cellulose (1% w/v aq solution).1000-2000 cps 5% Uniform Polymer not formed
10 Carboxymethyl Tamarid (1% aq solution). 1000 - 2000 cps 5% Uniform Polymer not formed
11 Carboxymethyl Tamarid (1% aq solution). 1000 - 2000 cps 10% Uniform Polymer not formed
12 Carboxymethyl Tamarid (8%w/vaq solution). 20000-40000 Cps 5% Uniform Polymer not formed
13 Carboxymethyl Tamarid (8%w/vaq solution). 20000-40000 Cps 10% Uniform Polymer not formed
22 Carboxy Methyl Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 10% Uniform Polymer not formed
23 Carboxy Methyl Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 20% Uniform Polymer not formed
24 Carboxy Methyl Starch (8% w/vaq solution, Hot & cold). 5000 - 10000 cps 10% Uniform Polymer not formed
25 Carboxy Methyl Starch (8% w/vaq solution, Hot & cold). 5000 - 10000 cps 20% Uniform Polymer not formed
26 Oxidized Starch/ Thin Boiling Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 10% Uniform Polymer not formed
27 Oxidized Starch/ Thin Boiling Starch (1% w/vaq solution, Hot & cold). 1000 - 2000 cps 30% Uniform Polymer not formed
28 Oxidized Starch/ Thin Boiling Starch (10% w/vaq solution, Hot & cold). 5000 - 10000 cps 10% Uniform Polymer not formed
29 Oxidized Starch/ Thin Boiling Starch (10% w/vaq solution, Hot & cold). 5000 - 10000 cps 30% Uniform Polymer not formed
34 Dextrinized Starch (1% w/v aq solution Hot & cold). 5,000-50,000 cps 18% Uniform Polymer not formed
35 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 18% 400 g/g

In many instances, Uniform Polymer not formed. Specifically, when Carboxy methyl Guar Gum, Oxidized Guar Gum, Carboxymethyl Cellulose, Carboxymethyl Tamarid, Carboxy Methyl Starch, and Oxidized Starch/ Thin Boiling Starch displayed a tendency to generate distinct agglomerates, resulting in a lack of uniformity within the samples.

Contrary to the above, use of certain grades (especially the grades of Dextrinized Starch which had a viscosity of 5,000-50,000 cps (for an aqueous solution containing 50% w/v aq, Hot & cold) resulted in formation of uniform polymer while certain grades of (especially the grades of Dextrinized Starch which had a viscosity of 1,000-15,000 cps (for an aqueous solution containing 1% w/v of Dextrinized starch, Hot & cold) did not result in formation of uniform polymer.

After the formation of uniform polymer or super absorbent polymer, the hydroxyapatite hybrid is loaded in the super absorbent polymer (which were formed as per the above table) to obtain a plant nutrient carrying absorbent polymer. The plant nutrient carrying absorbent polymer obtained is dried in a tray dryer using up flow and down flow of hot air at a temperature range of 80 °C for 90 min, followed by subsequent grinding of the dried plant nutrient carrying absorbent polymer.

It was observed that hydroxyapatite hybrid loading occurred exclusively on the Dextrinized Starch, leading to the formation of a uniform superabsorbent polymer. No nutrient loading occurred in cases involving non-uniform superabsorbent polymers.

Characterization of Hydroxyapatite incorporated super absorbent polymer:
The product as obtained at the end of the process as described above was subjected to FTIR analysis to cross-check formation of Hydroxyapatite incorporated super absorbent polymer. The result of the FTIR analysis is shown in Figure 9, which confirms formation of Hydroxyapatite incorporated super absorbent polymer. In particular, FTIR characterization confirms the presence of modified starch and polyacrylate. The presence of C=O in polyacrylate confirms by stretching frequency at around 1700cm-1 to 1678 cm-1 and the appearance of the band at 1552 cm-1 to 1550 cm-1 due to presence of carboxylate anion. The appearance of C-O-C glycoside bond observed at 1163 cm-1 confirms the presence of starch. Presence of C-H, C-O of modified starch and acrylate; N–H of crosslinker are confirmed by stretching frequency at 2935-2924, and 1401-1395; and 1450 cm-1, respectively. The N–H bending frequency of cross linker merge with the carboxylate. The appearance of the peak at 1014 cm-1 arises due to presence of PO43.

In an embodiment of the invention, Absorbency Results are in the range of 180-250 g/g.

Experiment 6: Continuous process for preparation of a plant nutrient carrying absorbent polymer loading with urea-hydroxyapatite hybrid:
Instead of loading hydroxyapatite onto the super absorbent polymers formed in Experiment 5, urea-hydroxyapatite hybrid as prepared in Example 4 was loaded on to the super absorbent polymers formed in Experiment 5. In particular, in case, uniform super absorbent polymer is formed, the same is passed through a dispersion containing 1-10% of urea-hydroxyapatite hybrid to obtain a plant nutrient carrying absorbent polymer. The remaining steps are performed as per Experiment 5.

Characterization of Urea-Hydroxyapatite hybrid incorporated super absorbent polymer:
The product as obtained at the end of the process as described above was subjected to FTIR analysis to cross-check formation of Urea-Hydroxyapatite hybrid incorporated super absorbent polymer. The result of the FTIR analysis is shown in Figure 10, which confirms the presence of modified starch and polyacrylate. The presence of C=O in polyacrylate is confirms by stretching frequency at around 1662 cm-1 the shift occurs from 1698 - 1693 cm-1 due to the electrostatic interaction between the carboxylate and metal ions in NF. The presence of carboxylate stretching (1552-1550 cm-1) is merged with the N–H stretching frequency which appears from the hydroxyapatite-urea NF. Presence of C-H and C–O of modified starch and acrylate are confirmed by stretching frequency at 2933 and 1395cm -1, respectively. The appearance of the peak at 1013 - 1018 cm-1 arises due to presence of PO43. From the analysis of the FTIR data it is confirm that hydroxyapatite-urea NF successfully incorporated into the super absorbent polymer.

In an embodiment of the invention, Absorbency Results are in the range of 180-250 g/g.

Experiment 7: Continuous process for preparation of a plant nutrient carrying absorbent polymer incorporating Dextrinized Starch and loading with hydroxyapatite:
A variety of Plant nutrient carrying absorbent polymer was prepared by a continuous process following the below described process:
a) neutralising an acrylic acid with an alkali hydroxide at a temperature of 30°C to a degree of neutralization in the range of 90%;
b) mixing a crosslinker to the neutralized acrylic acid to obtain a first reaction mass;
c) preparing an aqueous solution of modified starch; wherein the aqueous solution comprising 50% w/v of the modified starch has a viscosity in the range of 5000- 50000 cps at a room temperature;
d) mixing a crosslinker methylene bis-acrylamide (MBA) or Trimethylolpropane triacrylate (TMPTA) to the aqueous solution of modified starch to obtain a second reaction mass;
e) mixing the first reaction mass with the second reaction mass at 30-80 °C and further adding a mixed initiator system comprising of 0.02-0.10 wt% of redox including hydrogen peroxide solution and sodium ascorbate and 0.1-1.0wt% of ammonium persulfate for preparing a porous superabsorbent polymer; the quantity of the second reaction mass is such the wt/wt% of the starch is as per Table 7;
f) incorporating 5 wt% of hydroxyapatite into the super absorbent polymer for obtaining a plant nutrient carrying absorbent polymer (in case, uniform super absorbent polymer is formed, the same is passed through a dispersion containing 5 wt% of hydroxyapatite to obtain a plant nutrient carrying absorbent polymer);
g) drying the plant nutrient carrying absorbent polymer obtained in the step f) under a tray dryer using up and down flow of hot air at a temperature range of 140 °C -170 °C for 30-60 minutes; and
h) grinding the dried plant nutrient carrying absorbent polymer obtained in the step f) to get the targeted plant nutrient carrying absorbent polymer having particle size of 800- 1200 microns.

The plant nutrient carrying absorbent polymer thus obtained is tabulated in Table 7 provided herein below:

Table 7: Results of Experiment 7:

Sample No Name / Type / Source of polyglucosyl polymer Viscosity Range Brookfield RVT SP #4, 20 RPM at 25 °C) w/w% of polyglucosyl polymer in the SAP Remarks
71 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 25% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
72 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 30% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
73 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 35% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
74 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 40% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
75 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 45% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
76 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 50% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
77 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 55% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
78 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 60% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
79 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 65% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon
80 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 70% Plant nutrient carrying absorbent polymer was formed having hydroxyapatite loaded there-upon

Experiment 8: Continuous process for preparation of a plant nutrient carrying absorbent polymer incorporating Dextrinized Starch and loading with urea-hydroxyapatite hybrid:
A variety of Plant nutrient carrying absorbent polymer was prepared by a continuous process following the below described process:
a) neutralising an acrylic acid with an alkali hydroxide at a temperature of 30°C to a degree of neutralization in the range of 90%;
b) mixing a crosslinker to the neutralized acrylic acid to obtain a first reaction mass;
c) preparing an aqueous solution of modified starch; wherein the aqueous solution comprising 50% w/v of the modified starch has a viscosity in the range of 5000- 50000 cps at a room temperature;
d) mixing a crosslinker methylene bis-acrylamide (MBA) or Trimethylolpropane triacrylate (TMPTA) to the aqueous solution of modified starch to obtain a second reaction mass;
e) mixing the first reaction mass with the second reaction mass at 30-80 °C and further adding a mixed initiator system comprising of 0.02-0.10 wt% of redox including hydrogen peroxide solution and sodium ascorbate and 0.1-1.0wt% of ammonium persulfate for preparing a porous superabsorbent polymer; the quantity of the second reaction mass is such the wt/wt% of the starch is as per Table 7;
f) incorporating 5 wt% of urea-hydroxyapatite hybrid into the super absorbent polymer for obtaining a plant nutrient carrying absorbent polymer (in case, uniform super absorbent polymer is formed, the same is passed through a dispersion containing 5 wt% of urea-hydroxyapatite hybrid to obtain a plant nutrient carrying absorbent polymer);
g) drying the plant nutrient carrying absorbent polymer obtained in the step f) under a tray dryer using up and down flow of hot air at a temperature range of 140 °C -170 °C for 30-60 minutes; and
h) grinding the dried plant nutrient carrying absorbent polymer obtained in the step f) to get the targeted plant nutrient carrying absorbent polymer having particle size of 800- 1200 microns.

The plant nutrient carrying absorbent polymer thus obtained is tabulated in Table 8 provided herein below:

Table 8: Results of Experiment 8:

Sample No Name / Type / Source of polyglucosyl polymer Viscosity Range Brookfield RVT SP #4, 20 RPM at 25 °C) w/w% of polyglucosyl polymer in the SAP Remarks
81 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 25% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
82 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 30% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
83 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 35% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
84 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 40% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
85 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 45% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
86 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 50% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
87 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 55% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
88 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 60% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
89 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 65% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
90 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 70% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon

Experiment 9: Micro-Batch (Lab) Scale process for preparation of plant nutrient absorbent polymer loading with urea-hydroxyapatite hybrid:
A variety of Plant nutrient carrying absorbent polymer was prepared by a Lab scale process using differing quantities of Dextrinized Starch and loading with urea-hydroxyapatite hybrid.

The process involved mixing the acrylic acid monomer, Dextrinized Starch (in quantities as mentioned in Table 9), urea-hydroxyapatite and a cross linker and a polymerization initiator in a kettle. The temperature was maintained at about 65oC to obtain plant nutrient carrying absorbent polymer. The plant nutrient carrying absorbent polymer is subsequently cooled to room temperature and cut into small pieces. Thereafter, the cut pieces were dried in a hot air oven. The dried plant nutrient carrying absorbent polymer is grinded having particle size of 1000 microns.

The acrylic acid monomer taken in these experiments was neutralized using potassium hydroxide to an extent of 90%. The cross-linker used in these examples was methylene bis-acrylamide (MBA). The amount of urea-hydroxyapatite hybrid was 5% of the plant nutrient carrying absorbent polymer. The amount of cross-linker used was 0.5 wt% of the weight of the super absorbent polymer. The polymerization initiator was Ammonium persulphate and an amount of initiator used was 0.5 wt%. The different weight percentage of the starches in the super absorbent polymer, the viscosity of the starches which were used is tabulated in Table 9 provided herein below:

Table 9: Results of Experiment 9:

Sample No Name / Type / Source of polyglucosyl polymer Viscosity Range Brookfield RVT SP #4, 20 RPM at 25 °C) w/w% of polyglucosyl polymer in the SAP Remarks
91 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 75% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
92 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 80% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
93 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 85% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon
94 Dextrinized Starch (50% w/v aq solution Hot & cold). 5,000-50,000 cps 90% Plant nutrient carrying absorbent polymer was formed having urea-hydroxyapatite hybrid loaded there upon

Experiment 6: Eco-Toxicity Tests by Soil bearing Bacteria and Fungi
Since plant nutrient carrying absorbent polymer is primarily intended to be used in agricultural purposes, i.e. mixed with the soil where plants are growing, Eco-Toxicity Tests were performed on the plant nutrient carrying absorbent polymer prepared as per serial numbers 71 to 94.

Each of the plant nutrient carrying absorbent polymer as per serial numbers 71 to 94 was dissolved in hot water, yielding a saturated solution of the material. This solution was then subjected to agar cup method to determine toxicity towards Bacillus pumillus (ATCC14884), Bacillus megaterium (ATCC14581), Bacillus subtilis (ATCC6051), and Klebsiella sp. (MTCC Accession No. 13289), which are some of the soil borne plant growth promoting bacteria. Also, rigorous agar cup method to determine toxicity towards Colletotrichum sp. (MTCC Accession No. 3405), which is a soil borne plant growth promoting Fungi. The Eco-Toxicity of the super absorbent polymer is tabulated in Table 6 provided herein below:

Table 6: Results of Experiment 6:

Sample No Name of Organism Property of the Organism Toxicity
71 Bacillus pumillus Hormone Non-Toxic
72 Bacillus pumillus Hormone Non-Toxic
73 Bacillus pumillus Hormone Non-Toxic
74 Bacillus pumillus Hormone Non-Toxic
75 Bacillus pumillus Hormone Non-Toxic
76 Bacillus pumillus Hormone Non-Toxic
77 Bacillus pumillus Hormone Non-Toxic
78 Bacillus pumillus Hormone Non-Toxic
79 Bacillus pumillus Hormone Non-Toxic
80 Bacillus pumillus Hormone Non-Toxic
81 Bacillus pumillus Hormone Non-Toxic
82 Bacillus pumillus Hormone Non-Toxic
83 Bacillus pumillus Hormone Non-Toxic
84 Bacillus pumillus Hormone Non-Toxic
85 Bacillus pumillus Hormone Non-Toxic
86 Bacillus pumillus Hormone Non-Toxic
87 Bacillus pumillus Hormone Non-Toxic
88 Bacillus pumillus Hormone Non-Toxic
89 Bacillus pumillus Hormone Non-Toxic
90 Bacillus pumillus Hormone Non-Toxic
91 Bacillus pumillus Hormone Non-Toxic
92 Bacillus pumillus Hormone Non-Toxic
93 Bacillus pumillus Hormone Non-Toxic
94 Bacillus pumillus Hormone Non-Toxic
71 Bacillus megaterium Phosphate Non-Toxic
72 Bacillus megaterium Phosphate Non-Toxic
73 Bacillus megaterium Phosphate Non-Toxic
74 Bacillus megaterium Phosphate Non-Toxic
75 Bacillus megaterium Phosphate Non-Toxic
76 Bacillus megaterium Phosphate Non-Toxic
77 Bacillus megaterium Phosphate Non-Toxic
78 Bacillus megaterium Phosphate Non-Toxic
79 Bacillus megaterium Phosphate Non-Toxic
80 Bacillus megaterium Phosphate Non-Toxic
81 Bacillus megaterium Phosphate Non-Toxic
82 Bacillus megaterium Phosphate Non-Toxic
83 Bacillus megaterium Phosphate Non-Toxic
84 Bacillus megaterium Phosphate Non-Toxic
85 Bacillus megaterium Phosphate Non-Toxic
86 Bacillus megaterium Phosphate Non-Toxic
87 Bacillus megaterium Phosphate Non-Toxic
88 Bacillus megaterium Phosphate Non-Toxic
89 Bacillus megaterium Phosphate Non-Toxic
90 Bacillus megaterium Phosphate Non-Toxic
91 Bacillus megaterium Phosphate Non-Toxic
92 Bacillus megaterium Phosphate Non-Toxic
93 Bacillus megaterium Phosphate Non-Toxic
94 Bacillus megaterium Phosphate Non-Toxic
71 Bacillus subtilis Nitrogen Non-Toxic
72 Bacillus subtilis Nitrogen Non-Toxic
73 Bacillus subtilis Nitrogen Non-Toxic
74 Bacillus subtilis Nitrogen Non-Toxic
75 Bacillus subtilis Nitrogen Non-Toxic
76 Bacillus subtilis Nitrogen Non-Toxic
77 Bacillus subtilis Nitrogen Non-Toxic
78 Bacillus subtilis Nitrogen Non-Toxic
79 Bacillus subtilis Nitrogen Non-Toxic
80 Bacillus subtilis Nitrogen Non-Toxic
81 Bacillus subtilis Nitrogen Non-Toxic
82 Bacillus subtilis Nitrogen Non-Toxic
83 Bacillus subtilis Nitrogen Non-Toxic
84 Bacillus subtilis Nitrogen Non-Toxic
85 Bacillus subtilis Nitrogen Non-Toxic
86 Bacillus subtilis Nitrogen Non-Toxic
87 Bacillus subtilis Nitrogen Non-Toxic
88 Bacillus subtilis Nitrogen Non-Toxic
89 Bacillus subtilis Nitrogen Non-Toxic
90 Bacillus subtilis Nitrogen Non-Toxic
91 Bacillus subtilis Nitrogen Non-Toxic
92 Bacillus subtilis Nitrogen Non-Toxic
93 Bacillus subtilis Nitrogen Non-Toxic
94 Bacillus subtilis Nitrogen Non-Toxic
71 Klebsiella sp Potassium Non-Toxic
72 Klebsiella sp Potassium Non-Toxic
73 Klebsiella sp Potassium Non-Toxic
74 Klebsiella sp Potassium Non-Toxic
75 Klebsiella sp Potassium Non-Toxic
76 Klebsiella sp Potassium Non-Toxic
77 Klebsiella sp Potassium Non-Toxic
78 Klebsiella sp Potassium Non-Toxic
79 Klebsiella sp Potassium Non-Toxic
80 Klebsiella sp Potassium Non-Toxic
81 Klebsiella sp Potassium Non-Toxic
82 Klebsiella sp Potassium Non-Toxic
83 Klebsiella sp Potassium Non-Toxic
84 Klebsiella sp Potassium Non-Toxic
85 Klebsiella sp Potassium Non-Toxic
86 Klebsiella sp Potassium Non-Toxic
87 Klebsiella sp Potassium Non-Toxic
88 Klebsiella sp Potassium Non-Toxic
89 Klebsiella sp Potassium Non-Toxic
90 Klebsiella sp Potassium Non-Toxic
91 Klebsiella sp Potassium Non-Toxic
92 Klebsiella sp Potassium Non-Toxic
93 Klebsiella sp Potassium Non-Toxic
94 Klebsiella sp Potassium Non-Toxic
71 Colletotrichum sp. - Non-Toxic
72 Colletotrichum sp. - Non-Toxic
73 Colletotrichum sp. - Non-Toxic
74 Colletotrichum sp. - Non-Toxic
75 Colletotrichum sp. - Non-Toxic
76 Colletotrichum sp. - Non-Toxic
77 Colletotrichum sp. - Non-Toxic
78 Colletotrichum sp. - Non-Toxic
79 Colletotrichum sp. - Non-Toxic
80 Colletotrichum sp. - Non-Toxic
81 Colletotrichum sp. - Non-Toxic
82 Colletotrichum sp. - Non-Toxic
83 Colletotrichum sp. - Non-Toxic
84 Colletotrichum sp. - Non-Toxic
85 Colletotrichum sp. - Non-Toxic
86 Colletotrichum sp. - Non-Toxic
87 Colletotrichum sp. - Non-Toxic
88 Colletotrichum sp. - Non-Toxic
89 Colletotrichum sp. - Non-Toxic
90 Colletotrichum sp. - Non-Toxic
91 Colletotrichum sp. - Non-Toxic
92 Colletotrichum sp. - Non-Toxic
93 Colletotrichum sp. - Non-Toxic
94 Colletotrichum sp. - Non-Toxic

None of the plant nutrient carrying absorbent polymer prepared as per serial numbers 71 to 94 showed toxicity towards any of the 5 micro organisms.

Experiment 7: Bio-Degradability tests
Since the plant nutrient carrying absorbent polymer is primarily intended to be used in agricultural purposes, i.e. mixed with the soil where plants are growing, bio-degradability Tests were performed on the plant nutrient carrying absorbent polymer prepared as per serial numbers 71 to 94 as per ISO 17556:2019. All the plant nutrient carrying absorbent polymers prepared as per serial numbers 71 to 94 showed high degradation.

Experiment 8: Field tests to determine the effect of growing a variety of crops in soil containing the
Field Test 1:
In the Field Test 1, two fields each of having a size of 1000 m2 were prepared. In the first field, 25kg of DAP was applied and in the second field, 20kg of DAP and 5kg of Sample 79, and 20kg of DAP and 5kg of Sample 89 was applied. In the summer season, Guar plant was then grown in both the fields and the results thus obtained is tabulated in Table 8 and Table 9 provided herein below:

Table 8: Results of Field Test 1:

25 kg DAP (Control) 20 kg DAP + 5 kg of Sample 79
Population (5m) 8.21 12.14
No. of Seeds 9.06 10.07

Table 8: Results of Field Test 1:

25 kg DAP (Control) 20 kg DAP + 5 kg of Sample 89
Population (5m) 8.21 12.54
No. of Seeds 9.06 10.34

From Field Trials as undertaken, it was observed that both Sample 79, and Sample 89 increased one or more properties of the plant. Additionally, the amount of DAP (Di-ammonium phosphate) was reduced from 25 kg to 20 kg.

Advantages of the present invention:
The plant nutrient carrying absorbent polymer effectively retains water over a prolonged period of time, delivers macro-nutrients to the plants and increases yield of the plant. Additionally, the plant nutrient carrying absorbent polymer gets degraded within a short period of time and hence, no residue is left in the soil. The plant nutrient carrying absorbent polymer is not harmful to soil bearing bacteria and fungi.

While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. ,CLAIMS:WE CLAIM:

1. A plant nutrient carrying absorbent polymer comprising:
a super absorbent polymer comprising polyglucosyl polymer chain linked to at least one acrylic acid or acrylate polymer chain; and
a hydroxyapatite.

2. The plant nutrient carrying absorbent polymer as claimed in claim 1, wherein hydroxyapatite comprises un-modified hydroxyapatite having a size in the range of 1 to 30 nm and modified hydroxyapatite having a size in the range of 1 to 60 nm.

3. The plant nutrient carrying absorbent polymer as claimed in claim 1, wherein the modified hydroxyapatite comprises urea.

4. The plant nutrient carrying absorbent polymer as claimed in claim 1, wherein an aqueous solution containing 50% w/v of the polyglucosyl polymer chain has viscosity in the range of 5000-50000 cps at a room temperature.

5. The plant nutrient carrying absorbent polymer as claimed in claim 1, wherein the acrylic acid or acrylate polymer chain comprises acrylic acid monomer neutralized to an extent of 60 % to 90% by the neutralizing agent.

6. The plant nutrient carrying absorbent polymer as claimed in claim 1, wherein the acrylic acid or acrylate polymer chain is present in an amount of about 10% to about 50 % by weight of the plant nutrient carrying absorbent polymer.

7. The plant nutrient carrying absorbent polymer as claimed in claim 1, wherein the polyglucosyl polymer chain is present in an amount in the range of about 18% to about 90% by weight of the plant nutrient carrying absorbent polymer.

8. The plant nutrient carrying absorbent polymer as claimed in claim 1, wherein hydroxyapatite is present in an amount of about 1% to 10% by weight of the plant nutrient carrying absorbent polymer.

9. The plant nutrient carrying absorbent polymer as claimed in claim 1, wherein the super absorbent polymer comprises a cross-linking agent in an amount of about 0.1 to about 1% by weight.

10. The plant nutrient carrying absorbent polymer as claimed in claim 10, wherein cross-linkers are methylene bis- acrylamide (MBA) or Trimethylolpropane triacrylate (TMPTA).

11. A process for preparing a plant nutrient carrying absorbent polymer, said process comprising:
mixing at least one acrylic acid or acrylate monomer, a polyglucosyl polymer, a cross-linking agent and hydroxyapatite under a polymerizing condition to obtain the plant nutrient carrying absorbent polymer.