DESC:Field of the Invention
The present invention relates to a biopolymer based, biodegradable, super water absorbing polymer (SWAP) and process for its preparation. More particularly the invention relates to a biodegradable super water absorbing polymeric material (SWAP) comprising of at least one biopolymer containing polysaccharides, at least one chelating agent, and at least one fertilizer.

Background of the invention and prior art:
Superabsorbent polymers (SAP) are polymers that can absorb and retain extremely large amounts of a liquid relative to their own mass and have diverse application in various fields. Water absorbing polymers find application in bed liners, sanitary napkin, water retention agent (in horticulture), high strength concrete (especially repair concrete), water-penetration blocker, control of water spill, tissue engineering, biosensors and drug delivery. For example, Superab A-200 (202 g/g or 20200 %) manufactured by Rahab Resin Co. Ltd., Iran is used in agriculture. One of the most common applications of SAPs is in diapers and sanitary napkins. The current global market for diapers is about 22.2 billion US dollar per year. Typically diaper contains about 4 to 5g of SAP and cellulosics/pulp as backup material that absorbs water by capillary action. The production of SAP in 2013 is 2.2 million tons (623000 tons in Asia, mostly by Nippon Shokubai, Sa-Dia Polymers and Sumitomo Seika Chemicals; 490,000 tons in the North America by Degussa, BASF, Dow and Nippon Shokubai and 370000 tons in Europe, mostly by Degussa and BASF), clearly exhibiting the large market need of napkins based on SAP material.

Water absorbing polymers (hydrogels) absorb and retain a very large quantity of water. The amount absorbed depends on type and extent of crosslinking, porosity and ionic strength of the water (the absorbate). The technology of “Super Slurper” was first developed by the United States Department of Agriculture in the early 1960s. In this method the graft copolymer acrylonitrile-g-starch was used. This resulted in water absorption in excess of 400 times the mass of the absorber and retention of water under mild pressure. Subsequently other monomers such as acrylic acid, acrylamide (family) and vinyl acetate were used in grafting reactions with starch and starch-like polysaccharides.

The commercial SAP materials are based on acrylic acid and similar molecules that are derived from petrochemical products. These materials have a crosslinked structure and are made of carbon-carbon bonds that are not amenable to biodegradation and consequently pose risk in the environment. In commercial diaper products, crosslinked sodium poly(acrylate) is the most popular material that is used (for example in baby diapers). The other materials used include copolymers (of acrylamide; of ethylene-maleic anhydride; of vinyl alcohol), crosslinked polymers [poly(ethylene oxide); carboxymethylcellulose] and graft copolymers [poly(acrylonitrile) grafted to starch]. Crosslinked sodium poly(acrylate) can absorb up to 800 g of distilled water per gram while it is reduced to 50 g per gram if tap water (containing sodium, calcium cations) is used. The retention of water by a water absorbing polymer depends critically on the ionic strength and the concentration of cations, especially if it is a polyelectrolyte. Thus a 1 % aqueous solution of saline can bring down the extent of water uptake by one order of magnitude. One of the biggest disadvantages of the commercial super water absorbents and especially those used in diapers and sanitary napkins is that they are not biodegradable and would remain in the environment for centuries without undergoing major chemical or biochemical transformation.

If the SAP polymer can be designed using biopolymers such as chitosan that are known to degrade in soil in about two weeks (chitin, chitosan as well as acetic acid solution of chitosan is used in field as fertilizer; chitosan is sold as a pesticide – USDA NOP and EPA Rule on Chitosan, Federal Register Volume 72, Number 236, December 10, 2007, Rules and Regulations; Chitin and Chitosan Final Registration Review Decision, Document ID EPA-HQ-OPP-2007-0566-0019, December 11, 2008, pages 10 to 15), this would help in water conservation and significant improvement in protecting the environment. Thus water depletion from soil will be minimized dramatically, improving plant survival and growth especially in a country like India where monsoon dependent agriculture is prevalent. Biopolymer based SAP will also reduce water runoff and soil erosion. The typical water absorbing polymer used in soil is crosslinked acrylic acid-acrylamide copolymers neutralized with potassium. This polymer is not biodegradable and would remain in the soil for centuries without adding much value.

In the field of agriculture, the increasing global population from 1.6 billion to 7 billion during the last 120 years had placed a demand on higher production of agricultural products. This in turn has led to rapid and high turnout based aggressive production strategies, which is reflected by the depletion of soil quality of the agricultural lands as well as by the deteriorating quality and quantity of ground water. To compensate for the loss of fertility of soil, the macro-nutrients (nitrogen, potassium, phosphorous, calcium etc.,) and micro-nutrients (boron, iron, copper, nickel, zinc etc.,) [ Pandey, V. C., & Singh, N. (2010). Impact of fly ash incorporation in soil systems. Agriculture, Ecosystems & Environment, 136(1–2), 16-27)] are provided to the soil during cultivation through the use of a variety of synthetic chemicals. Urea is the most used nitrogen fertilizer as it is cheap when compared with other nitrogen containing fertilizers. It has nitrogen content over 45 %, which is higher than any other nitrogen containing fertilizers in the market. Its disadvantage is that it is unstable under high temperature and high humid climatic conditions. In such conditions, in the presence of urease enzyme in soil, it decomposes fast, liberating ammonia gas into the atmosphere by the chemical reaction [(Mori, S. (1927). The decomposition of urea by urease. J. Biophysics, 2(Copyright (C) 2014 American Chemical Society (ACS). All Rights Reserved.), xxiii)].In addition, the release of excess urea due to rundown of water into natural resources such as lakes and ponds also causes pollution. Therefore it will be more economical and eco-friendly if urea is made available to soil from a material in which urea is linked with a fairly stable yet bio-degradable matrix such as chitosan. The restricted release of urea from the matrix of a naturally occurring biopolymer can offer some advantage to address these issues.

The use of polysaccharides in the preparation of SAPs is reported. EP 1836227 B1 utilizes the crosslinking of polysaccharide. EP ‘227 particularly discloses a method for the preparation of a superabsorbent polymer hydrogel, which comprises the steps of (i) crosslinking a 3 % (overall) aqueous solution of carboxymethylcellulose sodium salt and hydroxyethylcellulose with 5 % carbodiimide, in the presence of an acid catalyst; (ii) washing the gel obtained at least once by swelling in a polar organic solvent; and (iii) drying the gel by phase inversion in a non-solvent for cellulose. This work exploits the reaction between the carboxylic acid groups of carboxylmethylcellulose and carbodimides reported earlier [(Nakajima, N., &Ikada, Y. (1995). Mechanism of Amide Formation by Carbodiimide for Bioconjugation in Aqueous Media.Bioconjugate Chemistry, 6(1), 123-130)].However, EP ‘227 is restricted to the use of carboxymethylcellulose and hydroxyethylcellulose. The crosslinking agent used here is carbodimide that produces urea as a by-product, which is rinsed away, post-reaction.
EP1496952 discloses multi-component absorbent composition comprising one or more modified starches and at least one or more components selected from a first component class selected from mannose containing polysaccharides, a second component class selected from ionic polysaccharides, and a third component class selected from gelling proteins or polypeptides.EP ‘952 is based on a physical mixture of polysaccharides and no chemistry or chemical reactions are involved in the preparation.

US8641869 (B2) discloses a method for making biodegradable superabsorbent particles in which carboxyalkyl cellulose is blended with starch in water and crosslinked with inorganic compounds to obtain a gel. The crosslinking agent is a non-permanent metal crosslinking agent (aluminium (III), titanium (IV), zirconium (IV), bismuth (III), boron (III) based compounds).

EP0627225 discloses superabsorbents formed by the reaction of acid and chitosan. EP ‘225 discloses both inorganic and organic acids, which can be used for reaction in the suspension with chitosan. Acids like mineral acids, sulfonic acids, carboxylic acids having from 1 to 4 carboxyl groups or hydroxycarboxylic acids are preferred. EP ‘225 utilizes chitosan as the only natural biopolymer. The chemistry involves partial reaction of the amino groups with organic acids (cationization), preferably hydroxyacids. The unreacted amino groups are crosslinked using dicarboxylic acids, dianhydrides, dicarboxylic acid chlorides, diepoxides or dialdehydes and even multifunctional acids containing up to four carboxylic acid groups but only in the presence of organic solvents. However, this technology requires organic solvent and also the water absorption reported does not exceed 100 g/g.

It is to be noted that the SAP supplied by Government of India (Pusa Hydrogel; The Hindu dated September 18, 2014, page 16, Business, Chennai Edition) as well as a number of State Governments is based on crosslinked poly(acrylamide) gels that are not biodegradable and can kill plants if unpolymerized acrylamide is not eliminated from the gel.

Thus there exists need for a biopolymer based, biodegradable super water absorbent polymeric material, which has higher water absorption capacity in a variety of applications. Such materials can be highly useful in agriculture and especially when the process followed in its preparation is a green synthetic route.

Objects of the invention:
A basic object of the present invention is to overcome the drawbacks prevailing in the prior art.

Another object of the invention is to provide a biopolymer based, biodegradable super water absorbent polymeric material applicable to be used in various applications.

Yet another object of the invention is to provide a biopolymer based, biodegradable super water absorbent polymeric material with higher water absorption capacity.

Yet another object of the invention is to provide a biopolymer based, biodegradable super water absorbent polymeric material, which could be used in agricultural field for the purpose of restricted release of water/nutrients/fertilizer and like.

Yet another object of the invention is to provide a biopolymer based, biodegradable super water absorbent polymeric material comprising a nutrient/fertilizer chemically connected in/crosslinked through breakable/cleavable bonds.

Yet another object of the invention is to provide a biopolymer based, biodegradable super water absorbent polymeric material useful for restricted release of urea, being constrained in view of its entrapment in a polymeric matrix.

Yet another object of the invention is to provide a biopolymer based, biodegradable super water absorbent polymeric material useful for the restricted release of a number of essential ions such Mg+2, Ca+2, Fe+2, etc.

Yet another object of the invention is to provide a green technology based process for the production of biopolymer based, biodegradable super water absorbent polymeric material.

SUMMARY OF THE INVENTION

According to one aspect of present invention, a biodegradable super water absorbing polymeric material (SWAP) is provided comprising of at least one biopolymer containing polysaccharides, at least one chelating agent, and at least one fertilizer.

According to another aspect of present invention, there is provided a process of preparing the biodegradable super water absorbing polymeric material comprising the steps of,

i. mixing the biopolymer in the weight ratio (1:2:2) to the fertilizer-chelating agent mixture in a poly(propylene) bottle with an air-tight lid;
ii. heating the reaction mixture of step (i) to 100°C at a rate of 5°C per minutes;
iii. maintaining the reaction mixture of step (ii) for 650 minutes at 100 °C; and
iv. cooling and purifying the product obtained from step (iii)with excess methanol.
Brief description of the accompanying drawings and Tables:
The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

Figure 1: illustrates solid state NMR spectrum of the biodegradable super absorbing polymeric material (CHEDUR) vis-a-vis the raw material chitosan subjected to the control experiment.
Figure 2: illustrates FT-IR spectrum of the biodegradable super absorbing polymeric material along with the raw material chitosan and a mixture of EDTA+ Urea subjected to the control experiment.
Figure3: illustrates thermal stability of the raw materials and CHEDUR as investigated by thermogravimetric analysis and differential thermal analysis.
Figure 4: illustrates powder XRD pattern of CHEDUR vis-à-vis chitosan.
Figure 5: illustrates experiment for testing water absorption of CHEDUR.
Figure 6: illustrates gel formation after water uptake by CHEDUR.
Figure 7: illustrates water uptake study results for CHEDUR, commercial diaper material and combination of CHEDUR with commercial diaper material.
Figure 8: illustrates saline water uptake study result for CHEDUR and commercial diaper material.
Figure 9: illustrates the formation of fibrous gel upon the absorption of water by CHEDUR.
Figure 10: illustrates water uptake and growth study results of plants in the presence of CHCAUR.
Figure 11: illustrates water uptake and growth study results of plants in the presence of CHCAUR and CHEDUR.
Table 1 illustrates the water uptake data for CHEDUR and controls.
Table 2 illustrates the water uptake data for CHCAUR and CHEDUR.
Table 3 illustrates the water uptake of the polymeric material and raw materials.
Table 4illustrates the water uptake by CHEDUR at different weight ratios.
Table 5illustrates the water uptake by CHCAUR at different weight ratios.

DETAILED DESCRIPTION OF THE PRESENT INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The present invention relates to a super water-absorbing polymeric (SWAP) material, which has large water uptake capacity. In an embodiment, the present invention provides a biopolymer based biodegradable super water absorbent polymeric materials comprising of a biopolymer, chelating agent and fertilizer. The inventors have surprisingly found a synergistic composition of biopolymers, chelating agents and fertilizers in a specific weight ratio of 1:2:2.

In a preferred embodiment, the present invention relates to biopolymer based biodegradable super water absorbent polymeric materials comprising of chitosan, EDTA or citric acid and urea.

The super water absorbent polymers can be used in agriculture as retainer of water (rainwater or the first watering that is done after ploughing). The base polymer used is a biopolymer and is known to be compatible with soil and is in fact used for soil applications. In fact, in the uncrosslinked form it is used to protect leaves against fungal attack in agriculture. This material can be crosslinked with fertilizer such as urea and nutrients such as chelates of ions of magnesium, calcium, iron, etc.
The other use is in diaper/napkin material. The unique advantage is that this material offers biodegradability in contrast to the existing materials. Also the present invention provides cost effective polymeric composition since the raw materials used herein are abundantly available (chitosan from sea food waste) and the present process is simple using cheaper raw materials thus making it a cost effective and biodegradable. The superabsorbent polymer of present invention can be used in the areas of tissue engineering, concrete technology, drug delivery and biosensor.
In an embodiment the biodegradable super water absorbing polymer material of the present invention is based on the combination of biopolymer(s), chelating agent(s) and fertilizer(s) present in a specific ratio/amount to obtain maximum water absorbing capacity, in the range of 500 to 800 g/g, preferably from 570 to 800 g/g, which is relatively higher to the water absorptive property of the known materials.
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Examples of biopolymers are selected from the group comprising of biopolymer(s) like polysaccharides with high abundance, which includes chitosan, cellulose, gums, alginic acid and similar marine polysaccharides. Preferably the biopolymer is chitosan. The amount of chitosan in the present composition is 20% by wt.

Examples of chelating agents are selected from the group comprising of multi-functional acids such as citric acid, ascorbic acid, malonic acid, succinic acid, maleic acid, or EDTA and its anhydride.
Preferably the chelating agent is selected from citric acid and EDTA. The amount of chelating agent in the present composition is 40% by wt.

Examples of fertilizers are selected from the group comprising of any nutrient (micro or macro) and amides (like urea).The amount of fertilizer in the present composition is 40% by wt.

In the present invention, various ranges of weight ratio of biopolymer(s), chelating agent(s) and fertilizer(s) up to 1:18:15 have been tested. It has been observed that, the water uptake is best when the biopolymer: chelating agent: urea is present in a weight ratio of 1:2:2in the composition and the water uptake does not increase beyond the said range. The water uptake decreases when the weight ratio is 1:1:1.
In another embodiment of the present invention provides a process for the production of the biopolymer based super absorbent polymer comprising of biopolymers, chelating agents and fertilizers in the weight ratio of 1: 2:2.
The process of preparing the biodegradable super water absorbing polymeric material comprises of mixing of the biopolymer in the weight ratio (1:2:2) to the fertilizer-chelating agent mixture in a poly(propylene) bottle with an air-tight lid; This is heated to 100 ºC at a rate of 5 ºC per minutes and then maintained for 650 minutes at 100 ºC. Later, it is cooled and purified by using excess methanol. It is then filtered and washed with methanol and allowed to stand for 30 minutes. Finally, it is dried to obtain the product of the present invention.
The process time for preparation of the biodegradable super water absorbing polymeric material of the present invention by the said process is approximately 48 hours.
The process developed for the preparation of super water-absorbing polymers is green and can be carried out with water by the hydrothermal route.
The present process requires methanol for work up in the last step. In addition, the process results in the formation of new amorphous regions that allow solvent to interact with the solute thereby enabling greater water absorption. The process involves combining or mixing the selective biopolymer(s) with chelating agent(s) and the fertilizer/nutrient(s) in a particular ratio/ amount that helps in enabling to achieve the best water absorption capacity and which subsequently makes the water absorbent polymer to be useful in various applications.
The process was performed at the temperature of 100 degree Celsius, which played a significant role for the production of super water absorbent polymer. Post processing of the product gel has to be done with methanol ammonia solution followed by rinsing with methanol to remove unreacted raw materials.
The specific high water uptake property is observed only with chitosan. Therefore the following advantages are retained:
· no compromise on the biodegradability of chitosan, as no new covalent bond is added;
· the chelation property of polycarboxylic acids is retained;
· urea is present in a form that it can directly function as a fertilizer (no new covalent bonds).

The expected shelf life would be more than one year as chitosan is known to resist the growth of bacteria and fungi. No specific storage conditions are recommended.

It has been reported that chitosan degrades in the soil in about a month’s time. Therefore the material can be applied every month or 45 days to ensure that the moisture retention of soil is maintained.

In another embodiment, a restricted release system of fertilizers or nutrients is provided. The chitosan matrix degrades in soil with simultaneous release of urea, organic acid and metal ion in a restricted manner dictated by the biodegradation rate of the chitosan matrix.
The term “restricted release” of urea and mineral ions (if bound through EDTA) means release that is consequential to the biodegradation of the chitosan matrix.

The invention is now illustrated by way of non-limiting examples.

Example-1
The super water absorption polymer is denoted as ‘CHEDUR’ prepared from chitosan, EDTA and urea. CHEDUR plays a vital role in agriculture as a new material for restricted release of urea (being confined to the chitosan matrix), water and micronutrients to soil besides the other identified applications as super water absorbing material.

The below described process is defined using various possible embodiments of the invention and the same should not be considered restricting the scope and various other alternate members falling in the same group could be used for the production of the super absorbent polymer of the present invention.
The materials used to conduct experiments in accordance to the subject matter of the present invention are raw chitosan (80% deacetylated), glacial acetic acid (GR grade), 25% v/v ammonia solution (GR grade), EDTA (GR grade), urea (GR grade), methanol (GR grade). These materials were purchased from M/s. R. K. Scientific Company, Chennai were used without further purification. Water absorbing material from “Huggies” [Kimbery-Clark Lever Ltd.] commercial baby diaper was used as received.
Synthesis of Chitosan-EDTA-Urea- Adduct (CHEDUR):
The required quantity of acetic acid (1-5% v/v; chitosan is soluble in dilute aqueous acetic acid solution in the concentration range of 1-5 % v/v) was taken in a 500 ml poly(propylene) bottle with an air-tight lid. To this, calculated amount of urea and EDTA (urea/EDTA mole ratio 4.9) were added and shaken well. This was followed by the addition of the required quantity of chitosan, such that the weight ratio of chitosan to urea-EDTA mixture was 1:1 to 1:2. The mixture was shaken manually for 5 minutes. It turned viscous due to the dissolution of chitosan in acetic acid. The poly(propylene) bottle was then placed in a programmable air oven. The reaction mixture was heated from room temperature to 100 ºC at a heating rate of 5 ºC per min. The heating was continued for further period of 650 minutes at 100 ºC (urea is soluble in this reaction medium, at room temperature itself. EDTA is sparingly soluble in this mixture at room temperature, but totally soluble at the reaction temperature). It was then allowed to cool to room temperature (35 ºC). This product was observed to be brown in colour and was either a loose gel or solution, depending on the weight ratio of the reactants and the concentration of acetic acid. The product obtained after the reaction was poured in to excess methanol with sufficient NH4OH solution to maintain pH in the range of 8 – 9. At this pH, the mixture was allowed to stand for 30 minutes and then it was filtered using suction. The gel was repeatedly rinsed with methanol to remove bye products due to neutralization and then allowed to stand in suction for 30 minutes. The product was dried at 50 ºC for 5 h in an air oven and then powdered well. This new material was denoted as ‘CHEDUR’.
CHEDUR was also synthesized by the hydrothermal route by using the procedure as in above without the use of acetic acid as the solvent for chitosan, with equal effect.
For comparison, control preparation was done without using EDTA and urea but only with chitosan. The same procedure was followed, and the final product after methanol washing was dried at 50 º C for 5 h. This was denoted as ‘Blank Chitosan’
Synthesis of Chitosan-Urea Adduct:
The procedure followed for the synthesis of chitosan-urea adduct was similar to the one reported in the previous paragraph except that EDTA was not used as one of the reactants.
Synthesis of Chitosan-EDTA Adduct:
The procedure followed for the synthesis of chitosan-EDTA adduct was similar to the one reported in the previous paragraph except that urea was not used as one of the reactants.
Analytical studies:
NMR (13C solid state) was carried out using BrukerAvance spectrometer (Bruker) operating at 100 MHz for 13C (probe diameter 4 mm; spinning rate 10,000kHz, repetition time = 5 sec, contact time = 2000 microsec., number of scans = 1024). FTIR was carried out using JASCO 4100 FTIR spectrometer (JASCO, Japan). The solid samples required for the analysis was prepared in the pellet form by mixing 3-5 mg of the sample with 100 mg of dry KBr. The thermogravimetric studies were carried out with TA Instruments Q500 Hi-Res TGA. The samples were heated at 10 °C min-1 under flowing N2 atmosphere. X-ray diffraction patterns of all the materials were recorded with a Bruker D8 Advance diffractometer equipped with Cu anode and a Cu Ka source of the wavelength of 1.5406 Å. SEM images were obtained using Quanta 450 Scanning electron microscope. Elemental analysis was done with Perkin Elmer CHNS/O 2400 Elemental analyzer. Surface area measurements were done with MicromeriticsASAP2020, using nitrogen adsorption at liquid nitrogen temperature and applying BET equation for surface area calculation.
Solid state 13C NMR:
The solid state NMR spectrum of CHEDUR as well as the product obtained by subjecting chitosan to identical reaction conditions in the absence of EDTA and urea (CHI-Blank) is shown in Figure 1. CHEDUR exhibits peaks at 22.5 (-NHCO-CH3), 49 (new; from EDTA part), 51.3, 55, 58 (new; from EDTA), 59.8, 74, 82.5, 83.6, 95.2, 103 (all from chitosan), 160.2 (new; from H2N-CO-NH2), 169.1 (new; from H2N-CO-NH3+), 171.1 (new; from EDTA), 173.1, 177.8 (new; from EDTA) ppm, respectively. The peaks are assigned by comparing the spectrum with those of the solid state NMR spectra of chitosan-blank. The new peak at 177.8 ppm in CHEDUR is new and most likely arises from the carboxylate carbonyl of EDTA that in turn is formed due to the protonation of amine groups of chitosan by the carboxylic acid group of EDTA. The peak at 171.1 ppm in CHEDUR arises from the EDTA carbonyl groups that are free. The new peak at 169.1 ppm could arise out of the urea carbonyl carbons adjacent to the protonated –NH2 groups in urea (with the carboxylic acid group in EDTA). The other new peaks at 49 and 58 ppm confirm the presence of EDTA moiety in CHEDUR. The peaks from chitosan backbone are also seen in CHEDUR at 51.3 (C2), 55 (C3), 59.8 (C6), 74 (C5), 82.5, 83.6 (C4), 95.2 (C1 with –NHCOCH3 in C2) and 103 (C-1 with NH2 in C2) (106 ppm), respectively [Saito, H., Tabeta, R., & Ogawa, K. (1987). High-resolution solid-state carbon-13 NMR study of chitosan and its salts with acids: conformational characterization of polymorphs and helical structures as viewed from the conformation-dependent carbon-13 chemical shifts. Macromolecules, 20(10), 2424-2430.)]. The extent of crosslinking could be determined by solid state NMR since the area under the respective carbons (with the exception of carbonyl carbons) appeared to be quantitative as shown in Figure 1. Based on this data and by comparing the area under the peaks between 48 to 65 ppm (from C2 and C6 of chitosan as well as from EDTA) and 92 to 112 ppm (arising only from the anomeric carbon) the degree of crosslinking is found to be 0.16.

Fourier Transform Infrared spectroscopy:
The FT-IR spectrum of CHEDUR along with EDUR and chitosan is presented in Figure 2 (2100 to 400 cm-1 only). The major peaks observed in the case of CHEDUR are assigned to the following vibrations: The prominent carbonyl stretching peaks associated with EDTA and urea that is observed at 1700 cm-1is seen to disappear although there is absorption in this region. A new peak is observed for CHEDUR at 1635 cm-1 that can be attributed to the EDUR (amide I of amide carbonyl moiety) present in CHEDUR, while the amide I band specific to –NHCOCH3 of chitosan and observed at 1655 cm-1 is seen to reduce in intensity. The specific absorptions (doublet-like) between 1625 to 1600 cm-1 seen in the case of urea is not observed in CHEDUR. The amide II band observed at 1567 cm-1 in the case of chitosan is shifted to 1558 cm-1 in the case of CHEDUR suggesting that the N-H could be interacting with EDUR. The peak observed at 1400 cm-1 for CHEDUR as well as EDUR arises from specific C-H bending of the CH2 group (present in EDTA but not in chitosan). EDTA and urea show very specific and sharp absorptions at 800 cm-1 that is seen to vanish in the case of CHEDUR. The FT-IR spectrum thus confirms that the product CHEDUR is formed as a result of reaction between chitosan and EDUR (EDTA and urea conjugate).
Thermogravimetric analysis:
The thermal gravimetric analysis data for the raw materials and CHEDUR as well as the differential thermogravimetric analysis data are compared in Figure 3. Urea being the least stable among the raw materials decomposes between 150-210 °C and loses almost 80 % of its weight. EDTA on the other hand is stable up to 200 °C and loses around 70 % of its weight in the temperature region 230 to 320 °C. Chitosan is stable up to 270 °C, ignoring the loss of moisture of around 5 % up to 150 °C, and then it loses nearly 35 % of its weight between the temperature ranges 270 to 320 °C. In comparison, CHEDUR loses mass in two steps, while all the raw materials lose weight in a single step up to 350 °C, if the initial moisture loss up to 150 °C is ignored. The weight loss between 150 to 260o C in the first step arises predominantly from urea (87 % of urea decomposes) and to a significant extent from EDTA (22.4 % of EDTA decomposes) and the weight loss between 250 to 350o C, in the second step arises principally from chitosan and EDTA. The residue left behind after heating to 900 °C in nitrogen atmosphere for CHEDUR is 28 %. Since chitosan, EDTA and urea leave 37.5 %, 10.8 % and 0.6 % residue, respectively, at 900 °C it follows that EDTA and urea are incorporated in CHEDUR.
Powder X-Ray Diffraction analysis:
The powder XRD pattern of CHEDUR and chitosan are shown in Figure 4. The prominent diffraction peaks for chitosan are observed at 2q values of 9.43 [d = 9.37 Å and (020)], 20.3 [d = 4.37 Å and (110)] and 29.58 [d = 3.02 Å and (104) of calcite present in chitosan]. The peak widths of chitosan are much higher and are also broad at the base suggesting the semi-crystalline nature of chitosan. The observed PXRD pattern of chitosan is consistent with that of reported in the literature for the chitin nanofibers (anti parallel crystal pattern of alpha chitin) [(Kumirska, J., Czerwicka, M., Kaczynski, Z., Bychowska, A., Brzozowski, K., Thöming, J., & Stepnowski, P. (2010). Application of Spectroscopic Methods for Structural Analysis of Chitin and Chitosan. Marine Drugs, 8(5), 1567-1636)] and calcite (which exhibits the most prominent diffraction peaks at 2O= 29 (104)). In comparison, CHEDUR exhibits diffraction peaks 2q values of 10.44 [d = 8.47 Å and (020)], 20.12 [d = 4.41 Å and (110)], 26.72 [observed in EDUR] and 29.58 [d = 3.02 Å and (104) of calcite present in chitosan]. The peak widths of CHEDUR are also larger compared to chitosan and therefore it suggests that CHEDUR is less crystalline and essentially amorphous in nature, as comparison to chitosan. The shift in the 2 value for (110) and (120) planes in CHEDUR versus chitosan to a higher value, indicate the decrease in inter planar distance, possibly due to crosslinking (as the EDTA is a tetra-functional molecule that can crosslink the chitosan with a free amine group in every repeat unit). It can also be inferred from the PXRD of CHEDUR that small molecular reactants (such as EDTA, urea) are absent. This further confirms that the product is not just a physical mixture of chitosan, EDTA and urea but chemically combined.
Scanning Electron Microscopic analysis:
The hydrogel formed upon the absorption of water by the new material exhibits fibrous morphology with the diameter of fiber bundles being ~ 250 nm as shown by the SEM picture in Figure 9.
Example 2
Preparation of ‘CHCAUR’
400 ml of water was taken in a 500 ml poly(propylene) bottle with an air-tight lid. To this, calculated amount of urea and citric acid were added. This was followed by the addition of the required quantity of chitosan, such that the weight ratio of chitosan to urea-citric acid mixture was 1:1 to 1:2 (6 g of chitosan, 12 g of citric acid and 12 g of urea). The poly(propylene) bottle was then placed in a programmable air oven. The reaction mixture was heated from room temperature to 100 ºC at a heating rate of 5 ºC per min. The heating was continued for further period of 650 minutes at 100 ºC. It was then allowed to cool to room temperature (35 ºC). The product obtained after the reaction was poured in to excess methanol with sufficient NH4OH solution to maintain pH in the range of 8 – 9. At this pH, the mixture was allowed to stand for 30 minutes and then it was filtered using suction. The gel was rinsed with methanol and then allowed to stand in suction for 30 minutes. It was then processed in one of the following two ways: 1) The product was dried at 50 ºC for 5 h in an air oven and then powdered well, purified by rinsing with methanol for 3 to 5 hours followed by drying at 50 ºC for 5 hours; 2) The product in the form of gel was directly purified by rinsing with methanol for 3 hours followed by drying at 50 ºC for 5 h. This new material was denoted as ‘CHCAUR’. Control experiments without urea revealed the formation of materials with poor water absorption.
Example 3
Water Absorption Studies:
Prior to the experiment, all the samples used in the water absorption studies were dried at 50 ºC for 5 h. In a typical experiment, around 20 mg of sample was exactly weighed (w1) into a filter cone. This was immersed into a 100 ml beaker containing 80 mL of distilled water (as shown in the Figure 5). The time was noted and weight gain of the sample due to water absorption was measured at different time intervals. After a particular time interval, the filter cone was removed from the beaker, the excess water was allowed to drip down for 5 min. When the dripping stopped, the tip of the filter cone was gently swiped one time with dry tissue paper. Then the weight (w2) of the material was noted. The water uptake per gm of material is calculated from the formula (w2-w1)/w1 g of water per g of material.
It was observed that CHEDUR composition forms a transparent gel when exposed to water as shown in Figures 5 and 6. With a view to prepare a gel of high water absorption property, the reaction condition was varied to obtain different materials. For this purpose the following variables were optimized: (i) mole ratio of EDTA/glucosamine repeat unit of chitosan (was varied between 0.4 and 10); (ii) mole ratio of EDTA/urea (was varied between 0.137 and 1); and the (iii) concentration and volume of the dissolution medium i.e., acetic acid between 1 to 5 % v/v. The maximum water absorption of 570 ± 20 g/g was obtained with the CHI (glucosamine repeat unit): EDTA: Urea mole ratio window of 1±0.2: 1±0.5: 5 ± 3. The reaction medium composition of 1 to 5 % v/v acetic acid was found to be most suitable although the reaction was equally successful when carried out in the absence of acetic acid.
The very high water uptake of CHEDUR can be attributed to two factors: i) the osmotic attraction of water molecules to the electrostatic bonds between chitosan and EDUR adduct and ii) to the change in the morphology from the semi-crystalline (in chitosan) state to amorphous state (CHEDUR) upon which the glucosamine repeat units with four hydroxyl groups are available for water absorption in contrast to the crystalline morphology where all the functional groups are buried inside the crystal structure. In contrast, the water uptake in typical diaper material [crosslinked sodium poly(acrylate)] is attributed to the strong electrostatic interaction between the water and the anion present in the crosslinked polymer, in addition to the chemical potential driven migration of the sodium from the polymer matrix to the water phase upon which the osmosis of water is facilitated. The results from the control experiments confirm that the three ingredients, namely, chitosan, EDTA and urea are necessary for the high water uptake. The nitrogen content of the new material was determined by elemental analysis. This suggested that the extent of water uptake increases as the nitrogen content increases from blank chitosan to chitosan-urea to chitosan-EDTA and finally the new material as given in the Table 1. This confirmed that CHEDUR had more nitrogen content than chitosan. The elemental analysis data shows that CHEDUR comprises carbon (36.7%), hydrogen (6.2%) and nitrogen (11.8%).
Table 1.Water uptake data for CHEDUR and control reactions.
Code Number Description % Nitrogen Water uptake g per g
RDAN 80 Blank Chitosan reaction 6.7 8.4
RDAN 81 Chitosan-Urea reaction 10.4 2.8
RDAN 79 Chitosan-EDTA reaction 8.4 6.6
RDAN 78 CHEDUR 11.8 570 ±20

The water (distilled) uptake of CHEDUR was compared with a commercial diaper material, and a mixture containing 1:1 weight ratio of CHEDUR and commercial diaper material. For this study, the water absorbing part of ‘Huggies’ baby diaper was used (the white powder alone that is dispersed in cotton fibre and not along with cotton fibre). The results thus obtained are plotted and shown in Figure 7. It can be inferred from this figure that the rate of water absorption of CHEDUR was the same as that of commercial diaper material in the initial five minutes. In case of the commercial diaper material the maximum water absorption capacity of 238 g/g is reached within 10 minutes, following which no further absorption is observed over a 1 h study period. However, CHEDUR shows water absorption over a period of 30 minutes with a maximum water uptake of 570 g/g, which is nearly 2.3 times that of the commercial diaper material used. The 1:1 mixture (by weight) of commercial diaper material and CHEDUR, follows the expected water uptake rate.
The rate of saline water uptake was investigated for CHEDUR as well as the commercial diaper material and the results are shown in Figure 8. It is clear from this study that CHEDUR is a better water absorber at lower concentration of saline while it is equivalent to the commercial diaper material at higher saline content.
Example 4
Comparative example a
Experiments were performed in which chitosan is reacted with various chelating agents such as tartaric, oxalic acid, ascorbic acids, EDTA and citric acid It was observed that best water uptake is provided by using EDTA and citric acid as the chelating agent.
Table 2.-Water uptake data for CHEDUR and CHCAUR.
S.No. Compound Weight ratio(Chitosan:Acid:Urea) Water uptake (g/g)
1 CHCAUR(chitosan, citric acid, urea) 1 : 2 : 2 800*
2 CHEDUR(chitosan, EDTA acid, urea) 1 : 2 : 2 570*
Note: *hydrothermal synthesis

Comparative example b
Similar experiment was performed with the composition with and without urea. The data shown in table 3 provides water uptake value of various combination.
Table 3.Comparative data of Water uptake of the polymeric material of the present invention vis-à-vis the raw materials.
S.No. Composition N % Water uptake (g/g)
1 CHEDUR(chitosan,EDTA and urea) 11.8 570
2 CHED (without urea) 8.4 6.6
3 CHUR (without EDTA) 10.4 2.8
4 CHCA (without urea) 7.46 30
5 CHCAUR (chitosan, citric acid and urea) 11.38 800

Observation: It was observed that chitosan along with EDTA or citric acid and urea are essential for the present composition to provide the desired effect.

Comparative example c
Experiments were conducted to show that the water uptake is critically dependent on the weight ratio of the components in the composition as evident from Table 4 and 5. The optimum effect is produced in the weight ratio of biopolymer: chelating agent: urea of 1: 2: 2. It was also observed that there is no increase in the water uptake with further increase in the weight ratio, thus establishing the criticality of the said weight ratio.

Table 4: Comparative data showing the effect on water uptake when the polymeric material of the present invention, CHEDUR is having the raw materials in different weight ratio.

S.No. Combination of chitosan, EDTA and urea) Weight ratio(Chitosan : chelating agent: Urea) Water uptake (g/g)
1 CHEDUR 1 : 0.5 : 0.5 20
2 CHEDUR 1 : 1 : 1 53
3 CHEDUR 1 : 2 : 0.5 108
4 CHEDUR 1 : 2 : 2 580
5 CHEDUR 1 : 3 : 3 180

Observation: It is observed from the comparative data that best working ratio is 1:2:2.

Table 5: Comparative data showing the effect on water uptake when the polymeric material of the present invention, CHCAUR is having the raw materials in different weight ratio.
S.No. Combination of chitosan, citric acid and urea Weight ratio Water uptake (g/g)
1 CHCAUR 1 : 1 : 1 225
2 CHCAUR 1 : 1 : 2 91
3 CHCAUR 1 : 2 : 2 800
4 CHCAUR 1 : 2 : 5 416

Observation: It was observed that the combination of chitosan, citric acid and urea works best in the ratio of 1:2:2.

Example 4
The experiment compares the water uptake and hence the growth of the plants in the presence of the biopolymer based biodegradable super water absorbent polymeric material. Plants were placed in a balcony that was closed on the top with metallic grills on three direction. This resulted in lesser exposure to sunlight (not exceeding an hour every day). The plants grown with soil and CHEDUR or CHCAUR (experiment) was watered once every three days, while plants grown only with soil (control was watered every day; otherwise the leaves start to droop if watering is done once every two days). The photographs presented here in the form of figures were taken outside the balcony under direct sunlight.
It was observed that the biodegradable super water absorbent polymeric material made from chitosan, citric acid and urea (CHCAUR in the Figure 10 is labeled E) appears to be doing far better than the control despite being watered once every three days. It must be noted that the growth depends on a number of factors including the nature of the seed used.

Similar experiments were conducted on chilly plants using CHCAUR and CHEDUR. It was observed that the biodegradable super water absorbent polymeric material (CHEDUR and CHCAUR in the Figure 11) appears to be growing far better than the controls despite being watered once every three days. This is attributed to the presence of biodegradable super water absorbent polymeric material. It must be noted that the growth depends on a number of other factors including the nature of the seed used.
,CLAIMS:1. A biodegradable super water absorbing polymeric material (SWAP) comprising of:
at least one biopolymer,
at least one chelating agent, and
at least one fertilizer and /or micronutrient,
wherein the weight ratio of biopolymer :to chelating agent :to fertilizer is 1:2:2.

2. The biodegradable super water absorbing polymeric material as claimed in claim 1, wherein said material is having a water absorption capacity from 500 to 800 g/g.

3. The biodegradable super water absorbing polymeric material as claimed in claim 1, wherein the biopolymer is chitosan.

4. The biodegradable super water absorbing polymeric material as claimed in claim 1, wherein said chelating agent is selected from citric acid and EDTA.

5. The biodegradable super water absorbing polymeric material as claimed in claim 1, wherein said fertilizer is urea.

6. The biodegradable super water absorbing polymeric material as claimed in claim 1, wherein said biopolymer is present in an amount of 20% by wt.

7. The biodegradable super water absorbing polymeric material as claimed in claim 1, wherein said chelating agent is present in an amount of 40% by wt.
8. The biodegradable super water absorbing polymeric material as claimed in claim 1, wherein said fertilizer is present in an amount of 40% by wt.
9. A process of preparing the biodegradable super water absorbing polymeric material, said process comprising the steps of:
i. mixing biopolymer, chelating agent and fertilizer in a weight ratio of 1:2:2 in a poly(propylene) bottle with suitable solvent (water or dilute aqueous acetic acid)an air-tight lid;
ii. heating the reaction mixture of step (i) to 100 °C at a rate of 5 °C per minutes;
iii. maintaining the reaction mixture of step (ii) for 650 minutes at 100 °C; and
iv. cooling and purifying the product with excess methanol.

10. The process as claimed in claim 9, wherein said process is hydrothermal.

11. The process as claimed in claim 9, wherein said biopolymer is chitosan.

12. The process as claimed in claim 9, wherein said fertilizer is urea.

13. The process as claimed in claim 9, wherein said chelating agent is selected from EDTA and citric acid.