ES2663129B2 - Double-acting electro-spun membranes for water treatment - Google Patents

Abstract

Double-acting electro-spun membranes for water treatment. The present invention consists of a process for the manufacture of active membranes based on submicron fibers that combine an antimicrobial action with the ability to retain apolar pollutants in aqueous solution. The membranes are produced by an electro-spinning process in aqueous solution from mixtures of a water-soluble polyacid and polyalcohol that are stabilized by a curing process and post-functionalized by incorporating dendrimers with amino termination by a process of grafted with the aid of a coupling agent. The application of the material is the production of membranes or components of multilayer membranes for water treatment with antimicrobial action and with the ability to retain apolar contaminants.

Description

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DESCRIPTION

DOUBLE ACTION ELECTROWAVE MEMBRANES FOR TREATMENT OF

WATER

SECTOR OF THE TECHNIQUE

The present invention falls within the field of materials technology, in the subsector of membrane technology with application in water treatment processes.

STATE OF THE TECHNIQUE

The dendrimers are hyperbranched monodispersed polymers that consist of a central nucleus from which radial branches known as dendrons that grow in successive layers called generations emerge (F. Vógtle, G. Richardt, N. Werner, Dendrimer Chemistry: Concepts, Syntheses, Properties, Applications , 2009). They are macromolecules with a globular and highly symmetrical structure that exposes a large number of surface terminal groups, which imparts great versatility in terms of chemical functionalization. In addition, they have relatively large internal cavities that allow them to encapsulate molecules inside (M. Malkoch, E. Malmstróm, AM Nystrom, Dendrimers: Properties and Applications, n: Polymer Science: A Comprehensive Reference, 10, 113-176, 2012 ). Dendrimers have been used and tested for a wide range of applications such as catalyst, detection, environmental and biomedical applications (D. Astruc, F. Chardac, Chem. Rev., 101, 2991,2001; D. Astruc, E. Boisselier, C. Ornelas, Chem. Rev., 110, 1857, 2010; S. Svenson, DA Tomalia, Adv. Drug Del. Rev., 57, 2106, 2005; MM Khin, AS Nair, VJ Babu, R. Murugan , S. Ramakrishna, Energy Env. Sc¡., 5, 8075, 2012).

The anchoring of dendrimers to surfaces has been proposed for various applications such as the preparation of supported catalysts by including metals in dendrimer molecules (J. Ledesma-García, IL Escalante García, FJ Rodríguez, TW Chapman, LA Godínez, J Appl. Electrochem., 38, 515, 2008; A. Bukowska, W. Bukowski, K. Bester, S. Flaga, RSC Advances, 5,49036,2015). The procedure has also been used for the synthesis of catalysts based on gold nanoparticles functionalized with polypropyleneimine-anchored G2 dendrimers (PPI) and for the encapsulation of ruthenium nanoparticles subsequently immobilized on silica (E. Murugan, R.

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Rangasamy, J. Polym. Sc. Polym Chem., 48, 2525, 2010; N.C. Antonels, M. Benjamin Williams, R. Meijboom, M. Haumann, J. Molec. Catal. Chem., 421, 156, 2016). The high density of amino terminal groups has been used to prepare catalysts for the condensation reaction of Knoevenagel from polysilane-grafted PPI G3 dendrimers (K. Mangala, K. Sreekumar, J. Appl. Polym. Sci., 132, 11 , 2015). Dendrimers have also been proposed of / with? surface immobilized for the creation of different types of dendritic sensors [Z. Altintas, Y. Uludag, Y. Gurbuz, I. Tothill, Anal. Chim. Acta, 712, 138, 2012; J. Satija, B. Karunakaran, S. Mukherji, RSC Advances, 4, 15841, 2014; O. Valdés, C. Vergara, F.M. Nachtigall, Z. Lopez-Cabaña, J. Tapia, L.S. Santos, Tetrahedron Lett., 57, 2468, 2016). In biomedical applications, active membranes modified with polyamidoamine dendrimers (PAMAM) have been proposed for cell capture including folic acid modified dendrimers for capturing cancer cells that overexpress folic acid receptors (PM Zhang, MX Gao, XM Zhang, Talanta, 153, 366, 2016; Y. Zhao, X. Zhu, H. Liu, Y. Luo, S. Wang, M. Shen, M. Zhu, X. Shi, J. Mater. Chem. B, 2, 7384, 2014) . Environmental applications have been proposed for PAMAM dendrimers functionalized with porphyrin-metal complexes and supported on mesoporous silica for the extraction of water nitrosamines (MM Sanagi, MH Chong, S. Endud, WAW Ibrahim, L. Ali, Micropor. Mesopor. Mater. , 213, 68, 2015). PPI dendrimers in cellulose membranes have been used for the selective retention of heavy metals in water (M. Algarra, Ml Vázquez, B. Alonso, CM Casado, J. Casado, J. Benavente, Chem. Eng. J „253, 472 , 253).

Electro-spinning is the only general technique available for the production of submicron fibers in which a fluid stream projects from a capillary thanks to a potential difference between the tip of the capillary and a grounding collector electrode of the order of tens of thousands of volts As a result, the charged jet is accelerated towards the collector while the solvent evaporates resulting in a solid fiber that can form an ordered array or a non-woven matrix (PK Bhattacharjee, GC Rutledge, Electrospinning and polymer nanofibers: Process fundamentáis , in: Comprehensive Biomaterials, 2011, pp. 497-512). Electro-spun fibers can receive a wide range of applications thanks to their high surface ratio. volume and versatility of the method for producing fibers with a wide variety of chemical or physical modifications by incorporating non-spun materials (A. Greiner, J.H. Wendorff, Angew. Chem. Int. Ed „46, 5670, 2007). The manufacture of bioactive fibers is

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one of the most studied areas including antimicrobial materials, tissue engineering supports, fibers for the controlled release of drugs or wound dressings among other applications (J. Quirós, K. Boltes, R. Rosal, Polym. Rev., 56,631 , 2016). The environmental applications of submicron membranes include their use as membranes for water filtration with minimal pressure drop and fibers capable of incorporating functionalizations for remediation (V. Thavasi, G. Singh, S. Ramakrishna, Energy Environ. Sci., 1 , 205, 2008).

Poly (acrylic acid) (PAA) and polyvinyl alcohol (Poly (vinyl alcohol), PVA), are water soluble polymers that can be processed without the use of organic solvents. In particular, the electro-spinning of PAA or PVA solutions can produce ultrafine fibrous materials that cannot be obtained by conventional spinning techniques. Various applications for PAA or PVA electro-spun fibers have been proposed as filtration materials and for biomedical engineering (B. Kim, H. Park, SH Lee, WM Sigmund, Mat. Lett., 59, 829, 2005; C. Zhang, X. Yuan, L. Wu, Y. Han, J. Sheng, Eur. Polym. J., 41, 423, 2005). The mixed fibers of PAA and PVA can be easily crosslinked with different swelling behavior depending on the time and temperature of the processing, the molecular weight of the polymers and their mixing ratio (K. Kumeta, I. Nagashima, S. Matsui, K. Mizoguchi, J. Appl. Polym. Sci., 90, 2420, 2003). The antimicrobial activity of rich PAA polymers has been recently documented (G. Gratzl, S. Walkner, S. Hild, AW Hassel, HK Weber, C. Paulik, Colloids Surf. Biointerfaces, 126, 98, 2015; J. Santiago- Morales, G. Amariei, P. Letón, R. Rosal, Colloids Surf. Biointerfaces, 146, 144, 2016).

There are no examples of functionalized fibers based on poyacid-polyol combinations on which dendrimers are grafted in order to obtain active membranes for water treatment.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a process for the manufacture of active membranes for water treatment based on submicron fibers that combine an antimicrobial action with the ability to retain apolar contaminants. The synthesis consists of an electro-spinning process in which a non-spun matrix is prepared, a thermal curing process that stabilizes the fibers making them insoluble in water and a

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post-functionalization stage of the fibers in which a dendrimer is grafted through covalent bonds.

In the first stage, the aqueous solution is started in percentages by weight not exceeding 10% of two polymers, a polyacid and a polyalcohol, both soluble in water with molecular weight greater than 80 kDa and dosed in such a way that the number of Carboxyl groups of the polyacid are similar to those of the hydroxyl groups of the polyalcohol. The preparation takes place by applying a potential difference between the tip of the injection capillary and the 20-25 kV manifold and with a separation between them of at least 20 cm. The result must be a non-spun matrix of straight fibers, free of defects and insoluble in water with uniform diameter and not exceeding 350 nm.

In a second phase the thermal curing of the fibers takes place, after drying at 50 ° C for 24 h, by heating in an oven at 140 ° C for at least 30 min. In this process the formation of ester bridges between the polyalcohol and polyacid fibers takes place, which results in a water insoluble assembly. The fibers are then washed thoroughly to remove material that has not been completely fixed and dried under vacuum (10 kPa) at 50 ° C for 24 h. After this stage, the membrane must retain the fibrous structure and must not release organic matter after a first immersion in water above 10 mg of total carbon / g membrane.

The third phase of the synthesis process is the anchoring of dendrimers for which membranes with a density of free carboxyl groups of at least 5 mmol / g measured by acid-base titration are used. The dendrimers used must have primary amines as surface groups and the bonding is produced by formation of covalent amide bonds with the carboxyl groups of the stabilized membrane. A coupling agent is used to carry out the reaction. The amount of dendrimer fixed on the membrane is maximum when it is used in aqueous solution and a non-hydroxylated fixing solvent is used. The dendrimers can be of any generation equal to or greater than 3 and are dosed with at least 0.2 mmol / mol COOH equivalent. The duration of the fixation process is at least 12 hours during which the membranes are kept in contact with the dendrimer and the coupling agent under slight orbital agitation. Then, the membranes are carefully washed with the solvent used for the

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reaction and with plenty of water. Finally, they are dried under vacuum (10 kPa) at 100 ° C for 24 hours.

DESCRIPTION OF THE FIGURES

Figure 1. A general scheme of the functionalized fibers is shown in which (1) the polyacid represented by poly (acrylic acid), (2) the polyalcohol, represented by polyvinyl alcohol and (3) the grafted dendrimer by amide bond is detailed (•) represented by a G4 polypropyleneimine molecule. The figure shows the curing process with an ester bond that links a polyacid molecule and a polyol molecule.

MODE OF REALIZATION

Next, two examples of membrane preparation and functionalization with a dendrimer are described in detail. The results are also indicated in terms of antimicrobial efficacy and retention of apolar contaminants.

Membrane Preparation

The preparation of a typical polyacid-polyalcohol electro-spun material in which the polyacid is poly (acrylic acid), PAA, of molecular weight 450000 and the polyalcohol is polyvinyl alcohol, PVA, of molecular weight 89000-98000 takes place as follows. An aqueous solution for electro-spinning is prepared from 8% solutions of PAA and 15% PVA in water until reaching a weight ratio of PAA to PVA of 35:65 with a total concentration of at least 9%. The solution is kept under stirring for 2 h at 25 ° C and degassed before inserting it into a 23G blunt tip syringe. The electro-spinning uses the following parameters: voltage, 23 kV; distance from the tip of the needle to the collector, 23 cm and total flow 0.8 mL / h. As a collector, a fixed plate or a rotating cylinder at low speed (100 rpm) can be used. The conditions of relative humidity and air temperature of the electrowinning chamber must be maintained at approximately 40% and 25 ° C respectively. The fibers are dried at 50 ° C for 24 h, after which they are subjected to a thermal curing process by heating in an oven at 140 ° C for at least 30 min. The cured fibers are washed with abundant distilled water and dried in a vacuum oven (10 k Pa) at 50 ° C for 24 h, after which they are ready for the dendrimer functionalization process.

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Functioning with a dendrimer

The functionalization of electrohited membranes by the covalent bonding of a dendrimer whose surface groups are primary amines is described in the case of a PAMAM G3 dendrimer using N-N-dicyclohexylcarbodiimide (dicyclohexylcarbodiimide, DCC) as a coupling agent. . Dimethylformamide, DMF, is used as the solvent for the coupling agent. For a typical reaction, a mixture of 8.0 mL of DMF, 41.2 mg of DCC and 1.83 pL of PAMAM G3 dendrimer (9.43% in water) equivalent to 0.2 mmol G3 / mol COOH, is kept 12 hours under stirring at 25 ° C. Approximately 25 mg of a PAA-PVA membrane prepared as indicated in the previous section is immersed in the PAMAM / DCC solution in DMF and kept under stirring in an orbital shaker at 100 rpm for 24 h. After the functionalization reaction, the membranes are extracted, washed in DMF with abundant distilled water to remove the unreacted dendrimer and the reagent residues. Finally, the membranes are dried in a vacuum oven (10 kPa) at 100 ° C for 24 hours or until constant weight is reached.

Results

The antimicrobial action is determined from the contact of a membrane with a PAMAM G3 content of 6.5 jimol G3 / g membrane prepared according to the specifications described in the previous sections. The assay consists in the inhibition of the colony formation capacity of the bacteria Escherichia coli (CETC 516) and Staphylococcus aureus (CETC 240) in a culture with an initial density of 106 cells / mL in NB 1/500 medium (NB, 10 g / L peptone, 5 g / L sodium chloride, 5 g / L meat extract, pH 7.0) in contact with the membranes at 36 ° C for 20 h. The determination of the number of viable colonies is done by counting on agar plates with the same NB medium (15 g / L solid agar) after 16 h of exposure of serial dilutions in phosphate buffer at 36 ° C. The antimicrobial capacity for S. aureus bacteria represents a greater than 99.5% reduction in the ability to form new colonies, while for £. coli the reduction is close to 50%.

Retention of apolar contaminants

The measurement of the capacity of the modified membranes with dendrimers for the retention of polar contaminants is evaluated using water toluene solutions according to the following procedure. Membranes that contain a density of

functionalized PAMAM G3 dendrimer according to the specifications described in the first two sections and with a density of dendrimer of at least 5 pmol G3 / g membrane, they are contacted with an aqueous solution containing 100 pg / L of toluene until equilibrium is reached at room temperature. The amount of membrane 5 used is in the range 10-400 mg / pg of toluene. The concentration of toluene in the water is measured by capillary gas chromatography coupled to solid phase microextraction (SPME). For this, 1.8 mL of saturated NaCI sample was subjected to extraction with 100 pm SPME fibers of polydimethylsiloxane (Polydimethylsiloxane, PDMS) for 30 min at room temperature.

10 The analysis, carried out according to usual practices, determines the retention capacity of toluene by the membranes that must be greater than 80% in the most unfavorable case.

INDUSTRIAL APPLICATION

15 The benefits derived from this patent would find applicability in the treatment of drinking water, in the regeneration of wastewater and in the treatment of process water in various industries.

Claims (6)

5 10 fifteen twenty 25 30 1. A procedure for the preparation of electro-spun membranes of submicron dimensions characterized by the following steps: a) Preparation of an electro-spun membrane from an aqueous solution containing two dissolved polymers, one of them being a polyacid and the other a polyalcohol. b) Preparation of a non-water soluble membrane by thermal curing of the membrane obtained in a). c) Functionalization of the membrane obtained in b) by the incorporation of a dendrimer terminated in primary amino groups with the aid of a coupling agent to give rise to an amide bond between the primary amine and the carboxyl groups of the electro-spun material described in b ). 2. Membrane produced according to claim 1 characterized in that the polyacid is a water soluble polymer with a repetitive unit containing a carboxyl group and which can be poly (acrylic acid), poly (methacrylic acid), poly (maleic acid), poly (itaconic acid) or its copolymers with each other and with other copolymerizable monomers such as acrylates or alkyl methacrylates. 3. A membrane produced according to claim 1 characterized in that the polyalcohol is a water soluble polymer with a repeating unit containing a hydroxyl group and which can be polyvinyl alcohol, cellulose, and other soluble polysaccharides. 4. Membrane produced according to claim 1 characterized in that the dendrimer is a polyamidoamine (PAMAM) or poipropyleneimine (PPI) whose terminal groups are primary amines and whose generation is 3 or higher. 5. Membrane produced according to claim 1 characterized in that the coupling agent is a carbodiimide such as N, N'-dicyclohexylcarbodlimide (DCC), N, N'-diisopropylicarbodiimide (DIC), 1-ethyl-3- {3'-dimethylaminopropyl) carbodiimide (EDC), N-tert-butyl-N'-methylcarbodiimide (BMC), N-tert-butyl-N'-ethylcarbodiimide (BEC) or bis [[4- (2,2-dimethyl-1,3-dioxolyl )] methyl] -carbodiimide (BDCC) or other coupling reagents based on the formation of an activated ester which can be phosphonium, uronium or guanidinium salts, Triazines such as 1,3,5-trichlorotriazine, 2-chloro-4,6-dimethoxy-1l3,5-triazine (CDMT), 4- (4,6-d¡methox¡-1,3> 5 chloride -triazin-2-¡) -4-metmorphol, (DMTMM) or boron-based agents such as trimethoxyborane or phenylboronic acid. Use of the membranes produced according to claim 1 as membranes antimicrobials for water treatment processes or as active layers of multilayer membranes, where the electro-spun membrane is physically deposited or chemically grafted onto functional groups of a base membrane, preexisting or induced by functionalization treatments. 10 7. Use of the membranes produced according to claim 1 as membranes for the selective retention of apolar compounds in water treatment processes or as active layers of multilayer membranes, where the electro-spun membrane is physically deposited or chemically grafted onto functional groups of a membrane. base membrane, preexisting or induced by functionalization treatments.