MODIFIED SUPERABSORBENT POLYMER CONTAINING A FERTILIZER

Abstract

A modified superabsorbent polymer (SAP) comprises a SAP matrix and urea in the form of crystals that is integrated into the SAP matrix. The SAP matrix and the urea are interpenetrated. A method for producing the modified SAP may comprise a) preparing a mixture comprising at least one urea solution and at least one SAP, b) swelling the SAP in the mixture, c) crystallizing the urea in the mixture obtained upon completion of step b), d) recovering the modified SAP in the mixture, and e) optionally, forming the modified SAP recovered at step d).

Claims

1. A modified superabsorbent polymer (SAP) comprising a SAP matrix and urea in the form of crystals that is integrated into the SAP matrix, the SAP matrix and the urea being interpenetrated.

2. The modified SAP according to claim 1, obtained by a method that comprises: a) preparing a mixture comprising at least one urea solution and at least one SAP; b) swelling the SAP in the mixture; c) crystallizing the urea in the mixture obtained upon completion of step b); d) recovering the modified SAP in the mixture; and e) optionally, forming the modified SAP recovered at step d).

3. The modified SAP according to claim 1, wherein the SAP is obtained from at least one compound selected from the group consisting of cellulose derivatives, alginate and glycosaminoglycans.

4. The modified SAP according to claim 1, wherein the SAP is obtained from at least one compound from the group consisting of acrylic polymers, methacrylic polymers, vinyl polymers, polyacrylamides and salts thereof, acrylamide/acrylic acid copolymers and salts thereof, and polyacrylonitriles.

5-7. (canceled)

8. The modified SAP according to claim 2, wherein the crystallization step c) is carried out by a cooling, drying, evaporation or lyophilization technique.

9. A method of using the modified SAP according to claim 1, comprising retaining water with the modified SAP and restituting the water to plants in a staggered manner, wherein the modified SAP comprises in percent by mass: 20 to 99% of the SAP; and 1 to 80% of the urea.

10. A method of using the modified SAP according to claim 1, comprising fertilizing plants with the modified SAP, wherein the modified SAP comprises in percent by mass: 1 to 20% of the SAP; and 80 to 99% of the urea.

11. A method of using the modified SAP according to claim 1, comprising burying the modified SAP in soil.

12. A medical device comprising the modified SAP according to claim 1, wherein the medical device is configured to generate cold on a portion of the body of a human subject or an animal.

13. The medical device according to claim 12, wherein the medical device is in the form of a patch, a compress or a pouch.

14. The medical device according to claim 12, further comprising a pouch that includes at least one sealed compartment comprising at least one divisible or frangible wall and a substance that contains a liquid, wherein the compartment is configured so that the substance hydrates the modified SAP when the wall is broken.

15. The medical device according to claim 14, wherein the substance that contains the liquid is an aqueous solution.

16. The method according to claim 11, wherein the modified SAP is buried in the soil in combination with implementing strip cultivation techniques.

17. The medical device according to claim 14, wherein the pouch is porous.

18. A method of producing a modified superabsorbent polymer (SAP) comprising: a) preparing a mixture comprising at least one urea solution and at least one SAP; b) swelling the SAP in the mixture; c) crystallizing the urea in the mixture obtained upon completion of step b); d) recovering the modified SAP in the mixture; and e) optionally, forming the modified SAP recovered at step d).

19. The method according to claim 18, wherein step e) is performed.

20. The method according to claim 18, wherein the crystallization step c) is carried out by a cooling, drying, evaporation or lyophilization technique.

Description

DESCRIPTION OF THE FIGURES

[0195] FIG. 1 is a graph comparing the water retention properties as a function of time (in minutes) of a 1.sup.st sample of a modified SAP according to the invention (in the graph: <<1.sup.St sample according to the invention>>) with those of a 1.sup.st sample of a SAP of the related art (in the graph: <<1.sup.st comparative sample>>).

[0196] FIG. 2 is a graph comparing the water retention properties as a function of time (in minutes) of a 2.sup.nd sample of a modified SAP according to the invention (in the graph: <<2.sup.nd sample according to the invention>>) with those of a 2.sup.nd sample of a SAP of the related art (in the graph: <<2.sup.nd comparative sample>>).

[0197] FIG. 3 is a graph comparing the water retention properties as a function of time (in minutes) of the 1.sup.st sample of a SAP of the related art (in the graph: <<1.sup.St comparative sample>>) with those of the 2.sup.nd sample of a SAP of the related art (in the graph: <<2.sup.nd comparative sample>>).

[0198] FIG. 4 is a graph comparing the water retention properties as a function of time (in minutes) of the 1.sup.st sample of a modified SAP according to the invention (in the graph: <<1.sup.st sample according to the invention>>) with those of the 2.sup.nd sample of a modified SAP according to the invention (in the graph: <<2.sup.nd sample according to the invention>>).

[0199] FIG. 5 is a photograph taken with a scanning electron microscope of a portion of urea pearl.

[0200] FIG. 6 is a photograph taken with a scanning electron microscope of a portion of granule of a synthetic SAP.

[0201] FIG. 7 is a photograph taken with a scanning electron microscope of a portion of granule of modified SAP according to a first embodiment of the invention.

[0202] FIG. 8 is a photograph taken with a scanning electron microscope of a portion of granule of a modified SAP according to a second embodiment of the invention.

[0203] FIG. 9 is a graph of the evolution of the temperature as a function of time of the content of beakers filled with water in which has been immersed either urea powder, or urea pearls, or a modified SAP according to the invention.

DESCRIPTION OF THE PHOTOGRAPHS

[0204] FIG. 5 is a photograph taken with a scanning electron microscope at a magnification of 300 times of a portion of urea pearl which is used as a fertilizer. In said photograph, it is possible to distinguish an agglomerate of urea crystals 5.

[0205] FIG. 6 is a photograph taken with a scanning electron microscope at a magnification of 300 times of a portion of granule of a synthetic SAP 1. More specifically, said SAP is a cross-linked copolymer of acrylamide and potassium acrylate which is in a non-hydrated state. In the photograph of FIG. 6, fracture lines 2 are visible. These fracture lines 2 of said SAP 1 have appeared during the mechanical fragmentation by grinding which is carried out in order to obtain the granules of the SAP 1 a portion of which is visible in the photograph of FIG. 6.

[0206] FIG. 7 is a photograph taken with a scanning electron microscope at a magnification of 300 times of a portion of granule of a modified SAP 3 according to a first embodiment of the invention. This modified SAP 3 contains, in percent by mass, 20% of a synthetic SAP of a cross-linked copolymer of acrylamide and potassium acrylate and 80% of urea. In the photograph of FIG. 7, it is possible to distinguish that the urea crystals 5 are interpenetrated with the matrix 4 of said synthetic SAP of a cross-linked copolymer of acrylamide and potassium acrylate. The matrix 4 is visible because it presents a lighter gray tone than the urea crystals 5. Thus, by comparison with the photographs of FIGS. 5 and 6 which present the starting constituents for obtaining a modified SAP according to the invention, there is noted the uniqueness of the modified SAP 3 according to the present invention which obviously presents an interpenetration of the crystals of the urea 5 with said matrix 4 of the synthetic SAP of a cross-linked copolymer of acrylamide and potassium acrylate. This interpenetration is obtained thanks to the implementation of the manufacture steps of the modified SAP 3 according to the present invention and which have been described hereinabove.

[0207] FIG. 8 is a photograph taken with a scanning electron microscope at a magnification of 300 times of a portion of granule of a modified SAP 6 according to a second embodiment of the invention. This modified SAP 6 contains, in percent by mass, 10% of a synthetic SAP of a cross-linked copolymer of acrylamide and potassium acrylate and 90% of urea. In the photograph of FIG. 8, it is possible to distinguish that the urea crystals 5 are interpenetrated with the matrix 7 of said synthetic SAP of a cross-linked copolymer of acrylamide and potassium acrylate.

[0208] In addition, the portion of the photograph of FIG. 8 which is above the dotted line is a section plane where it is possible to distinguish inclusions of said matrix 7 of the synthetic SAP of a cross-linked copolymer of acrylamide and potassium acrylate in the urea crystals 5.

[0209] Because the granule of the modified SAP 6 has been broken during cutting, this allowed highlighting, in the portion of the photograph of FIG. 8 located below the dotted line, how the matrix 7 of the synthetic SAP of a cross-linked copolymer of acrylamide and potassium acrylate is interpenetrated with the urea crystals 5 in a three-dimensional form. Hence, this photograph of FIG. 8 is very interesting, because it presents the interpenetration of the urea crystals 5 with the matrix 7 of the synthetic SAP of a cross-linked copolymer of acrylamide and potassium acrylate from different points of view, namely in section (the upper portion of the photograph) and in a three-dimensional form (the lower portion of said photograph). Thus, by comparison with FIG. 6 which also represents a synthetic SAP but within which no urea has crystallized, it is noted in the photographs of FIGS. 7 and 8 that the matrices 4, 7 of the synthetic SAPs of a cross-linked copolymer of acrylamide and potassium acrylate form a dilated network within which the urea 5 has crystallized.

[0210] Thus, the photographs of FIGS. 7 and 8 testify to the uniqueness of the modified SAP 3, 6 according to the invention in comparison with a SAP which has not been subjected to the steps of the manufacture method according to the invention which have been described hereinabove.

[0211] Experimental Part:

[0212] ITest of the Water Retention Properties of the SAP According to the Present Invention:

[0213] The following samples are prepared:

[0214] 1) 1.sup.st comparative sample consisting of a SAP based on a potassium salt of a cross-linked acrylamide/acrylic acid copolymer, with an average grain-size distribution of about 0.75 mm and a mass moisture content in the range of 5% (hereinafter abbreviated as <<PAM>>). It consists of a 1.sup.st comparative SAP, namely a SAP which is already known in the related art of the present invention.

[0215] 2) 1.sup.st sample according to the invention consisting of a modified SAP according to the invention which is obtained in the following manner: [0216] 12 g of urea are dissolved in 6 cm.sup.3 of water at a temperature of 80 C. so as to obtain a fertilizer solution. [0217] 3 g of a PAM-based SAP (namely, a SAP identical to the 1.sup.st comparative sample) are added to this fertilizer solution so as to obtain a mixture; [0218] This mixture is maintained at a temperature of 80 C., under manual stirring, until the complete integration of the fertilizer solution into the SAP which has therefore swelled. Translucent flexible small blocks of SAP, which have absorbed all the urea solution without any visible supernatant, are obtained. [0219] The blocks are cooled for 20 minutes down to a temperature of 30 C. while maintaining a slow brewing. [0220] The thus swelled SAP therefore containing the fertilizer is dried at a temperature of 30 C. so as to obtain a 1.sup.st modified SAP according to the invention.

[0221] 3) 2.sup.nd comparative sample consisting of a CMC-based SAP which is obtained in the following manner: [0222] The CMC is hydrated and linearized to 10% in a basic solution (NaOH 1% diluted in a phosphate buffer). [0223] Said CMC solution is homogenized manually, then the mixture is subjected to a temperature of 50 C., and this for 30 minutes [0224] A cross-linking is performed by means of a cross-linking agent consisting of a BDDE solution at 16% by mass. The cross-linking is carried out in two hours at a temperature of 50 C. [0225] The concentration of the cross-linked CMC solution is neutralized and set to 5% by mass by adding hydrochloric acid and a phosphate buffer and the CMC matrix is left to swell, and this until obtaining a gel with a CMC concentration of 5% by mass. [0226] A drying in a desiccators is performed at a temperature comprised 45-50 C. until obtaining a CMC concentration of 35% by mass. A SAP is thus obtained. [0227] The thus obtained SAP is ground by means of a RAPID type 150.21 grinder with a 5 mm mesh size. [0228] A final drying is performed. Thus, we have a 2.sup.nd comparative SAP, namely according to the related art.

[0229] 4) 2.sup.nd sample according to the invention consisting of a CMC-based SAP which is obtained in the following manner: [0230] 12 g of urea are dissolved in 6 cm.sup.3 of water at a temperature of 80 C. so as to obtain a fertilizer solution. [0231] 3 g of CMC-based SAP (namely, a SAP identical to the 2.sup.nd comparative sample obtained upon completion of the final drying) are added to this fertilizer solution so as to obtain a mixture; [0232] This mixture is maintained at a temperature of 80 C., with manual stirring, until the complete integration of the fertilizer solution into the SAP which has therefore swelled. Opalescent flexible small blocks of SAP, which have absorbed all the urea solution without any visible supernatant, are obtained. [0233] The blocks are cooled for 20 minutes down to a temperature of 30 C. while maintaining a slow brewing. [0234] The thus swelled SAP therefore containing the fertilizer is dried at a temperature of 30 C. so as to obtain a 2.sup.nd modified SAP according to the invention.

[0235] For each of these four samples (namely two samples according to the invention and two comparative samples corresponding to already known SAPs, or in other words according to the related art), the following steps are performed: [0236] A total amount of 60 g of water is progressively added. [0237] The four SAPs are left to swell, until their weight in the hydrated state is 20 times their weight in the dry state. [0238] We waited for one hour. [0239] 3 g of each of the thus obtained four swelled SAPs are collected and placed in an oven for a desiccation at 35 C. [0240] Measurements of the mass of each of these four SAPs are regularly performed. [0241] The percentage of the water mass evacuated from each of the SAPs is determined by comparing the initial mass of the SAP before desiccation and its measured mass.

[0242] Each of the graphs of FIGS. 1 to 4 express the percentage of the water mass evacuated from the tested SAP as a function of time.

[0243] For each of the graphs, at the initial time (t=0 minutes), the initial percentage of water is 100%. The percentage of the water mass decreases over time from the initial value of 100%, in other words with the mass of water evacuated over time.

[0244] More specifically: [0245] The graph of FIG. 1 expresses the percentage of the evacuated water as a function of time for the 1.sup.st sample of modified SAP according to the invention and for the 1.sup.st sample of SAP of the related art. [0246] The graph of FIG. 2 expresses the percentage of the evacuated water as a function of time for the 2.sup.nd sample of modified SAP according to the invention and for the 2.sup.nd sample of SAP of the related art. [0247] The graph of FIG. 3 expresses the percentage of the evacuated water as a function of time for the 1.sup.st sample of SAP of the related art and for the 2.sup.nd sample of SAP of the related art. [0248] The graph of FIG. 4 expresses the percentage of the evacuated water as a function of time for the 1.sup.st sample of modified SAP according to the invention and for the 2.sup.nd sample of modified SAP according to the invention.

[0249] Given the graph of FIG. 3, it is observed that the 2.sup.nd comparative SAP (namely based on the cross-linked CMCthe 2.sup.nd sample of SAP of the related art) has a water retention capacity higher than that of the 1.sup.st comparative SAP (namely based on the PAMthe 1.sup.st sample of SAP of the related art).

[0250] It is noted in the graphs of FIGS. 1 and 2 that the SAPs according to the present invention have a better water retention capacity than their respective comparative SAPs.

[0251] Finally, it is noted that the cross-linked CMC-based modified SAP according to the invention (namely the 2.sup.nd sample of modified SAP according to the invention) has a water retention capacity slightly higher than the PAM-based modified SAP according to the invention (namely the 1.sup.st sample of modified SAP according to the invention).

[0252] Thus, the modified SAPs according to the invention have a fully optimized water retention capacity.

[0253] IITest of the Plants Fertilizing Properties of the SAPs According to the Present Invention:

[0254] The following samples are prepared:

[0255] 1) 1.sup.st sample according to the invention consisting of a modified SAP according to the invention comprising, in percent by mass, 1% of PAM and 99% of urea which is obtained in the following manner: [0256] 12 g of urea are dissolved in 6 cm.sup.3 of water at a temperature of 80 C. so as to obtain a fertilizer solution. [0257] 120 mg of a PAM-based SAP are added to this fertilizer solution so as to obtain a mixture. [0258] This mixture is maintained at a temperature of 80 C., under manual stirring, until the complete integration of the fertilizer solution into the SAP which has therefore swelled. Transparent flexible small blocks of SAP, which have absorbed all the urea solution without any visible supernatant, are obtained. [0259] The blocks are cooled for 20 minutes down to a temperature of 30 C. while maintaining a slow brewing. [0260] The thus swelled SAP therefore containing the fertilizer is dried at a temperature of 30 C. so as to obtain a 1.sup.st modified SAP according to the invention in the form of quite friable granules, and presenting an urea crystallization at the surface. [0261] The surface of the granules is removed by mechanical crushing of the urea crystals. About 4 g of friable urea crystals are thus detached from the surface and are not integrated into the modified SAP granule.

[0262] 2) 2.sup.nd sample according to the invention consisting of a modified SAP according to the invention comprising, in percent by mass, 5% of PAM and 95% of urea which is obtained in the following manner: [0263] 12 g of urea are dissolved in 6 cm.sup.3 of water at a temperature of 80 C. so as to obtain a fertilizer solution. [0264] 630 mg of a PAM-based SAP are added to this fertilizer solution so as to obtain a mixture. [0265] This mixture is maintained at a temperature of 80 C., under manual stirring, until the complete integration of the fertilizer solution into the SAP which has therefore swelled. Transparent flexible small blocks of SAP which have absorbed all the urea solution without any visible supernatant, are obtained. [0266] The blocks are cooled for 20 minutes down to a temperature of 30 C. while maintaining a slow brewing. [0267] The thus swelled SAP therefore containing the fertilizer is dried at a temperature of 30 C. so as to obtain a 1.sup.st modified SAP according to the invention in the form of granules obviously larger than the PAM-based SAP granules integrated initially to the fertilizer solution and presenting a very slight urea crystallization at the surface. [0268] The surface of the granules is removed by mechanical crushing of the urea crystals. Less than 1 g of urea crystals is thus detached from the surface and is not integrated into the modified SAP granule. Almost all the urea is integrated (namely more than 90% of the urea) into the modified SAP granule.

[0269] 3) 3.sup.rd sample according to the invention consisting of a modified SAP according to the invention comprising, in percent by mass, 20% of PAM and 80% of urea which is obtained in the following manner: [0270] 12 g of urea are dissolved in 6 cm.sup.3 of water at a temperature of 80 C. so as to obtain a fertilizer solution. [0271] 3 g of a PAM-based SAP are added to this fertilizer solution so as to obtain a mixture. [0272] This mixture is maintained at a temperature of 80 C., under manual stirring, until the complete integration of the fertilizer solution into the SAP which has therefore swelled. Transparent flexible small blocks of SAP which have absorbed all the urea solution without any visible supernatant, are obtained. [0273] The blocks are cooled for 20 minutes down to a temperature of 30 C. while maintaining a slow brewing. [0274] The thus swelled SAP therefore containing the fertilizer is dried at a temperature of 30 C. so as to obtain a 1.sup.st modified SAP according to the invention in the form of slightly swelled granules, and presenting no urea crystallization at the surface. [0275] No urea crystal has detached from the surface by mechanical crushing. All the urea is integrated into the modified SAP granule.

[0276] The following steps are also carried out:

[0277] 1) 5 g of urea are placed on a cellulose filter with a 100 m mesh size.

[0278] 2) 6.5 cm.sup.3 of water are progressively poured in 5 minutes on said cellulose filter on which the urea are disposed.

[0279] 3) We waited for one hour.

[0280] 4) The cellulose filter is dried at 70 C. for 6 hours.

[0281] 5) The dry residues still present on the cellulose filter are recovered and weighted.

[0282] 6) The steps 2) to 5) are repeated for 2 additional cycles or until no more dry residues can be recovered on the cellulose filter.

[0283] For the 2.sup.nd Sample According to the Detailed Hereinabove Invention in This Part II of the Experimental Part, the Following Steps are Carried Out:

[0284] 1) 5 g of the 2.sup.nd sample according to the invention are placed on a cellulose filter with a 100 m mesh size.

[0285] 2) 6.5 cm.sup.3 of water are progressively poured in 5 minutes on said cellulose filter on which the 2.sup.nd sample is disposed.

[0286] 3) We waited for one hour.

[0287] 4) The cellulose filter is dried at 70 C. for 6 hours.

[0288] 5) The dry residues still present on the cellulose filter are recovered and weighted.

[0289] 6) The steps 2) to 5) are repeated for 2 additional cycles.

[0290] Table 1 below details the amounts of recovered dry residues depending on whether the test is carried out with urea or with a modified SAP according to the invention (namely a SAP containing urea2.sup.nd sample according to the invention in this part II of the experimental part).

TABLE-US-00001 TABLE 1 amount of recovered dry residues. Test with the 2.sup.nd Amount of dry residues sample according to recovered at step 5) upon Test with the invention completion of the: urea granules flakes 1.sup.st cycle: 0.3 g 4.6 g 0.4 g recovered dry residues (g) 2.sup.nd cycle: 0 g 4.4 g 0.2 g 3.sup.rd cycle: not 4.1 g 0.3 g measured

[0291] By 1.sup.st cycle, it is meant the amount of dry residues recovered upon completion of step 5) carried out for the 1.sup.st time.

[0292] By 2.sup.nd cycle, it is meant the amount of dry residues recovered upon completion of step 5) carried out for the 2.sup.nd time.

[0293] By 3.sup.rd cycle, it is meant the amount of dry residues recovered upon completion of step 5) carried out for the 3.sup.rd time.

[0294] The different cycles simulate the aforementioned leaching phenomenon to which the fertilizers are subjected. Each cycle also simulates the addition of water and the activation of the fertilizer dissolution endothermic reaction.

[0295] From table 1, it is noted that the urea is dissolved rapidly and has passed almost entirely through the cellulose filter. A small fraction of urea is impregnated into the filter and has crystallized at its surface.

[0296] Right from the 2.sup.nd cycle, the urea residues are no longer quantifiable and all the urea is leached through the cellulose filter.

[0297] On the other hand, the modified SAP according to the invention is impregnated with water, has swelled and has absorbed all the added water.

[0298] No water drop has passed through the cellulose filter.

[0299] A small fraction of the urea contained in the modified SAP according to the invention is impregnated into the cellulose filter and has crystallized at the surface of the filter, as well as at the surface of the granules of the modified SAP according to the invention. This fraction is recovered in the form of fine flakes. This is why a column quantifying the recovered fine flakes is added in table 1 hereinabove.

[0300] Most of the urea has remained contained in the modified SAP according to the invention and only a small fraction (less than 20%) is transferred into the cellulose filter or at the surface of the granules after three consecutive cycles (in other words, leaching or activation of the endothermic reaction).

[0301] IIITest of the Solubility Properties of the Fertilizer Contained in a Modified SAP According to the Present Invention:

[0302] Another series of experiments is carried out in order to demonstrate that the fertilizer which is interpenetrated with the matrix of a SAP in order to obtain a modified SAP according to the invention preserves an excellent solubility and is retained in a dissolved form during the absorption of water by the modified SAP according to the invention.

[0303] The solubility of the fertilizer may be highlighted by the endothermic reaction which intervenes during its dissolution.

[0304] Starting from a modified SAP according to the invention which used to comprise, in percent by mass, 90% of urea crystals interpenetrated with 10% of a matrix of a synthetic SAP of an acrylamide and potassium acrylate copolymer, the following steps are carried out:

[0305] 1) In a beaker, maintained at ambient temperature, 45 mL of purified water are poured then we waited for the temperature to stabilize.

[0306] 2) Afterwards, 33.3 g of the modified SAP according to the invention are added in this beaker as described hereinabove (in other words, a modified SAP according to the invention which used to contain 30 g of urea).

[0307] 3) The temperature of the content of the beaker is measured over time, while maintaining a slight stirring in order to homogenize and promote the dissolution of the urea contained in the modified SAP, and this as long as the content of the beaker contain two phases (solid/liquid).

[0308] In addition, two control tests are carried out by replacing the modified SAP according to the invention with two types of urea: [0309] urea for a laboratory use (commercialized by the Sigma company) in the form of a powder with a fine grain-size distribution, namely smaller than 150 m; [0310] urea for an agricultural use (commercialized by the OCl-nitrogen company) in the form of pearls with a diameter of about 3 mm.

[0311] The steps 1) to 3) are also carried out on these two control tests then a record of the temperatures of the content of the two beakers, in which are added either urea powder or urea pearls, is performed.

[0312] Table 2 below details the results of the records of temperature of the contents of the beakers in which are added either the urea powder, or the urea pearls, or the urea interpenetrated with the matrix of a SAP (namely a modified SAP according to the invention).

TABLE-US-00002 TABLE 2 record of the temperatures as a function of time for two control tests and for the modified SAP according to the invention temperature ( C.) Modified SAP time Urea Urea according to (min) (powder) (pearls) the invention 0 19.3 19.2 19.6 0.25 1.6 10.4 8 0.5 1.1 8 6.3 0.75 1.9 7.8 4.9 1 2.2 8.2 3.9 1.5 2 6.3 2.9 2 2.4 5.6 2.3 3 2.8 4.1 1.7 4 3.4 3.9 1.6 5 4 4 1.6 6 4.7 4.4 1.8 7 5.3 4.8 2 8 5.9 5.2 2.2 9 6.5 5.7 2.5 10 7 6.3 2.8 11 7.5 6.8 3.1 12 8.1 7.4 3.4 13 8.7 7.9 3.6 14 9.2 8.5 3.9 15 9.8 9 4.2

[0313] FIG. 9 is a graph of the evolution of temperature as a function of time of the content of these beakers filled with water in which is immersed either urea powder, or urea pearls, or a modified SAP according to the invention.

[0314] Given the results of table 2 and the graph of FIG. 9, it is noted that the most rapid drop in temperature is observed for the beaker which contains the urea powder, followed by the beaker containing the modified SAP according to the invention, and finally the beaker containing the urea pearls.

[0315] Considering the rapidity of the endothermic reaction, the dissolution of the urea in fine powder is therefore the most rapid.

[0316] In addition, given these results of table 2 and the graph of FIG. 9, it is noted that thanks to the porosity created in the modified SAP because of the urea crystals are interpenetrated with the SAP matrix, the absorption of water by the modified SAP according to the invention is rapid and the urea, although retained in the modified SAP, is dissolved more rapidly than the urea of the urea pearls for agricultural use.