BR102012019947A2 - SUPERABSorbent HYDROGEL - Google Patents

Abstract

SUPERABSORVENT HYDROGEL. This invention relates to superabsorbent hydrogels, which are obtained from intercrossing reactions of natural macromolecules, such as gellan gum and chitosan. The developed hydrogels present high water and fluid absorption in their three-dimensional structure, without the polymers undergoing dissolution. In addition, their biocompatibility with human tissues and the environment, as well as their biodegradability, make them applicable in the medical and agricultural areas.

Description

HYDROGEL süperabsorbent Caxapo da. invention:

This invention relates to superabsorbent hydrogels, which are obtained from crosslinking reactions of natural macromolecules such as gellan gum and chitosan.

The developed hydrogels have high absorption of water and fluids in their three-dimensional structure, without the polymers undergoing dissolution.

Moreover, their biocompatibility with human tissues and the environment, as well as their biodegradability, make them applicable in medical and agricultural areas.

Amenity of the invention:

Synthetic polymers, ie obtained from petroleum constituents, are materials that are easy to mold, insulate, have low weight and are easy to color.

Due to their advantages, they are used in industries to replace traditional materials such as wood, metal and ceramics. More recently, due to pollution from waste disposal, polymers and other natural macromolecules have been investigated.

Among the polymers, there are macromolecules which present high water absorption and possibility of formation of hydrogels. This means that when placed in excess water, the polymers swell quickly and conserve a large volume of water in their three-dimensional structure without dissolving.

In addition, hydrogels are non-toxic and still have the ability to swell in water and biological fluids, incorporation and controlled release of drugs, and elastomeric consistency, which makes them interesting for medical applications.

Another advantage of most of these polymers is their excellent biocompatibility property (with human tissues and the environment) and biodegradability, which can also be applied in the agricultural area.

Soluble polysaccharides in aqueous systems may become insoluble by the formation of hydrogels via chain crosslinking reaction with convenient reagents. This interlocking provides for the formation of covalent chemical bonds between the chains or just physical interactions between them, such as van der Waals forces.

Hydrogels can be swollen with water or aqueous solutions of drugs or fertilizers, keeping the solute concentration within an optimal range, above which it is wasted (overdose) and below which it is ineffective, promoting extended release using a single dosage or application is given.

Controlled release studies developed for pharmaceutical substances can still be used for agricultural inputs (such as fertilizers, nutrients and herbicides, among others), however, for both substances and different application media.

In the agricultural environment, the controlled release system increases the functional efficiency of synthetic or natural input, reducing its costs. It also promotes safety in the handling of these products, reducing the risks of toxicity to humans, as well as environmental contamination.

For agricultural purposes, hydrogels need to be small in addition to biodegradability, small (millimeter scale) to avoid significant variations in soil volume due to shrinkage / expansion effects.

The presence of hydrogels modifies adverse physical properties of the soil, such as low water retention capacity and excessive permeability, as they gradually release water and nutrients, prolonging their presence in the soil, reducing nutrient percolation and leaching losses and improving soil nutrient loss. aeration and soil drainage.

Currently, most commercially available superabsorbent hydrogels are cross-linked sodium polyacrylates, resistant to attack by microorganisms, and therefore not biodegradable. Also, because they are applied to disposable products, they can cause environmental pollution.

Latex-based interpenetrating networks for slow, self-controlled fertilizer release are known from the state of the art and were obtained by spray-coating deposition of a water soluble high molecular weight polymer layer with controlled release property on the granule surface. of carbamide fertilizer or its complex.

Nets formed from intercrossable starch mixed with another starch are used as a release system for pharmacological agents, as well as nutrients, vitamins, flavorings, fertilizers, herbicides, insecticides, fungicides or others. The degree of swelling of these nets is almost nil to the first order, giving good protective property to encapsulated agents, especially forming a good oxygen barrier.

Hydrogels still find application in cosmetic use, wherein the gelling agents are bonded via intermolecular hydrogen bonds and at least one of the agents is polysaccharide, such as gellan gum, xanthan gum and gelatin or synthetic polymers such as polyvinyl alcohol, poly (vinyl pyrrolidone), carbomer and poly (vinyl acetate).

The present invention proposes to obtain superabsorbent hydrogels from crosslinking reactions of natural macromolecules such as gellan and chitosan.

These hydrogels have excellent water retention properties, avoiding the loss of chemical substances incorporated by leaching and can also be applied for soil moisture control.

Gellan gum is a high molecular weight anionic polysaccharide consisting of repeated units of β-1,3-D-glucose, β-1,4-D-glucuronic acid and α-1,4-L-rhamnose in a ratio from 2: 1: 1. This polymer is obtained by fermentation of the non-pathogenic aerobic bacteria culture Sphingomonas elodea.

Gellan gum is commercially obtained in its native, high acetyl or deacetylated form in which approximately half of the glucose residues have an acetate substituent and an L-glycerate substituent.

The presence of the acetate group has a great influence on the gel characteristics: while the native form gives soft, elastic and dull gels, the deacetylated form generates firm, hard, non-elastic and high gloss gels.

Gellan gum has received considerable attention due to its property of forming heat reversible gels, i.e., demonstrating reversible properties in heating (temperatures above 80 ° C) and cooling processes. Gelation occurs by the formation of counterclockwise double helices, forming a three-dimensional network due to complexation with cations and formation of hydrogen bonds with water.

The electrostatic interaction between cations and carboxylate groups contributes to the double helix stabilization, creating junction zones. The gellan gum is still capable of forming thermally stable gels up to 120 ° C.

Studies have shown that gellan and scleroglucan gum-based polymeric networks to obtain drug release matrices or pesticides have good release profiles. Polyvinyl alcohol gellan nets - PVA - showed better mechanical properties than pure gellan gels and are indicated as excellent interpenetrating nets for drug release microspheres preparation. Interpenetrating gellan and agar nets have heterogeneity in their structure and the scale of the distance between their chains comparable to the size of their pores.

Chitosan is obtained by the N-deacetylation reaction of chitin, the main constituent of shellfish and crustacean exoskeleton, in which at least 50% of the acetamide groups are converted to amino groups. From a chemical point of view, it consists of a linear sequence of monomeric sugars (N-acetylglycosamine) and is presented as a copolymer composed of repetitive units of β- (1-> 4) -2-amino-2- deoxy-D-glucose joined by glycosidic bonds, also having unreacted residues.

Hydrogels from interpenetrating assemblies based on chitosan and charged and uncharged scleroglucan derivatives (bacterial polysaccharide) have already been obtained from the mixture of solutions without the addition of crosslinking agents or organic solvents.

State of the art:

Hydrogels cross-linked by the mixture of carboxymethyl chitosan (CMQ) with oxidized gellan gum in Shiff base reaction and Ca2 + ion complexation are already known in the state of the art. These hydrogels showed an increased modulus of elasticity to 278 kPa and an ability to return to original shape after weight removal. Swelling and degradation capacities depend on the degree of oxidation of gellan gum and the amount of CMQ used in the formation of nets.

In US 8025696 B2, it is described about the associated use of gellan and chitosan gum in obtaining an artificial meniscus to be allocated between the junctions subject to mechanical stress in an organism for prolonged times.

KR 2011/0027624 A describes a controlled release formulation containing a polysaccharide-type biodegradable polymer and a fertilizer in an inorganic crosslinked silicon oxide network through covalent bonds.

US 2003/040435 A1 describes the coating of fertilizer granules by a polymer having urethane or urea groups, preferably obtained from non-organic solvents, which provides for controlled release of the fertilizer. The coating must not be hard or brittle and must avoid agglutination due to storage and must not have a viscosity above 25 ° C.

WO 02/15702 A1 mentions a biopolymer matrix production process for storing and stabilizing biological and biocompatible materials to prolong their storage time and prevent degradation. The biopolymer is chosen from xanthan gum, acacia, guar, gellan and starch as well as combinations thereof.

WO 2009/021385 A1 describes the coating of fertilizer with a polymer obtained from the aqueous medium for its controlled release. The natural polymer is dispersed in water to gel and is then mixed with the aqueous synthetic polymer solution.

Svaaario of the invention:

The present invention reports superabsorbent hydrogels, which are obtained from cross-breeding reactions of natural macromolecules such as gellan gum and chitosan for application in soil moisture control and controlled release of fertilizers.

Brief description of the figures:

Figure 1 is a chemical representation of the cross-linked polymeric network formed by ionic and electrostatic bonds between chitosan and gellan gum.

Figure 2 is a schematic representation of the chitosan linear chain polymer network with the gellan gum with double helix regions.

Figure 3 is a diagrammatic representation of the process of obtaining dry hydrogel from chitosan and gellan gum.

Figure 4 is a diagrammatic representation of the process of incorporating fertilizer into the dry hydrogel obtained from chitosan and gellan gum.

Detailed Description of the Invention:

The superabsorbent hydrogels of the present invention are obtained from natural polymer solutions selected from the group consisting of chitosan, gellan gum and alginic acid.

Obtaining the solutions:

- Chitosan Solution (CH):

The solution is obtained by dissolving 1.0 g of 85% GD average molecular weight chitosan in 100 ml of 2% (v / v) acetic acid.

The mixture is kept under magnetic stirring for 12 hours and then filtered to remove undissolved residue.

- Gellan gum (GG) solution, which may have high acetyl content (GGHA) or low acetyl content (GGLA):

The solution is obtained by dissolving 1.0 g of high acyl group gellan gum in 1.0 L of Milli-Q deionized water. The mixture is kept under magnetic stirring and constant temperature of 80 ° C for 2 hours.

- Alginic acid (AL) solution:

The solution is obtained by dissolving 1.0 g of sodium alginate in 100 ml of Milli-Q deionized water under magnetic stirring for 2 hours. Then, acetic acid is added to the solution until it reaches approximately pH 3 under magnetic stirring.

Obtaining hydrogels:

After preparation of the solutions, hydrogels are obtained by mixing different proportions of the solutions under agitation, as follows:

GGHA-CH (1: 4, 1: 3, 1: 2, 1: 1, 2: 1, 3: 1 and 4: 1);

GGLA-CH (1: 4, 1: 3, 1: 2, 1: 1, 2: 1, 3: 1 and 4: 1);

- AL-CH (3: 1, 2: 1 1: 1); and

- GG-AL.

The process of obtaining the dried hydrogel from chitosan and gellan gum is schematically described in Figure 3.

Initially, chitosan and gellan gum solutions are mixed under strong mechanical stirring for 4 to 6 hours and heating.

The hydrogels are then extensively washed with 1 L of water and then with 100 mL of ethanol and filtered between washes using TNT blanket.

Finally, the obtained hydrogel is oven dried at 40 ° C.

Figures 1 and 2 respectively represent the cross-linked polymeric web formed between chitosan and gellan gum.

Figure 1 shows the ionic and electrostatic bonds of hydrogels and Figure 2 is a schematic representation of the polymeric network where the ionic bond points are indicated on the rings with (+) and (-) signs and the swelling regions are indicated. by the polymer chains in the form of propellers.

Tests:

- Analysis of the degree of water absorption:

The measurements of the degree of water absorption were made through hydration of the hydrogels and their weighing.

Samples of approximately 0.1 g of dry gel are submerged in water at room temperature (25 ° C) for 1400 minutes.

Then the hydrated gel is removed from the water and excess water is drained. The sample is weighed on the analytical balance to within 0,001 g and the degree of absorption (S) is calculated by the equation below:

S = Hydrated ~ Wseco Wseco

Where: WhIdrated = weight of hydrated gel Wseco = weight of dry gel.

Table 1 below indicates the water absorption grade (S) values for native gellan and chitosan gum hydrogels (GGHA: CH) in different proportions and at different water immersion times.

Table I: Degree of water absorption (S) as a function of water immersion time (water absorption kinetics) for native gellan and chitosan gum hydrogels (GGHA: CH)

GGHA Time: CH 4: 1 3: 1 2: 1 1: 1 1: 2 1: 3 1: 4 15 67, 71 56, 85 49, 56 45, 17 41.25 33, 16 28.26 25 105, 40 85.12 65.23 63, 87 54, 63 34.26 31, 66 60 137.10 10.47 72.24 74, 60 62, 52 37, 75 35, 40 120 150.92 120.15 88, 81 80, 61 66, 84 39, 02 38.29 180 170.01 134.69 103.48 84, 66 72, 36 47.78 41, 62 240 171.59 140.74 109.12 90, 27 82, 98 52, 03 45, 07 1320 219.70 173.12 126.46 108.56 98.18 78, 62 71.39 The results show that water absorption increases

with the time of immersion of hydrogels in water. The biggest

Water absorption values were obtained for the 4: 1 GGHA: CH composite sample. Still, it was observed that times greater than 1320 min. immersion in water do not promote greater absorption of water.

Table 2 below indicates the water absorption grade (S) values for native gellan and chitosan gum hydrogels (GGHA: CH) in different proportions.

Table 2: Degree of water absorption (S) for native gellan and chitosan gum hydrogels (GGHA: CH)

GGHA: CH S pH = 3 pH = 7 pH = 12 4: 1 177.10 219 159.12 3: 1 137.67 173 122.89 2: 1 103.68 126 87.45 1: 1 84, 54 108 76.15 1: 2 77, 57 98 66, 72 1: 3 63, 96 78 54, 37 1: 4 60, 11 71 50.22 The highest water absorption values were obtained at pHs 3, 7 and 12, for networks comprising GGHA: CH in 4: 1 ratio.

Decreasing the amount of gellan gum in the nets causes a decrease in water absorption capacity. It is possible to observe that a greater absorption of water occurs at neutral pH (7); at acidic (3) and basic (12) pH, water absorption is lower than at neutral (7), and is comparable between them.

- Fertilizer release:

The process of incorporating the fertilizer into the dry hydrogel obtained from chitosan and gellan gum is schematically described in Figure 4.

The dried hydrogel obtained from gellan and chitosan gum solutions is swollen with an MPK fertilizer solution for 24 hours at room temperature.

The

The hydrogel is then oven dried at 40 ° C, thus obtaining a dry hydrogel of chitosan mesh and gellan gum with fertilizer.

To assess the degree of release of the mono potassium phosphate fertilizer (KH2PO4; MPK), it was dissolved in Milli-Q deionized water, forming 1 and 4 g / L solutions.

The hydrogels having different compositions were submerged for 24 hours in these solutions and then dried in the desiccator and / or oven at 40 ° C.

The dried samples were then immersed in water and the conductivities were measured with a conductivity meter (Hanna HI-2550-01) every 10 minutes.

In the sense of comparing the release values of the

fertilizers obtained for the different samples, they were normalized by mass of the polymer network. In other words, a larger mass of hydrogel absorbs more water and therefore the values must be divided by the hydrogel mass.

Table 3 below indicates the release values of mono potassium phosphate (MPK) fertilizer in water for GGHA: CH gels.

Table 3: Release of MPK fertilizer in water for native gellan and chitosan gum hydrogels (GGHA: CH)

swollen in different MPK solutions

GGHA: CH in MPK / Water Solution (g / L) 1: 1 in 1 g / L 1: 1 in 4 g / L 1: 3 in 1 g / L 3: 1 in 4 g / L Release Time Release Time Release Time Release Time (min) MKP (min) MKP (min) MKP (min) MKP (mg / g (mg / g (mg / g (mg / g polymer) polymer) polymer) polymer) 1 56 , 8 2 143, 7 1 CO 1 36, 9 MD CN 1 5 206, 6 9 230, 1 6 82, 9 5 149.1 17 210, 4 13 256.2 19 148, 0 13 195, 6 27 234, 5 21 274, 7 28 174, 1 22 251, 9 41 238, 3 27 288.4 39 197, 9 29 276, 2 56 241.4 30 304, 4 45 208, 3 36 303, 5 84 243,7 35 324 , 9 55 215,40619 47 338,04253 109 245, 3 43 325, 9 65 225, 9 56 346, 3 1 29 248.0 49 331, 8 76 234, 6 65 364, 7 141 250, 1 56 339, 2 O 238, 8 73,372, 9 175 175 252, 4 73 339, 4 116 245, 5 91 376,1 190 254, 1 77 340, 8 137 249, 9 105 392, 5 210 256,2 88 344, 7 148 251, 4 130 395,1 1220 262, 6 99 355, 2 159 255, 8 142 399, 0 110 353, 5,170,260, 4,155,401, 6,118,361, 8,183,264, 5,172,405, 5,138,365, 2,196,275, 0,184,406, 8,166,367, 8,199,280,199,409,347,370, 6,204 283.0 212 411.9 212 374, 0 208 283.7 1234 417, 1 230 375, 0 229 288.1 238 375, 2 242 289.1 252 375, 2 267 288, 7 1212 382, 7 1312 296, 5 Through the obtained data, it is observed that the release occurs in 200 min. and is influenced by the concentration of the fertilizer used than by the composition / ratio GGHA: CH of the hydrogel. - Network Parameters:

To evaluate the interspersed structure of hydrogels, the density between intersections (dx) was calculated by the equation below:

dx = 1 vMc

Where: v = specific volume of polymer Mc = average molecular mass between intersections.

The average molecular mass between intersections was extensively studied by Flory, represented by the Flory-Rehner equation below:

Mc = -Pp V5 Vr 1/3

[In (I-Vr) + Vr + xVr2]

Where: pp = polymer density Vs = solvent molar volume Vr = polymer volume fraction χ = Flory-Hoggins parameter The polymer volume fraction is calculated from the equation:

Vr = [1 + Pp Ma + Pp] 1 Ps Mb Ps Where: ps = solvent density Ma = hydrated polymer mass Mb = dry polymer mass The Flory-Hoggins parameter is calculated using the equation:

X - VS (^ tpol - Stsol)

RT

Where: Vs = solvent molar volume Stpoi = polymer solubility parameter ôtsoi = solvent solubility parameter Table 4 below shows the density (dx) and average molecular mass between crossings (Mc) values, as well as the polymer volume fraction (Vr) for native gellan and chitosan gum hydrogels (GGHArCH) in different proportions.

Table 4: Vr, Mc and dx values for gum hydrogels

native gellan and chitosan (GGHA: CH)

GGHA: CH dx (IO-4) Mc <103) «<HOI> 4: 1 1, 07 18, 7 6.4 3: 1 2.56 7.8 8.2 2: 1 4, 35 4.6 11.1 1: 15.53 3, 6 13.0 1: 26 6.45 3.1 14, 3 1: 39 9, 52 2.1 17, 8 1: 4 11.1 1.8 19, 6 The data obtained indicate that GGHArCH hydrogels with higher GGHA content (4: 1, for example) have a smaller number of cross-breeds, therefore, larger Mc and lower d *.

According to the results obtained, it is clear that hydrogels have excellent water retention properties, avoiding the loss of chemical substances incorporated by leaching and can be applied to soil moisture control.

Claims (6)

1. A superabsorbent hydrogel characterized by the fact that it comprises intercrossing natural polymer networks in which the natural polymers are gellan, chitosan and alginic acid macromolecules. Superabsorbent hydrogel according to claim 1, characterized in that the natural polymer networks are formed from the mixture of gellan, chitosan and alginic acid solutions. Superabsorbent hydrogel according to either claim 1 or claim 2, characterized in that the natural polymer solutions are mixed in ratios ranging from 1: 4 to 4: 1. Superabsorbent hydrogel according to either claim 1 or claim 2, characterized in that it preferably comprises native gellan and chitosan in a ratio of 1: 4 to 4: 1. Superabsorbent hydrogel according to Claim 4, characterized in that the degree of water absorption (S) for the native gellan and chitosan gum hydrogel ranges from 20 to 300. Superabsorbent hydrogel according to Claim 4, characterized in that a fertilizer can be incorporated into the hydrogel by immersion.