FIELD OF INVENTION

The present disclosure relates to a hybrid hydrogel. BACKGROUND

Hydrogels, or hydrophilic gels, are hydrophilic polymeric materials having a three- dimensional cross-linked network capable of absorbing and holding large amounts of water. Owing to their hydrophilic properties, the hydrogels have good water interaction and swell when exposed to aqueous environment. Thus, they find application in hygienic products, agriculture, drug delivery systems, coal dewatering, food additives, pharmaceuticals, biomedical applications, wound dressing, waste management, etc. Particle size, porosity, hydrophilicity and cross-linking density are the major factors that control the swelling rate and extent of the swelling of the hydrogel.

In general, hydrogels can be prepared from either synthetic monomers or natural materials and are usually made from raw materials, like monomer, radical initiator, and cross-linker. Hydrogels obtained from natural materials such as collagen, gelatin, starch, alginate, and agarose are biodegradable. On the other hand, the hydrogels obtained from synthetic materials such as polyvinyl alcohol, polyacrylamide and maleic anhydride/butylene copolymers, although non bio-degradable are durable and have a high capacity of water absorption, and high gel strength.

Lately, another class of hydrogels is emerging, which comprise of both synthetic materials as well as natural materials, also known as hybrid hydrogels. These hybrid hydrogels are made of two independent cross-linked synthetic and natural components, contained in network form. Hybrid hydrogels are advantageous as they provide better control over the properties of the hydrogel and are also biodegradable to the desired extent.

SUMMARY

The present disclosure relates to a hybrid hydrogel comprising a crosslinked matrix comprising at least one natural source polymer, at least one monomer and a cross-linker. Said hybrid hydrogel has an absorbency under load of at least 15 grams/gram, a water uptake capacity of at least 100 grams/gram, a bacterial count of less than 100 cfu/gram, and a residual monomer content of less than 300 ppm. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates the scheme of addition of ingredients in accordance with an embodiment exemplified in Example 2.

DETAILED DESCRIPTION In its broadest scope, the present disclosure relates to a hybrid hydrogel. Specifically, the present disclosure relates to a hybrid hydrogel comprising a crosslinked matrix comprising at least one natural source polymer, at least one monomer and a cross-linker. Said hybrid hydrogel has an absorbency under load of at least 15 grams/gram, a water uptake capacity of at least 100 grams/gram, a bacterial count of less than 100 cfu/gram, and a residual monomer content of less than 300 ppm.

The term "absorbency under load", refers to the ability of a hydrogel to absorb an aqueous solution under applied pressure or restraining force in 1 hour. Said aqueous solution is 0.9 percent weight/volume (% w/v) or in other terms 0.9 % solution of sodium chloride in deionized water and the pressure is 0.7 psi (pound per square inch). As mentioned herein, gram(s)/ gram (or g/g) indicates the quantity of the aqueous solution absorbed per gram of the hydrogel.

The term "Residual Monomer Content" has been used in its ordinary meaning, as is known to a person skilled in the art. The term "water uptake capacity" refers to the water uptake as per test method illustrated in Example 1. The term "biodegradability" refers to % biodegradation as per test method illustrated in Example 2.

The 3D integrity of a hydrogel in its swollen state is maintained by either physical or chemical cross-linking. The absorbency under load provides a measure of degree and strength of this cross-linking. A better water absorption against pressure or load can be achieved if the surface of the hydrogel particle is densely cross-linked whereas the core of the particle is lightly cross-linked. In accordance with an embodiment, the hybrid hydrogel has an absorbency under load of at least 30 g/g.

In accordance with an embodiment, the hydrogel has a bacterial count less than 50 cfu/g, and preferably less than 10 cfu/g.

In accordance with an embodiment, the hybrid hydrogel has the water uptake capacity of at least 300 g/g and preferably at least 500 g/g.

In accordance with an embodiment, the hybrid hydrogel has a residual monomer content less than 250 ppm. A process of preparing said hybrid hydrogel is also disclosed. Said hybrid hydrogel is prepared by passing reactants comprising a natural source of polymer, at least one monomer, a cross-linker and a radical initiator through at least two co-rotating twin screw processors, arranged in series. Said co-rotating twin screw processors comprise an inlet zone, an outlet zone, and in between the inlet zone and the outlet zone, at least one mixing zone, at least one conveying zone and at least one back-mixing zone, wherein the back-mixing zone comprises of restricting elements which restrict the reactants from moving forward in the co-rotating twin screw processor until a forward force sufficient to overcome the restriction is achieved, such that the co-rotating twin screw processor provides sufficient shear energy and residence time for the reactants to react. Residence time in context of the present disclosure refers to the time spent by the reactants within the co-rotating twin screw processor. The residence time can be increased by causing back-mixing of the reactants. Back-mixing is achieved by restricting the forward flow of reactants in a predetermined zone of the co-rotating twin screw processor. The back- mixing of the reactants can be carried out anywhere between an inlet and an outlet zone of the co-rotating twin screw processor depending on the reactants and proportion of the reactants in the reaction mixture. Residence time required to prepare a hybrid hydrogel having specific water uptake and absorbency under load value can be manipulated by changing the screw configuration depending on the reactants or raw materials used. Screw speed is of also of key importance in maintenance of proper residence time of reactants within the co-rotating twin screw processor. In accordance with an embodiment, for the preparation of soy-based hybrid hydrogel, a screw speed of at least 550 rpm is maintained in the co-rotating twin screw processors.

The process further comprises curing, and drying the crude hybrid hydrogel obtained from the ultimate twin screw processor.

Curing involves conversion of a liquid material into a solid. In accordance with an embodiment, curing may be carried out by maintaining the crude hydrogel at room temperature till solid state is achieved or by using an energy source such as microwaves.

Drying of the cured hydrogel is carried out in order to attain desired moisture levels in the hydrogel. In accordance with an embodiment, drying can be performed at room temperature or by using a suitable energy source such as microwave or radio frequency waves. Conveyor drying tunnel may also be used for drying the hybrid hydrogel.

In accordance with an embodiment, prior to drying, the cured hybrid hydrogel is optionally subjected to a washing step utilizing either water or an organic solvent. This additional step removes unreacted monomers and low molecular weight products, resulting in a final hydrogel product having higher absorbency under load values. The washing step may be repeated in order to improve the absorbency under load values and water uptake of the hydrogel.

In accordance with an embodiment, the monomer(s) to be (co)polymerized is selected from a group consisting of methacrylic acid, acrylic acids, a, β-unsaturated carboxylic acids, their derivatives and mixtures thereof.

In accordance with an embodiment, natural source polymer is selected from a group consisting of proteins, cellulose, hemicelluloses, saccharides and mixtures thereof.

In accordance with an embodiment, the cross-linker is selected from a group consisting of trimethacrylates, ethylene glycol dimethacrylates, polyethylene glycol dimethacrylates, their derivatives and mixtures thereof.

In accordance with an embodiment, the radical initiator is selected from a group consisting of ammonium persulfate (APS), potassium persulfate (KPS), sodium persulfate, other alkali metal persulfates, peroxides, ammonium cerric nitrate and mixtures thereof. In accordance with an exemplary embodiment, a soy-based hybrid hydrogel obtained from soy protein and acrylic acid is disclosed. A process for preparation of said soy-based hybrid hydrogel is also disclosed. Herein, soy flour has been used as the natural source polymer for preparation of said hybrid hydrogel. Said process of preparing the soy-based hybrid hydrogel comprises passing defatted soy, a strong base, acrylic acid, a cross-linker and a radical initiator through at least two co- rotating twin screw processors, arranged sequentially. Chemically, said soy-based hybrid hydrogel is formed by free radical polymerization of the monomer- acrylic acid, the cross- linker and soy flour assisted by the radical initiator. In accordance with an embodiment, the process comprises of two steps carried out in at least two co-rotating twin screw processors. In the first step, defatted soy is passed through a first twin screw processor along with the strong base so as to cause denaturation of the defatted soy, followed by reaction of the denatured soy with acrylic acid and the cross-linker.

In the second step, output from the first twin screw processor is fed into a second twin screw processor followed by addition of the radical initiator to cause polymerization of the monomer and form crude hybrid hydrogel.

In accordance with an embodiment, in the first step comprising denaturation of the defatted soy, the first twin screw processor is operated at a suitable screw speed between 100-1500 rpm, and preferably in the range of 400- 800 rpm (revolutions per minute). In accordance with a related embodiment, the residence time of about 2-3 minutes is maintained by adjusting the screw configuration of the first twin screw processor. It provides sufficient time for the strong base like sodium hydroxide to completely penetrate the defatted soy particles. In accordance with an embodiment, the strong base used for denaturation of defatted soy is sodium hydroxide. The base has to be of suitable concentration so as to aid complete denaturation, during the residence time available for the reactants. In accordance with a related embodiment, an aqueous solution of sodium hydroxide having a concentration in the range of 25-40 % is used. Preferably, an aqueous solution of sodium hydroxide having a concentration in the range of 30-32% is used. In accordance with an embodiment, in the second step comprising processing denatured soy, monomer and cross-linker in presence of radical initiator, the second twin screw processor is operated at a suitable screw speed between 100-1500 rpm, and preferably between 400-800 rpm. In accordance with a related embodiment, the residence time of about 2.5 - 4 minutes, preferably around 3 minutes is maintained in the second twin screw processor. Uniform shear imparted to material in twin screw processor and adequate residence time results in enhanced polymerization and hence cross-linking of the monomer. This increases the water uptake capacity and absorbency under load values of the hybrid hydrogel. In accordance with an embodiment, soy flour and acrylic acid are mixed in a ratio such that there is optimum neutralization of the acrylic acid, wherein the acrylic acid is added after denaturation of the soy flour with sodium hydroxide. In accordance with yet another embodiment, soy flour and acrylic acid are mixed in a ratio such that there is 60-70% neutralization of the acrylic acid, wherein acrylic acid is added after denaturation of the soy flour with sodium hydroxide.

In accordance with an embodiment, the cross-linker is selected from a group consisting of trimethacrylates, ethylene glycol dimethacrylates, polyethylene glycol dimethacrylates. In accordance with a preferred embodiment, the cross-linker is trimethylolpropane trimethacrylate (TMPTMA). In accordance with a related embodiment, the cross-linker is added in an amount in a range of 0.12 to 0.24% by weight of the total weight of the reactants.

In accordance with an embodiment, the radical initiator is selected from a group consisting of ammonium persulfate (APS), potassium persulfate (KPS), sodium persulfate, other alkali metal persulfates, peroxides, ammonium cerric nitrate and mixtures thereof. Preferably, ammonium persulfate is used. In accordance with an embodiment, the radical initiator is added in an amount in the range of 0.7 to 10 % with respect to the total weight of the reactants. Preferably, the radical initiator is added in an amount in the range of 0.7 to 1.0% with respect to the total weight of the reactants.

In accordance with an embodiment, the reactants are maintained at different temperature in a range of 20- lOOoC across the co-rotating twin screw processors. The process further comprises curing, and drying the crude hybrid hydrogel obtained from the second twin screw processor. Such a cured and dried hydrogel has water uptake capacity greater than 100 g/g.

In accordance with an embodiment, one or both of curing and drying is carried out using microwave energy. Microwave energy may be provided using any known microwave source. In accordance with an embodiment, curing and drying are carried out in a single step. In accordance with a preferred embodiment, curing and drying are carried out in separate steps. In accordance with an embodiment, the hybrid hydrogel obtained from the co-rotating twin screw processor is exposed to microwaves in a microwave oven having an output in a range of 180-900 watts, and preferably 540 watts to effect curing. The curing time depends on the reactants. Subsequent to curing, the hybrid hydrogel is exposed to microwave for drying thereof. In accordance with an embodiment, the hybrid hydrogel is dried in a controlled manner such that the hydrogel is not completely dried. Incomplete drying is critical for achieving hybrid hydrogel having higher water uptake. In accordance with an embodiment, the unwashed hybrid hydrogel has a residual monomer content less than 2600 ppm. The method for estimation of residual monomer content is described in the examples. The unwashed hybrid hydrogel may be subjected to one or more washing steps to improve the absorbency under load values and water uptake thereof. In accordance with an embodiment, the unwashed hybrid hydrogel has an absorbency under load value of not less than about 15 g/g at 0.7 psi for 0.9% sodium chloride solution in deionized water.

In accordance with an embodiment, the unwashed hybrid hydrogel has a water uptake capacity of not less than about 100 g/g. In accordance with an embodiment, prior to drying, the cured hybrid hydrogel is optionally subjected to a washing step utilizing either water or an organic solvent. In accordance with an embodiment, the hybrid hydrogel washed with water and/ or methanol has a residual monomer content less than 300 ppm. In another specific embodiment, the hybrid hydrogel washed with methanol has a residual monomer content less than 250 ppm. In another specific embodiment, the hybrid hydrogel washed with methanol has a residual monomer content less than 220 ppm.

In accordance with an embodiment, the hybrid hydrogel washed with water and methanol has an absorbency under load value of not less than about 30 g/g at 0.7 psi for 0.9% sodium chloride solution in deionized water.

In accordance with an embodiment, the hybrid hydrogel washed with water and/ or methanol has a water uptake capacity of at least 200 g/g.

In accordance with an embodiment, the aforesaid co-rotating twin screw processor is a co-rotating twin screw extruder.

In accordance with an embodiment, the dried hybrid hydrogel is subjected to a grinding step. The hybrid hydrogel may be ground to form powder. In accordance with an alternate embodiment, beads or strands of the hybrid hydrogel are prepared.

An assembly of co-rotating twin screw processors for preparing said hybrid hydrogel is also disclosed. Each of the processor comprises of an inlet zone for receiving one or more reactants, an outlet zone for recovering the intermediate material or hybrid hydrogel, a conveying zone for conveying the reactants, a mixing zone for homogenous mixing of the reactants, at least one back-mixing zone, the back mixing zone comprising of restricting elements which restrict the reactants from moving forward in the co-rotating twin screw processor until a forward force sufficient to overcome the restriction is achieved.

In accordance with an embodiment, the back-mixing zone comprises of restricting elements selected from a group consisting of left hand elements, reverse elements and combinations thereof. Said elements impart high compression and back pressure on to the reactants which restricts the flow of reactants and causes back-mixing thereof.

In accordance with an embodiment, additional back-mixing zones may be present in the co-rotating twin screw processor. In accordance with an embodiment, the co-rotating twin screw processor comprises of a first back- mixing zone and a second back- mixing zone. In accordance with an embodiment, the first and the second back- mixing zones are separated by at least one mixing zone or at least one conveying zone or a combination of at least one mixing zone and at least one conveying zone. In accordance with an embodiment, the second back-mixing zone is proximate to the outlet zone.

In accordance with an embodiment, the co-rotating twin screw processor has a Do/Di greater than 1.55 and is preferably 1.71. In accordance with an embodiment, the processor has a length/ diameter (L/D) ratio in a range of 40: 1 - 60: 1.

In accordance with an embodiment, the co-rotating twin screw processor comprises one or more feeders for separate feeding of the different reactants into the processor. The position of feeders depends on the reactants. In accordance with an embodiment, one or more feeders are located on the inlet zone, the conveying zone and/or the mixing zone. The inlet zone comprises of conveying elements to enable conveying the reactants forward. The conveying zone comprises of conveying elements. The reactants are conveyed to the mixing zone. As it is conveyed, the reactants are subjected to thorough mixing to obtain a homogeneous mass.

In accordance with an embodiment, mixing zone comprises of mixing and reverse elements to enable uniform mixing of the reactants and to increase the residence time. In accordance with an embodiment, the mixing zone comprises of forward and neutral kneading elements. In accordance with an embodiment, the mixing zone comprises at least one fractional lobe element intermediate a first integer element (n) and a second integer element (N) {hereinafter referred to as a Fractional Mixing Element (FME)}. A fractional lobed element is an element intermediate a first integer element (n) and a second integer element (N) by a predefined fraction, such that N/n is an integer and the fraction determines the degree of transition between the first integer and the second integer. A single flight lobe and a bi-lobe can form fractional lobes such as 1.2.xx, where xx an be any number from 1 to 99. The numbers 1 to 99 define whether the fractional lobe will look more like a single flight element or a bi-lobed element. The numbers 1 and 2 in the notation 1.2.xx represent the lobe element intermediate a single flight element (1) and a bi-lobe element respectively (2). In accordance with an embodiment, the mixing zone further comprises at least one element having a continuous flight helically formed thereon having a lead 'L', wherein either the flight transforms at least once from an integer lobe flight into a non-integer lobe flight in a fraction of the lead 'L' and transforms back to an integer lobe flight in a fraction of the lead 'L' or the flight transforms at least once from a non-integer lobe flight to an integer lobe flight in a fraction of the lead 'L' and transforms back to a non-integer lobe flight in a fraction of the lead 'L' {hereinafter referred to as a Dynamic Stirring Element (DSE)}. This causes vigorous mixing of reactants.

In accordance with an embodiment, the co-rotating twin screw processor is a co- rotating twin screw extruder.

An assembly for preparing said hybrid hydrogel is also disclosed. Said assembly comprises above disclosed co-rotating twin screw processor for preparation of the hybrid hydrogel and a microwave source for causing curing and drying of the obtained hybrid hydrogel. The microwave source may be any known source, such as microwave oven. In accordance with an embodiment, the co-rotating twin screw processor is connected in series with the microwave source through a conveying element such that preparation, curing and drying of hybrid hydrogel is carried out in a continuous manner. In accordance with a further embodiment, at least two microwave source are connected in series with the co-rotating twin screw processor in order to first carry out the curing followed by drying of the hybrid hydrogel.

An assembly for preparing said hybrid hydrogel is also disclosed. Said assembly comprises above disclosed co-rotating twin screw processor for preparation of the hybrid hydrogel and a radiofrequency dryer for curing and/or drying of the obtained hybrid hydrogel.

In accordance with an aspect, the present disclosure also relates to a hybrid hydrogel comprising a crosslinked matrix comprising at least one natural source polymer, at least one monomer and a cross-linker. Said the hybrid hydrogel has a residual monomer content of less than 2500 ppm and a biodegradability of at least 14% in three weeks after initiation of biodegradation.

In accordance with an embodiment, such a hybrid hydrogel is suitable for agriculture uses.

In accordance with an embodiment, a process of preparing aforesaid hybrid hydrogel is also disclosed. Said process comprises passing reactants comprising a natural source of polymer, at least one monomer, a cross-linker and a radical initiator through a single co- rotating twin screw processor. Said co-rotating twin screw processor comprises an inlet zone, an outlet zone, and in between the inlet zone and the outlet zone, at least one mixing zone, at least one conveying zone and at least one back-mixing zone, wherein the back- mixing zone comprises of restricting elements which restrict the reactants from moving forward in the co-rotating twin screw processor until a forward force sufficient to overcome the restriction is achieved, such that the co-rotating twin screw processor provides sufficient shear energy and residence time for the reactants to react.

In accordance with an embodiment, the co-rotating twin screw processor is provided with feeders for separate feeding of the different reactants into the processor. This can be achieved by introducing each of the reactants as per the reaction sequence into the processor, altering the screw configuration and creating back mixing zones through selective placement of the reverse elements in the screw configuration. The output from the processor can be cured and dried as explained above.

SPECIFIC EMBODIMENTS ARE DISCUSSED BELOW

A hybrid hydrogel comprising a crosslinked matrix comprising at least one natural source polymer, at least one monomer and a cross-linker; the hybrid hydrogel having an absorbency under load of at least 15 grams/gram, a water uptake capacity of at least 100 grams/gram, a bacterial count of less than 100 cfu/gram, and a residual monomer content of less than 300 ppm.

Such hybrid hydrogel, wherein the hybrid hydrogel has the bacterial count of less than 50 cfu/g.

Such hybrid hydrogel, wherein the hybrid hydrogel has the bacterial count less than 10 cfu/g.

Such hybrid hydrogel, wherein the hybrid hydrogel has the water uptake capacity of at least 300 g/g.

Such hybrid hydrogel, wherein the hybrid hydrogel has the water uptake capacity of at least 500 g/g. Such hybrid hydrogel, wherein the hybrid hydrogel has the residual monomer content of less than 250 ppm.

Such hybrid hydrogel, wherein the natural source polymer is selected from a group consisting of proteins, cellulose, hemicelluloses, saccharides and mixtures thereof.

Such hybrid hydrogel, wherein the natural source polymer is obtained by denaturation of soy flour.

Such hybrid hydrogel, wherein the monomer is selected from a group consisting of methacrylic acid, acrylic acids, a, β-unsaturated carboxylic acids, their derivatives and mixtures thereof.

Such hybrid hydrogel, wherein the cross-linker is selected from a group consisting of trimethacrylates, ethylene glycol dimethacrylates, polyethylene glycol dimethacrylates, their derivatives and mixtures thereof.

Such hybrid hydrogel, wherein the hybrid hydrogel is formed by using the at least one monomer and the natural source polymer in a ratio ranging between 2: 1 and 1 : 1.

Such hybrid hydrogel, wherein the hybrid hydrogel is formed in the presence of a radical initiator selected from a group consisting of ammonium persulfate (APS), potassium persulfate (KPS), sodium persulfate, other alkali metal persulfates, peroxides, ammonium cerric nitrate and mixtures thereof.

A hybrid hydrogel comprising a crosslinked matrix comprising at least one natural source polymer, at least one monomer and a cross-linker; the hybrid hydrogel having a residual monomer content of less than 2500 ppm and a biodegradability of at least 14% in three weeks after initiation of biodegradation.

Such hybrid hydrogel, wherein the hybrid hydrogel has a water content ranging between 8 to 12%.

EXAMPLES

The following examples are provided to explain and illustrate the synthesis of hybrid oxide and do not in any way limit the scope of the invention as described and claimed. Example 1: Preparation of Hybrid hydrogel from acrylic acid and soy flour Extruder 1

Specification: Omega 20 P, L/D: 60, Screw Speed: 600 RPM

Temperature Profile:

Screw Configuration:

Extruder 2

Specification: Omega 30 P, L/D: 60, Screw Speed: 600 RPM Temperature Profile:

Screw Configuration:

List of Abbreviations for Elements

RSE: Right Handed Screw Element

RFV: Right Handed Shovel Element

RFN: Right Handed Transition Element

LSE: Left Handed Screw Element

DSE: Dynamic Stirring Element

RKB: Right Handed Kneading Block

NKB: Neutral Kneading Block

SKE: Schubkanten Element

RFV: Right handed Shovel Element

RFN: Transition element from RFV to RSE

SKN: Transition element from Schubkanten Element to RSE Composition: The composition of the sample prepared has been listed in Table 1, below. Feed rate (in grams/ minute) of the reactants has been listed in Table 2.

Table 1

Table 2

Procedure:

Preparation of Crude Hybrid Hydrogel: In Extruder 1, soy flour was denatured with 30% Sodium hydroxide (NaOH). Subsequent to denaturation, denatured soy flour was mixed with acrylic acid and TMPTMA, fed through barrel B9, to obtain "Premix A". Premix A was fed to barrel B 1 of Extruder 2. APS along with water was fed to barrel B2. Product obtained from outlet barrel was collected and cured and dried in two separate steps using a microwave at 560 watts to obtain crude hybrid hydrogel. Purification of Crude Hybrid Hydrogel: Cured hybrid hydrogel was cut in small pieces and kept in water for at least 7 hours so as to ensure that all the pieces swell properly. The swollen hydrogel mass was sieved in 40-60 mesh to remove excess water. Further, it was then squeezed to remove excess water. The hydrogel was subjected to methanol wash by keeping the hydrogel with methanol in a beaker to allow settling of hydrogel. Subsequently, the hydrogel was squeezed and exposed to sonication for 3 to 5 minutes. Excess methanol was removed from the hydrogel by sieving. The methanol wash was repeated 3-4 times to obtain a white purified hydrogel. This hydrogel was kept for drying at 50°C in a vacuum oven.

Water uptake results:

Method: Water uptake values were determined by cutting the samples of hydrogel into approximately 20-40 mg pieces followed by determining the total weight to the nearest 0.1 mg and immersing in excess distilled or deionized water. Given 300-400 fold expected water uptake values, 0.3-0.4 g total as-prepared hydrogel samples were selected as reasonable sized samples for water uptake values. To calculate water uptake values adjustment was made for the percent solids in different hydrogel samples to determine the swelling due to actual hydrogel weight. For instance, the total hydrogel solids content is 44.5% (the remaining being original water as well as "new" water formed from partial neutralization of acrylic acid) so the actual weight of a sample that is hydrogel is the sample weight multiplied by 0.445. Therefore, actual weight of a 0.3 g dried sample measured is 0.3 gx0.445= 0.1335 g which is then put in water overnight for swelling. Hence the Water uptakes values are calculated as (weight in grams of absorbed water/ weight in grams of dried sample) x 2.247. To determine water uptake values, 0.3 grams of dried hydrogel was kept in a plastic container. The container was filled with water (250gms-300gms) and kept at room temperature for 24 hrs.

The observations have been listed in Table 3, below:

The characteristics of the hydrogel product before washing with methanol, have been listed in Table 4, below:

Table 4

Residual Monomer Content: High Performance Liquid Chromatography (HPLC) was used to measure residual acrylic acid content in the hydrogel. Instruments used: A High performance liquid chromatography (HPLC) equipped with UV detector, Sonicator, Shaker and Analytical balance.

Acrylic acid 99.9% potency manufactured by Sigma-Aldrich was used as standard. Preparation of mobile phase:

Mobile phase-A: 1 ml of orthophosphoric acid + 1000 ml of HPLC grade water, mixed and sonicated for 5 minutes. Mobile phase-B: 900mL of acetonitrile + 100 ml HPLC grade water, sonicated for 10 minutes.

Chromatographic Conditions:

Column: Sunfire C18, 150mmx4.6mm, 3.5μιη

Flow: l.Oml/min

Column Temperature: 40°C

Sample volume: 5 μL

Wavelength: 210 nm

Run time: 30 minutes

Gradient programme: Time/%B: 0/0, 10/0, 16/90, 22/0, 30/0

Standard solution of concentration 300 μg/mL of acrylic acid was prepared.

Sample solution of lOOOmg of hydrogel powder in 250 ml of water was prepared and filtered through whatmann filter papers 41 followed by 42. The recommended sequence schedule for estimation of acrylic acid is illustrated in Table 5, below:

Table 5

Residual Acrylic acid content was measured using the following formula:

Where,

AS- Average peak area of Acrylic acid In standard solution including: bracketing.

AT- Average Peak area of Acrylic acid in sample solution.

WS- Weight of standard in mg .

WT- Weight of sample In mg.

P - Potency of Acrylic acid (as is basis)

Results:

Table 6

Absorbency under load (AUL):

Instruments used:

1. Petri dish of diameter 188 mm

2. Mesh screen of ASTM 40 is equal to 400 micron

3. Filter paper (Whatman) of 41 micron, diameter 125mm

4. Load of 49.21 g is equivalent to 0.7 psi

Solution used:

0.9% NaCl solution was used to perform the AUL test.

Test Parameters:

External pressure: 0.7 psi

Time period: 1 hour Method: Mesh of screen plate (ASTM 40) was put in Petri dish and whatman filter paper was placed on the mesh screen. 0.5 grams dried hydrogel sample was weighed and placed uniformly over a filter paper on mesh screen. A filter paper was placed over distributed sample and load of 49.21 grams was applied on it at the centre. 400 ml of 0.9% NaCl solution was added in the petri dish. After the 1 hour, the load was removed and weight measured. AUL was calculated using the following formula:

Calculations:

The Area under Load can be calculated by formula

Microbial Count

Microbial count of the defatted soy flour as well the hybrid hydrogel formed therefrom were determined. The results of the defatted soy flour as well the hybrid hydrogel have been listed in Table 8 and 9 below, respectively:

Example 2: Preparation of Hybrid hydrogel from acrylic acid and soy flour using a single extruder

Extruder Specification: Omega 30, Screw speed: 400 RPM

Temperature profile (°C):

Screw configuration:

SFV: Single Flight Shovel Element

SVN: Transition element from SFV TO RSE

FKB: Forward Kneading Block

LKB: Left handed Kneading Block

SSV: Single flighted Shovel Element

3DSA: 3Lobe Dynamic Stir Element

3RSE: 3Lobe Right handed Screw Element

3 RKB : 3Lobe Right handed Kneading Block

3 LSE: 3 Lobe Left handed Screw Element

Composition: The composition of the sample prepared has been listed in Table 10, below. Feed rate (in grams/ minute) of the reactants has been listed in Table 11.

Table 10

Table 11

Procedure:

Preparation of Crude Hybrid Hydrogel: In the Extruder, soy flour was denatured with 30% Sodium hydroxide (NaOH). Subsequent to denaturation, denatured soy flour was mixed with acrylic acid, TMPTMA and APS along with water. The scheme of addition of ingredients has been illustrated in Figure 1. Product obtained from outlet barrel was collected and cured and dried using a microwave for 120 Sec @ 540 watts to obtain crude hybrid hydrogel.

Observations and Results:

AUL value = 29.56g/g

Water uptake = 430

Acrylic acid monomer content (as crude) = 5036 ppm

(purified) = 2339 ppm

Water content = 8-12%

The hybrid hydrogel was subjected to test of biodegradability as per ASTM D 5338: 100 grams of test sample and control sample were taken to perform the test.

The data for % biodegradation of the hybrid hydrogel sample and cellulose is given in Table 12, below:

Observation: At the end of 45 days, % biodegradation of submitted sample is reported relative to the positive control i.e. cellulose.

Result:

Percentage biodegradation relative to positive reference

Mean: 19.19%

The reference material cellulose: 100%