WATER ABSORBENT COMPOSITE, PROCESS FOR PREPARING AND USES

FIELD OF THE INVENTION

This invention relates to a water absorbent composite containing a polymer and hydrogel. The present invention also relates to the process for preparing the water absorbent composite and its use for textile, medical, biological and engineering applications.

BACKGROUND OF THE INVENTION

[0001] A polymer is a large molecule or a macromolecule which essentially is a combination of many subunits. They cannot be classified under one category because of their complex structures, different behaviours and vast applications. A wide variety of polymers has low water absorption. Polyamides, polyolefins and polyesters, although have different structures, have in common the poor hydrophilic property, which is even worse for polyesters and polyolefins. The improvement of water absorption led to advantages in different fields such as better comfort in textile and medical fields and also better mechanical properties in engineering field.

[0002] Different attempts have been used to improve water absorption of polymers.

[0003] Published U.S. Pat. No. 4,698,404 describes a method of producing water-swellable polymer particles by inverse suspension polymerization of an aqueous solution of acrylic acid and alkali or ammonium acrylate in a hydrocarbon following cross-linking of the polymer. This method includes many steps and a lengthy process.

[0004] Some methods to produce water absorbent polymers use radiation such as ultraviolet rays as described in EP No. 0287970 to achieve low contents of residual monomers in water-absorbing polymers having carboxylic groups and/or carboxylate groups.

[0005] Published U.S. 4,931 ,497 describes hydrophilic water absorbent graft polymers containing radicals of different groups in a random distribution of the graft polymer.

[0006] However, described techniques require time-consuming processes, most of them including many steps and compounds, resulting in expensive methods.

[0007] Another method to prepare a superabsorbent polymer described in U.S. 5,534,304 consists in applying to the surface of a substrate a superabsorbent material. According to this technique, the superabsorbent property is only on the surface of the substrate and due to specificities of different substrates, some of them can not apply to this technique.

[0008] Chinese patent CN 107805336 describes a water absorbing masterbatch obtained by a blending process containing a carrier resin, water-absorbing agent, thermoplastic starch and a compatibilizer. This method includes amounts of water-absorbing agents from greater than 10% as a way to improve absorption of the polymers in the masterbatch.

[0009] Hydrogels are a network of crosslinked polymer chains that are hydrophilic and allow them to absorb large amounts of water. Hydrogels are able to swell and de-swell water in a reversible way.

[0010] Hydrogels have received considerable attention in the past 50 years due to a wide range of applications ranging from industrial to biological ones.

[0011] There is still no existing way to improve the water absorption of polymers able to be applied in different classes of them.

[0012] In view of the above, there is a need to provide a simple and better way to improve water absorption of polymers while using few components and able to be implemented in many types of polymers. [0013] Therefore, it is an object of the present invention to provide a water absorbent composite prepared by a simple process with the aim of improving applications in different polymers for use in textile, medical, biological and engineering applications.

SUMMARY OF THE INVENTION

[0014] The present invention relates to water absorbent composite containing hydrogel particles.

[0015] Pursuing its research in this field, the Applicant has now discovered a water absorbent composite containing very small amounts of hydrogel and able to be prepared by a simple and common process, not requiring the use of many compounds.

[0016] A first object of the present invention is, therefore, to provide a water absorbent composite of a polymer and hydrogel particles, with the amount of hydrogel being less than 10% by weight of total weight of the composite.

[0017] The composite of the present invention makes possible to improve water absorption of any polymeric thermoplastic material, both synthetic and biodegradable ones, the latter having the advantage of being sustainable.

[0018] Indeed, the Applicant has discovered, totally unexpectedly, that the use of very small amounts of a dried hydrogel in the composite can improve the water absorption of many polymers.

[0019] By composite, it should be understood as a solid material which is composed of two or more substances having different physical characteristics and in which each substance retains its identity while contributing to desirable properties for the whole.

[0020] Throughout the description, including the claims, all process terms should be understood as being synonymous with the term method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0021] The polymer for the present invention can be chosen in particular from the group comprising: polyamide 4X, polyamide 5X, polyamide 6X, X being an integer from 0 to 12; polyhydroxybutyrate (PHB), polylactic acid (PLA), poly(ethylene terephthalate), polyethylene, polypropylene, and mixtures thereof.

[0022] The above polyamides are well known in the art and are commercially available. They are obtained by polycondensation of a mixture of diacids and diamines monomers or a salt thereof, which are commercially available. The diamines for polyamide 4X is tetramethylenediamine (1 ,4-diaminobutane or putrescine), for 5X is pentamethylenediamine and for 6X is hexamethylenediamine (1 ,6- hexanediamine). The list of potential dicarboxylic acids is the following: butanedioic acid (succinic acid), pentanedioic acid (glutaric acid), hexanedioic acid (adipic acid), heptanedioic acid (pimelic acid), octanedioic acid (suberic acid), nonanedioic acid (azelaic acid), decanedioic acid (sebacic acid), undecanedioic acid, dodecanedioic acid. All those diacids are commercially available.

[0023] Polyester is a class of polymers which can encompass synthetic and natural different polymers. The process for obtaining them can vary from polycondensation for polyethylene terephthalate (PET), condensation or ring-opening polymerization for polylactic acid (PLA) to biotechnological process for production of biopolyesters such as polyhydroxybutyrate (PHB).

[0024] Polyolefins such as polyethylene (PE) and polypropylene (PP) are produced by polymerization of the olefins ethylene and propylene, respectively. Besides a wide range of processes and polymers, the polyesters and polyolefins are also commercially available.

[0025] By hydrogel, it should be understood as a three-dimensional network of hydrophilic polymers that can swell in water and hold a large amount of water while maintaining the structure due to chemical or physical cross-linking of individual polymer chains. [0026] Hydrogel structures are composed mainly of hydrophilic homopolymers or copolymers. Hydrogels may be synthesized in a number of chemical ways. These include one-step procedures like polymerization and parallel cross-linking of multifunctional monomers, as well as multiple step procedures involving synthesis of polymer molecules having reactive groups and their subsequent cross-linking, possibly also by reacting polymers with suitable cross-linking agents.

[0027] When obtained as particles, hydrogel can be used in different compositions. The hydrogel technologies may be used in applications such as hygienic products, agriculture, drug delivery system, sealing, coal dewatering, artificial snow, food additives, pharmaceuticals, biomedical applications, tissue engineering and regenerative medicines, diagnostics, wound dressing, separation of biomolecules or cells and barrier materials to regulate biological adhesions, and biosensor.

[0028] In one embodiment, the hydrogel particles are formed from polyacrylamide-co-acrylate (PAA), poly-N-isopropyl acrylamide (PNIAAm), polyacrylamide (PAAM), polyacrylic acid, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyurethanes, polyethylene oxide, carboxymethyl starch, carboxymethyl cellulose, hydroxymethyl cellulose, agarose, alginate, chitosan, collagen, gelatin, keratin, guar, or mixtures thereof.

[0029] The composites of the present invention can be prepared using different classes of polymers, both naturals or synthetics, and hydrogel particles.

[0030] Typically, the improvement on water absorption of polymers can be determined using gravimetric analysis by submitting the samples on different temperature/humidity conditions in order to simulate different exposures, both light and extreme. These exposures can be used to mimic light and drastic conditions that may occur depending on the application in variable fields in which different polymers can be applied.

[0031] According to the invention, the water absorption of the composite is from 0.3% to 25%, preferably 0.8 a 15% by weight of the total weight of the composite when submitted to alternating cycles of 4 hours of duration for absorption followed by desorption cycles for a total of four days under 20°C and 55 or 60% Relative Humidity for absorption cycles and 30°C and 80 or 90% Relativity Humidity for desorption cycles.

[0032] In another embodiment, water absorbent composite is obtained from hydrogel particles, which have been previously dried above 98°C for 24 hours, preferably at 105°C, and from a polymer containing an amount of water which is from 0.02 to 1.0 wt% of the total weight of the polymer, determined by thermal gravimetric analysis.

[0033] Particularly, the hydrogel particles of the present invention are previously dried due to its hydrophilic property.

[0034] The amount of water in the polymer can be determined by thermogravimetric analysis, by loss of mass measurement after heating the polymeric samples up to 105°C and monitoring the mass variation until no variation is obtained.

[0035] Advantageously, the hydrogel is a particle with mean particle size in the range of 150 to 300 pm.

[0036] As used herein, the term “particle” refers to an individualized entity.

[0037] In one preferred embodiment, the polymer is formed from polyamide 56, polyamide 6.6, poly(hydroxybutyrate), poly(lacticacid), poly(ethylene terephthalate), or mixtures thereof.

[0038] In another preferred embodiment, hydrogel is polyacrylamide- co-acrylate (PAA).

[0039] It has surprisingly been found that composites prepared using less than 10% of hydrogel particles and a diversity of polymers having variable characteristics were able to have the water absorption improved. It has been proven that the hydrogel, in different extension, plays an essential hole in the composite and can increase water absorption of water from less hydrophobic polymers, polyamides (PA) for instance, till very poor hydrophilic ones, such as polyethylene terephthalate (PET). [0040] Preferably, the amount of hydrogel is selected between 0.4 to 5% by weight of the total weight of the composite.

[0041] According to the invention, the composites may be prepared using a simple process, able to be applied for a wide range of polymers and without the need of inclusion of other compounds.

[0042] In another embodiment, the process for preparing a water absorbent composite comprises the following steps:

A- melt-blending a mixture comprising a) melted polymer, and b) hydrogel particles, previously dried and sieved in range between 150 and 300pm, thus dispersing hydrogel particles into the polymer and granulated by a co-rotating twin-screw extruder

B- cooling and drying the granules of composite obtained in step A.

[0043] Particularly, the melt blend of the present invention is processed by extrusion in an extruder selected from endless screw mixers or stirrer mixers, preferably, the extruder is a twin-screw extruder or a multi-screw extruder.

[0044] Typically, the extrusion process of the present invention occurs with the rotation extruder at about 100 to 500 rpm, more specifically between 200 to 400 rpm.

[0045] The step B of cooling the composite granules obtained at step A is conducted by any appropriate means, most often at a temperature below the softening temperature of the blend. Mention can notably be made by air cooling or quenching in a liquid.

[0046] The water absorbent composite of the present invention can be used for preparation of fibers, yarns, patches, films, tape, woven, filament or membranes.

[0047] Advantageously, the composite of the invention can be used in various applications, notably in textile, medical, engineering and biological fields. [0048] Particularly, the increasing in water absorption for fibers and yarns is responsible for improvement of comfort due to promotion of better breathability and avoiding direct contact between sweat and skin.

[0049] Typically, the composite is used for textile applications, preferably for sportswear, leisurewear and innerwear textile applications.

[0050] Several external wounds require the application of medicines many times a day. One way to ensure greater comfort to the patient and avoid mechanical injury to the wound is the use of patches, which can contain one or more drugs and ensure immediate or sustained release.

[0051] Alternatively, the composite can be used for medical applications, preferably for preparing wound healing patches.

[0052] Mechanical structure of different polymeric composites ensure its use in machinery manufacturing, electronics, transportation and other fields.

[0053] Additionally, the composite can be used for production of structural materials selected from interior and exterior parts of electrics, electronics, furniture, sport, mechanical engineering, sanitary and hygiene, medicine, energy and drive technology, automobile and other means of transport, apparatus for telecommunications, consumer electronics, personal computers and tablets.

[0054] Commonly, polymeric composites are used in membrane constitutions both in chemical, medical and biological fields for membrane separation processes.

[0055] Finally, the composite of the present invention can be used for dialysis, filtration, gas and/or liquid separation, energy applications, electrolytes, water treatments, water filtration, distillation, bioreactors, osmosis, desalination, chemicals separation, pervaporation.

[0056] Illustrating the invention are the following examples that are not to be considered as limiting the invention to their details.

EXPERIMENTAL PART [0057] The present invention will be illustrated by way of the following examples.

[0058] In the examples, the various abbreviations have the following meaning.

[0059] PHB: polyhydroxybutyrate polymer. The PHB is obtained by wherein the first polyamide under the name B!QCYCLE® 1000 (FE154).

[0060] PLA: polylactic acid polymer. The PLA is obtained by

Natureworks under the name Ingeo 4042D with content of D-lactic acid of 4.25 ± 0.55%.

[0061] PET: polyethylene terephthalate polymer. The PET is obtained by Mafissa under the name of Poliester 1471 .

[0062] PA66: polyamide 66 polymer. The PA 6.6 is produced by

Solvay and commercially available under the name of Polyamide 6.6 Brilliant.

[0063] PAA: Polyacrylamide-co-acrylate hydrogel is obtained from Recyc PHP under the name SAG-M85F, with mean particle size of 150 to 300pm.

[0064] The twin-screw extruder equipment: Co-rotating twin-screw Coupled to Thermo Scientific Torque Rheometer - model Polylab OS Rheodrive 7 / FIAAKE Rheomex OS Extruder PTW16, L/D 16 mm.

[0065] Thermal balance from Mettler Toledo, model Halogen Moisture Analyzer HG53.

[0066] Environmental Chamber from Visomer, model G-2538.

[0067] EXAMPLE 1

[0068] Water amounts in polymers were previously measured by Thermal Gravimetric Analysis.

[0069] The methodology consisted in heating the polymeric samples up to 105°C, and monitoring the masses until no mass variation. [0070] The amount of water was determined as being the mass lost from room temperature to 105°C, until no more mass variation was observed in the balance.

[0071] The results of the amount of water in each polymer, before processing to produce the composites, is described on Table 1.

[0072] TABLE 1. Water amount in the polymeric samples.

[0073] EXAMPLE 2

[0074] Composites were made according to the trial compositions available on TABLE 2.

[0075] Trial compositions were prepared by introducing the desired amount of previously dried hydrogel particles and polymer pellets and in a twin screw extruder device rotating at 300 rpm to prepare the composite.

[0076] The temperatures in the different zones of the twin extruder device varies between 250 and 270°C, with a throughput of 0.4 kg/h.

[0077] After the extrusion mixing the resulting composite is cooled into water and then separated from the water by filtration and dried at 100°C overnight.

[0078] The results obtained were described in TABLE 2 for the trial composites.

[0079] TABLE 2. Composites composition.

[0080] As can be shown different composites using a variety of polymers were prepared following trial compositions.

[0081] EXAMPLE 3

[0082] Trial compositions 1 to 7 from example 2 were submitted to a water absorption test according to below.

[0083] Prior to the test, the trial compositions were dried for 8 hours, at 105°C, in an oven. Samples were placed in a climatic chamber at 20°C and 60% humidity, during 12 hours after drying. Then, samples were placed in a second climatic chamber, conditioned at 30°C and 90% of humidity, for 4 hours. After, the samples were subjected to conditions of 20°C and 60% humidity, for another 4 hours. The procedure above was repeated with the same sample for four days in a row.

[0084] The water absorption was calculated by weight difference of each trial composition before and after placing them in climatic chambers cycles.

[0085] The results obtained were described in TABLE 3 for trials 1 to 7. [0086] TABLE 3: Water absorption of composites.

[0087] As can be shown, trial compositions 2, 3, 5 and 7 demonstrated an increase in water absorption compared to isolated polymers.

[0088] EXAMPLE 4

[0089] Trial compositions 8 to 1 1 from example 2 were submitted to a water absorption test according to below.

[0090] Prior to the test, the polymeric samples were dried for 8 hours, at 105°C, in an oven. Samples were placed in a climatic chamber at 20°C and 55% humidity, during 12 hours after drying. Then, samples were placed in a second climatic chamber, conditioned at 30°C and 80% of humidity, for 4 hours. After, the samples were subjected to conditions of 20°C and 55% humidity, for another 4 hours. The procedure above was repeated with the same sample for four days in a row.

[0091] The water absorption was calculated by weight difference of each trial composition before and after placing them in climatic chambers cycles.

[0092] The results obtained were described in TABLE 4 for trials 8 to 1 1 . [0093] TABLE 4: Water absorption of composites. [0094] Similar to results seen in example 3, trial compositions 9, 10 and 1 1 demonstrated an increase in water absorption compared to isolated polymers.

[0095] It should be understood that the invention is not limited by the above description but rather by the claims appended hereto.

[0096] Conclusion

[0097] Several polymers were investigated using a range of hydrogel amounts to test the composite preparation process (trials 2, 3, 5, 7, 9, 10 and 1 1 ).

[0098] Although a wide range of polymers of different classes and water absorption capacities were disclosed in the present invention, the improvement in water absorption could be observed for all of the classes.

[0099] Trials 2 and 3, composites of PA66, showed the best results of water absorption. In fact, the water absorption was surprisingly improved, even using a very small amount of hydrogel, such as (0.4% on Table 3 in trial 2). When compared to PA66 isolated, which demonstrated water absorption of 0.5 and 2.1 % at 20°C/60%RH and 30°C/90%RH respectively, trial 2 showed water absorption of 1.2 and 4.9% at the same conditions.

[00100] Trials 5 and 7, using PLA and PHB, showed similar results on increasing water absorption when using 5% of hydrogel (Table 3, trials 5 and 7). PLA isolated demonstrated water absorption of 0.3 and 0.5% at 20°C/60%RH and 30°C/90%RH respectively, while trial 5 showed water absorption of 1.1 and 2.2 at same conditions. In the same way, PHB isolated demonstrated water absorption of 0.3 and 0.8% at 20°C/60%RH and 30°C/90%RH respectively, while trial 7 showed water absorption of 1.0 and 2.1 at the same conditions.

[00101] For trials 9 to 1 1 , using PET, it was surprisingly found that the composite was able to significantly improve the water absorption of the polymer, even using small amounts such as 5% of hydrogel (Table 4, trial 11 ). When compared to PET isolated, which demonstrated water absorption of 0.05 and 0.06% at 20°C/55%RH and 30°C/80%RH respectively, trial 11 showed water absorption of 0.84 and 1 .38 at the same conditions.

[00102] Therefore, it was demonstrated that composites containing hydrogel, in small amounts, prepared by a process able to be used in different polymers were able to improve water absorption of different polymers. Unexpectedly, even polymers having very poor hydrophilic property, such as PET, showed an improvement in water absorption.